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:^^::.^*-
Modern milling machines, their
design, construction, and ...
Joseph Gregory Horner i,
1/
L
Library
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EmI Enflpa
Uixary
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MODERN MILLING MACHINES
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MODERN
MILLING MACHINES
THEIR DESIGN
CONSTRUCTION, AND WORKING
A HANDBOOK :,.•:•:
fot practical Aen an& fingineertna Students
•^ BY
JOSEPH G.-'HORNER, A.M.LMech.E.
AUTHOR OF "PATTERN MAKING," ** HOISTING MACHINERY," "TOOLS FOR
ENGINEERS AND WOODWORKERS," " ENGINEERS* TURNING," ETC. ETC.
WiTH 269 ILLUSTRATIONS
LONDON
CROSBY LOCKWOOD AND SON
7 STATIONERS' HALL COURT, E.G.
1906
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Printed at Thb Daribn Press, Edinburgh.
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PREFACE.
The present period is one of growing specialisation in
Technical Literature, as in Manufacturing. The books
which give a general treatment of a particular subject
appeal less to practical men than to students and
amateurs. No apology, therefore, is necessary for
issuing a work which treats of a single department of
machine-shop practice, and one of great and growing
importance. Its scope is very broad, as a perusal of
the contents of this work will show. Milling machines
have become highly specialised, and the work of milling
is now subdivided between different groups of hands
just as that of turning is, ranging from very plain to
very difficult work.
The Author has treated lightly those sections of
the subject which offer no special difficulties, and has
given considerable space to the manufacture of cutters
and the work of the machines that call for the exercise
of special skill. A number of typical methods of
holding work, as well as some fixtures and jigs, are
CG5311
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vi PREFACE,
shown, but more as a general guide to the machine-
attendant, than with any thought of their covering a
field that is immense in its extent and variety. Some
of the latest improved machines are illustrated with
fully detailed drawings reduced from workshop prints,
and special attention has been given to the vexed
question of obtaining speeds and feeds.
The thanks of the Author are due to the firms
who have kindly supplied drawings and photographs of
machines and operations.
JOSEPH G. HORNER.
Bath, Novetiiber 1905.
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1
CONTENTS.
CHAPTEK I.
THE LEADING ELEMENTS OF MILLING MACHINE
DESIGN AND CONSTRUCTION
PAGE
The Development of the Milling Cutter — The Utilities of the Milling
Machine — The First Machine — Early Improvements — The In-
fluence of the Emery Grinder in its Development — Existing
Machines Classified — The Lincoln Miller — The Characteristics of
this Type — Modified Forms — The Work of the Lincoln Miller
CHAPTEE II.
PLAIN AND UNIVERSAL MACHINES,
Pillar and ELnee Machines, with Horizontal Spindles — The Characteristics
of this Type— Typical Machines Described— Diflference between
the Plain and Universal — Variable Details — Headstocks — Tables
and Knees — Feeds — Whence Derived — Countershaft or iSpindle —
Numerous Examples — Micrometer Movements to Feed Spindles —
Vernier Fitting to Tables — Differences between Plain Machines
and Universals — Index Centres and Spiral Heads — Various
Examples — Footstocks ...... 16
CHAPTER III.
ATTACHMENTS AND BRACINGS.
Vertical and Angular Spindle Attachments to Horizontal Machines—
Examples — Heads that Swivel Bodily — Examples — Slotting
Attachments — Examples — The Overhanging Arm — Bracings —
Examples — The Work of the Pillar and ELnee Machine
b
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viii CONTENTS.
CHAPTER IV.
VERTICAL SPINDLE MACHINES.
VAQE
Vertical veratts Horizontal Spindle Machines— Vertical Spindle Machines
— The Profiling Machines — Various Examples — Designs of Vertical
Spindle Machines — Built after the Model of Drilling and of
Slotting Machines — Examples — Spindles coming from Below — The
Work of the Vertical Spindle Machine — The Work of the Pro-
filing Machines ....... 94
CHAl^TEK V.
PLANO-MILLERS OR SLABBING MACHINES,
Piano-Millers or Slabbing Machines— Their Characteristics — Details of
Spindles — Horizontal — Vertical — Rotary Planers or Ending
Machines ........ 130
CHAPTER VI.
SPECIAL MACHINES.
Special Machines for Gear Cutting, &c. — For Spur and Bevel Gears —
For Worm-thread Milling— For Robbing Worm Threads— For
Fluting Twist Drills — Three spindle Machines — Cam-cutting
Attachments — Profiling Mechanism — Milling Attachment for
Planer— Machine for Elliptical Holes - - - - 139
CHAPTER VII.
CUTTERS.
Differences in the Teeth of Milling Cutters and Single-edged Tools — Size
of Cutters and Spacing of Teeth for Roughing and Finishing Cuts
— Rake and Clearance — Spiral Form — ** Handing" of Spiral— ^m-
pensation for Wear — Attachment to Spindles — Inserted Tooth
Cutters — Various Examples — Manufacture of Cutters — Steel —
Hardening — Cutting the Teeth — Examples — Grinding and
Sharpening — Examples — Clearances — Form Grinding - - 162
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CONTENTS. ix
CHAPTEE VIII.
MILLING OPERATIONS.
FAOS
The Operations of Roughing, Finishing, and Profiling — Milling Compared
with Planing, Shaping, and Slotting — Examples — Holding Work
in Jigs — General Considerations — Examples - - 198
CHAPTEE IX.
INDEXING, SPIRAL WORK, AND WORM, SPUR,
AND BEVEL GEARS, ETC.
The Universal the Machine of Applied Geometry — The Spiral Dividing
Head — The Basis of Calculation — Worm and Worm Wheel — Index
Plate— Sector — Differential Indexing — Angles of Spirals — Rules
and Examples— Graphic Method — Milling Screw Gears — Relations
between Spiral, Helical, and Worm Gears— Elements of the Spiral
Gear — Velocity Ratio — Pitches — Graphic Methods — Examples —
Trigonometrical Rules — Worm Gears — Methods of Cutting - 243
CHAPTEE X.
SPUR AND BEVEL GEARS.
Spur and Bevel Gears — Diametral Pitch — Blanks — Cutters — Projection
of Bevel Wheels — Multiple Cutters — Multiple Centres — Milling
Squares — Tapered Work ...... 278
CHAPTEE XI.
FEEDS AND SPEEDS.
Governing Conditions — Feeds of more Importance than Speeds — Hard-
ness and Softness of Metal — Pickling — Its Limitations— Frequency
of Grinding — Examples of Feeds and Speeds • 291
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MILLING MACHINES AND THEIR WORK.
4*t»
CHAPTER I.
THE LEADING ELEMENTS OF MILLING MACHINE
DESIGN AND CONSTRUCTION
The Development of the Milling Cutter — The Utilities of the Milling Machine —
The First Machine — Early Improvements — The Influence of the Emery
Grinder in its , Development — Existing Machines Classified — The Lincoln
Miller— The Characteristics of this Type— Modified Forms -The Work of
the Lincoln Miller.
The Development of the Milling Cutter. — The rapid de-
velopment of milling processes during the lifethne of the present
generation is one of the most remarkable and interesting facts in
the history of workshop practice. At one time tliese processes
were regarded by engineers of the old school with disfavour, and the
belief was very general that they could have but a limited applica-
tion in the formation of only small surfaces of comparatively simple
outlines. Neither would much improvement have been possible but
for the fact that the development of emery-grinding machines has
kept pace with the elaboration of the milling cutters. Milling,
therefore, affords an illustration of ideas long latent, good in them-
selves, failing of translation into general practice in consequence of
necessary conditions not having developed sufficiently.
There is an early, possibly one of the earliest milling cutters
in existence in America, made by Vaucanson, a famous French
mechanic, born 1709, died 1782. It is pierced with a hexagonal
hole, and its profile is approximately that of the cutters for gear-
wheel teeth. The pitching of the teeth is very fine, more like
that of a saw than a modern milling cutter, and they are iiTegular.
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2 MILLING MACHINES.
Mr Bodmer, of Manchester, it is stated, had made a milling
machine so early as 1824. But the general use of milling cutters
in England dates only from about twenty-five years past — since
emery wheels were introduced for grinding the faces of the teeth.
The late Mr Dixon stated that, as the result of careful inquiries,
he found that the use of the emery wheel for sharpening milling
cutters was due to a Mr George Haiinay, of Ulverstone, a brother
of Mr Hannay of the firm of Schneider & Hannay, the original
founders of the Barrow Steel Works.
The difficulties of cutter formation having been got over, there
remained another equally great, relathig to the construction of the
machines. The depth of cut which can be taken by a tool, con-
ditions remaining the same, diminishes w^ith increased breadth of
cutting edge. Deep and broad cuts do not coexist. Roughing
tools are narrow, the finishing tools are broad. This fact holds
good in relation both to single-edged tools, and to milling cutters.
One result is that the latter cannot take the deep cuts that the
former are capable of doing. More than that, when the width
of such cutters increases beyond an inch or two; the stresses are
so severe, even with shallow cuts, that vibrations are set up whicli
strain the machines, and detract much from the accuracy of the
work. This is the key to the difficulties which have been ex-
perienced by the builders and users of milling machines.
The Utilities of the Milling Machine.— The study of the
operations of milling machines' involves the consideration of a type
of rotating tools differing in all respects from those used in drilling
and boring. The boring head with cutters has some resemblance
to a mill. In fact, some mills with inserted teeth are constructed
very similarly to the boring head. But there the resemblance
ceases. Mills have a larger number of cutters, and their functions
are quite different. Some will bore circular work. But that is
not the chief function of milling cutters. Their function is that
of universal tools, capable of operating on surfaces plane, curved,
regular or irregular, straight or spiral. In short, I can think of
no tooling in the machine shop, save that of drilling, which is not
also done by means of circular milling cutters. The circular form
is, of course, merely a convenient method of arranging a large
number of single cutters at equal distances around the axis, the
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DESIGN AND CONSTRUCTION 3
mill being in effect a multiplication of single-cutting tool edges or
points, each of which operates in quick succession without any
return stroke. The number of teeth and the resulting diameter
of a mill are therefore not of a hard-and-fast character, these
being details which are settled by practical considerations and
convenience. Thus, it would not matter in the case of most jobs
whether a mill were 3 or 5 inches diameter, the results in the
shape imparted to the work would l)e the same. Considerations
of cost, stability, and class of machine used will determine the
choice of one size in preference to that of another.
No milling machine has yet been constructed suitable for all
classes of work. There are universal machines, capable of per-
forming all varieties of operations; but they lack the stability
necessary for the heaviest work, and the range requisite for many
operations. Compromises in milling machines have not been very
successful : hence it follows that for nearly every special class of
work a special machine is obtainable, and the nature of the jobs
to be done should always determine the selection of a machine.
Very mucirmillhig is of such a character that the cutters
become subsidiarj^ to measurement ; either a single cutter may be
made to definite dimensions, or two or more cutters may be
arranged in series or gangs, with or without provision for adjust-
ment for wear. The value of arrangements of this kind over
single-cutting tools is apparent. With the latter there is a lot of
preliminary experimental setting and adjustment required, much
of which work, so far as dimension adjustments are concerned, is
saved by the use of milling cuttei-s. The question of higher cost
of cutters in the first place has to be considered, but as the practice
of milling increases, the relative cost of these diminishes.
Milling machines are of less value in general engineering shops
than in those which deal with specialities. As these machines
received their first development in the manufacture of pistols,
rifles, sewing machines, and articles of kindred character, so these
shops and those of analogous character still afford the best illustra-
tions of the practice of milling. In some manufactories of this
kind there will be scores of milling machines performing every
conceivable kind of operation on iron, steel, and brass. The wide
extent, precision, and economy of the operations performed must,
however, be studied in several shops in order to be fully appre-
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4 MILLING MACHINES,
ciated. In these firms, and others of which these are types,
milHng is reduced to a system in which interchangeability of parts
is secured at a ridiculously low cost per piece. And in proportion
as shop systems approach more nearly to these does the value of
milling increase. Growing specialisation and the increase in
number of small fittings are the conditions most favourable to this
class of work. Such, however, is the tendency of modern engineer-
ing practice, and therefore that practice is favourable to the
increasing use and development of the milling machine. Planing, "
shaping, slotting, all labour under the disadvantages of having a
non-cutting return stroke, besides being unsuitable for cutting
surfaces which have very irregular contours. And when these
last are cut, they cannot be done at once, but must Ije produced
in detail with traverse feeding. In the milling machine, on the
contrary, broad surfaces of irregular contours can be cut with mills
having those contours, witliout any traverse feed.
Yet, though it is true that milling lends itself more readily to
special work than to that of a general cliaracter, the assumption
has teen too often hastily made that it has little chance in the
general shop. It certainly would be most injudicious to make a
radical change in the methods of a general shop already equipped
with single-cutting tool machines. But it is wise to introduce
milling gradually, beginning with those classes of work for which
the long experience of other firms has proved tliem suitable. In
any general shop there are a lot of articles which without doubt
can be treated more economically by milling than by any single-
tool machine. An enumeration of such articles is hardly worth
attempting, but in the work of nearly any finn it would be easy
to select scores of pieces to which milling would be eminently
superior to any operation done on planer, sliaper, or slotter. Tliis
remark is applicable not only to plane surfaces, but to those in
which profile cutters can complete at one traverse many jobs which
must otherwise be done by more than one cutter, and more than
one series of traverses, and often by setting on more than one
machine. Illustrations of these kinds will appear in later chapters ;
for the present it is sufl&cient to note the fact. There are also
machines which are capable of dealing with heavy work — using
long fluted cutters, or gangs of cutters, or face cutters with inserted
mills; and there are many bulky castings which can be tooled
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DESIGN AND CONSTRUCTION 5
more rapidly thus than with the single tools of the planer and
slotter. Machines of this class are not of recent origin, but they are
being developed and brought more under the notice of engineers,
their value becoming better recognised than they were a few years
since. These facts afford an indication that the milling machine
is destined yet to occupy as important a place in the general shop
as the single-cutting tool machines have done.
Milling has not nearly reached its possible developments with
us yet. The planer, shaper, and slotter still hold their own, with
little rivalry in some shops, and surfaces are slowly tooled which
could be done more expeditiously and often with equal accuracy
under a good system of milling. Many machinists would be
astonished at the large areas and the intricate sections which
ai*e milled in some shop practice, where milling is the rule, and
planing and shaping are of secondary importance. The real era
of the milling machine will not arrive with us perhaps until the
pressure of closer competition develops its yet latent possibilities.
It is from milling and grinding that the greatest developments of
machinists' work are to be anticipated in the future.
The selection of milling machines to perform general, or special
functions is a question for individual choice, and must depend
mainly on the requirements of any given shop. One of the
favourite types to-day — the Brown & Sharpe — also one of the
oldest, has either a wide range of functions or is absolutely
universal. A machine equal to it in value for general work is the
vertical one, with slotting machine type of framing, and compound
tables. Strictly specialised machines are confined mostly to shops
which do a special class of work. In the future, these, like other
classes of machines, may be expected to become more common.
Thei-e is no machine in the shop which requires more skilled
attendance. Even the gear cutters do not need such constant
attention as the universal milling machines, because the work of
the former is more repetitive than that of the latter. The care of
the various milling cutters themselves, the methods of lubrication,
the setting of the work, the best arrangements of tooling in order
to produce in all cases the most accurate results, in the most eco-
nomical ways or by the means at disposal, the relations of depth of
cut and feed, the most suitable treatment for the quality of material
being cut, the best form of cutters to use for any given job — these
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6 MILLING MACHINES,
points have all to be settled by an intelligent apprehension of the
circumstances of each case, and not by the perfunctory attention of
the mere machine minder. There is an immensely greater variety
of jobs on the universal machine than on others, the lathe excepted,
and the mind must be always on the alert if the capacities of the
machine are to be utilised to the utmost. It is in truth a beautiful
piece of mechanism, the uses and application of which are ever
being extended in the machine shop ; and the greater the intelli-
gence brought to operate it the greater is its value. It is therefore
unwise for employers to give such machines in sole charge of
lads or unskilled labourers, who will bring the machine and its
work into disrepute. Tliey should be attended to by intelligent
mechanics, or by men who have had a good deal of experience in
their charge. Unskilled men or boys can attend to machines
doing plain or repeat work, but then they should simply be
attendants, working under the supervision of another who is re-
sponsible for the scheming of methods, setting of work, regulation
of feeds, and so forth. Machines doing a variety of work like
those of the universal type can only be operated economically, and
their full capabilities realised by highly skilled attendance.
One result of milling is increased responsibility thrown on
the tool maker. Good tool makers are always in demand. The
accuracy of results depends on the making of the tool, and its
setting. Especially is this the case in the built-up gang mills.
After this the attendant has little responsibility. The man who
minds a slabbing machine therefore has less on his shoulders than
the operator of a universal machine. Although the work of the
miller and the planer are much in rivalry, yet the planer hand has
more of initiative than the man w4io has charge of a piano-miller,
when the cutters are made and set by a tool maker. The planer
hand has to manipulate his single-edged tools to produce various
shapes, the attendant at the milling macliine may mind three
or four machines after they have been started. The planer
tools have mostly to be made to produce many shapes, the milling
cutter will only reproduce its own outlines.
The milling machine should diminish the work of the fitter.
Whether it does so or not depends on the way in whicli the
milling is done. For it does not follow by any means that the
possession of these machines carries the certain result of good
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DESIGN AND CONSTRUCTION 7
work. That depends on the way in which they are treated.
Always regard must be had to the power of a machine. To
attempt to drive it quicker, and to feed harder than its capacity
will justify, can only result in chatter and untrue work, which
must afterwards be corrected by the fitter. It is not the mere
revolution marks left by the cutters, which occur in all work,
but the departure from truth due to the springing of the arbor
and cutter, which will make surfaces convex, or otherwise distorted
from the profile that the cutters should impart. Unduly heavy
feeduig, therefore, is incompatible with true work. Further, the
care of the cutters themselves influences results. Even when
properly formed and fluted, the maintenance of the cutting edges
by grinding is a vital matter, since dull edges will not cut so truly
as keen ones, due to the spring of the arbor.
Another point in connection with milling is this — that the
hard scale on forgings and castings, which does so little injury
to the single-edge cutting tools, for the simple reason that they
are able to penetrate beneath it at once, is ruinous to the delicate
edges of the milling cutters. Hence in every shop where milling
is adopted as a system it becomes a matter of economy to remove
the hard skin by pickling the iron and steel work in dilute
sulphuric acid, and the brass work in nitric acid.
The capacities of the milling machine are more limited in one
sense than those of the average machines in the shop. The reason
is that an arbor of great length is objectionable because of the
vibration set up in it by heavy, or even moderate, cutting. The
size of arbors is limited by the diameter of the holes in the
smallest mills. To increase the diameter of arbor would preclude
the employment of small cutters, and restrict very much the utility
of the machine. It becomes therefore impossible to put work of
very large dimensions on ordinary milling machines. Exceptions
occur in the heavy slabbing tools which do not fulfil universal
functions, and the ending or rotary machines, which are used
only for facing large work laid on a table alongside the machine.
Milling has conduced to general machining of a higher degree
of excellence, both in respect of accuracy and of finish, than was
formerly economically possible. Very much work that is done
well and cheaply by milling was formerly done laboriously and
imperfectly by the single-tool machines, or by hand, or by grinding.
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8 MILLING MACHINES,
The single-tool machines are accurate, but there is no one of
them which is capable of performing so great a variety of processes
as the milling machine. Neither is it possible, without taking
two or three cuts, the last one with a broad tool, to produce so
smooth a finish as a milling cutter will produce with one cut.
Hand labour is too costly to hold a place against modern condi-
tions, neither is it adapted for repetitive work. The excellent
results which are producible by milling have rendered inferior
work, by whatever method done, imjustifiable and inadmissible, so
that a shop well provided with milling machines is able to turn
out work not only better, but often cheaper, than a rival shop
working by the older methods. In another way milling has acted
on machine-shop practice. It has favoured the cheap production
of repetitive work of small dimensions, so that uniformity of
dimensions and form, and interchangeability, unknown and im-
practicable not so many years ago, are now becoming the rule.
The First Milling: Machine.— The late Mr E. G. Parkhurst,
known best by wire-feed reputation, but great in all that concerns
the manufacture of small arms, has given an account of what
is probably the first milling machine ever constructed. He saw
the machine, and gathered the facts relating to it in 1851 from
a Mr Robert Johnson, who gave the year 1818 as that in which
it was first set to work. This was at a gun factory in Middletown,
Conn., on a site known then, as now, as Mill Hollow.
At that period the file was the principal tool used by the gun
makers, and the new milling macliine was used as a roughing
tool to lessen the labour of rough filing, leavuig the finishing to
be done by liand. Its application was confined to plane faces,
and did not include either curves or profiled forms. It was a
hand-operated machine for several years l)efore a self-acting feed
was added.
The machine, shown in Fig. 1, comprises the following parts : —
A bed plate a, a rough casting measuring about 24 in. by 18 in.
by 2 in. thick. A headstock B, removed from an engine lathe,
was bolted to the bed, and carried a spindle with a square-tapered
socket to receive the cutter spindle. The cutter was a plain one,
with filed teetli. It measured about \\ inches in diameter, by
1-inch face. The cone pulleys were of wood, of about 2^ -inch
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DESIGN AND CONSTRUCTION 9
face, the largest being about 8 inches in diameter. The drawing
shows the grooved pulley at the rear for feed, a later addition
to the first design.
The work was traversed under the cutter by the hand crank c,
turning a pinion a, engaging with a rack screwed on the under
side of the table D. The edges of the table were vee'd to fit the
vee notches cut in the plugs t, 6, carried in drilled holes in four
upriglits E, E, lx)lted to the bed, and secured by and rendered
adjustable for wear l)y set screws c, c. The work was gripped in
the piece f, fitted with pinching screws, liaving pointed ends. If
a piece of work required a second cut, it was packed up in F with
paper or sheet metal.
This macliine, in existence three years after Waterloo, though
crude in the extreme, is a venerable relic worthy of illustration
in a book that deals mainly with present-day construction. Spite
Fig. 1.— The First Milling Machine.
of its simplicity, the workmen are said not to have taken kindly
to it at first, considering it an innovation on filing !
Early Improvements. — The first great improvement which
was effected in the milling macliine lay in the substitution of
provision for vertical adjustments of the spindle bearings, for the
fixed l)earings of the first machines. This is said to have originated
at the works of ^Ir Eli Whitney, of New Haven, Conn.
Little furtlier progress was made until the early fifties, at
which period tliere were a great many millers in existence, but
mostly manufactured by firms for their own use. About this
period they began to take rank as precision tools for duplicating
pieces, previously to which they had retained their first function —
that of roughing-down machines to the filers. Gang mills began
to figure al)out this time, and an unsuccessful attempt was made
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10 MILLING MACHINES,
to build a slabbing machine, somewhat on the lines of the planer.
Soon after, 1850, the Howe machine was brought out, and then
the Ames Manufacturing Co. of Chicopee, Mass., made numerous
machines, one being a modified Howe, designed by Mr C. MTarland.
These machines much resembled in outline the Lincoln miller,
designed by Mr F. A. Pratt in 1854, a type on which probably
more machines have been made than of any other. Its dis-
tinguishing feature was the substitution of a screw feed in place
of the pinion and rack feed hitherto applied. The quick return
was effected by hand. In 1848 came the Koot machine by Mr
E. K. Root, superintendent of Col. Colt's armoury at Hartford.
This was in the main built on the Lincoln and other earlier
models, but the table was driven by a worm gearing into a spiral
rack underneath the table. It embodied also a yielding clutch,
with a hand lever for operating it, for the purpose of disengaging
the driving cone pulley, so that the spindle could be stopped
from the countershaft. There was also an automatic knock-off,
which stopped the machine instantly, leaving the table standing
at any desired part of its traverse. Some of these machines have
remained in service for fifty years. Between 1861 and 1866,
during a portion of which the American Civil War was raging,
the hundreds of thousands of small arms turned out in govern-
ment and private factories gave the opportunity for the improved
milling machines, and they became firmly established as precision
tools. At that period, too, sewing machines were booming, and
so after 1863 nearly all the armoury-milling machines, which
were being abandoned in consequence of tlie closing of the war,
were purchased by the sewing-machine manufacturers.
Up to this period, therefore, forty-five years after the inven-
tion of the milling machine, there was Init one type in use, the
modern representative of which is the Lincoln miller. All these
machines had horizontal spindles, and housings adjustable verti-
cally. Most had tailstocks also, but the Root introduced an
overhanging arm with movable centre, in place of the tailstocks.
Back gears were fitted and compound tables. The legs in every
case were of the A form, in lathe fashion. The pillar and knee
machine had not appeared, nor the vertical spindle machines, nor
any successful slablring miller, nor rotary face mills with inserted
^^pth, nor any cutters of large dimensions.
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DESIGN AND CONSTRUCT/ON 11
The Influence of the Emery Grinder. — The milling machine
would never have attained its present development but for the
growth of the emery grinder. Its era dates from this period,
notwithstanding that the milling cutter itself is more than a
century old, and the milling machine was born about eighty
years ago. In the older methods the temper of the cutters had
to be drawn for sharpening, and rehardened, and this was incon-
sistent with accuracy, and with economy. It is to the emery
wheel also that we owe the displacement of cast gears by cut
ones. The old cutters were not accurate enough for such work,
nor would they retain their shape unimpaired by grinding but for
the form type of cutter.
Existing Machines Classified. — The types of machines,
ranging from plain to universal, are as varied as the classes of
work which are done by milling. These types also merge into
one another, so that strict classification is not possible. The
following will, I think, be a comprehensive and serviceable one : —
1. Lincoln millers.
2. Pillar and knee machines with horizontal spindles.
*^. Vertical spindle machines and profiling machines.
4. Piano-millers or slabbing machines.
5. Special machines for gear cutting, &c.
The Lincoln Miller, Figs. 2 and 3. — This is one of the most
common types of milling machine, dividing favour about equally
with the pillar and knee types. As it was the first to be invented,
it has retained a permanent place in favour notwithstanding the
advent of new forms. Its great value lies in its stability and
rigidity, the arbor being supported from the bed below, and the
table being backed up by a solid l)ed resting on the ground, instead
of by an overhanging knee. Its slight disadvantage is that the
table and its work are partly beliind the foot block or end support
of the arl3or, so that the workman cannot get round tlie job so
readily as when an overhanging arm is used. But this does not
interfere with the ordinary work put upon the miller, largely con-
sisting of that which would otherwise go to the small planer, or to
the shaper.
As the table has no provision for elevation in the Lincoln
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12 MILLING MACHINES.
machines, all movements of this kind are imparted to the spindle.
The spindle bearings in the smaller macliines slide in housings
within the head and foot stocks, Fig. 2. In the larger ones they
slide on the front upright faces of these heads, Fig. 3, each in-
Fig. 2.— Lincoln Miller. (Pratt & Whitney Co.)
volving different operating meclianisms. Independent hand wheels
and vertical screws are used, in some mitre geai*s operate the
screws, as in the elevating mechanisms of planers. Frequently the
bearings of tlie head and tail stocks are moved in unison by a
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DESIGN AND CONSTRUCTION
13
single set of gear on the head, by tlie simple device of connecting
the two spindle bearings with a stiff round bar, Fig. 3. This bar
is made rigid enough to ensure the alignment of the spindle at all
vertical positions. In some machines exa<)t heights can be ob-
tained by micrometric divisions of thousandths, or sixty-fourths of
an inch. In one type of machine the dial boss revolves with the
Utc::^
Fig. 3.— Lincoln Miller. (J. E. Reinecker.)
screw by a spring friction, but is adjustable by hand, the index
finger remaining stationary. The mass of the spindle and bearings
is counterbalanced in all but the smallest machines by weights
suspended from chains passing over pulleys.
Generally the headstock is a fixture, sometimes cast with the
bed, and the tailblock is adjustable to and from the head to a small
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14 MILLING MACHINES.
amount, in order to permit of inserting cuttere of different widths.
The carriage of the table also has a lateral adjustment of three or
four inches to accommodate the work slightly to the cutter after
the latter has been fixed. In a few machines the headstock is also
capable of some adjustment along tlie bed.
The forms of the beds varJ^ In the small machines the bed
much resembles that of a lathe, Fig. 2, and is surrounded in
modern machines with a deep waste-oil tray, and carried upon legs.
Fig. 4. — Modified Lincoln Miller. (Tangye Tool & Electric Co., Ltd.)
In larger machines the cabinet form of bed. Figs. 3 and 4, reaching
to the ground is adopted.
The spindle drive is from stepped cones and through gears,
provision being embodied to permit the spindle gears to engage at
all heights. The feeds are derived from smaller stepped cones, the
first of which is on the main cone shaft, the second on a shaft
running alongside the bed, having a worm which drives a worm
wheel, and thence through other gears the table feed screw. The
feed is tripped, and the worm dropped automatically out of engage-
ment at the end of a cut.
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DESIGN AND CONSTRUCTION 15
There are numerous modifications of this general type of machine.
The principal difierences are those due to increasing size. The
machine begins to resemble the planer, Fig. 4, the head and foot
stocks developing into two large housings bolted against the sides
of a bed, which carries a table of greater proportional length than
that of the ordinary Lincoln machine. These in strictness are not
Lincoln machines, but they form an obvious link between these
and the piano-millers. Allied to these are the double-headed
milling machines, carrying horizontal spindles for face milling,
and the machines with one head removable, so converting them
into open-side machines.
With scarcely an exception the Lincoln machines are of plam
type. There is an example of a universal machine, rendered so by
the fitting of a swivel table, and a dividing head.
The Work of the Lincoln Miller. — The work put on this
machine is generally of small dimensions, l^ecause the tables and
their traverses are short in the standard machines. But within
these limits there is a large volume which the machine will take.
It has scored most in the work of the gunsmiths and sewing-
machine makers, and then in engineers' work of a similar character.
The greater volume done is horizontal milling, either plain or pro-
file, the conditions being very favourable to the latter by reason of
the good support given to the spindle and the table. Cuts as
heavy as the teeth of the cutters will stand can be taken in con-
sequence. Face milling is also done. In many cases the footstock
is readily removable to permit of the insertion of wide pieces of
work to be tooled thus. Small pieces of work are frequently
arranged in series, up to the capacity of the machine.
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CHAPTER II.
PLAIN AND UNIVERSAL MACHINES,
Pillar and Knee Machines with Horizontal Spindles— The Cliaracteristics of this
Type — Typical Machines Described — Difference between the Plain and
Universal — Variable Details — Headstocks — Tables and Knees — Feeds —
Whence Derived — Countershaft or Spindle— Numerous Examples— Micro-
meter Movements to Feed Spindles— Veniier Fitting to Tables — Differences
between Plain Machines and Universals — Index Centres and Spiral Heads —
Various Examples— Footstocks.
Pillar and Knee Machines with Horizontal Spindles. —
The reason why so many, probal)ly the majority of milling
machines, are of the pillar and knee kind is traceable to the fact
that the early milling was of a light character, for which machines
of this type are eminently adapted. As this was among the
earliest, so it is in its elements the simplest form of machine.
Fig. 5 shows the earliest macliine of this kind, and interesting
comparisons may be made between that and machines in subse-
quent pages.
Among the simplest types of pillar macliines are those which
comprise in the main a lathe type of headstock, cast with or bolted
to the pillar, and having a compound table on the knee to carry
the work. There are three movements to the table — that in the
vertical direction with the knee, one towards and aw^ay from
the spindle, one transversely to the spmdle. A few machines of
this class have hand feeds only for all movements for the slides,
through screws and handles, and through hand wheel and screw for
the knee. Such machines have but a limited range, though with
a dividing apparatus fitted to the table they are useful to brass-
finishers and others for cutting hexagonal and other faces, and
nicking screw heads, while boys can attend to them. Machines of
this kind, too, generally have a screwed nose to receive chucks, the
idea being that cutters can be turned up in place by means of tools
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17
held and operated on the table. There is no support to the outer
end of the cutter arbor, and therefore neither long cutters can be
used nor heavy tooling done. Those most generally employed are
Fig. 5. — First Universal MiUing Machine built.
(Exhibited by Brown & Sharpe, Paris, 1867.)
fly cutters, or of the face or end type, and as these lie close up to
the headstock, they are stiff enough for the work which they have
to do. Generally such machines are single-geared only.
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18 MILLING MACHINES.
For die sinking, special pillar and knee machines are fitted
with vertical spindles, driven by belt through guide pulleys at the
back. In such types the movements of the table are generally by
hand, or the longitudinal traverse may be self-acting. A circular
table is also sometimes fitted with a rotary motion through worm
gear.
These machines are not standardised forms, but are generally
of a somewhat special character. The simplest standard machines
of pillar and knee type are those in which the spindles are
horizontal, but in which the outer end of the arbor is steadied by
an arm. These are generally termed " plain *' machines, to dis-
tinguish them from the universals, which are built upon the plain
types by the addition of an angular movement to the table, and of
dividing heads and change wheels. On the plain machines rect-
angular relations only are obtainable. The methods of actuating
the diflferents movements will vary in considerable degrees, render-
ing these movements of a more or less automatic character, but the
range of the operations is still limited rigidly to rectangular
planes.
A pillar milling machine, to be thoroughly complete and
efficient must fulfil many conditions — conditions which are com-
bined in one by the best manufacturers. Good useful machines at
moderate prices are, however, made by many firms, and the low-
priced ones will often be as well adapted for some classes of work
as the more complete but higher-priced tools. In this as in other
matters every tool user must consider his own special needs and
requirements and pocket.
The leading dimensions of pillar machines are : — Distance from
centre of spindle to the overhanging arm, which limits the diameter
of the mills that can be used ; the distance from the end of the
spindle to the centre in the overhanging arm, which governs the
length of mills that can be used. The height from the centre of
the spindle to the top of tlie table, when the latter is in its lowest
position, which limits the height of the work that can be tooled.
The size of the table, and the length of longitudinal and transverse
feeds, that regulate the dimensions of work that can be operated
on. The terms " longitudinal " and " transverse " movements are
used somewhat loosely by tool makers, the same terms sometimes
indicating movements of opposite character. It will be better to
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PLAIN AND UNIVERSAL MACHINES, 19
state precisely the direction in any case. Properly, longitudinal
traverse denotes the movement of the table at right angles with
the spindle ; and the transverse movement, that to or from the
pillar.
The range of work which can be done on a plain milling
machine, though usually restricted to rectangular movements only,
is yet wide enough for nearly all the requirements of some firms ;
those, for example, who have no heavy milling, or gear cutting, or
spiral-cutter making, or form milling. The work of the plain
machine is done mostly by cutters threaded on an arbor. The
diameter of arbor will range between about \ inch and If inches
in the smaller and larger machines respectively, and the length of
arbor from alx)ut 10 inches to 24 inches respectively. The func-
tions of the plain pillar machine lie chiefly in axial and edge work,
done in strictly longitudinal planes. End mills can be used by
supporting the arbor at the headstock end simply. It is con-
venient sometimes to be able to use an end mill, but such work is
not as a rule so readily done thus, as it would l>e on a vertical
spindle machine. Parallel grooves of tee or of plain section can
be cut thus, and a series also of parallel grooves, by utilising the
vertical movements of the knee. The principal utility of the
machine consists, however, in the facilities which it affords for face
and edge milling, using single cutters or gangs of cutters of plain
and of profile outlines.
The principal points which are essential to the stalrility and
good working of a pillar milling machine are, first, a substantial
framing, well spread out at the base, to counteract the top-heavi-
ness of the structure, and the one-sided arrangement of the knee
and table ; a large well-fitted spindle, with provision to take up
wear, and bearings made of durable material ; sufficient support to
the outer end of the arbor, to maintain it steadily while cutting
is being done — an important fitting, respecting the details of
which opinions and practice vary. Another essential condition is
the perfect alignment of the centre in the arm which enters the
outer end of the arlx)r, with the centre of the spindle, in any
position, whether closer in or farther out from the headstock.
This means very perfect, close, and parallel fitting of spindle and
of arm. The arm must be so fitted and held that it can be easily
moved, yet firmly clamped in any position, or swung out of the
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20 MILLING MACHINES,
way or removed altogether. It is essential, too, that the knee or
table and the slides have large bearing surfaces, be fitted in the
best manner, and in very accurate rectangular relations to each
other and to the spindle, and with provision for taking-up wear.
These points are all essential in the plainer, cheaper machines, as
in those more elaborately fitted. They are details which are not
apparent at a glance, and hence must be made matters for test, or,
Fig. 6. —Vertical Section through PiUar and Knee Machine.
which is generally sufficient, taken on the guarantee of a high-
class firm.
That which may be fitted, or not, to a plain machine, according
to individual requirements, is provision for movements of a more
or less automatic character. It is seldom that the longitudinal
traverse motion is effected by hand only, since the addition of
cones, a telescopic shaft, and gears is a simple matter. But in a
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PLAIN AND UNIVERSAL MACHINES.
21
number of machines the automatic movement is restricted to this
alone. Another detail relates to the revei-sal of the table, which
may be by hand only, or made automatic, with quick return. The
use of adjustable stops in connection with this reversal, and, in
fact, with all movements of the slides, is inseparable from perfectly
equipped machines. Related to this closely is the need for micro-
meter readings. These are fitted to the bosses of the operating
handles, so that exact depths of cutting can be done. A wide
range of feeds also is necessary for the longitudinal traverse of
the table.
r\
d
JaJLtzi
U J
WS
V^
% -if ,>»>^^*>y>^ I
Fig. 7. — Plan, and Part Section of PiUar and Knee Machine.
Fig. 6 is a vertical section taken through a machine of the
pillar and knee type, such as may, in its general features, be seen
in large numbers of shops; and Fig. 7, a plan view, with knee
and other details omitted. It is a type which is being subjected
to much modification, particularly in the matter of feeds (see page
32), while the details of construction adopted by different makers
vary in most parts of the design. The broad characteristics which
distinguish all these are the horizontal spindle, the height of which
is fixed, and the knee, which is capable of vertical adjustment on
the pillar, or column. It is therefore a type of an exactly opposite
kind to that of the Lincoln macliine, with spindle vertically adjust-
able, and a table at a fixed height. The elements of the machine
are as follows : —
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22 MILLING MACHINES,
The pillar a, of hollow or boxed section, and cast usually, as
shown, in one with the headstock B, and having slide faces to
receive the knee c. In a poorly designed machine, and in all in
some degree, the head and the knee are the weak elements, the
arbor being insufficiently supported, and the knee being liable to
spring under heavy or wide cutting. Hence the reason for the
fitting of the overhanging arm when edge milling is Ijeing done,
and the fitting of bracings rigidly connecting arm and knee (see
also page 86).
In the figure the upper part of the headstock is made continu-
ous, forming a long boss a. Figs. 6 and 7, instead of having separate
bearings, which is the case in many machines, particularly in the
older designs. In the boss, the overhanging arm D is clamped by
screws passing through split lugs. This arm is an important
element, and is varied in design. It cannot be used for face
milling, and is thrown up out of the way when this is being
done. It receives a bushing to support one end of the arbor,
in the example shown. Often a bracket is employed instead,
sliding along a plain parallel bar, and the arbor is supported
in that. Either arm or bracket is adjustable through the boss
a, of the headstock, to receive arbors of dififerent lengths. The
advantage of the straight arm is that it need not be turned up,
or removed when some adjuncts of the machine are put on the
table.
The main spindle is generally back geared, as indicated in both
Figs. The knee c carries the cross slide e, and the table F, the
first having a transverse cross movement, or one to and from
the pillar; the second a longitudinal, or traverse one, that is
tangentially to the pillar. The mechanisms by which they
are operated are varied greatly. Hand feeds are employed, and
power. Power feeds are derived from the three-stepped cones G
and H, driving in this example from the main spindle to the
telescopic shaft 6, which is jointed tlius in order to permit of its
following the vertical movements of the table. The objections to
this method of feeding are stated on page 31, and substitutes for
it are illustrated and described in some detail, c is the screw for
cross traverse, or transverse movement, d that for vertical feed
when efifected by hand, which actuates the screw e, through bevel
wheels, also used for power feeding. The screw / forms an
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PLAIN AND UNIVERSAL MACHINES,
23
adjustable stop for the height of movement of the knee. The
table F is traversed by a screw, indicated at g, in universals,
but often by a rack in plain machines. The advantages of a
screw are finer precision in operating, and that the table remains
at a standstill immediately the feed is disengaged. A rack permits
Fig. 8. — Vertical Section through Spindle and Back Gears, No. 5 Plain
Milling Machine. (Brown & Sharpe Manufacturing Co.)
of making more rapid adjustments by hand when setting, and
removing work. A universal also has a swivel table above F,
which introduces other details. A universal head (see page 63)
can be used on plain machines as well as on universals. But its
utilities are limited on the first-named, spiral gears for example,
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24
MILLING MACHINES.
requiring a swivelling table. Plain machines are also generally
built stiflfer than the others, and are sometimes termed manu-
facturing machines, to denote their greater power.
Other points to note in Fig. 6 are the waste-oil trough cast
round the base of the pillar, and the shelves j,j within it for
receiving tools, also the hole h cast in the base to permit the screw
Fig. 9.— Rear View of Fig. 8.
Fig. 10.— Sectional Detail of Eccentric
Movements and Locking Pin
in Figs. 8 and 9.
to pass down througli the floor as the table is loweie<l This is
not a good device, and an example is given of a telescoi)ic screw
(page 53) to obviate this objection.
Headstocks. — Figs. 8-10 show the headstock details of the
Brown & Sharpe largest size of plain milling machine.
Fig. 8 shows the headstock in vertical section, with the back
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PLAIN AND UNIVERSAL MACHINES,
25
geai-s placed below, where they are covered in and protected. In
the arrangement shown, the drive takes place from the cone
pinion A to B, on an intermediate spindle, then through c, D, E, F,
and G to H on the main spindle. The ratio thus obtained is 13'3
to 1. Both the back-gear shafts K and L have eccentric move-
ments. On the gear quill on the shaft L there is a disc M, which,
in the position shown, prevents the clutch N from being thrown
into engagement. But when the gears D and E are thrown back
and out, by the eccentric spindle L, that movement throws down
the disc also, so permitting the clutch N to be engaged. When
this is in, the drive takes place from the pinion A, through the
gears B and g to H, with a ratio of 3*677 to 1. The upper gears
can be thrown out also by the eccentric movement of K, giving a
simple belt drive. By means of a two-speed countershaft, and the
three-stepped pulley, and double-back gears, eighteen different
speeds are available, ranging from 10 to 403 turns per minute, in
geometrical progression as follows : —
Spindle Speeds in Revolutions per Minute.
Wiihxmt Back Gears.
403
325
262
211
170
137
CA
3. Speed F
ast.
Slow.
With First Back Gears,
110
88-5
71-3
57-5
46-3
37-3
C. S. Speed Fast
Slow.
With Second Back Gears.
30-4
24-4 19-7
C. S. Speed Fast
15-9
12-8
10*3
Slow.
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26 MILLING MACHINES,
The illustration, Fig. 11, shows the new headstock by the
Cincinnati MilUng Machine Co., designed mainly with a view to
the employment of cutters of high-speed steel. The features
present are, that a high belt speed can be used in conjunction with
the power of back gears, and that the latter are double, providing
a large range of spindle speeds, eighteen in number, as follows : —
11, 13, 16, 20, 25, 30, 36, 44, 54, 66, 81, 99, 119, 146, 178, 218, 267,
and 326. The countershaft speeds are also high, having 145 and
260 revolutions per minute. The smaller cone steps are larger
Fig. 11. — Headstock of Ciucinnati Milling Machine.
than usual, for greater power. The steps measure 9|, 10 J, and 12
inches diameter respectively.
The action of the back gears, seen in Fig. 11, is as follows: —
The gears A and B slide in imison with a quill, which slides on
the back-gear eccentric quill. A gears with c, producing slow
driving from E to F. When B is slid into engagement with
D, E drives F quickly. To bring either set into gear, the eccen-
tric shaft must be thrown out, and the gears thrown in. The
run seen on B prevents it from engaging u when A and c are
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PLAIN AND UNIVERSAL MACHINES, 27
driving. When the machine is in operation, the back gears are
encased
Fig. 12. — Headstock Spindle of Cincinnati Milling Machine.
Fig. 1 2 ilhistrates the lieadsfock spindle of the latest Cincinnati
machines, having the double back gear shown m Fig. 11. The
spindle is hollow, of
forged crucible steel,
running in adjustable
tearings. The hinder,
parallel bearing has two
lock nuts for adjusting
diametrical wear. The
front coned neck has
but one. End play is
taken up on this by
turning the lock nut A
on the spindle to the
right, or in the direc-
tion in which the
spindle turns, so draw- Fig. 13.— Garvin Front Spindle Bearing,
ing the latter into a
close bearing. The clamping plate B for the spindle gear c is
made separately from the cone pulley, and is fitted into the latter
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28 MILLING MACHINES,
at front and back. The gear c is connected to the cones by the
spring plunger d. Other details, as the keying of the back gears
32
6
H
\4
r
54)
on the cone boss to the rear, provision for lubrication, the pro-
tecting cap to the front bearing, &c., will be noticed.
Fig. 13 illustrates the Garvin form of front spindle bearing.
The neck is tapered to an angle of 5 degrees, and end play is
prevented by the washers which come against the collar A.
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PLAIN AND UNIVERSAL MACHINES. 29
Two of these washers a, a are hardened and ground, the third h
is a soft one, which can be taken out and its thickness reduced
in the lathe by the amount to which end play might have developed.
The washers and spindle are held in contact by the cap B, screwed
in front. Lubrication is provided for by the groove and channels
seen. The hinder l)earing is parallel, with a bushing tapered
externally.
Other details of spindles and bearings will be found on pages
Fig. 15. — Transverse Section through Knee and Table, No. 5 Miller.
34, 36, and 39, in connection with illustrations of feeds. In the
meantime we consider the details of knees and tables.
Table and Knee Feeds. — Figs. 14-19 show the table and
knee details of the Brown & Sharpe plain miller. In Fig. 14
the fitting of the table A to the cross slide B, on the knee, is
shown in section, with the take-up strip. The table is rack
driven, as is usual with plain millers, the vertical rack being
indicated at a, compare with Fig. 1 5, and the pinion at 5, on the
short vertical shaft c. This is actuated by hand from the front
of the machine by the shaft D, through the l)evels seen, and by
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30 MILLING MACHINES,
power from the pinion E, driven from worm gearing, the worm
wheel F being on the opposite end of the shaft c that carries E.
The feed is automatically tripped by the lever G, Fig. 16,
without dropping the worm H, which is a frequent device, and the
objection to which is that it leaves the table unlocked. If the
worm is allowed to remain in gear the table remains fixed in its
place whenever stopped. But it is necessary to disengage the
worm when the table movement has to be efifected rapidly by
hand, and this is done by moving an eccentric J, Fig. 16, that
throws down the hinged bearing in which the spindle d, of the
worm H, is carried.
A crank handle in
front of the knee, at
K, operates the quick
feed through the bevel
wheels on shafts d
and c. There is also
a fine hand feed to the
table, with gradua-
tions reading to TTnnF^h
of an inch, operating
the worm gear through
an intermediate pinion
L, Fig. 15.
When the auto-
matic feed is tripped.
Fig. 16. -Vertical Section through Worm Gear, .. . , fhrniicrh tlifi
&c., driven by Telescopic Feed Shaft. ^^ ^^ ^^^® tHroUgn tUe
No. 5 Miller. kver G moving an ec-
centric sleeve m bodily
along, and so disengaging the clutch N, Fig. 16. This clutch is
constantly running, being in the train of connections between the
sprocket cham drive from the spindle to the box of feed gears, and
thence through the universal joint to the table feeds just described.
The eccentric sleeve M, which is connected with or disconnected
from the clutch, is employed to reverse the table feed, engaging
either directly from pinion o to pinion p, or through the inter-
mediate L, for revereal, being operated by a lever.
The cross and vertical feeds can be operated by power, or be
disconnected. The worm h furnishes the drive in both cases.
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PLAIN AND UNIVERSAL MACHINES,
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Fig. 17.— Horizontal Section through Worm,
&c. , driven by Telescopic Feed Shaft,
B. & S. Miller.
For the cross-feed screw Q, the drive takes place from pinion p,
through/, g, h, and/, — j being driven from the splined chitch on Q.
The tripping arrangements of the table are shown in the
detailed drawings, Figs. 18 and 19. The method of elevation of
the knee by hand, or
power, is clearly shown
in Fig. 14, R being the
horizontal spindle driving
the vertical feed screw s
through bevels, the mass
of the knee, &c. being
carried on a ball race.
A good deal of discus-
sion has taken place on
the question of the best
method of imparting
milling machine feeds. The old plan was, and it is still the one
chiefly adopted, to drive the feeds directly from cones on the end
of the main spindle (see Fig. 6, page 20). The result is that only
a medium range of workable feeds is available when using the
medium - spindle speeds,
while at the extremes of
small cutters it is impos-
sible to get feeds at all
suited to the speeds at
which those cutters should
be run economically. Using
a large cutter, requiring a
slow-spindle speed, the feed
will be much too slow.
Using a small cutter requir-
ing a high-spindle speed,
the feed will be much too
fast. The case has been
put by Mr P. V. Vernon thus : —
"Assume spindle speeds vaiying from, say, 10 up to 300 turns
per minute, giving a 30 to 1 ratio of highest to lowest speeds.
" Assume, as a suitable range of feeds for slowest spindle speed,
^ inch up to 8 inches per minute, giving a 16 to 1 ratio of highest
Fig. 18.— Trip Movement, B. & S.
No. 5 Machine.
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MILLING MACHINES.
to lowest feeds. (The above ranges both of speeds and feeds are
well within the usual limits.)
"At the highest spindle speed (300) the above feeds would
become 15 up to 240 inches per minute, as they would increase
with the speed of the spindle, and would of course be quite useless
on the higher speeds.
" Conversely, if the range \ inch up to 8 inches per minute
could be obtained on the highest spindle speeds, these feeds would
be only ^^ ^^ ^'^^^ amount on the slowest spindle speeds, and
would also be of very little use, the highest feed for the slowest
spindle speed being only about \ inch per minute.
" In order to obtain
the proper range {\
up to 8 inches) at all
spindle speeds it would
be necessary to have
a total range of feed
variation provided by
means of the change
mechanism giving a
total ratio of (30 x 16)
to 1=480 to 1, which
is obviously imprac-
ticable."
The case is thus
very strongly put for
the driWng of feeds
from the countei-shaft,
or if from the spindle, hi such a way thfit they sliall not respond
to the variations in spindle speeds, but be driven from a speed
independently capable of variation to suit tlie sizes of the whole
range of cutters being used.
Numerous designs have been fitted which provide independent
feeds by means of gears — hence termed positive feeds. An
objection to these is that they will not slip in case of slip of the
main belt occurring, and the feed going on, is likely to cause
fracture of something. A slipping clutch, or breaking piece, is
therefore sometimes fitted in the feed-gear trains.
But the question of belt versus geared feeds is still in a state
Fig. 19.— Trip Movement, B. & S. No. 5 Machine.
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PLAIN AND UNIVERSAL MACHINES, 33
of transition. Many prefer the belt because it would slip rather
than cause a jam. There need not be much virtue in gears
over belts in point of power, though the belief is usually tacitly
accepted. That is strictly true only when comparison is made
with the narrow belted feeds hitherto used. A belt feed can be
made powerful, and a sufficient nimiber of variable feeds obtained
therefrom, provided it is not driven from the spindle speeds, but
from the countershaft. Though it is not possible to get a powerful
feed from a slowly rotating main spindle, it can be obtained from
the countershaft.
Whichever method is adopted, the separate feed gear not only
provides an independent range of feeds, but it simplifies calcula-
tions in two ways. It is easier to understand feeds irrespectively
of varying spindle speeds, than in connection with them. Also
it takes account of the diameter of the cutter, or number of teeth,
instead of feeds per revolution, which does not consider cutter
diameter, or nimiber of teeth.
It may also be pointed out that economy in power is studied
by separating the feed drive from the spindle drive. When the
latter drives the former, power is taken directly from the spindle,
which would be better utilised for heavier cutting, unless there is
excess of belt power.
One advantage of the geared feeds in the heavier machines is
that they are better able to feed heavy knees, carrying heavy work
vertically, than the ordinary belt feeds are.
The objection to an independent feed for milling machines,
that is, one obtained by arrangements entirely disconnected from
the main machine spindle, is that the spindle belt may slip under
heavy duty while the feed continues in operation, with disastrous
results. But the independent feed is nevertheless desirable, and it
has been embodied in many machines of late years. Feed is given in
inches per minute, or parts of inches per revolution, and this cannot
be estimated directly, but only by reference to the spindle speed.
The desirability of having a table feed independent of the
spindle speed induced Messrs Brown & Sharpe to design a machine
with constant and uniform belt speed, and variable spindle speed,
and variable table feed, derived from the constant-motion spindle.
It has been in operation for some years, and given satisfaction.
The single-driving speed renders the machine adaptable to an
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MILLING MACHINES.
ordinary belt drive, or motor drive with sprocket chain. The
spindle speeds range from 15 to 376 revolutions per minute,
arranged in geometrical progression. They provide, with a surface
speed of cutter of 20 feet per minute, for a range of cutters from
yV inch to 5 inches in diameter ; with a surface speed of 30 feet
per minute, for cutters from yV inch to 7^ inches ; and with a
surface speed of 40 feet, for cutters from f inch to 10 inches. The
speed mechanism is as follows : —
Fig. 20. — Vertical Section through Main Spindle, No. 2 Universal Machine.
(Brown & Sharpe Manufacturing Co. )
The main driving pulley is seen at A, Fig. 20. This drives
the long pinion B, which, through an idler c. Fig. 21, may actuate
either a, 6, c, or d. The lever D slides the idler c along to engage
with either wheel in the series, and the lever E then lifts it into
gear. The drive as shown is taking place from a to c, but a
lever provides means for sliding c out of gear, and bringing the
larger wheel /into engagement with the smallest wheel d. A fast
or slow motion is thus obtained for any one of the combinations
obtained between B and the cone of gears a, 6, c, d.
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PLAIN AND UNIVERSAL MACHINES, 35
Besides this, there is a back-gear set, derived from c and /,
which wheels slide upon a quill G. This is shown in the next
Fig. 22, where H is the back-gear spindle. This has a cam </,
which actuates a forked lever, and this in turn a collar j, con-
nected to locking pins i. The handle K engages the back gear,
the first action of which is to withdraw the pins t, and the final
action is to throw the collar j to the left. This causes compres-
sion of the springs behind the pins, which, on the first turn of the
machine, throws the pins
into place with a sharp
snap.
The guard which en-
closes the back gear is cut
away as shown. Fig. 22, to
permit the quill, encircling
the eccentric spindle H, to
be ;turned by the hand, in
order to bring the gears
into a position to engage,
and the outside of the quill
is knurled with that object. >
A small gear is shown
at ^^ which can be made to
engage with the main back
gear M by pulling out the
knob Z, but at other times
it is kept clear of the;
wheel by the encircling Fig. 2i.-End View of Headstock,
spring shown. The reason B. & S. Machine,
for this is to permit the
spindle to be turned by hand when the drive is by motor, as in
that case the sprocket chain with its wheels is enclosed by a
shield.
The table feed is rendered independent of the spindle drive as
follows (Fig. 23) :—
The sprocket A, driven by a pitch chain, drives the long
pinion B. An idle wheel, not indicated, but which is similar to c
in Fig. 21, and carried by the frame d, engages with either a, 6, c,
d, e, or/ by the lever E, after its position has been located by a
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36 MILLING MACHINES.
lever similar to D, in Fig. 21. In the figure, 6 engages with g on
the telescopic feed shaft F ; but by reversing the lever g, g is slid
out, and h put into engagement with/, so giving choice of fast or
slow feeds for either one of the combinations of the cone of gears,
as in the speed drive just noted in Fig. 20.
Gear plates are provided for speeds and feeds, and are placed
directly above the speed and feed-changing levers. The speeds
given for each position of the stop pin of a lever are marked
immediately above the stop-pin hole for that position.
Fig. 22. — HorizoDtal Section through Back Gears, B. & S. Machine.
Some other feed arrangements applied to the Brown & Sharpe
machines are shown in Fig. 24. The feeds are derived from the
spindle, driving down to the sprocket wheel A, in the first place.
The shaft B is thus rotated, b carries two wheels, c and d. c runs
on B, and has a long boss which forms a journal for wheel D.
These wheels are engaged by the clutches a and 6, operated by a
lever outside the gear box, the range of movement being controlled
by a knob, c operates a slow series of feeds, D a series of fast
ones. These first movements are transmitted through the wheels
on the intermediate shaft E to the wheels on the feed shaft F,
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PLAIN AND UNIVERSAL MACHINES. 37
whence the table is operated through a telescopic shaft. The
details are as follows : —
The two nests of gears G, H are keyed upon their shaft E. The
gears J, K are loose on their shaft F. The latter wheels have long
sleeve bosses, and either one in the nest is engaged with its fellow
on the shaft E by means of a series of six locking pins, two of
which are shown at c and d, and which enter recesses in the
Fig. 23.— Section through Feed Gears, B. & S. Machine.
bosses of the gears. Their positions are controlled by an index
disc e, that turns on the disc /, and carries a cam for actuating
levers which are fastened to the ends of small pinions that engage
with rack teeth (not shown), cut in the locking pins. The pinion
levers drop into a recess in the index disc, and as there is but one
recess, only one feed can be engaged at a time.
The feeds of the recently designed motor-driven pillar and
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38 MILLING MACHINES,
knee machines of the Cincinnati Milling Machine ("o. are shown in
section in Fig. 25. The machine is driven by a variable-speed
motor, having field control. The entire range of speeds is obtained
by the motor, supplemented by two sets of back gears. The total
range gives a surface speed of 20 feet per minute to cutters of from
yV inch to 6 inches diameter, or of 40 feet per minute to cutters of
from I inch to 12 inches diameter. Power is taken from the
motor to a friction clutch in the first place, and thence to a sleeve
on the main spindle. The friction clutch is introduced into the
Fig. 24.— Another B. & S. Geared Feed.
drive in order to permit of instant starting and stopping of the
machine without waiting for the motor either to stop or to attain
full speed, which must be done when the drive is effected directly
from the motor. The spindle can also be turned by hand on dis-
connection of the clutch. The field rheostat is not disturbed when
starting or stopping the machine, whether done by the friction
clutch or the main switch. It is set once for all to the required
speed, and is not altered unless a change of speed is wanted.
In Fig. 25 the motor drives through a sprocket chain the
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PLAIN AND UNIVERSAL MACHINES, 39
wheel A, which drives the sprocket B through the clutch c,
operated by the lever D, coming within reach of the attendant.
The second chain comes from B to the wheel E, which is
mounted on a sleeve f. This wheel and sleeve either drive
the spindle g directly through the usual pin a, or through
the back gears H and J, or K and L. These are thrown
Fig. 25.— Section through Feed and Spindle Gears of Cincinnati Machine.
into or out of engagement by the usual eccentric spindle and lever,
the boss of which is seen at 6. The endlong movement is effected
by sliding the sleeve of j and L along the main sleeve c, A flange
or shroud d on the wheel J prevents risk of endlong movement
taking place when either pairs of gears are engaged. The gears M
transmit the feed motion. The small pulley N is for driving the
oil pump.
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40 MILLING MACHINES.
The transmission of the feeds of the recent Cincinnati machines
is obtained through the gears M directly from the rear end of the
spindle. One box of gears is placed there, the other at the rear of
the column, and the two are connected by a vertically inclined
shaft. The first box is shown in section in Fig. 26. It provides
by the sliding sleeve A, with its two pinions engaging with the
pinions a and 6, on the spindle end, two speeds for each cone
speed. The sleeve is operated by a lever c, outside the encased
box. Thence the mitre wheels B transmit motion to the feed
gears in the box below on the column. In the latter are nests of
Fig. 26. — Sliding Gears at Rear of Spindle of Cincinnati Machine.
gears driven in the first place by two wheels, the common spindle
of which is actuated by mitre gears from the telescopic shaft.
Each of these two wheels is in permanent engagement with a
wheel on one of two nests of spur gears below, arranged in cones
in the manner now so common in feed gears. These cones of gears
are mounted loosely on their shaft, and are independent of each
other. The larger of the two upper wheels is in engagement with
the smallest wheel on one set of cones, and the smaller wheel with
the largest on the other set of cones, so that the two sets of cones
are run at widely different rates. Variable rates are transmitted
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PLAIN AND UNIVERSAL MACHINES 41
thence to the machine slides by an intermediate sliding gear on a
separate spindle, which can be slid along and engaged with any
wheel on either series of cone gears. There are two levers used in
this box, one of which is set opposite to figures on a quadrant, that
indicate the rate of feed in thousandths of an inch per revolution
of the spindle. The upper lever next brings the intermediate
wheel into engagement.
Fig. 27 illustrates a feed gear fitted to the Garvin machines for
Fig. 27. — Feed Gears of Garvin Machines.
feeding the knee and its slides, with provision for a series of
eighteen changes by the movement of handles.
The gears are enclosed in a box within the column or pillar of
the machine. A portion of the gears projects at the back, being
covered with a removable cap, and the operating levers are at the
side adjacent within reach of the left hand of the attendant.
The power for feeding is transmitted from the main spindle to
the sprocket wheel a, on the outside of the box. Tliis engages by
a sliding clutch with the spur wheel B to the left, which is in
engagement with the wheel c above, on a short shaft, on which
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42 MILLING MACHINES,
three gears, D, are keyed fast. These drive to either of the three
wheels below, which are loose on their shaft, and are put into
action by a sliding spring key seen in the broken section. The
lower shaft carries also to the right, three gears, f, keyed fast
upon it, which communicate the motion derived from either one
of E, to three others, G, above, loose on a short shaft, which has
no connection with that on which the wheels D are keyed. The
motion of G is then transmitted to the knee by the mitre wheels H,
and the feed shaft J.
For any one position of the left-hand key in the wheels E,
there are three changes available by the right-hand key engaging
with the wheels g, and since any combination of three can be made,
nine total changes are available. And besides, as the gears B and
c are reversible on their spindles — on the removal of the protecting
caps (not shown) — the series of nine changes can be doubled.
These range from i^\^ inch to \ inch per revolution of the spindle.
Each sliding key is provided with a lever a, 6, having a notched
sector or dial plate c, rf, for the right and left hand key respectively.
The notches are numbered, and a table at the side of the pillar
shows the combinations which give certain feeds. But before any
change can be made, the locking lever K has to be raised, which
movement disengages the clutched sprocket wheel A from wheel B,
and so stops the movements of the gears, while the keys are being
shifted, though the machine continues running.
The wheels are of hardened steel, and run in a bath of oil.
The sprocket chain is tightened by the set screw l, which adjusts
the box bodily in the vertical direction.
Fig. 28 illustrates a knee feed for the Kempsmith pillar and
knee miller. It gives sixteen changes, ranging from 0*004 to 0*150
inch per revolution of the spindle. The gears are enclosed in a
box at the side of the pillar, and are driven from the spindle
through a sprocket chain to the wheel A. The sectional view is
drawn as though the shafts were arranged in one plane, though
they are not so actually.
The sprocket wheel A is keyed to its shaft B. A double-ended
clutch c is capable of a sliding movement on this shaft, by the
lever D, which is rocked by the pin of the eccentric shaft, indicated
in end view. The clutch can thus be engaged with either the
wheel E or f, which, it will be noted, impart either a faster or
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PLAIN AND UNIVERSAL MACHINES. 43
a slower motion to the cone of gears on the shaft G. The corre-
sponding gears are mounted on the shaft H, in a swinging cage J,
Fig. 28. — Feed Geai-s of Kempsmith Machine.
actuated through intermediate wheels, one of which is shown at K.
These are made to engage in the different pairs of cone gears by
means of a lever l, to the left. A back gear M is mounted in a
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MILLING MACHINES,
frame N, and drives the pinion o ; P and Q are clutches, keyed, and
pinned to the shaft H. A sleeve R has a helical groove which is
operated by a lever s, to the right, to engage either p or Q. The
i—
.-l
FUN
Fig. 29.— Feed Box Details. (A. Herbert Limited.)
Section in Plane h-h.
end of the telescopic shaft is seen to the left. A plate attached
to the gear box indicates the position of the levers for any feed.
Figs. 29-32 illustrate a geared dial feed fitted by Messrs
Alfred Herbert Ltd. to recent machines, Fig. 33. The views
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PLAIN AND UNIVERSAL MACHINES, 45
comprise plans and sectionis of the gear box attached to the main
framing. The feature to be noted is that the simple turning of an
index wheel A gives at once the rate of feed to which the pointer
is set.
The nests of gears, entirely enclosed, are carried on three vertical
spindles which revolve and carry the various gears. Tracing the
feed movements from the shaft B, in the first place, belt driven,
compare with Fig. 33 ; this drives mitres c, the second of the pair
having a spur D on its spindle, which engages with a wheel on
the shaft E. There are four such wheels on a sleeve running
loose on shaft E, and each is engaged with the gears F on shaft G
Either one of the latter gears is made to drive the shaft G, by
means of the sliding spring key H, retained and pivoted in the
Fig. 30.— Feed Box Details. Section on Driving Shaft.
collar J, and actuated by the lever K. Tlie method of moving this
lever is the most interesting feature of the device, being effected
by the movement of the index wheel A, which revolves a cam
block L, havuig grooves cut around its body, which grooves coerce
pins in the lever K, as seen in Figs. 29 and 32, and so rock the
levers upwards or downwards accorduig to the direction of rota-
tion of the index wheel. The shaft G is thus rotated at either one
of four different speeds, and imparts motion to four gears M, keyed
on it through the medium of a sleeve forming part of the smallest
gear. Then these four gears drive others N, on a shaft o, fitted up
with a sliding key P, and collar Q, actuated also by a cam gi*oove in
the block L. Sixteen dififerent speeds are thus obtained through the
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MILLING MACHINES.
movement of the hand wheel A. Finally, the gears R, s, T convey
the movement to the splined vertical feed shaft u, Fig. 29, which
drives the horizontal feed shaft to the table through spiral
gears.
The machine to which
the feed lx)x just described
is fitted is shown by the
photo in Fig. 33. It com-
bines several features of
well-recognised value with
some novel ones.
The principal novelty
lies in the dial feed box
just described, by means of
which any required feed can
be obtained by the simple
movement of the hand wheel
seen over the box in Fig. 33,
the feeds being marked con-
secutively round the edge
of a disc on this hand wheel,
the dial being rotated until
the number corresponding
to the feed required comes
opposite the pointer. No
other movement whatever
is required.
I Another feature is that
the feed can be driven
eitlier from the counter-
shaft, or from the spindle as
desired, the combination
giving the most complete
feeding arrangement's. In
another machine by this
firm, the vertical spindle
one, illustrated on page 108, the feed is driven from the counter-
shaft only. Another detail which is also illustrated in that
machine, as well as in Fig. 33, is that the usual telescopic feed
V-*i-vx3:-:r::i,^!^:^i
o::;
" '^ ■." •■**r >
^iif'n!
I
ff---^??|7i
"fV.Jil^.ir.JL-'...,
(^
^--^
'o'
o
Fig. 31.— Feed Box Details.
Front Elevation.
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PLAIN AND UNIVERSAL MACHINES,
47
shaft is abandoned in favour
of gear drives through shafts
at right angles.
Other valuable points in
this machine are the follow-
ing: — The knee is of boxed
form, being completely closed
underneath. Its bearing on
the column extends above the
plane surface of the knee, so
conducing to steadiness of
movement. Telescopic cover
plates are fitted to prevent
dust and cuttings from falling
on the mechanism within the
knee. The table is thick and
massive, and is oiled from the
side, so that fixtures and vices
need not be disturbed for the
purpose of lubrication. This ^
is a point of much importance v-
when a machine is kept a long
time in service with the same
fixture upon it, doing repetitive
work. The screw by which
the table is operated does not
rotate, is always in tension,
and is not splined. A covered
channel in the table extends
from end to end to enable the
water used in lubricating the
cutters to pass away freely.
The good practice of fit-
ting hand wheels to move the
slides in preference to using
levers is embodied. The rim
of a hand wheel is readily
felt, while a crank handle has
to be searched for round the
32.— Feed Box Details.
Side Elevation.
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48 MILLING MACHINES.
circle. Also when the knee is lowered, the attendant has not to
stoop to a hand wheel, while he would often have to do so for a
Fig. 33.— Milling Machine with Dial Feed.
handle. Another feature is that the feed shafts are separated
sufficiently far to permit of having an independent hand wheel
for each motion, so avoiding the trouble of changing wheels
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PLAIN AND UNIVERSAL MACHINES.
49
when making adjustments. These are apparently minor matters,
but they tell up in the economies of the work of the machine.
The elevating screw is of the telescopic type, so doing away with
the necessity of cutting a hole in the floor. All motions of the
slides have clamping handles. The feed has automatic trips, and dead
stops. All motions have adjustable graduated index discs. The
head fittings embody the best practice. The head, with its sleeve,
is cast solid with the pillar. The sleeve is tubular, embracing the
overhanging arm, and pinching it with clamping handles. The
arm is of solid steel bar. The spmdle, of crucible steel, is bored
right through. Its nose is threaded, and protected with a cap
Pig. 34.-^Feed Gear Box. Plan View.
when not in use. Provision is made for adjusting diameter and
end thrust independently. The broad base of the machine will
be noticed. The interior is fitted up as a cupboai-d. All gears
are encased. A pump is fitted.
A design of variable feed gear by Messrs A. Herbert Ltd., to
be driven either from spindle or countershaft, is shown in Figs.
34-36. If from the first, there are sixteen changes, if from the
second, thirty-two, independently of the speed of the spindle. The
dial feed just described has been designed to supersede this.
The upper feed cone, which drives to the cones A, on the feed
box is geared to the spindle, and runs at twice the spindle speed,
doubling the power by comparison with a cone mounted directly
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50
MILLING MACHINES.
on the end of the spindle. As the cones have four steps, and are
interchangeable, this accounts for eight changes. By interchange-
able is meant that the driving and driven cones can be made to
change places, so reversing the speed relations, a smaller driving
to a larger, and vice versa ; a method which is commonly adopted
in all or nearly all machines in which cones for feeds are retained.
Looking at Fig. 36 it is seen that the cone fits on the sleeve which
it drives by a short key over which it is slid, and it is secured end-
wise by the knurled nut B,
so that the changing of the
cones is only a work of two
or three minutes. All the
various speeds obtainable
on, each step, for the two
changes of the cones, are
given in the plates usually
attached to machines.
These changes are
doubled in the feed box
shown by the movement of
the lever c, the eflfect of
which is shown clearly in
Fig. 36. Two gears in the
lower part of the box, fast
on the cone sleeve, engage
with two gears in the upper
part of the box loose on
their sleeve. Either one is
caused to be driven from its
lower gear by the sliding of
the lever c, moving a pin and its key along into the boss of either
gear. The spring pin a, in Fig. 35, automatically locks the lever
in a position to drive one wheel or the other, or in a middle
position of no drive. The great advantage of this device is that a
change from a roughing to a finishing cut, and vice versa, can be
made without shifting the belt, or stopping the machine.
The feeds transmitted from telescopic or horizontal shafts are
made to actuate the two movements of the table and that of the
knee in the most complete machines. In addition to these, hand
Fig. 35.— Feed Gear Box. End View.
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PLAIN AND UNIVERSAL MACHINES,
51
movements are also fitted Many modifications are efiFected in
the details of these by different firms, the practice of which also
changes from time to time. Eeference may be made to Figs.
14-19, pages 28-32, for a present-day design.
The Knee. — The knee and its method of fitting on the latest
types of pillar machines possesses several characteristic features
which are worth noting. In the first place it often has a solid
Fig. 36.— Feed Gear Box. Front Elevation. (Dotted Pulley for larger Machine.)
top, which is better calculated to resist stresses of certain kinds
than one which is open on the top. The latter type is likened
to a box without a bottom, which is not so well able to resist
stresses as one with a solid bottom. The weakness of an open
knee is generally recognised, and is to some extent lessened in
many cases by the practice of casting internal ribs and fillets, so
narrowing the area of the opening. Another objection to the
open top is the tumbling down of chips on the screws and gears
that lie within the knee. This however can be avoided by the
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52
MILLING MACHINES.
use of telescopic slides. But the solid top at once stiffens, and
affords protection. Its advantages from the point of view of
stifl&iess are not so veiy pronounced when work lies within its
area. But they are most evident when heavy cutting is being
done with the table rim out a good way over one side, with the
result of producing a considerable amount of leverage, the fulcrum
of which is on one edge of the knee, while the effect is to lift
or attempt to lift the slide on the other edge. To prevent a
wedging action against the vee'd edges under such conditions is
the object of imparting square edges to the slides, but these are
not considered necessary with solid knees.
LtO
Fig. 37.- Garvin Knee, with Solid Top.
The Garvin knee shown in Fig. 37 has a solid top, and also has
its sliding face extended above the top slide, a feature which is
conducive to stability. In these machines the screw for the cross
traverse movement is placed alongside the knee, outside to the
right, lying in a recess. The nut is bolted to the slide, being also
fitted thereto with a tongue. The method of taking up slackness
due to wear consists in splitting the screwed boss into two portions,
one of which is rigid, the other slightly elastic. The latter can
be tightened against the traverse screw by an adjusting screw,
effected similarly to the taking-up of the wear endwise on a worm
made in two parts, by which means it is not necessary to take the
precaution of allowing for backlash when making exact settings
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PLAIN AND UNIVERSAL MACHINES. 53
Fig. 39. -Stationary Screw. ball race a.
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54 MILLING MACHINES.
I
IS
Table Feeds. — The method by which the table feed is trans-
mitted from the telescopic shaft in the Garvin machines is shown
in Fig. 40.
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A is the universal joint on the end of the telescopic shaft,
whence the first driving shaft B is actuated. The shaft carries
a gear c, that actuates tumbler gears D or e; the pins for
these are carried in a swinging casting F, the bottom of which
Fig. 41.— Cross Section through Table and Swivel Carriage.
Le Blond Universal Machine.
forms an oil box. The reversal can be effected by hand when
the machine is running by pulling out the knob g, and throwing
the rocker casting F over to the other position. The feed is
transmitted and tripped as follows : — The tumbler gears actuate
the wheel H, on the shaft to which the worm j is fastened.
Fig. 42. — Longitudinal Section through Table Screw. Le Blond Machine.
J drives the worm K, mounted on the feed screw. The bearings
of the worm shaft are in a solid casting, and include the oil bath
for the worm. The casting is pivoted at 6, and retained during
feeding by the latch c. The feed is tripped by the button d, on
the table, pressing down the spring plug e. The eflfect of this is
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66 MILLING MACHINES.
to thrust the trip rod L, that 'Supports the latch pin c, outwards,
so letting the worm bearings drop, and disengaging the worm from
gear with K. The feed can be disengaged by hand by pulling at
the knob of L. It is thrown in by pressing down the handle M,
which is attached to the drop bearings.
Figs. 41 and 42 show the table sections of the R. K. Le Blond
Universal machine, illustrating the two methods of driving ; that
of a rack (not shown) from the pinion A, and that of a screw
B. The feed is necessarily driven through the centre of the
saddle. The screw B, adequately supported in long bearings, is
Fig. 43. —Micrometer Fittings to Feed Spindles.
encircled by a mitre wheel c, driven by one on the stem of
which A is keyed, c runs freely on the screw, but is made to
rotate it by the clutched sleeve D, splined to the screw and slid
along by the double-forked lever E. The latter is operated by
the handle F, or by the dogs, one of which is seen at G. These
thrust down a plunger H, a rack on which gears with the pinion
J, cut in the spindle which actuates the lever E. The gib K is a
tapered one.
Fig. 43 shows the micrometer fitting applied to the various feed
spindles of the Garvin machines, the upper view being an external
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one, the lower the same in section. On the spindle there is a steel
collar A, bevelled, and graduated to indicate thousandths of an inch,
and knurled to permit of turning it to start at zero. It is slackened,
and again tightened when set, by the small knurled screw B at the
end, which presses up a pin with a bevelled end suited to the
bevelled end of the screw.
The best table stops are of precision type, set by a micrometer
screw, which is bound by a clamp screw. Their value lies in the
means which are afforded of feeding up to a given point, and up to
shoulders.
Fig. 44 illustrates a vernier, applied to the tables of the B. & S.
milling machines for the purpose of effecting fine adjustments of
the table, reading to thousandths of an inch. The scale A is 24
inches long, the finer divisions
being omitted in the engraving,
and is attached by screws, and
tee-headed nuts entering the
slot which receives the trip
dogs. The vernier b is attached
to the front of the saddle of
the machine by the bolt shown,
a is the clamping screw for the
vernier, and 6 the fine screw by
which it is adjusted to zero.
The vernier, whether ap-
plied to machine or to caliper, is a means by which fine readings
can be taken by inspection from comparatively coarse dimensions.
It comprises two parts, the "vernier" proper and the "beam."
Dififerent units of division are adopted by different makers, but
the most useful is one which is embodied in the Brown & Sharpe
vernier calipers for English divisions of a thousandth of an inch.
Figs. 45-47 show one of these much enlarged for the sake of
clearness. Each inch in length of the " beam " A is divided into
ten equal parts, and each of these again into four, making forty
parts to the inch ; so that :fV> or 0'025 inch is the value of each
part. The vernier b is divided into twenty-five parts on a total
length which equals twenty-four parts of the beam. These divi-
sions are not so fine but they can be readily seen, and yet they
register ^^j^ inch easily, thus : —
Fig. 44.— Vernier applied to Table
of B. & S. Machines.
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MILLING MACHINES.
liiiliiitiiilinhl
As twenty-five parts on the vernier correspond in extreme length
with twenty-four parts on the beam, = twenty-four fortieths of an
inch, then ^V of T?r = l>000th of an inch.
When the vernier is set at zero, Fig. 45, there is then a
difiFerence in the next two lines of division, of yrnnr of an inch,
and so on, — nnnr for each successive division, until they correspond
again at the 25 division on the vernier.
If the zero marks are set to-
gether, as in a caliper, no frac-
tional parts exist, but whole
numbers, corresponding with the
inches, as 1, 2, 3, &c. But when
the zero on the vernier comes
elsewhere, then, first, the number
of inches, tenths, and parts of
tenths are read, by which the zero point on the vernier has
moved from the zero point on the beam. Thus in Fig. 46 it
has moved from zero a distance of one tenth, and also past two
of the four divisions of the second tenth on the beam. That
is one tenth added to twice 0*025 inch, equalling 010 4- 0*05 = 0-15
inch.
In Fig. 47 the vernier is shown moved past the second sub-
division^f the second tenth. To read this the eye must be run
Fig. 46. — Vernier set to Zero.
A^ ^
Fig. 46. — Vemier'set to an
Exact Division.
Fig. 47. — Vernier set to
Fractional Division.
along to find where coincidence occurs between vernier and beam.
This occurs at the twelfth division, and represents the number
of thousandths to be added to the distance read off on the bar,
giving 0-012 + 15 inch = 0162.
If the readings are taken decimally, calculation is facilitated.
The tenths on the beam are then 100, or one hundred thou-
sandths, and the fortieths, or fourths of tenths on the vernier
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PLAIN AND UNIVERSAL MACHINES. 59
are 0'025, or twenty-five thousandths. Thus in Fig. 46 the jaw
is open one tenth, and two twenty-five thousandths = 0150 thou-
sandths. In Fig. 47 it is open one tenth, two twenty-five
thousandths, and twelve thousandths = 0'162.
Differences between Plain Machines and Universals. —
Sometimes the plain milling machines are made with rack feeds, and
sometimes with screws to the tahle ; the universals have screws.
The latter are more exact, and better suited to micrometric
dimensions; the former permit of more rapid adjustments by
hand. There are not so many joints for the table as in the
universals, there being no swivelling arrangement; it is stiffer,
therefore, which is more favourable to slogging. The universal
milling machine wa^ patented by J. E. Brown in 1865. See
Fig. 5, page 17. It was exhibited at the Paris Exhibition of 1867.
A modern machine by the firm is shown in Fig. 48. In this
type of machine the table is capable of three movements: one,
that of the table transversely along with its saddle; the other,
that of the table alone, longitudinally, by means of a feed screw ;
the third, by the knee. The saddle swivels in a horizontal plane
on a bed having vee'd edges, which bed slides along the top of
the knee bracket, that moves vertically on ways on the front of
the standard. The table carries the dividing head, with its gear,
and the loose headstock or " footstock."
The universal machine will fulfil the functions of the plain
machine of the same type. The essential difference between a
plain machine and a universal is, that the latter has, in addition
to the fittings of the former, a spiral head, index plate, sector,
and change gears, with a swivel table. The index plate furnishes
circles of divisions, change gears give variable rates of spiral move-
ments, while the table is being traversed a certain distance by the
feed screw. By these additions any angle up to 45** can be given
to the table, which can also be fed automatically at any
angle, and a definite rotary movement can be given to the work.
There is . nothing therefore in the range of small gear cutting,
cutter or tool making, or the tooling of small parts within the
dimensions covered by the machine, which cannot be accomplished
on the universal type. It owes its chief value therefore to the
fact that there is no job of milling of moderate dimensions which
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60 MILLING MACHINES.
cannot be done upon it. Every shop should have at least one of
these, but it is a mistake to suppose that it is economically adapted
for all kinds of jobs, even though these may be of medium dimen-
Fig. 48. — Universal Milling Machine. (Brown & Sharpe Manufacturing Co.)
sions. Many such can frequently be tooled to better advantage in
large quantities on the larger and more specialised machines of
various kinds. It is not judicious to attempt heavy tooling on a
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PLAIN AND UNIVERSAL MACHINES, 61
universal, for which almost any other types are better suited.
It is a somewhat delicately-constructed piece of mechanism
by comparison with some others. The table is not quite so rigid
under stress; and as it is driven by screw instead of by rack, the truth
of the screw should be retained as long as possible. It is a little
top-heavy. The universal head is a piece of delicate construction ;
there is a deal of gear introduced for the automatic movements, all
of which details are incompatible with heavy tooling. Only work
should therefore be put on the universal which cannot be done at
all, or at least so conveniently elsewhere, and specially that which
requires the assistance of the head and the swivelling arrange-
ments of the table. A skilful man is required to attend to a
universal machine, because the work done upon it is of an
intricate character, and also because calculations have to be
made for the cutting of teeth of spiral form; and when gears
are cut, calculations also for the nimibers of teeth. A good
attendant will turn out a large volume of excellent and varied
work from a universal machine, and he will prove the best in-
vestment.
The table is fed automatically from the cone pulleys through a
telescopic rod and worm gear in the older machines, but through
bevel gears and a screw in others ; and the automatic movement
can be stopped or reversed. The automatic drive is effective at
any angle of the table. The table can be operated by hand from
either end. The movements of the table in any direction, includ-
ing the angle to which it may be set, are indicated by micrometer
dials, reading to thousandths of an inch. Changes of feed range
between eight and thirty-two in number on different machines, the
wide range being obtained by transposing stepped cone pulleys and
pulleys at the back of the machine, or by gears, or both in
combination.
The handles for operating the three movements of the table —
longitudinal, transverse, and vertical — ^are at the front ; and two
of these — that for the cross feed and that for the vertical move-
ment — are often provided with clutches. The idea is that the
handles can be instantly disconnected ; and being loose on their
respective shafts, the adjustment of the slides would not be
affected should the attendant accidentally shift the handles round.
At the same time, they are ready for immediate use.
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MILLING MACHINES.
The handle for the vertical movement of the table by hand is
often placed at an angle, instead of just below the cross-feed
handle, so that they do not interfere with one another, neither has
either of the handles to be removed, but remain permanently on
their spindles. It is easy therefore to operate two handles at one
time.
Ball bearings are commonly applied to the feed screw of the
table, as well as to the vertical feed screw. Quick return can be
employed to the table. Its base is of large diameter, and graduated
on the outside into degrees for milling spirals, or work of similar
character.
In conformity with an agreement adopted by the manufac-
turers of milling machines in the United States the movements on
plain milling machines are as follows : —
No. of Mftohlne.
Inches.
6
15
18
1
li
2
3
4
5
TraDSverse movement
Vertical movement -
Automatic table feeds
Inohes.
7
19
24
Inches.
7
19
24
Inches.
8
19
28
Inches.
10
20
34
Inohes.
12
20
42
Inohes.
12
21
50
The movements on universal milling machines are as follows :-
Na of Mftohine.-
1
14
2
3
Tranaverse movement
Vertical movement •
Automatic table feeds
Inohes.
7
18
Inches.
7
18
20
Inches.
8
18
25
Inches.
10
19
30
Index Centres and Spiral Heads. — The index centres used
on milling machines range from those which are quite plain to
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PLAIN AND UNIVERSAL MACHINES. 63
those which are universal in character. A plain type, of which
there are several varieties, consists of centres without any pro-
vision for setting to a vertical angle, and without any means of
sub-division in the head except that aflPorded by holes drilled in a
dial. A tapered pin inserted in the holes locks the spindle while
teeth are being cut or edges milled equidistantly.
In a more elaborate kind, the centres, as before, have no means
A
Fig. 49.— Universal Indexing Head.
of angular adjustment, but a nearly universal range of indexing
can be obtained by the employment of index plates with circles of
holes and a worm and worm wheel, the latter being on the head-
stock spindle.
In the most perfect type the index head will angle from a few
degrees beneath the horizontal to a few degrees over the perpen-
dicular, giving a total range of 118° or 120° of adjustment in a
vertical plane. Index plates in combination with worm gears give
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64 MILLING MACHINES,
a large range of numbers for division. The spindle also of the
loose headstock has a slight vertical range of angular adjustment,
suitable for taper taps and reamers and work of that type, and
a vertical movement also bodily. Such
centres fulfil universal functions, in-
cluding the cutting of all gear wheels
and spiral cutters and spirals. The
universal head, in this its most perfect
form, combines two movements, one
of rotation and division in itself, the
other one, of longitudinal movement
through the table; the first being
eflfected through a division plate, the
second through change gears and the
table feed screw. By the first it is
Fig. 50.— Universal Head. possible to mill out equal divisions,
Vertical Section. as on gear wheels and cutters ; by a
combination of the two, any nimiber
of spirals situated equidistantly can be milled. The feed screw,
being of a definite pitch like a lathe feed screw, is the basis for
the calculation of change gears. The division plates used are
like those on geometric
lathes, divided into
circles of holes which
receive the index
peg.
Figs. 49-52 illus-
trate one of the divid-
ing heads of this class
as fitted to the Nos. 2
to 4 Brown & Sharpe
universal machines.
Fig. 49 is a view
taken partly outside, Fig. 51.— Qniveraal Head. Transverse Section,
partly in section, show-
ing the head A fitting on the table B of the machine, c being the
feed screw. The head can be revolved either by hand or by the
feed screw. Enclosed within the head a are a worm and worm
wheel, seen in Figs. 50 and 51 at a and h respectively. The
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65
latter rotates the spindle, irrespective of any angle at which
the spindle may be set. The worm a is turned l^y the crank
handle E, Fig. 49, or it is rotated automatically by the feed screw
c through the change geara at the left. These operate through
spiral wheels enclosed in the head, and seen dotted in Fig. 49.
The worm gives divisions ; the
change gears impart precise rotary
movement to the spindle during
cutting, which produces spirals.
The spindle can also be rotated by
hand when cutting coarse divisions
like those required in reamers, end
mills, &c. The mechanism by which
this is accomplished is seen in Figs.
51 and 52. It is necessary first to
throw the worm out of gear with its wheel, which is done as
follows : — The knob c is turned by a tommy about a quarter
of a revolution in the opposite direction to that indicated by
an arrow which is stamped on the knob c. This loosens the
nut d, which retahis an eccentric bushing c. Then with the
Fig. 52. — Universal Head.
Disengaging Motion.
Fig. 53.— Universal Head.
fingers the knobs c and /are turned in unison, when the eccentric
])ushing e will ])e revolved, and the worm a thrown out of gear.
The spindle can then be turned quickly by hand, and locked
by the plate (j and pin h, Figs. 49 and 50. To throw the wonn
into gear again, turn the knobs c and/ in the direction which the
arrow indicates, and tighten the knob c with the tommy.
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MILLING MACHINES,
In these machines the cutting of 68 different spirals is provided
for. Three index plates are sent with the machines, having 15, 16,
17, 18, 19, 20; 21, 23, 27, 29, 31, 33; and 37, 39, 41, 43, 47, 49
holes respectively. The plate g, for rapid indexmg on the nose of
the spindle, has 24 holes.
Fig. 53 shows the spiral head used on the No. 1 B. & S.
universal machines. It is simpler than that just illustrated.
Fig. 54. — Plain Indexing Centres.
In this, as in the former one, tlie worm wheel has forty teeth,
80 that one turn of the index crank A, and worm shaft B, moves
the spindle c through one-fortieth of a revolution. By means
of the index plate D, tlie fortieth of a revolution can l)e further
sub-divided, and the sector E is set to divide the holes without
counting. The crank A is adjustable radially, so that the pin can
l^e used in any circle of holes.
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PLAIN AND UNIVERSAL MACHINES. 67
Bushings of steel encircle the spindle B and form a durable
pivot for the box F. The spindle and ])ox can be swivelled, and
set to any angle from 5" below the horizontal to the perpendicular.
One side of the hetd is graduated. Change geai-s transmit motion
from the feed screw to two mitre gears, one of which is seen in
the Fig.
Plain indexing centres by the Cincinnati Milluig Machine
Company embody some special features. The headstock has no
ix)wer of angular adjustment; but instead, the centre of the
Fig. 55. — Le Blond Dividing Head. Longitudinal Section.
tailstock is made movable in a vertical direction. The principal
elements of these centres are shown in Fig. 54, in sectional eleva-
tion, plan, and front-end elevation.
The spnidle A is carried in bearings B and c, the latter of whicli
is split to clamp the spindle, this being rendered necessary by the
fact that it has a power of endlong movement imparted to it,
because there is no such motion in the spindle of the tailstock.
To move the spindle endwise, grooves are formed for the grip of
the hand on the body of a sleeve D, which encircles tlie spindle a
about the centre, the spindle and sleeve being mutually threaded.
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68 MILLING MACHINES,
The sleeve on being turned by hand, while coerced by the uprights
B and c, moves the spindle A endwise. In order that the sleeve
shall not move accidentally, and that it shall turn when the index
plate is moved, it has frictional connection with the spindle by
means of a small screw a pressed on the spindle. By means of the
split bearing c the spindle is clamped after adjustment.
The spindle has a tapered socket at the front end to receive
the centre E, while a thoroughfare hole permits of the insertion of
a bar for shooting the centre out.
The indexing is done by the plate F at the rear of the spindle,
two or more of which are supplied. The pin G is adjusted up and
Fig. 56. — Transv^erse Section through Le Blond Dividing Head.
down, and clamped in a slotted standard cast in the top of the rear
bearing. The position is adjusted by means of a tinger, which
moves with the bearing of the pin over a scale on the standard, and
which indicates tlie row of circles in which it will engage in any
given position.
Figs. 55 and 56 illustrate the Le Blond dividing head, the
leading features of which are the following : — The body is circular
in form, and a solid casting, capable of swivelling through an arc
of 200^ or 10** below the horizontal on each side. A dovetail is
turned on each side. Fig. 56, by which it is clamped to the base with
two bolts, the heads of which are turned to the radius of the dove-
tail. The drive from the table screw, through simple or compound
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gear, takes place through a bracket bolted to the side of the base
(not shown), and which carries the quadrant for the change gears.
At the opposite end to the quadrant, a bevel wheel engages with a
bevel (not shown), running on a stud «, Fig. 56, in the centre of the
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70 MILLING MACHINES,
swivel head, and a spur gear connected to this bevel drives a spur
h on the sleeve of the index plate. The positions of the gears are
thus maintained at all angles of the swivel head. The head A is
bored taper to receive the spindle B. A worm wheel c encircles the
spindle, rotated by the worm D, solid with the spindle that carries
the division plate E ; F is the index pin. The spindle is clamped
by the locking plug g. The worm and its shaft are carried in an
eccentric sleeve provided with a slot, and stop, so that it can be
thrown into and out of gear rapidly. The worm gear can thus
be quickly disconnected when quick indexing is required by a
Fig. 58. — Longitudinal Section of Dividing Head.
dividmg plate alone, as in fluting taps, reamers, and cutting some
small geurs, sprockets, &c.
Figs. 57-59 illustrate a spiral headstock by the Cincinnati
Milling Machine Co. Fig. 57 shows the head in elevation. Fig.
58 is a longitudinal section through the head, and Fig. 59 a
transverse one.
Heads are mostly confined to angular movements, ranging
from 10" below the horizontal, to 10° beyond the vertical. In this
example the spindle A is carried in a swivelling block B, which is
capable of a complete revolution in a vertical axis, and the edge
of which is graduated into degrees. An advantage of this complete
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PLAIN AND UNIVERSAL MACHINES. 71
swivel is that it permits of the cutting of right and left hand
work without changing the cutter, and the cutting of the same
piece on each side of the vertical. Another is that the swivelling
block is always in any position contained wholly within its
bearings, and therefore adequately supported.
No strain is thrown on the spindle in clamping, which is done
on two clamping rings c, c, Fig. 59, embracing trunnions on the
block. The rings are pinched by the cap screws D, Fig. 57. As
the circumference of these is so large, no strain or distortion can
aflfect the spindle, or the worm gear.
Fig. 59. — Transverse Section of Dividing Head.
The spindle A is provided with a clamping ring at E, which
secures it endwise. Wear is taken up ])etween the coned neck
at the front of the bearing, and the coned bushing at the back.
The dividing mechanism includes the worm and wheel, index
plate, and sector, and another index plate F, added for low numbers,
or those under forty, the ordinary sector plate teing reserved for
those over forty.
Plate F, used for direct indexing, is provided with three circles
of holes on the back, namely, 24, 80, and 36, into which the index
pin Vx is inserted. The holes for divisions 4 and 6, which are
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MILLING MACHINES.
so often wanted for fluting and nut milling, are indicated by
corresponding figures on the edge to save the trouble of counting
round.
The regular index plate is seen at H with its index pin. It
is drilled from both sides to increase the divisions by simple re-
versal of the plate. Divisions are obtained by this in conjunction
with the worm K and its wheel L. The worm — right handed — is
single threaded, with 2\ threads per inch. The wheel has forty
teeth, so that forty turns of the index handle M turn it through
one revolution. The handle M turns the worm and wheel through
equal gears, P, Q, for dividing, or indexing only. For spiral work,
R is the gear through which changes in pitch are effected through
trains of wheels.
The worm K can be thrown out of gear by dropping it, with
its bearings, bodily, by the eccentric pin
N, the case being hinged about the pin a
as a centre. As the casing o is confined
in the lateral direction, the eccentric end
of the pin is inserted in a bushing, which
has an endlong movement in the worm
case. The latter is fastened to the
block containing the bushing with screws,
which afford means for adjusting the
w^orni to the wheel. The worm runs in a
bath of oil, and this can l)e cleaned out
on removal of the cap c.
The change gears are seen in Fig. 57, s being the lead screw,
with ball thrusts, T the swing plate, and u one of the two studs
for compound gears. Motion is transmitted through tlie l)evel
wheels v actuating the spur wheels in Fig. 57.
At \v a ratchet and pin are shown which permit of making
fine adjustments of the index plate for the purpose of re-setting
work.
Fig 60.— Footstock.
Footstocks. — The footstock of the Cincinnati Company is
shown in Fig. 57. The housing A carries the longitudinal slide B,
fitting with a dovetail. It is traversed by the knob c, and clamped
by the bolt D. The centre E is double ended, one end being the
ordinary centre for heavy work, the other being reduced on the
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PLAIN AND UNIVERSAL MACHINES,
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top face to permit cutters to clear it when depthing flutes. The
centre is therefore reversihle. It is adjusted vertically with a rack
and pinion, actuated hy a knob F, and is clamped by the bolt Cf.
The centre can be tilted forwards, or swivelled about the centre D,
exact angles being given by graduations at the rear of the housing.
The Brown & Sharpe footstock is shown in Fig. 60. Its
I f
Ih
B
Q
® :
» !
Fig. 61.— Footstock.
centre is adjustable for milling tapered work. Being adjustable,
it is set in a horizontal position by taper pins. It is elevated and
depressed by means of a small rack and pinion through a nut.
The nuts a, &, c clamp the centre in position.
Fig. 61 illustrates another tailstock in two horizontal sec-
tions, in vertical longit\idinal section, and in plan. The bar centre
A, it will be seen, moves vertically in the l)ody in a dovetailed
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74 MILLING MACHINES.
groove. It has rack teeth on the back, which are actuated by a
long pinion a, turned by a milled head B. The bar A has two
centres : one for stiff work of large diameter, the other for that
of small diameter, the face being cut away close down to the
centre. The pinion spindle is prevented from endlong movement
by a set screw h entering into a turned groove. The centre
A is clamped by means of a l)olt, the head of which is chamfered
to bed against the bevelled edge of the sliding centre.
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CHAPTER III.
ATTACHMENTS AND BRACINGS.
Vertical and Angular Spindle Attachments to Horizontal Machines— Examples
— Heads that Swivel Bodily — Examples— Slotting Attachments— Examples
— The Overhanging Arm — Bracings— Examples— The Work of the Pillar and
Knee Machine.
Vertical and Angular Attachments to Horizontal Machines.
— Several firms make an attachment for their universal milling
machines by means of which the direction of cutting can be
changed either to the vertical or to any angle. It comprises a
tool-holder which is clamped to the overhanging arm vertically or
at an angle. Its main spindle is driven by the horizontal spindle
of the machine, and drives through spiral gear or through bevel
gears the cutter spindle. It renders the machine available for
revolving cutters for key seating, for tee slots, for sawing off work
to definite lengths, &c. The spindle can be set at any angle in a
vertical plane through a graduated index.
The convenience of being able to do vertical, horizontal, or
angular milling on one machine is largely a concession to the small
shops. None of the early machines had this convenience. They
were either horizontal or vertical. Now there are many machines
of horizontal design that are rendered capable of vertical milling,
and many vertical spiiidle machines with provision for horizontal
milling. Angular work is usually included. These are often
effected by separate attachments, rather than l)y the swivelling of the
main spindle bearings ; but there are many instances of the latter,
especially in Continental practice, where it is very common,
examples of which are given on pages 78-82.
Fig. 62 illustrates a vertical spindle head by the Cincinnati
Company attached to a horizontal machine. It is fixed to the piece A
bolted to the headstock, by a large circular flange b, 8| inches in dia-
meter, and four f -inch bolts in an annular tee groove c, by which a
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76 MILLING MACHINES,
movement of 360' is available. A subsidiary advantage of this
swivel is that the head can be swung to an angle for the purpose
of changing cutters conveniently, which is done more easily thus
Fig. 62. — Vertical Spindle Attachment.
than with a rigidly fixed vertical spindle. Further support is
afforded to the swivelling body D by a bracket E, clamped to tlie
overhanging arm F.
The spindle g is tapered at the lower end for take-up of wear
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ATTACHMENTS AND BRACINGS. 77
by the lock-nut a, and runs in a bearing of babbitt. The upper
bearing is of bronze, tapered externally for taking up its wear, the
taper being drawn along in the bore of the head by the nut &.
The lower end of the spindle is clutched to match clutches on the
I I
I...
'-. (
Fig. 63. — Attachment for Spiral Milling.
shanks of the cuttei-s, which affords a positive, or non-slipping
drive. The taper is the same as that of the liorizontal spindle,
so that arbore are interchangeable on both. The ends of the
shanks are tapi)ed to fit the |-inch bolt shown at ii, by which
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MILLING MACHINES,
they are secured. The shoulder seen next the tail of the bolt
serves for backmg a shank out of its hole, as well as for drawing
it in. The nose of the spindle is threaded externally, like the end
of the horizontal spindle of the machine, so that chucks or disc
cutters are interchangeable on both.
The illustration. Fig. 63, is that of an attachment made to the
Cincinnati milling machines, to permit of doing spiral milling
when the angles exceed 45°. It will mill these when either right
or left handed, and also i)lain spur gears and racks.
The casing A of the attachment is lx)lted to the front of
the headstock, and further
steadied by the overhanging
arm. The cutter arlx)r a is
slewed to any horizontal
angle, and set by the l)olt 6
by the graduated horizontal
edge of the head A. The
drive takes place from the
main spindle through an
arbor B, which fits the spindle.
It is feather-keyed into the
driving bevel wheel, which
rotates the vertical spindle c
through another bevel wheel.
From c the cutter spindle a is
driven through spiral gears,
having a ratio of 2 to 1. The
advantage of this is, that as
the speed of the cutter arbor is
only half that of the main spindle, the belt is run at twice its
usual speed, and power is gained for heavy milUng. Gears of 3
diametrical pitch arc thus milled at a single cut. The thrusts
of the vertical and cutter spindles are taken with ball bearings.
A gauge is provided for setting the cutter centrally with the
blank. It can be adjusted laterally to bring the vee central with
the tooth of the cutter, and then reversed to bring the centre of
the tailstock central with the vee.
Fig. 64. — Swivelling Spindle Bearing.
Swivelling Heads. — A large group of machines have heads
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ATTACHMENTS AND BRACINGS.
79
that swivel bodily, in preference to making loose swivelling attach-
ments to ordinary machines. Arrangements are very diverse. A
selection, therefore, is given here.
The firm of Pr^tot, of Paris, make machines in which the spindle
bearing is pivoted near the cutter end, being moved over a quad-
rant B at the other, Fig. 64, in which it can be clamped at any angle
from vertical to horizontal. Adjustment is made by hand in the
smaller machines, but in the large ones by a hand wheel, which
actuates mitre wheels that turn a screw in a nut, which is connected
Fig. 65. — Swivelling Head.
to the bearing through the slot of the quadrant. The screw is
pivoted to give freedom of movement at varying angles. The driv-
ing and the guide pulleys are carried in a cast-iron frame of U shape,
which is attached to the upper end of the spindle bearing. The
spur gears, seen within the belt pulley, are used in conjunction
with two others, hidden by the pulley, as back gears, giving a slow
drive, more powerful than the belt alone will carry.
Vautier & Co. obtain vertical and horizontal movements by
using two separate spindles. Fig 65. The vertical one has to be
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80
MILLING MACHINES.
swivelled to one side to permit of the horizontal one being used.
To permit of this, the vertical head A swivels on top of the pillar B
to any horizontal angle, a provision which permits of doing angular
milling without swivelling the table. The horizontal cutter arbor
is carried between tlie horizontal spindle and an overhanging
bracket c having a centre, which arrangement is indicated by
dotted lines. The spindles are both belt-driven, the vertical one
direct over guide pulleys, the horizontal one from the cone pulley
through a pair of equal spur gears.
Fig. 66 illustrates the arrangement in the (French) Bariquand
& Marre machines. The head A can be set to any vertical angle
Fig. 66.— -Swivening Head.
on the face B of the pillar. The vertical sphidle is driven from the
horizontal one, through spur and mitre geai-s. When the horizontal
is in use, the head is turned round 1 80" on the vertical face B, to
bring the overhanging centre c for the outer arbor support into
line with the horizontal spindle.
A head by Sculfort & Fockedey has the spindles arranged as in
Fig. 67. The horizontal spindle is driven directly by the stepped
cones, or through back gear. That of tlie vertical is derived from
the horizontal, through the long pinion A, sliding on its shaft, and
pushed into engagement with the gear c by the knob B. a is
always in gear with a imiion enclosed in the hood D, on a
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ATTACHMENTS AND BRACINGS,
81
Fig. 67.— Swivelling Spindle Head.
Fig. 68.— Swivel Head Machine.
horizontal sliaft, which drives the vertical spindle through mitre
wheels. The bracket E can be set to any vertical angle on the
face of the graduated arm.
Figs. 68 and 69 illustrate a machine l)y E. Dubosc, of Turin.
F
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82
MILLING MACHINES.
The head A is adjustable for vertical angle on the face B of the
pillar, to bring either one of the two spindles into operation.
The horizontal spindle
BA is driven directly
through the stepped
cones c, with or with-
out back gears. The
vertical spindle is
driven from the spur
wheel next the large
cone step through a
spur wheel i). The
swivelling head has a
socket to receive a
steady bar E, which
carries a centre to support the overhanging end of the horizontal
arbor.
Fig. 69. — Head of Duboac Machine swivelled
for Horizontal Work.
Fig. 70.— Slotting Attachment for Pillar Machines.
Slotting Attachments. — Fig. 70 illustrates a slotting attach-
ment fitted to the Brown & Sharpe pillar machines. The
overhanging arm A receives the main casting B, clamped thereon
by the boss and split lug above. B is provided with a curved
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ATTACHMENTS AND BRACINGS.
83
slot below, which permits it to be radiated about the arm a, within
the limits of 10° on each side of the perpendicular, so that tapered
edges can be tooled as well as those which stand square, which
provision renders it suitable for the cutting of smiths* stamping
di«k To increase its rigidity, the main casting is bolted through
the curbed slot to a piece c, which is attached to the slide on the
front of the column of the machine.
The ram ie driven in the first place from a tapered shank,
Fig. 71.— Slotting Attachment.
shown broken at D, that fits into the spindle nose, and which has
a disc E, at its outer end, slotted on the face to receive a crank
pin, adjustable for radius, to give different lengths of stroke to
the ram f, connection being made through the rod g. The ram
slides between guides, one of which has a take-up strip.
The tool, of circular section, fits the hole a, a key in the tool
shank fitting the groove seen in a, to fix it in its correct position.
After being set, the lug &, slewing on the pin c, is brought round
and over the tool to receive the thrust of the latter ; h is locked
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84 MILLING MACHINES,
by the spring plunger entering by its pointed end a countersink
in the pin c.
A slotting attachment by E. M. Clough, of Tolland, Conn., is
shown in Fig. 71. A is the main milling and drilling spindle of the
machine, which carries a four-threaded worm B, driving the wheel c,
which reciprocates the connecting rod D, and thence the ram E.
The object in having a four-threaded worm is to reduce the speed
of the ram for slotting. As the wheel has forty-four teeth, it is
rotated but once to eleven revolutions of the spindle. The tool
holder F is pivoted on a pin at a, which lessens the dragging of
the tool on the return stroke, a spring above pulling it up to its
bearing in the ram ready for the next cut.
In the machine the milling spindle A is carried by a sliding
head moving on the face of the machine, similarly to many drilling-
machine spindles. It is racked vertically by the handle G, operating
an enclosed pinion and rack on the sliding sleeve. The bearing
is split to take up the wear of the sliding sleeve. The handle H
throws the worm wheel out of action when slotting is not being
done.
The Overhanging Arm. — The type of overhanging arm in
tlie pillar machines considered in this chapter, which is very gene-
rally adopted, follows in this respect the early Brown & Sharpe
model. It is fitted into and pinched in a socket above the cones.
The advantage is that it can be reversed end for end, turned
aside, or taken right away. These are conveniences, but some
rigidity is sacrificed thereby, and some trouble in readjustment
for centres. It ivS, when properly fitted and pinched, a very
satisfactory fitting, but only when so made. It is so seldom that
it is necessary to remove tlie arm itself that a good many firms
think it better to make it a rigid portion of the machine framing.
In these types the overhanging arm, cast with the headstock, is
a rectangular bar, grooved to receive an adjustable stay, with
movable centre. The adjustment of the stay is strictly lineal,
and it is therefore not liable to get out of line with the main
spindle. It is clamped to the arm in any position required. In
another type the headstock cap is prolonged to form a straight
overhanging, turned arm, and a socket, sliding along this, carries
the adjustable centre for the arbor. In this the socket can be
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ATTACHMENTS AND BRACINGS. 85
turned out of the way, but the arm remains fixed. This method
is adopted in the No. 4 B. & S. machine, the heaviest of their
imiversals, and on some of the heavier plain machines. Still the
arched arm is in greatest favour, because it is less in the way
when swung aside than a rigid arm cast with the head, and it
can be removed entirely. When a cross bracket is bolted up in
addition, connecting the arm to the knee, the arbor is absolutely
rigid under the heaviest cutting.
In the universal machines, not l)eing designed for the produc-
tion of the heaviest kind of work, but more specially for light
milling, gear cutting, fluting, and grooving, the overhanging arm is
often left unsupported. For the heavier classes of work, however,
for which the plain milling machines are better adapted, sup-
Fig. 72. — Arbor supported in Bushiug in Arm.
port is commonly afforded to the outer end of the overlianging
arm by means of two crossing slotted ribs, pivoted against the
knee below, and bolted to bosses in the end of the arm above.
These have a very slight appearance, but their triangular dis-
position affords ample stiffness under heavy cutting. Examples
of other supports, more or less substantial, are given in succeeding
pages.
One reason, perhaps the principal one, why overhanging arms
are nearly always now made of circular in preference to rectangular
section, is that the former is the better design for resisting all
the stresses which come upon it from all directions.
Fig. 72 illustrates an alternative to point centres for affording
support to the outer end of the arbor or mandrel. This is
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86
MILLING MACHINES,
a parallel end A, encircled by a split bush of phosphor bronze B,
fitting with a parallel body, and short tapered neck into the hole
in the arm. It is drawn in by the screw c entering into its end.
In this example three key-ways are milled in the bush, so that it
can be turned one-third round to equalise wear.
Bracings. — The pillar and knee type of milling machine is
seldom made without some form of bracing to tie the knee and
the overhanging arm together. However rigidly the knee may
Fig. 73. — Bracing composed
of Screwed Rods.
Fig. 74. —Bracing formed of Pivoted
and Slotted Rods.
be built, it is nevertlieless unsupported on one side, and there is
under heavy cutting operations some tremor perceptible, which
leaves its result in more or less chatter. For this reason some
firms prefer to abandon the overhanging design and provide a
solid base under the table, as in the Richards* design, making the
cutter spindle adjustable vertically.
But the greater number of firms retain the convenient form
of the open side table and vertically adjustable table and knee,
using bracings in some form or anotlier, which are more common
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ATTACHMENTS AND BRACINGS.
87
on the plain machines than on the universals, the reason being
that they have, as a rule, heavier duty to perform. For a large
number of operations on the latter the bracing may be dispensed
with.
A simple form of bracing is shown in Fig. 73. Two screwed
rods are brought down from lugs in the outer arm support through
similar lugs provided in the front of the knee. After adjustment
is made for height, the double nuts will securely tie the knee to
the overhanging arm above.
Fig. 75. — Bracing, with Rods in Clamping Bosses.
The earlier and a still common type of bracing comprises two
slotted bars crossing each other. In one design they are attached
by bossed ends to the cross-slide face as far apart as the width
of the slide will allow. They are then crossed against a boss on
the overhanging arm, to which they are bolted, the three bosses
fornimg a triangle.
In another form, Fig. 74, two bosses are provided on the over-
hanging arm, so that each brace has its separate lx)lt, and the
braces cross liigher up. In each case adjustment for height is
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88
MILLING MACHINES.
obtained through long slots in the braces, which slide over the
bolts.
An objection to braces of this kind is that they encroach
slightly on the cross traverse of the table, and in some cases they
prevent the putting on of wide pieces of work overhanging the
table, which it would often be desirable to do, but which the
presence of such bracing prevents.
In several Continental machines the brachigs provided are
different from any of those made in England or America. Two
round rods. Fig. 75, with bossed ends, are in some cases used,
these fitting and pivoting over a large pin in the overhanging
c
I
it*
i
r* ' — ^"n
n
Fig. 76.— Double Cast Bracing with Slot-hole Attachments.
arm. The free ends of the rods go through split lugs at the ends
of other rods, which lie horizontally along on each side of the
knee, passing through split lugs on the sides of the same. Both
sets of lugs have clamping Ix^lts, so that, at whatever angle and
height the braces are set, they are readily secured. A wide range
of horizontal adjustment of the rods and braces is obtainable in
this design to permit of the insertion of broad work.
Bracings of wrought iron or steel rods are not, however, so
rigid in themselves as it is sometimes desirable that they should
be. The methods by which they are attached make rigid con-
nections, but the bars themselves are subject to some vibration
when heavy cutting is being attempted. Theory indicates, and
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ATTACHMENTS AND BRACINGS.
89
experience is in favour of cast-iron braces, the substance of which
is more rigid and solid, and in which there is a better chance of
massing and proportioning the metal.
One of the stiftest bracings of this type is illustrated in Fig.
76. The vee*d edges of the knee are embraced by a vertical
standard, the two slotted uprights of which are connected at the
bottom with a deep cross bar, but having a space above which
Fig. 77. — Bracing screwed to Knee
with Bolts, with Adjustment
Slots.
Fig. 78. — Deep Bracing, on Arm,
Knee, and Base, with Slot
Adjustments.
cleara the overhanging arm when the knee is raised to its higher
IKJsitions. The end of the overhanging arm is embraced by the
boss of another bracket clamped on the arm, and having horns
with slot holes coincident with those in the lower bracket. The
two are bolted together at any vertical j)osition of the knee, with
four bolts. Tlie horns of the upper bracket are tied together with
a cross bar, and a boss serves as an outboard support for arbors.
Such a bracing as this is perfectly rigid, making of the knee and
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92 MILLING MACHINES.
is attained in many different designs, according to the ideas of
different firms.
The Work of the Pillar and Knee Machine.— It would be
more easy to say what this type of machine cannot do, than what
it is able to do. Its only limitations are those of dimensions, for
within its capacity, it is, in its highest developments, of universal
range. For the type includes l)oth the plain and universal designs,
while in most of the later machines some provision or other is
made not only for horizontal, but also for vertical and angular
cutting (see page 75). Besides this, the type is made larger and
stiffer than formerly, and better braced, so that, subject to its
limitations in capacity, it is the most generally useful machine
in the shop.
In this machine the height of the spindle being unalterable,
the feeds are unparted to the knee, and all that it carries in the
form of table slides, gears, &c. This taxes the elevating mechanism,
and requires good fitting if unsteadiness is to be avoided.
The alignment of the outer support of the spindle bearing is
embodied in the machine. The task of the workman therefore is
confined to setting the work truly in all directions, and attending
to the feeds. Methods of holding are illustrated in later chapters.
Plain edge and profile milling are the special work of the machine,
but a good deal of face milling is also done. Tiie universal
machine will do all that the plain miller will do, but the utilities
of the latter are limited by comparison with the former. The
plain machine being, however, built more heavily of the two, is
preferably to be selected for heavy duty, and the univeraal for
lighter, and for that specially requiring the swivel table and spiral
head. Work requiring the dividing head alone, without the spiral
movement, is better done on the plain machine if heavy cutting is
desired. The functions of tlie two, therefore, notwithstanding their
general resemblances, are kept distinct in shops where economical
considerations are allowed to prevail.
On the universals there is no operation of the machine shop
which cannot be i)erfornied, not merely as a makeshift, but as a
perfectly fair and legitimate function. This, of course, excludes
the work of the turning lathes. It is also true to say that any
operation of the machine shop can Ije i)erformed on the lathe if
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ATTACHMENTS AND BRACINGS. 93
fitted with suitable appliances and adjuncts. But much of this is
not l^itimate work for the lathe; in fact, many jobs when so
done are not done economically, but from necessity or through
force of circumstances and conditions. On the milling machine
it is all regular work, for which the machine has l)een specially
designed. The exception noted to the work of turning is not
absolute either, since wheels with very light rims are often milled
more rapidly and more accurately than they could be turned in a
lathe. The universal machine, therefore, fitted with suitable
adjuncts, is capable of milling in rectangular relations, or at an
angle, of milling circular outlines, or spiral flutes in a wide range
of pitches, of cutting spur, bevel, worm, and rack gears, and cams,
and all with a degree of precision for which little or no provision
is embodied in other classes of machines, some of the most modern
lathes and gear cutters alone being exceptions. The universal
machine, as made by a few firms, is about the most beautifully
designed and fitted article in the machine shop.
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CHAPTER IV.
VERTICAL SPINDLE MACHINES.
Vertical vermu Horizontal Spindle Machines — Vertical Spindle Machines— The
I^rofiling Machines — Various Examples — Designs of Vertical Spindle
Machines— Built after the Model of Drilling and of Slotting Machines —
Examples — Spindles coming from Below — ^The Work of the Vertical Spindle
Machine— The Work of the Profiling Machines.
Vertical versus Horizontal Spindle Machines. — ^A question
that often arises is the relative utilities of vertical and hori-
zontal spindle machines, and also the relative values of face and
edge cutters.
The principal advantage of having the face of the work lying
horizontally is that it is under observation, and that heavy masses
can be handled and set better, as a rule, in that position. Fasten-
ing flatwise directly to a table is usually more convenient than
bolting to the vertical faces of an angle plate. With a vertical
spindle, both faces and edges can be milled with face and edge
cutters respectively, without re-setting the work. This is not so
conveniently done with horizontal spindles. Hence we find that,
piano-millers excepted, the vertical spindle machines are more
frequently employed than the horizontals for general engineers'
work. The Lincoln miller is used more largely, in some of the
lighter industries, but not so in engineers' shops. Besides which
it was the first in the field, and has therefore had more time to
become established.
Face and edge milling are often employed indiflFerently on
vertical and horizontal faces. An advantage of working on vertical
faces is that the chips fall away at once. On horizontal faces they
should be swept off with a hand bnish. Sometimes a suction
pipe or a blast pipe with compressed air is used for the purpose.
Whether the spindle of a milling machine shall be horizontal
or vertical depends mainly on the class of work for which it
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VERTICAL SPINDLE MACHINES, 95
is selected. On the universal machine the horizontal position is
preferable, because it is more convenient for gear cutting and
fluting, and for work done by form cutters with linear traverse.
The lubricant, too, lies on the work more efficiently under hori-
zontal cutters. Generally, for broad-edge cutters also, the hori-
zontal position of the spindle is best.
Vertical spindles are generally preferable when end mills are
used. Profile milling must generally be done with vertical
spindles.
On the other hand, the heaviest work is performed with
horizontal spindles on machines of the planer and slabbing type.
Better support can be aflforded thus to the arbor, and therefore
longer arbors can be used on the horizontal than on the vertical
spindles. The latter are frequently supported at the lower end for
heavy work, but not so efficiently as the former can be on their
sliding heads on stifiP uprights. Heavier cutting can be done on
the planer type than on the vertical type.
Vertical Spindle Machines. — The pillar and knee type of
machine has to be greatly modified when a vertical spindle is
employed, and dimensions increase. The knee, always a weak
element, is then frequently abandoned, the base of the pillar being
extended — ^in slotting-machine fashion — to carry compound tables
having no vertical feed. Then the vertical feed is imparted to
the spindle and spindle head, and these are counterbalanced. The
machine thus much resembles in outline a powerful drilling
machine. Frequently also geared drives are abandoned in favour
of the belt drive over guide pulleys.
These machines include examples of the heavier and the lighter
types, constituting a large group, the members of which are
employed more extensively than others, the Lincoln, and pillar and
knee excepted. They have both their advantages and disadvan-
tages. They take the place of the slotter in tooling circular pieces,
and perform the work more correctly, because the slotting tools
produce minute facets, leaving finish to be imparted in other ways.
The vertical miller tools internal and external portions on a
piece without re-setting, or on segmental pieces arranged in
circular order. Both faces and edges can be tooled without
re-setting — faces with face mills, and edges with edge mills.
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96 MILLING MACHINES,
It is also the best type of machine on which to fit profiling
attachments.
The disadvantage of the type is that due to milling on hori-
zontal faces, which does not permit the cuttings to fall away as
they do from vertical faces tooled from horizontal spindles. And
when vertical faces are being tooled on it with edge mills, limita-
tions of depth come in, due to the spring of the arbor. This is
controlled in the heavier machines by a bottom supporting bracket,
which fulfils the same function as the outer arbor support on the
horizontal spindle machines. This support is variously fitted,
being sometimes brought down from the lower spindle bearing,
sometimes hinged at the side of the upright. But the essential is
that it shall have provision for being swung aside, to permit of
doing work for which the support is not required.
Within the very comprehensive generalisation of the vertical
machines there is included a large number of designs, varying in
the methods of the drives, through gears or belts, with vertical
adjustments imparted to tables or to spindles, and with heads
having one range of movement only, or combining horizontal or
angular settings.
The Profiling Machines may be common vertical spindle
machines first, to which profiling movements are added, or the
profiling may be the principal function, plain milling being a
secondary thing. The first division generally embraces the larger
machines, the second the smaller ones.
In profiling machines the table is not adjustable vertically,
but that movement is effected in the spindle. The machines in
some cases have rigid knees, on which the main table slides, in
others a bed of greater or less length carries the table, which
then resembles the general type of planing machine, and the spindle
slide is carried on a cross rail adjustable on the faces of housings
attached to the bed.
Methods of profiling are described later. The essential of a
profiling cutter slide is that it shall be coerced, not by screws,
but by the pull exercised by a weight suspended from a chain.
The friction of the slide is lessened as much as possible by
fittmg rollers to the lower or the upper bearing edges, and
steadiness is secured by giving a long contact l)etween the slid-
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VERTICAL SPINDLE MACHINES. 97
ing parts. The former pin may or may not have a range of
adjustment. The spindle is driven directly by belt in the smaller
machines, through cones and back gears in the heavier. The
mass of the spindle and its bearings is counterbalanced. Though
most profiling machines have vertical spindles, an exception
occurs in some made by Messrs Webster & Bennett, of Coventry,
which have horizontal spindle heads resembling those of lathes,
on a lathe form of bed.
Small machines for general milling and profiling have vertical
spindles of from f inch to 1^ inches diameter. A horizontal cross-
head is cast with two uprights, and the latter are bolted to a box
base which carries guides for a table, upon which the work is
traversed under the mill. A carriage slides transversely along the
crosshead, adjustable by handle lever, and the spindle slide moves
vertically on the carriage, its movement being adjustable by means
of vertical stops. In these the spindle is revolved by means of a
belt and drum only. The traverse of the carriage, and also that
of the table, is effected by hand. Light double-spindle profiling
machines are also made nearly similar, so far as the methods of
operation of the slides by hand are concerned. The traverse
movement of the slide is efifected through spur gear and a rack
on the bottom edge of the slide. The driving of each spindle is
from a long drum at the rear, driving lialf -crossed belts on to the
spindle pulleys, the drum being fitted with fast and loose pulleys.
The spindles are balanced with springs above.
A vertical spindle machine of simple design, by Messrs Webster
& Bennett, is shown in Fig. 82. The style of frame provides for
carrying the table slides without vertical adjustment, this being
imparted to the spindle slide only.
The method of driving the spindle A is by the belt pulley B,
which runs upon a sleeve, in order to relieve the side pull ; to B
the belt is carried over idler pulleys c, from the driving one D.
A four-stepped cone on the same spindle as d provides for varia-
tions in speed. Some types of this machine are without gear, but
others have a back gear contained within the pulley B.
The spindle is moved up or down by the slide E, which is
travelled by the balanced handle F. On the same shaft as the
latter is a worm, which drives a wheel working upon a vertical
screw, so imparting a fine feed to the slide E. As the lower end
G
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MILLING MACHINES,
of the spindle A is confined in E with collars, it partakes of the
movements up or down, the upper splined end passing through
the pulley B, in which keys drive on to the spindle, while stUl
permitting the latter to slide endwise. A stop screw G, in a boss
on E, abuts against a lug standing out from the fixed frame, seen
D
Fig. 82. — Vertical Spindle Machine.
in the figure, and so provides for a definite depth of feed, which
may be repeated as often as desired on repetition pieces.
Tlie table movements are effected by the handles seen, or the
longitudinal feed by power through the four-stepped cone H,
driven from a pulley forming an extension of D. H imparts motion
to another cone J, revolving a shaft K. The latter drives a worm
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VERTICAL SPINDLE MACHINES. 99
beneath the apron L, engaging with a wheel which is splined on,
and rotates the feed screw, on the end of which the balanced
handle is seen.
An automatic knock-out is provided, which drops the worm
Fig. 83.— Vertical Spindle Machine.
out of engagement with its wheel at a predetermined position of
the table travel. This is effected by dogs bolted on the under
ledge of the table at m. When one of the dogs strikes against
the end of the lever N, the latter, which normally holds the worm
in a hinged box up to engagement, allows it to drop, so letting
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the teeth out of mesh, and stopping the feed. The cases where
this feed are used comprise those in which a long cut is taken,
and the stop is set to trip the feed at its termination. For short
work the hand feed is employed.
Fig. 83 is a vertical spindle machine by J. Parkinson & Son,
which embodies vertical movement to the table instead of to the
spindle. The latter is driven by a plain pulley A, through idlers
B, B ofif a pulley c, the latter being given four speeds through the
cone D on the same shaft.
The tables are operated through the handles seen, or the
longitudinal and cross movements are actuated by power. The
feed is derived first from the three-stepped cone E, on the same
shaft as c and d. e drives up to another cone F. On the same
shaft is a two-speed pulley g, driving down to a similar one H.
It will be seen that, by means of the two sets of cones, five rates
of feed can be obtained for each rate at which the spindle may be
driven.
From the shaft of H a pair of mitre gears j drives a short
horizontal shaft K, upon which a worm and worm wheel convey
the motion to a vertical shaft L, mitre gears M at the top of which
drive a horizontal shaft within the knee. The shaft L is splined
to slide through the worm wheel, to accommodate itself to the
vertical table movements. The shaft N, driven by the mitres M,
first rotates the feeding screw above it (on which is the handle o)
through a pair of gears, and also the screw in the longitudinal
table P through mitres, seen dotted in the views. A trip device
is fitted to the table P, seen in the front elevation, the block Q
striking a lever R, which disengages the feed within the table.
The vertical travel of the knee, and table is effected by the handle
s, working bevel gears which rotate the vertical feed screw T, turn-
ing in the threaded foot at the base.
A profiling attachment is made for use on this machine, which
embodies the principle of the former or templet, controlling the
movements of a roller. Three views of this device are seen in
Fig. 84, in plan, and front, and side elevations. A circular revolv-
ing table A is driven by worm gear through spur wheels, actuated
by another worm gear, which derives motion from a telescopic
shaft, the latter being employed because of the irregular move-
ments of the table under the guidance of the former. The work
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VERTICAL SPINDLE MACHINES. 101
is carried upon a small table B, the edge of which is shaped to
the required outline to be milled ; a roller c presses against the
edge, being held in a bracket D. The holder of the roller c is
capable of adjustment with a screw E, to permit of milling sizes
larger or smaller, and giving the depth of cut. The sliding table
A, and small table b, are pulled against the roller c by weights F.
y
Fig. 84. — Profiling Device for Parkinson's Machine.
It will be seen therefore that on revolving the table A, it will
partake of the motion given by the profile of B (which is that
of an ellipse in the illustrations), and so bring the work likewise
against the cutter.
A circular table, also fitted to the machine, is shown in Fig. ^'^^,
It is bolted down to the tee slots of the main table, and is pro-
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vided with a worm and hand wheel, which rotate it. Graduations
are made around the edge. The worm can be thrown out of
engagement, to enable the table to be rapidly turned for purposes
of adjustment. It can also be locked when straight portions
have to be milled, the circular ta,ble being then carried along
bodily by the machine tables.
A vertical profile milling machine by Messrs Webster &
Bennett of Coventry is shown in Fig. 86.
The drive to the spindle is by belt from a drum at the
rear, which is necessarily made long to permit the belt to follow
the cross traverse of the carriage c along the cross rail D, in the
act of profiling. The carriage runs on rollers on the top of the
cross rail, in order to reduce the friction as much as possible.
The spindle slide E has a
j^—— -g^j—^— gj vertical adjustment on c.
S^ 1*^^^^^ The former pin is seen at fl.
This is held closely against
tiie form or pattern by the
pull of the weight seen at
the side, which draws the
slide c by the chains in-
dicated, passing over pul-
leys. The saddle c can be
clamped on the cross slide
Fig. 85.-Circular Table for Parkinson's Machine. I> when Ordinary mUling
has to be done.
The table F has a longitudinal feed, that is, perpendicularly
to the faces of the slides, derived from the stepped cone G,
through the train of spurs, and worm gear shown, to the rack
beneath the table. The stops h &, on striking the lever c, reverse
the motion through the claw clutches rf, on the worm shaft H.
A handle put on H affords a hand feed to the table.
The table also has a circular feed through worm and spur
gears, which can Ije disconnected instantly by throwing out the
clutch c. A pump J is belted from the main driving shaft. The
body of the machine forms a sud tank.
With increase in the diameter of spindles, the profiling
machines approach more nearly in the length of table and bed, and
in general appearance to the planmg machine framing. A circular
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t
^ I <S
53
a
1
table is also often included, being detachable from the rectangular
table when not required. This is provided with a central arbor, and
with worm gear for rotating the work. A cutter stay is also
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104 MILLING MACHINES.
attached, being made so that it can support the lower end of the
mandrel or arbor in any position. It is attached to and swivelled
upon the spindle slide, and locked in any position. In some
machines the slides are indexed with steel rules, and the circular
tables are also indexed. Machines of this kind are made with
spindles up to 6 inches diameter.
As the capacities of these machines increase, nearly every
detail becomes much modified. The hand lever, by which the
cross traverse of the spindle slide is adjusted in the light
machines, gives place to a weight, the chain of which passes over
pulleys at the head of the framing. Tables are extended, so that,
instead of getting a table traverse of from 12 to 18 inches, we
have traverses equal to those of the average planing machines,
so that objects can be profiled up to 4 ft., 5ft., and 15 ft. in length.
Tiie tables are, in fact, like those of planing machines, made with
numerous tee slots, and running on flat beds with vee'd edges.
They are driven by screw, have self-acting feeds, reversals, and
quick traverses by power. Troughs around the edges are provided
to catch the oil. The feeds of the traverse carriage, though still
capable of being operated by hand, are also rendered self-acting,
and variable, and reversible. Again, though machines of very con-
siderable dimensions, up to those with 2-inch spindles, are driven
by belt, the spindles of those of large sizes are driven through
stepiped cones and bevel gears. In some machines, again, the cross
slide is not confined horizontally by the uprights, but slides verti-
cally upon them, exactly as in a planing machine, being adjustable
by hand or by power. To all machines of this kind a centrifugal
pump is fitted for the lubrication of the cutters.
These types of machines are equally suitable for the work of
general milling, the profiling attachment being a convenient adjunct
superadded, and one which extends the usefulness of the machine,
without detracting from its value as a piano-miller.
The principal vertical spindle machines may be broadly
classed as those having tables fixed in regard to height, and
those in which the tables have vertical adjustments and
feeds.
The first-named great group have framings much resembling
those of the slotting machine, or the similar outline of drilling
machine framings. There is a broad base, usually cast in one piece
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VERTICAL SPINDLE MACHINES, 105
with the uprights, with slides to carry the table slides, and an
overhanging head, either cast with the upright, or bolted to it.
The spindle bearings are movable vertically, and the lower bearing,
or the entire bearing arrangements have vertical adjustments, not
only to suit the height of the work, but also to afiford support to
the cutter close to the latter. The spindle ranges from 3 in. to
5 in. diameter. The spindle slides are counterbalanced in various
fashions, and are adjustable by hand, and also by power in the
heavier machines, the latter being a slow motion by a belt-operated
worm and a wheel. Tlie spindle drive takes place through
stepped cones, with back gears included, and through bevel gears
for changing the direction of motion in all the older, heavier
machines, and in the majority of the recent ones. But a consider-
able number of the latter are now fitted with high-speed belt drives,
even in heavy machines. The belts then come over guide pulleys,
driving immediately to the spindle, which can be operated directly,
or through back gears. Bevel wheels are eliminated in this design.
The pull of the belt does not take place directly on the spindle,
which would produce unequal wear in the bearings, but on a sleeve
which encloses the spindle (see page 109).
Feeds are taken from belt cones, and all the table motions are
self-acting, and controllable by the attendant at the side or front
of the machine. A circular table is almost invariably included,
also made self-acting through worm gears. Tiie tables are com-
pound ; if the additional table is not circular, but square, it has
the circular motion. The feeds, which are towards or away from
the vertical frame, transversely thereto, and circular, are each self-
acting and reversible through gears and screws, and worm and
wheel, similar to those employed in slotting machines. The
reversals are effected by hand, either through three bevel gears
and a sliding clutch in many machines, or by means of a friction
disc and roller. Each feed motion also is capable of disconnection
by means of friction clutches, and of quick hand traverse. The
circular table is in the way of fixing work for plain milling, and
is therefore removable. But in some designs this is rendered
unnecessary by the simple device of flanking the circular table
with wing tables, which partake of the rectilinear movement of
the slides below. The faces of these stand a trifle higher than
the face of the circular table, so that work bolted to them clears
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106 MILLING MACHINES.
the Qircular one, and can be thus tooled without removing the
latter. On vertical spindle machines, fitted with compound slides
and circular table, all rectilineal work can be done with face or
edge mills ; and all curves, alone or in combination, with straight
edges.
It is an exceedingly useful tjrpe, better suited, perhaps, than
any other to the requirements of the general shop. It covers a
large volume of work, and will take heavier and larger pieces than
the pillar machines pre\^ously noted. It is made in a wide
range of dimensions. Some of the machines of this class which
have been constructed in recent years are exceptionally massive
and stifif, capable of doing plenty of heavy cutting. The details
are worked out in many ways by different makers, so that
beyond the main design there is not much in common between
them.
An imsatisfactory feature of the ordinary slotting-frame type
of milling machine is the projecting unsupported spindle, re-
sembling in this respect the ordinary drilling and slotting macliines.
It is not possible in some jobs to use the bottom supporting bracket
provided in many machines of this class. There are two methods
in use, therefore, for supporting the spindle and increasing its
stiffness as far as possible, one of which in its essential features
is embodied in most American drilling machines, and on a very
limited number of slotters.
In a vertical milling machine by Hulse & Co. Ltd., steadiness of
the spindle against the pressure due to the stress of the cutting
action is ensured by enclosing it in a long, hollow square slide,
making it run in conical bearings therein. The slide is made
capable of vertical movement, and can be set and clamped by
a locking screw at any height required. Vertical movement of
the spindle is provided for by means of a pinion that embraces
it, and which is driven by a pinion long enough to cover the whole
range of travel of the spindle. The weight of the spindle and slide
is slightly overbalanced by means of a balance weight. Several
firms, both in England and America, construct vertical milling
machines of the slotter type in wliich the spindle head can be
adjusted vertically by a hand wheel and gear to suit work of
different depths.
In the second great group of machines the knee is adjustable.
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VERTICAL SPINDLE MACHINES. 107
the arrangements then resembling those of the pillar and knee
machines. The objections to this design increase with mass, and
therefore it is not adopted much for the heaviest types, though
some good massive examples occur. Tlie vertical adjustments of
the knee are not always employed for feeding as in the ordinary
pillar and knee machines. Frequently it is a movement of adjust-
ment only, the cutting feeds being imparted to the spindle, as being
more convenient. These generally have a micrometric device, and
in good machines an adjustable dead stop which regulates the depth
of cutting for any number of similar pieces.
Tlie three views, Figs. 87-89, give general and side elevations
of a vertical milling machine by Messrs Alfred Herbert Ltd., of
Coventry, which combines the best points of present-day practice.
It is a massive tool, weighing about 6,000 lbs. The leading dimen-
sions are: — Longitudinal feed of table, 36 inches; transverse feed,
12 inches; vertical adjustment of table, 12 inches. The spindle
is 2f inches diameter. The circular table is 16 inches diameter.
The maximum distance from the surface of the table to the spindle
is 19 inches. Feeds are automatic, are reversible, and have auto-
matic trips in both directions, and dead stops to table feed. Gears
are all enclosed, and lubrication is amply provided for. The
machine is of the type in which the knee is adjustable vertically,
and the spindle has similar adjustment, the fine adjustments
being given with the latter. The spindle is belt-driven, direct
or through spur gears, no bevels being used anywhere in the
driving mechanism. These are the leading elements, whence we
now proceed to work through the details, enlarged views of which
are given in subsequent Figs. 90-97.
In Fig. 88 the countershaft is driven by two sets of pulleys, A
and B, at 375 and 150 revolutions per minute respectively. The
single-shipper lever shown actuates each set of striking gear by
being pulled into contact with either one of the two sets of blocks
a, a on the shipper bars. The three-stepped cone pulley c drives
to the spindle, the two-stepped cone D to the feed cones, and the
pulley E to the pump.
Commencing with the spindle details, the cone pulley F is
driven by c. As these have three steps, and there are two counter
speeds, this gives six spindle speeds for either belt or back gear,
so making twelve in all. They range from 20 to 500 revolutions
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108 MILLING MACHINES,
Fig. 87.— Vertical Spindle Machine. (A. Herbert Limited.)
per minute, the quicker speeds l)eing reserved for tine finishing
with the smaller cutters. The drive takes place from the pulley G
on the cone sliaft Ijelow, over the two guide pulleys ii to the
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VERTICAL SPINDLE MACHINES, 109
spindle pulley J. The latter, it is to be observed, is not keyed
directly on the spindle, but its pull is taken by an intermediate
bush or sleeve K encircling the spindle, relieving the spindle of
Fig. 88.— Side Elevation of Herbert Vertical Spindle Machine,
side pull, which would cause unequal wear. The driving of the
spindle is transmitted as follows (compare with the details which
are shown enlarged in Fig. 89) : —
The boss of tlie pulley J is keyed on a boss encircling the sleeve
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K, and this boss forms an extension of the firat gear J. h drives c,
with which gear d is solid, and d drives e. c is secured to a driver
plate/. L is an equalising driver, whence motion is transmitted
to the spindle by two keys g, Qy to receive which the spindle is
splined on opposite sides down a good portion of its length to
allow of its sliding motion taking place. In this way the spindle
Fig. 89.— Details of Spindle Drive.
drive is given through the back gears &, c, rf, and e. All these are
enclosed by the light cast-iron casing shown in Figs. 87-89.
The back gears c and d are mounted on an eccentric spindle,
whicli is thrown in or out by worm gear, indicated in the figure,
and actuated by the hand wheel h to the left of the machine.
Direct driving then takes place on locking the wheels e and h
with a spring pin j, seen in the detail to the right of Fig. 89, the
spindle being rotated by the driver L and keys g,g as before. The
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handle h in the figure is used to revolve the driver until the pin j
comes over its hole, the casing preventing this operation being done
by pulling on the wheel itself. The tension of the belt on the pulley
J is maintained in an alternative design of the machine by means
of the sliding bracket N, Fig. 88, and of its set screw in opposition
to the abutment piece on the main framing.
A slide which carries the lower bearing of the spindle is
capable of vertical adjustment to move the latter and afford con-
tinual support close to the cutter. Exact feeding is attained with
the hand wheel o at the front, operating through a worm and
wheel enclosed in the casing seen. On the same spindle as the
Fig. 90. — Side Elevation of Reversing Gear Box.
"worm wheel is a pinion, which gears into a reujk on the machine
frame, and so racks the bearing up or down. A dial I, mounted on
the hand-wheel spindle, is graduated into thousandths, and is
adjustable to zero in any position, in which it may be then locked.
The motion of the spindle bearing can be arrested at any height
by the setting of the vertical stop m, which has fine screw adjust-
ment and a lock-nut. A handle n locks the slide when face cutting
is being done, and both this handle and the stop handle " lock "
when in the horizontal position. The slide is balanced by weights
p within the framing, the chain for which passes over guide pulleys,
the anchorage being at o.
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MILLING MACHINES.
The conical spindle bearing is of hard phosphor bronze, with
provision for taking up wear. The end thrust is taken by washers
of hard tool steel and phosphor bronze. The spindle is of crucible
steel, bored throughout. Its nose has a No. 10 taper, with a
clutch drive for the arbors. The latter are retained in place with
a draw bolt. The nose is threaded to receive large cutters, and
when these are not in use the thread is protected by a cap.
Tracing next the table feeds from the countershaft pulleys D
to the pulleys Q on the machine, these drive four-stepped cones R
and s, giving eight feeds, doubled by the pulleys A and B on the
counter. They range from -500 to 12"75 inches per minute. The
Fig. 91.— End Elevation of Reversing Gear Box.
feed motion for the circular table is transmitted through the revers-
ing gear box T to the vertical shaft u, thence through spiral gears
to the horizontal shaft v. A comparison of the views of this box
in Figs. 90 and 91 will render much description unnecessary. The
reversal is effected by the handle jp, which slides a splined clutch
into engagement with either one of a pair of loose bevels, so driving
the wheel in the nest of three gears in one direction or the other
in a manner well understood. The extreme positions of the handle
are fixed by the studs outside the box.
The table feeds, derived from the shafts u and v, may now be
studied in Fig. 92, compared with the general views. Figs. 87 and
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VERTICAL SPINDLE MACHINES, 113
88. The two views of the machines are not wholly alike, because
the general views include a circular table which is not illustrated
in the details ; but that does not affect the main table drive, which
we are now to consider.
Taking up the connection at the vertical shaft u, and horizontal
shaft v, the function of these is to drive the circular table in the
manner indicated in the side view, Fig. 88, but not shown in detail
there. The drive of the oblong table takes place from a vertical
shaft w within the framing, which is actuated from bevel gears
dii-ect from the gears in the reversing box (compare Figs. 91 and
Fig. 92.— Detail of Knee, and Table Drives,
92 with Figs. 88 and 93). At the upper part of w a sliding spiral
gear q^ is seen, which is the first element in the table feed, g', with
a nest of gears is carried in a bracket which is bolted to the back
of the knee, and therefore moves vertically with it, the corre-
sponding sliding of the gear q being provided for in the splining
of the vertical shaft w. y drives a spiral of equal size at right
angles on the end of a shaft which carries four spur gears driving
four smaller gears on a shaft s. On the latter, and mounted be-
tween the spurs, are two worms driving worm gears 5' s on the
shaft and screw t, t, the worms being double-threaded. The shaft
H
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MILLING MACHINES.
and screw t, t come out through the knee nearly to the front, Figs. 92
and 94, where, by means of a train of three spur gears each, the
middle one being an idler, they are connected to the hand wheels
X, X at the front of the knee. The hand wheels are thus separated
sufficiently far to permit of both being retained on their shafts at
one tune, while the idler wheels allow the rotation of the hand
wheels to take place in the same direction as the shaft and screw.
As the worms can be dropped out of mesh with the worm gears,
the shaft and screw can be worked either by power from the one
end, or by hand from the other.
c-a
1
;. i.
Fig. 93. — Detail of Driving Gears in (Doluniu.
Tlie connection between one of the shafts t and the screw Y
that imparts the longitudinal feed to the table is easily seen, being
traceable through the mitre gears in Figs. 92 and 95. The trans-
verse feed to the knee saddle is through the medium of the nut u
seen in Fig. 95. The vertical adjustment to the knee is clearly seen
in Figs. 92 and 94 The three screws for these motions, are of
the Acme form. The weight of the knee is taken on a ball race,
and the crown bevel wheel is of large diameter. From these
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VERTICAL SPINDLE MACHINES. 115
s
ja
^
o
t
three movements we now pass to notice the locking and other
arrangements.
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MILLING MACHINES.
h
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VERTICAL SPINDLE MACHINES, 117
It will be observed that every slide h«ts its locking handle or
handles. These include the table, knee, and saddle. The various
locking handles are all distinguished by the letter v in the views
(see also Fig. 96). All the feed screws have micrometer adjust-
ments, the dials for these being indicated by the letter w^ and
one is shown enlarged in Fig. 97. The handles z, z, Figs. 92 and
95, are for dropping the worms on the shafts into and out of
engagement with their wheels. These handles drop the box x
which carries the worm shaft s. The box pivots around the axis
of the shaft p, and thus the movement of z and the rod y throws
it down or up, breaking or effecting gear between the worms and
their wheels s', /. This is a spring plunger to cause the box to
drop with certainty (see Fig. 92). The movement of the rod y
Fig. 96.— Locking Handle of Gib. Fig. 97.— Micrometer Dial.
automatically, constituting an automatic trip, as shown in Figs. 92
and 95. The adjustable stop z clamped to the tee slot on the edge
of the table, coming into contact with the top of the spring plunger,
seen adjacent to it, thrusts down the lever aa, and with it a lever
within the knee which bears on the upper ends of rods hh, Fig. 92.
Tliese press on the rods y, and so throw out the gear box x at any
predetermined point. The spring plungers in the knee under the
rods y serve to just hold up the latter from dropping when in
gear and locked. In addition to these automatic trips, dead stops
are fitted — ^blocks clamped in the tee slots of the table edges,
and abutting solidly against the automatic plimger casing instead
of passing over the rounded top of the plunger. All these stop
blocks are tightened up with handles instead of providing hexagon
nuts, so that no separate spanners are required.
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MILLING MACHINES.
r"
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Fig. 98. — Side Elevation of Vertical Spindle Machine.
(B. & S. Manufacturing Co. )
Very complete arrangements are made for lubrication. There
are the pump, tank, and feed pipes seen in the general views, Figs.
87 and 88, and the numerous waste-oil trays and lubricators shown
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VERTICAL SPINDLE MACHINES.
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Fig. 99.— Front Elevation ofMachine.
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MILLING MACHINES,
Fig. 100. —Plan of Head, and Sectional Elevation of Head.
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VERTICAL SPINDLE MACHINES. 121
in the details. Especially should those in Fig. 92 be observed, to
be supplied through the doorway marked "Oil Gears," Fig. 93. Also
Fig. 101.— Details of Spindle Feed.
the taps for drawing oflf the lubricant from the trough around the
table in Fig. 95. When the full system of piping is fitted, unions
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122 MILLING MACHINES,
go in these holes, and allow the liquid to run down through the
flexible pipes, shown in the general views, into the tank to be
again pumped up.
The drawings of this beautiful machine will repay a more
extended study than we have afforded it, many minor details
being passed over without comment. A high-class machine tool
such as this possesses an interest and fascination which increases
with closer knowledge.
Figs. 98-103 illustrate the latest Brown & Sharpe vertical
miller. Its principal interest centres in the feeds, which are
derived from a shaft running at constant speed, instead of from
stepped cones. The general outlines of the machine are shown
in Figs. 98 and 99. It is of the elevating knee type, the
vertical movement being 15 inches. The spindle has a range of
vertical feed of 4 inches up or down. The latter makes from
17 to 354 revolutions per minute, and has fine hand feed, and
quick return by separate hand wheels. The table travels 34 inches,
and has a transverse movement of V6\ inches. The arrange-
ments for feeding are to the right of Fig. 98, driving to the
telescopic shaft.
Fig. 100 shows the head in plan view and in sectional eleva-
tion. The spindle, of crucible steel, runs in bronze bushings, the
lower one of which has provision for adjustment. The spindle
is hollow to receive a draw-through bolt for cutters, and the end
is coned, threaded, and clutched. Its mass and that of its sliding
bearing is counterbalanced, as shown in Fig. 100.
The mechanism of the spindle feed is shown in Fig. 101. The
fine hand feed and quick return are effected by different hand
wheels. The first is through worm gear, the second by a pinion
gearing into the rack direct. The worm shaft is automatically
driven from a sprocket.
The spindle is driven by a Renold chain A, Fig. 100, from a
vertical shaft at the rear, which is connected by bevel gears with
the driving mechanism at the rear of the pillar. The spindle is
back geared in the ratio of 4*97 to 1. All these gears are enclosed
(see Figs. 98, 99, and 100).
The drive from the countershaft (or motor) takes place to the
pulley B, 14 inches diameter, Fig. 98, whence the mechanism of
the gear box c is actuated. This is shown in detail in Fig. 102.
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The shaft of b makes about 310 revolutions per minute. Between
this and the shaft which is geared to the vertical shaft through
the bevel wheels, there is an intermediate shaft D that carries
[f'i:::'^s
c
<^)■
o(2)J
Fig. 102. — Details of Variable Feed Mechanism for driving Spindle.
four gears. Through the medium of an idler indicated at E,
either one of these is engaged with a long pinion on the driving
spindle. On another shaft are two gears constantly engaged with
two of those in the cone of gears, and either of which may be
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124
MILLING MACHINES.
engaged by the splined clutch seen to the right. The knobs F
and lever G control the idler. F slides, and G unlocks and locks
by downward and upward movements respectively. The position
of the index slide for a given speed is set by bringing the knob
F opposite the column of spindle speeds on the outside of the box.
Fig. 103.— Details of Feed Box.
The crank handle ii controls the two clutch gears above, giving
two series of speeds. In this way 16 speeds are obtained
through gear box, and back gears, ranging from 17 to 354 revolu-
tions. The gear ratios range from 1 to 1, to 18 to 1.
The feed box is seen at J, Fig. 98, and its details in Fig. 103.
The general design is similar to that for the spindle drive, though
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VERTICAL SPINDLE MACHINES.
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not quite identical. It is driven at a constant speed through a
chain to the pulley K, thus rendering the table feeds independent
of the spindle speeds. A cone of six gears is driven through an
idler and thence to the telescopic shaft. A sliding knob and
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126 MILLING MACHINES,
lever, seen in the box below, gives the feeds in inches per minute,
ranging from 1 J to 17.
The table has, in addition to its automatic movements, a hand
feed by the wheel seen below the table in Figs. 98 and 99. It
has a quick return through a screw of coarse pitch, to effect which
the feed worm is disengaged and a crank handle used.
There is a valuable class of machines, at present the speciality
of one firm, that of Curd Nube, of Offenbach-on-Main, the leading
feature of which is that the principal spindle comes up from
below through the table. This feature alone is embodied in some
of the machines by this firm, and there is consequently no over-
hanging arm, and nothing above the table. But in another group,
an upper vertical spindle is also included, and in another, a third
spindle horizontally. In addition the head swivels for angle.
Fig. 104 illustrates a machine of this complete type in vertical
section. The spindles can be operated in unison or independently,
and the upper spindle is capable of receiving vertical adjustments.
The machine is capable of doing milling, drilling, and die cutting.
The tables have compound movements. In machines which have
no upper spindle, the table has provision for vertical adjustment.
The essential mechanism of the complete three-spindle machine
in Fig. 104 may now be traced out. All three spindles are
driven from the cones A, back geared, each spindle B, c, D, through
its own set of mitre gears. The top bearing of B is protected
with a cap a. The spindle fittings, and the method of taking up
wear are similar in each, the lock nuts pulling against the coned
bearing necks. The method of attaching the arbors is only
indicated in the horizontal spindle, comprising a screw in addition
to the taper of the shank.
The compound table is carried on the knee R, capable of
vertical adjustment on slide faces at the front of the main framing.
It is elevated and lowered by the worm geara E, actuating a
vertical screw, threaded into the boss F, which is let into the
machine framing. The knee also encircles a boss G, fitting by
a turned check into a bored hole in the framing. It is clamped
on G by the set screw &. On the knee the traverse slide H is
moved to and from the pillar by the screw c and its hand wheel.
The transverse slide J is moved at right angles to the direction
of that of H by its screw and hand wheel, and the circular table
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VERTICAL SPINDLE MACHINES. 127
k is rotated on J by worm gear, the wheel being cut solidly around
the edge of the table. K carries stepped chucking strips d, rf,
which have setting-up and clamping screws (not indicated), and
by means of which dies or other pieces with parallel or with
tapered edges are gripped. It is thus seen that though the bottom
spindle B has no vertical movement, the table can be adjusted
for height with great precision, and within a large range, and
clamped securely, so being adaptable for work of different depths,
and for coarse and fine feeding. Also that cuttings fall away
down into a hollow space in the knee,
and together with waste lubricant are
received in the tray L. Any other
chips and lubricant are received by the
channel that is formed all round the
foot of the main framing.
The vertical spindle c is carried by
the swivel plate M, which pivots around
the axis of the driving shaft c, M has
an index or zero mark on its flanges by
which the spindle is set perpendicu-
larly, or to an angle, to riglit and left,
with graduations on the corresponding
flanges of the main framing, and is
clamped by bolts, one of which is seen
at /. The spindle c can slide in the
sleeve N, thus accommodating itself to
the vertical adjustments of the sliding _. ,^„ . .. ,^ . „rui.
, . mi 1 i-i. i\ ^ ^*g- lOo.— A Pratt & Whitney
bearmg o. The latter moves on flat Spindle,
slides on the swivel head M, when
operated by the mitre wheels P, and screw, the wheels being
turned by a hand wheel standing out to the front (not shown),
o receives an overhanging arm Q, with a centre for the arbors held
in the horizontal spindle D. s is a pulley which supplies self-acting
feeds to the table when required.
This is a brief description of one of a great gi'oup of machines
which possess a very wide range of utility.
One method of elevating the table in one of the types of
machines by this firm is this: the support to the tables has a
long cylindrical boss, encircling a long boss that forms a prolonga-
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128
MILLING MACHINES.
tion of the base. A large hand wheel is threaded to fit this, and
serves to elevate the table slides bodily.
Fig. 105 illustrates the spindle of one of the double-spindle
profiling machines by the Pratt & Whitney Company. A hori^ntal
shaft, splined, carries a spiral gear which engages with another
■ALAMCC tPMlIVS
FOAMIM PlMCi««Pll«6 KMrwf
Fig. 106.— Spindle of Garvin Profiling Machine.
spiral gear, encircling the cutter spindle by a long boss, and keyed
to it. The pressure on the spindle, and its own weight are taken
on ball thrusts. Wear is taken up on conical necks with ring nuts.
The cutters fit by taper shanks, and are held in by a long bolt that
passes up through the hollow spindle. The nose is protected
by a cap.
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VERTICAL SPINDLE MACHINES. 129
The Garvin spring-balanced slide is shown in Fig. 106, in
which the spindle, driven at the top by a universal joint, runs in
adjustable bearings in a casting, which carries also the former pin.
The balancing spring is contained within a tube, and is provided
with an adjusting screw.
. The Work of the Vertical Spindle Machines. — Excepting
work involving the employment of the spiral head and swivel
table, these machines include everything, plane and curved, that
comes within the range of their individual capacity, including face
and edge milling. They are equally adapted for both of the latter
methods of cutting. But the machines are eminently suitable for
curved work, using edge mills, and the range of radius covered is
large» Combinations of curves with straight parts are also as
readily done, by combining the movements of the linear slides with
those of the circular table. Work that is bored can be chucked
by the bore, through the arbors which are fitted to the centre of
the table, as in slotting machines. Faces of diflferent depths can
be done with face mills, which is convenient in cutting recesses
such as those in smiths* dies for stampings.
The Work of the Profiling Machines. — The general
mechanism of these machines has been described, pages 96 to 104.
The work done consists in making and attaching a suitable former
to the table of the machine, and adjusting the work to the milling
cutter, and both in relation to the former pin. In some cases pro-
%'iflion is made for adjusting the latter, but generally there is none,
excepting sometimes the choice of two holes, in either of which the
pin may be clamped. The pin is tapered, which permits, by its
vertical adjustment, of deepening the successive cuts.
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CHAPTEK V.
PLANO'MILLERS OR SLABBING MACHINES.
Piano-Millers or Slabbing Machines — Their Characteristics — Details of Spindles —
Horizontal — Vertical — Rotary Planers or £nding Machines.
Piano-Millers or Slabbing Machines. — This is a name that
seems most appropriate to designate that large and growing
group of machines which is built on the model of the common
planing machine, with bed, table, housings, and cross rail carrying
spindle heads. These are the most obvious rivals to the planing
machines. They differ from planers in the slower table feeds,
and in the character of the vertical feeds imparted to the miUing
cutters. But the piano-millers have gone beyond this design,
for many machines include both horizontal and vertical spindles,
and some with angular movements, others also have profiling
attachments, and many include circular tables on the reciprocating
ones. Besides this, some machines have two tables moving side
by side, and these again may be run independently, or coupled
for simultaneous movement, to carry wide work. Then there are
numerous machines convertible into the open side type, and
special forms of these.
The principal points which should characterise a good milling
machine of the planer type. Fig. 107, are, besides massiveness in
framework and in spindles, and ample bearing proportions: provision
for taking up wear, balanced slides or heads (when these are of con-
siderable weight), easy, accurate, and smooth movement to the table ;
a wide range of table speeds and cutter feeds, provision for rapid
movement of the table in each direction for setting work, quick
movement of the heads for setting spindles, fine vertical adjust-
ments for the cross rail, fine adjustments for the table and
heads, self-acting feeds to the table, with automatic knock-out;
provision for lubrication by pump, an oil trough round the table,
ample belt and gearing power, and convenient location of handles
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PLANO'MILLERS OR SLABBING MACHINES. 131
for the various movements. In proportion as a given machine
embodies these general characteristics may its value be estimated.
All machines do not include the whole of these : some are deficient
in most of them ; some are very well designed in regard to certain
details, while deficient in others.
In selecting a slabbing machine regard also should be had to
the class of work which has to be mainly done. If both faces
and edges on the same piece of work have to be tooled, then,
having a horizontal arbor only, the work will have to be re-set
for each separate face. But if, in addition, there is a vertical
arbor, then two faces can be tooled at one setting. If there are
three or four arbors — ^which is the case in some i?iachines — the
range of duty is correspondingly increased.
The number of firms who make small milling machines of
excellent design and workmanship is greater than that of those
who construct heavy ones. One reason lies in the fact that fewer
shops are equipped for the building of heavy machine tools than
of light ones. But the principal reason is that the practice of
heavy milling is of much more recent development than hght
milling. The economy of heavy milling versus planing is as yet
a matter open to question in the minds of some engineers. The
planer type of machine is, however, becoming more and more
adapted to the work of heavy milling, and cutters are made more
capable of taking heavy feeds.
As remarked in a previous page, the early uses of milling were
all confined to the tooling of small articles, and not at all to
service in general machine shops, nor for heavy work. Of late
years that has been changing, and a good deal of heavy milling
is now done on the slabbing machines, both with edge mills and
with face mills having inserted teeth. During this development
lessons have been learned, the results of which have been utihsed
in later designs, so removing the objections and prejudices to
heavy milling, which have been due to want of knowledge of
proper conditions and necessary limitations. The stresses due
to the use of wide cutters with continuous edges being much
greater than those due to the use of single-edged tools are the
cause of the greatest difficulties in milling considerable widths.
Though these are diminished by the spiral grooving of cutters
and by staggered teeth, true work, when of considerable width.
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132 MILLING MACHINES.
can only be done by the use of stiff machines, stiff arbors (by
supporting both ends of the arbor in long bearings), or by both
devices in conjunction, and by taking shallow cuts and slow feeds.
Without these precautions, milling which is at once broad and
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PLANO-MILLERS OR SLABBING MACHINES, 133
accurate is impracticable. And so we find that the best machines
to-day are designed and constructed of very massive proportions.
Yet the best are none too stiff now for much of the duty imposed
upon them.
Of the planer types of milling machines there are various
modifications. The first variation occurs in machines in which
one upright is made either extensible or removable, to receive
work wider than the normal capacity will take. Another occurs
in the entire removal of one upright, making a permanent form
of open-sided machine. Each of these general designs is con-
structed with variations in detail.
The four-spindle machines are specially designed to operate
on two faces, vertical and horizontal respectively, of two pieces
of work at one time. There are two sliding on the cross rail, and
Fig. 108.— IngersoU Spindle (Horizontal).
two on the uprights. All are driven from one cone shaft, and all
liave independent adjustment.
The spindles of the Ingersoll machines are constructed in the
way shown in Fig. 108, being for the 36-inch size. In these
figures A is a fixed bearing on the cross rail, B the wheel which
drives the spindle, c is the movable bearing on the cross rail,
and D the parallel portion of the spindle, which slides in the boss
of A, as c is adjusted endwise. The arbor support E also can be
slid endwise on the cross rail and over the arbor F. It will be
seen that the spindle is fitted with double reverse cones. The
front cone G is kept pulled back to its bearing by the adjustment of
the hinder cone H, tightened by the lock nut i. The cone, which
encircles the spindle, is of cast iron. Its bearing is of phosphor
bronze. The wheel B drives the spindle, while permitting its
parallel end D to slide endwise through it in the sleeve extension J.
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134 MILLING MACHINES,
This sleeve runs in the bearing of A, and is prevented from
moving endwise in either direction, the spindle D moving along
with c. A couple of keys are fitted in the bush. These slide
in the key grooves in D, and rotate D in any position covered
by the range of the key groove. The inner end of the arbor fits
the tapered hole of the spindle. The outer end F runs in a
parallel bearing in the bracket E, and wear is taken up by the
lock nuts and cone.
Fig. 109.— IngersoU Spindle (Vertical).
The vertical spindles of the IngersoU piano-millers are so
designed that the speeds of the same spindle can be changed by
clutclies from fast to slow and vice versa, the device employed
being that of spiral gears and worm gears driving to the same
spindle. The details of the arrangement are shown in Fig. 109,
which represents two vertical sections taken in planes at right
angles with each other.
In these figures the hollow spindle A has its bearings in a sleeve
B that slides vertically in a boss cast solidly with the saddle plate c,
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PLANO'MILLERS OR SLABBING MACHINES. 135
which traverses on the cross rail. The sleeve is adjusted by the
pinion and rack shown, operated by the cross handles a, and is
clamped by the screws &, h.
The rotary movements of the spindle A are derived in the first
place from the horizontal
feed rod d, splined to drive -'^-
the spur wheel E and the
worm F. F engages with
its worm g, and B drives
the spiral gears through
h; h being on the end of
the spindle that carries the
small spiral wheel J engag-
ing with the large wheel
K. Wheels G, H, and K
are all loose on their
spindles, K and G fitting
with sleeves, and are there-
fore put into engagement
by the sliding clutches L, m,
and N respectively. L and
N are slid along by the
locking levers o, P. The
worm and spiral gears are
enclosed by the casings
Q and R.
Fig. 110 gives a verti-
cal section of the spindle
details of a massive double-
headed machine of the
planer type by Messrs
John Hetherington & Sons
Ltd.
The cross slide is seen Fig. 1 10. —Hetherington Spindle (Vertical).
at A enclosing the two feed
screws B, B, one for each head, c, c show operating dogs, adjustable
along the feed rod, by which, through clutches and levers, the screws
B, B are tripped. The rollers by which the friction of the carriage
is lessened when profiling, run on the lower flange of the cross
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136 MILLING MACHINES.
slide, one being shown at i). The take-up strip E, of gun-metal, is
on the top flange. The milling spindle on each head derives its
motion from the horizontal shaft F. A nest of bevel wheels with
spurs connect shaft and spindle, and a clutch, moved to right or
left by the lever G between the bevels on the shaft F, effects
reversal. The driving spur pinion is on the crown bevel. The
driven spur h drives the spindle J through an intermediate sleeve
R, which nms in the bearing L. The object of this device is to
relieve the spindle of strain due to the pull of the belt. If the
wheel H overhanging its bearing had no such aid, the pressure of
driving would cause the spindle to wear the bearing to one side.
M is the vertical feed screw operated by bevel wheels above, driven
from a horizontal shaft. The screw runs in a gun-metal bush in
the bottom spindle bearing N. Wear is taken up by lock nuts
P and similar nuts below. The arbor Q fits with a taper of 1 in
20. It is secured with the tang and screwed cottar seen. Clutch
jaws engage the spindle end to give a positive drive. A support
or stay to the lower end of the arbor is included, seen at R. This
carries a gun-metal bush for the arbor end, tapered 1 in 6, and
the bush has adjustment for wear.
The three or four-spindle milling macliines of the planer type
are admirable tools for a large class of work hitherto done on the
planer. They ensure the correct tooling of three faces at right
angles without re-setting tlie work, and using face cutters with
inserted teeth, they remove material rapidly. If sufficient care is
taken they will also effect fine finishing cuts accurate enough for
all tlie ordinary run of engineers' work, such as faces against
whicli attachments are to be bolted, the feet of brackets, the ends
of distance pieces, and specially that class of work in which ends
and edges or surfaces and edges have to stand at right angles.
They are also admirably adaj)ted for tooling two independent sets
of work simultaneously when there are two vertical spindle heads
and two horizontal ones. The utilities of these machines, though
recognised more than they were three or four years ago, are not
appreciated as they might be.
The space available for work set on the piano-milling machine is
not so large as that on the beds of the rotary planers. Fig. Ill, with
traversing heads. The space is limited in the first by the capacity
between heads. In the latter the work may cover the area of the
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PLANO-MILLERS OR SLABBING MACHINES, 137
Fig. 111.— Rotary Planer.
table, and extend much beyond it if necessary. The difference is
analogous to that which exists between the limitations of the
ordinary planing machine and the large dimensions which can be
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138 MILLING MACHINES.
got upon the beds of the vertical planers and of the edge planers. The
classes of work, therefore, for which the two machines are specially
serviceable are different. Each can be used for fine tooling. But
the ending machines are frequently employed for jobs which would
otherwise be done on the plate-edge planer, or with a cold saw, or
in the lathe, or with a vertical planer — such work as squaring the
ends of beams and girders, facing column ends, ends of standards,
and engine and machine framing of various kinds, besides tooling
pieces arranged in series on the bed.
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CHAPTER VI.
SPECIAL MACHINES,
Special Machines for^Gear Cutting, &c. — For Spur and Bevel Gears — For Worm-
thread Milling— For Robbing Worm Threads— For Fluting Twist Drills—
Three-Spindle Machines — Cam-cutting Attachments — Profiling Mechanism
— Milling Attachment for Planer — Machine for Elliptical Holes.
Special Machines for Gear Cutting, &c.— Figs. ] 12-119
illustrate a machine by Brown & Sharpe for cutting both spur and
bevel gears. In the main the machine is built on the pattern of
the spur gear cutters by this firm, with the diflerence that the
cutter slide is made to angle. This example is selected as repre-
senting a modern high -class fully automatic machine, which
embodies the following valuable features : —
Stiffness of build, a large number of changes of speed and feed,
to be noticed presently. Protection of the working parts. Support
afforded to the cutter spindle. A high speed of positive indexing,
which, with the return of the cutter slide is independent of the
speed and feed of the cutter. The elevation and lowering of the
work spindle slide by power in the largest machines. The drawings,
with the following brief remarks, will be readily understood.
Fig. 113 is a rear elevation of the machine, Fig. 114 a right-
hand end elevation, Fig. 115 a plan view. A, the base, is fitted as a
cabinet, and B, the pillar, is fitted with shelves for gears or tools.
A carries the cutter slide c, i) ; D being adjustable on c to any angle
to 90°, by means of a quadrant rack, so that it is suitable either for
cutting spurs or bevels. The slide c has longitudinal adjustment
by hand through pinion and rack, and power feeds and quick return
operated by gears enclosed. The motion is communicated at any
angle of the slide d, through the splined shaft e, by means of bevel
gears at both ends, enclosed. The pulley F, driven from the counter-
shaft, drives the cutter spindle, and the pulley G, the cutter slide,
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140 MILLII^G MACHINES.
tlirough gears and a quick pitched screw, so making the move-
ments of slide and spindle independent of each other.
The cutter spindle has ten changes of speed, ranging from 30
Fig. 112. — Automatic Spur and Bevel Gear Cutter.
(B. & S. Manufacturing Co. )
to 163 revolutions per minute obtained through change gears.
Fig. 116 gives a section through the spindle and its bearings, with
the details of the method of adjusting it.
Tiie cutter has sixteen changes of feed, ranging from 0*012 to
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SPECIAL MACHINES,
141
0*235 inches per revolution of spindle, in geometrical progression.
These are obtained through change gears enclosed in the box H.
When cutting bevel gears there is a cross slide which can be moved
to bring the cutter to either side of the centre. The mechanism
for this movement is seen at J, Fig. 115, while the vernier is seen
in Fig. 118.
Fig. 113.— Rear Elevation of Gear Cutting Machine,
The work spindle head K is adjusted by the hand wheel, Fig.
115. The thrust of the elevating screw is taken by ball bearings.
A graduated dial reads to thousandths of an inch. The spindle is
hollow, with a 1^-inch hole, and tapered at the front to No. 12
taper. It is threaded to receive a face plate or other fixture. An
overhanging arm M aflFords support to the outer end of the arbor.
Large gears are supported by a rest behind the rim opposite the
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U2 MILLING MACHINES.
cutter. The worm wheel, enclosed in the casing n, is driven by a
vertical worm, and the indexing change gears provide for cutting
all numbers of teeth from 12 to 50, and all numbers from 50 to
400, excepting prime numbers and their multiples. The indexing
mechanism is shown in Fig. 117. Fig. 119 is an indicator for
setting the cutter.
Worm-thread Miltiii«:.
— A worm - thread milling
machine, by J. E. Reinecker,
is shown by the accompany-
ing Figs. 120 and 121. There
is no doubt that the milling
of worm threads, though a
comparatively recent innova-
tion, will in time displace the
single-cutting lathe tool for
that class of work. The
cutter, of rack section, gives
no trouble with regard to
clearing itself. The present
demand for multiple-threaded
worms is the opportunity for
the development of machines
of this class, which are now
made in Great Britain, the
United States, and Germany.
As the cutter in the
Fig. 114. -Right-hand End Elevation Reinecker machine is fed
of Machine. longitudinally in relation to
the worm blank, while the
worm is rotated, this involves two distinct sets of mechanism, each
with its change gears. Figs. 120 and 121 show the arrangements
of the machine as a whole.
The arbor, indicated at a is carried in the headstock A and
tailstock B. The spindle is made hollow, in order to take the
axles of worms, when in one piece with their worms, so that they
can be gripped and supported close to the threads. The cutter is
held on the arbor 6, the bearings of which are carried on the
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SPECIAL MACHINES.
143
plate c, adjustable for angle on the face of the head D. The blank
is rotated from the cones E, through the two sets of worm gears F,
Fig. 115. — Plan View of Machine.
Fig. 116. — Section through Putter Spindle, showing Method of Adjustment.
and G. The shaft c, that carries the worm that drives G, on the
headstock spindle, also actuates the set of change gears h, whence
the correct longitudinal feed is imparted to the head D, which
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144 MILLING MACHINES.
carries the cutter arbor. The due proportion or ratio between the
diameter and the pitch of any worm being milled is thus obtained
by changes in the gears H, the worm drive teing constant from the
Fig. 117. — Indexing Mechanism.
stepped cones e. Changing the belt on the steps of e does not, of
course, aflFect the relations of the worm gears and change wheels.
The rotation of the milling cutter is effected by an independent
set of mechanism, derived
from the cones J. The
course of the motion can be
traced from j, through
bevels and spurs to the last
spurs, K and L. K, it will be
noticed, has the axis of its
shaft central with the swivel
plate c, and L runs in a
bearing in a boss projecting
inwards from the plate c, so
remaining in gear with K at
Fig. 118. -Vernier and Screws for adjusting ^^ ^"g^^^^ positions of the
Cutter Spindle. cutter arbor 6; L drives a
spiral gear d through the
plate, which engaging with another 6, on the arbor 6, rotates the
latter at four variable speeds obtained from the cones.
There is an indexing device shown at M, over the headstock
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SPECIAL MACHINES.
145
spindle, for obtaining settings for multiple-threaded worms. This
has been abandoned on later machines in favour of direct indexing
with holes and index
peg.
Hobbing Worm
Gears. — A remark-
able machine, Figs.
122 and 123, by the
same firm, for hobbing
worm gears by the
method just described,
also cuts both spur
and spiral gears either
with a hob, or with an
ordinary cutter. Its
movements are auto-
Fig. 119.— Indicator.
Fig. 120.— Worm-thread Milling Machine.
matic, and the results theoretically as well as practically perfect.
The worm wheel blank to be bobbed is put on the arbor a, and
K
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146
MILLING MACHINES.
the hob (which is fed in endwise) goes on the arbor B. The
mechanism is designed to effect the relative movements required.
The distance from the centre of the hob to the centre of the
blank remains unchanged from start to finish of the opera-
tions. The rotation of the hob and that of the blank are so
proportioned as to be exactly the same as those of the wheel
and its worm. The longitudinal feed may be varied, and does not
affect the pitch, or the diameter, and number of teeth in the worm
and worm wheel. The driving mechanism is actuated from the
Fig. 121. — Worm-thread Milling Machine.
cone c, belted from one of the coimtershafts. From it, through
the change speed gears d, the vertical splined shaft is actuated,
and from this the rotation of the hob is effected by the pinion
F, and wheel G, while the rotation of the master wheel ii, and
from it the blank, is imparted by a set of change gears (not
indicated, but situated behind wheels F and g). The mechanism
of this rotational movement is carried through the centre of
the carriage to change gears K, at the opposite end of the table.
The feed, or longitudinal travel of the table J, is derived from
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SPECIAL MACHINES,
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the feed cones L, driven from a separate countershaft. From
L, the vertical feed rod M is driven through the worm and
mitre gears seen in the figure, at variable rates, and thence
the horizontal feed shaft N. The latter operates two sets of
Fig, 122. — Universal Gear Cutter.
worm gears o, o, one for longitudinal traverse of the table J,
the other for the cross traverse of the carriage p. Both sets
of worm gears are clutched for throwing out and in. These
movements are capable of reversal through the dogs a, a on
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MILLING MACHINES.
the horizontal rod situated above the worm shaft N, which through
various levers actuates the clutch of the bevel gears Q. The object
of the change gears K, is to add the proper rate of rotation to the
blank on the arbor a, to compensate for the forward motion of the
Fig. 123.— Universal Gear Cutter.
hob, which is the most marked peculiarity of this machine, neces-
sary because the hob is fed at a tangent to the blank, and being
so fed, the worm R, which drives the master wheel H, must be fed
similaxly, with which object its bearings are carried on the slide s.
The ratios of these movements are the same as those existing
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SPECIAL MACHINES,
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between the hob and the wheel which it cuts, and the master
wheel and its worm. The rates of rotation of the hob and worm
are similarly proportioned.
For cutting spiral gears, the slide J is mounted on a swivel
table, a special milling attachment being added. The dividing is
done by hand by means of a dividing plate and change wheels.
For cutting spurs, the carriage p is traversed towards and from the
column.
Fig. 124.— Flute Milling Machine.
Fluting Twist Drills. — Though the flutes of twist drills can
be cut on a universal machine, only one flute can be done at a
time. A special Eeinecker machine, designed for cutting both
flutes simultaneously, is shown by the illustrations. In it the drill
is fed forward and rotated between cutters, the centres of which
move apart tb give the increase of thickness from point to shank
that is necessary to strength. Relieving as well as fluting is
done. The machine shown is the larger size of two made, its
maximum capacity being a 4-inch drill, 40 inches long. The
following is a description of the principal elements of the
mechanism : —
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150 MILLING MACHINES,
Fig. 124 illustrates the machine in side view parallel with the
drill. Fig. 125 is a front-end view looking towards the drill. The
bed is made in two portions, standing at right angles and bolted
together, one part carrying the drill and feeding arrangements, the
other the spindle head.
The drill blank A is carried in a chuck B, which may have
either a Morse taper, as shown, or a straight shank, and it is fed
forward and rotated by a long screw c, splined to permit of its
Fig. 125.— Flute Milling Machine.
endlong movement througli its operating gears. The worm gear D
feeds, and E rotates, and the rates of both are controlled by the
change gears, indicated by the dotted circles, which establish the
desired relation between the pitch of the feed screw c and the lead
of the spiral of the twist drill. Eough adjustments of the forward
and the rotary motions can be effected by the handles seen. A
stop a can be set to gauge the termination of the cut.
The fluting cutters are seen at F, F. They are carried on arbors
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SPECIAL MACHINES. 151
which fit by taper shanks in the spindles G, carried in long sleeves
in the head H. The tail supports 6, 6 are fitted in slide ways to
permit of their movement and setting for removal and insertion
of cutters. The swivel heads are adjusted for angle on the
headstocks J, j, on which they are set with tee-headed bolts.
The angle, of course, varies
with drills of different dia-
meters.
The spindles G have a
small amount of vertical
adjustment on a feather
seen in the section, and
they are driven on the
sleeve, the spur wheel being
keyed thereon to avoid
direct pull and wear on the
spindle. The drive to K is
readily seen in Fig. 125,
coming from a spur wheel
on the same spindle as the
stepped cones, thence
through bevels to the spur
that gears with K. The ad-
justments of the heads J, j
towards or from the drill
blank are effected by the
hand-operated screws L, L,
working through nuts in
the base, the rectilinear
movements being controlled
by vee'd edges. Divisions
on plates on the base of each
head permit of making fine Fig. 126.— Three-Spindle Machine,
adjustments, and micro-
metric divisions are effected by the discs and pointer seen at
rf, d. After the cut starts, the heads are gradually separated by
mechanism that is only partly indicated on the drawings, but
which is derived from the rod M lying beneath and parallel
with the screw c. This actuates a pinion c engaging with a
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MILLING MACHINES.
rack, whence connection is made by levers with the nuts that
operate the heads.
The centrifugal pump N draws its supply of lubricant from
the tank o, being driven by the pulley P. The pipe arrange-
UtO
Fig. 127.— Three-Spindle Machine.
ments include a flexible tube connected up to the cutters. The
drainage back into the tank takes place through the pipe g,
but chips and dirt are discharged into the box Q, which, like
0, can be pulled out at the front like a drawer to be emptied
and cleaned out.
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SPECIAL MACHINES,
153
Three-Spindle Machines. — ^The Eempsmith Manufacturing
Company have a fitting to their pillar and knee machines which
permits of the simultaneous operation of three vertical milling
spindles. The particular application of this device is the milling of
the tee slots in machine tables.
The drive is effected by an extra or auxiliary slide carried
between the headstock and the vertical brace in front of the knee.
This fitting carries a horizontal spindle in line with the main
spindle. Three angle wheels, capable of adjustment along it, drive
three similar angle wheels on vertical spindles, which have their
D "
D£V£LOPMEfiT OF SUlfFACB
END VIEW
Fig. 128.— Development of Surface of Valve, cut on Three-Spindle Machine.
bearings in slides adjustable along the face of the auxiliary slide.
The lower ends of the spindles carry the milling cutters, which,
after being adjusted for centres, are driven simultaneously through
the angle wheels. The work is bolted to the table and so traversed
under the cutter.
Figs. 126 and 127 illustrate a vertical three-spindle machine by
the Beaman & Smith Company for duplicating small pieces, and Fig.
128 illustrates the development of the surface of a valve so cut.
The periphery of the valve waa divided into degrees, and the loca-
tion of each cutting was fixed by a graduation of the hand wheel A,
shown on the fixture in the machine. There is a driving spindle B,
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154
MILLING MACHINES.
Fig. 129 — Plan View of Cam -cutting Attachment.
Fig. 130.— Front Elevation of Cam-cutting Attachment.
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SPECIAL MACHINES, 155
at the left of the machine which carries a point that runs over
the maater valve, and on three blanks placed under the operating
spindles the cutting is performed simultaneously. This fixture
can be removed from the table and any other substituted. The
mechanism of the three-spindle machine itself is sufficiently clear
from the drawing.
Cam-cutting Attachments. — A cam-cutting attachment by
the Brown & Sharpe Manufacturing Company is shown in Figs.
129-131. It is
mounted on a base A,
which is bolted to
the table of the ma-
chine. A carries a
sliding table B, which
is capable of longi-
tudinal travel, and
upon which the head
and footstock shown
are bolted. The
spindle in the head-
stock is driven by
the worm and worm
wheel c, seen at the
right-hand end, the
worm wheel being
driven l)y the hand
wheel 1). The handle Fig. 131.— End View of 'Cam-cutting Attachment.
a of this wheel can
1)0 drawn out to give sufficient leverage for turning heavy
work round. The outer face of the worm wheel has two tee
slots J, 6, at right angles with each other, against which the
former is lx)lted. This is of flat steel, or cast iron, and has its
edge shaped to suit the cam to be cut. At the end of the slide B
is a vertical guide F, in which slides a rack, having a hardened steel
roll at its upper end that comes in contact with the edges of the
former. The rack engages with a pinion n, turning on a stud in the
slide B, which pinion is also in gear with a horizontal rack, attached
to the base a. Hence when the vertical rack is forced down-
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156
MILLING MACHINES.
ward, the slide B is moved to the right, and when pressure is
removed from the rack, the slide b is pulled to the left by the
weight J, and the vertical rack is run up. The roller is therefore
always held in c*ontact with the former. And also when the
work is rotated by the hand wheel D, the former in turning with
the hand wheel produces the longitudinal movement in the slide.
When a cam is being cut on a cylinder, the arrangement is
that shown in the figures. But when a face cam is being done,
the headstock is set round with its spindle parallel with that of
the machine. The vertical rack and guide F being carried round with
Fig. 132. — Cam-cutting Attachment.
the head, the rack then engages with the pinion k. Fig. 129. This
pinion is fast on a shaft L, which carries on its inner end a pinion
M, that engages with the horizontal rack in the base A, operating
the slide B, as already described, when the headstock is at right
angles with the machine spindle.
An attachment for cutting cams on the machine table is shown
in Fig. 132, an example by the Cincinnati Milling Machine Com-
pany. It is shown at work on a face cam. The arrangement
comprises a mandrel to carry the work, and the master or former-
cam behind. This mandrel is revolved at a suitable speed, and, by
means of the weight seen to the right, the entire slide is pulled
constantly sideways, so that the master-cam presses against the
roller.
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SPECIAL MACHINES,
157
Profiling Mechanism. — The profiling mechanism of a
machine by Messrs Webster & Bennett is illustrated in Fig. 133,
the piece being a cycle fork crown A. The first Figs., 1 and
2, show it attached to the cam plate B, and just commencing
Fig. 133.— ProfiliDg Mechanism.
its revolution in the direction of the arrow. The cam plate B is
held against the roller in the ordinary way, until the position
shown in the next 3, is reached, at which point the cam is
assisted by a roller at the rear of the automatic head, in the
manner illustrated in 4. An inclined bracket c is bolted
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158
MILLING MACHINES,
to the bed, against which the roller pushes. The result is that
as the bracket will not move, the whole head is pushed over
bodily in the direction of the arrow. This has the effect of
j!l.
Fig. 134.— Adams' Planer Attachment.
drawing the cam out of the awkward position of the previous
figure, and allow it to proceed on its revolution, the large wheel
being mounted on a friction cone to permit it to shp sUghtly in
the operation, the lost motion being taken up in a division plate,
the small holes in which are in-
dicated in the last diagram 4.
Milling: Attachment to
Planer. — The illustrations,
Figs. 134 and 135, are those of
an application of the milling
head to the planer, by the
Adams Company, the drawings
showing the sectional details
of the spindle drive.
When in use, the ordinary y'\%. 135.— Bracket for Tail End of Arbor,
tool box of the planer is run
to the end of the cross slide, out of the way, and the miUing head
takes its place, being adjustable on the cross rail. The spindle-
head A swivels by an annular tee groove on the slide B, so that
either vertical, horizontal, or angular milling can be done. There
la
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SPECIAL MACHINES. 159
is also a bracket to aflford support to the tail end of the arbor in
horizontal milling, Fig. 135.
In Fig. 134, c is the driving pulley, which is operated from a
separate countershaft, distinct from that of the planer. As the
axis of the pulley stands at right angles with that of the cutter
spindle, the direction of drive is not affected by the angling of the
spindle. The length of the belt is, but the slack is taken up by
a weighted pulley. The drive to the spindle is through worm
gear d, the worm being of hardened steel, and having ball-bearing
thrust collars, and the worm wheel of bronze, enclosed in an oil
chamber. The spindle is tapered at both ends, so that cutters
can be used at either end. Or, when two heads are used, the
cutters can be placed to right and left. The inner bearing sleeves
are of bronze. One has a flange at its inner end, and the other
a square thread to receive a steel ring at that end, by which end
play is taken up. The sleeves have a longitudinal slot, which
is fitted with a compressible metal at the outer end, but retains
the oil elsewhere. The outer sleeves, of cast iron, are split, and
,are threaded at the outer ends to receive the ring nuts seen.
The outer sleeves fit the bore of the casting, and are fitted
to the inner by a double taper. Wear is taken up by tiuning
the ring nuts on the outer end of the larger sleeves. The
countershaft has two belts for different speeds. As the table
of the planer must be driven at a much slower speed for
milling than when planing, the planer countershaft is driven for
milling through worm gear, the worm wheel being on this shaft.
The worm can be thrown out by a lever, and when out, the
table can be returned at the quick planer speed. Feeds are
made variable through a friction disc, the roller being on the
worm shaft. Feeds up to five inches per minute are thus
obtainable.
Machine for Elliptical Holes.— Fig. 136 illustrates a milling
machine for cutting elliptical or round holes in boiler plates, made
by Curd Nube, of Offenbach-on-Main, Germany.
Cutting the manholes in boilers and boiler plates, and round
holes in boilers, is still in many cases effected by hand, with
hammer and chisel, or with apparatus in which an analogous
process is employed. The machine permits of cutting such
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MILLING MACHINES
holes automatically, by means of a rotary cutter with teeth of
sufficient length to enable it when working on plates, or the
periphery of cylindrical boilers, to reach through the whole
thickness of the material to be cut. The method of operation
of the machine is as follows : —
A spindle 6, carrying a rotary cutter c, is driven from an
overhead countershaft, through suitable gearing a, or. The bearings
of the cutter spindle 6, and the intermediate shafting d rf, are so
arranged that the cutter c can be moved both vertically and
horizontally in any direction. The cutter spindle is carried in an
Fig. 136.— Milling Machiue for Cutting Elliptical or Round Holes
in Boiler Plates.
arrangement e in a circular guide, which, with the guide, can
be shifted and fixed in position on a plate /. This device per-
mits the cutting of circles or manholes of varied sizes. The
motion of the cutter c is obtained by means of an eccentric g, y
with adjustable throw ; moved by a spindle A, while a ring i to
which the plate / carr}'^ing the bearing c of the cutter spindle h
is fixed, revolves round this eccentric, in the opposite direction.
This rotation in opposite directions of the spindle h of the eccentric
g, g on the one hand, and the ring i with the plate / fixed to it,
and the cutter c on the other hand, is obtained by worm wheels A-,
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SPECIAL MACHINES, 161
and worms, and gears l, I. This arrangement, and hence that of
the cutter c, is driven from a double-throw eccentric which receives
its motion from the driving shaft of the machine, so that when
the latter is thrown out of gear this movement is also stopped.
The double-throw eccentric m, m for circular or elliptic motion is
itself variable as to stroke, so that small holes can be cut in a
shorter time, larger ones in proportion with the longer travel in
a longer time.
The machine is arranged for 100 mm. (3|| inches) difference of
diameters, but it may also be adjusted for other differences.
Ovals can be cut up to 450 x 350 mm. and circular openings up
to 400 mm. diameter. The time within which a normal manhole,
12 in. X 16 in., can be cut in an 18-20 mm. boiler plate is about
If to 2 hours ; a 10-inch circular hole can be cut in f to 1 hour.
To do this by hand would take from 6 to 7 and from 4 to 5 hours
respectively. All that is required before cutting is to trace a
cross representing the major and " minor " axes of the ellipse on
the piece of work, and to drill a hole at the end of one of these
axes, to give the cutter a starting point. The machine as shown
in the figure is fixed to the wall, and the pieces of work go on
the ground. The weight of the machine is 1,000 kilogrammes.
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CHAPTER VII.
CUTTERS,
Diflferences in the Teeth of Milling Cutters and Single -edged Tools — Size of
Cutters and Spacing of Teeth for Roughing and Finishing Cuts — Rake and
Clearance — Spiral Form — "Handing" of Spiral — ^Compensation for Wear —
Attachment to Spindles — Inserted Tooth Cutters — Various Examples —
Manufacture of Cutters — Steel — Hardening — Cutting the Teeth — Examples
— Grinding and Sharpening — Examples — Clearances — Form Grinding.
Differences in the Teeth of Milling Cutters and Single-
edg^ed Tools. — It is not necessary in this chapter to give draw-
ings of all the numerous forms of milling cutters made, even
if the scope of this book permitted it. Illustrations of the
principal kinds occur in this chapter dealing principally with
the tooth forms, and the care of the cutters generally.
In several respects the forms of the teeth differ from those of
single-edged tools. They are generally much weaker, approaching
in most cases to the form of saw teeth, namely, triangular. They
seldom have any front rake, nor ever more than a very slight
amount, while most single-edged tools have several degrees of front
or top rake. The amount of clearance is generally the minimum
of that present in single-edged tools. The spiral or twisted tooth
adopted on all edge mills, excepting those of about an inch in
width and under, has its analogue in the diagonal or shearing devices
embodied in other cutting tools. The mills with staggered teeth,
whether solid or inserted, are in effect assemblages of single-edged
tools. All milling cutters except the last-named differ from single-
edged tools in their fine cutting. They are not in any sense rough-
ing tools, though the term " roughing cuts " is used to distinguish
the relative difference between a first and a finishing cut. As
they do not and cannot penetrate deeply, there results one of the
chief difficulties incidental to these cutters, namely, the inefl&ciency
of a mill which is not ground accurately and supported on a stiff
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CUTTERS. 163
arbor carried in a stiff machine. If the depth of cut is divided
between the number of teeth, it is clear that the minute fraction
apportioned to each tooth may well exceed the degree of radial
inaccuracy resulting from indifferent grinding. How fine this
inaccuracy may be is evidenced by the revolution mark visible in
all milled work.
The revolution mark is due to the impossibility of grinding
teeth exactly alike, because the grinding wheel itself becomes
smaller as the work proceeds. Though the difference is extremely
minute, it is enough to account for the effects seen.
Size of Cutters and Spacing of Teeth. — The size of mill-
ing cutters and the spacing of teeth are two questions that arise
first for settlement. With regard to the first, the smaller cutters
should generally have preference over the larger, because their
traverse is less for a given length of surface cut. The smaller
cutter has to move a smaller distance than the larger, and there-
fore occupies less time in reaching to, and receding from the
work.
Messrs Brown & Sharpe state that a difference of half an inch
only in diameter has been found to make 10 per cent, in the cost
of the work in their practice. In some cases a small cutter is
objectionable, as sharpening the edges of milling cutters with a
small wheel produces concave edges, but that may te got over by
angling the wheel.
The number of teeth in a cutter is now nearly fixed in practice
by pitching them at from \ inch to \ inch apart. Early cutters
were pitched too finely, with the result that crowding and choking
occurred. It is well open to question now if coarser pitching than
is usual would not be advantageous in roughing cutters and in
those for brass, though the practice is to use the same cutters for
all metals and alloys, and for roughing and finishing.
Mr Addy's rule for the pitch of cutters from 4 inches to 15
inches diameter
Pitch in inches = Vdiameter in inches x 8 x 0'0625.
In another method, from a German source, the thickness of
tooth is first obtained, and thence the number of teeth and pitch,
thus: — The diameter, D, of the cutter is first obtained. This
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MILLING MACHINES,
depends upon the work to be done, and should be as small as
possible. The thickness of teeth, t, should then be determined
from the following formula that has been derived from practical
experience : —
10
For cutters up to - - 2 inches diameter c=^ inch,
from 2 inches to 4
4
4f
6
n
4f
6
n
8
C — 5^
c=0
In order to determine the number of teeth, the nearest whole
number to the quotient of should be taken. Thiis for a
cutter of 4 inches diameter we should have 24 teeth, and this
would cause a modification of the calculated thickness of the tooth
from 0-55625 inch to 0-5027 inch.
Spacing: of Teeth for Roug^hing and Finishing Cuts.—
In the spacing of the teeth of milling cutters sufficient allowance
is not made for the difference between roughing and finishing cuts.
It has been demonstrated that coarsely pitched cutters absorb less
power than those of fine pitch. Tests were made in a Cincinnati
motor-driven machine on two cutters of the same diameter, but
one having twice the number of teeth of the other. The results
are given in the table below : —
Finely Pitched
Gatter.
Coarsely Pitched
Gatter.
Diameter of cutter - - - -
Number of teeth in cutter -
Width of cutter ....
Depth of cut ....
Number of teeth in contact with metal
Volts
Amperes .....
Feed of table ....
Revolutions of cutter per minute -
Thickness of chip per tooth
4 inches.
30
Vff inch.
i i>
5
110
13-5
0-134 inch.
40
0-0044 inch.
4 inches.
15
^z inch.
3
110
10-5
0134 inch.
40
00088 inch.
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CUTTERS,
165
The conditions, it will be noted, were precisely alike in respect
of size, speeds, feeds, &c., only that while one cutter had 30 teeth,
the other had 15. But the 15-toothed cutter took a chip 8,000ths
of an inch in thickness, while the 30-toothed one took a chip of
only half that thickness. But the latter required 13*5 amperes,
while the former took but 10'5 amperes, a difference of about 22
per cent, in favour of the coarse-toothed cutter. As the 30-toothed
cutter had 5 teeth always in contact with the work, while the
other had only 3 teeth in contact, the differences above-named
were due evidently to the better clearance afforded to the chips.
The case is therefore analogous to the coarse
pitching of the inserted tooth cutters and
those with staggered teeth.
Wide spacing is favourable to heavy
feeding, because the chips escape freely, so
that the advantage both of deep cutting and
of free cutting is secured. Finishing cuts
demand fine-toothed cutters to leave a
smooth surface. Hence, though it is not
usually done, a difference should be made in
cutters for roughing and finishing when the
amount to be removed in the first cut or
cuts is considerable. For much work, where
the total amount to be removed is small, the
distinction is of no importance. But when
milling comes into rivalry with the planer
and shaper for hea\7' work, the difference
ought to be made if the best results are to
be secured.
Fig. 137 shows a cutter designed by Mr James Vose, and used
in the shops of Messrs Meldrum Brothers Ltd. for milling gun-metal
fittings. It will be recognised as simply a series of brass scraping
tools, very coarsely pitched, to leave room for the cuttings to clear.
Mr Vose says that more than seven teeth only seems to produce
useless rubbing on the finished surface.
WMIW
Fig. 137. — Coarsely
Pitched Cutter for
Gun-metal Fittings.
Rake and Clearance. — Angle of front rake is not generally
imparted to the teeth of cutters. It is found that for ordinary
duty radial teeth cut as well as those with rake. Undercut teeth
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166 MILLING MACHINES,
score with slow speeds, and coarse feeds, but not in the opposite
conditions. Experiments were made by Mr E. G. Herbert, of
Manchester, with three cutters 6| inch diameter, ^^ inch thick,
with 1-inch hole. In each case there were 30 teeth, which in
one cutter were radial, and in the other two were undercut 10°
and 15° respectively. The cutters, running at 20 revolutions per
minute, or a cutting speed of 42 feet per minute, were fed sepa-
rately into the vertical faces of heavy blocks, first of cast iron, and
then of mild steel, until the machine stopped. The feeds varied
from 1'4 inch per minute to 046 inch per
minute, and there was no perceptible slip
of the feed belt.
"T The results of the tests were some-
JG^ what complicated, but they failed to show
; any decided advantage of one tooth over
i another. The general indication seemed
: to be that the advantage rested with the
; undercut teeth with a big feed, and the
I radial teeth gave better results with a
; fine feed.
A very slight rake is, however, given
j in some ordinary cutters, ranging from
T to 5^ the latter for wrought iron.
This, however, should not be adopted in
*' -JS^) ' formed cutters, which have to be ground
:f}J}T on their faces.
Fig. 138.— Standard "^^^ angle of clearance (which is that
Cutter. given by grinding the top edges of the
cutters) ranges from 3" to 8^ the latter
being rather excessive unless used habitually on brass. This
amount is fixed by the setting in the gi-inding machine by the
tooth rest.
The two broad groups into which milling cutters are divided
are the axial, in which the teeth are in planes parallel with the
axis ; and the end, or radial, in which they are at right angles with
the axis. There are many sub-types, as for instance tapered mills
and profiled mills in the first, and convex-ended and other forms
under the second.
The axial mills generally go on arbors. Fig. 138 is from a shop
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CUTTERS. 167
drawing giving a section of a cutter of this kind, with Mr Bray-
shaw's remarks thereon below.
" According to this drawing, it has been determined that if the
eiTor in the thickness of a ^-inch cutter does not exceed one-
thousandth (O'OOl) of an inch, it is good enough. This is clearly
shown, and the grinder must adhere to the limits given, but must
not waste time in making every ^-inch cutter to within one half-
thousandth (0-0005) of the nominal size.
"Again, it has been found that about one-hundredth (O'Ol) is a
reasonable allowance for cleaning out the turning marks on the
sides after hardening. It is, however, quicker to grind off a few
extra thousandths than to turn them oflf, and the turner must
keep within the limits — ten to fifteen thousandths above \ inch
r y He has no excuse for leaving too much or too little
for grinding, nor yet for wasting time by taking a cut of two-
thousandths (0-002) oflf the side.
" It is shown that the actual diameter is not important, and the
turner has a limit of one-hundredth (0*01) of an inch, which he
must keep within. No grinding size is given here, wliich means
that the grinder must just clean out the turning marks.
" The drawing shows that the side recesses may vary in dia-
meter by one-tenth (0*1) of an inch. The clearance each side is
stated as ^°, and it is essential that this shall run out to the
extreme tips of the teeth."
Messrs Brown & Sharpe give about five one-hundredths in one
inch for clearance for mills that have to cut grooves. That is, a
grooving mill should be about one-hundredth of an inch thinner at
one inch from its circumference than it is at the edge. The firm
gives a limit of two-thousandths in thickness to their grooving
mills. Mr Brayshaw's ^ ^^ ®*^h side causes the cutter to beqame
two-thousandths (0*002) thinner wlien \ inch has been ground oflf
its diameter. More clearance would cause it to lose its proper
thickness too soon. Extra clearance might be given to cuttei-s
when the width of grooves is not particular, or when they are
used only for roughing.
Spiral Form. — The spiral form given to all but the narrowest
axial mills varies from about 15° to 40". Its object is to reduce
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168
MILLING MACHINES,
the stress on a tooth by causing it to cut in detail, in a shearmg
fashion. Its vahie is more pronounced in the fibrous metals, as
wrought iron and mild steel, than in cast. In ordinary axial mills
it may be low or high in amount, and right or left handed in direc-
tion. But in end mills, and those which cut profiles, conditions
come in which fix these things arbitrarily.
If cutters operate by their
sides only, the inclination may
be large, ranging up to 30" or
40^ which in wrought iron
gives a marked advantage.
But in end mills this should
not exceed 20\ because the
teeth would be too keen, and
become broken, due to the
large angle of front rake im-
parted to the end teeth.
Fig. 139. Fig. 140. Fig. 141.
Examples of End Mills.
" Handing " of Spiral— The question of which hand the flutes
in a milUng cutter should run may seem of little moment. In the
case of end mills going deeply into the work it seems best that the
flutes of the sides should be right handed, like those of twist drills.
These then tend to draw^ the chips out of the gi'oove, while left-
hand spirals would
tend to force them
down towards the cut.
The handing of the
twist is important in
certain cases. Fig. 139
is a right-hand spiral
with right-hand teeth.
Fig. 140 is a left-hand
spiral with right-hand
teeth. The differences in the two in working are these : — Fig. 140
is only suitable for edge milling, since the end teeth have negative
rake, and the direction of twist tends to push the cutter into its
socket, and the work down to the table, and to thrust the cuttings
downwards. But for use as an end mill, the form in Fig. 139 is
fioiTect, because tlie teeth have front rake, and the tendency is to
Fig. 142. — Mandrel Set for Turning Diagonal
Joints of Cutters.
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CUTTERS,
169
draw the cuttings upwards. For general end milling, the cutter
in Fig. 141 is more often used, giving no trouble of any kind.
Compensation for Wear. — When it is desired to make com-
pensation for wear in side mills, they are jointed diagonally, or the
D
CfSf)
Fig. 143. — Common Method of holding
Shell Cutter on Arbor, with Round
Key to Drive, and Screw to Hold on.
Fig. 144. -Shell Cutter Arbor,
with Nut for Forcing off
the Cutter.
teeth are interlocked, or sometimes every alternate tooth on the
meeting faces is cut away to make room for the teeth on the other
mill. Either of these permits of the insertion of thickness slips of
Fig. 145. — Cutter held on Arbor with Nut, Arbor forced out
of its Hole with a Nut.
paper or other material. Diagonal jointing of smooth faces is not
open to the objection of leaving a mark on the work, which parallel
flat cutters would do, if jointed. The diagonal jointing is done by
turning the faces on a mandrel. Fig. 142, having two sets of centres,
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170
MILLING MACHINES,
one for turning the parallel faces of the cutters, tlie other situated
at about y\ ^^^ owt of centre, used for turning the diagonal faces.
When the faces are
tooled, the two por-
tions are put together
and united with a pin,
the key groove is cut,
and the teeth milled,
hardened, and ground.
Attachments to
Spindles. — Mills fit
into taper sockets in
their spindles, or they
fit over arbors. Small
mills are used in both
, ways, but large ones.
Fig. 146.— Muir'8 Fig. 147.— French Method of , , ., ^
Coupling Mandrel. dripping Cutter with ^^^^ ^^^^ ^"® greater
Parallel Shank.
numljer of any size employed, fit
arl)ors only.
Figs. 143-148 illustrate taper
sockets for mills, which are nearly
self - explanatory. Solid shank
mills are seen in Figs. 139-141.
Fig. 143 shows the common
method of holding shell cutters
on an arbor, using a round key to
drive, and a screw, the head of
which lies in a recess in the
mill to secure it. In the next
example, Fig. 144, a nut is fitted
above instead of a plain collar.
The object of this is to push off
the cutter by the simple pressure
of turning tlie nut, a feature ap-
preciated if cutters stick. In Fig. 145 a nut and washer are
shown, with a forcing-off nut. Fig. 146 is Muir's coupling.
Fig. 148. — Large Face Cutter locked
with Clutch and Ring Nut.
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CUTTERS.
171
The arbor is retained in place with a screw collar, the cutter
is threaded to receive the arbor, and a lock nut above holds
it securely. A method of holding a parallel
shank cutter in a split tapered grip with an
encircling nut is seen in Fig. 147. The arbor
is retained by a screw on its end. In Fig.
148 a cutter of large diameter is driven from
the spindle end by means of an interlocking
clutch, and held with a ring nut turned with
a tommy.
Very thin mills are ground straight through
to fit the arbors, and wider ones are recessed as
in Figs. 138 and 145. The key groove should be
of half-round section, to lessen risk of cracking
in hardening. Some, however, ha^'e square
grooves with radii. The thinnest cutters are
not keyed, but pinched between shoulders. The diagrams. Fig. 149,
and tables below give standard sizes of both shapes of key ways.
rfl^
Fig. 149.— Diagrams
for Proportions
of Key Ways.
Square Key Way.
Size hole, A
ItoA
}toi«toli
lAtolf
lA to li IH to 2
•2A to 2412^, to 3
Width, B .
A
i A
A
i
A
i
A
Depth, C -
A
A 1 A
A
\
A
A
A
Radius, R -
■020
•030 1 033
•040
•050
•060
•060
•060
Half-round Kky Way.
Size hole, A
itot
iJtoB
1 to lA
lltol.'i
1
lito2 2^to2A
2ito3
Width, B -
1
A
i
A
s
A
\
Depth, C -
A
A
\
A
A
\
Inserted Tooth Cutters. — The growing employment of the
inserted toothed cutters for face mills has done as much for the
extension of the practice of milling as perhaps any other single
improvement or innovation. The terms face milling and rotary
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172
MILLING MACHINES.
planing are both applied to this practice. The latter is the more
suitable term, because it distinguishes between the single cutters
inserted in a disc, and the end milling as done with teeth on the
ends of solid cutters.
The ordinary solid mill with finely pitched teeth is never a
roughing tool in the sense of removing material in quantity,
its depth of cut is far too limited. It roughs, of course, but
always in a depth measured in hundredths of an inch. But the
coarsely pitched inserted cutters are narrow planer tools with
penetrative capacity, and they therefore rough deeply when backed
up by machines of suf-
ficient power. They are
made and used in all
dimensions from a few
inches up to several
feet, and on vertical
and horizontal spindles.
There would appear to
be no limitations in
reason to the size of a
face mill. It fills a most
valuable place in the
work of roughing down,
and in that rough finish
which is commercially
good enough, in perhaps
half the volume of en-
gineers* work done. Its
utilities lie in the facing of flanges and feet, and of the areas to
which they are to be attached. It is of especial value in plates
and constructional work, in facing the ends of beams and stanchions,
of columns, and pipes, and the edges of plates superimposed, in-
volving numbera of similar pieces. The front rake which is imparted
to the cutters in most of these heads makes them true cutting tools,
and their coarse pitching permits the chips to get away freely,
which is further facilitated by the horizontal setting of the majority
of the spindles which carry the rotary planers.
Fig. 150 shows a common and good form of inserted tooth
cutter. The l)ody is split, and the cutters are fixed by taper
Fig. 150.— Inserted Tooth Mill.
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CUTTERS,
173
Fig. 151.— Inserted Tooth Mill.
pins driven into every alternate spacing. In various modifications
this device of tapered tightening pins is adopted.
A widely used method of holding the blades is shown in
Fig. 151. The blade A is ground on the sides, on a magnetic
chuck. The bush B is
turned parallel, and
has a flat milled on it
at an angle with the ,
centre line. This bush,
which fits in a recess,
as shown, is simply a
wedge, and is knocked
in. There is a screw c
to prevent it l)ecoming
loose. A second screw D, the patent of Mr W. S. Baskersdlle, is
shown for adjusting the blades sideways.
Fig. 152 shows the construction of a large inserted tooth
cutter, nine inches diameter, by twelve inches long. The cutters are
inserted in diagonal
grooves, and secured
with set screws press-
ing a wedge piece
against their faces.
The cutting faces are
radial, and of helical
shape. This was
produced after the
fixing of the cutters
in the diagonal milled
grooves, the machine
being geared to cut
the spiral faces.
The tooth gaps
are cut to alternate,
and not in a spiral
fashion. Each alternate cutter was put in place, and the gaps cut
at intervals. Afterwards these cutters were removed, the other
alternate set inserted, and the grooves cut to come behind the
teeth in the first set. The objection to cutting them spirally, as
Fig. 152.— Inserted Tooth Cutter.
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174
MILLING MACHINES,
though screw-cut, is that one side of each gap would be prevented
from clearing.
Fig. 153 illustrates a novel form of inserted tooth cutter made
by the Garrard Manu-
o d h o.
"V"
LrU
m
Fig. 153.— Inserted Tooth Cutter.
facturing Company Ltd.,
of Birmingham. Its main
feature is the adjusta-
bility of the cutters in
the head, to permit of
backing off' by simple
turning. The teeth a
have their inner ends con-
vex to fit down in con-
cavities in the head. The
latter consists of three
pieces, the body or stock
B, and the caps c, c, and
the latter are clamped
against the teeth by the
nuts on the mandrel that
secure the head. Conical
lugs a, a are provided on the sides of the teeth w-hich enter into
annular recesses in c, c, tapered on tlie outer edges to tighten
the teeth by the screwing up of the
clamping nuts. When the caps c, c
are slackened, the cutters can be
turned through a small arc in either
direction, to the extent of the
difference in their thickness, and
the width of their grooves. The
cutters are pushed over to one side,
and clamped to be turned. They
are then removed, and hardened.
When replaced they are moved
over to the opposite side, which
gives the angle required for cutting,
when they are again clamped.
Fig. 154 is an inserted tooth cutter of French design, in which
set screws are used to hold the tool points.
Fig. 154.— Inserted Tooth Cutter.
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CUTTERS,
175
Fig. 155 illustrates a German type of large cutter by the
Maschinen Fabrik Lorenz. Provision is made for adjustment of
the cutters by means of tapered operating screws (one of which is
shown in section adjacent), and clamping is by the outer screwed
ring.
Fig. 156 shows an inserted tooth cutter having front rake, used
in one of the A. Herbert machines, with swivel head attachment.
The fastening of the cutter is by means of splits, similar to Fig. 150.
Fig. 157 shows details of the fitting of a large cutter by the
Tangye Tool & Electric Company Limited. The diameter over the
Fig. i:
-Inserted Tootli Cutter.
cutter is 2 ft. 6 in. The block carries thirty-four roughing tools,
1 inch square in section, and two finishhig tools, IJ inch by f inch
section. The tools are inserted at an angle of 5** right hand, and
are adjusted l)y means of f-inch screws, tunied with a podger, in-
serted in a square hole, and locked with a nut. Two set screws
hold each cutter firmly. A pinion rotates the cutt-er block through
an internal ring of teeth. It is used on the style of machine
shown on page 137.
The cutter of the Goliath milling machine at the Fairfield
AVorks measures 16 feet from point to point of tool. It has fifty-
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176 MILLING MACHINES.
Fig. 156. — An Inserted Tooth Cutter on Herbert's Machine with
Swivel Attachment,
five roughing and five broad-faced tools. It makes one revolution
in 3 minutes 25 seconds. The feed is 2 J inch per revolution, equal
to about '66 inch per minute. The depth of cut is | inch. The
cut per tooth is 0*04 inch per revolution, omitting the broad-faced
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CUTTERS.
177
tools. This multiplied by the depth of cut makes the cross
section of cut 0*03 square inch per tooth. This, with a cutting
speed of about 22 feet per minute, shows a good record by com-
parison with a single planing machine tool.
In some shops wliere a good deal of face milling is done, in-
serted cutters are cast in their heads. The experience of people
who liave tried these differs, some saying that the teeth work
loose, and that the teeth cannot be tempered. Others use them
n^
Fig. 157. — Block with Inserted Cuttei-s. (Tangye Tool & Electric
Company Limited. )
regularly, and find them satisfactory for finishing as well as
roughing. The method adopted is this : —
Either Mushet self-hardening steel is used for the cuttere,
or ordinary- good tool steel. They are cut off to 2 or 2| inches
long, and set with the cutting ends downwards in the bottom of
a core box, and rammed round with core sand, which is dried.
The core containing the cutters is then dropped into a print
impression obtained from the pattern head, and so cast, some
extra hot iron being poured through the mould to ensure union,
M
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178 MILLING MACHINES.
imitating the practice of burning-on. The act of casting anneals
the steel, so that the teeth can be trued up after the shank of
the head has been turned. Or they can be roughly ground, after
which they are finished in the tool grinder in the ordinary way.
They are then hardened. In some of these cutters made by Pro-
fessor Sweet, 10** of face angle or rake is given in setting the
cutters in the mould. It is necessary to prevent rust forming
in the steel before casting. Tliey are therefore ground bright on
the emery wheel, and put directly into the mould ; or preferably
coated with boiled oil, or else are tinned, either of which methods
effectually prevents the formation of rust. The presence of rust,
even in traces, causes a blow, and prevents union of the metal.
Manufacture of Cutters. — The question of making verms
buying milling cutters is often a vexing one. Cutters are not
cheap, neither are the lathes, milling machines, and grinding
machines by which their teeth are formed. Cutters purchased
from an experienced firm are reliable. Those made by the shop
tool smith and in the tool room are not always so, either as regards
truth or temper. The case is much akin to that of twist drills
and reamers : few small firms make their own, but prefer to buy
them. Still, the making of milling cutters is work that a firm can
get mto gradually. Having a universal milling machine in the
shop, the teeth can be cut spirally or straight ; hardening and
tempering should be managed in the tool room, and grinding
machines are semi-automatic. Many large firms make their own
cutters. The more unusual the forms required, the greater the
reason why they should be made on the premises. This is the
case in all formed cutters, the outlines of which are almost
infinite, and large numbers of which are used in some shops.
In such cases it is better to be independent of outside help,
which often means delay and misunderstanding of precise require-
ments.
Steel. — The production of a suitable class of steel for milling
cutters is of cardinal importance. It is useless to spend a lot of
time on mills, and then fail through buying cheap steel unfit to
stand the work demanded of it. The following tables illustrate the
chemical composition of high-class steels suitable for miUs : —
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CUTTERS,
179
Crucible Cast Steel.
Per cent.
C-arbon -
-
-
-
1-2
Silicon
-
-
-
0112
Phosphorus
-
-
-
0-018
Manganese
-
-
-
0-36
Sulphur -
-
-
-
0-02
Iron, by difiference
-
-
98-29
Iron
-
-
about 98
Carbon
-
-
from
1-0
to 1-5
Manganese
-
-
>i
0-10
,, 0-40
Silicon
-
-
y>
0-10
,, 0-25
Sulphur
-
-
}}
0-003
„ 0-004
Phosphorus
-
-
if
0-01
„ 0-02
Actually when steel is wanted for mills, the manufacturer
must be informed of the specific purpose for which it is required,
and a good price paid.
The quality of the steel cannot be judged by inspection, nor
can cutters made of good or bad steel be distinguished one from
the other after manufacture. The temptation to use cheap steel
i^ due, not only to the lessened first cost, but to the lower expense
of machining it. The economy of using such steel is considerable
on large cutters, sometimes effecting a saving of one-third or one-
half ; but it should not be allowed to weigh in small ones, par-
ticularly those which have profiled edges or which are to be built
up and thus involve extra work in the jointing. This is one of
the advantages of the inserted types — the ability to use cutters of
the best material in the commoner matrix.
After cutters have been shaped by turning, grinding, and
milling they should be allowed to rest for a few days previous to
hardening. If they are to be annealed, Mr Brayshaw recommends
keeping an excess of cliarcoal near them in the furnace to main-
tain a reducing atmosphere and prevent risk of their becoming
decarbonised.
Hardening. — With regard to the methods of heating and
hardening much has been said and written, with much difference
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180 MILLING MACHINES.
in expression of opinion. Two or three essentials are clear — that
heating must be gradual and uniform, that overheating must be
avoided, that every different brand of steel needs a different
temperature, that there is a best and an exact temperature for
quenching a steel, that cutters of different shapes require differ-
ences in the ways of heating and quenching, and that the virtues
of particular quenching liquids are of a somewhat indeterminable
character. Some of these matters call for extended remarks.
A gradual heating up is one of the virtues in the process. By
it risk of cracking is greatly lessened. Even though heating may
be uniform throughout, yet it is better if brought slowly to that
condition than rapidly. The importance of these facts is so great
that it is desirable to have some precise and mechanical means of
regulation instead of the old method of the forge. As the dimen-
sions of cutters have increased, the necessity for the substitution
of the mechanical for the rule of thumb has become more apparent.
Hence the efforts made to utilise a liquid for heating instead of a
furnace heated by air, and employing a pyrometer for registering
the exact heat of the liquid or of the heating furnace. Though
molten lead has been employed, there are several objections to its
use. Whatever means of heating be adopted, the pyrometer is
becoming a most valuable instrument for ensuring uniformity of
temperature.
Overheating may be present without cracking resulting if the
heat be very uniform. It is an axiom that the lowest heat whicli
will give sufficient hardness is the best to adopt. Cracks may be
detected by sand-blasting a cutter after hardening, when they will
be revealed.
The question of frequency of grinding a mill is one of
economical importance. The time lost is that due to changing
mills in the machine with stoppage of the latter, the tune occupied
in grinding, and the more rapid wear and shorter life of a soft mill
over that of a suitably hardened one. This is one way to look at
the subject of hardening suitably done or improperly.
This, however, may be less serious than the question of harden-
ing cutters with the least risk of cracking. It is less risky to
make cutters medium hard than to make them sufficiently hard to
be durable, combined with sufficient toughness to avoid risk of
cracking.
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CUTTERS, 181
Cracks are the great evils to which cutters are liable, and the
larger a cutter and the more abrupt the forms of its teeth the
greater is this risk. Slight distortion does not matter, because
that is corrected in grinding ; but cracks are fatal, and these some-
times do not develop until the first grinding is done and the skin
being removed.
Eisk of cracking is lessened by avoiding keen angles in the
roots of the cutters. Hence, though the teeth sections may be
angular, the roots should have radii. But the important work lies
in the methods of heating and cooling adopted. The chief points
to be observed after a suitable temperature are equal heating and
the avoidance of draughts.
The temperature must be graded to suit a given brand of
steel. It may be estimated by the eye or by the pyrometer, but
it should not be allowed to fluctuate. Hence the open fire lb not
suitable for mills as it is for single-edged tools. If employed
at all, the cutters must be thrust into a tube ; but a gas furnace,
such as those used for case hardening, or one of the special
furnaces made, is the proper thing. The work is placed in a
muffle or in iron boxes, either open or enclosed in hardening
mixtures. Some hardeners prefer mixtures for the larger mills,
such as charred leather and charcoal pounded to the size of a pea,
within wliich the mill is completely enclosed and kept for three
or four hours at a low red heat. The mill is then quenched in a
bath of raw linseed oil, being moved about rapidly to bring fresli
oil into contact with the teeth, and there kept till cold. Mills
with large teeth treated thus need not have the temper drawn
subsequently. Smaller ones may be drawn to a light straw or at
a temperature of about 430° Fahr. In this packing method, which
Mr Markham adopts in preference to open heating and water
quenching, a great deal depends on the quality of the leather used.
The scrap shoe sole leather from factories is recommended. This
should be prepared by packing in one of the hardening boxes, luted
with fireclay, and put in the furnace just long enough to allow it
to become charred sufficiently to be pounded up well.
Another important point in the work of hardening is to
remove internal strains by slightly warming the cutter immedi-
ately after quenching. Mr Markham attaches great importance
to this in all mills of over \ inch diameter. The suitable tempera-
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182 MILLING MACHINES.
ture is that at which the hand cannot be held on the cutter, but
not so hot as to show any temper coloui*s. The explanation is
that which applies to all annealing — the heating of the external
hardened parts sufficiently to allow them to adjust themselves
to the changes of the interior, which go on for some time after
the outside has set rigidly. This reheating can be done either
over the fire, or, in the case of the smaller cutters, in a tray
immersed in a tank supplied with boiling water.
The difficulty of hardening without cracking is due to mass,
and whateA'er counteracts the effect of this lessens risk. In a
large mill the l)ody continues to shrink after the teeth have set,
and so tears itself away from some of them, or else the metal
remains in a state of internal tension ready to develop cracks on
the slightest occasion. Any suitable method of annealing there-
fore lessens this risk, whether done before or subsequently to
hardening. For the same reason all cold draughts and unequal
and sudden changes in temperature are to be avoided in the work
of heating mills.
The methods of quenching are generally familiar. It is well
understood that long cutters must be plunged vertically and flat
ones edgewise, done in both cases to avoid warping. The object
is to cool all parts simultaneously, and to allow of free access of the
water to all parts alike. Similar methods of letting down are
adopted as in other tools. As soon as the teeth are chilled they
may be lifted out, and the internal heat allowed to diffuse into the
teeth and then quenched again, the final quenching being done at
a pale straw or medium orange.
Water that has been used repeatedly is considered by old smiths
a better medium than fresh water. The reason seems to be that
the air is driven off, and that the presence of air prevents free
access of the water. Others use warm water raised to from 90" to
100" F. A safe, suitable bath is made by disvsolving soft soap in
boiling water to the consistency of cream.
Oil is used also. It does not cool so quickly as water. The
cutter teeth sliould l>e as hard as the teeth of a file.
Milling cutters with holes are best stored on vertical boards
studded with wooden pins. These are frequently hinged, with
pins on opj)osite sides, either enclosed in cupboard fashion or
ranged down passages along which the man in charge can walk.
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CUTTERS.
183
Cutting the Teeth. — ^There is often much similarity between
the methods of cutting the teeth of mills and of grinding them.
That is, the sectional shapes of the cutters and the grinding wheels
are often identical. This only holds good, however, when a tooth
space is ground entirely, and not when the tips or the faces alone
are done. The following are illustrations of both kinds.
Fig. 158 is an example of a cutter with straight teeth, having
its teeth formed with a cutter of the general shape seen in Fig.
Fig. 159.— Usual Type of Cutter
for Pi*oducing Teeth.
Fig. 158.— Cutting Teeth of Milling
Cutter having Straight Teeth.
Fig. 160.— Deepening Teeth, or
Cutting New Teeth with
Kmery Wheel.
Fig. 161.— Cutter for Spiral Mills.
159. Such a cutter would be sharpened afterwards on its edges,
but as it l)ecomes worn its teeth would require to be deepened
occasionally witii a grinding wheel like Fig. 160, or the teeth
might be cut in the first place with an emery wheel, though that
is an unusual and unsatisfactory method. These are ordinary
cutters, which, if profiled in section, lose their shape by re-
grinding. Fig. 161 shows the cutter suitable for a spiral mill
with the same form of tooth.
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MILLING MACHINES,
The most valuable improvement introduced into milling-cutter
practice, ranking only second to that of the development of special
cutter-grinding machines, was that of making " formed " cutters.
This term was given by the firm whence they emanated — the
Brown & Sharpe Manufacturing Company. The advantage is that
the cuttei*s never lose their original sections by regrinding. The
grinding is done only on the cutting faces. The profile forms are
Fig. 162.— Cutting Backed OflFMill
having Straight Teeth.
Fig. 163.— Chitting Backed OflF Mill
having Spiral Teeth.
Fig. 164.— Twist Drill Fluting.
Fig. 165.— Cutting Reamer Flutes.
maintained correctly until the tooth thickness is gi^ound away,
by the simple device of striking them from a different centre tlian
the centre of the cutter diameter. This is now adopted, not only
in the cutters for wheel teeth, l)ut in those also for milling most
profiles of irregular kind. The value of the device in prolonging
the life of cutters and ensuring the interchangeability of parts is
incalculable.
Figs. 162 and 163 show formed mills being cut, the first with
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CUTTERS,
185
straight, the second with spiral teeth. Afterwards the teeth are
backed off in a relieving lathe or in a rig-up on an ordinary lathe.
Grinding is always subsequently done on the radial cutting face,
never on the backed-ofif portion, and thus the sectional shape
remains unchanged until the teeth are too weak to perform
service.
Some special cutters are shown in succeeding figures operating
on cutting tools. Fig. 164 shows the milling of a flute of a twist
drill. Fig. 165 cutting a concave- toothed reamer, Fig. 166 a convex-
toothed reamer or boring tool, and Fig. 167 cutting tap flutes.
Grinding and Sharpening. — To go into the construction of
Fig. 166.— Cutting Four-lippecl
Boring Tool.
Fig. 167.— Milling Tap Flutes.
the cutter-grinding machines would lead us too far afield. They
are numerous, ingenious in design, and the results are arrived at
in various ways. We are content to deal with the results acliieved.
Fig. 168 must suffice for illustration.
This machine provides for universal movements to perform all
classes of grinding. The table is carried on a knee, which may be
swivelled around the circular column and clamped at any location
thereon. The table also swivels, and a head is fitted to the latter
having capacity for horizontal and vertical angling, so that the
work may be presented to the wheels at any angle. All these
angles can be read off on dials, so that their precise amount is
known. The table travels to and from the column by means of a
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186 MILLING MACHINES.
Fig. 168.— Cincinnati Cutter (irinder.
graduated screw, allowing of movenients of one-thousandth inch
being read off. Adjustable stops limit the travel.
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187
The head can-ies two wheels — a cup and a disc — which are
employed according to their respective suitability, for the work in
hand. Two speeds are available. The talJe attachments, l)esides
the angling head mentioned, include a tailstock with a spring
plunger allowing for endlong expansion of w^ork, a vice mounted
on a swivel face to allow of angular movement being given to the
work gripped in the vice jaws, an internal grinding attachment
having a small spindle running in long sleeve-bearings and carry-
ing a little wheel at the end. This is driven l)y a pulley on the
spindle actuated from the overhead countershaft. A gear-cutter
grinding attachment is fastened to the table, having a vertical stud
to carry the cutter by its bore and a pawl to lock eacli tooth in
Fig. 169.— Cutter (Jrinding with Edge Wheel.
correct radial position. Another special device for grinding the
tooth faces of fonn cutters takes the form of cranked centres,
which overhang from the table so as to bring the work under-
neath the wheel, enabling the latter to pass along the radial
faces. For grinding on dead centres, a loose-running pulley is
fitted to the table-head, driving the work as it lies l)etween the
centres. The height of cutters in relation to the wheels is regulated
by the table elevating mechanism provided with a micrometer.
The capacity of the machine is IG inches between centres by
8 inches diameter. Face mills up to 12 inches and saws up to 24
inches can be treated.
Almost invariably cutters are ground and sharpened in one of
two ways — eitlier by passing the grinding wheel over the edges of
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188 MILLING MACHINES,
the teeth as in common mills, or along the faces as in formed mills.
The practice of sharpening over the entire tooth space (in saw-
sharpening fashion) is unusual l)ecause wasteful of time and pro-
ductive of heating.
Taking the edge grinding first, this may be effected by different
wheel shapes. The principal results desired after the equal length
1
Fig. 170. — Grinding with Edge Wheel on a Cincinnati Machine.
of teeth are a connect and uniform clearance angle, and a flat face
rather than one concave.
Figs. 169 and 170 illustrate the most common method of grind-
ing axial cutters. The only objection to this is the concavity formed
by the wlieel. To diminish this, the wheel is selected as large
as is convenient, and so long as it does not foul the tooth above, it
may be any diameter in reason. In different machines the wheel
is presented differently, either in the manner shown, or vertically
al)ove. Many prefer to use a cup wheel, Fig. 171, which leaves
a flat face to the edge of the tooth.
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CUTTERS,
189
The tooth rest is an essential fitting, not only for pitching the
teeth and supporting the wheel, but also for fixing the angle of
clearance. After the rest, in Fig. 169, has been set to suit any
one cutter, its position is not changed until the cutter is completed,
but each tooth in turn comes round on it. The socket which
carries the rest is provided with a wide range of movements to
suit plain, cylindrical, spiral, and angular cutters. The blade
is often formed of an elastic strip of steel, sometimes solid,
sometimes divided as in Fig. 172. The object of dividing it is
Fig. 171.— Cutter Grinding with Cup Wheel.
V. ^^
Fig. 172. —Tooth Rest.
that the narrower portion can be sprung out and in from tooth
to tooth, without running the rest quite clear, so saving time, and
avoiding risk of missing a tooth.
The amounts of clearances on milling cutters are important.
They should vary only from about 5** to 7", the first being suitable
for finishing, the second for roughing. The Cincinnati Milling
Machine Company gives tables by which these clearances can be
obtained by the settmg of the tooth rest below the centring gauge.
The tables are for cup wheels, and for disc wheels, and are given
overleaf.
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190
MILLING MACHINES,
Cup Wheel Clearance Table.
For setting tooth rest to obtain 5"* or 7° clearance wlien grinding
peripheral teeth of milling cutters with cup-shaped wheel.
Diameter of Cutter.
For 5° Clearance.
For 7° Clearance.
Inches.
Inches.
Inches.
i
011= 1-64-
015= 1-64
t
015= 1-64
022= 1-64 -H
\
022= 1-64-1-
030= 1-32
\
028= 1-32-
037= 1-32-1-
\
033= 1-32
045= 3-64
I
037= 1-32-1-
052= 3-64-1-
1
044= 3-64
060= 1-16
li
050= 3-64-1-
067= 1-16-1-
li
055= 1-16-
075= 5-64
li
066= 1-16
090= 3-32
If
077= 5-64
105= 7-64
2
088= 3-32-
120= 1-8
2i
099= 3-32-1-
135= 9-64
n
110= 7-64
150= 5-32
n
121= 1-8
165 = 11-64
3
132= 1-8-1-
180= 3-16
3i
143= 9-64
195 = 13-64
H
154= 5-32
210= 7-32-
n
165= 5-32 -t-
225= 7-32 -J-
4
176 = 11-64
240 = 15-64
4i
187= 3-16
255= 1-4
4i
198 = 13-64-
270 = 17-64
4|
209 = 13-64-1-
285= 9-32
5
220= 7-32
300 = 19-64
H
231 = 15-64
315= 5-16
5i
242= 1-4-
330 = 21-64
5|
253= 1-4
345 = 11-32
6
264=17-64
360 = 23-64
6^
286 =^ 9-32
390 = 25-64
7
308= 5-16
420 = 27-64
n
330 = 21-64
450 = 29-64
8
352 = 23-64
480 = 31-64
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CUTTERS,
191
Disc Wheel Clearance Table.
(xiving distance for setting centres below centre of spindle to
obtain 5° or 7° clearance with wheels of different diametei"8
when grinding with periphery of disc wheel.
Diameter
of Emery
Wheel.
For 5°
Clearance.
For 7°
Clearance.
Diameter
of Emery
Wheel.
For 5°
Clearance.
Inches.
For 7°
Clearance.
Inches.
Inches.
Inches.
Inches.
Inches.
2
3-32
1-8
•li
3-16
17-64
^i
3-32+
9-64
' 4i
13-64
9-32
-'^
7-64
5-32
1 4j
13-64-1-
19-64
2f
1-8
11-64
5
7-32
5-16
,S
1-8-1-
3-16
' 5i
15-64
21-64
n
9-64
13-64
5J
15-64-1-
11-32
'S\,
5-32
7-32
1 5J
1-4
23-64
3f
5-32-1-
15-64
6
17-64
3-8
-i
11-64
1-4
1
NoU, — If emery wheel selected is too large, that is, if it scores the next
tooth, a smaller wheel should be chosen and the centres readjusted so as to be
right for this wheel.
It makes no difference if the mill is spiral. In tiie latter
during its traverse, the teeth bed upon the rest, Fig. 173, and the
Fig. 173.— Tooth Rest set for Spiral Cutter.
Fig. 174.
Grinding Tapered Cutter.
portion of the length of the spiral which is being ground at any
instant is passing the cutter at a constant height, which is fixed
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192
MILLING MACHINES.
by the setting of the rest. The rest is also used for staggered
mills and hobs. The teeth of angular cutters also receive support
from tooth rests. Taper mills are
treated similarly, the axis of the
cutter is set to half the taper;
and edge or cup wheels are used,
Fig. 174.
The side teeth of cutters are
ground with disc cutters, Fig. 175,
with a wheel as large as possible
without fouling the tooth above.
Or frequently the wheel is set ver-
tically over the cutter, with the
Fig. 175. Grinding Side Teeth. ^^^is of the latter vertical instead
Fig. 176.— Grinding Side Teeth with Cup Wheel.
of in a horizontal plane. Or cup wheels are used alternatively,
as shown in Figs. 176 and 177, the cutters being set for angle
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CUTTERS.
193
of clearance in each case, but the wheels being differently pre-
sented.
Fig. 177.— Grinding Side Teeth with Cup Wheel.
The teeth of end mills are ground with cup wheels, Fig. 178,
the wheel axis, or that of the cutter, is set out of parallel by
the amount required to give
clearance to the teeth. Fig. 179
shows the hole of a cutter being
ground with the internal attach-
ment.
Profile mills if ground on
their edgefe are done by the aid of
a former. An example is given
in Fig. 180. In this class of work
the relieved cutters are generally
to be preferred, because being
ground on their faces, they can be done in any machine without
rigging-up a profile arrangement.
N
Fig. 178.-Grinding End MiU.
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il94
MILLING MACHINES.
O
e3
I
^
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-"^^ tgta
'^,
^t
a
Fig. 181.— Elevation of Form Cutter Grinder.
Fig. 182.— Plan of Form Cutter Grinder.
D
Fig. 183.— End View of Form Cutter Grinder.
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196
MILLING MACHINES.
Figs. 181-183 illustrate a form cutter grinder by the Aetien
Gesellschaft fur Schinirgel tind Machinen Fabrikation, of Bocken-
heiin. A is the base, bolted to a bench or a pillar. On it the
sliding table B is capable of adjustment by the handle c, operating
a screw. The emery wheel
carriage is pivoted at D, and
is lifted, lowered, and con-
trolled by the handle E. The
form or profile piece is bolted
Q;. PI to the bracket f, made in
j 1 three pieces, giving adjust-
ments in the vertical direction,
I V~
Fig. 184.— Grinding Formed Cutter.
and horizontally, on a
sliding face on the table
B. The tooth rest G, on
the opposite side, has
vertical adjustments, and
two horizontal ones at
right angles with each
other. The work spindle
H is held in a head J,
having endlong adjust-
ments on the base K,
which swivels on the
table B, upon which it
can be clamped. The wheel has two speeds by coned pulleys, the
tension being adjusted by a screw and nut in the wheel arm.
The second method of grinding adopted, that of faces for
form mills, is simple. The shapes of the wheels used and their
Fig. 185.— Grinding Formed Cutter.
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CUTTERS.
197
presentations are illustrated in Figs. 184 and 185. The re-
semblance to that of grinding a tap is shown in Fig. 186.
The economy of regrinding is too valuable
to be neglected. It is not only that better
work is produced by keeping cutters sharp, but
that the operation of grinduig is also more
readily done. Heavy grinding produces heating,
and distortion, and draws the temper, as in-
dicated by blueing. If a cutter has been treated
badly by being allowed to become very dull, it
is better to regrind it while revolving on a
mandrel, before taking it tooth by tooth. Dry
grinding is usually adopted. In some firms the
cutters are sharpened more finely by rubbing
each tooth with an oil stone, or with an emery rubbing stone, or
a carborundum stick. Firms who adopt the practice speak highly
of the results.
Fig. 186.
Sharpening Tap.
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CHAITER YIII.
MILLING OPERATIONS,
The Operations of Roughing, Finishing, and Profiling — Milling Compared with
Planing, Shaping, and Slotting — Examples — Holding Work in Jigs —
General Considerations — Examples.
The Operations of Roughing, Finishing, and Profiling. —
The time has now come when the true position of the milling
machine in the engineers' shop may be considered as practically
determined, at least for a long term of years. We have seen that
its utilisation in engineers' work did not follow until half a
century subsequent to its invention, its applications during that
period lying in the small-arms and sewing-machine industries.
Then, for many years, engineers used it for light operations only,
and chiefly in those which had been hitherto performed at the
vice. Milling did not come into much rivalry with the general
operations of the machine shop until within about the last ten
years. An exception must be made in the case of slabbing face-
milling cutters, with inserted teeth, which have been used for
twenty years or more, in some shops for rough facing.
About ten years ago tbe milling machine began to boom in
general engineers' work, and it made its appearance in many
shops where it had hitherto not been seen at alL Then something
like a reaction occurred, and many thought that the multiple cutter
was going to displace the single cutter on planer, shaper, and
slotter. Practical mechanics did not, as a rule, share that
delusion. Wliat has happened is, that though some displacement
has occurred, the milling machine has taken charge of a compara-
tively new field of work, the nature of which we propose now to
consider briefly.
From this point of view we may regard milling in three broad
aspects — that of roughing, finishing, and profiling.
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MILLING OPERATIONS. 199
The first two divisions correspond in the main with two broad
types of cutters — the inserted tooth type, and the ordinary continu-
ous edged cutters. Under the first are included the staggered
mills. The difference in working between the two broad type^
is, that the first are capable of slogging, the latter are not nearly
so well adapted to that operation. The first comprise a series of
single-edged tools, the second resemble the float-cut file in their
action. The first are frequently true cutting tools, witli ftont
rake, the second are rarely so, since their cutting faces are radial,
or normal to the surface being cut. These broad differences
between separate and conthiuous edges, and l)etween cutting and
scraping tools lies at the basis of the distinction between roughing
and finishing operations.
But roughing is a term of relative meaning, denoting generally
the first, or often the second cuts on a job, as preparatory to the
final or finishing cut. A cut may be a roughing one without being
deep, but a finishing one is always fine. Both are generally doneJ
with the same mill, fed deeper, or shallower. But no cut taken
with continuous edged mills can ever be as deep as that wliich is
taken with a single-edged tool, or with staggered mills. Tlie
difference is that between scraping and cutting, between broken
shavings and coarse chips. It is because this distinction has been
often neglected that too much has been expected from milling
cutters.
Limits are set to the action of single-edged tools in lathe, planer,
shaper, and slotter by the spring of rests, of cross rails, and rams.
The stresses on a broad-cutting finishing tool prevent any but very
shallow cuts being taken. Yet milling cutters exceed in width
many times those used for broad finishing, and therefore so much
less depth of cut can be expected of them. This increased breadth
of action, the breaking up of the chips by the scraping process',
and another fact, the small spacing of the teeth, tending to cause
choking and dragging, are the disadvantages under which the
milling cutter does its work.
What has partly disguised these facts is the abundant lubrica-'
tion imparted to these cutters in the best practice, which contrasts
strongly with that of the single-edged tools ; the wider spacing of
the teeth given for some kinds of work, the more efficient support
afforded to cutters and work than of old, and the spiral arrangement
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200 MILLING MACHINES.
of teeth, which effects a shearing cut. Features wliich may conduce
to a better solution of the difficulty are the adoption of a more
rational method of feeding, and a further stiffening up of the
machine elements.
The roughing operations of the milling cutter may simply mean
the first, or the second cuts of the common mill, preimratory to the
finishing cut of the same tool. Or it may mean roughing performed
preparatory to planing, either l)y a common mill, or gang of cutters,
or by means of an inserted toothed mill, or of a staggered toothed
solid mill. Or it may mean rough tooling only, as in that large
class of face cutters which are used for ending rolled l)e>ams, or
facing the feet of standards or brackets, or other castings in which
the object is to remove the rough exterior, and leave a roughly
faced surface, suitable for attachment to other parts. Each of
these is largely represented in the practice of the shops. The
finishing operations of the miller include the greater portion of the
work done on these machines, and these can never l)e any but
very shallow cuts, consistently with accurate results, and the wider
the surface, the less must be the depth tooled. So that j)ractically
we may say that broad and accurate finishing is not where the
miller scores best, though it is possible under the conditions just
named. Its best work is done on narrow pieces, or on those of
medium width only.
Milling Compared with Planing, Shaping, and Slotting. —
Milling over a broad surface or on a number of narrow pieces
arranged side by side having their aggregate area covered with a
single broad cutter is a rival operation to the single tool, or
couple of tools held in the tool box of a planing machine. When
the question is one of roughing down, the milling machine scores ;
when it is that of very accurate finishing, the planing machine is
found superior in accuracy, though not perhaps in smoothness of
surface. The question, therefore, is not an absolute one, but relative.
And the reason is fairly clear to a practical hand, being due to the
difference between the spring of a broad cutter operating over a
width, say, of 12 to 20 inches, and the rigidity of a shanked tool
taking a narrow cut. It is practically impossible to avoid spring
on any cutting that is both heavy and broad in character. Spindles
are being constantly stiflfened up, more attention is given to their
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MILLING OPERATIONS. 201
bearings ; cutters are serrated and staggered for breaking up the
chips, and provided with teeth having a high angle of spiral for
finishing, yet they spring and chatter. And even though the
amount is not much, it is sufficient to destroy the very fine accuracy
that is required in machine tool slides, and in other intimately
fitting parts. The conditions are not comparable with those of a
narrow milling cutter on a stiff arbor. Lathe men will understand
this when they remember that heavy cutting and very accurate
results are incompatible ; that fine precision of results requires
light cuts, and that it is better to rough coarsely and finish finely
than to reverse the process.
The mills with spiral teeth are better for finishing, since they
take extremely shallow cuts. But what they lose in depth they
may gain in area, and thus show considerable economies over
planing : lience their special value for preliminary operations.
In fine finishing, no less than in roughing down, a stiffly built
machine, whether planer, miller, grinder, or lathe, is essential. It
may sometimes seem incongruous to see a massive machine weigh-
ing several tons revolving a tiny milling cutter or emery wheel,
nibbling at a bit of work, removing perhaps a hundredth or a
thousandth of an inch of metal. Apart from experience, this dis-
proportion would appear absurd. This has not been arrived at by
calculation, but it is a case of evolution in the workshop. When
the effects of vibration, or slackness of spindle and slides, or even
of the spring of parts that are too slender to hold the work or the
cutter stiffly, are found to occur in the smallest work, it is not
difficult to see what may happen in the case of a very large cutter.
The faintest trace of vibration, of yielding of frames and spindles,
produces unevenness in the surface of the work, which is fatal to
the finer degrees of accuracy required in the production of high-
class machinery; hence machines are constantly being built of
more massive design than their predecessors.
Plain surface tooling — using mills which cut by their edges —
constitutes the largest class of work done. For this the mills
should be longer than the width of the surface which has to be
operated on. They are either vertical or horizontal. The work
may be a single piece, or a number of pieces arranged in series.
Mills of this general type are used on every class of machine,
and on an infinity of duties. Mills about an inch in width
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202 MILLING MACHINES.
have the teeth arranged spirally to give a shearing cut, which
separates the metal in detail, and puts less strain on the arbor.
The amount given varies widely by different firms, but in
recent years the angle of spiral is greater than was formerly
adopted.
When employing broad cutters, a great deal of work is either
ground or planed after being milled, being so treated in order to
impart a higher degree of accuracy than is found practicable under
ordinary conditions when using broad cutters in the milling
machines. When work leaves a planing or shaping machine it is
finished, except when scrapii^ for high-class work only is required.
The practice just instanced seems a proof that broad, heavy milling,
with axial mills at least, is not yet so accurate as planing. There
are exceptions, but they serve to accentuate the rule that the
milling of heavy work with deep cuts and rapid feeds is chiefly
valuable in removing the bulk of the material and producing a
fairly accurate surface, which then has to be finished by light
grinding or planing. Much of this is probably due to the employ-
ment of light machines on work for which they are not adapted,
and to the practice of performing too heavy cutting on large areas,
with arbors also too light for tlie work.
Wide faces and inner edges can be tooled with broad face and
side mills, many examples of which occur in the slides of machine
tools. Smaller flanking mills may cut edges sunultaneously. The
angular mill affords good facilities for tooling the angles of slides
accurately.
Face-milling cutters are preferalJe for some purposes to
cylindrical cutters, since they are useful for depthing, as well as
for surface work.
Another advantage which the large face mills with inserted
teeth possess over single-edged planer tools is, that these will
reach down or across to surfaces that cannot be reached with a
planer tool, properly supported. There is a great difierence
between the overhang of tlie shank of such a tool from the tool
box, and the mass of a cutter head.
A limitation of the milling machine is that a mill cutting
axially must always leave a radius in corners of recessed portions
of work. If this is objectionable, it wiU often happen that a face
mill can be substituted. But in many cases a radius is to be
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MILLING OPERATIONS, 203
preferred. The following are some of the principal jobs done by
milling, several examples of which are shown on subsequent
pages : —
The flanges of steam chests can be tooled by a face mill on
a horizontal spindle, and the truth of the work will be ensured by
bolting one end flange, already faced when boring, on the machine
table. At the same setting the ports can be milled.
Three sides of parallel bars can be tooled simultaneously with
rotary mills on a machine of the planer type, fitted with one
vertical and two horizontal heads. Or two edges can be milled
simultaneously with a machine having two vertical spindles only.
The shoulders between brasses are shaped parallel, with mills
having teeth on ends and edges. All kinds of brass fittings have
their angular faces tooled in special or plain machines. Bearing
caps have their edges milled with edge mills on vertical spindles.
The faces of eccentric straps are tooled with edge and with end
mills. So are keys and cottars, slide valves, and eccentric rod links.
The edges of cycle cranks are tooled with profile cutters. Taps,
reamers, and twist drills are grooved, as already shown, between
centres with cutters having the profiles of the grooves. Tee
grooves and vee grooves are milled with cutters of corresponding
sections carried in vertical or horizontal spindles. Vee ways for
slides of moderate width can be tooled at once with a one solid
mill. The teeth of racks are milled, several at a time, by a gang
of cutters. The rims of gear wheel blanks are milled to section
on periphery and edges, the blank being fed circularly on a
horizontal spindle. The square ends of spindles can be cut with
end mills. Vice jaws can be milled, and oil channels in small
tables. Slits for tightening purposes are cut with slitting saws
on a milling machine instead of casting them. Then there is
besides the work of cutting all kinds of gear wheels, which subject
will be treated in another chapter.
Key ways and that class of grooves can be tooled with mills
cutting at bottom only, or at bottom and edges at once, the shaft
or other piece of vork being clamped to the table or in the vice.
The tool is a disc with teeth on the periphery only in the narrower
sizes, but with teeth also on the sides in the wider ones. In the
narrow ones the teeth are square across, in the wider a spiral
twist is given to them.
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204 MILLING MACHINES,
Faces and outer edges can be tooled simultaneously by what
are termed straddle mills, and a constant width maintained easily
in a large number of pieces. By turning the side mills round, the
outer edges can be used after the inner ones have become dulled.
Also, edges can be tooled thus without touching the face by insert-
ing a plain distance piece between side mills. Or a single edge can
be tooled with a side mill of suflScient size to cover the area required.
A convex edge is a very simple detail. These edges occur
with great frequency in engineers' work. The old method was to
plane or shape them, adjusting the tool slides by hand, or to file
them. The modern method is to mill them with concave cutters
if half -circles, or with cornering or radius cutters if quarter-circles.
These can be used equally well on vertical or horizontal arbors.
Concave forms can be milled.
Half -bearings or keeps can be milled singly or in series, instead
of boring.
More elaborate sectional forms can be cut by mills operating
by edges and ends : and these may run in one plane or iiTcgularly,
as in profile work. They may be formed in one piece or built
up in gangs. There is no limit to such combinations, save the
strength of arbors and the capacity of machines.
Large profile cutters are multiplied in gangs on an arbor to
tool several sections at once. The ways of small lathe and machine
beds are thus shaped. Tliese gangs are made up more cheaply
than by forming solid mills for intricate work, besides which the
separate mills can be used for plain work. They may lie closely
together, with or without overlapping of teeth, or plain distance
collars may be used to separate them, if the cutting is not con-
tinuous. Edge mills may also fulfil the function of distance
pieces. Mills are locked together in gangs by projections on one
entering recesses in the one adjacent. Several similar mills may
be arranged side by side for duplicating work. In cases where an
exact dimension ticross faces has to be worked by, two mills may
cut on each face at once, whether the faces are internal or external.
Where the alteration in size of a single mill is objectionable
because the later pieces tooled would not be of the same dimensions
as those first done, then, for inner faces, interlocking mills are
used, and for outer ones mills separated by a collar, either device
of which permits of micrometric readjustment.
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MILLING OPERATIONS. 206
The utilities of the miller are very great on form, and on
profiled work. The distinction made is that between the work
of the gang mill operating on a plain surface longitudinally,
and that of any edge mill, gang or otherwise, operating on a
surface which is irregular in the plane of the axis of the mill.
There is no other tool in the machine shop which will produce
such surfaces. Before the mill came they were done by hand at
the vice, or in a rough fashion by a succession of settings of tools
and cuts on the planer, shaper, and slotter. On the milling
machine they can not only be done cheaply, but with nearly
absolute uniformity, which was not possible under the old system.
This, therefore, is a new sphere which the miller has almost
wholly created for itself.
There is another aspect of the methods which either came in
with the milling machine, or the development of which it has
greatly helped. Since cutting, to be accurate, must be shallow,
and since slight allowances are only consistent with very close
approximation to dimensions, the practice of milling has reacted
on the work of the die forger, and of machine moulding. As these
methods are only economically available when considerable
numbers of similar pieces are required, they have favoured the
development of interchangeable methods, and the practice of
jig making. The latter has reacted on the work of the smith
and moulder, in demanding the closest adherence to dimensions,
and the smoothest surfaces possible, because it is difficult to
design jigs for pieces of work that vary in size and form, and
it is wasteful of time to have to set such pieces in jigs. And
as allowances diminish, the presence of scale becomes more
objectionable than when a good roughing cut can be taken with
a single-edged tool, penetrating below it at once. Pickling there-
fore is resorted to, both for castings and forgings, in shops where
consideration is given to the permanence of the edges of cutters.
The relative degree of accurticy of surfaces which is desirable
or essential must frequently control the decision of the alternative
methods of planing or milling. There is, for example, no com-
parison practicable between milling a number of girder ends, or
stretcher ends, or pipe flanges, and milling a long lathe bed, or
planing machine bed, or slides. The two classes of work, and the
large group of which each is broadly representative, stand in an
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;2a6 MILLING MACHINES.
entirely diflferent cat^ory. Lathe and machine beds are not con-
sidered true enough unless they are within about ^^^ of an
inch in a length of 6 feet. Now an extremely slight amount of
deflection under cutting will produce this minute degree of in-
accuracy. But for a large proportion of faced work, rJ^ of an
inch would be suflBciently accurate.
Then further, the question of whether roughing. or finishing is
being done is on a par with that of relative degree of accuracy. If
a piece of work has to be finished by grinding, then fine accuracy
in the roughing is not important, but the roughing may correspond
with the degree of accuracy, say ^\js of an inch, which might be
the finish limit in a diflferent grade of work.
The springing of work under cutting is a matter of which
account must be taken when comparing alternative methods of
tooling, and deep or shallow cutting, coarse or fine feeds. It may
be accepted as beyond doubt that all planing or milling causes
some deflection and springing, though the amount would be very
variable under diflferent conditions. But its presence and amount
would in numerous instances be the principal factor in deciding
the choice between planing and milling, or between roughing by
one method and finishing by the other, or between taking heavy
and light cuts, or between using inserted tooth rotary face mills
or solid edge mills.
The question of milling versus planing lathe beds has been and
is to an extent an open one. In some cases it is solved by employ-
ing milling as a roughing operation, and planing as a finishing one.
But planing involves the employment of a gauge or gauges as the
work proceeds, and several settings of the tools. Hence the idea
of a single gang of mills tooling the shears at one operation has its
fascinations. But such work is only practicable under certain
conditions.
The great diflficulty encountered is that of spring, both that of
the gang of cutters, and that of the beds, and these forbid the
employment of any but very shallow cuts for broad finishing. A
single-edged tool, though heavily fed, can be trusted not to cause
spring in a bed, but the case is on an entirely diflferent footing in a
gang of cutters operating over a width of several inches.
This elasticity may be minimised, but not eliminated entirely.
Stiflf arbors are essential, and careful levelling and packing up of
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MILLING OPERATIONS, :207
the beds with wedges, or with special appliances, as stools and
clamps in a fixture attached to the machine bed. Clamps must
also always be pinched right over the points of support that are
employed. After a rough cut has been taken, the clamps should
be slackened to note if the bed has sprung in consequence of the
removal of the skin, which is liable to happen in the lighter class
of castings. Also light cuts taken over the rough skin of a casting
ruin milling cutters, so that between these and the heavy ones,
which are impracticable, there is little if anything to be gained by
milling, especially when extra expense may be entailed for final
scraping.
The work however may be divided with advantage, either by
roughing down with single-edged planing tools on the planer, and
finishmg with very light cuts by a gang of cutters operating over
the whole width. This involves setting at two machines, unless a
combined planer and piano-miller is available. Or the roughing
down may be done by mills, roughing sections of the work only,
with coarse feeds, to be finished as before with a broad gang mill.
Given machines specially rigid in beds, tables, arbors, and cross
slides, there is no reason why milling should not be both broad and
accurate in character. Thus, at Messrs L. Loewe & Co/s, lathe
beds are roughed out on the milling machine, and finished on the
planer, the latter being employed to ensure greater accuracy. The
precaution is taken of allowing the work to stand for several
weeks, after rough milling, before it is finished by planing, to give
time for the slight change of shape that occurs to take place.
Screw machine beds are regularly milled in the Warner &
Swasey shops with gang mills on a planer type of machine. The
gang mill goes over the surfaces of the vees, the bed edges, and the
rack bed. Supplementary spindles in special heads, with a slight
vertical range of adjustment, mill the bottom faces for the gibs,
using shank mills. Eoughing and finishing cuts are taken thus.
The beds are finally corrected by scraping.
The problem of milling versus planing is not only governed by
the spring of the work, and the relative quantities of metal removed,
but by the relative facilities existing for tooling faces at different
angles and in different planes. The planer is the more accommo-
dating of the two in this respect, because tools can be cranked and
set to operate on undercut faces, often in situations that neither
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208 MILLING MACHINES,
vertical nor horizontal cutter spindles are able to reach. In con-
sequence of this, numerous jobs can be tooled at a single setting on
the planer that would require two on the milling machine. And
some could not be finished at all on the latter, or if so, an expensive
special tool would have to be made, and special tools are not to be
considered in the work of the general shops.
Face, and edge milling afford two alternatives which often have
to be discussed and considered in relation to special jobs. The
question of rotary planing is also often included when face milling
is concerned. In a good many cases there is no alternative, as
when faces on the same job lie, some horizontally, some vertically ;
or as when a job can only be fixed one way on the machine. But
when choice can be made, the face mill has the advantage that the
chips fall away from the work at once. In edge milling the action
of the cutter is impeded by
?;J3 the presence of the chips.
S'<H •; I, ;*A
which do not get away freely
from between the teeth, and
this acts as a limitation on
the depth of cut and feed.
187.— End Mill working on Thin And when castings are not
PieoeheldwithSide Strips w^ged j^j^j^j ^^^ ^^^^ ^^^ ^^
against Bound Pins put in Holes f . . ' _ , « , , .,
in Table. lyi^^g ^^ "10 path of the teeth
aggravate results, so that the
horizontal face mill scores more heavily still than when working
on clean surfaces. For the roughest class of milling, therefore,
the face mill on a horizontal spindle is the best rival to the
planing machine.
Some examples of milling work which would alternatively go
on the planer are shown in subsequent figures. Taking thin pieces,
there are two or three ways of holding, as follows :— A few parallel
pieces, Fig. 187, a, of various widths and lengths, chamfered off to
a narrow edge down one side and planed parallel, are kept handy
to suit different jobs. The thin edges go against the sides of the
work, and, being shallow, do not interfere with the milling of the
top face. The shorter pieces are used for short bars, the longer
ones for long bars. They may be held in place by means of
wedges simply, and used in pairs, as in Fig. 187. The holes in
the Fig. or the tee slots in a machine table rim pretty close
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MILLING OPERATIONS.
209
together, and, by selecting parallel pieces of different widths to
suit varying sizes of bar being tooled, any width can l>e held on
the table. In Fig. 187 plain pins B, inserted in one set of holes,
take the thrust of one parallel piece, while the other piece is forced
agauist the bar by means of wedges c, c driven against pins B in
other holes.
Another way is to hold one of the parallel pieces A down with
a bolt, which may be long or short, Fig. 188, and the other B
--J
Fig. 188.— Edge Mill working on Thin Piece held with Side Strips
wedged against Blocks Bolted in the Slots.
wedged c against a pivoted block D. Or pinching is done by
means of adjustable points or fingers and screws. The fingers
are bits of round rod, flattened at the ends which Ijear against
the work, and they are hollowed at the other end to receive
the push of the tightening screws. The screws are tapped
into stops, which, fitting into the table groove, take the re-
action due to the tightening up of the screws. Or a bracket of
larger size, with feet, can be used, and tightened down with bolts
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210
MILLING MACHINES.
Fig. 189.— End Mill working on Piece held
with Clamping Plates and End Stop.
fitting in the table slots.
Long parallel guides are
further useful in im-
parting steadiness to
narrow, weak bars by
affording them some
measure of support.
Being also parallel, they
serve to set the work
true with the tee slots
or holes.
Bars of rectangular
section often have to be
milled on all four faces,
as, for example, the
wrought-iron guide bars
used for hydraulic rams,
and also those for some
engines. In such cases
no clips can be used for
holding down the bara
on the table. There are no
side flanges either to afford
a bearing for plates. Such
work is held by end or by
side pressure alone. Then
one of the methods shown in
Figs. 189 and 190 is adopted.
Fig. 189 shows a long
guide bar for a hydraulic
ram. The actual clips by
which the bar is held are
shown at A. These, it will
be observed, are pressed
against the sides by leverage.
Tliey stand at an angle, and
are jammed between the
sides of the bar and the tee-
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Fig. 190.— Broad End Stop which steadies
and keeps a Piece square.
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MILLING OPERATIONS,
211
head bolts. The tightening of the bolts c presses down the
plates B upon A, the plates B being supported at the outer face
upon the packing pieces d. As the plates A are longer than the
parallel distance between the sides of the bolts c and of the bar,
it is obvious that the tightening of the bolts c must wedge them
against the bar, and the more tightly c c are turned the more
securely will A a be pinched against the sides of the bar, so that
it is held perfectly rigid, and the top face is left clear for milling.
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Fig. 191. — End Mill operating on Claw Clutch clamped by its Collar.
The number of bolts and plates will depend on the length of the
bar being tooled. There may be four, six, or even eight sets, tlieir
distances apart ranging from about 2 feet to 2 feet 6 inches.
A stop block is often placed at the end, as seen.
In some light work even, in which it would be practicable to
effect a hold with clips upon the top face, it is better to adopt the
method illustrated in Fig. 189, because the flank pressure obtained
thus is not nearly so liable to pull the work out of truth as the
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212
MILLING MACHINES.
pressure exercised by the direct pinching down of a clip on a light
bar, or forging, or casting.
Another way of arranging clips of this kind is to place them at
the ends, or a broad steady piece like Fig. 190 may be used. It
is suitable for work of no very great length, say, not exceeding
Fig. 192. —Edge Mill operating on Two Thin Strips clamped between
Angle Brackets.
3 feet. Fig. 191 illustrates another way of gripping with clips,
taking a bearing on a recessed portion — a claw clutch, in this case,
but equally adaptable to straight pieces having recessed portions.
Bai-s may be held on edge by tlie rig-up shown in Fig. 192, by
means of brackets held with tee-head bolts, one set of brackets
carrying pinching screws.
^J-
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Fig. 193. — Motion Bar, tooled on Face and Edges with Straddle Mill, while
bolted against Angle Plate, and supported on Packing Blocks.
Fig. 193 shows how cast-iron guide bars may be held for
milling. No clips can be pinched on the top faces of the guide
bars because they have to be machined all over, and neither are
there holes of any kind which can be utilised as means of hold-
ing down. The rib affords the only convenient means of attacli-
mcnt.
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MILLING OPERATIONS,
213
Fig. 194 shows the fixing of the cun^ed side plates for tanks,
going at the bottom and side of the tank, illustrating the setting
of the plate A for milling the longitudinal edges. It is laid
Fig. 194.— Corner Tank Plate, having Joint Faces tooled with End Mills
while Clamped, and adjusted between Angle Plates.
directly upon the table of the machine, or on shallow packings
a, a, and set and bolted to angle plates B, B, which are bolted to
the table. These plates always form quadrants of circles. The
caulking strips down the longitudinal edges are therefore at right
%ESr
Fig. 195.— End Joints of Comer Tank Plates being tooled with End Mills
while held down with Clamping Bolts and Plates.
angles with each other, and the lines of the right angle, when pro-
longed, meet at the centre from which the radius of the curv^e of the
plate is struck. To set the plates, therefore, they are first lightly
bolted to the angle plates when brought nearly into position, and
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214
MILLING MACHINES,
then adjusted exactly with the square and rule. The square is
held against one strip or " fillet," and measurement is taken with
the rule to the outside of the curve. When this distance — usually
either 6 inches or 9 inches — equals the radius of the curve, plus
the allowance for tooling on the lower strip, then the plate is
square, and the bolts can be tightened ready for milling the strips.
Both top and bottom strips are tooled at one setting.
To mill the ends, several plates are laid in line across the table
D ^
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Fig. 196. — End MiU facing a Boss Bearing pinched between Special Clamps,
with Stop Blocks.
of the machine, Fig. 195, and bolted down with clips near the ends,
the clips clamping adjacent plates as shown. The longitudinal
edges already tooled must be set square across the table. Both sets
of ends will be milled at the same time. The lengths of these
plates must be the same as the lengths of the square plates, and
will be measured with a gap gauge of sheet steel.
Fig. 196 shows a boss bearing which cannot be gripped on top
nor on edge without special angle brackets. One of these. A, is
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MILLING OPERATIONS.
216
urr
fixed by tee-head bolts in the table slots ; the other, B, is permitted
a limited amoimt of adjustment before it is tightened by the
reaction of the screws c, c against the stop blocks D, D bolted in
the grooves.
Fig. 197 shows how eccentric straps are machined preparatory to
being bored. A number of half -straps are bolted to an angle plate
by means of a clip, the joint faces
being levelled properly. After the
joints are milled, the bolt holes
are marked and drilled at the same
setting on the angle plate.
There are very many types of
that kind of work which are
comprehended under the term
"brackets." They constitute a
large class. Many bearings are
so denominated, rather loosely;
but such is the usage. The
method of fixing brackets for
machining will depend partly
on their shape and proportions,
partly on the number of simi-
lar castings. Small brackets, of
which there are but one or two
castings, will generally be either
bolted to the angle plate or held
in the vice. If numerous, they
will be arranged in series on
the milling machine, and a con-
tinuous cut taken over the lot.
Shallow brackets will be tooled
with the foot uppermost. Deep
brackets are tooled while laid upon their sides, the feet standing per-
pendicularly, and then they may either be milled superimposed, or end
to end, or in some cases an alternative will be to mill deep brackets
witli their feet uppermost, lying horizontally while bolted to an
angle plate attached to the table of the machine. The reason why
the mode of fixing shown in Figs. 198 and 199 is not suited for deep
brackets is that it would not be firm enough to ensure steady cutting.
E]L
Fig. 197.— End Mill tooling Joints of
Eccentric Straps clamped against
Face of Angle Plate.
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216
MILLING MACHINES.
Fig. 198 illustrates two brackets held down for milling the
feet In this case the brackets have been already bored, which,
when practicable, is generally done ])efore tooling the feet. It
cannot always be done, but in very many cases — in most instances
Fig. Ids. — Edge Mill tooling Feet of Brackets carried on a Mandrel in Vee
Blocks, Mandrel clamped down.
probably — it is as easy to bore first as afterwards. Then, suppos-
ing the setting is done accurately, the foot is bound to be parallel
with the bore.
Through the bored holes in the brackets a turned shaft a is
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cm:
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m
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Fig. 199.— Angular Mill facing Bracket supported in Vee Blocks.
thrust. The ends of this are laid on vee blocks B, B, and
plates c, c rest upon the bosses and upon packing pieces D, D, and
are held down with bolts E, E in the tee slots. In a space left in
the middle between the two brackets a clip, laid directly upon the
shaft, is pulled down with two bolts.
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MILLING OPERATIONS.
217
These suffice to hold the shaft A down, and with it the
brackets. But the latter would turn or cant upon the shafts
under the stress of cutting, and so it is necessary to pack them at
each side under the feet. Pieces of bar might be used, but they
must either be of the precise length required, or else the length
must be made up with thin iron or steel wedges inserted imder
their ends, or bolts y may be used, the
precise adjustment for length being
made by turning the nuts.
Two brackets only are shown in
Fig. 198. More than two can be
arranged in line, taking care to have
a sufficient number of strips for clamp-
ing. Also, two similar rows can be
clamped side by side, and two cutters
be brought into operation at once.
Cases arise in which it is not
practicable to insert a shaft through
holes, because the latter cannot be
bored until the brackets have been
tried in place, in which case the holes
will be either rough cored or left solid.
Then the brackets can be held with
side clips, still being sustained from
cantmg sideways by means of bars or
bolts.
Fig. 199 illustrates a regular jig for
bracket work. Capped vee blocks are
bolted to the table, and the proper
adjusting screws take the place of
tlie bolts F in the previous figure.
Fig. 200 is an example of two
double bearings set back to back, and
bolted and clamped down thus together to the table of the
machine. Such bearings could be set end to end simply,
and milled in line. This method would be more economical of
time than that shown in Fig. 198, because the cutter would
only have to travel about half the distance. But the method
shown in Fig. 200 has this counterbalancing advantage — the
Fig. 200.— Two Brackets, set
Back to Back, being faced
with a Rotary End Cutter.
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218
MILLING MACHINES.
brackets being set back to back, are in the precise position
which they will occupy during boring, and also when bolted in
their places to receive their shafts. The alignment of the
brackets is therefore assured by doing as shown, while adopting
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Fig. 201.— Bellied Connecting Rod being miUed on Centres.
the end to end method there is just a risk that after the
feet have been milled the holes might be bored out of line : or,
if set truly for boring, they might not bore out clean, or " hold
Fig. 202.— Planer Tool cutting
Tee Grooves.
Fig. 203.— Milling Tee
Grooves.
up " to dimensions everywhere. Hence the reason for the adoption
of this method.
Or again, the brackets might be bolted to an angle plate. But
being in line, the same objection would exist.
The joints of fly-wheels, cast in halves, are often milled in
similar fashion to Fig. 200.
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MILLING OPERATIONS,
219
Fig. 201 illustrates the use of centres in milling the faces of a
connecting rod. Vee blocks might be used, if the rod were not
bellied. It is centred by the centres left from the lathe, is packed
on blocks at each end, and clamped down, blocks being inserted
immediately under the bolts,
Fig. 204.— Milling Dovetailed
Gi-ooves.
Fig. 205.— Nut Milling with
Straddle Mill.
Fig. 202 illustrates the familiar method of planing out tee
grooves in machine tables. Fig. 203 shows how they are milled.
Fig. 204 is a slot of another kind being similarly treated. In each
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Fig. 206.— Gang of Six Cutters, with Adjusting Screws, operating on
Six Faces of a Bed.
case the milling cutter has the advantage of sizing as well as
sliaping.
Fig. 205 shows a straddle mill cutting nut faces, thus sizing
as well as shaping. No lining out is wanted, but a division
plate sets the exact angles. Fig. 206 is an example of a built-up
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220
MILLING MACHINES.
straddle mill tooling six faces, and edges of a bed Adjustment
for side wear is by the nuts at the centre of the arbor.
Small work is generally held for tooling in the vice, rather
than by bolting by the tee grooves. There are two main classes
of vices — those which swivel, and those which do not. The first
are employed on the majority of jobs, but the second are often
handy. The ordinary milling machine Wee is a squarely con-
structed appliance, the hinder jaw sliding over broad surfaces.
There are many special forms. In one of the latter, made by the
Garvin Machine Company, the fixed jaw is adjustable on the base
by means of tee grooves, to facilitate rapid adjustment. In
another the vice is made to swivel, but the swivelling can be
gdi? r
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Fig. 207.— Walker Magnetic Chuck.
either in a horizontal or vertical plane, by the simple plan of
having two bases at right angles with each other, which brings
the plane of the swivelling face into the vertical or horizontal.
In the Brown & Sharpe Company's universal vice the upper
part consists of two portions: the lower, which swivels in a
horizontal plane ; the upper, hinged to the lower to swivel in a
vertical plane anywhere between the horizontal and 90°. The
clamping of this portion of the vice is done by tightening the
hinge bolt, and also by a bolt which connects a double-bracing
lever, by which the freely moving part of the vice is connected
to the lower portion.
In another type of universal vice, the base, which swivels in
a horizontal plane, has two uprights cast upon it, between which
the upper portion pivots on a pin running right through. Two
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MILLING OPERATIONS, 221
quadrant slots in the iipriglits receive a through lx)lt, by which
the upper part is allowed to swing through 100°, and permits of
clamping in any position.
Figs. 207 show end views of the No. 5 standard type magnetic
chuck by 0. S. Walker & Co. The underlying principle of these
chucks is clear from the figures. The first one shows the chuck set
up for surfacing the flat side of the parallel piece A, which lies
against the back strip B, and the vertically adjustable back rest
c, the edges of which are exactly square with the chuck top.
In the next figure is shown the method of holding the piece
A, for finishing one of the edges— note that its bottom edge is
slightly beveUed. When placed on the chuck, with the acute
angle outward, this piece is magnetically held, not only downward
against the chuck top, but also against the back strip b, and back
rest c, which latter has been elevated to come near the top of the
piece. In this manner the top edge of the piece can be tooled
square with the side. The magnetic action on the piece when
adjusted in this position is illustrated in the next figure. The
dotted circles and arrows serve to indicate the course of the
magnetic lines of force. The broken lines a, h represent the
positive and negative magnetic poles, the magnetic force seeking
an easy path across the gap between these poles. The lines of
force therefore preferring a metallic circuit to an air gap, travel
through the piece of work a, and then dividing and passing down
through c and B to the other pole of the magnet. Owing to the
peculiar construction of the magnet face, a strong side pidl is
obtained as well as a direct down pull of the work. In milling,
this piece would require additional staying at the side to hold
it in place, and across the end of the chuck there is fastened a
vertically adjustable strip that forms an end stop, this not being
shown in the drawing.
The next figure illustrates the chuck with the back rest c
removed, and the chuck holding the strip D, for finishing one of
the flat sides. A portion of the end of the chuck is broken off
to show the coil chamber. E represents an ordinary knife-edge
switch, which is protected by a guard on the edge of the chuck
as shown.
The next figure shows the method employed for liolding a
number of parallel pieces at one setting. In this case additional
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222
MILLING MACHINES.
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vr
holding power is got by laying a strip of non-magnetic metal F
between the pieces to prevent the magnetic lines from flowing
horizontally through the pieces toward the back strip B, thus
diverting the power from the face of the chuck. This view also
shows one of the slotted fingers for staying the work and preventing
the side slewing. Tlie last figure illustrates how the piece G, with
a right-angular projection, can be held.
In case the chuck is to l)e
used with water, the coil is given
a waterproof treatment and the
terminals are capped over en-
tirely, leading the wires through
a rubber hose to some convenient
position outside of the area of
the water where the switch may
be attached.
A duplex switch is used
with these large chucks. This
is very desirable, especially for
large work which is difficult to
remove from the chuck. It con-
sists merely of a double throw
with cross connected wires, so
that, when the handle is thrown
completely over, the current is
led through the coil in the
op]:)osite direction. The contact
must be timed exactly right to
prevent recharging the chuck face
with the polarity reversed.
Fig. 208 illustrates the milling
of the joint faces of brasses instead of putting them on the shaper.
The half brass is clamped against an angle plate, and additional
steadiness secured by a piece of wood packing at the front end.
In Fig. 209 a cap is clamped through the medium of a clip, and the
joint face and edges and cap faces are milled.
So much clutch work is done that the old style of using the
teeth as they are cast, without tooling, is not considered good
enough for any but the roughest class of work. Even though the
Fig. 208.— Brass held with Angle
Plate, for milling Joint Face.
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MILLING OPERATIONS,
223
teeth are cast, as in the larger elutclies, they are tooled subse-
quently, the case of spiral teeth excepted. At one time all such
work was done at the shaper, and is so done still in some firms :
the clutch being held in the vice, and turned about to present
successive faces to the tool. In the absence of dividing apparatus
Fig. 209. — Cap held with Clip for milling Faces and Eklges.
the jaw edges were lined out, and a templet kept to check them
by. Such work is now often properly appropriated by the milling
machine, using an indexing head for effecting the divisions
correctly, without lining out or templating.
Fig. 210 illustrates one method of milling the teeth, which ap-
plies alike to clutches having the teeth cast, and to forged or cast
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224
MILLING MACHINES,
ones having the teeth milled
from the solid. The work is
clamped as in Fig.l91,page 211.
A cutter is selected having
teeth on the edge and sides, its
U LU I
n
J
Milling Claw autch.
Fig. 210.— aaw Clutch to be Milled.
axis being set at right angles
with that of the clutch. Its
width must be a trifle less
than the space between ad-
jacent teeth at the inner part,
next the hole, where the space
is narrowest. It is then set
to mill one side of a tooth,
and fed across down to the
full depth of tooth, or nearly
so, depending on whether a
fine finishing cut will be taken
all over the bottom subse-
quently. The table is then
run back, and the index set for
the next tooth, and so on until the sides of all the teeth which
face in that direction are done. The other side of the cutter is
Fig. 211.— Milling a Slot.
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MILLING OPERATIONS,
225
next set to do all the opposite sides of the teeth in the same
manner. Finally the bottoms are finished with the same cutter.
Fig. 211 is an example of slot milling versus slot drilling.
The formation of circular bossed ends is often done on the
slotting machine and on the shaper. It is usually more convenient
to set small levers on the shaper for bossing, and large ones
Fig. 212.— lUustrates Value of Circular Table for Boss Milling.
on the slotter. There is rather more difficulty in setting them on
the latter than on the cone mandrel of the shaper, which is
self-centring. On the slotting table, measurement alone is fre-
quently the only means of setting. Many tables with a central
hole are, however, fitted with a central arbor or mandrel, standing
up vertically, upon which the bored holes of bossed ends are
p
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226
MILLING MACHINES,
centred. Such arbors are turned parallel to different diameters
to suit different jobs, or one of a constant small diameter can be
used, and bushes slid over it for
holes of larger diameter.
Fig. 212 shows a common job
which is preferably done by milling,
that leaves a smoother surface than
slotting. When such a piece is
slotted, the boss is turned down as
far as the web. This is not neces-
sary in milling, for by altering the
height of the cutter the boss can lie
milled all round. Figs. 213-215
illustrate useful attachments for
milling circular work, borrowed
from the shaper arbor. Fig. 213 is
a fixture for bolting directly on the
centre of the circular table. Tlie
lever shown is held by the conical
centres, and clamped, and this par-
takes of the circular movement of
the table. Fig. 214 is a fixture derived from the previous one,
but it is l)olte(l to an angle plate, and holds a double-ended lever
Fig. 213.— Cone Mandrel to l>olt
on Circular Table.
H
s
"W w
Fig. 214.— Angle Plate with Cone Mandrels for Clamping Levers by for Milling.
while the web is being milled. A washer is inserted between the
forks to prevent them from being closed inwards by the bolts.
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MILLING OPERATIONS,
227
Fig. 215 is an auxiliary table or plate bolted to the machine table
for holding objects having holes, so as to mill both bosses and webs.
The milling machine has invaded the province of the lathe to a
slight extent. Some jobs that are not infrequently done are the
rims of very light spur-wheel blanks that are rather delicate and
springy to operate on in the lathe. Bevel-wheel blanks are also
tooled as in Fig. 216. Belt pulleys are sometimes so treated, Fig.
217, and roi)e pulleys, Fig. 218. In each of these cases the cutters
are Iniilt up, and the entire rim is tooled at one operation.
?E
Fig. 215. — Auxiliary Table with Cone Mandrels for Objects having Holes.
Milling is largely taking the place of otlier machine tool opem-
tions in die cutting. Fig. 219 shows a group of cutters used in this
w^ork. They comprise tools for tapered edge, and for parallel work,
for producing concave portions, for roughing and finishing. They
fit directly into tlie spindle, or into an intermediate fitting shown
in the figure.
Fig. 220 shows a job of profiling being done in which the
tai^ered form of tracer or former pin is seen bearing against tlie
form carried on a bracket bolted to the table and controlling the
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228
MILLING MACHINES.
operation of the cutter on a pile of six pieces of work. The tracer
pin is adjustable in a slot by the screw indicated. For remarks on
profiling machines, see pages 96 and 100 to 104.
Holding Work in Jigs. — Tliere are several
ways to look at this subject, and many things to
1)0 considered in so apparently simple a thing as
gripping pieces of work to bo milled. Other
matters besides holding merely have to l)e l)orne
in mind. The following are the chief considera-
tions : —
Security of course is necessary ; but avoidance
of risk of distortion is essential. So is rapidity
of gripping. Also a method of holding that will
not interfere with tlie freedom of movement of
the cutter or cutters; frequently, too, facility
for changing the position of the work to expose
fresh surfaces to be milled. The question of ad-
justment of rough or of
Fig. 216.
Milling a Bevel -
Wheel Blank.
tooled surfaces in relation to other sur-
faces of the work, or of holes, often
affects the question. So does that of
fixing one or of several pieces for
simultaneous milling. Frequently the
table of the macliine receives the piece
or pieces of work, as in tlie examples
previously given. But in many instances
this would not afford sufficient con-
veniences for holding, as in cases wliere
numerous important and necessary rela-
tions of parts have to be taken account
of, and tlien the special jig has to be
devised for one particular khid of article
made in quantity, or sometimes for
articles that are not very dissimilar in
shape or size.
Going a step further, the same jig is
often designed to include another operation besides milling — that
of drilling of holes, effected at the same or another setting in the
Fig. 217.— Milling the Rini
of a Belt Pulley.
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MILLING OPERATIONS.
229
jig, which is done in order to ensure
tlie correct relations of such parts
without resorting to measurement or
check.
Tlien further, in another stage, a
gauge piece is sometimes included, by
which to adjust the relations of the
mill and the work, and so to ensure
correct height or thickness for tooling,
without resorting to direct measure-
ment.
The first and most obvious method
of holding work directly on the tables
of milling machines, with only the aid
afforded by the tee grooves, has l)een
already illustrated. The clamping
plates or pieces used are held.] with
tee-headed bolts in these grooves, and
the clamps
Fig. 218. -Milling the Rim of
a Rope Pulley.
Fig. 219. -Group of Mills
for Die Cutting.
may bear on top, or against tlie edges of
the work, either by the sides or the ends.
Or the work may be held against the
face of an angle bracket or plate clamped
to the table. Pieces to )je milled
circularly are held by an arbor in the
centre of a rotary table. Holes are fre-
quently drilled first to receive plain or
conical arbors inserted in the circular
table, or attaclied to angle plates. If
jigs are used, these are provided with a
tongue in the l)ottom to fit the table
grooves, to which they are lK)lted down.
These summarise the general methods of
holding work for milling.
It is more difficult, as a rule, to make
suitable jigs for castings than for rolled
metals, as shafts and plates, or for drop
forgings. This is due to the fact that
variations occur in nearly every dimen-
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230
MILLING MACHINES.
sion of the separate castings, tlioiigh made off the same pattern.
From experience I should say that no two castings, when hand
made, are ever exactly alike when brought to the test of the jig
maker. With good machine moulding they are generally imifonn,
though not always. Variations increase with increase in dimensions.
This difference in hand and machine work is that due to rapping
in delivery, and mending up in the first case, and the coercion
exercised by the machine lift in the second, and the fact that
mending up is rarely attempted. The reason why slight differences
m>^l iNm
ij-lj iLi t5~Z5^-S
Fig. 220. —Milling with a Former.
do sometimes occur in machine-made castings is that difllerences in
metal involve variable shrinkage amounts, and changes occur in the
mould in the act of pourhig, sucli as scabbing, swelling, j)roducing
rougli surfaces ; and lumps, straining of boxes increase the dimen-
sions. Increase in dunensions of castings gives larger masses on
which these causes operate.
The jig maker has to be on his guard, therefore, wlien making
provision for holding castings, and his appliances must eml)ody
some elasticity in design to permit of the embracing of castings that
vary in dimensions, even if only by slight differences.
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MILLING OPERATIONS, 231
The metliods generally adopted include vee'd spaces for bosses,
and adjustment screws. Bosses generally when present are taken
as the parts from which to commence the settings, in order to locate
their holes centrally. It looks bad to see holes out of centre,
whereas a trifle of difference in the thickness of a foot or facing is
of little moment.
Fig. 221. — Jig for Locking-Plate CaatingB.
In some jobs that are nominally left rough cast on a lower face
it is often advisable to take a liglit cut over that surface, simply
for convenience of clamping the face down to the table, to avoid
packing up. The same may often be done with advantage when
the face has to be finish-tooled subsequently. This appUes more
particularly to light flimsy castings, or forgings which are most
liable to spring. Such precautions are more necessary in the case
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232 MILLING MACHINES,
of milled work than in that of work to be tooled on planer or shaper,
because of the greater pressure of tlie cut in milling, with increased
risk of distortion. If only the high parts are removed, bedding can
take place there, and the clamps be brought opposite them. In
some cases this will be quicker, and almost always safer than
attempting to pack up with wedges, or thickness strips. For a
Fig. 222.— Turret Fixture.
similar reason it is often found necessary to toucli oil' the high
spots or lumps on castings and forgings before they can be inserted
in their jigs, even thougli those localities liave to be subsequently
tooled all over to dimensions.
Fig. 221 illustrates a very interesting piece of work being
done on one of the Herbert horizontal spindle machines, consist-
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MILLING OPERATIONS. 233
iiig of locking-plate castings for railway signal interlocking
apparatus. These have to be interchangeable, and the accuracy
of the gang of cutters has to be maintained permanently. The
castings are rough on the back and ends, but they are held in a
special jig which allows of variations in the rough backs of the
castings. The casting is giipped at the two ends, and is supported
Fig. 223.— Turret Fixture.
about the centre against the stress of cutting by spring plungers
in the bottom of the jig, which l)ear against the under surface of
the casting, and are afterwards locked by the square-head screws
which are seen at the front of the fixture. The cross slots are
milled subsequently in the same machine, in another fixture.
The interlocking of tlie cutters on the ** hit and miss " style will
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234 MILLING MACHINES,
be noticed, whicli provides for adjustiiieiit to keep the width of
grooves constant, to compensate for resharpenings. The stiffness
of the outer bracings may be noted, as important elements in the
work of heavy cutting.
Figs. 222 and 223 show an advanced piece of milling practice
as done in the shops of A. Herljert Ltd. It comprises a turret
Fig. 224.— Fixture for Toggle Levers.
titthig to the table of a horizontal machine, rigged up specially
for millhig the heads of bolts. The two illustrations show the
fitting from two points of view.
There are six cutters — two outside, and two pairs in inter-
mediate positions. The bolts are fastened in the turret, and the
latter rotated into six equidistant angular positions, in each of
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MILLING OPERATIONS,
235
Fig. 225.— Jig for Milling Arbor Tangs.
wliich three l>olts have two opposite faces milled simultaneously,
the equivalent of a single bolt finished at each position of the
turret.
The cover for the cutters includes an arrangement for lubricat-
ing them. The finished
bolts are removed, and ^ fEiSzt
fresh ones inserted
while the machine is
in operation. One man
operates two machines
in the Herbert works,
but tliis could be ex-
ceeded in a screw fac-
tory, or on some chisses
of work.
Fig. 224 illustrates
the milling of malle-
able-iron toggle levers
that form a portion of
the automatic chuck on tlie Her))ert hexagon turret lathe. Three
grooves are nulled at once, to fine limit gauges, the work Ijeing
interchangeable. The cutters are of the in-
serted tooth kind, alternate teeth cut on
opposite ends, thus permitting adjustments to
be made to compensate for wear — effected by
driving the teeth farther through the body
of the cutter in both directions. The clamping
of the pieces in the fixture is interesting. The
levers to be milled drop into recesses in the
jig, and as clamping by the top edges would
interfere with the cutter arbor, they are
clamped on rods coming out at the sides.
The rods are inserted in holes previously
bored in the pieces.
A neat rig-up for milling the tangs on
the ends of taper shank drills, arbors,
reamers, and which is adaptable alike to the square necks of
hand taps and hand reamers, is illustrated in Fig. 225. It
consists of a bracket, fitting on the table, with a tongue for
Fig. 226.
Setting Gauge.
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236 MILLING MACHINES,
the table grooves, being thus set in line with the spindle hole in
the index head, and clamped in position. It is bored to receive
Fig. 227.— Fine Gang MiUing.
a si)lit bush which takes the end of the drill, or reamer, &c., and
wliich is clamped by a set screw in a split lug. The cutters are
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MI LUNG OPERATIONS. 237
Fig. 228.— Jig for Profile Milling.
indicated in their relation to the work. Bushes of various sizes
can be substituted, all fitting alike in tlie bracket, but having
holes of different sizes, as many as may be required.
Fig. 226 illustrates a jig in the Ludwig Loewe shops for setting
cutters used for making the teeth in spiral mills. It comprises
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238 MILLING MACHINES,
a graduated beam with a fixed jaw A, and a movable jaw B. The
graduations on the beam give the diameter of tlie cutters to be
Fig. 229.— Link Type of Jig.
milled, so that, when the movable jaw is clamped to a given
graduation, one element is fixed. The other — the position of the
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MILLING OPERATIONS, 239
o
r
I
to
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240 MILLING MACHINES.
cutter — ^is determined by the notch in the fixed jaw A, and when
the machine is set by these two positions, the work can be com-
menced; and continued without any experimental cuts being
required. The hole in the sliding jaw takes bushings that fit the
arbors on which the cutters are placed to be milled.
A good many devices have been schemed to permit of a milling
machine attendant fixing work on one end of a jig, while the
machine is milling similar pieces at the end opposite; an idea
which is sometimes utilised on double-headed planers. The
advantage lies chiefly in forgings and castings, which, being
more or less rough and uneven, take more time in their adjust-
ments than pieces of sheet metal, or pieces partly machined
would do.
An example of extremely fine work in gang milling is seen
in Fig. 227, done in the shops of A. Herbert Ltd. It is the
cutting of slots in burners for gaus fires. Large numbers of slots
were cut in one traverse, the widest burner having 120 slots,
requiring the fitting of 120 saws on one arbor. The difference in
time between this and cutthig single slots is enormous.
The photo in Fig. 228 illustrates profile milling on a Herbert
macliine, the work consisting of shaping the edges of the links
for chain conveyors, two of whicli are seen lying in front of the
fixture, which is a vice especially designed for holding them. The
links are first drilled uniformly in a jig, and they are then located
in line by bars passing through the holes. The cutter is made in
tliree parts. As the work Ls broad, the necessity for a very rigid
support to the cutter is obvious. How this is ensured is seen
in the illustration, the bracing affording a support as rigid as a
solid housing could be.
A very interesting photo is that shown by Fig. 229 from
the practice of the same firm. It is a special fixture made for
the liorizontal milling of objects of irregular outline, the particular
example on the machine being a mould such as is used for pressing
tiles. It is concave in form, the radius being very large. The
apparatus is mounted on links resembling those of an ordinary
ruler, thus ensuring a parallel motion. On the under side of the
table on which the work is mounted there is a former, the edge
of which is seen, and its face is the exact complement of the object
being milled. The former can thus be made in the first instance, if
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MILLING OPERATIONS. 241
convenieut, by fitting it into an actual piece of work. It rests
upon a roller which is carried upon the knee of the machine,
the outer end of which is visible. As the machine table is fed
transversely carrying the jig, the former in passing over the roller
gives the required curvilinear movement to the face of the work,
and the parallel links accommodate themselves thereto, while
coercing the work rigidly in other directions.
Fig. 231. — Milling Qiiadrant Piece for Change Gears.
i
^ There are other interesting points to note about this job.
One is the clamping down of the plate. Two of the clamps are
seen in the front, and it will be noticed that their lower edges
work on an incline, causing them to pull the work down when the
nuts are tightened up.
The very coarse pitch of tlie cutter is remarkable. This su))ject
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242 MILLING MACHINES,
has been discussed on page 164, and is a feature which is likely
to grow in favour. Messrs Herbert say that in their experience
very much coarser pitch cutters can be used with advantage than
is common practice.
Fig. 230 illustrates a fixture for millmg the feet of headstocks
with a gang of cutters in the Ludwig Loewe Works. Fig. 231
shows the tooling of both faces of a quadrant piece with built-up
cutters in the Cincinnati shops, the circular table being used to
rotate the work.
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CHAPTER IX.
INDEXING, SPIRAL WORK, AND WORM, SPUR,
AND BEVEL GEARS, ETC,
Tlie Universal the Machine of Applied (Jeometry — The Spiral Dividing Head —
The Basis of Calculation — Worm and Worm Wheel — Index Plate-Sector —
Difierential Indexing — Angles of Spirals — Rules and Examples — Graphic
Method — Milling Screw Gears — Relations between Spiral, Helical, and
Worm Gears — Elements of the Spiral Gear — VeUxjity Ratio — Pitches —
Graphic Methods — Examples — Trigonometrical Rules — Worm Gears —
Methods of Cutting.
The Machine of Applied Geometry. — ^The luilling machine
has been termed "the machme of applied geometry," because of
the combinations which are possible in a univei-sal. Tlie universal
is a notable exception to the general rule that machines that
combuxe many functions are not so economical as those which
deal with special operations. There is hardly any operation of
the machine shop which is not done on the universals by the aid
of the numerous adjuncts that are legitimately fitted to it, that is,
they are not of the nature of makeshifts. It includes plane
surfaxies, and circular, both external and internal, drilling, reamer-
ing and boring, thread cutting, key grooving, profiling, gear cutting
of all classes, and such work is done at all angles. It includes
the correct spacing of holes and distances, and nuich besides,
regularly done on pieces of mediiun dimensions.
The advantages are most apparent in work recpiiring several
settings or spacings, as an alternative to liidng out by hand
methods. The latter are never strictly accurate, and are generally
tedious. The milling machine is both accurate and rapid.
The Spiral Dividing Head. — The leading elements of the
spiral dividing head are the rotation of the spindle irrespective of
the angle at which it may be set, the change gears by which a
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244 MILLING MACHINES.
precise and definite rotary motion may be imparted to the spindle
relatively to the pitch of the lead screw, and therefore to the
travel of the table, and the divisions effected by the index plate.
The Basis of Calculation. — The basis of calculation is the
single-threaded worm, and the 40-toothed worm wheel, which by
general consent, and its great convenience in subdividing into
thousands, is adopted in milling machines. As the worm thread
and the worm-wheel teeth are as 40 to 1, forty turns of the crank
produce one revolution of the spindle, and one turn of the crank
a fortieth of a revolution of the spindle. To obtain forty divisions
to the circle, therefore, the handle would be turned forty tunes.
To obtain eighty divisions the crank would be turned half-way
round for each division, but, to obtain twenty, two turns would be
required. The rule is therefore : —
Divide 40 by the number of divisions required, and the quotient
will be the number of turns or parts of a turn which will have to
be imparted to the crank. Thus —
Wheel, 40
= 1 turn.
= 0*5, or half a turn.
Number of divisions, 40
Wheel, 40
Number of divisions, 80
^_Wheel40_ 2 turns.
Number of divisions, 20
By means of the index plate a turn of the worm shaft can Ije
divided into a very large number of equal parts, and the fortieth
of a revolution of the spiral spindle correspondingly subdivided.
Index plates furnish several circles of holes, from one of which
selection can be made for the majority of jobs required, that will
permit of obtaining equal divisions. Thus, for eighty divisions,
the crank beuig turned half-way round, a circle will be selected
that will divide into two equal parts. If three divisions, a circle
must have a number of holes divisible by three, and so on.
To facilitate counting the divisions in the circles of holes is the
object of the sector A, Fig. 232. Circles of holes on the index
plate being selected which will divide equally as even numbers,
or multiples of even numbers, the sector is used to avoid the
counting of every hole at each partial rotation of the crank.
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SPIRAL WORK AND WORM GEARS.
245
40 5
If 144 divisions are required, then — — = r ^, and thus the
144 18
index crank has to be moved y^ of a turn to obtain each of the
144 divisions. A circle of holes is selected containing either 18
holes or a multiple of 18, and 5 spaces are measured off on an
18-hole circle, or 10 spaces on a circle of 36 holes.
Or, to cut 96 teeth — iq . q
96^24
The index pin must be moved J J of a turn, or, selecting a
24-liole circle, 10 holes
for each division.
Instead of counting
every division of five or
ten, as the case may be,
the sector is set once,
and pinched by its set
screw, and then after-
wards it is simply
moved round into con-
tact with the index
pin, and then, after a
cut has l)een taken, it
is moved round and the
pin inserted in the next
division for the next
cut. Only in setting the
sector first, one more
hole than the number required for the division must be taken,
l)ecause that has to be occupied l)y the pin (see Fig. 232, a). The
operation of tumhig and setting has to be repeated as many times
as there are divisions required — 144 times in the first example, 96
times in the second given, and in each case the spindle and the
work will have made a complete revolution. Tliis is the method
of simple or plain indexing.
The index tables are furnished with index plates, and save calcu-
lation for a large numter of divisions. But they do not cover excep-
tional cases, nor, in fact, all the divisions which are possible for any
one circle of holes. This matter is discussed at length on page 248.
Fig. 232.— Index Plate with Graduations.
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246
MILLING MACHINES.
The tables supplied by makers of milling machines give but
one circle of holes for any given division. But it is not necessary
to change a plate simply to place on the one named in the tables.
A simple calculation will show whether divisions can be effected
with the plate that happens to be on the machine. Thus there
are six circles on the B. & S. machine which are divisible by 3,
namely, 89, 33, 27, 21, 18, and 15, though the index table gives
the first only. Mr E. Gauthier prepared a table to save the slight
trouljle of calculating, which, with some improvements made by the
American Machinist, is given below.
a
e
^
1
o
o
Divisi
Circle
00
E
H
i
•s ®
5 C
CO
g
a
H
1
1 1 1
i 1
^ 1
2 any
20
...
12 15
3
5
25 20 ]
L 12
f 39
13
13
13 39
3
3
26 39 ]
L 21 ,
33
13
11
14(*9
I 21
2
42
27 27 ]
L 13
o] 27
13
9
2
18
^^? ]
L 21
''\ 21
13
7
(■39
2
26
L 9
18
13
6
33
2
22
29 29 ]
[ 11
I 15
13
fj
irj 27
2
18
('39 ]
L 13
4 any
10
• . •
10 ^
21
2
14
33 ]
L 11
5 any
8
18
2
12
oj 27 ]
^% 21 ]
I 9 1
(■39
6
26
I 15
2
10
L 7
33
C
22
(20
2
10
18 ]
L 6
1 21
G
18
IG-^ 18
I 16
2
9
il5 ]
L 5
G
14
2
8
31 31 ]
L 9 ,
18
6
12
17 17
2
6
32 f 20 ]
."^\ 16 ]
L 5
lis
G
10
Hll
2
6
L 4
.f49
^i 21
5
35
2
4
33 33 ]
L /
5
15
19 19
2
2
34 17 ]
L 3
8 any
f)
20 any
2
Htl ]
L 7
9^^
\ 18
4
12
21 21
19
L 3
4
8
22 33
27
HT>> ]
I 3
10 any
4
. . .
23 23
17
L 2
11 33
3
21
(?>9
26
37 37 :
I 3
f 39
3
13
33
22
38 19 ]
I 1
33
3
11
.4] 27
-*1 21
18
39 39 ]
L 1
12
29
3
9
14
40 any ]
L • . •
'
21
3
i
18
12
Degree
B.
1 ll8
1
1
3
6
I 15
10
1 18 ..
2
1
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SPIRAL WORK AND WORM GEARS.
247
An improved form of division plate has been designed by
Messrs Brown & Sharpe for attachment to the machine, the feed
and speed mechanisms of which were described on pages 34 and 35.
One object sought is to avoid the diflSculty which sometimes occurs
when a cut has to be started at a definite point of the work and
the index pin will not drop into a hole. To obviate this, the index
pin is made adjustable by means of the screws A, A, Fig. 233.
Another improvement does away with the necessity for count-
ing the holes when setting the sector, a process just described, page
245. A graduated circle is fitted. Fig. 232, and a column is
provided in the index table for the maxjhine, which gives the
number of divisions of the graduated circle that corresponds with
the adjustment of the sector to span the number of holes required.
Though the graduations do not in all cases bring the sector
exactly to the holes required,
they are sufficiently close to
prevent risk of error in lo-
cating the holes.
The Compound System
of Indexing: is sometimes
used when it is desired to
obtain divisions for the work
other than those which can
be obtained liy the direct indexing methods just described, from
the index plates furnished with the machine. Compoimd indexing
means that, instead of moving the pin straight ahead on a single
circle, two index settings are taken, which involve the addition
or subtraction of fractions. Thus the work may be moved
througli a certain number of spaces in one circle and then turned
in the opposite direction a certain number of spaces in another
circle. These are indicated in tables supplied with universal
milling machines by the signs + and — , the plus sign showing
that the two indexings are added together or that the movement
of the work in both indexings is in the same direction, while the
minus sign shows that we take the difference between the two
indexings or that we move one indexing in one direction and the
second indexing in the opposite, the principle in making the
calculations being simply the addition or subtraction of fractions
Fig. 233.— Adjustable Index Pin.
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248 MILLING MACHINES.
The denominators of the fractions indicate which circles of holes
are used in the index plates. The following is from Brown &
Sharpe : —
" To illustrate the manner of using the machine in compound
indexing it may be supposed that we desire to divide the work into
69 paiiis. Reference to the table (supplied by the firm) shows that
the work is moved through 21 spaces or holes in the 23-hole circle,
and then turned in the opposite direction 11 holes in the 33-hole
circle of one of the index plates. The first movement is made in
the ordinary manner. The stop or back pin is placed in the
33-hole circle, the index crank pin is pulled out of the 23-hole
circle and the index crank is turned through 21 holes in the
desired direction, the holes l)eing measured by the sector. For the
second movement, the index crank pin is left in the 23-hole circle,
the back pin is pulled back from the plate, and, as the minus sign
is given in the table, the crank is turned 11 holes in the direction
opposite to that of the former movement. In this part of the
indexing the index plate and crank turn together, and, as there is
no sector on the back of the plate, the holes or spaces have to be
counted directly in the plate. Had the plus sign lieen given, as in
the indexing to obtain 77 divisions of the work, both movements
of the crank would have been in the same direction. Ordinarily
the order of the movements is not material, and if more convenient
for any reason, the back pin could usually be withdrawn first, and
the movement described as the second could be made first. In
some instances, indeed, for example, in dividing the work into 174,
272, or 273 parts, the outer circle is naturally used first."
Differential Indexing. — A new method of indexing has been
i*ecently applied to the Brown & Sharpe entire line of universal
milling niachuies. It is much simpler than the compound method
heretofore employed for obtaining divisions that are prime numbers.
The indexing is obtained in the same manner as for plain indexing,
excepting that the spiral head spindle is geared to the index plate.
Differential indexing differs from the comjMDund method in that
the movement of the spiral head spindle in relation to the index
crank is positively made by gearing. The index plate is geared to
the spindle, thus giving a differential motion that allows the index-
ing to l)e made with one circle of holes and the index crank to be
Digitized by VjOOQIC
-
-
INDEX
1
TABLE-
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Plain and Diffcrvntial
UnivtiitAL Milling Machines I
Indexing.
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Digitized by V:iOOQIC
SPIRAL WORK AND WORM GEARS, 249
turned in one direction, the same as in plain indexing. This
enables spacings to be made that cannot be obtained with an index
plate locked with a stop pin in the usual way. When geared for
differential indexing, the machine cannot be used to cut spirals, as
the spiral head spindle is then geared to the lead screw.
In the differential method there is little opportunity for error.
The index crank being moved the same as for plain indexing, it is
necessary only to place the proper gears in position, as indicated
by the table that accompanies the machine. The change gears and
index plates furnished provide for all divisions from 1 to 382, in-
cluding all the prime numbers, and enable the divisions to be made
with no more care than is required in plain indexing. With addi-
tional change gears and index plates a lai^e number of divisions
l)eyond 382 can be obtained. In the compound method, however,
it is necessary to exercise great care, as two circles are employed,
and the direction in whicli the crank is to be moved, right or left,
must be kept constantly in mind.
The Table adjacent is plainly and conveniently made up to in-
clude both plain and differential indexing, thus avoiding the necessity
of two separate tables. It gives all divisions from 1 to 382.
The index spacing number is 40. In other words, forty revolu-
tions of the index crank are required to make one complete revolution
of the imlex spindle. Therefore, if the index plate is geared to the
spindle, using one idler to rotate one turn in the same direction as
the crank, and the crank pin enters the same index plate hole, the
result will Ije the spacing number 39, for the reason that while the
crank lias made forty turns and the plate one, in the same direction,
the crank lias passed a given point only thirty-nine times. With
this same gearing, and the addition of another idler, the motion of
the index plate is in the opposite direction to that of the crank,
and the plate gains one revolution while the crank has made forty,
resulting in the spacing number 41.
With the spacing numter 39, it is possible to obtain divisions
equal to 3 x 39 with a circle of three holes, 4 x 39 with a circle of
four holes, &c. This will apply equally well to the spacing number
41. Any division not obtainable with the index plate can there-
fore l)e made up with proper gearing.
In general, if the plate rotates in the same direction as the
crank, subtract the turns of the plate to one turn of the spindle
Digitized by VjOOQIC
250 MILLING MACHINES,
from the turns of the crank to one turn of the spindle, and the
remauider is the spacing numher. If the plate rotates in the
opposite direction to the crank, the spacing number will be the
sum of the turns of the plate to one turn of the spindle, added to
the turns of the crank to one turn of the spindle.
Fractional Spacing^. — This class of spacing is often required,
and, to illustrate the application of the differential method, assume
that it is required to space a vernier to read yV of ^ degree, or
5 minutes.
Usually the method adopted is to have the vernier spaces
occupy a distance corresponding to 11 degrees, and divide this into
12 parts or spaces, which may be expressed as follows: ^W-rl2 =
tWis^ which is equal to one space. Therefore, there would l)e
-f j~ spaces in the whole circle, or 392 jy divisions. The indexing
of J or 360 gives the difference between 392yy and 360, which
equals 32y\ to be obtained with the gearing. 32yy = -Yr, which
when multiplied l)y \, the value of one indexing gives -W- X ^ = y?
and the proper gears will be -^^- or —- — -- , or gear on spindle 64
teeth; first gear on stud 100; second gear on stud 40; gear on
worm 44.
Angfles of Spirals. — We have now to consider the method of
calculating the angles of spirals for milling cutters, helical teeth,
twist drills, reamers, &c., in which the change gears and table
screw come in. This mechanism is distinct from that of the spiral
head, which effects divisions, or spacing only.
The feed screw of the table has four threads per inch, and
must therefore make four revolutions to move the table along one
inch. As forty revolutions of the worm in the spiral head are
required to give one turn to the worm wheel, and the spiral head
spindle ; then, if change gears of equal size are used, the table must
move lengthwise 10 inches for each turn of the wonn wheel and
spindle. This relation between a revolution of the spindle and the
movement of the table is termed the lead of the screw, or a 10-
inch lead; and being constant, is often conveniently adopted as a
basis for calculations. In other words, instead of the pitch of the
screw, the distance of the table travel for one revolution of the
Digitized by VjOOQIC
SPIRAL WORK AND WORM GEARS, 251
spiral head is employed. Hence the common term, lead of a screw
thread, or spiral, equivalent to its pitch, is referred to lead of the
machine table.
The change gears are calculated similarly to those of a screw-
cutting lathe, the ratio of the driven to the driving gears equalling
the ratio of the lead of the spiral required to the lead of the
machine. Put in the form of an equation, it stands —
, V Driven gears _ lead of spiral required
Driving gears lead of machine
or,
.,v Product of driven gears __lead of required spiral
Product of driving gears 10
That is, the compound ratio of the driven to the driving gears is
represented by a fraction, the numerator of which is the lead to
l)e cut, and the denominator of which is 10.
Or the ratio is as the required lead is to 10.
Or the ratio is as one-tenth of the required lead is to 1.
Or, lastly —
, V Driven gears _ 4 times the lead of spiral required
Driving gears 40
As in screw-cutting gears, ratios can be broken up into fractions,
and numerator and denominator multiplied by numbei^ to find
suitable wheels.
Taking examples in each case and taking equation (a) —
Say the lead of the spiral required is 24 inches, then 10 to 24
is the ratio of the gears. Both terms of the factor are multiplied
by a number that will give numbers corresponding with the teeth
of the change wheels. Thus —
24^3 8
10 2 5
Then—
And 72 and 64 are the driven, and 48 and 40 are the drivers ; and
either 72 or 64 can go on the worm, and either 48 or 40 on the
screw, the others going on the stud in the same way that trans-
positions are effected on tlie swing plate of the lathe.
Digitized by VjOOQIC
252 MILLING MACHINES.
Taking {b\ the rule becomes : — Divide ten times the product
of the driven gears by the product of the drivers, and the quotient
is the lead of the resulting spiral in inches to one turn. Tliis rule
is of value in ascertaining what spiral might be cut with gears at
hand. Thus, what spiral would be cut by gears of .'»2 and 56
driven, and 24 and 40 drivers ? Then —
10x32x56 1^ . , . . .
- — — — — — = 16 inches to 1 turn.
28x40
Taking (c), to cut a spiral with a lead of 21 inclies, multiply
21 by 4 = 84. The lead screw must then make 84 turns to 40
turns of the worm. The ratio then stands —
Driven gears _ 84
Driving gears 40
The ratio — ■ \^ broken up : —
40
40 4 10
Then-
7 Q 56 ,12 , 48
5x8 = -,and-^x4 = _
Then ij^Xj^ are tlie gears required, 56 and 48 being the
driven, and 32 and 40 the drivers.
The foregoing can be put into words, thus : —
Multiply the lead of the spiral required by 4, because tliat is
the pitch of the lead screw. The number thus obtained will
be a numerator, and 40 — the number of teeth in the wheel — a
denominator of a fraction, which w411 give the ratio required,
that is —
Driven gears
Driving gears'
Break this up into two fractions. Multiply the numerator
and denominator by a convenient number or numbers to obtain
those corresponding with the number of teeth in the change
wheels supplied with the machine. The numbers must be the
same for each fraction, l)ut not necessarily the same for both
fractions. In fact, it is not often possible to find numbers that
Digitized by VjOOQIC
SPIRAL WORK AND WORM GEARS. 253
will serve for both, and several trials may have to be made to get
these. The numbers of teeth corresponding with the numerators
will represent the teeth in the driven gears, and the numbers
corresponding with the denominators will represent the teeth in
the driving gears.
Simple trains of gears can often be used with an intermediate
wheel. Thus, to cut a spiral with a lead of 12 inches, the ratio is
48
12x4 = 48=—-. Then the 48 gear can be put on the worm
40
shaft, and the 40 on the screw, with any intermediate that will
make the connection.
When the change geai-s are obtained, the bed or table has to
1)0 set to the angle of spiral reijuired. This is done either by a
diagram, or from a table of natural tangents.
If obtained graphically, a diagram of a right-angled triangle is
drawn, having one side equal in length to the circumference of the
screw to be cut, and the side adjacent equal in length to the lead
or pitch, while the hypotenuse, or, strictly, the angle included
between the lead and the hypotenuse, is the angle of the spiral.
It is l)y this that the table has to ]>e set.
The angle may l)e measured, and the spiral l)ed set to a corre-
sponding angle by the graduations on the clamp bed, or the angle
can 1)0 marked on the work by a protractor, and the machine set
so that tlie spiral sliall be in line with the cutter.
The second method depends on the fact that the natural
tangent of the angle of tlie spiral is the ipiotient of the circumfer-
ence of tlie piece divided by the lead of the spiral. In this
method, therefore, the circumference of the piece is divided by the
lead. Then note is taken of the numl)er of degrees opposite the
figures that correspond with the quotient in a table of natural
tangents. Having obtained the angles tlius, the spiral bed is set
by the graduations on tlie clamp bed.
Milling Screw Gears. — In considering these gears we must
bear in mind the fundamental relations between spiral, helical,
and worm gears, which are all alike screw gears. In the first
place the only ditterence between spiral and helical gears lies in
the direction of the axes of the wheels engaged. If the axes are
parallel the gears are termed helical ; if they are at right or other
Digitized by VjOOQIC
254 MILLING MACHINES.
angles, they are spiral. The diflferenee is that m the first case
the screw sections must be of opposite hands, or right and left ;
while in the second they are of the same hand. In the first case
also the angles are similar, in the second they are only similar
when the axes of the wheels cross at angles of 90".
With regard to worm gearing, although as a general statement
it is true that a worm is a spiral of very short lead, or axial pitch,
yet occasional exceptions occur, as when three or four threads are
exceeded. The requirements of electric-motor reductions have
given a great impetus to the development and expansion of worm
driving, so that some many-threaded worms differ in no respect
from common spiral gears, excepting in their greater length.
Worms of from six to twelve threads are cut successfully and
accurately, and worm wheels hobbed to gear with them. Such
work lies outside that of the pattern maker, which is seldom
practised when worms exceed from two to three threads, and is
as a rule confined to single-threaded worms. The growth of the
practice of bobbing has enabled good worm gears to be produced,
besides which tlie accurate work of gear-cutting machines permits
of the making of gears that have a curious appearance to old-time
hands. Examples of this kind occur m the case of worms and
their wheels, having say equal numbei-s of teeth, done to avoid
the excessive sliding that would occur in spiral gears. Others are
found in the small sizes of worm wheels that are commonly made,
having a much smaller num])er of teeth than the regulation thirty,
which is the limit to gears properly proportioned in regard to
depth of pitch line, in relation to the length of tooth.
When commencing to design helical gears, the number of
teeth or diameters corresponding with velocity ratios are calculated
as for spurs, and the circumferences are taken on the faces of
the wheels. Then the angle of tooth is considered, and settled
(it should not exceed 120''), and cutters selected for the normal
pitch (see page 261), w^hich in these wheels scarcely differs from the
circular pitch. Double helical wheels are cut as single wheels
of opposite hand, and bolted together. As tlie methods of cutting
these do not differ from that of spiral geai^, the remarks on the
latter (page 261) may be referred to.
The same remark about cutters holds good in respect of worms.
The pitch measured along the axis, and the normal, are practically
Digitized by VjOOQIC
SPIRAL WORK AND WORM GEARS. 255
the same in worms of one or two threads, but when these are
exceeded a difference becomes apparent.
Cutters are used for the worms only in the best practice, the
wheels being hobbed. Exceptions occur in the straight diagonal
toothed type of worm wheel, the teeth of which are cut similarly
to other spiral or helical gears, since tliey differ in no respect
from these. The cuttnig of worm gears is treated on pages 274
and 275. We first consider at length the principles and practice
involved in cutting spiral gears.
The cutting of spiral gears is one of the duties for which the
milling machine is eminently adapted. Geara of large dimensions
are not easily tackled, because of the small size of the dividing
wheel, and the limitations of the power of the machines. But
large gears are not often wanted, and then tliey can be cast from
patterns ; or if they have to l)e cut in quantity, a special type of
machine can be built, or specially heavy dividing heads fitted to
a stiff machine.
The term spiral gears is used in deference to common usage,
though it does not correctly define the form of gear to which it
is applied. The term screw gears is correct, but, as a worm gear
is as truly a screw gear as the '* spiral " form, it is convenient to
make the usual distinction in terms. Worm gears and spiral
gears differ only in proportions, and not in the principle of their
design. A worm helix or thread has a short lead or total pitch,
a spiral wheel has this dimension very long by comparison. A
worm contains at least one complete revolution of its helix, the
spiral wheel usually has but a portion of a revolution of a helix.
Worm threads seldom exceed three or four in number, spiral gears
may contain portions of ten", twenty, forty, or more threads. The
relationship of both to the rack is seen in spiral rack drives, which
may be worm, or spiral driven, for slow or rapid speeds. A rack
tooth is the basis for both alike in interchangeable gears.
Elements of the Spiral Gear. — Fig. 23-4 shows the spiral
gear in its essentials, v is the primary or axial pitch, ^/ the normal
ditto, and d the circumferential, a the tooth angle of the teeth of
a wheel of width of face A.
The case of these geara is not difficult to grasp, if we bear in
mind the fact that the pitches of spirals are the bases of velocity
Digitized by VjOOQIC
256 MILLING MACHINES.
ratios. That is, a ratio of 2 to 1 would require a wlieel having
twice the pitcli of spiral of its pinion ; and ecjual ratios pitches of
ei^[ual length. But only in the single case of equal ratios are the
circular pitches equal, because making tlie ratios and diametera
unequal alters the tooth angles, and consequently the circular
pitches, though in all cases tlie normal pitclies must be alike.
This is where difficulty is often experienced. Moreover, the gi-eater
the difference in diameters, the greater will be the differences in the
angles, and in the circular pitches, so that the latter will hardly
look as though they could be capable of gearing correctly, since
one may measure twice or more that of its mating pinion. It
follows that the diameters of the pitch lines measured on the
wheel faces must have the same ratio as the velocities in spur
wheels, to the exclusion of the normal pitch.
I » . • \ \ ^\
i ^.... J. -.../> «
Fig. 234.— Elements of Spiral (iear.
Velocity Ratio. — Tlie first operation necessary in estimating
gears is to determine the sizes corresponding with velocity ratio,
whether equal or unequal. The rule for this is : —
Divide the centres of the gears by the sum of the terms of the
ratio, find the product of twice the quotient by each term sepai-ately,
and the two products will Ije the pitch diameters of the two wheels.
This rule is not affected by the angles of spirals or worms, but
applies to all gears alike.
Example, — Two gears are wanted with a ratio of 2 to 1, the
distance between centres to be 6 inches.
Then 2 + 1 = 3
^ = 2 X 2 = 4in. X 2 = 8-incb diameter of pitch circle of large wheel,
o
2 + 1 = 3
^ = 2x1 = 2 in. X 2 = 4-inch diameter of pitch circle of pinion.
o
Digitized by V:iOOQIC
SPIRAL WORK AND WORM GEARS, 257
Showing that wheels of 8-inch and 4-inch pitch diameter fulfil
the conditions required.
And, having the number of teeth of two gears given, to find
the centres : —
Divide half the sum of the teeth of both gears by the pitch.
Say 60 teeth, and 20 teeth of 8 diametral pitch : —
60 + 20 = 80
— - = 40 and -^ = 5-inch centres.
2i o
Spiral gears are used to transmit equal or different velocity
5t
Fig. 235. — Elements of Spiral Gear.
ratios with shafts set at right or other angles, and either between
wheels, or between a wheel and rack. In this work puzzles arise
in relation to pitch and angle.
In the first place it is well to mention, by way of caution, that
the outside diameter or periphery of the blank is not the surface
in reference to which calculations refer. These are always taken
on the pitch diameter, and the blank (in the diametral pitch
system) is always two standard pitches larger than the pitch
diameter, just as in spur and bevel gears. The tooth angle at the
surface is a steeper one than that at the pitch plane. The cutter,
therefore, on its first setting in does not show the true angle of
R
Digitized by VjOOQIC
258 MILLING MACHINES,
the teeth. The correct angle is obtained by the setting of the
table.
Fig. 235 iUustrates the relations of the angles of spirals and
tops of teeth for the pair of wheels shown.
Pitches. — The pit<ih of a spiral gear is measured in the plane
of its rotation, or parallel with the gear faces. But as the cutter
used operates along the plane of the spiral, the result is that
cutters have to l)e selected wliich do not correspond with the
circular pitch, but with the normal pitch, and which is measured
at right angles with the plane of the spiral. Also the cuttere
to be selected must vary with changes in the angles of spirals.
But the same cutter must always be used for gears which have
to engage together.
Tlie utility of the circumferential pitch is, therefore, as a basis
for the measurement of the diameter of the wheel blank, the
diameter of which must correspond with the number of teeth, or
velocity ratios required, although the cutters must always l)e
selected in reference to the normal pitch.
The angle to whicli the table carrying the blank has to be set
must correspond with the angle of the total pitch or lead of the
spiral, of which the wheel teeth are short portions only. The
problem, therefore, is to impart one turn to the imaginary cylinder
of which the blank forms a short length, while the tiible is fed
along a distance equal to the total pitch or lead.
Angle of spiral is governed by diameter as well as by lead.
The smaller the diameter the less the angle, and the larger the
lead the less is the angle. It follows that in every pair of gears,
excepting those which have their axis at an angle of 45° and their
spirals equal, there is no relation common to both wheels except
the normal pitch. In wheels of 45** with spiral angles ec^ual,
normal, circumferential, axial or primary pitches, and numl)er of
teeth coincide, but in all others the first-named only.
Velocity ratios in spiral gears differ from similar ratios in spur
gears in an important way. In these last, ratio depends on diameter
and number of teeth strictly. That is, a certain number of teeth
of a given pitch are inseparable from a certain circumference.
But with spiral gears the rule does not follow, except in the case
of gears having spirals of 45" of angle. In all other cases the
Digitized by VjOOQIC
SPIRAL WORK AND WORM GEARS, 259
velocity ratios depend on the number of teeth, and not on diameter.
Taking an extreme case, that of worm gears, the diameter of a
worm exercises no influence on the velocity of the wheel which it
drives, but only its number of threads, as one, two, or three. A
spiral gear is only a wonn of coarse pitch, as also the worm may
be considered as a spiral gear of fine pitch.
It follows that by varying the angles of the spirals, in other
words, the primary pitches or leads of the helix, it is practicable
to make spiral gears in which the ratios will be very different,
and greater or less than those which the diameters have (page
271). It is also possible to have coarsely pitched strong teeth
on gears of small diameter. In such cases the gear whose circular
pitch or angle of spiral is the gi-eater will be the driver, because
of the greater obliquity of its teeth.
Graphic Methods. — The problems of spiral gears thus range
themselves under two heads, namely, axes at right angles and axes
not at right angles, nmnbers of teeth ec^ual and numl)ei-s of teeth
unequal.
Tliere are two methods of working out spiral gears — the graphic
and tlie method of calculation. Both are safe, but the last can be
obtained more quickly by the assistance of tables. Many, however,
feel safer with the graphic.
Tlie following is a concise statement of the graphic method for
obtaining angles and teeth of spirals :—
To find the angle of the spiral for a given pitch (axial or
primary pitch) and diameter of work, or to find the pitch corre-
sponding to a given angle and diameter, set out a triangle with the
pitch as a horizontal line and the perpendicular equal to the
circumference of the work, and draw the hypotenuse. The angle
of the latter with the horizontiil, or pitcli length is the angle of the
spiral. It is the angle to which the slide of the milling machine
is set.
Again, if the angle of spiral is given, draw the perpendicular
equal to the circumference of the work, and then draw the
hypotenuse at the given angle, to an indefinite length. Complete
the triangle by drawing the horizontal until it cuts the slant
line. The length of the horizontal so obtained is the primary
pitch.
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260
MILLING MACHINES,
Again, the circumference divided by the pitch gives the tangent
to the angle.
To find the pitch, subtract the given angle from 90°. The
tangent of the remaining angle multiplied by the circumference
gives the pitch.
It must be remembered that in all that has been hitherto
stated the pitch surface of the wheels is meant, and not the outside
of the wheels. So that to attempt to check the work on the
outside by these rules would result in apparent discrepancy. The
angle which the cutter would skim over on a trial cut is not that
of the pitch surface.
Two equal spiral wheels with right-hand spiral teeth are shown
>s?-f ^•
,_ P ITCH ^
(OIV/0£0)
Fig. 236.— Equal Spirals with 45° of Angle.
in Fig. 236, of the kind which most commonly occurs. The angles
between their axes are 90**, and the teetli make angles of 45' with
these axes and with the wheel faces. The tooth angle is also
indicated by a deep line on the upper gear. In order that this
angle of 45** shall exist, the pitch or lead of the spiral nmst
obviously be equal in length to the circumference at the pitch line,
because any differences in these lengths would not give an hypo-
tenuse of 45°. Stated in another way, the circumference and the
pitch of the spiral must be alike, because the tangent of 45" is 1.
The development of the wheel is shown to the left, the perpendicular
equalling in length the circumference of the wheel, and the length
of the base the pitcli of the spiral. We lay out the length of the
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SPIRAL WORK AND WORM GEARS. 261
base equal to the circumference, \vithout reference, in this case, to
any direct attempt at measurement, because we know such must
be correct if the angle of the spiral is to be 45°. Fig. 236 also
shows the pitching-out for a 12- toothed wheel. We take no
notice yet of the top and bottom of the teeth, because the diameter
of the blank gives the first, and the cutter takes charge of the
second. The relation between the circumferential pitch a-h and
the normal a-c, in this case (see the diagram to the right, where
a-h is the hypotenuse of a c &), is that of a 45 '^ of angle, being
that of the wheel teeth. The circumferential pitch a-h can be
measured directly ; ))ut if calculated, it is obtained for an angle of
45° by multiplying tlie normal pitch a-c l)y 1*4142, because 1*4142
is the secant of the angle of 45°, or the normal pitch can be divided
by the sine of 45°, "TOTIO, to obtain tlie same result. Conversely,
the circumferential pitch can be multiplied by the sine '70710 of
45° to obtain the normal.
This diflference between the two pitches is very important in
determining the selection of cutters for wheels. It is clear that
although the circumferential pitch a-h, Fig. 236, must be taken for
sizing the blanks, the cuttei*s suitable for that pitch, having a
thickness of half a-h at the pitch line, would cut spaces too wide
and leave teeth too thin when cutting normally to a-c. Thinner
cutters njust therefore be selected than those used for spur wheels
of the same nominal pitch. Hence the rule : — As the angle ahc
equals the angle of the spiral, and the. line h-c corresponds with its
cosine, multiply the cosine of the angle of the spiral by the
circumferential pitch. The product will be the normal pitch,
one half of which will be the thickness of the cutter at the
pitch line.
The reverse of this rule is to be borne in mind also : —
Divide the normal pitch by the cosine of the angle of the
si)iral. The product will be the circumferential pitch. {N,B, —
"Circumferential" and "circular" pitch are terms used here loosely
to denote the same pitch — that in the plane of the wheel faces as
distinguished from the normal, and not necessarily in contrast to
diametral pitch.) The diametral pitch of the gear can te obtahied,
after tlie selection of the cutter, by multiplying the diametral
pitch of the latter by the secant of the angle of the tooth. A
useful table is given overleaf for different pitches and angles.
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262
MILLING MACHINES.
Table of Spiral Gear — Diametral Pitches.
Diametral
Depth to
Pitch of
bo cut in
Cutter.
Gear.
Inch.
24
•090
22
•098
20
•108
18
•120
16
•135
14
•154
12
•180
11
•196
10
•216
9
•240
8
•270
7
•308
6
•359
5
•431
4
•539
3
•719
2
1078
Angle— 15°.
Corresponding
Diametral Pitch
of Spiral Gear.
Angle— 30".
Angle— 45*.
Corresponding Corresponding
Diametral Pitch Diametral Pitch
of Spiral Gear, i of Spiral Gear.
Inch.
•0431
•0470
•0517
•0575
•0647
•0739
•0862
•0941
•1035
•1150
•1294
•1479
•1725
•2070
•2588
•3451
•5176
Inch.
•0481
•0525
•0577
•0641
•0721
•0824
•0962
•1049
•1154
•1283
•1443
•1649
•1924
•2309
•2886
•3849
•5773
Inch.
•0589
•0643
•0707
•0785
•0883
•1010
•1178
•1285
•1414
•1571
•1767
•2020
•2357
•2828
•3535
•4714
•7071
The diameter of the hlank, equalling two pitches, added to the
pitch diameter must be calculated on the basis of the normal pitch
for which the cutter is selected, and not on the circumferential
pitch, and the same remark applies to the depth of tooth. And
hence, too, tlie circimiference of a j^ear blank equals the numl)er of
teeth multiplied l)y the normal pitch, multiplied by the secant of
the angle of spiral, plus two standard pitches.
Or,
Circ. = numl)er of teeth x normal pitch x secant n + 2^).
Also, the pitch or lead of the spiral and the circumference of
the wheel stand in the i«lati(m of secant and cosecant of the same
angle of spiral. Hence the lead of the spiral equals the numl)er
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SPIRAL WORK AND WORM GEARS.
263
of teeth multiplied by the normal pitch, multiplied by the cosecant
of the angle of tlie spiral.
Or,
Pitch, or lead of spiral = number of teeth x
normal pitch x cosecant a.
If a piece of paper is cut, as in Fig. 237, and wrapped round a
cylinder of the same diameter
Pi T c H-
as the pitch plane of the
spiral gear in Fig. 236, but
considerably longer than the
thickness of the wheel, we
shall have the result shown
in Fig. 237, in which the
primary pitch or lead of the
spiral is also the base of the triangle, the circumference is the same
as the perpendicular, and the angle of spiral is the hypotenuse.
Also in Fig. 236 the spiral wheel is shown developed along the
Fig. 237. — Triangle wound round
a Cylinder.
/»/ re// or B-
Fig. 238.— Spiral Geara of Different Diametera, but Equal Angle.
edge of the circumference, from which the fact is clear that a
spiral rack is only a developed spiral wheel, and hence such gears
will engage correctly.
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264
MILLING MACHINES,
Going a stage further, and keeping still to wheels the axes
of which are at right angles, the question of unequal velocity
ratio arises. The velocity ratio can be altered in gears at right
angles by manipulating the numbers of teeth and retaining the
same angles of spiral. The pitch diameters vary exactly as the
velocity ratios, and either wheel or pinion can drive or be driven
just as in the previous example. Tlie relations of gears witli 2
to 1 ratio are shown in Fig. 238, and a comparison of the diagrams
illustrates the fact that the length of tlie spirals and the diameters
of the cylinders are exactly 2 to 1 to produce equal angles of
45". Tlie angle of the tangent line being equal, the nonnal and
circumferential pitches would be alike in each wheel.
PI T c H
Fig. 239.— Spiral Gear, and Rack.
Again, one spiral wheel may be imtigined to be spread out
flatwise, and then we have a spiral rack, Fig. 239, which the spiral
wheel will drive. The normal and circumferential pitches here
are alike in the rack, provided, as before, the common tangent
stands at an angle of 45" with the axes. The wheel outlined
in Fig. 239 would be impracticable wdth a 45° tooth angle, but
such a gear would l)e possible by altering the tooth angles.
It is practicable to impart unequal velocity ratios to spiral
gears of the same diameters and with their axes at right angles ;
Init then neither of the spirals will be of 45*" angle, but each will
have an angle different from the otlier. Then tlie wheel with the
larger number of teeth will be based on a spiral having the same
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SPIRAL WORK AND WORM GEARS,
265
PITCH Of A
Fig. 240.— Spiral Gears with Teeth of
Different Angles.
relation to the other as the ratio required. If the ratio is as 2 to 1,
then the ratios of the length of spirals will he as 2 to 1. The line
of action or tangent line conmion to the two spirals and i)assing
through the pitch point
will divide the axes in
the relation of 2 to 1,
Fig. 240. The angles of
the two spirals are shown
projected in Fig. 240,
with the outlines of the
developed wheels indi-
cated.
In geai-s with unequal
numbers of teetli, that
having the most acute
angle, or the spiral of
shorter ju-imary pitch,
or tlie coarser circular pitch, is the driver.
Ix)oking at the diagram, Fig. 240, of the developed wheels, we
see that the circular pitches p\ p differ l)y a considerable amount,
though the normal pitches ^>, p)
are alike. The pitches can l)e
obtained in this way, though a
simple calculation gives them
readily, see page 261.
Spiral gears with their axes
not at right angles may be geared
in equal or unequal ratios. If
equally, tlie angle included be-
tween the axes, or, what is tlie
same thing, the angle between
the middle plane of the wheels,
may be bisected equally, and the
line of bisection will coincide
with the tangent line conunon to
the teeth of both wheels, and
passing through the pitch point. Fig. 241, where ^r, a are equal and
their sum equals h. The development of Fig. 241 is shown to the
left, and here the circular pitches are alike in both wheels.
V- PlTCH-'^,
Fig. 241.— Spiral Gears with Teeth
of Same Angle.
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266
MILLING MACHINES.
K""'^
•"";
>
^
^^
i '^
\'^\
^
X*-^
\ , *
<^
S-^
\ \'
V*
s
t'fl
Sv !
\ ^>
yn
■^ Nyl
\ \
V
^•\ ^v
1
V
\
■PhJCH^fB'\
\
»----■
■FITCH Of A-
- --«
Wheels with their axes set at an angle must 1x3 bisected
unequally for uneciual ratios, Fig. 242, in which case the spirals
are of diff'erent angles and the circular pitches different. The
development is shown in
^ -^ Fig. 242 for wheels A and B.
Kacks or spur gears can
he mated with spiral wheels
at an angle. In such cases
the spirals must be the
drivers. In Fig. 239 a
spiral wheel with its teeth
set at an angle of 45** was
shown engaging a rack, or
a spur wheel might be sub-
stituted for the rack. In
Fig. 243 a spiral with an
angle of 45° engages a spur
wheel. In both these cases
the pitch of the rack or spur
is the same as the normal
pitcli of the spiral gears.
This helps to illustrate the reason why cutters must l)e selected
Imsed on normal pitch for any spiral gears irres^iective of the
differences in circular pitch. In these examples, the shading only
indicates the circular forms of the gears.
Trigonometrical Rules. — Many prefer
to employ these graphic methods, which are
safe. But they may be dispensed with by
using a few of the simple rules of plane
trigonometry. Since the functions of angles
are constant, the relations of circumference,
pitches, angles of spirals, and normal and
circular pitches are obtainable. These will
1k3 first briefly explained, and then formula for spiral gears based
thereon tabulated.
Fig. 244 illustrates the functions of a right-angled triangle,
which are applicable to spiral and Ixivel gears having axes at
right angles.
Fig. 24*2. — iSpirals with Unequal Ratios.
Fig. 243.— vSpiral Gear-
ing with Spur.
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SPIRAL WORK AND WORM GEARS,
267
ABC represents the triangle, in which A c is the ba^e, B c
the perpendicular, and A B the hypotenuse. In this we recognise
also the base as equivalent to the pitch of a spiral, the perpen-
dicular as equal to the circumference of the cylinder, and the
angle of the hypotenuse as the same as the angle of the spiral.
If a piece of paper is cut to the shape of the figure and wound
round a cylinder of the same circumference as the length of the
perpendicular, the spiral will l)e developed on the cylinder.
An arc is shown struck from c to D from A as centre. The
perpendicular c B is the tangent to this arc, and it is perpendicular
to the base, or radius A c which meets it at the point of tangency.
The tangent CB is also the tangent to the angle cab, and is used in cal-
culation. If the length of the iKjrpendicular or tangent c B is known,
the number of degrees in the angle CAB can be found in a table of
tangents, and this, as we see, is
equivalent to the angle of spiral.
There are two angles in any
right-angled triangle, either of
which may be required to be
known. Hence, when speaking
of the angle cab, the base c A
is termed the side adjacent to
that angle, and, when speaking
of the angle c B A, the i)erpen-
dicular c B is the side adjacent
to that angle.
The following rules are based
on the functions of right-angled triangles : —
To find the tangent of either acute angle in a right-angled
triangle —
Divide tlie side opposite the angle by the side adjacent the
angle, and the quotient will l)e the tangent of the angle. In
Fig. 244 the rule might read correctly : — Divide the perpendicular
l>y the base, and the quotient will be the tangent of the angle c A B.
Angles are measured by arcs in degrees and minutes. Thus a
is the measure of the angle cab, and h that of the angle c B A.
The complement of an arc is the difference l^etween it and 90".
Thus a I) in Fig. 244 is the complement of c D, and vice versa.
The sui)plement of an arc is the difference between it and 180',
Fig. 244. — Trigonometrical Functions.
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268 MILLING MACHINE^.
or of a semi-circle. The sine of an arc is the line drawn from one
extremity of the arc perpendicular to the diameter passing through
the other extremity. Thus ^ D is the sine of the arc a D, and it is
equal to half the chord of the arc D c. The versed sine is the length
a h between the chord and the arc. A d is the secant of the arc a i).
The complements of the functions of an arc are denoted by the
prefix CO — as cosine, cotangent, and cosecant. Thus the arcs c D,
P a l)eing the complement of eacli other, tlie sine, tangent, and
secant of either is the cosine, cotangent, and cosecant of the other.
Thus h D, the sine of a D, is the cosine of D c. P r, tlie sine of P c, is
the cosine oi a\)\ a d, the tangent of a P, is the cotangent of P c ;
c B, the tangent of c P, is the cotangent of ai)\ a rf, the secant of a p,
is the cosecant of P c ; and A B, tlie secant of p c, is the cosecant of
a p. In any arc a p, therefore, the versed sine a b and cosine P e
make up the radius A « or A P. And the radius A a, the tangent
a dy and the secant a d make the right-angled triangle A a d. Also
the radius A c, the cotangent c B, and cosecant A B make the other
right-angled triangle A c B.
The sine of an angle is the sine of the arc that measures the
angle. It is always inside the arc, and can never be longer than
the radius. As the arc approaches 90°, the sine comes nearer to
the radius, or 1. Thus (a), the sine and cosine can never be
greater than unity; and (&), the secant and cosecant can never
he less than unity ; while (c), tlie tangent and cotangent can have
any value between zero and infinity.
Referring again to Fig. 244, the trigonometrical ratios of the
angle at A may be summarised as follows : —
The sine of A=.Pf^-pendicular^BC
hypotenuse A B
base AC
The cosine of A =
The tangent of ^^Perpenaiciilar^iu,
^ base A c
hypotenuse A B
dicular_
se
base A c
The cotangent of A = - ,. ,
perpendicular B c
mi . e hypotenuse A B
The secant of a = -^ =- —
base A (;
rpi i. £ . hypotenuse A b
The cosecant of A = — ^ — - — =— = —
perpendicular B c
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SPIRAL WORK AND WORM GEARS, 269
We have now the following trigonometrical rules for spirals. In
Fig. 244 the circumference of the cylinder around whicli the spiral
is wound corresponds with the perpendicular of the triangle, or the
side opposite the angle of the spiral.
In words the rules are : —
To obtain the angle of the spiral —
Divide the perpendicular (circumference of cylinder or spiral)
by the base (number of inches of spiral to one turn), and the
quotient will be the tangent of angle of spiral.
When the angle of spiral and circumference are given, to find
the pitch —
Divide the perpendicular (circumference of cylinder or spiral)
by the tangent of angle, and the quotient will be the base (pitch of
the spiral).
When the angle of spiral and the pitch
of the spiral are given, to find the circum-
ference —
Multiply the tangent of angle by the Fig. 245. -Circular and
pitch, and the product will be the circum- Normal Pitches,
ference (perpendicular).
The angles which the circular and normal pitches make with
each other bear the same relation as the axes of the wheels and
the tooth angles. Hence they can be deduced one from the other
trigonometrically as well as by direct measurement. In Fig. 245
rt c is the circular pitch, and a b the normal, and the angle b a c is
the same as that of the spiral, a b is the cosine of the angle b a c.
Then-
Circular pitch X cosine angle = normal pitch,
and —
normal pitch . , ., ,
■-^r- = circular pitch,
cosine angle
We have seen (page 264) that the ratios of diameters are alike in
some instances, and different in otliers. In the latter case the
condition to be observed is that the pitch of the spiral of each gear
shall be equal to the circumference of the other, or any fraction of
the same, depending on the ratio desired. The velocity ratio is
measured by the number of teeth, and not by the diameters. The
object first is to select the angles, and from these the corresponding
diametrical pitches.
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270 MILLING MACHINES.
Example, — Eequired two gears at right angles, measuring
respectively 2-ineh and 4-inch diameter, the 4-inch gear not to be
used for speeding up the 2-inch, but for speeding it down, in the
ratio of 2 to 1. The circumference of 4 inches is 12-5664, that of
2 inches is 6*28319. Half the circumference of the 2-inch gear is
3141 59, which is the lead of the spiral of the 4-inch gear. But
the lead of the spiral of the 2-inch would be twice the circum-
ference of the 4-inch gear (the axes being at 45"*) or 25*1328 inches.
Dividing the circumference by the pitch gives the tangent of the
angle. Hence —
Circumference of 4-inch = 12*5664.
19-5664
And "l =4, and 4 = a tangeut of angle of nearly 76°. 76°
from 90° leaves 14°, which must be the angle of the 2-inch gear.
These relations are shown in the diagram, Fig. 246.
To obtain the cutters by the rule (page 261) : —
The secant of 76^ is 4*1330. That of 14^ is 1*0306. Selecting
an 8-pitch cutter, and multiplying this by the secant of the angle,
we have : —
4*1336 X *1250 = *5167 = the corresponding diametrical pitch for
76°. And 1*0306 x '250 = -1288, that for 14^
The numbers of teeth that will work out nearest to the sizes of
wheels required are : —
24 for the 4-inch wheel —
24 x*5167 = 12*4008 circ.
And, 48 for the 2-inch wheel —
48 X -1288 = 6*1824 circ.
So that diameters would have to be slightly modified, and the
leads of the spirals corrected to suit.
Another way of putting it is this : —
The tangont of the _ pitch diam. of wh eel x number of teeth in pinion
spiml of wheel pitch diam. of pinion x number of teeth in wheel
and
The tangent of thepitcih di am. of pinio n x number of teeth in wheel
spiral of pinion "pitch diam. of wheel x number of teeth in pinion
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SPIRAL WORK AND WORM GEARS,
271
The illustration given, Fig. 246, is an extreme case, and it is
not a desirable gear, but it shows the flexibility of the spiral gears.
When axes are at any angle. When the numbers of teeth in
the two wheels are given the angles are found by a graphic method.
In Fig. 247, a h and c h are the axes of gears which include the angle o
l)etween them. On these axes distances are set off b a,b c repre-
senting the velocity ratios, and a parallelogram completed, so that
the numl)er of tlie teeth in the wheel : the nimiber of teeth in the
pinion ::a died. The tangent b d, if common to the teeth passing
through the point of contact, ensures the least amount of sliding.
But if the angle o is bisected at c b, the end thrust is equally
distributed on lM)th shafts. If an angle is taken, 6/ bisecting e b d,
a slight advantage of each kind is gained.
Fig. 246.— Spirals with Velocity
Ratios that do not corre-
spond with Diameters.
Fig. 247.— Angles of Spiral obtained
from Numbers of Teeth.
Fig. 248 illustrates the milling of a Ri)iral gear in the shops of
Ludwig Loewe & Co.
Worm Gears. — There is more trouble experienced in getting
good worm gears than spurs, or even IkjvcIs. I have seen some
so l>adly cut that the wheel teeth have had to be trimmed and
filed to make a decent fit, and have also known gears, machine-
moulded from pattern blocks, sul)stituted for those which have
been cut, and better results obtained thereby. There are three
reasons for this poor practice : one is that special types of machines
are best adapted for cutting the concave forms of worm-wheel
teeth; that a rather costly hob is generally necessary; and, in
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272 MILLING MACHINES,
the case of small wheels, the conditions required to ensure good
gear are not always understood.
A worm wheel in which the teeth are straight, and inclined
at an angle corresponding with tlie angle of the thread of the
worm, is easily cut with a rotary cutter, and it is sufficiently good
for a large quantity of work. Wheels used for dividing purposes,
and for light running, are mostly made like this. But when heavy
work has to be done, and good wearing capacity is desired, it is
Fig. 248.— Mimng Spiral Gear.
the usual practice to make the teeth envelopes of the worm. Such
gears, when rim at moderate speeds, are very durable. Good
results are obtained when both wheels are in cast iron, provided
they are well lubricated with plumbago and grease. Sometimes
steel worms run with cast-iron wheels, because iron worms always
wear out before their wheels. The best results are found when
tlie worm is of phosphor bronze running in an iron or steel wheel.
The breadth of tlie teeth of a worm wheel is about half the
diameter of the worm, though it is often less. There is no advan-
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SPIRAL WORK AND WORM GEARS.
273
Fig. 249.— Cutting Worm Wheel
Teeth with Common Cutter.
tage in excessive width. Three complete turns of a thread are
sufficient for contact in any case. The diameter of a worm is
generally from four to five times the
circular pitch. Worm-wheel teeth
are reckoned by circular .instead of
diametral pitcli. The i)itch is measured
along the axis of the worm and in
the middle plane of the wheel, and
is therefore axial. Normal jntcli,
though more correct, would not l)e so
convenient a working basis. There
is a way of reckoning pitch which
differa from that of common gears,
and which gives it as so many threads
in the linear inch, as 1 pitch or 2
pitch.
Worm wheels frequently have
tlieir concave teeth cut with rotary
cutters, Fig. 249, on milling machines. The results are satis-
factory as far as pitching and tooth angle are concerned, l)ut the
curved teeth are not true en-
velopes of the worm, as they are
when wheels are liobbed. There
is doul)tless more surface conta<3t
l)etween the teeth tlian when
straight teeth are employed, but
the advantage is probably not
very great.
When teeth are cut thus, the
wheel l)lank is carried tetween
the index centres, and the centre
of the wheel brought under the
centre of the spindle which car-
ries the cutter. The table is
set with the saddle brought
to the angle of the teeth, and
the vertical feed of the table
takes the cutter into the proper depth.
Cutting wheel teeth to become true envelopes of the worm
s
Fig. 2oO. — Obtaining the Shape of
Tool for Cutting Worms.
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274 MILLING MACHINES.
can only be done properly by a hob in shape like the worm, or by
a machine in which a single cutter is presented at various angles.
This requires a stiff machine, support to the wlieel rim against the
cutting, and a motion of the wheel blank relatively to the hob at
the same rate as the velocity ratios of the wheels when finished.
The involute tooth is accepted as the proper form of worm
gear, not l^ecause cycloidal forms
cannot l)e cut, but because it simpli-
fies matters to turn or mill the worm
tliread with a vee-shaped tool or
cutter of definite angles, and to make
Fig. 251. ^l^^t — ^^^ "^^^ tooth — the basis for
W^orm Gear Teeth. all wheels.
Though the threads of worms are
very connnonly turned in the lathe, yet they are also done
more properly in tlie milling machine, using a swivel head set
to the proper angle, and a rotary rack cutter.
Turnhig a worm tliread is just like turning any screw thread
in the lathe, whether it be single, double, or treble threaded.
Fig. 250 shows how the shape of tlie tool for cutting the rack-
shaped teeth is obtained. Upon a
Hue AB draw a circle AC, bd.
From B lay ofl* the distance B c and
BD, each equal to one quarter the
diameter of the circle. Draw CA,
D A, which make an angle of 20° —
the angle of inclination of the
sides of the rack tool. Make the
breadth of the tool at the end .*' — //
equal to 03 1 of the circular j)itch.
The width of the top of the thread Fig. 252. -Hob for Worm \\\lieel.
of a worm is 0*835 of the circular
pitch. The relations of the worm and wheel teeth are shown in
Fig. 251.
The hob, Fig. 252, by means of which the wheel teeth are cut,
is turned in steel to the same shape as the actual w^orm, plus a
little extra in diameter, sufficient to give the l»ottom clearance
between worm and wheel. The i)roi)ortions of tlie hob should l>e
these: — The diameter exceeds that of the worm bv twice the
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SPIRAL WORK AND WORM GEARS. 275
amount of bottom clearance in the wheel teetli. Tlie depth of tlie
hob thread is equal to that of the working depth, plus the clearance ;
the diameter at the bottom of the hob thread is the same as that
of the bottom of the worm threads. Grooves are then slotted out
in order to form teeth, which are backed off and hardened, con-
verting it into a cutting tool. The grooves are planed or milled
out with a round-edged cutter, the straight portion terminating at
the bottom of the thread, leaving the concavity below the bottom.
When a wlieel has its teeth cut in tliis way, every portion of
each tooth comes into successive contact with the thread of the
worm during the revolution of the latter. At no instant is a tooth
face a perfect envelope of the worm thread, and therefore any
attempt to cut such teeth perfectly with a single rotary cutter, as
in Fig. 249, must needs result in a tooth space of uniform section,
which would not give a correct gear. Neither teeth sections nor
spaces are uniform and symmetrical, and the departure from
symmetry is more pronounced with multiple-threaded than with
single-threaded worms. The forms obtained result from the
peculiar relations of the worm and the concave section of the
wheel rim, and the effect is exactly as though the worm cut out
its wheel teeth in a softer substance. The wlieel blank is rotated
through change wheels, regulated to move it at the proper velocity
ratio in relation to the worm. This is essential to ensure i)erfect
results, notwithstanding that a worm will cut its wheel teeth
without change gears. To have the i)itcli right, however, l)y this
method it is first necessary to block out the teeth ; l)ecause if this
precaution is not taken — that is, if the hob cuts its way into the
blank from the l)eginning, — the first cutting will take place on a
diameter larger than the })itch diameter, and l)y the time the wheel
is finished the pitch on the pitch diameter will be less than that
of the worm, and the teeth too many in number.
A relieved hob is formed on the same principle as tlie relieved
milling cutters, so that its sectional form does not alter by regrind-
ing on the front faces of the teeth.
J. E. Keinecker, one of the leading toolmakers in Germany,
cuts wonn wheels with a hob shaped as in Fig. 2oo, to which
an endlong movement is imparted, as shown in its successive
advances in Fig. 254, during its revolution. The advantage is
that the hob has not to be fed deeper into the blank as it cuts.
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276
MILLING MACHINES.
but it is set to correct centres once for all. The blank is mounted
on an arbor in a machine illustrated on pages 147 and 148.
Fig. 253.— Triple- threaded Tapered Hob.
Fig. 254. — Reinecker Hob Cutting Worm Wheel.
Table of Worm Gear — DiaxMETral Pitches.
Brown & Sharpe Standard Depth.
Pitch Corresponding Working Pitch
of j Diametral | Depth of ' of
Worm. Pitch of Gear. , Worm Thread. Worm.
nches.
Inch.
1- 8
•0:398
1- 6
•0531
1- 5
•0687
1- 4
•0796
1- 3
•1061
3- 8
•1193
4-10
•1273
1- 2
•1592
Inch.
•0796
•1062
■1274
•1592
•2122
•2388
•2546
•3184
Inches.
5
8
\
I
1
li
lA
If
2
Corresponding j Working
Diametral Depth of
Pitch of Gear. , Worm Thread.
Inch.
•1988
•2388
•2785
•3183
•3982
•4774
•5573
•6366
The depths given do not include the clearance.
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SPIRAL WORK AND WORM GEARS, 1*1*1
Rule, — Multiply the corresponding diametral pitch by the
number of teeth to get the pitch diameter, and add the working
depth of the tooth to this to get outside diameter.
Example, — 40 teeth, 4-pitch worm. -0796 inch x 40 = 3*184 inches
pitch diameter. To the pitch diameter add the working depth
of thread, 1592 inch, which gives 3*343 inches as outside diameter
of flat top gear, or throat diameter of curved face gear.
There are indications that the practice of milling screws instead
of cutting them in the lathe will assume great importance in the
machine shop. The sizes produced are constantly increasing, and
considerable economies effected over lathe work. The two best
known machines, the Liebert, and the l^att & Whitney, are con-
structed in a number of sizes, and produce both square and vee-
threaded screws, the cutters being of special type. In the Liebert,
cutters of pressed sheet steel are employed. The machine has a long
bed, carrying a head which supports the blank, the latter being
fed by change gears situated at the end of the ted. The cutter
head has adjustment for height, and a swivel motion, to bring the
cutter into correct angling with the screw being operated upon.
In the Pratt & Whitney a somewhat different design is made,
the screw being carried between a head and a tailstock, in lathe
fashion, while the cutter slide travels along the bed, and has a
swivelling head for the cutter arbor. The largest Pratt & Whitney
machine takes up to 12 in. diameter by 48 in. in length, teing
therefore suited for the production of large worms, spiral gears, etc.
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CHAPTER X.
SPUR AND BEVEL GEARS.
Spur and Bevel Gears — Diametral Pitch — Blanks — Cutters — Projection of
Bevel Wheels — Multiple Cutters — Multiple Centres — Milling Squares —
Tapered Work.
Spur and Bevel Gears. — The diameters of spur and bevel
wheel blanks, in common with spirals and worm wheels are de-
termined by the amount of addendum added to pitch diameter.
This is generally equal to one
diameter pitch. Thus in
wheels of 4-pitch the adden-
dum would measure \ inch,
because there are four teeth
for each inch of diameter in a 4-pitch wheel. This is a simple
iiiiitiiiiiiii "H'"mi<«'
°)
Fig. 255.— Gear Tooth Rule.
rule, and easily borne in mind
and applied. It simply means
tliat the blank has to be turned
to pitch diameter plus two dia-
meter pitches.
To save risk in making even
so simple a calculation some firms
make specially gi^aduated rules,
divided into 18tlis, 20ths, 22nds,
and so on, Fig. 255. Then, to
size a wheel, the number of teeth
is taken on the line of corre-
sponding divisions. If a 20-pitch,
say, the number of divisions cor-
responding with the number of teeth is read off on the line of
20tlis, and two of tlie 20th di\'isions added thereto gives at once
the total diameter of the blank.
Fig. 256.— Diametral Pitch.
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SPUR AND BEVEL GEARS,
279
The use of diametral pitch, illustrated l)y the diagram in
Fig. 25G — an 8-pitch wlieel — simplifies matters in calculation. It
is very easy to lay down numbers of simple calculations (which
need not l)e given here) all referable to this, and all facilitating
the work of gear cutting, while, when necessary, diametral and
their corresponding circular pitches can l)e ascertained by dividing
3-1416 l)y tlie diameter pitch for the circular pitch, and the latter
can be converted to diametral by multiplying it by 0-3183, which
is a short way of dividing by 3-1416.
Table of Diametral Pitch, with its Equivalent Circular
Pitch in the Adjoining Column.
Is
Circular
Pitch.
Circular
Pitch.
1
3* Circular
g- Pitch.
Diametral
Pitch.
Inch,
h
•SS
1
2
1-57
11
•280
1|
1^79
J
419
^i
1-.S9
12
•262
li
209
u
4^57
2}f
1-25
14
•224
ItV
2^18
s-
r,-03
2?
114
IG
•19G
n
2-28
5^.-.8
.S
l-Of) '
18
•174
lA
2^39
i
6^28
.'ii
•898 '
20
•1.^.7
u
2^ol
iV
7-18
4
•78.-,
22
•14.i
ivV
2G5
8-38
5
•G28
24
•i;{0
n
2^79
3
10^06
(i
•r,24
2G
•120
ItV
2^96
J
12^5G
7
•448
28
•112
1
' 314
IS
1675
8
•;{92
:50
•104
I s
.3-35
*
2.T12
. 9
•?,m
;52
•098
I
, 3-r,9
1
Iff
r>0^24
10
•:n4
...
Iff
: 3-86
...
Blanks. — When sizing tlie blanks of l>evpl and mitre wheels
the safest course is to draw them carefully in section, Fig. 257,
adding, as in spurs, one diameter pitch beyond the pitch line on
the large dianu^ter. \\y drawing all lines in section tlie dimen-
sions at the small end are ol stained, and tlie working depth of tooth
and the thickness of tootli or tooth space, which are equal, on
the small end. The working depth is of course ecjual to^the
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280
MILLING MACHINES,
addendum. The l)ottom clearance, added below this, is generally
equal to one-tenth the thickness of the teeth on the pitch line,
measured on the large side. The thickness of a tooth on pitch line,
leaving no flank clearance, is half the pitch. It is obtained in
diameter pitches by dividing 1*57 by the diametrical pitch. In a
1-570
5 -pitch it would be
= 0'314, and a tenth of this would be
I
%
(
Fig. 257. — Development of Bevel ({ears.
Fig. 258.— Oaugefor
Tooth Length.
0*0:U lH)ttom clearance for a 5-pitch tooth. Tables are used
in
The blank, Fig. 258, is turned to the dimensions taken from
the drawing. Fig. 257, and it is well to run round two lines taken
from the drawing giving the depth of tooth to be cut, Fig. 258,
using a gauge for the purpose, one of which is supplied for each
pitcli by firms wlio manufacture cutters, &c. The depth of bottom
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SPUR AND BEVEL GEARS.
281
clearance c, Fig. 257, is generally made alike at large and aniall
ends in wheels which are cut with rotary cutters.
There is no extra trouhle involved in striking-out wheels
which work at angles other than right angles, or wheels of
ditterent diameters. The methods illustrated in Fig. 257 show
how the bounding faces of the teeth converge to the aj)ex of
the cones, and that the ends of the teeth stand at right angles
with the pitch planes.
Cutters. — For gears most cutters now have a centre line round
the edge which facilitates their setting. It is usual in spur wheels
uj) to about 4 or 5 pitch to rough and finish at one traverse. In
large teeth a stocking cutter, Fig. 259, generally removes the bulk
of material, the finishing cut l>eing taken by another, Fig. 2G0. It
Fig. 259.— Stocking Cutter.
Fig. 260.- -Gear Cutter.
is always judicious to test the first tooth and tooth si)ace cut as to
thickness before going round the wheel, and jjarticularly so when
the cuttera or the machine have had much service.
Tlie shapes of cutters are determined on a definite basis, which
is that of a generating circle in the case of cycloidal teeth, that of
the angle of the path contact or of pressure in hivolutes. In
standard gears the latter is 75** with the line of centres, or 14^"
with a line cutting the line of centres at right angles. This is the
ecpiivalent of the generating circles of the cycloidal-toothed wheels.
Tlie base of the system is a rack having teeth with straight
sides, each inclined at an angle of 14^", and therefore including an
angle of 29" between them. Figs. 250 and 251. This is an extremely
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282
MILLING MACHINES.
simple and convenient system, both in design and in cutter forma-
tion, but with wheels having less than thirty teeth it leads to some
undercutting. If it is necessary to have small pinions without
undercutting, then the angle of obliquity of the path of contact
has to be hicreased to 20" or more, which means a special set of
cutters designed on that basis, and a correspondingly high angle of
pressure.
Manufacturers follow the Brown & Sharpe initiative in having
eight cutters for a set of involute teeth of one pitch, which are
well known by their numbers. As the numbers of teeth increase,
the cutters include a wider range on w^hich they will operate. A
different set of cuttei*s is properly used for spurs and l)evels, the
latter l)eing thinner by 0-005 than the tooth space at the narrow
end, taking tlie tooth length as not longer than one-third the
distance from tlie larger diameter of the teeth to the apex of the
Fig. 261.— Mining Bevel (icar Teeth. Fig. 262. — Milling Bevel Gear Teeth.
cones. If wheels of longer face have to \\e manufactured, thinner
cutters have to be s])ecially made.
Cutting the t^^eth of spur wheels with rotaiy cutters is an
accurate metliod. Not so that of l)evel whends. Ditticulties occur
in setting the wheel blanks to the proper angle laterally, but
chieHy to the fact that a given cutter can only l)e of correct form
for one sedition of the wheel tooth. If we look at the section of
the bevel wheel in Fig. 257, we see that the longer the teeth of a
wheel are, the more unfavourable are they for fairly correct cutting ;
that in a length of d the ditt'erence in the secti<m of the two ends
is not so great as it would be in a length of c.
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SPUR AND BEVEL GEARS, 283
The forms of the cutters are variously taken as correct at the
large end of the teeth, which is the most general practice, at a
distance of one-third of the length of tlie teeth inwards, and, in tlie
case of exceptionally wide teeth, at half-way along hetween the
large and small ends. The intention, therefore, is to have the
teeth true, or very approximately correct at tlie large end, and to
allow such inaccuracies as are inseparable from the use of a single
cutter to accumulate towards the smaller end. Here they will
not be so very pronounced, by reason of the diminished length of
teeth, and consequently of the diminished profile of the cutter
in actual operation, and there will also be only the minimum
of metal to be removed by the file for the purpose of correction..
It is an excellent illustration of a method which is theoretically
incorrect Ijeing made to produce in skilful hands fairly good
results.
An important point in cutting is that the care of the profiles
at the smaller ends counts for much
less than shaping the widths of the
tooth spaces and tooth thicknesses
correctly at the pitch lines. The first
may l)e corrected, the second not at
all, or not without a good deal of
trouble.
On commencing to cut the teeth
of l>evel wheels, the first care is to
set tlie blanks to the correct vertical
angle, which corresponds with the Fig. 263.— Gauging Gear Teeth,
angle at the bottom of the clearance
space c in Fig. 257, keeping this parallel with the addendum
length. Then the angle in the other plane is set with as close
an approximation to accuracy as is practicable, Fig. 261, and a
cut taken down one side. Here the need of having the cutter
thinner than the tooth space at the small end of the wheel in
a wide one is apparent, as a wide cutter would take out too
much metal there. The gear blank is then set over at the
opposite angle, and a cut taken down the opposite side of the
space, Fig. 202. The widths of the space on major and minor
pitch line are now cheeked before going further with a gauge,
Fig. 26;i
(\LnJ
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284 MILLING MACHINES.
Projection of Bevel Wheels. — The cutters selected for mitre
and for bevel wheels are not those which correspond with the
inunl)ers of teeth in the wheels, as they are in the case of spurs,
but those which correspond wuth the number of teeth of the
diameters projected frmn tJu tooth end^ to cut the axes of the wheels.
In some wheels with a slight bevel the difference will not be great ;
in those of flat bevel it will be very diflferent. Only in mitre
wheels, and wheels which nearly approach them, will one cutter
suffice for both wheels. In most pairs of bevels a distinct cutter
will be used for each of the pair.
The method of ascertaining what cutter should be selected for
bevel-wheel teeth is similar to that employed for striking out the
teeth on the projected faces.
In Fig. 257 the pitch diameter A of the wheel, and B of the
pinion, and the actual number of teeth, are not those upon which
the size of cutters is based ; but the diameters a' and B' projected
in line with the ends of the teeth to cut the centre lines have to
be taken. Thus in Fig. 257 the distances f-g^f-h correspond, so
far as the selection of cutters is concerned, with the radii of spur
wheels. So that these distances have simply to be multiplied by
2 to obtain diameter, and the product multiplied by the diametral
pitch, which gives the number of teeth that would correspond
with spur wheels of radii/-//,/-/*. If the radius f-y is 14 inches,
then twice 14 inches is 28 inches, and 28 inches multiplied by a
diametrical pitch, say, of 5 = 140, the number of teeth which
corresponds with the size of a wheel projected on the plane /-</,
for which a No. 1 or " rack " cutter must be selected. For f-h
the radius is 3J inches, and this multiplied by 2 gives 6^ inches,
and by the diametrical pitch 5 = 31-25 inches, which requires a
No. 4 cutter.
This takes the cutters as being right for the large ends of the
teeth, which is often done ; but see page 283, except in the special
cases of very long teeth. In mitre wheels, since the lengths of
the projected radii would be equal, a single cutter serves for the
teeth of both wheels.
The formation of the teeth by rotary cutters is done under the
most favourable circumstances wlien the teeth are short. The
proportion of one-third is given as an ordinary working limit ; but
this is too great in many instances. The most favourable condi-
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SPUR AND BEVEL GEARS.
285
tions are those in whicli the pitch is coarse and the teeth not
longer than about two and a half times the pitch. In teeth of fine
pitch and of greater width, accuracy depends very much upon
the care with which the cutting is supplemented by filing.
In some wheels used for gearing which is required to run with
exceptional smoothness at high speeds, the cutting has l)een
supplemented by grinding in a suitable framework with emery
and oil.
It is clear now why the mere possession of accurate cutters
does not ensure correct l)evel-wheel teeth. The cutter which is
right for one end is not right for the other or for any intermediate
position. Here the skill of the work-
man comes in. Different men adopt
varied methods to get the best ap-
proximation to truth, of two evils
choosing the lesser. The evil is that
of having to file the faces of the teeth
at the small end off" to nothing at the
large, as in Fig. 264, where the metal
left for filing is indicated by dotted
lines on the tooth on the left hand.
The amount of filing can be lessened
by using a cutter that gives more
rounding of the faces, but then that
imparts too much rounding to the
faces at the large ends. Or an extra
cut can be taken upon the small ends,
which' means another set of cuts all round on each face. Inaccu-
racies, too, arise due to the rolling of the gear sideways for obtaining
the taper of the teeth, which tends in small pinions to cut too
much off* the faces, though scarcely apparent in fiat bevels. The
setting of the gear blank out of centre for cutting the faces to the
correct bevel is not a simple matter for calculation, because the
same part of the cutter which cuts the large end of the tooth at
the pitch line does not cut the corre8i>onding portion at the small
end, but a narrower portion of the cutter. This is (me reason why
trial cuts between teeth are made at the commencement l)efore
going round, and the thicknesses of the teeth gauged at pitch lines.
When the first tooth and two spaces are all right, the rest of the
Fig. 264.— Effect of Cutting
Bevel Gear Teeth with a
Rotary Cutter.
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286 MILLING MACHINES,
cutting can be done all round one side fii-st, followed by all the
cutting on tlie other Bide.
Cycloidal as well as involute-shaped cutters are supplied for
spur gears, but not for bevels, for which they would 1x3 unsuitable.
If cycloidal bevels are wanted, they would have to Ije produced l)y
a i)laning jirocess. Coniiiaratively few cycloidal cutters are used
even for spurs, l)eciiuse a larger set is wanted — twenty-four for
each pitch in place of eight for involutes — and because, generally.
Fig. 2Go. --Cutting Twelve Wheels at once.
the system is not so elastic as that r)f the involute. In tlie latter
it is well known that slight ditlerences in centres do not affect the
working of the gears. A slight ditt'erence in the depth of the
cutters, increasing or lessening the bottom clearance, makes no
difference in the action of the gears. But in cycloidal teeth the
pitch lines must roll together, and, in fact, the depth of tooth is so
important that the cutters are made with shoulders which prevent
cutting going below the exact depth suitable for the gear. This
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SPUR AND BEVEL GEARS. 287
involves the necessity for very accurate sizing of the l)lank8. On
the other hand, many, inchiding the writer, think that, for smooth
and easy running, double-curve cut teeth are preferable to involute,
and that when the question is one of the best possible results they
should be selected.
Both circular and diametrical pitches are employed in the
cycloidal system of cutters, and the diameter of blanks is sized hi
the latter as in involutes by adding two diameter pitclies to the
pitch diameter.
The difference l»etween the range of the involute and cycloidal
cutters is very wide. In the first-named, three cutters, 6, 7, and
8, cut numl)ers of teeth from 12 to 20. But in the second, nine
cutters are re(juired, one to each separate wheel. In the higher
numbers the difllerence is also nearly as great — three cutters from
21 to 26 teeth in the d()ul)le-
curve system, against one
cutter from 21 to 25 in the
involute, and so on.
The gear - cutting ma-
chines have appropriated a
large volume of spur and
bevel gear cutting formerly i
done on the milling machine. y\^. 266. ^Multiple Cutters.
Still, the work is that of
rotary cutters. But the regular machines liave the advantage in
point of economy, being stiff'er, and often designed for operating,
in the case of spurs, on several spui's at once. A fine example is
given in Fig. 265, where twelve wheels are l)eing cut at once in
the shops of Ludwig Loewe & Co.
The Gould & Eberhardt system of multiple cutters is another
device to increase the output of a machine. Fig. 266 shows tliree
such cutters in operation. They are, of course, only suitable for
wheels of one size. On the milling machine duplication is often
effected by having two or more sets of centres in which pitcliing is
done by division i)lates witliout indexing. These are used for
small gears, taps, reamers, and articles having low numbers. Hacks
are cut with special attachments, one or several teeth l)eing cut at
once.
Fig. 267 illustrates multiple centres by the Garvin Company
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288 MILLING MACHINES,
suitable for fluting taps, reamers, milling small keyways, &e. A
number of small pieces are operated upon
at one time, and all are indexed together,
so saving a great deal of time. The
spindles are geared together and are
turned by a handle on the dial or by a
ratchet handle. The No. 1 headstock
spindles shown with l:J-inch centres of
spindles are fitted with hardened centres of
No. 1 Morse taper, and these centres are
cupped out and provided with four
grooves, which hold the work by the
square end and drive it round, so that
no chucks or dogs are necessary.
The . No. 2 headstock spindles have
® 2-inch centres of spindles, which have
I No. 3 Moi-se taper holes and are fitted
^ witli a doulile set of liardened centres.
o. One set is cupped similar to the No. 1,
3 and the otlier set are regular centres,
'^ each carrying a dogging jaw. These
»^ dogging centres enable ordinary round
t! work to be handled.
S The tailstocks are adjustable along
the base block, and can be fastened at
any point. The tail spindles have a
spring movement, and are thrown back
l)y separate levers, and are all l)ound
simultaneously by one handle. Kegular
centres with Morse taper are fitted. The
cutters can work close to the centre line.
Multiple-spindle centres are made with
from two to six spindles, both large and
small, especially adapted for certain pur-
poses, such as fluting taps and reamers,
making milling cuttei-s, hardware sj)eci-
alities, &c. They are built of several
centre distances, some being arranged for
spiral fluting, and others being made to adjust for taper work.
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SPUR AND BEVEL GEARS.
289
Fig. 268.— Indexing Device for Squares.
They are designed to index simultaneously. These centres are
for the most part set in large cast-iron pans, and arranged for
pump connection to oil reservoir. Their efficiency is due to the
fact that so much more work
can be turned out by the
same machine and the same
attendance as compared with
single-spindle centres.
Fig. 268 shows an index-
ing device in the Ludwig
Loewe shops for milling
squares on two reamers or
two taps at one time.
The two discs A, B are on
the indexing spindles, and are
connected by a link c, so that when moved by the handle D they
must turn in unison. Their movement is arrested in one direction
by the index pin h coming against the stud a, and in the direction
opposite by the pin c
Q coming on a, which
diflference is exactly
equal to one-fourth of
a turn. The clamp E
pinches the discs when
set, and the square
necks are milled by
straddle mills. Two
mills thus cut four
opposite faces at each
setting.
The upper figure
in Fig. 269 is intended
to show the effect of
doing tapered work
between centres on
the milling machine. A is the bent tail of the dog encircling the
work B, and pinched by the set screw c. The result is that the
tail is always wriggling about angularly and longitudinally
relatively to the set screw, springing and straining the work.
T
Fig. 269. — Improved Dog for Tapered Work.
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290
MILLING MACHINES.
The lower figure is designed to obviate this. The tail A is of
cylindrical form, and is off-set so that its axis is in line with the
end of the work B when the dog is set flush. An adjustable clamp
c is attached to the regular driver, which holds any size of dog,
and permits the tail to swivel and slide.
Table to Facilitate Calculations involving Fractions.
1 .
Ff -
1 .
3 .
ITT-
1-16 =
6 _
FT ■
a _
^2 -
7 _
1-8 =
8 .
FT-
6 .
11 -
FT-
3-16 =
13 .
¥:
FT"
1-4 =
•01563
•03125
•04688
•0625
•07813
•09375
•10938
•125
•14063
•15625
•17188
•1875
•20313
•21875
•23438
•25
17 .
FT-
9 .
19 .
FT-
5-16 =
21 ,
FT"
11 -
FT-
3-8 =
26 ,
FT-
IH .
2 7 ,
FT-
7-16 =
FT"
16 _
ai ,
FT-
1-2 =
•26563
•28125
•29688
•3125
•32813
•34375
•35938
•375
•39063
•40625
•42188
•4375
•45313
•46875
•48438
•5
3 3 _
FT"
17 ,
a6 _
FT"
9-16 =
37 .
FT"
19 .
ai _
FT"
5-8 =
%\Z
4 a .
FT-
11-16 =
2 a .
47 .
FT-
3-4 =
•51563
•53125
•54688
•5625
•57813
•59375
•60938
•625
•64063
•65625
•67188
•6875
•70313
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•73438
•75
49 _
FT-
26 _
^T-
61 .
FT-
13-16 =
63 _
FT-
2 7 .
66 .
FT-
7-8 =
67 .
FT-
29 .
HI
FT"
15-16 =
61 _
FT-
31 _
83 _
FT-
1 =
•76563
•78125
•79688 ]
•8125 '
•82813 ;
•84375 I
•85938
•875
•89063
•90625
•93188
•9375
•95313
•96875
•98438
1^00000
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CHAPTER XI.
FEEDS AND SPEEDS,
Governing Conditions— Feeds of more Importance than Speeds— Hardness and
Softness of Metal — Pickling — Its Limitations— Frequency of Grinding —
Examples of Feeds and Speeds.
Governing Conditions. — Feeds and speeds are dependent on
several circumstances, such as hardness or softness of metal, the
character of the cuttera, whether finely or coarsely pitched; on
the stiffness of the machine and arbor, or whether castings and
forgings have been pickled or not, besides other conditions of a
mmor character. The frequency of grinding is an important item
also. If a cutter is reground frequently, it will stand much more
than one which is worked for several days in a more or less dull
condition. Then it becomes a question of the greater economy of
slowing down to suit a dull cutter, or stopping -for a while to
change and grind the cutter.
In making comparisons of speeds and feeds account must be
taken of all these. And a distinction fully as important as any
is the diflference between ordinary work, and record work made
as tests. It is easy by using sharp cutters, running for short
periods, to make a big show by comparison with work done under
ordinary shop conditions. The question then is an economical
one. Record work as a rule is not paying work, and therefore
not much is done in that way in ordinary shop practice. These
matters, which are discussed at greater length in diflferent sections
of this work, have to be all well weighed in making comparisons
between milling speeds and feeds.
Speaking broadly, the same rule obtains as in the work of
single-edged cutting tools. That under identical conditions a slow
cutting speed and deep cutting may be combined, while a high
speed is only possible with shallow cutting.
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292
MILLING MACHINES,
Then, further, the rate of feed must depend largely on the
degree of accuracy or finish required. No accurate work can be
done on light articles with heavy cutting. The lighter the articles
and the greater the amount of accuracy needed, the lighter must
be the depth of cut, and rate of feed. In all work, even where
the roughing cuts are heavy, the finishing cuts must be light —
that is, the depth of cut must be small, though the speed and feed
may be increased beyond those used for the roughing.
The feeds of milling cutters are of more importance than the
Feeds should be made as fast as the cutters will stand,
consistently with good work. Average surface speeds are usually
given as 20 feet per minute for steel, 40 for cast iron, and 60 for
brass. The speeds in gear cutting are higher, because the machines
are designed specially and stiffly for that work alone : 40 feet per
minute for steel, GO for cast iron, and 80 for brass represent average
speeds. The speeds of high-speed cutters can be increased by from
50 to 75 per cent, above those of ordinary steel.
Table op Average Cutting Speeds, Periphery Speed of Cutter
(in Feet) per Minute.
Brass.
Wronsrht Iron. Cast Iron.
CartSteeL
Roughing
Finishing
Feed per minute
80
100
2iin.
40
60
f in. to 2 in.
30
40
\ in. to 1| in.
20
25
J in. to J in.
The rate of feed will vary from ^V i^^ch to yV ii^ch per foot of
cutter speed, according to the strength of the work or the cutter
and arbor, or the finish required and the material operated on.
Thus, taking a 4-inch diameter of cutter, and maintaining the
average cutting speed of 41 feet per minute (say 40 revolutions
of cutter), the rate of feed may require to vary from \ inch to
2^ inches per minute, according to the various conditions of the
work, and also the breadth of cut; as a rule, the broader the
cutter and the deeper the cut the slower should be the feed,
although this to a great extent depends upon the power and
stability of the machine.
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FEEDS AND SPEEDS,
293
Table of Feeds
IN RELATION TO DePTH AND
Width of Cut in Ordinary
Cast Ikon, giving Revolutions of Cutter for 1 Inch of Feed.
Diameter of
cutters
2 in.
3 in.
4 in.
6 in.
Width of cut -
i in. 2 in.
\ in. 2 in. \ in. 2 in.
i in. 2 in.
Revolutions,
to i in. deep 45 40
i Finishing, ^ in.
1
30 25 25 22
15 12
1 deep - . 35 30
22 20
18 15
10 9
rrii. .,1 r u- i • i. T f ced of work to each 12 inches of cutter
This will average for roughing A inch J . - i ^ • u * ^^^
rrn.. -11 r x: • L- • ■ i. "i Circumference, or each 4 inches of cutter
This will average for finishing ^ inch (^ ,.
For broader cuts and harder material the number of revolutions per inch of feed
should be increased.
Hardness or softness of metal makes a great difference in the
results obtained by the use of milling cutters. These differences
will easily halve, or double the feeds and speeds, and weight of
metal removed. In any comparisons, therefore, of this kind the
quality of the metal or alloy must be known. Iron castings vary
greatly in hardness, covering a wide range of differences. Certain
grades of steel are very tough, and must be annealed before
tooling, and then they and the cutters require a large volume of
lubricant.
Cast metals may be soft, homogeneous, and cut sweetly; or
they may be hard, honeycombed with blow-holes, interspersed
with cold sliuts or chilled parts, which strain or break the tools.
Forged metal may be clean and homogeneous, or it may be spilly,
seamy, open, trying to the tools.
Pickling has its limitations. It cannot be conveniently
practised in the case of big work. Neither is it worth while in
smaller pieces, portions only of which have to be tooled, as, say,
valve faces, or cover plates, or bosses. Neither is it of much
utility in work where the allowances for tooling are considerable,
as in many hand-made forgings, or those such as cranks, in which
wel>s are milled from the solid, or in castings where allowances of
\ inch or % of an inch are made for facing-off feet or flanges. There
are ready means of getting below the skin in such cases, eitlier
by single-edged planer tools, or by rotary cutters with inserted
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294 MILLING MACHINES.
teeth. But where pickling scores is in small forgings and castings
where allowances are cut uniformly fine, say from ^V iiich to ^V inch,
as in stamped work, and in machine-moulded work, and in which
the shallowness of the allowance would not permit the cutters
to get below the hard skin and scale.
The frequency of grinding cutters has a very close relation to
the volume of work which can be got through in a given time.
Frequent grinding means faster and deeper cutting, but it also
involves frequent stoppage of the macliine for taking out and
replacing cutters. If cutters are kept in duplicate, the loss of
time is not so great as when the machine has to stand while
regrinding is being done. For doing record work it is understood
that cutters must be kept very sharp. But it is none the less
desirable, in doing the ordinary work of the shop only, that a
reasonable mean must l)e struck. Too frequent stoppages mean
loss, sharpening too long delayed involves losses of time also, but
in other ways. These losses are due to the necessity for slowing
down or feeding more finely, and to the inefficiency of the cutter
to produce true results, due to spring caused by the friction of its
dulled edges. Of the two it is better to err on the side of frequent
grinding than in the other way.
A list of speeds and feeds is given below, taken from various
sources. Its value lies in the guidance it affords in practice.
General statements are nearly valueless, but these figures give
rates under all conceivable conditions, for all classes of cutters,
on all kinds of machines, and they should therefore be lielpful for
reference and check.
The thickness of a chip can be ascertained by dividing the
table feed per revolution of cutter by the number of teeth. If
the feed were 0*300 inch per revolution, and the teeth 30 in
number, the thickness of each chip would be
o|oo=o-oio,
or a hundredth of an inch thick. This is extremely thin by com-
parison with the chip removed by a single-edged tool, yet it is
fairly coarse for a milling chip.
The following is from the shops of A. Herbert Ltd., on fine
classes of work, and in the ordinary course of practice without
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FEEDS AND SPEEDS, 295
any attempt to establish records, some of which are shown in
previous photos.
A gang of cutters milling the faces of hexagon nuts of mild
steel held in a tuiTct head, six faces on three nuts being done
simultaneously. Cutters of ordinary tool steel, 6 inches in diameter,
36 teeth, 46 revolutions per minute, equal to 72 feet per minute,
feed ^ inch per minute. This gives a cut per tooth of 0-0003 inch.
The heads of thirty-five |-inch bolts were milled per hour.
A form mill tooling the sides of links of mild steel for cliain
conveyors ; diameter of largest part of cutter 4 inches. The total
width of cut 9| inches, the number of teeth 14, 48 revolutions per
minute, equal to 50 feet per minute, feed J inch per minute,
giving a feed per tooth of 0*0007 inch.
A gang of saws cutting slits ^V inch wide in gas burners of
cast iron, cutting 120 slits in one batch with 120 saws. Saws
3 inches in diameter, ^V i^ich wide, number of teeth 30, 51 revolu-
tions per minute, equal to 40 feet per minute, feed 2 inches per
minute, or feed per tooth 'OOIS.
A forhi mill profiling bars of mild steel. Cutter 5 inches
diameter, by 3f inches wide, with 12 teeth. Speed 32 revolutions
per minute, equal to 42 feet per minute, feed ^ inch per minute,
giving a feed per tooth of 0*0013 inch.
A gang of three saws cuttmg ofif blanks for screwing dies of
ordinary tool steel. Cutters 4 inches diameter, by \ inch wide,
36 teeth, 32 revolutions per minute, equal to 33*5 feet per minute,
feed \ inch per minute, giving a feed per tooth of 0*00043 inch.
A face mill with inserted cutters of Armstrong- Whitworth
high-speed steel, and having front rake, surfacing capstan slides.
The cutter was 12 inches in diameter, with 16 teeth, 11 J inches
width of cut, jfff inch depth of cut, 24 revolutions per minute,
equal to 75 feet per minute, feed 7^ inches per minute, or a feed
per tooth of 0*015 inch.
The foregoing, the last excepted, were done on horizontal
spindle machines of the pillar and knee type, the arbor being in
each of the examples supported at the outer end.
The following examples are of work done with rotary face
mills, with inserted cutters, on horizontal spindles.
Tooling listings very hard and with hard spots, and not
pickled. Cutter 27 inches diameter, 36 teeth, width of cut
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296 MILLING MACHINES,
15 inches, depth ^iiich to/u^ inch, speed 2^ revohitions per minute,
equal to 17 feet cutting speed, feed 3| inches per minute, giving
a feed per tooth of 0*038 inch. The cutters were of Mushet steel,
and tempered once only in 10 days.
Tooling castings of similar hard quality. Cutter 40 inches
diameter, with 52 teeth, width of cut 32 inches, depth ^ inch to
y\ inch in places, speed 1| revolutions per minute, equal to 17 feet
cutting speed, feed 3 inches per minute, giving a feed per tooth
of 0-033 inch. The cutters were made of Mushet steel, sharpened
once in from twelve to fifteen days.
Castings not so hard, but rougli. Cutter 11 inches in diameter,
with 8 teeth, width of cut 8 inclies, depth \ inch, 7 revolutions per
minute, equal to 20 feet cutting speed, feed 2 inches per minute,
giving a feed per tooth of 0*033 incli. Cutters made of Ann-
strong- Whitworth steel, sharpened once in four days.
An inserted toothed slabbing cutter operating on a plane
surface of cast iron, took a cut 8^ inches wide, with a depth
ranging from ^^ inch to /^ inch from a scale surface, at a speed of
cutter of 40 feet per minute, and a rate of feed of 8 J inches per
minute.
Examples of milling a tee groove in milling-machine platens.
In one the body of the slot was first rouglied out, and the bottom
done on the milling machine, with a rate of feed of 6^ inches per
minute. In another the tee slot was roughed out with an end
mill, at a feed of 6 J inches per minute, after which the tee was
done at a feed of 6f inches per minute. This was only possible by
the application of a compressed air blast to clear out the chips.
The following . are from the shops of the Cincinnati Milling
Machine Company, using Novo steel.
In milling gibs of grey cast iron, 2 inches wide, an edge cutter
4 inches diameter, with 18 teeth, which it will be noted is a coarse
pitch, is driven at a peripheral speed of 90 feet per minute, with
a feed of 0*300 incli per revolution of the cutters. The strip
travels under the cutter at a rate of 27 inches per minute ; and
the cut is /if inch deep.
The finishing cut is taken l)y a face mill, removing 0*010 inch
in depth, with a feed of 0*200 inch per revolution of cutter, or
10 inches per minute.
Another is milling cover plates of grey iron, measuring
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FEEDS AND SPEEDS, 297
6x4 inches. A slabbing spiral-toothed cutter, 3 inches diameter,
with 16 teeth, makes 51 revolutions per minute, feeds at 0*210
inch per revolution, or 10*7 inches per minute, and removes
\ inch depth of metal.
Another job is milling tee slots in the tables of the firm's
milling machines. These are first milled over the face, and the
vertical cut for the slots taken. Then a stem cutter, measuring
I jV iiich X \ inch, with 8 teeth, tee-slots each groove at a travel
of 12 inclies per minute. The chips are removed l)y an air blast.
In these shops, extra duty is regularly got out of the milling
cutters by utilising a blast of comf)ressed air to drive the chips
away from the cutters. Branch pipes are led to the machines, and
a hose having a nozzle, with a spring-closed valve, is opened by a
slight pressure of tlie thumb. Without the air blast, the chips
would clog or break the cutters in heavy liorizontal milling.
Another device employed is that of a strong jet of oil delivered
against the cutters, with the same object — that of clearing away
the chips.
The Holroyd patent pressed steel milling cutters have the
following records : —
Two ordinary steel patent cuttere, 2f inches diameter, running
600 revolutions per minute, cutting drawn brass screws ^-inch
diameter, ^-inch lead, J-inch pitcli, width and depth of cut xV inch,
feed 6^ inches per minute — these were ground once eacli week.
Two high-speed steel cutters, cut on three edges, 2J inches
diameter, running 200 revolutions per minute, cutting bright drawn
screw 1-inch diameter, ^-inch lead, J-inch pitch, width and depth
of cut \ inch, feed 4 inclies per minute — these were ground every
II hours.
One ordinary steel cutter, cut on three edges, 3 J inches diameter,
running 90 revolutions per* minute, cutting mild steel screw 3J
inches diameter, 3J inches lead, 3 starts, width of cut xV inch,
depth of cut xV inch, feed 1^ inch per minute — this was ground
every 5 hours.
Two high-speed steel cutters, cut on three edges,- 2| inches
diameter, running 200 revolutions per minute, cutting bright
drawn screw |-inch diameter, J-inch lead, J-inch pitch, width and
depth of cut xV inch, feed 4J inches per minute — these were
ground every 9 hours.
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298 MILLING MACHINES.
One high-speed steel cutter, cut on three edges, 2f inches
diameter, running 1,700 revolutions per minute, cutting cast hrass
screw 1-inch diameter, J-inch pitch, ^-inch lead, width and depth
of cut \ inch, feed 60 inches per minute — there was no appreciable
wear after the cutter had milled a gross of these screws, each
2 inches long.
Also two high-speed armour-plate bolt cuttere made of Arm-
strong-Whitworth steel — one of the cutters, making 160 revolu-
tions per minute, cutting 6 inches peripheral speed, was ground
every 8 hours ; the other, making 200 revolutions per minute, and
cutting 12 inches per minute feed, lasted 2 hours.
A pair of high-speed steel cutters 2J inches diameter, worked
eight weeks continuously, and cut 3,000 feet of double thread.
When new they were 2| inches diameter, and lost \ inch dia-
meter through grinding in eight weeks. The cutters were still
in fair condition.
MILLING CUTTERS.
Table op Cutting Speeds. (See opposite page.)
(Morse Twist Drill & Machine Company.)
The table will be convenient for finding the number of revolutions per
minute required to give a periphery speed from 5 feet to 50 feet per minute of
diameters from \ inch to 30 inches.
Examples. — A mill 2 inches in diameter, to have a periphery speed of 35 feet
per minute, should make about 67 revolutions, while a l^-inch mill should make
120 revolutions to have the same periphery speed. If a J-inch mill makes 250
revolutions per minute, the periphery speed is about 50 feet.
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FEEDS AND SPEEDS.
299
Table op Cutting Speeds.
I Feet
per
>fiiiate
Dlam
Inches.
i
i
I ^'
. li
i U
11
18
if
•2
2i
^*
I*
I'
I'
7
8
9
10
11
12
13
14
15
16
17
18
19
20
; 21
22
23
I 24
25
26
27
28
29
I 30
10
15
20
25
35
40
45
Revolutions Per Minute
38-2
76-4
114-6
30 6
61-2
91-8
25-4
50-8
76-3
21-8
43-6
65-5
191
38-2
57-3
17
34
510
15-3
30-6
45 8
13-9
27-8
41-7
127
25-4
38-2
11-8
23-5
35-0
10-9
21-8
32-7
10-2
20-4
30-6
9-6
19-1
28-7
8-5
170
25-4
7-6
15-3
22-9
6-9
13-9
20-8
6-4
12-7
191
5-5
10-9
16-4
4-8
9-6
14-3
4-2
8-5
12-7
3-8
7-6
11-5
3-5
6-9
10-4
3-2
6-4
9-6
2-7
5-5
81
2-4
4-8
7-2
21
4-2
6-4
1-9
3-8
5-7
1-7
3-5
5-2
1-6
3 2
4-8
1-5
2-9
4-4
1-4
2-7
41
13
2-5
3-8
1-2
2-4
3-6
11
2-2
3-4
11
21
3-2
1-0
20
30
1-0
1-9
2-9
•9
1-8
2-7
•9
1-7
2-6
•8
1-7
2-5
•8
16
2-4
•8
1-5
2-3
•7
1-5
2-2
•7
1-4
21
•7
14
20
•7
1-3
2-0
•6
1-3
1-9
152-9
122-5
101-7
87-3
76-4
68-0
61-2
55-6
50-8 1
47-0
43-6
40-7
38-2
34-0
30-6
27-8
•25-5
21-8
191
16-9
15-3
13-9
12-7
10-9
9-6
8-5
7-6
6-9
6-4
5-9
5-5
51
4-8
4-5
4-2
40
3-8
3-6
3-5
3-3
3-2
31
2-9
2-8
2-7
2-6
2-5
191 1
229-3
267-5
1531
183-7
214-3
127-1
152-5
178-0
1091
130-9
152-7
95-5
114-6
133-8
85-0
102-0
119-0
76-3
91-8
106-9
69-5
83-3
97-2
63-7
76-3
89-2
58-8
70-5
82-2
54-5
65-5
76-4
50-9
611
71-3
47-8
57-3
66-9
42-4
510
59-4
38-2
45-8
53-5
34-7
41-7
48-6
31-8
38-2
44-6
27-3
32-7
38-2
23-9
28-7
33-4
21-2
25-4
29-6
191
22-9
26-7
17-4
20-8
24-3
15-9
191
22-3
13-6
16-4
19-1
11-9
14-3
16-7
10-6
12-7
14-9
9-6
11-5
13-4
8-7
10-4
12-2
8-0
9-6
111
7-3
8-8
10-3
6-8
81
9-6
6-4
7-6
8-9
6-0
7-2
8-4
5-6
6-7
7-9
5-3
6-4
7-4
5-0
6-0
70
4-8
5-7
6-7
4-5
5-5
6-4
4-3
5-2
61
4-1
50
5-8
4-0
4-8
5-6
.3-8
4-6
5-3
3-7
4-4
51
3-5
4-2
5-0
3-4
41
4-8
3-3
4-0
4-6
3-2
3-8
4-5
305-7
244-9
203-4
174-5
152-9
136-0
122-5
lU-l
101-7
93-9
87-3
81-5
76-4
68-0
61-2
55-6
51-0
43-6
38-2
34-0
30-6
27-8
25-5
21-8
191
17-0
15-3
13-9
12-7
11-8
10-9
10-2
9-6
9
8-5
8-0
7-6
7-3
6-9
6-6
6-4
61
5-9
5-7
5-5
5-3
5-1
344-0
275-5
228-8
196-3
172-0
153-0
137-4
125-0
114-6
105-7
98-2
91-9
86-0
76-2
68-8
62-5
57-3
49-1
43
38-1
34-4
31-3
28-7
24-6
21-1
19-1
17-2
15-6
14-3
13-2
12-3
11-5
10-7
10-1
9-6
9-1
8-6
8-1
7-8
7-5
7-2
6-9
6-6
6-4
6-1
5-9
5-7
50
382-2
3061
254-2
218-9
1911
1701)
153-1
138-9 .
127 1
117-4 I
1091
101-9
95-5
85
76-3
69-5
63-7
54-5
47-8
42-4
38-2
34-7
31-8
27-3
23-9
21-2
19-1
17-4
15-9
14-7
13-6
12-7
11-9
11-2
10-6
10-1
9-6
91
8-7
8-3
8-0
7-6
7-3
71
6-8
6-6
6-4
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INDEX.
ACCURATE work, oonditions of, 7
Angles of spirals, 250-253 .
Angular movements to spindles, 75-82
Arbors for cutters, 170, 171
— support of, 85
Arm, overhanging, 22, 84, 85.
Attachments for spiral work, 78
— for slotting, 82-84.
— to horizontal machines, 75-84
BACK gears, 22, 25, 26, 35, 39, 110
Belt feeds, 32, 33
Bevel and spur gears, 278-290
Bevel gears, cutters for, 281-283
— gears, development of, 279-281, 283,
284
Bracings for overhanging arm, 86-91
CAM cutting, 155, 156
Casting cutters in heads, 177, 178
Centres, multiple spindle, 287-289
Classification of machines, 1 1
Clearance of milling cutters, 165, 166,
167, 189-191
Compound indexing, 247, 248
Conditions of accurate work, 7
Cone mandrels, 226, 227
Circular tables, 102, 103
Cutter arbors, 170, 171
Cutters, 162-197
— built up in gangs, 219
— for bevel gears, 281-283
Cycloidal and involute teeth, 286, 287
DEVELOPMENT of bevel gears,
279-281, 283, 284
— of milling cutters, 1
Diameter of milling cutters, 163
Diametral pitch, 278, 279
Differential indexing, 248-250
Dividing heads, 63-72
Drills, fluting, 149-152
ELEVATING screws, 53
Elliptical hole milling, 159-161
Emery grinder, influence of, 11
FEEDS, 29, 30, 31, 36, 37, 39, 46, 60,
105, 107, 112, 124, 140
— and speeds, 291-299
— belt, 32, 33
— positive, 32, 36, 37, 39, 40-50
~ spindles, micrometer fittings to, 56
Finishing, 201
First milling machine, 8, 9
Fluting twist drills, 149-152
Footstocks, 72-74
Form-cutter grinding, 196
Former, 227, 230
GANG cutters, 219
Gear cutting, machines for, 139-
149
Gears, velocity ratios of, 256, 257, 264,
265
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302
INDEX.
Gears, worm, 145-149
General shop, milling in, 4
Graphic methods for spiral gears, 259-
271
Grinding milling cutters, 185-197
HANDLES, 61
Hardening cutters, 179-182
Headstocks of milling machines, 24-29
Heads, swivelling, 78-82
— universal, 63-72
Hobbing worm gears, 145-149
Hobs for worm gears, 274-276
Holding work for milling, 208-227
Horizontal machines, attachments to,
75-84
— spindle machines, 10, 16
— V. vertical spindle machines, 95
INDEX centres, 62-72
— plate, 244-247
Indexing and spiral work, 243-271
— compound, 247, 248
— diflFerential, 248-250
Inserted tooth cutters, 171-178
Involute and cydoidal teeth, 286, 287
TIGS, 228-242
K BYWAYS in cutters, 171
Knees, 51-53
~ and tables, 29-31
— elevating screws of, 53
LIMITATIONS of milling machines, 7
Lincoln machines, 10-15
Locking handles, 117
Lubrication, 118, 121, 152, 199
MACHINES classified, 11
— special, 139-161
Machining improved by milling, 7
Magnetic chuck, 220-222
Micrometer fittings to feed spindles,
56
Milling, and the reciprocating tools, 5
— and tool making, 6
— compared with planing, etc. , 200-202,
206, 207, 208-217
— cutters, 162-197
— cutters, arbors for, 170, 171
— cutters, cast in head, 177, 178
— cutters, cutting teeth of, 183-185
— cutters, development of, 1
— cutters, diameter of, 163
— cutters for die work, 227, 229
— cutters, grinding and sharpening, 185-
197
— cutters, hardening of, 179-182
— cutters, inserted tooth, 171-178
— cutters, key ways of, 171
— cutters, oil stoning, 197
— cutters, rake and clearance of, 165,
166, 167
— cutters, spacing of teeth, 163-165
— cutters, spiral form, 167-169, 173
— cutters, steel for, 178, 179
— cutters, the first, 1
— cutters, tooth rest for grinding, 189-
192
— cutters V. single-edged tools, 162
— cutters, wear of, 169
— effects of, on machining, 7
— elliptical holes, 159-161
— holding work, 208-227
— in the general shop, 4
— machine, early improvements in, 9,
10
— machine feeds, 29, 30, 31
— machine for drill fluting, 149-152
— machine headstocks, 24-29
— machine knees, 51-53
— machine, limitations of, 7
— machine requires skilled attendance,
5,6
— machines for elliptical holes, 159-161
— machines for gear cutting, 139-149
— machines for worm hobbing, 142-149
— machines, horizontal spindle, 10, 16
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INDEX.
303
Milling machines, indexing and spiral
work, 243-271
— machines, pillar, 16-24
— machines, pillar and knee, 16-74
— machines, piano-millers, 130-138
— machines, profiling, 96, 97, 102
— machines, special, 139-161
— machines, tables and knees, 29-31
— machines, the first, 8, 9
— machines, the Lincoln, 10-15
— machines, three-spindle, 153-155
— machines, utilities of, 2-5
— machines, vertical spindle, 94-129
— on planer, 158, 159
— operations, 198-242
— operations summarised, 203-205
— screw gears, 253-255
— spiral gears, 272
— spur and bevel gears, 278-290
— work in specialities, 3, 4
— worm gears, 271-277
— worm threads, 142-149
Multiple cutting, 287, 288
— spindle centres, 287-289
OIL stoning cutters, 197
Operating handles, 61
Operations on milling machines, 198-242
Oval hole milling, 159-161
Overhanging arm, 22, 84, 85
— arm, bracings for, 86-91
PILLAR and knee machine, general
description, 21-24
— and knee machine, work of, 92
— and knee machines, 16-74
— machines, 16-24
— machines, dimensions of, 18
— machines, points in, 19
Pitch, diametral, 278, 279
— of spiral gears, 258
Plain machines and universals, difier-
ences in, 59-61
— machines, work of, 19
Planer, milling attachment to, 158, 159
Piano-millers, 130-138
Positive feeds, 32, 36, 37, 39, 40-60
Profile milling. 227, 230
Profiling attachments, 100, 101, 157, 158
— machines, 96, 97, 100-103, 128, 129
RAK£ of milling cutters, 165, 166,
167.
Reciprocating tools, and milling, 5
Revolution mark, 163
Rotary planers, 136-138
Roughing, 199, 200
SCREW gears, milling, 253-255
Screw milling, 277
Sector, 244, 245
Sharpening milling cutters, 185-197
Single-edged tools r. milling cutters, 162
Skilled attendance in milling, 5, 6
Slabbing machines, 130-138
Slotting attachments, 82-84
Special machines, 139-161
Specialities and milling, 3, 4
Speeds, 124
— - and feeds, 291-299
— of spindles, 25, 26, 31, 32, 34
Spindle bearings, 27, 28, 34, 36, 39
— speeds, 25, 26, 31, 32, 34
Spindles, 27, 34, 36, 39, 105, 106, 112,
122, 126, 127, 128, 133-136
— angular movements of, 75-82
Spiral gears, graphic methods, 259-271
— gears, pitch of, 258
— gears, trigonometry of, 266-271
— heads, 62-72
— mills, 167-169, 173
— work and indexing, 243-271
Spirals, angles of, 250-253
Spur and bevel gears, 278-290
Standard movements, 62
Steel for cutters, 178, 179
Stops, 117
Straddle mills, 219
Swivelling heads, 78-82
TABLES, 54-67, 102, 103, 104, 126
— and knees, 29-31
— vernier applied to, 57, 58
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304
INDEX,
Tapered work, 289
Teeth of cutters, spacing, 163-165
Three-spindle machines, 153, 155
Tool maker and milling, 6
Tooth rest for cutter grinding, 189-192
Trigonometrical functions of spiral gears,
266-271
Trips, 117
UNIVERSAL heads, 6372
— machine, first, 16, 17
Universals and plain machines, difier-
ences in, 59-61
VELOCITY ratios of gears, 256, 257,
264,265
Vernier applied to tables, 57, 68
Vertical spindle attachment, 76
— spindle machines, 94-129
— V. horizontal spindle machines, 95
w
EAR of cutters, 169
Work of pillar and knee machine,
92
Worm gear hobbing, 145-149
— gears, 271-277
— gears, hobs for, 274-276
— thread milling machine, 142-149
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