George Davidson
1 R9 _T Q1 T
Pr.ofessor of Geography
University of tTafifdrrfia
' -
' "^jS -^ *"1>4 '
IHE STARRETT BOOK
for
MACHINISTS' APPRENTICES
BY
HOVARD P. FAIRFIELD
i *
Assistant Professor Machine Construction, Worcester Polytechnic Institute
AND
CARL S. DOW, S. B.
Editor-in-chief Practical Mechanical Engineering
Editor-in-chief Practical Shop Work
PRICE, 50 CENTS
THE L. S. STARRETT COMPANY
The World's Greatest Toolmakers
ATHOL, MASSACHUSETTS
COPYRIGHT 1917
THE L. S. STARRETT COMPANY
INTRODUCTION
Laying out work preliminary to machining is trans-
ferring blue-print instructions on to the metal. While
the blue-print gives dimensions accurately, without any
great precision in the drawing itself, lines laid out on
the metal are to be worked to and must therefore be
accurate. No one can consider himself a skilled machinist
unless he can lay out his own work and, when called
upon, lay out work for the less experienced.
To become skilled in laying out should be the aim of
every apprentice. Possessing this skill gives more op-
portunity to show ability than the running of a machine.
It is a qualification one must have for advanced posi-
tions such as toolmaker, foreman, or superintendent.
But laying out requires some knowledge of mathe-
matics, some skill at mechanical drawing, and an acquaint-
ance with machinists' fine tools and shop operations.
Attention to details and extreme care are of utmost im-
portance. Increased labor cost, as well as material
wasted because of errors in laying out, are the penalties
of mistakes.
The apprentice, then, should lose no opportunity to
make himself capable of laying out work. Close observa-
tion of pieces laid out by skilled machinists is one way
of becoming acquainted with the art. The fortunate
apprentice may also have opportunity to observe a
skilled machinist while laying out various jobs.
The number of measuring and laying out tools or
instruments now purchasable is very great and the ap-
prentice must become familiar with practically all of
them. He must know what he can accomplish with each
so that he will instinctively select those best suited to the
job in hand.
M510983
THE STARRETT BOOK
Economy of time in laying out is another element of
success. Time-saving tools, such as the dial test indi-
cator, quick-acting micrometer, and combination set,
should be among those ready for use. The combination
set, for instance, combines a rule, square, miter, protrac-
tor, center square, depth gage, height gage, and level. The
fewer the tools used, provided the ones at hand are really
good ones, the less the bench will be littered with tools
which may be used only occasionally.
The tools in a machinist's tool-box are a sure indica-
tion of his ability. A well-fitted kit of fine tools helps
him hold a job in hard times and is one of the best
assets a man can have when applying for a job. The pos-
session of many fine tools indicates a love for accurate
work, freedom from the borrowing habit, and a deter-
mination to do work which will demand recognition.
Next to having a complete outfit of fine tools is the dis-
position on the part of the apprentice to add the best
tools as rapidly as he can afford them.
In preparing this book, the aim has been to select
those elementary features most essential to the advance-
ment of machinists' apprentices and students in techni-
cal and manual training schools. It is intended to give
such students a portion of the instruction ordinarily
given by the teacher or by more experienced machinists.
It will also serve as a reference book for data not to
be memorized.
THE S T ARRETT BOOK
READING WORKING DRAWINGS
Drawing is the language of the engineer, designer,
and machinist. Unless a machinist can at least read
working drawings he cannot be known as a skilled me-
chanic. Certain conventions relating to views, lines,
scales, sections, and other representations, are what make
up the language of drawings, and the correct use of
these is readily learned. A set of working drawings
consists of
GENERAL DRAWING, showing the entire machine
with all the parts located in their proper relation to one
another. This drawing is usually made to a reduced
scale; for example, one-quarter or one-half size; it is
often termed the Assembled or Assembly Drawing.
DETAIL DRAWINGS show each part of the machine
separately; they are often termed "detail," or "details."
A detail drawing should be supplied with complete data
for constructing the part, such as dimensions, material
used, number of pieces, operations to be performed, etc.,
and should consist of sufficient views to be easily read.
In practice some firms group several details upon a single
sheet others place a single detail upon a sheet.
SECTIONAL DRAWINGS show certain assembled
portions, as if a part of the stock had been sliced away
to more clearly illustrate the interior construction, often
termed "sections." Position of "section" is shown by a
full line drawn through a "view" and lettered at each end.
BOLT AND SCREW LISTS. On these are tabulated
all bolts, screws, etc., which are common to the stock-
room, and necessary to the erecting of the machine.
MOTION DIAGRAMS. Instruction is sometimes nec-
essary concerning the relation of certain centers to the
motion of parts, velocity ratios, and direction of motion;
therefore where a machine has a number of more or less
complicated motions, motion diagrams are provided.
THE STARRETT BOOK
THE STARRETT BOOK
THE STARRETT BOOK
VIEWS. All material things have three dimensions;
length, breadth, and thickness or height. The draftsman
of necessity makes use of some method of projection to
get his various views on a flat surface on which only two
dimensions can be shown the method of projection in
machine-shop use places the front view with the other
views grouped around in the order of their names, as
top view above, bottom view below, etc.; each view cen-
tering on either a horizontal or a vertical center line.
FULL LINE
DOTTED 1TINE
CENTER LINE
DIMENSION LINE
SHADE LINE
LINES. Full lines on a drawing indicate the visible
lines or edges of the object. Dotted lines indicate hidden
or invisible lines and edges. Broken lines, made up of
dots and dashes, indicate center lines. All lay-outs
should start from center lines.
Dimension lines are usually full lines with a break
in the line for dimension figures and an arrow head at
each end to indicate the surfaces dimensioned. Section
lines are parallel lines drawn across a surface which is
represented as being in section; they are usually drawn
at an inclination of 45 or 60, and equally spaced.
By using for sections various combinations of full and
dotted lines and special spacings, different materials of
construction, such as cast iron, steel, etc., can be indicated.
SCALES. Where convenient, all drawings are made
actual size, termed full scale. When the object is too
10
THE STARRETT BOOK
large to be conveniently represented full size, the draw-
ing is made to a regularly reduced size, called a reduced
scale drawing. The usual scales are full-size, half-size,
quarter-size, and eighth-size, also known as 12", 6", 3",
and IV 2 " to 1 foot. When working from drawings the
dimension figures should be invariably followed meas-
urements should not be taken from the drawing.
BRASS OR BRONZE
WHITE ALLOYS
ALUMINUM
LEAD
ZINC
11
THE STARRETT BOOK
ABBREVIATIONS. All information on a drawing is,
when possible, abbreviated as follows:
CONVENTIONAL ABBREVIATIONS
Finish: Surface is
to be finished
Scrape: Surface
is to be hand-
scraped
R. H.: Right Hand
Grind: Surface is
to be ground
' : Feet
L. H.: Left Hand
Face : To square
up
" : Inches
W. L: Wrought
Iron
Bore: Use of bor-
ing tools or bars
Dia. : Diameter
C. I. : Cast Iron
Ream : Hole should
be reamed
Rad. : Radius
M. S.: Machine
Steel
T. S.: Tool Steel
C. R. S.: Cold
Rolled Steel
Tap : Hole is to be
tapped
Thd.: Thread
C. S. : Carbon Steel
H. S. S.: High
Speed Steel.
Drill: Hole is to
be drilled
U. S. S.: United
States Stand-
ard
Running Fit, Drive
Fit, Force Fit,
Shrink Fit, Taper
Fit: Allowances
to be made in
size of shaft
SCREW THREADS, STRUCTURAL RIVETING, PIPE
FITTINGS, LINE SHAFT BEARINGS, etc., are so stand-
ardized that conventional representations are always
used by the draftsmen.
12
THE STARRETT BOOK
MEASURING TOOLS
Measurements in general are those of length, area,
and volume. In machine-shop practice the measurement
of length is the common one. This is of such impor-
tance, and many of the measurements are of such exact-
ness, that a multitude of measuring tools are being
marketed, nearly all of which are for the main purpose
of obtaining linear measurements.
THE YARD. In the United States the Standard of
length is the British yard, of which two copies are owned
by the United States Government.
THE METER, which is the French standard of
length, is also coming into use in the United States,
notably in instrument work. The meter equals 39.37
inches.
The use of measuring tools in machine work is
largely confined to the thirty-sixth subdivision of the
yard, or the inch. The inch is subdivided into various
lengths, of which the ten-thousandth part is the short-
est practical shop measurement. Measurements shorter
than this are, however, common enough in scientific
laboratory work.
The practical machinist and toolmaker divides his
work into two classes :
(a) Flat Work and (b) Round Work. While it can-
not be said that each class has its distinctive line of
measuring tools, the workman who handles flat work
only will usually have a somewhat different set of meas-
uring tools from the workman on round work.
FLAT WORK
In general the worker on flat work will need to be
provided with steel rules, dividers, protractors, straight
13
THE STARRETT BOOK
Combination Set
Toolmakers' Calipers Micrometer Depth Gage
14
THE STARRETT BOOK
edges, steel squares, surface, height, depth, and thickness
gages, center punches, parallels, slide calipers, etc.
ROUND WORK
For round work the measurements are by contact, and
the usual tools are those having contact points. Contact
measurements are made in two ways: (a) The contact
tool is first set to some standard of length, as, for ex-
ample, a steel rule, or a standard gage. The "set" dimen-
sion may then be used as a standard for testing the work.
(b) The reverse of this method may be used for deter-
mining sizes, viz.: by first setting the contact points to
the surfaces of the work, afterward using the steel rule
or standard gage to read the size.
"FEEL"
The accuracy of all
contact measurements is
dependent upon the sense
of touch (feel). In the
case of skilled workmen,
as, for example, toolmak-
ers, the sense of touch is
highly developed. Using
suitable contact measur-
ing tools, the skilled me-
chanic can readily "feel"
the difference in contact
made by changes of di-
mensions as small as
0.00025".
In the human hand
the sense of touch is most prominent in the finger-tips.
Therefore the contact measuring tool should be held by
15
THE STARRETT BOOK
the fingers only, and in such a way as to bring it in con-
tact with the finger-tips. If the tool is harshly grasped
by the fingers, the sense of touch or feel is much re-
duced. For this reason the tool should be delicately and
lightly held instead of gripped tightly.
The more common tools for contact measurements
are inside and outside calipers, used in conjunction with
steel rules, plug and ring gages, and dimension blocks.
While it is possible to transfer by "feel" a length
with an error not exceeding one-quarter of one thou-
sandth inch, the results are not always easily read; for
this reason mechanics prefer to use direct reading tools
for the more accurate contact work. Two methods of
direct reading are in common use.
VERNIER CALIPERS
This tool is a combination of contact points and
steel rules. One of the contact points is a fixed part
of a graduated steel rule, while the other contact point
is a part of a graduated slider mounted upon the blade
of the first. By combining the use of the separate scales,
direct readings of one-thousandth part of an inch are
readily made.
FRONT
16
THE STARRETT BOOK
VERNIER HEIGHT GAGE
^^-*~"
'1
Another adaptation of the vernier is the
height gage. By means of the vernier it is
easy to make readings as minute as one
thousandth part of an inch. This instru-
ment is used chiefly where close, accurate
measurements of height must be obtained;
the method of using is clearly shown on
page 105 where it is used in finding the
center to center distance of a pair of jig
buttons.
By means of suitable adjustments, one
of which is shown on the accompanying
illustration, its use is extended to include
making accurate measurements of depth.
The tool is thus rendered particularly de-
sirable for use in jig-making for the depth
of a recess inside the jig frame may be read-
ily obtained. The removable jaw allows the
user to make reverse measurements on the
jig frame.
17
THE STARRETT BOOK
THE STARRETT BOOK
MICROMETER CALIPERS
With the invention of the micrometer screw there
came into use a new method of direct readings in contact
measurements. The great accuracy of the micrometer
screw becomes evident when it is realized that threaded
spindles with a limit of error of 0.001" in one-foot
lengths are commercially possible. In micrometer con-
struction with a used length of screw thread of one inch
only, the error is negligible. A micrometer head con-
sists of a spindle, threaded forty to the inch, fitted
through a threaded sleeve, having an enclosing thimble
fastened to its outer end. Suitable graduations made
axially on the threaded sleeve combined with the grad-
uations on the edge of the rotating thimble give direct
readings of one-thousandth part of one inch. By means
of a vernier scale used on the rear of the sleeve direct
contact readings as small as one ten-thousandth part of
one inch can be readily made.
Micrometer screws are mounted in a frame which
may be varied in shape and size to render it convenient
for the desired purposes. The contact points are also
shaped to the particular use desired, and instruments of
this type in a variety of styles and of the highest degree
of accuracy, convenience, and finish are purchasable,
for either inside or outside measurements.
For measurement by thousandths up to one-half inch.
19
THE STARRETT BOOK
Micrometer Measurements
The limit of accuracy obtained by measuring between contacts depends on
the graduations on the instrument. It is evident that as the fineness of the
graduation increases, the chances for mistaking one graduation for another also
increase so that some other method of determining extremely accurate measure-
ments must be devised.
The commpn instrument for making such measurements is known as a
micrometer-caliper. It combines the double contact of the slide calipers with
a screw adjustment which may be read with great accuracy.
20
THE STARRETT BOOK
HOW TO READ A MICROMETER
The pitch of the screw threads on the concealed part
of the spindle is forty to an inch. One complete revolu-
tion of the spindle, therefore, moves it lengthwise one
fortieth (or twenty-five thousandths) of an inch. The
sleeve D is marked with forty lines to the inch, corre-
sponding to the number of threads on the spindle.
Each vertical line indicates a distance of one-fortieth
of an inch. Every fourth line is made longer than the
others, and is numbered 0, 1, 2, 3, etc. Each numbered
line indicates a distance of four times one-fortieth of
an inch, or one tenth.
The beveled edge of the thimble is marked in twenty-
five divisions, and every fifth line is numbered, from
to 25. Rotating the thimble from one of these marks
to the next moves the spindle longitudinally one twenty-
fifth of twenty-five thousandths, or one thousandth of
an inch. Rotating it two divisions indicates two thou-
sandths, etc. Twenty-five divisions will indicate a com-
plete revolution, .025 or one-fortieth of an inch.
To read the micrometer, therefore, multiply the num-
ber of vertical divisions visible on the sleeve by twenty-
five, and add the number of divisions on the bevel of
the thimble, from to the line which coincides with the
21
THE STARRETT BOOK
horizontal line on the sleeve. For example, in the en-
graving, there are seven divisions visible on the sleeve.
Multiply this number by twenty-five, and add the number
of divisions shown on the bevel of the thimble, 3. The
micrometer is open one hundred and seventy-eight thou-
sandths. (7 X 25 = 175 and 175 + 3 = 178.)
HOW TO READ A VERNIER
Readings in ten thousandths of an inch on caliper
squares, micrometers, etc., are obtained by the use of
a Vernier, named from Pierre Vernier, who invented the
device in 1631. For the Vernier caliper, the scale on the
tool is graduated in fortieths of an inch (0.25). On the
Vernier plate is a distance divided into twenty-five parts,
and these twenty-five divisions occupy the same distance
as twenty-four divisions on the scale. The difference
between one of the twenty-five spaces and one of the
twenty-four spaces is one twenty-fifth of one-fortieth,
or one thousandth of an inch.
To read the tool, note how many inches, tenths (or
.100), and fortieths (or .025) the mark on the Vernier
is from the mark on the scale; then note the number of
divisions on the Vernier from to a line which exactly
coincides with a line on the scale.
In the engraving above, the Vernier has been moved
to the right one and four-tenths and one-fortieth inches
THE STARRETT BOOK
(1.425"), as shown on the scale, and the eleventh line
on the Vernier coincides with a line on the scale. Eleven
thousandths of an inch are, therefore, to be added to
the reading on the scale, and the total reading is one and
four hundred and thirty-six thousandths inches (1.436"),
which is the distance the jaws have been opened.
HOW TO READ A VERNIER MICROMETER
Readings in ten thousandths of an inch are obtained
ON THE MICROMETER by the use of a Vernier, which
operates on the same principle as the Vernier on the
caliper. In this case, however, ten divisions on the sleeve
occupy the distance of nine divisions on the thimble.
The difference between the width of one of the ten
spaces and one of the nine spaces is one-tenth of a
THIMBLE
LO O
JJ'I J I I I I
division on the thimble. Now each division on the
thimble represents one-thousandth of an inch, and one-
tenth of one-thousandth equals One ten-thousandth. To
read a ten-thousandth micrometer, first note the thou-
sandths as in the ordinary micrometer. Then observe
the line on the sleeve which coincides with a line on the
thimble. In the diagram shown above there are nine
vertical divisions visible on the sleeve, and 9 X 25 = 225,
so that the reading of the ordinary micrometer would be
.225. Line marked "7" on the sleeve coincides with a
line on the thimble and, therefore, we add seven to the
reading of the ordinary micrometer. This seven is seven
ten-thousandths (.0007), and the readings will be .2257.
THE STARRETT BOOK
JHHsflHiE
h-r-izsl ta^u.'V'
'.062S
i 3 .16
\S .312
L/M7S
Half-Inch Micrometer
For measurement
by thousandths up to
one-half inch.
The anvil is shortened, for
use in places where the ordinary
anvil is too long to be inserted.
Has lock nut and ratchet
stop.
Quick-Adjusting Micrometer
Has ratchet stop and lock nut.
Six-Inch Micrometer
For measuring round work to 4% inches and flat
work to 6 inches.
24
THE STARRETT BOOK
OPERATION AND ADJUSTMENT OF MICROMETERS
QUICK MEASUREMENTS. A micrometer having the
quick-adjusting feature can be instantly opened or closed
to any size within its capacity. Pressure of the finger
on the end of the plunger allows the spindle to move
instantly to the desired size without turning the thimble.
When the finger is removed, fine adjustments may be
made in the usual way.
MICROMETER AS A GAGE. By means of a knurled
lock nut the spindle can be firmly fixed in position,
making the micrometer a solid gage. Turning the lock
nut contracts a split bushing around the spindle, keep-
ing it central and true.
READJUSTMENT FOR WEAR. When slight wear
makes correction necessary, the readjustment is accom-
plished by various means depending upon the kind of
micrometer. With the Starrett micrometer the anvil is
fixed, not movable, and correction is quickly made by
inserting a spanner wrench and turning until the line on
the sleeve coincides with the zero on the thimble. This
feature does away with the frequent use of a test piece.
25
THE STARRETT BOOK
TRANSFERRING MEASUREMENTS
Transferring a measurement may be a delicate job
or not, wholly depending upon the degree of accuracy
sought. The most common of all machine-shop tools
for transferring measurements are steel rules and
spring calipers. With these tools, either in combination
or used separately, are made the bulk of common ma-
chine-shop measurements, whether those of inside or
outside surfaces.
STEEL RULES
These are thin blades of steel of varying lengths,
widths, and thicknesses, usually graduated in inches and
various subdivisions of the inch upon each edge of both
sides and often at the ends. The makers term the vari-
ous subdivisions of the inch by graduation numbers,
for example, No. 4 Graduation, 1st. edge 64ths; 2d. edge
32ds; 3d. edge 16ths; 4th. edge 8ths. By means of slid-
ing or fixed attachments a great variety of length meas-
urements may be made with the ordinary steel rule.
SPRING CALIPERS
The most commonly used tool for contact measure-
ments is the ordinary spring caliper, which is used for
measuring over surfaces or between surfaces. In- shop
language this is called making-outside-or-inside meas-
urements. The legs of the spring caliper are curved
down, to make two opposite contact points, the distance
between being controlled by a screw which works against
a tension spring. For either outside or inside measure-
ments they may be set to or they may be read to a
graduated steel rule. In this way a workman can trans-
fer lengths with an error of less than 0.002". Where
THE STARRETT BOOK
specially accurate spring caliper measurements are de-
sired, fixed gages are used for setting the contact points.
The degree of accuracy of contact is dependent upon
what the workman terms "feel." To accurately transfer
a dimension with spring calipers the sense of "feel"
must be well developed by the workman, for the contact
points are at the ends of very slender arms.
Spring calipers, both for inside and outside work,
can be set to dimensions either larger or smaller than
the gages used by introducing thickness strips between
the contact points and the over or inside surfaces.
Hard, thin tissue-paper may be used as thickness
strips, or, better still, steel thickness gages or " feelers."
Calipering Over a Flange
27
THE STARRETT BOOK
SPRING DIVIDERS
In this tool the contacts are points at the ends of
straight legs. Dividers are used for measuring dimen-
sions between lines or points, for transferring lengths
taken direct from a graduated steel rule, or for scribing
circles or arcs. " Feel " does not
enter to such an extent into the
transfer of dimensions when using
spring dividers as it does with
spring calipers; however, a certain
delicacy of touch is essential. A
magnifying glass is a wonderful
help for the accurate transfer of
dimension with dividers. If a con-
siderable length is to be transferred,
it is best to use the type where the
points are adjustable along a bar,
known as a Universal Divider, for
the points do not then incline to
the surfaces worked upon.
THE STARRETT BOOK
FITS AND FITTING
In machine construction many of the parts bear
such a close and important relation to one another,
that a certain amount of hand fitting is essential to make
the surface contacts as they should be. If the surfaces
in contact are to move on each other the fit is classed
as a sliding or running fit. If the surfaces are to make
contact with sufficient firmness to hold them together
under ordinary use, the fit is classed either as a driving,
shrink, or forced fit.
SLIDING FIT. Under this head may be classed the
litting of cross and traversing slides of lathes, milling
machines, drilling machines, boring machines, grinding
machines, and planers. In most of these fits the moving
and stationary parts are held in contact with each other
by means of adjustable contact strips or gibs, sometimes
known as packing strips. In some cases, such as the
tables of grinding and of planing machines, their weight
keeps them in sufficiently close contact.
RUNNING FITS. The journal bearings of spindles,
crank shafts, line shafting, etc., are classed under this
heading.
FORGED FITS AND SHRINK FITS. Under this
head are classed those fits where the separate parts must
become in use as if they were a single piece; as, for
example, the crank pins and axles in locomotive driving
wheels, the cutter heads and spindles of numerous wood-
working machines, as .well as many other cases.
LIMITS. In the case of running and of sliding bear-
ings a certain amount of hand fitting is necessary to
obtain desired results, and in all cases certain limiting
requirements obtain. In sliding and running bearings
the limits are usually those of alignment and of contact,
while in either journal bearings or in flat sliding bear-
ings it is essential that certain accurate contact between
29
THE STARRETT BOOK
the surfaces shall be made, and there will also be a limit
of alignment with other parts of the machine. For ex-
ample, in the engine lathe the ways or vees and the
cross slide of the tool carriage must be parallel to or
at right-angles to the axis of the spindles within set
limits. In engine lathe construction the limit set for
this is 0.001" in a foot of length. In testing the parts
use is made of the Universal Test Indicator with the
needle reading on a dial or upon a sector arm. The
indicator may be clamped to a test bar, a straight edge,
or direct to the lathe spindle; also, if desired, it can be
and often is held upon a special slider stand fitted to
the vees of the machine.
In the making of shrinkage and forced fits the
limits are usually those of size. The amount of pressure
necessary to place the two parts together is the limiting
fact in the case of forced fits. In forcing the axles into
locomotive driving wheels, the specifications may limit
the pressure to between one hundred to one hundred
and fifty tons. However specified, it in fact reduces to
limits of size and the use of measuring tools. These can
be of the direct reading contact type, as the micrometer
and vernier bar, or of the indirect reading contact type,
as, for example, the ordinary spring caliper used in con-
junction with thickness gages or "feelers."
AMOUNTS TO LEAVE. Where pins, spindles, etc.,
are to be forced irito holes, or where collars, hubs,
flanges, and other machine parts are to be shrunk on to
spindles, it is customary to make the diameter allow-
ance upon the spindle rather than upon the hole. The
amount which it is necessary to add to the spindle or
shaft diameter must of necessity vary with the length
and diameter of the hole, the metals used, and the form
of the surrounding hub. The following tables give cer-
tain practice.
30
THE STARRETT BOOK
Allowances for Different Classes of Fits Table 1
(Newall Engineering Co.)
Class
Tolerances in Standard Holes*
Nominal
Diameters
Up to W
%.M'
!Vi6"-2"
2yi"-3"
3*M"
4*"-5
A
High Limit
Low Limit
Tolerance
+0.0002
0.0002
0.0004
+0.0005
00002
0.0007
+0.0007
0.0002
0.0009
+0.0010
0.0005
0.0015
+0.0010
0.0005
0.0015
+0.0010
0.0005
0.0015
B
High Limit
Low Limit
Tolerance
+0.0005
0.0005
0.0010
+0.0007
0.0005
0.0012
+0.0010
0.0005
0.0015
+0.0012
0.0007
0.0019
+0.0015
0.0007
0.0022
+0.0017
0.0007
0.0024
Allowances for Forced Fits
High Limit
+0.0010
+0.0020
+0.0040
+0.0060
+0.0080
+0.0100
F
Low Limit
+0.0005
+0.0015
+0.0030
+0.0045
+0.0060
+0.0080
Tolerance
0.0005
0.0005
0.0010
0.0015
0.0020
0.0020
Allowances for Driving Fits
High Limit
+0.0005
+0.0010
+0.0015
+0.0025
+0.0030
+0.0035
D
Low Limit
+0.0002
+0.0007
+0.0010
+0.0015
+0.0020
+0.0025
Tolerance
0.0003
0.0003
0.0005
0.0010
0.0010
0.0010
Allowances for Push Fits
High Limit
0.0002
0.0002
0.0002
0.0005
0.0005
0.0005
p
Low Limit
0.0007
0.0007
0.0007
0.0010
0.0010
0.0010
Tolerance
0.0005
0.0005
0.0005
0.0005
0.0005
0.0005
Allowances for Running Fits t
X
High Limit
Low Limit
Tolerance
0.0010
0.0020
0.0010
0.0012
0.0027
0.0015
0.0017
0.0035
0.0018
0.0020
0.0042
0.0022
0.0025
-0.0050
0.0025
0.0030
00057
0.0027
Y
High Limit
Low Limit
Tolerance
0.0007
0.0012
00005
0.0010
0.0020
0.0010
00012
0.0025
0.0013
0.0015
0.0030
0.0015
0.0020
0.0035
0.0015
-0.0022
0.0040
0.0018
z
High Limit
Low Limit
Tolerance
0.0005
0.0007
0.0002
0.0007
0.0012
0.0005
0.0007
0.0015
0.0008
0.0010
0.0020
0.0010
0.0010
0.0022
0.0012
0.0012
0.0025
0.0013
* Tolerance is provided for holes, which ordinary standard reamers can pro-
duce, in tw9 grades, Classes A and B, the selection of which is a question for the
user's decision and dependent upon the quality of the work required ; some prefer
to use Class A as working limits and Class B as inspection limits.
t Running fits, which are the most commonly required, are divided into three
grades : Class X for engine and other work where easy fits are wanted ; Class Y
for high speeds and good average machine work ; Class Z for fine tool work.
31
THE STARRETT BOOK
LIMITS OF TOLERANCE
While it is possible to produce machine parts with
measurements refined to any degree of accuracy, ex-
treme precision may prove too costly for commercial
work.
To avoid waste of time, lahor, and money, the Taft-
Peirce Manufacturing Company has formulated a set of
rules which defines the degree of accuracy to be expected
in those cases where specifications and drawings do not
call for greater precision than the rules provide for.
(1) Full information regarding limits of tolerance
should be clearly shown by drawings submitted, or be
definitely covered by written specifications to which
reference must be made by notations on the drawings.
(2) Where the customer fails to supply proper data
as to limits, this Company's Engineers will use their
best judgment in deciding just what limits it may be
advisable to work to. The Company will not, in any
event, assume responsibility for possible excessive cost
brought about through working to closer limits than
may be necessary nor for permitting greater latitude
than may subsequently be found to be proper.
(3) Where dimensions are stated in vulgar frac-
tions with no limits of tolerance specified, it will be
assumed that a considerable margin for variation from
figured dimensions is available; unless otherwise or-
dered, the Company's Engineers will proceed according
to the dictates of their best judgment as to what limits
should be taken.
(4) For all important dimensions Decimal figures
should be used and limits clearly stated on detail draw-
ings. If Decimal figures are not used for such dimen-
sions a notation referring to the degree of accuracy
required must be placed prominently on the drawing.
(5) It is frequently necessary to reduce fractions
32
THE STARRETT BOOK
representing fourths, eighths, sixteenths, thirty-seconds,
and sixty-fourths to decimal equivalents. When a dimen-
sion of this character is expressed in a decimal equivalent
and carried out to three, four, or five places and limits
are not specified it will be assumed that a limit of plus
or minus .0015 is permissible unless otherwise ordered.
(6) Where dimensions are stated in decimal figures
derived by other processes than those explained in para-
graph five, but with limits not specified, the following
variations from dimensions stated may be expected:
Two place decimals .005 plus or minus
Three " " .0015
Four " " .0005
Five " " .0002
(7) Where close dimensions, such as the location of
holes from center to center in jigs, fixtures, machine
parts, and other exact work of like character are re-
quired, detail drawings should be prominently marked
"ACCURATE" and clear instructions be given.
(8) The dimensions of internal cylindrical gages,
external ring gages, snap gages, and similar work speci-
fied to be hardened, ground, and lapped, will be obtained
as accurately as the best mechanical practice applying
to commercial work of the particular grade specified
will permit.
(9) As drilled holes vary in size from .002" to .015"
(and in some cases even more) over the size of the drill
used, those which require to be made accurately to defi-
nitely specified sizes should be either reamed, ground, or
lapped, and detail drawings thereof should bear nota-
tions accordingly.
(10) U. S. Standard form of thread and pitches will
be used for *4 -inch and all sizes above. A. S. M. E. Stand-
ard will be used for numbered sizes below ^4 -inch. In
the absence of specifications to the contrary, U. S. Stand-
ard form of thread will be used for all SPECIAL sizes.
33
THE STARRETT BOOK
THE STARRETT BOOK
BENCH WORK
Bench work includes laying out, chipping, filing,
polishing, hand reaming, hand tapping, and all the many
shop jobs done at the bench or in a vise.
LAYING OUT. This is the shop term which includes
the placing of lines, circles, and centers upon curved or
flat surfaces for the guidance of the workman. It is some-
what analogous to mechanical drawing. It differs in one
important respect, however, that while a line drawing
is seldom scaled and therefore exact accuracy of spac-
ing is not required; in laid out work, the lines, circles,
centers, etc., are to be followed exactly. All lines, cen-
ters, etc., should therefore be exactly located and placed,
and all scriber, divider, and center points should, while
in use, be exact and sharp. Particular care must be
maintained to insure fine and accurate laying out.
PREPARING THE SURFACE. If work of no special
accuracy is desired, carefully rubbing chalk, or white
lead mixed with turpentine, upon the surface of the
work will be sufficient as a coating. For fine exact lay-
outs a special marking solution must be used. The one
in common shop use is a mixture of one ounce copper
sulphate to four ounces water. A little nitric acid may
with advantage be added. This solution applied to a
cleaned iron or steel surface gives a dull coppered sur-
face, and the finest line scribed upon it is brilliantly
visible.
SCRIBING LINES. The usual scribing points are
those common to dividers, hermaphrodite calipers,
scratch awls, scratch gages, surface gages, and trammel
points. Combined with the scribing points, may be used
steel rules, bevel protractors, steel squares, steel straight
edges, levels, end measuring rods, micrometer or vernier
height and depth gages, and the various center punches.
Ability to so combine and make use of the various tools
35
THE STARRETT BOOK
THE STARRETT BOOK
as to insure accuracy is a considerable asset to the lay-
ing-out man.
PROTRACTORS
As made for machine-shop use the common protrac-
tor is provided with attached straight edges, and can be
used either to measure or to lay off lines at an angle to
each other. Measuring the angularity of two or more
lines with a protractor is termed "reading the angles."
As oftentimes its use is determining the angle made by
two surfaces (a bevel), the tool is usually termed a bevel
protractor. Protractors for common shop use are grad-
uated to degrees through a length of circumference of
one hundred and eighty degrees. An attached vernier
enables the user to read angles to one-twelfth of a degree
(five minutes).
LAYING OUT PLATE. If desirable results are to be
37
THE STARRETT BOOK
obtained in laying out flat work, special metal plates
upon which to rest the work and the tools must be pro-
vided. These are known as leveling, surface, or laying-
out plates; they furnish an accurate plane surface upon
which work and tools may be placed. The size of these
plates varies from those of small areas used in laying out
small jigs, etc., to those for large pieces, having sides
several feet in length. The work may be laid directly
upon the surface of the plate or held upon leveling strips
or blocks placed on the plate, and the gages, squares, and
other tools used around the work. In other cases it is
convenient to clamp the work to knee or angle irons,
which are then placed upon the leveling plate.
CHIPPING
Formerly many of the surfaces of machine parts
were hand-chipped and filed to a fit. While the mechanic
in the modern shop can usually find methods of machin-
ing most of the surfaces he needs to fit up, there are still
occasions when the work has to be hand-chipped.
TOOLS USED. The common chipping tools are a
hand hammer and a hand chisel. The hand hammer
should weigh not less than three-quarters of a pound
nor over two pounds, and may be either of the ball peen
or flat peen type. A chipping hammer should balance
well in the hand when fitted to a handle not more than
sixteen inches long. The handle near where it enters
the hammer should be thinned and worked down to a
shank that is somewhat flexible, so that the shock to the
arm and hand will be less. The face of a good chipping
hammer should crown slightly.
Chipping chisels, ordinarily termed cold chisels, are
of various sorts, and are often known by the shape of
the cutting end; for example, flat, cape, roundnose, dia-
mond, and gouge chisels. The steel from which they are
THE STARRETT BOOK
made should be eighty to ninety point carbon, of octa-
gon cross-section, with the cutting end forged to the
desired shape, well packed by the forge hammer, hard-
ened, and the temper drawn to a medium blue. The
hammer end of the chisel should be forged from the
octagon to a reduced round but not hardened. Flat-
chipping and cape chisels should be ground with straight,
symmetrical, cutting edges, at as acute an angle as the
nature of the work will permit.
39
THE STARRETT BOOK
In hand chipping the hammer handle should be
grasped near the end and the hammer swung free from
over the shoulder with an easy forearm movement.
Hold the chisel loosely in the hand at an angle with the
work that permits an even chip of right depth. The
vision should be directed to the cutting edge of the
chisel, rather than at the end struck by the hammer.
Avoid gripping hammer or chisel tightly, as this rapidly
tires the hand and arm.
In shops which have compressed air, use is made of
the modern pneumatic chipping hammer, which does
remarkable work of the heavier sorts.
FILING
The file is essentially a finishing tool, and in skilled
hands surfaces may be made very accurate and smooth.
Files are designated thus (a) by their length this
does not include the tang; (b) by their cross-section, as,
for example, square, round, half-round, triangular, flat,
knife-edge, etc.; (c) by their cut single or double cut;
(d) by the degree of coarseness.
Files for some purposes are made tapered in their
length, and for other uses have straight sides. The de-
grees of coarseness are designated by the following
names as rough, coarse, bastard; 2d cut, smooth, and
dead smooth; extra fine files are designated by numbers,
No. 00, No. 0, No. 1, etc., to No. 8. The degree of coarse-
ness varies with the length, for example, an 8-inch file
second cut is coarser than a shorter file bastard cut.
This confuses the user somewhat, unless he is familiar
with practice.
Single-cut files are those having teeth made by single
parallel cuts across the face at an angle of twenty-five
degrees. In double-cut files the teeth are made by break-
ing up the single cuts into points by a second cut made
at an angle with the first.
40
THE STARRETT BOOK
Rasp files are those having teeth made by a punch.
Used for hoofs, wood, etc.
HEIGHT OF WORK. This must of necessity vary
with the height of the worker. A common rule is to have
it the height of the worker's elbow as he stands erect.
For very light free-hand filing the work may be much
higher, in some cases the height of the shoulders.
41
THE STARRETT BOOK
POSITION OF THE HANDS. If the worker wishes
to avoid tiring, position is very important; position also
has direct bearing upon the quality and quantity of the
product. The worker should clasp the file handle with
the extended thumb on top, grasping the point with the
fingers and thumb of the remaining hand with thumb
on top. In heavy filing the point of the file may be
grasped by the fingers and the palm of the hand with
the palm on top.
In hand-filing the worker should train his hands,
arms, and body to carry the file across the work with
regular, even, and controlled strokes. As the file is in
no sense self-guided the worker must train his body to
regular controlled motions if he is to do effective work.
DRAW FILING. Used to set the grain somewhat
smoother than regular cross-filing. The worker should
clasp the blade of file near its ends in each hand and
then draw the file, held crosswise, along the length of
the work. A fine grain surface results.
TESTING FLAT FILING. Flat work is tested by the
use of steel straight edges, steel squares, bevel protrac-
tors, etc.
THE STARRETT BOOK
POLISHING
Where a particularly smooth surface is necessary, as,
for example, journal bearings, or where brilliancy of
finish is desired, the surfaces are polished with some
fine abrasive. For ordinary polishing of machine parts,
journals, etc., common grain abrasive is used, glued to
cloth or leather.
Grain abrasives are known by numbers, as, for ex-
ample, No. 100, which means that the particles are of
a size to readily pass through a sieve having one hundred
meshes to the linear inch. The finer sizes are often
known as flours.
GRADES OF EMERY
The numbers representing the grades of emery run
from 8 to 120, and the degree of smoothness of surface
they leave may be compared to that left by files as follows :
8 and 10 represent the cut of a wood rasp.
16 20 a coarse rough file.
30
40
60
80
100
120F and FF
an ordinary rough file,
a bastard file,
a second cut-file,
a smooth file,
a superfine file,
a dead-smooth file.
SEVERING METAL WITH HACK SAWS
Hack saws are narrow, thin blades of hardened steel
with teeth cut along one edge, and are used for severing
metal. They are held in suitable hand or power frames,
which have the necessary adjustments for holding the
blade in stiff tension. It is obvious that it requires care
and good sense in using a hack-saw blade if good results
are expected.
If the stock to be cut is both hard and thin, particular
care is required to avoid injuring the blade.
43
THE STARRETT BOOK
CUTTING SPEED. When hack sawing, under aver-
age conditions and without a lubricant, a cutting speed
of fifty to sixty strokes per minute should be main-
tained. If the saw is used in a power machine, and the
material is soft steel, a cutting speed of one hundred
strokes per minute may be made, using a suitable lubri-
cant. Unannealed tool steel should be cut under the
above conditions at not to exceed sixty strokes per
minute.
MOUNTING THE BLADE. The blade when mounted
in a hand-frame should have the cutting-teeth rake for-
NO.I45
TAKES 8 IN.TOI2 IN. SAWS
ward; that is to say, the saw should cut on the for-
ward stroke. In machine cutting this is usually so, but
not so with some makes of machines. The cutting stroke
is always the pressure stroke, and the return stroke is
made as light as convenient without actually lifting the
blade from its work.
The blade should be under considerable tension
when in use. It must be held in the plane being cut,
and all tendency to bending the blade avoided. Suitable
blades and frames may be purchased for almost every
service, and the user should consider this fact if com-
mercially economical results are desired.
44
THE STARRETT BOOK
HACK SAW MACHINE
Hack saw blades used in cutting up bar stock or
structural shapes are much more efficient in a machine so
designed that its several motions and adjustments can be
properly controlled. Such a machine is as sensitive to
the operator as a hand frame.
The machine shown above has been especially de-
signed to efficiently operate hack saw blades. The base
column carries the working parts and the work-holding
vise. By means of suitable weights, the cutting pressure
upon the blade may be regulated according to the material
being severed, and the stroke length of the blade-carrying
frame can be adjusted to use the entire blade length, no
matter what diameter of bar is being severed, thus getting
the full efficient service from each blade.
To avoid blade breakage through careless handling,
a safety device in the form of a dash pot is connected
with the blade-carrying frame to prevent the blade from
being dropped suddenly upon the work. The blade-carry-
45
THE STARRETT BOOK
ing frame is raised by a foot lever leaving the hands free
for work adjustments and measurements. The cutting
lubricant is conveyed to the blade from a tank in the
column by means of a small rotary pump.
What Hack Saw to Use
No. 103 in hand frames, to cut cast steel, cast iron, tool steels and all solid
metals.
No. 103B in hand frames, to cut cold rolled stock and soft metals.
No. 102 in hand frames, to cut sheet metal and tubing 16 to 18 gage.
No. 253 in hand frames, to cut sheets and tubing thinner than 18 gage.
No. 112 for heavy hand frame work and light power machines, on tool steels.
No. 112B for light power machine work on soft steel, and heavy hand frame
work.
No. 114 for general work in medium weight power machines.
No. 115 on electrical conduit, pipe, brass stock, light angle and channel iron.
No. 255 on high speed machines cutting tool steels.
No. 255B on high speed machines cutting machinery steel, cast iron, etc.
No. 262 for cutting angle iron, brass stock and ornamental iron work.
No. 254 for heavy high speed machines, to cut tool steel.
No. 254B for heavy high speed machines, to cut cold rolled shafting and
machinery steel.
No. 259 for cutting iron pipe, light structural iron, auto frames, etc.
No- 256 for extra heavy power machines, to cut tool steel.
No. 256B for extra heavy power machines.
46
THE STARRETT ROOK
DRILLING
DRILLS. A drill is an end-cutting tool, consisting
usually of two cutting edges set at an angle with the
axis. The more common types of drills are flat flat-
twisted straight-fluted spiral-fluted and gun-barrel.
The most common, and for most purposes the most effi-
cient, type is the spiral-fluted, known as a twist drill.
Twist drills are made with two, three, or four cut-
ting lips. The two-lip drill is used when drilling solid
stock. The three and four lip drills are used for en-
larging holes previously cored or drilled. When drilling
solid stock with a two-lipped drill, the point of the drill
controls the cutting edges, and if the drill is correctly
ground the resulting hole will be reasonably round,
straight, and the size of the drill. When a drill is used
for enlarging holes already made, either by coring or by
previous drilling, the drill is guided by its sides and a
three or four fluted drill will give better results.
FORM OF POINT. In
the types referred to all
except gun-barrel drills
are cone-pointed on the
cutting end. The gun-
barrel drill, used when
especially straight, round,
and true holes are essen-
tial, has a blunt end with
a single cutting lip.
A cone-pointed drill of two or more cutting lips
depends for its efficient working upon four factors:
(a) All the cutting lips shall have the same inclina-
tion to the axis of the drill.
(b) Cutting lips should be of exactly equal length.
(c) A proper lip clearance of the surface back of
the cutting edges.
FIG. 1
47
THE STARRETT ROOK
FIG. 2
(d) A correct angle of lip clearance.
Figs. 1, 2, and 3 show the result of careless free-hand
grinding. Figs. 4 and 5 show how to test the length
of the cutting lips, also their inclination to the axis.
After sharpening a
drill free-hand, use the
hand-feed at first and ob-
serve (a) the chips made
by the cutting; (b) the
size of the hole. If the
cutting lips are shaped to
a proper clearance, the
chips will curl as they
start from the cutting
edge; but if the cutting
lips lack a proper clearance the resulting chips have the
appearance of being ground off rather than freely cut.
If the cutting lips are of uneven length the hole will be
enlarged over the diameter of the drill. Drillings from
cast iron should look as in Fig. 6, and those from steel
as in Fig. 7, if the drill is properly sharpened.
Free-hand grinding
results are usually so dis-
appointing that in most
machine shops the drills
are sharpened in a spe-
cial drill-grinding ma-
chine. The design of this
machine is such, that
when it is set for grind-
ing any size of drill the
cutting lips are made of
equal length and of the correct form. Fig. 8 shows how
the cutting lip is located to correctly grind the edges.
FEEDING THE DRILL. To get the best results from
drills and drilling machines, the drill should advance
FIG. 3
48
THE STARRETT BOOK
into the work a definitely regulated amount for each
revolution. The distance which the drill advances per
revolution is termed the FEED, and must be adjusted
to suit the conditions under which the work is being
performed. Table No. 2 gives the feeds per revolution
recommended by one manufacturer of drills. They are
recommended for average conditions; they can be greatly
exceeded under some conditions, but must be reduced
for others.
FIG. 4 FIG. 5
Feeding the drill freehand, if skilfully done, may
answer in certain cases, but is less effective than power
feeds, except for small wire drills.
DRILL SPEED. This is the surface or peripheral
speed of the drill in feet per minute, and is rated at the
outer diameter. Under average conditions the peripheral
speed recommended for carbon steel drills is thirty feet
49
THE STARRETT BOOK
to forty feet, and for high-speed drills seventy feet to
one hundred feet. Working conditions may at times
cause a change in these figures. When the extreme outer
corners of the cutting edges wear rapidly it is evidence
of too high a surface speed.
FIG. 6
FIG. 7
Table No. 3 gives the revolutions per minute at
which to run drills for various cutting or surface
speeds. For example, with a 1-inch drill and seventy
feet as the selected cutting speed, read across from
1-inch in the left-hand column and under heading 70'
find 267, the revolutions per minute.
FIG. 8
60
THE STARRETT BOOK
Speeds and Feeds for Drilling* Table 2
High-Speed Steel Drills
Size
of
Feed
Bronze,
Brass,
OAA
Cast
Iron,
An-
Cast
Iron,
Mild
Steel,
Drop
Mai.
Iron,
Tool
Steel,
Cast
Steel,
Drill
Re C v.
300
Feet
nealed,
170
Hard,
80 Feet
120
Feet
Feet
90
Feet
60
Feet
40
Feet
Feet
Inches
Inches
R.P.M.
R.P.M.
R.P.M.
R.P.M.
R.P.M.
R.P.M.
R.P.M.
R.P.M.
Vie
0.003
18300
10370
4880
7320
3660
3490
3660
2440
Vs
0.004
9150
5185
2440
3660
1830
2745
1830
1220
%e
0.005
6100
3456
1626
2440
1210
1830
1220
807
Vi
0.006
4575
2593
1220
1830
915
1375
915
610
H
0.007
3660
2074
976
1464
732
1138
732
490
%
0.008
3050
1728
813
1220
610
915
610
407
0.009
2614
1482
698
1046
522
784
522
348
0.010
2287
1296
610
915
458
636
458
305
0.011
1830
1037
488
732
366
569
366
245
0.012
1525
864
407
610
305
458
305
203
%
0.013
1307
741
349
523
261
392
261
174
1
0.014
1143
648
305
458
229
349 -
229
153
0.016
915
519
244
366
183
275
183
122
1V2
0.016
762
432
204
305
153
212
153
102
1%
0.016
654
371
175
262
131
196
131
87
2
0.016
571
323
153
229
115
172
115
77
Carbon Steel Drills
Size
of
Drill
Feed
JK.
Bronze,
Brass,
150
Feet
Cast
Iron,
An-
nealed,
85
Cast
Iron,
Hard,
40 Feet
Mild
Steel,
60
Feet
Drop
Forg.,
30
Feet
Mai.
Iron,
45
Feet
Tool
Steel,
30
Feet
Cast
Steel,
20
Feet
Feet
Inches
Inches
R.P.M.
R.P.M.
R.P.M.
R.P.M.
R.P.M.
R.P.M.
R.P.M.
R.P.M.
We
0.003
9150
5185
2440
3660
1830
2745
1830
1220
0.004
4575
2593
1220
1840
915
1375
915
610
9ie
0.005
3050
1728
813
1220
610
915
610
407
V4
0.006
2287
1296
610
915
458
636
458
305
0.007
1830
1037
488
732
366
569
366
245
%
0.008
1525
864
407
610
305
458
305
203
7 Ae
0.009
1307
741
349
523
261
392
261
174
%
0.010
1143
648
305
458
229
343
229
153
%
0.011
915
519
244
366
183
275
183
122
K
0.012
762
432
204
305
153
212
153
102
%
0.013
654
371
175
262
131
196
131
87
1
0.014
571
323
153
229
115
172
115
77
ttt
0.016
458
260
122
183
92
138
92
61
m
0.016
381
216
102
153
77
106
77
51
1%
0.016
327
186
88
131
66
98
66
44
2
0.016
286
162
77
115
58
86
58
39
* Copyright, 1911, by the Henry & Wright Mfg. Co.
51
THE STARRETT BOOK
The Speed of Drills Table 3
A feed per revolution of .004 to .007 for drills M inch and smaller, and from
.007 to .015 for larger is about all that should be required.
This feed is based on a peripheral speed of a drill equal to :
30 feet per minute for steel ; 35 feet per minute for iron ; 60 feet per minute
for brass.
It may also be found advisable to vary the speed somewhat according as the
material to be drilled is more or less refractory.
We believe that these speeds should not be exceeded under ordinary cir-
cumstances.
Table of Cutting Speeds
Ft. per
Minute
15'
20'
25'
30'
35'
40'
45'
50'
60'
70'
80'
Diam.
REVOLUTIONS PER MINUTE
ttein.
917.
1223.
1528.
1834.
2140.
2445.
2751.
3057.
3668.
4280.
4891.
%
459.
611.
764.
917.
1070.
1222.
1375.
1528.
1834.
2139.
2445.
tt
306.
408.
509.
611.
713.
815.
917.
1019.
1222.
1426.
1630.
ft
229.
306.
382.
458.
535.
611.
688.
764.
917.
1070.
1222.
ttj
183.
245.
306.
367.
428.
489.
550.
611.
733.
856.
978.
%
153.
204.
255.
306.
357.
408.
458.
509.
611.
713.
815.
7 Ae
131.
175.
218.
262.
306.
349.
393.
437.
524.
611.
699.
M
115.
153.
191.
229.
268.
306.
344.
382.
459.
535.
611.
%
91.8
123.
153.
184.
214.
245.
276.
306.
367.
428.
489.
%
76.3
102.
127.
153.
178.
203.
229.
254.
306.
357.
408.
%
65.5
87.3
109.
131.
153.
175.
196.
219.
262.
306.
349.
l
57.3
76.4
95.5
115.
134.
153.
172.
191.
229.
267.
306.
H6
51.0
68.0
85.0
102.
119.
136.
153.
170.
204.
238.
272.
m
45.8
61.2
76.3
91.8
107.
123.
137.
153.
183.
214.
245.
1%
41.7
55.6
69.5
83.3
97.2
111.
125.
139.
167.
195.
222.
1%
38.2
50.8
63.7
76.3
89.2
102.
115.
127.
153.
178.
204.
1%
35.0
47.0
58.8
,70.5
82.2
93.9
106.
117.
141.
165.
188.
1%
32.7
43.6
54.5
65.5
76.4
87.3
98.2
109.
131.
153.
175.
1%
30.6
40.7
50.9
61.1
71.3
81.5
91.9
102.
122.
143.
163.
2
28.7
38.2
47.8
57.3
66.9
76.4
86.0
95.5
115.
134.
153.
2K
25.4
34.0
42.4
51.0
59.4
68.0
76.2
85.0
102.
119.
136.
2V 2
22.9
30.6
38.2
45.8
53.5
61.2
68.8
76.3
91.7
107.
122.
2%
20.8
27.8
34.7
41.7
48.6
55.6
62.5
69.5
83.4
97.2
111.
3
19/1
25.5
31.8
38.2
44.6
51.0
57.3
63.7
76.4
89.1
102.
52
THE STARRETT BOOK
CUTTING COMPOUNDS. To maintain high cutting
speeds, it is necessary to use a lubricant. Those recom-
mended have stood the test of service :
For hard and refractory steel, turpentine, kerosene,
or soda water.
For soft steel and wrought iron, lard oil, or soda
water.
For brass, paraffine oil.
For aluminum, turpentine, kerosene, or soda water.
For cast iron, a jet of air if anything is used usu-
ally worked dry.
LAYING OUT. Locating the centers for drilled holes
upon the body of the work is termed "laying out." On
the smaller jobs, laying out and drilling are usually done
by the workman. Larger amounts of work warrant a
skilled "layer out."
Laying out for drilling comes under two heads, viz. :
APPROXIMATE and ACCURATE. Unless the holes when
drilled are to match up with other holes or with fixed
studs, it is enough if the center is laid off with a chalk
pencil and a steel rule. For jig, tool, and experimental
work, the centers must be accurately laid out and scribed
upon the surface of the work. The practice is to scribe
two or more lines which intersect at the exact desired
point as shown in Fig. 9. Assume that the link is to
FIG. 9
63
THE STARRETT BOOK
connect two studs. Proceed to scribe two intersecting
lines upon one of the hubs, as shown in Fig. 9, using a
combination square fitted with a center head. At the
intersection accurately place a light center-punch in-
dentation. Place one leg of a spring divider with its
point in the center mark and adjust the other leg to have
its point touch the edge line of the hub and note the
concentricity of the center. If correct, close dividers to
scribe a circle the diameter of the required drilled hole,
setting the points by the scale graduations upon a steel
FIG. 10
rule. Locate light center-punch marks on the scribed
circle as shown in Fig. 10.
When the work is laid out by another than the
FIG. 11
54
THE STARRETT BOOK
driller, a second circle, having a slightly greater diameter,
should be scribed. This check will show whether the
hole was drilled to the original lay out. If no impor-
tance is attached to the center to center distance of the
holes proceed as before with the second hub. Where
the center to center distance is important, set the points
of the universal dividers to the center length, and with
the point A, Fig. 11, in the previously located center mark
scribe on the opposite hub. Scribe a short line across
its face afterward, proceeding as before.
For all accurate work use the automatic center-
punch, Fig. 12, and for heavy work the machinists'
center-punch, shown in Fig. 13.
PREPARING THE SURFACE. For
accurate laying out, clean the machined
surfaces and wet the portion to be
worked upon with the copper sulphate
(blue vitriol) solution., When dry, the
surface will distinctly show any lines
which are made upon it. Chalk well
rubbed into the surface is sufficient for
the less accurate jobs.
STARTING THE DRILL.
After laying out and previous
to drilling, greatly enlarge the
center holes with a center-
punch to assist the starting of SCRIBING CIRCLES WITH DIVIDERS
the drill. Start the hole with
drill point in the enlarged center, using hand feed until
a reasonable dimple is made in the work. Observe if
this is central with the scribed circle, and if not central
use center gouge, as in Fig. 14, and repeat until accurate.
TO DRAW A DRILL. When starting a drill it often
has a tendency to slide or crowd off to one side. Where
it is essential that the drilled hole coincide or center
with some previously scribed circle or layout, the drill
55
THE STARRETT BOOK
FIG. 12
must be brought back into the correct posi-
tion. This is accomplished by the use of a
small gouge-pointed chisel, sometimes called
a center chisel, and the process is termed,
"drawing the drill." First, note toward which
side of the small dimple left by the drill-point
it is necessary to shift the drill. Then
chisel a small groove in that side of
the dimple.
If the start is very eccentric, sev-
eral chisel grooves may be necessary;
whereas, if only slightly eccentric, a
mere touch of the chisel will often
suffice. It is readily seen that the drill
is made to cut more easily where the
grooves are, and therefore the natural
resistance of the opposite side pushes
the drill toward the side cut by the
gouge-pointed chisel. Drill drawing
can only be done previous to reach-
ing the full diameter of cut.
HOLDING THE WORK. Careless-
ness in holding the work is respon-
sible for many drilling accidents. If
no special holding device is available,
the work should be held in a drilling
vise, clamped directly to the drilling-
machine table, or clamped to an angle
iron. Fig. 15 illustrates a method of
holding the work safely. When once
the work is clamped in position on
the drilling-machine table, adjust the
table to center the located hole with
the drill rather than reclamp the work.
HOLDING THE DRILL. In Fig.
16, at A, the drill is shown held di- FIG. 13
66
THE STARRETT BOOK
rectly in the spindle. This is a good method if several
holes of the same diameter are to be drilled at a single
setting. When frequent changing of the drill is neces-
sary, as in drilling holes of numerous sizes, using a
single-spindle machine, some form of quick-acting collett
chuck should be used. The changes can then be made
without stopping the machine.
FIG. 14
DRILLING FOR REAMER. When it is essential that
the holes be of an exact standard diameter, it is cus-
tomary to use a drill somewhat smaller than the given
diameter, and afterward ream the holes to standard size.
The amount left for reaming depends upon whether one
or two reaming operations are necessary, and whether or
not the reaming is to be done directly in the drilling
machine. If the drilling is done through jig bushings
and the holes are short as compared to their diameter,
H
FIG. 15
57
THE STARRETT BOOK
a single reaming operation will often suffice. If the holes
are relatively long, the drill should be 1/64" to 1/32"
smaller than the finished hole diameter, to allow for
passing a machine reamer 0.005" small through the hole
which is afterward hand-reamed. This method gives
results as accurate as any, except by grinding, and is
accepted practice for good work.
DRILLING FOR TAPPING. Where a full thread
depth is essential the hole to be tapped should be made
with a drill of a diameter smaller than the nominal
diameter of the bolt by an amount equal to double the
depth of the thread. In practice the nearest commercial
size of drill is listed for drilling tapped holes.
THE STARRETT BOOK
Letter Sizes of Drills Table 4
Diameter
Decimals
Diameter
Decimals
Inches
of 1 Inch
Inches
of 1 Inch
A i% 4
.234
N
.302
B
.238
%
.316
C
.242
P 2 V 6 4
' .323
D
.246
Q
.332
E M
.250
R 1 V32
.339
F
.257
s
.348
G
.261
T 23/ 64
.358
H 17/ 6 4
.266
U
.368
I
.272
V */8
.377
J
.277
W 2 %4
.386
K % 2
.281
X
.397
L
.290
Y i%2
.404
U 1% 4
.295
Z
.413
Sizes of Tap Drills Table 5
Tap
Diameter
Threads
per Inch
Drill for
V Thread
Drill for U. S.
Standards
Drill for
Whitworth
M
16, 18, 20
5 /32 %2 M/64
%6
3 /16
%2
16, 18, 20
%6 13 /64 13 /64
5 /16
16, 18
7 /32 15 /64
M
15 /64
*%
16, 18
1 A 17 /64
H
14, 16, 18
M %2 %2
%2
%2
%2-
14', 16, 18
19 /64 2 V 6 4 2 V64
7 /16
14,16
21 /64 ^32
1 VS2
Hb
15 /32
14,16
2 %4 H
1 A
12, 13, 14
Z /8 2 %4 25 /64
13 /32
H
9 /16
12,14
%6 29 /64
7 /16
N
10, 11, 12
15 /32 Y 2 l /2
l /2
y 2
Hie
11,12
O/ Q/
V16 716
K
10, 11, 12
19 /32 ^ 5 /8
%
18 /16
10
2 V32
%
9,10
45 /64 23 /32
28 /32
2 %2
15 Ae
9
49 /64
1
8
13 /1 P
27 /32
27 /32
See also pages 78, 176 and 177.
THE STARRETT BOOK
Handy Equivalent Tables
Made of Spring Steel
NO.
THE L.S.STARRETT CO.
ATHOL. MASS. U.S.A.
DECIMAL
EQUIVALENTS
H 3
590
THE L.S.STARRETT CO.
ATHOL. MASS U.S.A.
\ TAP DRILLS I;
FOR
MACHINE SCREW TAPS
r OR STEEL WORK USE
AP DRILLS ONE OR TWO
SIZES LARGER THAN. UST
jto V
N -(ii) 591
THE L.S. STARRETT CO.
ATHOL. MASS. U.S. A.
DRILL SIZE
f TABLE fP
1 LETTER SIZES 1
yji it 11 1
1
ijj
i
~~K j
^r ~*
-3p-
290 <
-I? 4
295T -
: .4)3
22 5 \
^-:8i5
IS?- -3
i -I
20^ -4
f~Hf~
2O4 '
2 1 '
.07 5
It '
|3E1
IS :
1 Pi
-4e Zc
1E3
ISP
: I
182 5
1
*w
ij
fr-i
MF
a
59
za
157
\ .0'
It
54
S:^
n
r ^ J
HE
s
-hr--
E^s -
yt.
if:
C E :
f^ T
z 5
ES -
4t t
iH ^
s-"^
ffi
If ->
f-$Hhd
IO 7
51 3B
JB5 7
2 .02
40 1
fcjjM
1^
- .J-';f-
THE STARRETT BOOK
SIZES OF TAP DRILLS. Because of the large num-
ber of screw thread standards in use, many tables would
be required to cover all selections of tap drills.
The sizes of tap drill for all pitches of V threads may
be found by the following formula.
1.400
Tap drill = D -
T
in which T = number of threads per inch
D = dia. of tap or thread
EXAMPLE. What diameter
of tap drill should be used for a
% X 10 tap?
1.400
Tap drill = .75 -
= .75 -
10
.14
NOTE. For U. S. Standard
threads use same formula, but
1.3 should be used in place of
1.4.
FIG. 17 DRILLING LARGE HOLES.
Twist drills are sold, ranging in
size from No. 80 wire gage to four inches in diameter.
As the drill increases in diameter the web is corre-
spondingly thickened, and as the cutting edges at the
web do not cut as effectively as they do outside the web
thickness, considerable pressure is required to force the
larger drills into the work at an efficient cutting feed.
For this reason many workmen first drill a lead hole,
using a drill whose diameter approximates the web thick-
ness of the larger drill, as shown in Fig. 17. A lead hole
will also assist in centering the drill upon an inclined
surface. However, if the inclination is considerable it
is necessary to butt mill or hand chip a spot giving
61
THE STARRETT BOOK
sufficient surface to work upon. The practice of some
firms is to use in place of a single large drill a relatively
smaller one, afterward enlarging the hole by some method
of counterboring at a much less expense for tools and
at as rapid a production rate as by entire drilling.
BOLT HOLES. When the bolts are for holding pur-
poses only and are not used for aligning the several
pieces, it is customary to drill the holes through which
the bolts pass somewhat larger than the bolt diameters.
This allows for a variation in the bolt sizes and for in-
accuracy in locating the centers.
DEEP HOLE DRILLING. Under this name may be
classed the drilling of holes through the axes of spindles
lathe, milling-machine, and grinder and that special
line of drilling known as gun-barrel drilling. While for
spindle drilling it is possible to use ordinary twist drills
with extended shanks, it is customary in efficient drilling
of this sort to use special drills designed for the purpose.
Fig. 18 shows a special hollow drill often used for
drilling axial holes in lathe spindles, and Fig. 19 shows
the machine with the drill guides in working position.
FIG. 18
In all cases of deep-hole drilling it is better to rotate
the work rather than the drill. The drill must be started
exactly concentric with the axis of the machine. For
this reason a starting-hole the exact diameter of the drill
is first counterbored.
COUNTERBORING. There are many cases in which
it is desirable to enlarge a hole throughout a portion of
THE STARRETT BOOK
FIG. 19
its length. If a drill is used for this purpose there is
no certainty that the two diameters will be concentric.
The practice is to enlarge the already drilled hole by
using a cutting tool having a pilot or leader to guide the
cutting edges. This tool is known as a counterbore, and
its use is termed counterboring. In Fig. 20 are shown the
tool in operation and its purpose.
THE STARRE T T BOOK
THE STARRETT BOOK
THE LATHE
CARE OF THE LATHE. The engine lathe is capable
of producing the largest variety of product of any of
the machine-tool family. Especial attention should be
given to applying a suitable machine oil to all the bear-
ings, for improper lubrication of the wearing surfaces
is one of the immediate causes of excessive wear. A
medium-size flexible-bottom squirt can is best for this
purpose, and oiling should be frequent on those bear-
ings which are given the severest service, either from
excessive pressure or from high-speed rubbing. All oil
holes should be kept free and clean, and where possible
should be protected from entering dirt. Those bearings,
as, for example, the ways upon which the carriage moves,
which by construction are hard to protect "from dirt,
should be frequently cleaned and reoiled. At least once
a week the lathe should receive an all-over cleaning,
and the bearings should be washed out with kerosene.
A plugged oil hole prevents the proper lubrication of the
bearing.
INDICATING AND ADJUSTING. Upon the condi-
tion of the centers, rests to a large degree the accuracy
of the work produced. After attention to lubrication
the competent workman proceeds to prepare and test
the centers. Remove both centers and after cleaning
them and the tapered holes note whether they return to
their places with a successful fit. The "dead" or foot-
stock center should have a hardened point to resist wear.
The cone-points of the centers should be smooth and an
exact sixty degrees. The centers should align with each
other in the vertical and horizontal planes, and the "live"
or head-stock cone-point should rotate truly concentric
with its axis.
The trial and error method of adjusting the centers
in alignment is to first bring the cone-points nearly into
65
THE STARRETT BOOK
contact, and by adjusting the foot-stock frame upon its
cricket bring them into as exact truth as is reasonably
possible. With the foot-stock clamped in position to
receive the work, surface the diameter of a trial piece
for a length sufficient to allow testing its diameter at
several places. If the diameter increases or decreases
as the tool passes along the length of the work, readjust
the foot-stock and repeat the test until the required
UNIVERSAL DIAL TEST INDICATOR
FIG. 21
degree of accuracy is obtained. To test the live center
for concentricity, place in the tool-post a universal test-
indicator, as shown in Fig. 21, with the feeler in touch
with the cone-point. Rotate the head-stock spindle
slowly by hand and note the dial. If the dial shows an
eccentricity in excess of the allowed limits for the job
66
THE STARRETT BOOK
to be done, the cone-point should be machined true. In
cases where it is customary to have the live as well as
the dead center hardened, the cone-point must be trued
by some grinding attachment, as, for example, a tool-post
grinding fixture. By many workmen the live center is
left unhardened, and can be trued with a square nose-
cutting tool, and afterward lightly filed to a smooth sur-
FIG. 22
face. To test either center for its proper cone-point
angle use is made of a center gage, shown in Fig. 22.
TEST INDICATOR. This is a tool for indicating
minute contact variations upon a graduated dial or upon
67
THE STARRETT BOOK
Truing Work in Chuck
Truing Jig on Face Plate
Indicator Used with Surface Gage on Bench Plate
68
THE STARRETT BOOK
a graduated arc. The graduations are usually one hun-
dred in a complete circle with an easily read width of
spacing. The instrument is built in such a way that one
of these spaces represents a movement of the contact-
point of 1/1000 inch.
Various mechanisms are employed for multiplying
the movement of the contact-point, all of which are
based upon a combination of short and long arm levers.
USE. The test-indicator may be used with advantage
in any of the common machine tools, to in-
dicate eccentricity in the lathe, milling ma-
chine, or grinding machine; to indicate uni-
formity of height in the planer, shaper, boring
machine, or milling machine; to indicate par-
allelism, and to test for alignment in any_
machine.
WORK CENTERS. Most turned work is
done upon the lathe centers, and it becomes
necessary to provide suitable cavities in the
work, coned to- fit the cone-points. This is
termed "centering the work," and consists in
first locating the position of the cavities and
afterward drilling and reaming them to form
and size. Best practice in this respect is to use
a combination drill and center reamer, as it
insures exact concentricity in the drilled and
reamed hole.
LOCATING THE CENTERS. It is evident
that the centers should be so located that the
entire diameter of the turned job shall finish
to size. Beside this, efficient turning demands HE RMAPHRO-
that the chip taken shall be of practically uni- DITE
ftfrm depth as the work rotates against the CALIPERS
cutting tool. For these reasons some degree of accuracy
in centering is necessary. Where the turned job is made
from ordinary black bar stock, the centers may be located
THE STARRETT BOOK
LATHE TOOLS
1 LEFT-HAND SIDE TOOL
2 RIGHT-HAND SIDE TOOL
3 RIGHT-HAND BENT TOOL
4 RIGHT-HAND DIAMOND POINT
5 LEFT-HAND DIAMOND POINT
6 ROUND-NOSE TOOL
7 CUTTING-OFF TOOL
8 THREADING TOOL
9 BENT THREADING TOOL
10 ROUGHING TOOL
11 BORING TOOL
12 INSIDE THREADING TOOL
70
THE STARRETT BOOK
by scribing lines at an angle across the ends, using a
combination square with a center head and the provided
scriber. In place of this tool a hermaphrodite caliper
may be used to scribe the ends of the stock. The center
is located with a center-punch at the intersection of the
scribed lines and the concentricity tested by spinning
the bar upon the lathe centers. If necessary, the center-
punch marks are shifted. If the piece is bent it must,
after centering, be straightened to reasonable truth. For
exact turned work the centers should afterward be lightly
rereamed to correct the errors in their alignment due to
the straightening of the bar.
When the' job is to be turned from a forging, it is
usual to roll the forging on straight edges and scribe
lines across the ends, using a surface or height gage.
In such cases the forging is so located with reference to
the straight edges as to give a fair average of the surface
errors due to forging. It is also usual to leave a greater
excess of stock for finishing purposes upon a forging
than upon rolled bar stock. When the centers are well
located the holes may be drilled under a drill-press or
in a hand-lathe, as convenient. Where much bar stock
must be centered a special self-locating centering machine
is often used.
LATHE TOOLS. A set of tools for use in the engine
lathe is shown in the chart on page 70. While in com-
mon shop language all these are known as cutting tools,
technically speaking, many of them separate the stock in
a manner that is analogous to crowding off the metal
rather than by pure cutting action. Cutting in its proper
sense is a splitting action, and a properly ground and
properly set cutting tool is a wedge in that it splits off
the excess stock. Among the common lathe tools, the
side tool and the diamond-point tool are the best exam-
ples of wedge or splitting action.
The nose of a cutting tool has several sides, two of
71
THE STARRETT BOOK
which come together at some angle to form a cutting
edge. The angle formed by these surfaces must be suffi-
cient for strength, and to furnish enough metal to con-
duct away the heat generated by the cutting action. For
turning ordinary soft steel and soft gray iron an angle
of sixty degrees is good practice. For harder material^
the angle may be increased. In the case of forged lathe
tools, the working end of the tool is forged upon the end
of a short piece of square or rectangular bar stock. The
length and size of the shank of the forged tool depend
upon the size of chip and the machine used.
RAKE. The angle which the upper side of the tool
makes with the horizontal is termed the rake. If the
CLEARANCE
FIG. 23
SIDE
CLEARANCE
slant is away from the work it is termed front rake; if
in the direction of the axis of the work, it is termed side
rake. A cutting tool may have its upper face forged and
ground with either a front or a side rake or a combina-
tion of both. (See Fig. 23.)
CLEARANCE. By clearance is meant the angle which
the under side of the tool makes with the vertical. As
in the case of "rake" the clearance directly away from
the axis of the work or lathe is termed front clearance,
72
THE STARRETT BOOK
that along the axis of the work side clearance. With
the tool in cutting position the clearances must be in any
case not less than three degrees, and in most cases not
more than ten degrees.
RIGHT-HAND TOOLS. These are tools having the
rake, clearances, and cutting edges formed to turn or
square from the right towards the left.
LEFT-HAND TOOLS. When the rake, clearances,
and cutting edges are formed to cut from the left to the
right the tool is known as a left-hand tool.
SETTING THE LATHE TOOL. It is very important
that the lathe tool be properly set in relation to the axis
of the work and the direction of the cut. While there
are exceptions, notably that of the diamond point, lathe
tools are usually set with the cutting point at the exact
height of the axis of the lathe. In the case of the dia-
mond point, the front clearance is usually forged to
fifteen degrees or over. It is necessary, therefore, to set
the point above the axis height to obtain a working clear-
ance of not to exceed ten degrees'. Unless the cutting
tool has a bent shank it is usually set at right-angles to
the surface of the work.
GRINDING LATHE TOOLS. Lathe tools made from
carbon tool steel should be sharpened by grinding upon
a wet emery-grinder, or upon an ordinary water-drip
grindstone. If made from the newer high-speed steel
the grinding should be upon a dry and rather coarse
abrasive wheel. The grinder should have a suitable
work-rest upon which to support the tool in sharpening
the larger tools, or for resting the hands in the case of
the smaller tools.
For purposes of safety, the work rest should be firmly
and securely clamped as close as possible to the used face
of the wheel. The grinding may be done upon the pe-
riphery of a disk-wheel or upon the sides of a cup-wheel,
as desired. In any case the wheel should rotate to force
73
T t H E STARRETT BOOK
the tool upon the rest rather than from it, and should
run true and in balance. Efficient cutting depends very
largely upon the correct sharpening, as well as the cor-
rect setting of the cutting tool, and great care should be
taken when grinding a lathe tool to have the several
faces true and making correct angles with each other.
The manner of doing this is a pretty good index of the
workman. The usual lathe-cutting tools have well-de-
45V
FIG. 24
fined cutting edges, and the angularity of the surfaces
which meet to form the cutting edge can often be meas-
ured with a bevel protractor, and in the case of a sixty-
degree angle the center gage is suitable. This tool is
also used to test the angle when grinding a vee-pointed
thread tool, as illustrated in Fig. 24.
TESTING THE CUTTING ANGLES. As the usual
machine construction materials are not excessively hard,
a cutting angle of not far from sixty degrees may
be maintained on such tools as the side tool and the
diamond point. In this case the angle can be tested by
use of the usual center gage. Where cutting angles other
74
THE STARRETT BOOK
than 60 are used, also for testing clearances, the uni-
versal Bevel Protractor is useful.
TOOL HOLDERS. The high cost of the materials
used for modern cutting tools has resulted in the mar-
keting of a variety of holders designed to hold cutting
points. In this manner a large number of relatively
inexpensive cutting points are made to interchange in
a single shank or holder. One form of tool-holder is
made to hold points forged in the regular forms shown
in the chart, page 70. In some examples, however, the
holders are made to carry short bits broken from square
bar stock and afterward sharpened into some resem-
blance to the true forged shape. (See Fig. 25.)
FIG. 25
MATERIALS FOR GUTTING TOOLS. These are
known as carbon steel (tool steel), high-speed steel, and
a new product of the electric furnace sold under the
trade name of "Stellite." Carbon steel, or, as it was
formerly termed, "tool steel," is high in carbon, eighty
point to one hundred and twenty-five point, and when
correctly heated and afterward plunged in cold water,
hardens to a very high degree. Unfortunately for high-
speed cutting the hardness is drawn at a comparatively
low heat, and care must obtain not to overheat or blue it.
High-speed steel is a special steel having its com-
position alloyed with tungsten and perhaps vanadium
or molybdenum. While heat treatment does not give it
the exceeding hardness of tool or carbon steel, high-
75
THE STARRETT BOOK
speed steel has the peculiar property of retaining its
hardness at temperatures considerably in excess of those
which readily soften tool steel. Tools made from high-
speed steel are used at speeds, feeds, and cuts which
heat the tools and chips to a dull red.
Stellite is a new cutting material composed of chro-
mium, cobalt, and sometimes tungsten. It is cast into
form and cannot be forged. Its hardness is equal to the
diamond, and under favorable conditions marvelous turn-
ing may be done.
MANDRELS. Where the work is to be turned true
with a hole through it, as, for example, turned pulleys,
work-centers must be provided for holding it on the lathe
centers. The common way is to force or drive into
the work-hole a bar having center holes in its ends. This
bar should be classed as a tool-room tool, and is properly
known as a mandrel, although often called an arbor.
A standard set of mandrels varies in diameter and in
length, according to the shop conditions. They are
made of either tool steel hardened and ground true with
the centers, or from soft machinery steel, case-carbonized
and afterward ground. The ends for a short distance
are reduced in diameter and provided with flats for
clamping on the dog. Mandrels usually taper at the rate
of 0.0005" in an inch. The diameter of the hole fitted
by the mandrel is stamped upon the larger end. As the
quality of the work depends upon the truth of the man-
drel it should be tested upon dead centers with a test-
indicator before being used. To use, drive or force it into
place, using a Mandrel press for forcing or a lead hammer
for driving, carefully removing dirt, chips, or pieces of
lead from the centers before placing the work in a lathe.
Lathe drive with the usual lathe-dog as for any job done
on the centers. Avoid forcing or driving the mandrel
into a hole that is neither round nor straight. Also avoid
scoring the mandrel with the cutting tool.
76
THE STARRETT BOOK
SCREW THREAD CUTTING. A screw thread is a
helical groove cut or formed into the surface of a bar,
rod, or bolt, or inside a nut. For ordinary machine
screws, bolts, studs, etc., the threads are made with
special tools called threading dies. These are screwed
upon the bolt, screw, or stud to be threaded by rotating
either the work or the die. Threading dies are used
both by hand and in power-driven machines.
SCREW THREADS. There are numerous screw-
thread standards in more or less general use. The so-
called United States standard is in this country the more
generally accepted one, and is therefore illustrated in
Fig. 26 and Table 6. It will be noted that in addition
to a definite form of thread cross-section each diameter
has a specified number of threads per inch of length.
The United States standard thread, when sectioned, shows
a truncated sixty degrees triangle with the space and
the land alike.
PITCH AND LEAD.
Pitch in a thread is the ; j /WIDTH
distance measured from the "^ OF FLAT
center of one thread to ~T
the center of an adjacent DEPTH
thread. If the screw thread OF P,
is a single helix, the lead is
equal to pitch. If the helix
is double, the lead is double FlG - 26
the pitch. While strictly speaking pitch is the reciprocal
of the number of threads per inch, as, for example, 1/7"
pitch for a screw thread 7 per linear inch, shop men
speak of it as 7 pitch, written, 7 P.
THREADING IN A LATHE. When screw threads
are cut in an engine lathe, the point of the cutting tool
is shaped to the exact form of the spaces between threads.
By means of a lead screw and a train of gearing the tool
is compelled to move along the axis of the work at a
77
THE STARRETT BOOK
U. S. Standard Screw Threads Table 6
Diameter
No. of Threads
per Inch |
Diameter at
Root of Thread
Diameter of
Tap Drill
Area in
Sq. Inches
, Dimensions of Nuts
and Bolt Heads
1
h^
k ->!
H
a
H
&
Of
Bolt
At Root
of
Thread
M
20
0.185
13 /64
0.049
0.026
H
0.578
0.707
1 A
1 A
H
18
0.240
H
0.076
0.045
19 /32
0.686
0.840
5 A6
19 /64
16
0.294
5 Ae
0.110
0.068
Hie
0.794
0.972
H
H'32
7 A 6
14
0.345
2 %4
0.150
0.093
2 %2
0.902
1.105
%e
25 /64
H
13
0.400
27 /64
0.196
0.126
%
1.011
1.237
H
7 Ae
%e
12
0.454
15 /32
0.248
0.162
3 V32
1.119
1.370
9 Ae
3 V64
H
11
0.507
17 /32
0.307
0.202
!Vl6
1.227
1.502
5 /8
17 /32
H
10
0.620
4 V 6 4
0.442
0.302
\\i
1.444
1.768
%
N
8
9
0.731
%
0.601
0.419
1 7 /16
1.660
2.033
7 /8
23 /32
8
0.838
5 %4
0.785
0.551
1%
1.877
2.298
1%6
V/8
7
0.939
3 V32
0.994
0.694
1 13 /16
2.093
2.563
V/8
29 /32
1M
7
1.064
1%3
1.227
0.893
2
2.310
2.828
1M
1
1H
6
1.158
1%2
1.485
1.057
2 3 /16
2.527
3.093
IN
1%2
1H
6
1.283
1H&2
1.767
1.295
2^
2.743
3.358
i^
1 3 /16
iff
V/2
1.389
! 27 /64
2.074
1.515
2% 6
2.960
3.623
1%
1%2
i%
5
1.490
! 17 /32
2.405
1.746
2M
3.176
3.889
1%
1^
V/8
5
1.615
l%a
2.761
2.051
2 1 % 6
3.393
4.154
IK
1!%2
2
4M
1.711
1 4 %4
3.142
2.302
33^
3.609
4.419
2
1%6
2M
4X 2
1.961
2V 6 4
3.976
3.023
3^
4.043
4.949
2M
Ik
2^
4
2.175
2' %4
4.909
3.719
3%
4.476
5.479
2^
1^46
2%
4
2.425
2%4
5.940
4.620
i
4.909
6.010
2M
2^
3^
2.629
2i%e
7.069
5.428
4N
5.342
6.540
3
2% 6
3J
3^
2.879
2i%e
8.296
6.510
5
5.775
7.070
3M
2^
33^
3^
3.100
3iy 64
9.621
7.548
5^
6.208
7.600
VA
2^6
3%
3
3.317
3^g
11.045
8.641
5
6.641
8.131
VA
2>i
4
3
3.567
3^
12.566
9.963
6H
7.074
8.661
4
3Vi6
4^
2^
3.798
32% 2
14.186
11.340
6>i
7.508
9.191
4^
VA
4^
VA
4.028
4% 2
15.904
12.750
6K
7.941
9.721
4K
3%6
4%
2 5 /8
4.255
45A 6
17.721
14.215
7M
8.374
10.252
4M
3^
5
V/2
4.480
49/16
19.635
15.760
7%
8.807
10.782
5
3i 3 Ae
5M
2 l /2
4.730
4*%6
21.648
17.570
8
9.240
11.312
53
4
5^
zy*
4.953
5% a
23.758
19.260
8^
9.673
11.842
5^
4%6
5^
2*/8
5.203
5% 2
25.967
21.250
8^
10.106
12.373
5^
4^
6
2 1 A
5.423
5 J /i
28.274
23.090
9.H
10.539
12.903
6
4%6
COURTESY OF " MACHINERY "
See also pages 55, 56, 168 and
78
THE STARRETT BOOK
definite rate of advance as the work- rotates. As the
train of gears usually furnished with an engine lathe
can be changed to give different rates of advance, it is
in this manner possible to cut threads of a. large variety
of pitches. In practice a set of several gears having dif-
ferent numbers of teeth are furnished with each lathe.
Those furnished will usually provide for cutting all the
threads within the usual range of the lathe with which
they come. These are known as "change gears," and
their use is obvious.
SELECTING CHANGE GEARS. Given the number
of threads per linear inch to be cut and the number of
threads per linear inch of the lead screw, the problem
is to select gears giving the desired ratio of cut to lead
screw. For example, it is desired that single seven
threads per linear inch shall be cut upon a li/d-inch
bolt, and it is found by scaling that the lathe lead screw
has single five threads per linear inch. The ratio of cut
to lead screw is then that of seven to five (7/5). The
change gears selected should, therefore, be as seven is
to five. If both members of a fraction are multiplied
by the same number, the ratio is not changed. This
allows of raising the fraction to suit the gears which are
7 5 35
in the set furnished; for example, - X - = . If gears
5 5 25
having thirty-five teeth and twenty-five teeth, respec-
tively, are found in the furnished set, the selection of
these gears will give, when rightly placed, the desired
tool advance for cutting seven threads per linear inch.
The directions above refer to the most simple form
of lathe. Various lathe manufacturers have introduced
different arrangements of the gearing, but with any lathe
the above procedure will give correct results if it is first
determined what number of threads per inch will be
cut if gears of the same number of teeth are placed on
spindle stud and lead screw. This number called the
79
THE STARRETT BOOK
Lathe Set Up for Thread Cutting
Note Thread Stop at A
80
THE STARRETT BOOK
"lathe screw constant" should then be considered as
being the number of teeth on the lead screw gear even
though it is not the actual number.
PLACING THE CHANGE GEARS. The common
engine lathe has projecting through its headstock a shaft
known as the "stud." This projects a sufficient distance
STUD
GEAR
COMPOUND
GEAR
OUT OF
MESH
INTERNED
GEAR
SIMPLE TRAIN OF GEARS FOR THREAD CUTTING
81
THE STARRETT BOOK
to allow of mounting gearing and usually the upper
cone for the feed belt. Gears mounted or to be mounted
upon this projecting stud are termed "stud gears." Those
mounted upon the projecting end of the lead screw are
known as lead gears. When the number of threads to be
cut is more per linear inch than that of the lead screw,
the smaller of the selected gears is placed upon the
"STUD" and the larger upon the lead screw. In the
example, the 25-tooth gear would be placed on the stud
and the 35-tooth gear on the lead screw. Reverse the
order if the number of threads per linear inch is less
than that of the lead screw. The number of teeth in the
large idler gear has no bearing upon the results, as it
simply conveys the motion of the upper or stud gear to
the lower or lead-screw gear. In the above it is assumed
that the stud rotates in unison with the lathe spindle.
COMPOUNDING THE GEARS. As a means of en-
larging the range of threads per linear inch possible to
be cut with any set of change gears, most lathes are
provided with an adjustable compound auxiliary stud
which is provided with two locked gears having a ratio
each to the other of two to one. As an example of their
use, assume that a gear having ninety teeth was needed
upon the lead screw to cut a given number of threads.
If the set of gears furnished failed to provide a ninety
gear, but did provide one of forty-five teeth, placing
this on the lead screw and meshing the two to one com-
pound stud into the train completes the desired ratio,
and advances the tool as if the 90-tooth gear had been
used.
THREAD TOOL. Among the tools listed on page 70
is shown the ordinary threading-tool point. It is obvious
that this or any other form of point must be formed and
tested to give the correct form of thread. The point
shown has sides at an angle with each other of sixty
degrees. The point can therefore be tested with a center
82
THE STARRETT BOOK
STUD
GEAR
INTERMEDI
GEAR
COMPOUND GEARS FOR THREAD CUTTING
gage or rule. The same gage may also be used in setting
the tool square with the axis of the work (see page 74).
GRINDING THREAD TOOLS. It is important that
the point of the thread tool shall conform to the outline
of the groove between the adjacent threads, and that
the surfaces below the cutting edge properly clear the
stock being cut. When grinding a thread tool, particu-
83
THE STARRETT BOOK
lar care should be given to have the clearances sufficient
for the lead of the thread.
SETTING THE TOOL. Set the tool point at the
exact height of the lathe centers, and at right-angles to
the axis of the lathe.
USES OF CUTTING LUBRICANT. Use lard oil
when threading steel, wrought, and malleable iron. Cut
the cast metals dry.
THREAD CUTTING TOOL SET AT HEIGHT OF LATHE CENTER
RIGHT AND LEFT THREADS. A right-hand thread
results when the threading tool is advanced from right
to left as it cuts. If the tool when cutting advances
from left to right the resulting screw has a left-hand
thread.
MEASURING AND TESTING SCREW THREADS.
For ordinary purposes screw threads when cut are fitted
to some threaded hole. This may be a hardened and
ground gage, or may be an ordinary threaded nut,
depending upon the accuracy of the work. Where the
quality of the work demands special- accuracy, or where
84
THE STARRETT BOOK
standard threaded gages are not available, the thread
is tested by measurements made with calipers. If the
point of the thread tool has been carefully and exactly
formed and accurately set in place, measuring the diam-
eter at the root of the thread may give sufficiently accu-
CALDPERS FOR TESTING THREADS
rate results, and this may be done with a set of thin
point spring calipers. When greater accuracy than this
is required, micrometers having special thread-measur-
ing points are resorted to x (see Fig. 27). In all this it
is assumed that the thread tool is ground, set, and oper-
ated to give an exact thread outline.
MEASURING LATHE WORK. Work done in the
engine lathe is of such a variety that a considerable list
of measuring tools may be needed to cover all cases.
Ordinarily, however, the diameter measurements can be
85
THESTARRETT BOOK
made with spring calipers, micrometers, or some of the
usual bar calipers. Cylindrical plug and ring gages,
as well as limit snap gages, are also used for diameter
measurements, and many of these may be used in meas-
uring the shorter lengths. For the longer measurements
of length, steel rules are provided with or without sliders.
The more accurate measurements are usually made by
using a micrometer.
FIG. 27
TAPER TURNING. Where two parts are to fit firmly
together when in use, as, for example, centers into lathe
spindles, and it it desirable to have them easily remov-
able, what are known as taper-fits are used. For this
purpose several rates of change in diameter have become
standards. Pages 87 and 88 give the more common stand-
ards. The Brown & Sharpe Standard is in general use
for the spindle tapers in milling machines. The Morse
taper is the one commonly used for all drills and drill-
ing machinery. Either of these may be used for the
tapered hole in lathe spindles, while some lathe manu-
facturers have established standards of their own.
86
THE STARRETT BOOK
T
IT
T
i
s '
I
1
i
H
|
ANY
* i
1
l^v
1
1
s^
Brown & Sharpe Taper Shanks Table 7
COLLET
OR SPINDLE
Taper per ft. is Yz in., except for No. 10 shank, where the taper is 0.5161 in. per ft.
Number of
Taper
Diam
End o
0.239
0.299
0.375
0.385
0.395
0.402
0.420
0.523
0.533
0.539
0.599
0.635
0.704
0.720
0.725
0.767
0.898
0.917
1.067
1.077
1.260
1.289
1.312
1.498
1.531
1.797
2.073
2.344
2.615
2.885
3.156
3.427
t"0_*i
gc
f o
11%2
2T/32 2
21%2
1%
2%6
2%2
2i % 2
327/32
3%
4%
4y 4
4iyi6
48 /4
617/32
71%2
9%r
10 8 /8 82
18
2y 8
2%
i2y 32
2%2
2 3 /10
2%e
2 7 /8 6
3%
417/32
4%
4%
47/6
615/ie
6*%2
9%2
92y 32
ioy 4
o -o
1
(5 C/5
0.200
0.250
0.312
0.312
0.312
0.350
0.350
0.450
0.450
0.450
0.500
0.500
0.600
0.600
0.600
0.600
0.750
0.750
0.900
0900
1.0446
1.0446
1.0446
1.250
1.250
1.500
1.750
2.000
2.250
2.500
2.750
3.000
il
2
U4.
iiyie
1%
2
2%
2%
sy 4
27/^
3
3%6
4y f
6% 2
6/4
9H
w
2i %4
3iy 6 4
218/32
517/32
8%2
817/32
Length
Keywa
H
15 /10
Width of
Keyway
0.135
0.166
0.197
0.197
0.197
0.228
0.228
0.260
0.260
0.260
0.291
0.291
0.322
0.322
0.322
0322
0.353
0.353
0.385
0.385
0.447
0.447
0.447
0447
0.447
0.510
0510
0.572
0.572
0.635
gth of
ngue
27/So
27/32
83
* o
SH
M
%-
&
%
8/8
Vl!
n
87
THE STARRETT ROOK
Morse Standard Taper Shanks Table 8
ANY
r
1
i
i
i
K
i ">
1
i 1
f
ft!
SOCKET OR
SPINDLE
^
^
|H
!o w
"S w
P 3 rt
I E I
0.252
0.369
0.572
0.778
1.020
1.475
2.116
2.750
Dia. at End
of Socket
0.356
0.475
0.700
0.938
1.231
1.748
2.494
3.270
4Vie
5%e
U QC
^
2H32
3Me
3/4
4%
6
4^8
5V4
lOfc
K
4i%
7
9%
Length o
Keyway
2%
ou
II
JH
*>*
Thickness
of Tongue
%
Width of
Keyway
W
0.160
0.213
0.260
0.322
0.478
0.635
0.760
1.135
11
2%2
2%
.625
.600
.602
.602
.623
.630
.626
.625
Short Shanks
0.271
0.388
0.600
0.816
1062
1.532
2.201
2.857
0.356
0.475
0.700
0.938
1.231
1.748
2.494
3.270
! 5 /8
1%
2 ?
34*
4^8
5 5 /8
3^8
4Vl6
5Me
7Vie
9^6
2 Vie
5%
! 27/ 32
2 7/ 82
Tfc
! 5 Ae
?'*
2%
3%
V4
%6
V2
I
1V4
! 5 /8
0.195
0.260
0.387
0.514
0.639
1.014
1.266
1.642
1 27 &2
2
6%
.625
.600
.602
.602
.623
.630
.626
.625
The dimensions given above for regular (full length) Morse taper shanks are
those which have been accepted as standard and are used by most manufacturers.
In a recent catalogue of the Morse Twist Drill & Machine Co., however, a table is
given in which the length of the tang and, consequently, the whole length of the
shank is slightly increased. The increase in length, however, is so slight that it
does not prevent the shank from fitting into the ordinary standard taper socket.
THE STARRETT BOOK
TURNING TAPERS. Ordinary tapers are rated at
the amount which the diameter changes in a foot's length;
as, for example, the Brown & Sharpe taper of % inch
per foot. To turn a taper it is necessary to use a lathe
provided with a taper attachment or to adjust the foot-
stock of the engine lathe sufficiently off center to give
TAPER TURNING IN LATHE
89
THE STARRETT BOOK
the required rate of diameter change. As all taper attach-
ments are graduated to read direct, they are easily set
for the required taper. Adjustment of the foot-stock of
an engine lathe is not so simple as the taper attachment.
In setting the taper attachment, the axial distance the
center points are apart is not important, while this dis-
tance must be considered in setting over the foot-stock
of the lathe.
AMOUNT TO OFFSET CENTERS FOR GIVEN
TAPER. If the distance the center points enter the
work or the mandrel is ignored, the mandrel length can
be considered as the distance apart of the center points.
The calculation necessary to determine the distance which
the centers shall be offset, is that of multiplying the
length of the work or mandrel in feet by one-half of the
required taper in inches. To turn a Brown & Sharpe
taper on a piece of work nine inches long the problem
would work out as follows:
.500 9 3
_ x - - = 0.1875 = -
2 12 16
and the foot-stock would be set over 3 Ae inch.
In the above illustrative example both length and
amount of taper are given, but the amount of taper is not
always known. Suppose a piece is 8 inches long and a
taper is to be turned on one end, the tapered portion to
be 4 inches long. The difference in diameters of these
4 inches is to be % inch. How much must the tail stock
be offset? If the taper is % inch in 4 inches it would be
1% inches in a foot and the tail stock would be moved
over one-half of 1% inches or % inch, if the piece were a
foot long, but as it is only 8 inches or % of a foot long,
the tail stock should be moved over % multiplied by %
or V 2 inch. Had the piece been 18 inches long, the tail
stock should be moved over % multiplied by % or 1%
inches.
90
THE STARRETT BOOK
It has been assumed for these simple calculations
that the lathe centers merely touch the ends of the piece,
thus making the length of the piece the same as the dis-
tance between centers. But in actual work the distance
the centers enter the piece must be considered. The
calculation should be as accurate as possible to avoid
continually changing the tail stock to get a reasonably
good taper fit. The necessity of considering the distance
the center enters the piece depends somewhat upon its
length. If the piece is very long, the actual taper will
differ considerably from the calculated taper. If each
center enters the piece one-fourth inch they would enter
a total of one-half inch, and the length of the piece
should be reduced by one-half inch in the calculation.
While turning the taper the calipers should be used fre-
quently so that it may be soon determined whether or not
the tail stock is correctly placed.
For coning pulleys, set the foot-stock away from the
operator when adjusting. In most taper work, however,
the center is offset towards the operator.
SETTING THE TOOL. The tool-point should be set
at the exact height of the axis of the lathe.
TESTING THE TURNED TAPER. To test the taper
as it is turned, ground, or filed, it should be pressed
lightly into a standard tapered hole and worked back and
forth sufficiently to mark the places where bearing occurs.
If the work has been lightly covered with some marking
pigment, the bearing points will be more distinct. Care,
however, must obtain that the coating is not sufficient to
smooch, as it will deceive the workman. Adjust taper-
setting until a correct fit is obtained.
ECCENTRIC TURNING. While for the most part the
lathe is used for work exactly concentric with the axis,
it can be used for turning work not concentric with the
axis. Work of this sort is termed "eccentric," and an
example of such work is seen in the eccentrics which
91
THE STARRETT BOOK
Amount of Taper in a Given Length, When the Taper per
Foot is Known Table 9
v<
Taper per Foot
j!
Me
%2
tt
Vi
%
*
0.600
%
M
1
1V4
Hi
.0002
.0002
.0003
.0007
.0010
.0013
.0016
.0016
.0020
0.0026
0.0033
T/
0003
0005
0007
0013
0020
.0026
.0031
0033
0039
00052
00065
%
.0007
.0010
.0013
.0026
.0039
.0052
.0062
.0065
.0078
0.0104
0.0130
vie
.0010
.0015
.0020
.0039
.0059
.0078
.0094
.0098
.0117
0.0156
0.0195
^4
.0013
.0020
.0026
.0052
.0078
.0104
.0125
.0130
.0156
0.0208
0.0260
%6
.0016
.0024.
.0033
.0065
.0098
.0130
.0156
.0163
.0195
0.0260
0.0326
%
.0020
.0029
.0039
.0078
.0117
.0156
.0187
.0195
.0234
0.0312
0.0391
%e
.0023
.0034
.0046
.0091
.0137
.0182
.0219
.0228
.0273
0.0365
0.0456
Vz
00?fi
0039
.0052
0104
.0156
.0208
.0250
.0260
.0312
0.0417
00521
%e
.0029
.0044
.0059
.0117
.0176
.0234
.0281
.0293
.0352
0.0469
0.0586
.0033
.0049
.0065
.0130
.0195 .0260
.0312
.0326
.0391
0.0521
0.0651
Hie
.0036
.0054
.0072
.0143
.0215
.0286
.0344
.0358
.0430
0.0573
0.0716
%
.0039
.0059
.0078
.0156
.0234
.0312
.0375
.0391
.0469
0.0625
0.0781
1 %e
.0042
.0063
.0085
.0169
.0254
.0339
.0406
.0423
.0508
0.0677
0.0846
%
.0046
.0068
.0091
.0182
.0273
.0365
.0437
.0456
.0547
0.0729
0.0911
1 y^e
.0049
.0073
.0098
.0195
.0293
.0391
.0469
.0488
.0586
0.0781
0.0977
1
.0052
.0078
.0104
.0208
.0312
.0417
.0500
.0521
.0625
0.0833
0.1042
2
.0104
.0156
.0208
.0417
.0625
.0833
.1000
.1042
.1250
0.1667
0.2083
3
.0156
.0234
.0312
.0625
.0937
.1250
.1500
.1562
.1875
0.2500
0.3125
4
.0208
.0312
.0417
.0833
.1250
.1667
.2000
.2083
.2500
0.3333
0.4167
5
.0260
.0391
.0521
.1042
.1562
.2083
.2500
.2604
.3125
0.4167
0.5208
6
.0312
.0469
.0625
.1250
.1875
.2500
.3000
.3125
.3750
0.5000
0.6250
7
.0365
.0547
.0729
.1458
.2187
.2917
.3500
.3646
.4375
0.5833
0.7292
8
.0417
.0625
.0833
.1667
.2500
.3333
.4000
.4167
.5000
0.6667
0.8333
9
.0469
.0703
.0937
.1875
.2812
.3750
.4500
.4687
.5625
0.7500
0.9375
10
.0521
.0781
.1042
.2083
.3125
.4167
.5000
.5208
.6250
0.8333
1.0417
11
0573
.0859
.1146
.2292
.3437
.4583
.5500
.5729
.6875
0.9167
1.1458
12
.0625
.0937
.1250
.2500
.3750
.5000
.6000
.6250
.7500
1.0000
1.2500
92
THE STARRETT BOOK
operate the valves of steam engines. If the work has a
hole through it, as in the above example, the hole is first
finished to required dimensions. A mandrel is then used
for carrying the work on the centers. While the mandrel
has been built on one set of centers exactly true with its
axis, for eccentric turning it has a second set of centers
which are offset the amount required for the eccentricity
specified. In the case of eccentrics made solid with the
FIG. 28
shaft, the two sets of centers, one t for turning the shaft
and the other for finishing the eccentrics, are made
side by side in the ends of the shaft, as shown in Fig. 28.
When the specified eccentricity is too extreme to
allow both pairs of centers coming within the limits of
the diameter of the shaft, special ends may be cast or
forged on the ends of the work, and can afterward be
machined off. In crank-shaft turning, special attach-
ments are provided for the ends of the shaft. Special
eccentric turning chucks .may be made to hold the work.
CHUCKING. Chucking includes, not only the mount-
ing of the work in the chuck, but performing the neces-
sary operations on it while so held. The name "chuck"
is given to a line of tools having a variety of form, all
93
THE S T A R R E
T BOOK
94
THE STARR E T T BOOK
of which are designed to hold work or tools upon the
nose of a spindle. In general the heavier sorts are
mounted upon a face-plate which screws upon the end
of the spindle, while smaller sizes are fitted with a taper-
shank which fits tightly into the tapered hole in the
spindle. The smaller sizes are used for carrying tools,
such as drills, also screws, studs, wire pins, etc.; and are
known as drill-chucks.
The larger sizes are widely used for holding work
for machine operations, and are sometimes called "work-
chucks." On their face they are provided with adjust-
ing jaws movable regularly to and from the center; these
jaws are so designed that a considerable variety of work
may be readily held and successfully worked upon with
common cutting tools. The jaws are moved by means
of screws or gears, and can be adjusted independently,
the chuck being called an independent jaw-chuck; or,
all the jaws may be made to move together, in which
case it is known as a Universal chuck.
HOLDING THE WORK. The work must be clamped
firmly in the chuck while being machined. Care must
also be taken that the clamping of a slender piece is
not so firm as to distort or spring it. If work slips,
tools may be broken, and if held too tightly and sprung
or crushed, the work is injured and in some cases en-
tirely ruined.
TRUING THE WORK. Adjusting the chuck-jaws
so that the work will run as true as desired is termed,
"truing up the work." This is preliminary to any tool-
ing which may be done on the job. Often this truing
of the work can be accomplished by holding a piece
of chalk to just touch the work, leaving a plain mark-
ing this method is used when chucking rough pulleys
for drilling out the hole in the hub. Where greater
accuracy is required, the work is indicated with a Uni-
versal dial test indicator.
95
THE STARRETT BOOK
CHUCKING TOOLS. With the work located in the
chuck it may be tooled with ordinary lathe tools, such
as shown in the tool-chart (page 70), or it may be drilled
with two, three, or four fluted twist drills, and reamed
with machine reamers, or special shell bits and coun-
terbores.
CHUCKS ON TURRET LATHES. In turret lathe-
work, for bar-stock, the chuck is a part of the regular
tool equipment; these chucks are often of special design,
so made that they open and close by hand-operated
levers or automatically-operated cams.
KNURLING. The surfaces of adjusting screws and
small machine parts are often given a regular rough sur-
face for easy gripping. In the machine shop this is
done by using a tool known as a "knurl" or "knurling
tool," which consists of one or more indented rollers or
knurls mounted to rotate in some form of holder.
32nds.
I 0312
3 0937
5 .1562
7 .3187
9 .2812
II .3437
I-
1-4- .250
3-8 .375
IBths.
.0625
3 .1875
5 .3125 NO 232
7 .4375 15.4687
THELaSTARRETTCD
ATHOLMASS.USA
FIG. 29
These knurls are forced
into and fed along the stock
until the indented design has
been sufficiently imprinted
into the surface. When neatly
and effectively done the re-
sults give a fine gripping sur-
face and a rather pleasing effect to the eye. The knurling
tool may be fed along the surface of the work by hand,
but usually the power traverse feed is used. The process
is repeated if one passage of the tool does not give suffi-
cient depth.
Fig. 29 shows knurling on a micrometer.
96
THE STARRETT BOOK
TOOL-MAKING
Under the name "tools" are listed the various small
or tool-room tools used either by hand or in various ma-
chines. So important has their use become that large
industries are devoted to their manufacture, and most
machine-building firms now buy their more common
tools rather than maintain a tool-making plant of their
own. For example, drills, reamers, milling cutters,
counterbores, colletts, etc., are usually purchased in the
open market. Every skilled machinist, however, should
know the principles upon which such tools are made,
and should be able to make any or all of them.
DRILLS. Drills are now largely of the twist type,
and the most efficient are machined and milled from
solid bar-stock, and for this purpose both Carbon-tool
steel and high-speed steel are being used. The prevailing
type has a straight or a tapered holding shank, spiral-
milled flutes and a cone-point with effective cutting lips
as noted under drill sharpening. The flutes or lands
taper slightly from full diameter size at the cone-point
to several thousandths inch smaller at or near the hold-
ing shank. To prevent rubbing on the sides of a hole,
the flutes are also cleared back from the front edge
throughout their length. The grooves are milled with
cutters having a form that gives the maximum chip
capacity, yet leaves the cutting edge of the drill-lip a
straight line.
Several makers of twist-drills increase the lead of
the twist when milling the grooves; such drills are known
as "increase twist" drills. The web is as thin as con-
sistent with the required strength, and with some makers
is thicker near the shank than at the point. Drills
are carefully heat-treated, straightened, and ground to
diameter.
REAMERS. The term "reaming" is given to the proc-
97
THE STARRETT BOOK
ess of enlarging a drilled hole. Reamers are of two well-
defined types, known as "fluted" reamers and "rose"
reamers. The fluted reamer is one having numerous
flutes on the circumference of the cutting portion of
the tool. In other words, the cutting is done on the cir-
cumference instead of at the end, as with a drill.
The number of flutes on the surface of a reamer
varies with the diameter, and with some makes the num-
ber of flutes is greater for a given diameter when the
reamer is to be used in a machine instead of for hand
reaming.
As its name implies, a fluted hand reamer is made
for hand use, and is seldom called upon to enlarge a
hole more than .007" for any diameter, and not more
than .003" in the smaller sizes.
In the case of machine or lathe reamers, the length
of the flutes for any given diameter is fifty per cent
less than the standard length for hand reamers. The
depth of flute is usually somewhat in excess of that of
hand reamers. In most cases machine reamers are used
for enlarging drilled holes to a diameter which only
allows sufficient stock for hand reaming. When the holes
are not to exceed a diameter in length, machine reamers
may be used for finishing the drilled hole to its full
diameter; but when straight, round, accurate holes are
to be of exact diameter the better practice is to first drill
1/32" to 1/16" under size, enlarge to hand reaming size
with a machine reamer, and then carefully hand ream to
exact size.
ECCENTRIC FLUTES. Formerly fluted reamers had
an odd number of flutes, such as nine or eleven. Although
this method eliminated chattering to some extent, it had
the disadvantage of making it difficult to caliper the
diameter of the cutting edges. Eccentric fluting, as it
is called, consists in milling the flutes with uneven spac-
ing to obviate chattering, but having them exactly oppo-
98
THE STARRETT BOOK
site, so that a diameter measurement may be made with
a micrometer.
A rose-reamer is an end-cutting tool, and is often
used in place of a drill in cored holes. It is never made
for hand use, and in general practice is seldom used for
exact diameter.
MILLING CUTTERS. In lathe work the cutting tool
is fixed and the work rotates. In a milling machine the
cutter rotates and work is fed against it. The rotating
cutter, termed a "milling cutter," has an almost unlimited
variety of sizes and shapes for milling regular and irreg-
ular forms. Milling cutters are made from some of the
tool steels, heat-treated to give the right cutting quali-
ties, the stock coming to the tool-maker in the form of
rough blanks, carefully annealed. Where the cutter has
a hole through it this is first drilled, bored, or reamed to
a diameter somewhat smaller than that in the finished
cutter. The reason for this is that all the exact true sur-
faces must be finished after the cutter has been hardened
some grinding process being necessary which requires
an excess of stock.
When the length of the cutter is greater than about
one-half inch, it is usual to chamber the hole to a shape
that renders it necessary to diameter grind the holes at
the ends only. In cutters of considerable length the
saving in grinding by this procedure is considerable.
The sides of the blanks are usually recessed, giving a hub-
and-rim effect at the sides of the cutter. An even num-
ber of teeth is preferable, and these are spaced to a cir-
cumferential pitch varying from three-eighths to three-
quarters inch for ordinary cutter sizes.
When the teeth are milled into the solid blank, a
cutter giving a space angle of sixty degrees is preferred
for cutting the peripheral teeth, while one of seventy
degrees is generally used for the side teeth. Where
milling cutters are made in quantity, special space cutters
99
THE STARRETT BOOK
are worked out to give the maximum chip room con-
sistent with tooth strength.
After the cutter has been heat-treated to the proper
hardness, it is finished to the specific dimensions by
grinding.
GRINDING THE HOLE. Unless special methods
and tools are employed the hole is completely finished
as the first operation of grinding. This is accomplished
by holding the cutter trued in a chuck screwed on the
spindle of a Universal grinder and grinding out the hole
to standard size, using an internal grinding attachment.
GRINDING THE SIDES. Fig. 30 shows how to
grind the sides with the cutter held flat against a face-
plate. If the cutter is to be used for deep cuts, the face-
plate is set to give a slight concavity to the sides of
the cutter.
FIG. 30
CLEARANCE OF THE TEETH. The teeth of milling
cutters are given a slight clearance back from the cutting
edges; five degrees is usually sufficient.
100
THE STARRETT BOOK
JIGS AND FIXTURES
Jigs and fixtures are special devices designed to put
manufacturing upon an efficient basis. Three distinct
purposes are served by the use of jigs: (a) Reduction of
cost per piece; (&) interchangeability of parts; and (c)
accurate production.
Jigs and fixtures are usually made from cast iron or
steel. Their use practically does away with fitting, as
this term is known in shops not using jigs.
JIG DESIGN. A jig is a device for holding the
work and for locating the tool work to be done upon it.
A good example of this is shown in the drill jig, Fig. 31.
Jigs are of the plate type which lies upon and is
clamped to the surface of the work; of the open-box
type; and of the closed-box type.
In designing a jig, the piece is first drawn upon a
sheet of paper, which is sufficiently large to allow locat-
ing the views some distance apart. This permits build-
ing the jig in the drawing around the "coupon," as the
piece is often called. To start the design, first determine
and lay down the locating points or stops, then arrange
the clamping device. A jig should be so designed that
the work can be put into position in only one way.
Provide for supporting the thrust of the cutting tools
in such a manner as to avoid springing the work. Make
the jig as simple as possible, avoiding every feature in
design that complicates the workman's use.
While in the larger shops the jigs are designed by
the draftsmen, in many shops the tool-maker both de-
signs and builds the jigs, and in no other way can a
workman so clearly show his ability and ingenuity as
in the building of jigs.
JIG BODY. The jig body is usually of cast iron,
which is first rough planed or milled on all surfaces
which are to be finished. These surfaces are then finish
101
THE STARRETT BOOK
planed to final dimensions. In some cases jig bodies
are finished by grinding in a surface grinder.
LOCATING BUSHING HOLES. If no particular
accuracy is demanded, the holes for bushings can be
located directly by careful attention to ordinary laying-
out methods, and the hole drilled and reamed directly.
FIG. 31
When the allowable error is very small a more accurate
scheme must be followed, and the best of several meth-
ods for the average tool-maker is that known as the
button method. In this the holes are located by laying
out scribed center lines and locating intersections where
the holes are to be centered. Instead of drilling and
reaming the bushing holes, holes are drilled and tapped
to fit the button screws. The jig buttons are small,
accurately ground cylinders, as shown in Fig. 32. These
are held by means of the screws, lightly clamped in place,
102
THE STARRETT ROOK
and exactly located to centers by accurate measurements.
The highest possible accuracy in locating holes is secured
bv this method.
FIG. 32
BORING HOLES. The holes for the hardened bush-
ings are usually bored by swinging the jig body upon a
face-plate in an engine lathe. The jig body is then
shifted upon the face-plate until a button indicates true
THE STARRETT BOOK
with a Universal Dial Indicator, as shown in Fig. 33.
The jig body is then clamped tightly upon the face-plate.
After removing the jig button, the hole is first rough-
ADJUSTING BUTTONS TO SIDE OF PLATE
BUTTONS IN PLACE
ADJUSTING BUTTONS WITH MICROMETER
104
THE STARRETT BOOK
THE STARRETT BOOK
106
THE STARRETT BOOK
drilled approximately to size, and afterwards carefully
bored exactly to size. This prepares the hole for hold-
ing the hardened steel bushing; the process is repeated
for all the previously located buttons.
JIG BUSHINGS. If the holes in a cast-iron or soft-
steel jig body were left as bored, they would soon lose
accuracy by wearing off center; To prevent this wear
the holes are lined with hardened and carefully ground
bushings, pressed or driven tightly into place. These
bushings are made with a hole having a diameter equal
to that of the tool which passes through them. The
bushings are sufficiently long to support the drill. In
case the jig bushings must be removed frequently, they
are known as slip bushings, and the hole in which they
slip is lined with a steel lining, itself hardened and
ground. In some cases the bushing locates the work as
well as the tool, and if so the bushing screws through
the body of the jig and against some prominent part of
the work, as a boss for example.
107
THE STARRETT BOOK
TOLERANCES. In all construction work a certain
amount of inexactness is allowable. In other words,
it is impossible to obtain absolute precision, and the
allowable errors in exactness are termed "tolerances."
In some cases a tolerance of one-sixteenth inch might
be allowed, while in others exactness to the fraction of
a thousandth part of an inch may be necessary. See
pages 31 and 32.
JIG FOR DRILLING BOLT HOLES IN CYLINDER FLANGE AND HEAD
The projection on the jig keeps it concentric with
the bore of the cylinder, and the recess fits over the pro-
jection on the head.
108
THE STARRETT BOOK
GRINDING
In the machine shop the term "grinding" refers to
the producing of finished surfaces by means of rotating
grinding wheels, and the process of grinding as used
in finishing machine parts is to-day the most efficient
method devised for the purpose. With a proper selec-
tion of grinding machine and grinding wheel, all of the
common machine construction materials may be readily
and accurately finished.
Grinding machines are classified into two groups,
(a) those for curved surfaces; as, for example, cylin-
drical work; and (5) those for plane or flat surfaces.
The first of these is usually called a cylindrical grinder,
and the second is known as a surface grinder. Each
group has many designs, made necessary by the varied
uses to which grinding is adapting itself.
GRINDING WHEELS. These are now known as
abrasive wheels, and the material from which they are
made is termed an abrasive. The abrasives in common
use are the minerals emery and corundum, and the
manufactured abrasives, sold under the trade names of
Alundum, Aloxite, Carborundum, Crystolon. Owing to
the uniformity of the product as it comes from the
electric furnace, manufactured abrasives are at present
more largely used than natural abrasives.
MAKING ABRASIVE WHEELS. An abrasive wheel
is made up of one of the above-named ABRASIVES and
a BOND. The bond is, as its name indicates, something
for holding the abrasive in mixture. Grinding wheels
are made by three processes, known as Vitrified, Silicate,
and Elastic.
VITRIFIED WHEELS. In wheels made by the Vitri-
fied process, the bond is of earth or clay which hardens
or vitrifies' when subjected to a temperature of about
2500 F. to 2800 F. for a definite period of time. Vari-
109
THE STARRETT BOOK
Allowances for Grinding Table 10
Diameter,
Inches
Length, Inches
3
6
9
12
15
18
24
30
36
42
48
Allowance, Inches
X
K
i
1M
U4
2
2K
VA
3
3^
4
V/2
5
6
7
8
9
10
11
12
0.010
0.010
0.010
0.010
0.010
0.015
0.015
0015
0.010
0.010
0.010
0.010
0.015
0.015
0.015
0.015
0.010
0.010
0.010
0.015
0.015
0.015
0.015
0.015
0.010
0.010
0.015
0.015
0.015
0.015
0.015
0.020
0.015
0.015
0.015
0.015
0.015
0.015
0.020
0.020
0.015
0.015
0.015
0.015
0.015
0.020
0.020
0.020
0.015
0.015
0.015
0.015
0.020
0.020
0.020
0020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.025
0.020
0.020
0.020
0.020
0.020
0.020
0.025
0.025
0.020
0.020
0.020
0.020
0.020
0.025
0.025
0.025
0015
0015
0.020
0.020
0020
0.020
0.020
0.025
0.025
0.025
0.025
0.015
0.020
0.020
0.020
0.020
0.020
0.025
0.025
0.025
0.025
0.030
0.020
0.020
0.020
0.020
0.020
0.025
0.025
0.025
0.025
0.025
0.030
0.020
0.020
0.020
0.020
0.025
0.025
0.025
0.025
0.025
0.030
0.030
0.020
0.020
0.020
0.025
0.025
0.025
0.025
0.025
0.030
0.030
0.030
0.020
0.020
0.025
0.025
0.025
0.025
0.025
0.030
0.030
0.030
0.030
0.020
0.025
0.025
0.025
0.025
0.025
0.030
0.030
0.030
0.030
0.030
0.025
0.025
0.025
0.025
0.025
0.030
0.030
0.030
0.030
0,030
0.030
0.025
0.025
0.025
0.025
0.030
0.030
0.030
0.030
0.030
0.030
0.030
0.025
0.025
0.025
0.030
0.030
0.030
0.300
0.300
0.030
0.030
0.030
0.025
0.025
0.030
0.030
0.030
0.030
0.030
0.030
0.030
0.030
0.030
0.025
0.030
0.030
0.030
0.030
0.030
0.030
0.030
0.030
0.030
0.030
110
THE STARRETT BOOK
ous grades of hardness are obtained by using bonds of
different tensile strength. The ideal bond is one which
retains the grains of abrasive until sufficiently dulled
by use, and then allows them to break away, and in this
manner bring fresh cutting edges and points into grind-
ing contact.
SILICATE WHEELS. Silicate of Soda is the bond
used in silicate wheels; and wheels made by this proc-
ess are most efficient for tool and knife grinding.
ELASTIC WHEELS. This process of bonding is
generally used for the very thin wheels used for slitting
metals. The principal ingredient of the bond is shellac.
GRADING THE ABRASIVE. By numerous crushing,
grinding, cleansing, and sorting processes, the abrasive is
graded into a series of sizes which give the wheel its
grain number. This number conforms to the sieve mesh
through which the abrasive is passed; for example, grain
No. 40 indicates that the abrasive was graded through a
sieve having a mesh of forty to the linear inch.
COMBINATION WHEELS. For many grinding pur-
poses the combination wheel is preferred to a wheel of
single grade. Combination wheels are made up of abra-
sives of several grain numbers.
BONDING. The ideal bond is one which is imper-
vious to moisture, does not soften by heat, and which
holds firmly the cutting points of the abrasive until they
become dulled by use. The bond then releases the dull
abrasive and permits fresh, sharp points to begin cutting.
With abrasives of equal quality the maker who nearest
approaches the ideal bond produces the superior wheel.
GRADING THE WHEELS. In grinders' language,
abrasive wheels are known as hard wheels and soft
wheels. The maker, therefore, lists his wheels as hard
or soft by some scale of numbers or by letters. A prom-
inent firm uses the letters of the alphabet, as shown in
the following list in which "M" is medium.
Ill
THE STARRETT BOOK
Norton Grade List
The following grade list is used to designate the
degree of hardness of our Vitrified and Silicate Wheels,
both Alundum and Crystolon.
E Soft
F
G
H
I Medium Soft
J
K
L
MEDIUM M MEDIUM
N
O
P
Medium Hard Q
R
S
T
Hard U
V
W
X
Extremely Hard Y
The intermediate letters between those designated as
soft, medium soft, etc., indicate so many degrees harder
or softer; e. g., L is one grade or degree softer than me-
dium; O, two degrees harder than medium, but not quite
medium hard.
Elastic Wheels are graded as follows: 1, 1 V 2 , 2, 2^, 3,
4, 5, and 6. Grade 1 is the softest and grade 6 the hardest.
112
THE STARRETT BOOK
CYLINDRICAL GRINDING. When the piece being
ground is rotated, the process is known as cylindrical
grinding, and the development of machines for grind-
ing cylinders has given the process a great impetus.
While it is possible to grind from the rough stock with-
out previous lathe work, the method usually followed is
to first rough turn the work.
ROUGHING FOR GRINDING. This process includes
the work done in removing excess stock previous to
finishing to size in the grinding machine. Unless a study is
made of the conditions surrounding the whole operations
of the lathe and the grinding machine, lack of efficiency
may result. In general where the work is to be ground it
is best to consider the lathe as a mere roughing machine
for removing the excess of stock at as deep a cut and as
coarse a feed as is consistent with an efficient cutting
speed, leaving the job of finishing to the grinding machine.
AMOUNT TO LEAVE FOR GRINDING. If the grind-
ing machine is modern in design as much as 1/32 of an
inch, or even more may be left on machinery steel parts
for removal in the grinder; the amount varying with
the size of the work itself. An allowance of 1/64 of an
inch is general on the smaller machine parts, but this
allowance should be increased on larger sizes. Table 10,
page 110, shows allowance for grinding as recommended
by one maker of grinding machines, and Table 11 shows
grinding wheel speeds.
SELECTING THE WHEEL, the selection of the
wheel to be used in any grinding operation can, per-
haps, best be made by reference to Table 12, page 115,
which fairly represents general practice. As the hard-
ness of material and the area of contact made by the
wheel have a marked influence, no table can entirely
solve the problem, but it may be used as a start in the
right direction. In general a soft wheel should be used
on hardened work and a harder wheel on soft materials.
113
THE STARRETT BOOK
Table of Grinding Wheel Speeds Table 11
Diameter Wheel
Millimeters
Rev. per Minute for
Surface Speed of
4.000 Feet,
or 1,200 Meters
Rev. per Minute for
Surface Speed of
5,000 Feet,
or 1,500 Meters'
Rev. per Minute for
Surface Speed of
5,000 Feet,
or i, 800 Meters
1 inch
about 25
15,279
19,099
22,918
2 "
50
7,639
9,549
11,459
3 "
75
5,093
6,366
7,639
4 '
100
3,820
4,775
5,730
5 '
125
3,056
3,820
4,584
6 '
150
2,546
3,183
3,820
7 '
175
2,183
2,728
3,274
8 '
200
1,910
2,387
2,865
10 '
250
1,528
1,910
2,292
12 f
305
1,273
1,592
1,910
14 '
355
1,091
1,364
1,637
16 '
405
955
1,194
1,432
18 '
455
849
1,061
1,273
20 '
505
764
955
1,146
22 '
515
694
868
1,042
24 '
610
637
796
955
26 '
660
586
733
879
28 '
710
546
683
819
30 '
760
509
637
764
32 '
810
477
596
716
34 '
860
449
561
674
36 '
910
424
531
637
38 '
965
402
503
603
40 '
' 1,015
382
478
573
42 '
1,065
364
455
546
44
' 1,115
347
434
521
46 '
' ' 1,165
332
415
498
48 '
' 1,220
318
397
477
50 '
' 1,270
306
383
459
52 '
' 1,320
294
369
441
54 '
' 1,370
283
354
425
56 '
' 1,420
273
341
410
58 '
" 1,470
264
330
396
60 "
" 1,520
255
319
383
The R. P. M. at which wheels are run is dependent on conditions and style
of machine and the work to be ground.
Wheels are run in actual practice from 4,000 to 6,000 feet per minute; in some
instances as high as 7,500 feet.
114
THE STARRETT BOOK
Grade and Grain of Grinding Wheels for Different Materials*
Table 12
(The Norton Co.)
Class of Work
Alundum
Crystolon
Grain
Grade
Grain
Grade
Aluminum castings
36 to 46
3 to 4
Bias.
20 to 24
20 to 24
24 to 36
16 to 24
16 to 24
30 to 46
16 to 30
20 to 30
16 to 24
20 to 30
20 to 30
PtoR
QtoR
PtoR
PtoR
OtoQ
JtoL
JtoL
QtoS
QtoS
Q
OtoQ
Brass or bronze castings (large)
Brass or bronze castings ^small)
Car wheels cast iron
Car wheels, chilled
Cast iron, cylindrical
Cast iron, surfacing
Cast-iron (small) castings
Cast-iron (large) castings
Chilled iron castings
Dies chilled iron .
20
24 comb.
20 to 46
24 to 30
16 to 20
20 to 30
JtoK
HtoK
PtoR
QtoR
PtoU
Dies, steel
36 to 60
20 to 30
JtoL
PtoR
Drop-forgings
Internal cylinder grinding . . .,
Internal grinding, hardened steel
Machine shop use, general
Malleable iron castings (large)
Malleable iron castings (small)
Milling cutters, machine grinding . .
Milling cutters, hand grinding
Nickel castings
Pulleys, surfacing cast iron
Reamers, taps, etc., hand grinding. .
Reamers, taps, special machines
Rolls (cast iron) wet
30 to 60
ItoL
46 to 60
20 to 36
14 to 20
20 to 30
46 to 60
46 to 60
20 to 24
46 to 60
46 to 60
24 to 36
70
JtoM
OtoQ
PtoU
PtoR
HtoM
JtoM
PtoQ
KtoO
JtoM
JtoM
!Hto2
Elas.
"RtoS
QtoS
R '
KtoL
16 to 20
20 to 30
20 to 25
30 to 36
24 to 38
70 to 80
30 to 46
30 to 50
jtoM'
I^to2
Elas.
2 to 3 Elas.
KtoM
Rolls (chilled iron), finishing
Rubber .'
30 to 50
36 to 50
60
24 comb.
46 to 60
24 to 36
24 comb.
46 to 60
36 to 46
12 to 20
20 to 30
16 to 46
16 to 24
46 to 60
36 to 60
12 to 30
46 to 60
JtoK
MtoN
OtoQ
LtoN
LtoN
HtoK
K
JtoL
HtoK
SSS
LtoP
PtoR
M
KtoM
PtoU
KtoM
Saws, gumming and sharpening ....
Saws, cold cutting-off
Steel (soft), cylindrical grinding. . . j
Steel (soft), surface grinding
Steel (hardened), cylindrical grind- 5
ing {
Steel (hardened), surface grinding . .
Steel, large castings
: ::::;
Steel (manganese), safe work
Structural steel
Twist drills, special machines
Wonrlwnrkincr tnnls . .
* The information contained in this table is general and intended only to give
an approximate idea of the grade used under ordinary conditions.
116
THE STARRETT BOOK
MOUNTING THE WHEEL. The wheel should be
so mounted that there are no unequal stresses set up.
Suitable guards should be provided to prevent injury
to the workmen in case of the wheel bursting. The
accompanying illustrations show RIGHT and WRONG
methods of mounting wheels carefully study the cuts.
MEASURING THE WORK. The use of micrometers
for obtaining exact measurements is nowhere better
illustrated than in grinding. Fig. 34 shows an oper-
ator adjusting his micrometer for obtaining a measure-
ment on a cylindrical piece, and Fig. 35 shows the
operator as he makes his reading. While in lathe
work the position of the operator leads naturally to
adjusting the micrometer spindle with the fingers of
the right hand, the left hand grasping the frame, in
grinder work the reverse is generally true, hence he
occupies the position as shown.
GRINDING FLAT SURFACES. Flat surface grind-
ing may be divided into two general classes : (a) Machine
116
THE STARRETT BOOK
FIG. 34
parts, such as boxes, tables, cross-slides, faces of nuts,
etc.; and (b) fine tool work, as, for example, steel blades,
scales and rulers, straight edges, etc. Until recently the
first-named class of work was done by reciprocating
the work beneath the circumferential face of an abrasive
wheel in a machine which, in principle, is not unlike a
small planer. The use of machines with CUP WHEELS
has practically revolutionized such grinding, and an
exactness of surface is being obtained on fine flat work
which leaves little to be desired.
LAPPING. In certain lines of work the final grind-
ing process is often made, not with abrasive wheels as
previously described, but by using metal discs, rings, or
cylinders, the surfaces of which have been charged with
a fine flour abrasive. Such a tool is called a "lap," and
its use "lapping." Laps were first used by lapidaries in
finishing the surfaces of mineral specimens, but laps
have been in common use for a considerable time on fine
work in the machine shop.
117
THE STARRETT BOOK
Laps are generally made of some material soft
enough so that the abrasive can be readily pressed into
the surface; or, as it is correctly termed, the surface
is "charged." Soft, close-grained cast iron, copper,
brass, or lead may be used for the lap, and any of the
flour abrasives may be charged into the surface by roll-
ing the abrasive into the lap either with a hardened roll
or on a hardened surface.
FIG. 35
In some of the finer grinding operations the lap is
charged with diamond dust which has been precipitated
or settled in a suitable dish of olive oil. The several
grades are denoted by the time taken to precipitate; as,
for example, fineness No. 5 takes ten hours.
Since lapping is a somewhat slow and tedious proc-
ess it should be used only for the removal of small
amounts of stock.
COMMON USES OF LAPPING. The more common
uses of lapping are those of finishing micrometer ends,
plug and ring gages, holes in jig bushings, and in the
finest die and punch work.
118
THE STARRETT BOOK
LOCATING AND ALIGNING
MACHINERY
When the product of the shop is determined, the
proper location of the machines may be found by means
of a plan or location drawing worked out in the draft-
ing room. An easy way to do this is to provide rectangu-
lar slips of cardboard, each representing to some definite
scale the plan outline of each machine. Placing these
upon the floor plan of the room, the better of several
arrangements may be found, and by using push pins the
cardboard representations may be fixed in position.
FIG. 36
Having decided upon the location, the machinery
may be aligned in these positions by measurements from
some base line made upon the floor or ceiling; or a
leveling instrument,* such as shown in Fig. 36, may
be used.
Ordinarily the machines are aligned by simple meas-
* See page 124 for directions for setting up a level.
119
THE STARRETT BOOK
urements and the countershafting hung from the ceil-
ing vertically over the machine by plumbing up from
the previously located machines. In such work thought
must always be given to the line shafting and pulleys.
Unless care is used, there may be such interferences
as to necessitate repeating the work. As the efficiency
of the shop depends to a considerable extent on a con-
venient arrangement of the machines, all interferences
should be taken care of on the ceiling rather than alter-
ing the arrangement of the machines.
ALIGNING THE SHAFTING. With the locations of
the several lines of shafting determined upon, the usual
method of alignment is to stretch a wire or cord the
length of the room at the desired level of the shaft and
at a distance from its location sufficiently great to give
easy working room. With the two ends of the wire in
position it should be stressed to bring it taut and should
be supported at frequent intervals by wire hangers.
FIG. 37
With the shafting hangers in approximate position
and the shafting in place, the necessary shifts can be
made to bring the shaft parallel with the wire. A light
stick notched at one end to rest upon the shaft and a
wire brad at the other end for a feeler is all that is neces-
sary for ordinary alignment. Leveling the shaft is done
with special spirit levels having metal frames, the bases
of which have been carefully grooved to set upon the
shaft. Such a level is shown in Fig. 37. Special level-
ing and aligning attachments for setting and lining up
120
THE STARRETT BOOK
shafting are sometimes used. Shafting is often lined by
plumbing up from a data line on the shop floor with a
mercury plumb bob.
Mercury Plumb
Bobs
121
THE STARRETT BOOK
LEVELING INSTRUMENT
While the surveyors' transit can be used in shop level-
ing and in shaft aligning a much simpler and a more
inexpensive instrument termed a leveling instrument is
all that is needed.
It consists of a table capable of being adjusted in the
horizontal plane, which carries a yoke which in turn
carries a twelve-inch brass tube. The whole instrument
is placed upon a suitable tripod. The tube has no lenses
and therefore is not a telescope as in the surveyors'
instrument.
At one end of the tube are the usual cross hairs
which locate the axis and at the opposite end is a peep
hole or sight piece for the eye. The yoke which carries
the tube is attached to a graduated arc which is let into
the upper part of the table; this allows the instrument
to swing to read angles in the horizontal plane.
ADJUSTING THE INSTRUMENT. In using this in-
strument it is important that the table be carefully lev-
eled. It is pivoted on the tripod tube by a ball and socket
joint. Three knurled-head adjusting screws threaded
through the tripod top and resting against the under side
of the table furnish a means of adjusting the table. Upon
the table carrying the yoke is a bent-tube spirit level with
a sensitive air bubble. After the tripod legs have been
placed to roughly level the instrument, adjust the knurled
leveling screws to give .as correct a centering for the
air bubble as is possible. To test this adjustment swing
the yoke, which carries the air bubble, to several posi-
tions and note any change in the position of the bubble.
If there is a change, readjust the leveling screws until
the yoke can be swung through its travel with the air
bubble maintaining its central position.
USING THE LEVELING INSTRUMENT. While it is
possible to so mount the leveling instrument upon a plat-
122
THE STARRETT BOOK
form that its height will be sufficient for the use of
targets mounted upon the shaft, the usual method is to
hang targets upon the shaft and adjust them to swing low
enough to allow the leveling instrument to be set with
its tripod on the floor or on some convenient foundation
spot.
THE TARGETS. These consist of stirrups which
carry a spirit level and block with vertical and horizontal
lines crossing each other. A plumb is hung upon the stir-
rup in such manner as to be readily raised or lowered.
One of the targets may be hung upon the shaft free to
swing plumb, the other is used as a fixed wall target.
USE. After the shafting has been roughly aligned
with the wall of the building or with a line of columns,
this being done by measurement, the leveling instrument
is placed vertically beneath one end of thfc shaft. To
locate the leveling instrument, plumb down from the
center of the shaft, using the hanging target plumb bob,
and locate a point in the floor or board placed on the
foundation. A prick punch mark in the flat head of a
wire brad previously driven into the floor provides a
permanent point. Set the tripod of the leveling instru-
ment directly over this point, using the plumb bob hang-
ing from the center of the table. Next carefully level
the table as already described. Hang the portable target
closely in front of the cross-hair end of the tube and
level and adjust its height until the horizontal cross hair
of the tube coincides with the horizontal cross line of
the target.
Remove the target to the far end of the shaft and
swing the tube of the leveling instrument until the sight
through the tube coincides with the vertical line on the
target. With the hanging target displaced, mount a fixed
target upon the wall at the far end of the shaft and
adjust it until its cross lines coincide with the cross
hairs of the tube as sighted. If the instrument is in its
123
THE STARRETT BOOK
original position with the plumb bob over the point in
the floor, the setting up of the instrument is complete.
By reference to the fixed target it can at all times be
checked.
Replace the hanging target at the far end of the shaft
and adjust the adjacent hanger so that the cross lines
of the target coincide with the cross hairs when sight-
ing through the tube. Repeat for each hanger until the
target can be hung upon the shaft adjacent to any hanger
and show perfect coincidence of target cross lines and
tube cross hairs.
Note that after the instrument and target have been
set neither should receive further adjustment except in
case of accident the shaft itself receives the adjust-
ments.
HOW TO SET UP THE TRANSIT
The Starrett transit or level can be used for the same
purposes as any engineer's transit and level, and because
of its simplicity and freedom from complications, it
can be used by any one in laying out foundations for
buildings, aligning machinery, and in building dams
and raceways for simple water-power developments.
The transit combines in one instrument the facili-
ties for measuring both horizontal and vertical angles,
and enables the operator to lay out anything that does
not require excessive refinement. The level is for meas-
uring angles in a horizontal plane only, and it should be
borne in mind that the level will do all that the transit
will do, except measure vertical angles. The transit,
which is furnished either with a telescope or plain-sight
tube, is mounted on a tripod, and has a plate carrying
a graduated arc. The telescope or sight-tube is connected
to a graduated vertical arc so that vertical angles may
be measured as well as horizontal. It is provided with
124
THE STARRETT BOOK
leveling screws, and with a ground level vial for adjust-
ing the level of the graduated plate.
To level the instrument, the legs must be firmly set
into the ground or floor, so that neither wind nor acci-
dental touch will disturb the adjustment. It should then
be made as nearly level as possible by adjusting the
lower parts of the extension legs. It should then be
brought to a perfect level by means of the leveling screws
between the plate and tripod head. This is done by
bringing the level over any one of the leveling screws
and turning one screw in and another out until the
bubble appears in the center of the level glass. The sight
tube or telescope should then be turned through an
angle of about ninety degrees and again the bubble ad-
justed to the center of the glass by means of two leveling
screws. This operation should be continued until the
bubble stands in the center of the glass, no matter in
what direction the telescope may be turned.
To find differences of level of two places, the instru-
ment should be placed in a position about equally dis-
tant from the two points. First obtain the height of
the target on one of the rods by means of the cross line
in telescope or sight tube and make record of the same.
Then carry the rod to the other position and find the
height of the target at that point. The difference be-
tween the two heights, as read on the rod, will be the
difference of level of the two places, that place being
higher at which the height of the target is less.
125
THE STARRETT BOOK
ELEMENTARY ALGEBRA
Many engineering and shop problems can be solved
more readily with algebra than by means of arithmetic.
In fact, some problems cannot be solved by arithmetic;
as, for example, when the conditions are not fully and
concretely stated. Algebra is applied by expressing the
relations in algebraic terms, forming them into an equa-
tion, which states the conditions, and then solving the
equation.
In arithmetic a figure has a definite value, 4 or 20
for instance, and the value remains unchanged; it is
always 4 or 20. In algebra letters are used, and as these
letters do not always have a definite value, their use adds
flexibility to mathematical operations. Some find it easier
at the beginning to think of the letters as abbreviations.
SYMBOLS
Some of the symbols or signs of algebra are the
same as those used in arithmetic.
THE SYMBOLS OF QUANTITY are the figures used
in arithmetic and the letters of the alphabet.
THE COMMON SYMBOLS OF OPERATION are the
signs used in arithmetic; they are as follows:
+ is the sign of addition, called plus. If no sign
precedes numbers or letters the plus sign is understood;
that is, 2abc is + 2abc.
is the sign of subtraction, or difference, called
minus.
X is the sign of multiplication, called times. When
there is no sign between letters or between letters and
figures, multiplication is understood. Thus Serf means
3 X c X d. But this does not apply to numbers : 328
is not 3 X 2 X 8, but 328, same as in arithmetic.
126
THE STARRETT BOOK
*
-*- is the sign of division, read " divided by." Divi-
sion may also be expressed by a horizontal line between
a 16
the quantities, as, a -*- b = or = 16 -*- 4.
b 4
COEFFICIENT. The numerical factor or number is
generally called the coefficient; in 5abc, 5 is the coeffi-
cient; but, strictly speaking, 5a is the coefficient of be,
and 5a& is the coefficient of c. Again in the expression
3a (b c), 3a is the coefficient of (b c), or in the ex-
pression (a + b) x, (a + b) is the coefficient of x.
When no numerical coefficient is expressed, it is
always unity or 1. Thus a = la.
EXPONENT. The small figure or letter written at
the right and a little above a number or letter is called
the exponent; it shows how many times the number is
to be taken as a factor.
Thus 2 2 is read "2 squared" or "2 with the exponent
2." The number 2 is to be used twice as a factor, or mul-
tiplied by itself. Similarly a 3 is read "a cubed" or "a with
the exponent 3." The letter a is to be taken three times
as a factor, or a X a X a. In the same way (m + n) 4 =
(m + n) X (m + n) X (m + n) X (m + n).
Again a*bc*d*=a X aXbX cX cXcXdXd XdXd.
Note this difference
m*= m X m X m X m
4m = m + m + m + m
SYMBOLS OF RELATION show the relative values
of letters.
= is the sign of equality, read "equals" or "equal to."
a = b means that a is equal to b, or whatever value is
given to a, the same value must be given to b. If 4a = 3&,
4 times some quantity represented by a is equal to 3 times
some quantity represented by b, but it is evident that a
does not equal b.
: is read "is to" or "to." It indicates ratio.
127
THE STARRETT BOOK
If two ratios are equal, they may, 01 course, be con-
nected by the sign of equality, but more often they are
connected by this sign : :
SYMBOLS OF AGGREGATION
( ) Parentheses.
[ ] Brackets.
| j Braces.
Vinculum.
V Radical Sign (square root).
Letters or quantities enclosed in parentheses are to
be handled as a single quantity.
5 (c + d) means that c + d as one quantity is to
be multiplied by 5.
Or (a + b) -5- (x + {/) means that a + b taken as a
single quantity is to be divided by x + y taken as a sin-
gle quantity. Another way of expressing it is, the same
operation performed on a must be performed on b also.
Again (a + b) means that the sum of a and b taken
as a single quantity is to be subtracted. It does not mean
that a alone is to be subtracted.
THE RADICAL SIGN. This sign is used as in arith-
metic; that is, it shows that some root of the quantity
is to be found, or expressed.
The small number or index used in connection with
the radical sign denotes what root is meant. Thus ^/~a
is read "the cube root of a." ^/6 is read the fifth root
of ft." When no index figure is used the square root is
understood. Vx + y = the square root of x + y.
When the horizontal line extends over the expression
it means that the indicated root is to be found of the
entire expression. V m + n = "the square root of m + n."
128
THE STARRETT BOOK
Let m = 36 and n = 64.
V~m~+ n= V"367F 64 = VIM" = 10
V/n + n=V36+ 64=6 + 64-70
Vm + Vn = V36+ V64=6+ 8 = 14
POSITIVE AND NEGATIVE TERMS
A term or quantity preceded by the plus sign, or by
no sign at all, is a positive term, and one preceded by the
minus sign is a negative term. This applies whether the
term is a simple one like 3a (a monomial) or (x + y)
(a binomial) or (a 2 + 2ab + b 2 ) (a polynomial).
SIMILAR TERMS. When several terms have the
same letters, but may differ in numerical coefficients,
they are called similar terms. Thus 4ac, 5ac, and 3ac
are similar terms.
In arithmetic we say that + 5 and 5 cancel; that
is, if we have five units and subtract five units we get
zero. Similarly in algebra 5a cancels 5a, or Gcfxy
cancels Qa 2 xy.
ADDITION
Addition is finding the sum of two or more quantities.
Arithmetic Algebra
4 apples 4ab
3 apples 3a&
10 apples lOafr
17 apples 11 ab
When the terms are alike, we add them by adding
the coefficients; when they are not alike the addition
is expressed.
6ac added to
6ac
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THE S T A R RETT BOOK
If the terms have different signs they can be added
by algebra.
6ac added to ISac = 12ac
6ac added to ISxy = I8xy 6ac
When there are several quantities which are alike,
but the signs unlike, we add them by adding all the posi-
tive or plus terms, then subtract the sum of all the nega-
tive or minus terms. For instance,
5/nn
2mn
3/nn
6mn
15mn
The positive terms in the above equal + 23mn and
the negative terms equal 8mn, the result being
23mn 8mn = 15mn.
Had all the signs been changed, the answer would
have been 15/nn; for the sign prefixed to the answer
is that of the greater sum.
SUBTRACTION
Subtraction in many ways is like addition; that is,
like terms can be subtracted in the same way that they
can be added, and unlike terms are subtracted by indi-
cating the difference.
Subtraction is the process of finding the DIFFER-
ENCE between two quantities.
In arithmetic the larger cannot be subtracted from
the smaller, but in algebra this can be done by express-
ing the difference.
In arithmetic 11 cannot be subtracted from 4, but
in algebra 7 11 = 4; that is, 7 lacks 4 of being equal
to 11. It is minus 4.
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THE STARRETT BOOK
The difference (in number of units) between 8 and
2 is 6, whether it is 8 2 or 2 8. Whether the differ-
ence is 6 or + 6 depends upon which number is being
subtracted.
These few rules should be remembered.
Subtracting a + quantity is the same as adding a
minus quantity.
Subtracting a quantity is the same as adding a
plus quantity.
The sum of a minus quantity and a plus quantity is
the difference between the quantities, with the prefixed
sign of the larger.
The difference between a plus quantity and a minus
quantity is equal to the sum of the quantities.
MULTIPLICATION
Multiplication is a short method of addition; that is,
if you add 4ac five times, the result is the same as mul-
tiplying 4ac by 5.
4ac
4ac 4ac
4ac 5
20ac
Multiplication is a process of taking a given quan-
tity as many times as indicated by a number or another
quantity.
Multiplication differs from addition in that unlike
quantities can be multiplied.
5abx multiplied by Qaxy =
131
THE STARRETT BOOK
This simple example shows that to multiply we first
multiply the coefficients, then annex the letters, multi-
plying them when alike by adding the exponents; for
instance, a X a = a 2 , x X x = x~.
SIGNS. If both quantities are plus, the product is
plus; if both are minus, the product is plus; if one is
plus and the other minus, the product is minus.
Multiplying more complicated quantities, those con-
sisting of two or more terms each, is illustrated by this
example in arithmetic:
Multiply 4 + 3 + 2-1 by 6
Instead of adding before multiplying let us multiply
each number by 6 :
4+ 3+ 2-1
6
24 + 18 + 12 - 6 = 48
If we use letters also, we proceed in the same way :
Multiply 4ac + Sab + 2e c by 6a.
4ac + 3afc + 2c - c
6a
24a 2 c + 18a 2 fc + 12ac - 6ac
Combining similar terms, 24o 2 c + 18a 2 + 6ac
Multiply 2a + 4b by 3a - 66
6a 2 +
Go 2 -24&'
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THE STARRETT BOOK
The above example should be thoroughly understood,
for it involves multiplication, addition, and cancellation
of like terms.
If three quantities are to be multiplied, first multiply
two of them, then multiply the product by the third.
DIVISION
Division is the process of finding how many times
one quantity is contained in another.
In arithmetic dividing 20 by 4 is finding how many
times 4 is contained in 20.
In algebra dividing 25a 2 fcc by Sac is finding how
many times 5ac will go in 25a 2 c.
First divide the coefficient 25 by 5, then divide the
letters by subtracting the exponents of the same letter,
a 2 -*- a = a because 2 1 = 1. When no similar letter is
in the dividend, as in the case of b, there is no exponent
to subtract, therefore we put the b in the quotient. In
the case of the letter c, c goes in c once or 1.
5ac )
25a c
ab
Another way to state this is to divide the terms into
factors :
5ac
=5ab
The 5 cancels 5 in the numerator, a cancels one a
in the numerator and c cancels c. These cancel because
the exponents become zero; for instance, 1 1 = 0, and
c with the exponent zero equals one or unity.
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THE STARRETT BOOK
SIGNS. Since division is the converse of multipli-
cation, the rules governing signs are practically the same :
When both divisor and dividend are + the quotient
is +.
When both divisor and dividend are the quotient
When the divisor is + and the dividend is the
quotient is .
When the divisor is and the dividend is + the
quotient is .
The process of polynomials is merely an extension
of the process of dividing monomials.
Example: Divide 40a 4 35a 3 & + Sa 2 b lab 2 by
8<f - lab :
So 3 - lab) 40a 4 - 35a 3 fc + Sa 2 b - lab 2 (oa 2 + b
40a 4 35a 3 fc
8a 2 b - lab 2
Sa 2 b - lab 2
EQUATIONS
AN EQUATION is an algebraic expression in which
two or more terms or quantities are connected by the
sign of equality. The two terms or expressions are called
members or sides of the equation; the term on the left-
hand side is called the first, and that on the right-hand
side is called the second term.
The letter whose value is to be found is called the
"unknown quantity," and it is usual to represent the un-
known quantity by the letter (x).
To solve an equation is to find the value of the un-
known quantity, either in terms of numbers or in terms
of numbers and letters.
A very important fact to remember about equations is
that if the same operation is performed on both sides of
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THE STARRETt BOOK
the equation the left-hand side will still be equal to the
right-hand side.
The equation will continue to be an equation if
a. The same quantity is added to both sides.
b. The same quantity is subtracted from both sides.
c. Both sides are divided by the same quantity.
d. Both sides are multiplied by the same quantity.
e. Both sides are raised to the same power.
/. The same root of both sides is extracted.
This fact is made use of in solving an equation; for
instance,
So: = 20
Dividing both sides by 5, we have
x = 4
Again, 1/5* = 20
Multiplying both sides by 5, we have
5 X 1/5* = 5 X 20
* = 100
Before solving an equation it is usually easier to
rewrite or rearrange the terms so that x with its coeffi-
cient will be alone on the left-hand side. Changing the
terms from one side to the other is called "transposing."
It is evident that in transposing the truth of the sign of
equality must not be destroyed.
Bearing in mind the fact that if the same operation
is performed on both sides of an equation the left-hand
side remains equal to the right-hand side, we can trans-
pose terms.
x - 2a = b
Adding 2a to both sides, we have
x - 2a + 2a = b + 2a
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THESTARRETT BOOK
As 2a cancels + 2a, we have
x = b + 2a
We see from this that the 2a has been transposed
from one side to the other, and that in transposing the
only thing that happened to it was that its sign was
changed.
Numerous examples would show this simple fact that
to transpose a quantity from one side of an equation to
the other, it is only necessary to write the quantity on
the other side with its sign changed; plus changed to
minus or minus to plus.
If the term containing x is a fraction, the denom-
inator can be eliminated, so that x will be alone, by mul-
tiplying both sides of the equation by the denominator.
c~ b
First, combine the fractions on the right-hand side,
because they have the same denominator, thus:
x m 2 + n 2 n
To get x alone on the left-hand side, multiply both
sides by c.
_ c (m 2 + n 2 - n)
x
b
Suppose x is in the denominator instead of in the
numerator.
61 *
a H- b
x~ lOc
Multiplying both sides by x gives
(a + b)x
10c
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THE STARRETT BOOK
Now transpose all terms
(a + b) x
- = 6
lOc
Or dividing both sides by -'. - , the coefficient of x,
lOc
we have
(a + b)x We 6 (lOc)
_______ \x _____ ____
lOc a + b~ a +b
60c
a+ b
The short cut to the same result is to invert both sides.
x lOc
6 a + b
Then multiplying both sides by 6,
60c
~
a + b
SHOP AND ENGINEERING
FORMULAS
The letters which we have used are given a meaning
in shop and engineering formulas by assigning to each
a definite numerical value. The letters are connected
by signs to represent the conditions.
In a certain shop one-fifth of the output is milling
machines, two-thirds is lathes, and the rest is twenty-
eight shapers. How many milling machines and lathes
are produced?
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THE STARRETT BOOK
If we let x represent the total number of machines,
x 2x
- equals the number of milling machines and equals
5 3
x
the number of lathes. The total is equal to - added to
5
2x
, and this sum is added to 28 to equal the unknown
3
quantity x.
x 2x
z=- + + 28
5 3
Multiplying both sides by 15, the common denomi-
nator, to eliminate the fractions, we have
15* = 3* + 10* + 420
15x = 13* + 420
Transposing
15* - 13* = 420
2x = 420
x=2W
x 210 2x 420
= = 42 milling machines and = = 140 lathes.
5 5 3 3
In designing, formulas are used, and these formulas
are in the form of equations, the letters having definite
values. Usually the values of all but one letter are known
or assumed. The problem then is to find the numerical
value of the unknown by substituting the known values.
For instance, in designing keys some use this formula:
126,000 X H.P.
DN
in which P = the total twisting moment on the shaft,
H. P. = the horse-power transmitted, D = diameter of
shaft in inches, and N = number of revolutions of the
shaft per minute.
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THE STARRETT BOOK
If 20 horse-power is transmitted at a rotative speed
of 40 revolutions per minute and the shaft is 2 inches in
diameter, the twisting moment is found by substituting
the known values and solving for P.
126,000 X 20
P -
2 X 40
= 31,500
In finding the thickness of the hub of a pulley, some
designers use this formula :
T = .14^B~D
in which T = thickness of hub in inches,
B = width of face in inches,
D = diameter of pulley in inches.
If the face is 8 inches and the pulley 27 inches in
diameter, we have
T = .14^8 X 27
= .14 X 6
= .84 inch or % inch
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THE STARRETT BOOK
MENSURATION
ANGLES. Of all the plane figures which the machin-
ist has to deal with, the angle is the most important, and
also the most troublesome. Examples of working to an
angle are found in the setting of the compound rest when
taper turning, setting the head of the milling machine
for milling spiral flutes in twist drills or reamers, and
in the cutting of bevel gears. In laying out work the
machinist must understand the properties of angles and
the use of the protractor, so that he may work to the
angle that is wanted, not to some other angle.
An angle is sometimes defined as the difference in
direction of two straight lines; another definition is: an
angle is the space between two straight lines that meet,
or would meet if produced. Angles are also used for
measuring rotation or circular movement.
If a circumference of a circle is
drawn, having for a center the vertex
of the angle, the measure of the angle
will be that arc included between the
sides of the angle. Angle A B is meas-
ured by the arc A B.
The circumference of the circle is
divided into 360 equal parts, each called
a degree. Each degree is divided into 60
equal parts called minutes. Each minute
into 60 equal parts called seconds. The
angle A B will be an angle of 60 if
the arc A B is one-sixth of the circum-
ference.
It makes no difference what the radius of the circle
or arc may be, the difference in direction is the same,
and the number of degrees is the same.
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THE STARRETT BOOK
A RIGHT ANGLE is one formed by two lines per-
pendicular to one another. The arc which measures it
is a quarter circumference or 90. The tool most com-
monly used for measuring a right angle is a try-square.
Two right angles are formed when a line so meets an-
other line that the two angles are equal.
AN ACUTE ANGLE is any angle of less than 90.
AN OBTUSE ANGLE is any angle of more than 90.
The complement of an angle is the angle which must
be added to the given angle to make a right angle or 90.
The complement of an angle of 37 is 53. Either of
these angles is the complement of the other.
The supplement of an angle is the angle which must
be added to the given angle to make 180, or two right
angles. The supplement of an angle of 63 is 1X7. Either
of these angles is the supplement of the other.
The instrument most commonly used for measuring
angles is the protractor. It may be in the form of the
combination set (page 14), or the protractor shown in
the accompanying illustration. The protractor is a grad-
uated disc on a fixed blade and adjustable stock. Any
given angle may be laid out or measured by setting the
blade at the desired angle with the stock. The angle
shown here is a little less than 55.
To set the protractor at an angle of less than 90 is
an easy matter, because the instrument reads directly,
being graduated from zero to 90. But when the desired
angle is greater" than 90, the supplement of the angle
must be found and the protractor set to the supplement.
Thus, to lay off an angle of 150 we first find the supple-
ment or 30 and set the protractor at 30. But the proper
scale must be selected. It often happens that a protractor
set to 60 actually measures 120. With the Starrett com-
bination set, all angles are read directly because of the
two scales, each graduated from zero to 180.
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THE STARRETT BOOK
BASE
TRIANGLE
PROTRACTOR
A plane figure of three sides if all
three sides are equal in length the tri-
angle is equilateral and also equiangular;
that is, all the angles are equal.
The sum of all three angles is equal
to two right angles, or 180.
Any angle equals 180 minus the sum
of the other two.
The areas of two triangles are equal if they have
equal base and equal height or altitude.
If the three sides of a triangle are proportional to
the corresponding sides of another triangle, the triangles
are similar and the corresponding angles are equal.
If the angles of a triangle are equal to the corre-
sponding angles of another triangle, the triangles are
similar and the corresponding sides are proportional.
The area of any triangle = product of base and
altitude divided by 2.
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THE STARRETT BOOK
RIGHT TRIANGLE
A right triangle is one having one
right angle.
The hypotenuse is the side opposite
the right angle.
The square of the hypotenuse is
equal to the sum of the squares of the
other two sides.
The area =
base X side
Hypotenuse = V base squared + side squared.
Base = V hypotenuse squared side squared.
Side = V hypotenuse squared base squared.
A plane figure of four sides. All
four angles are right angles, and the op-
posite sides are equal and parallel. The
sum of all the angles equals four right
angles, or 360.
Area = square of a side.
the square of a diagonal
SQUARE
Side = V area
= diagonal X .7071
X 1.414
X 1.414
Diagonal = V area
= side
A plane figure of four sides. All
four angles are right angles, and the op-
posite sides are equal and. parallel. The
sum of all the angles equals four right
angles, or 360.
The difference between a square and a rectangle
RECTANGLE
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THE STARREST BOOK
TRAPEZOID
is that the adjacent sides of a square are equal; the
adjacent sides of a rectangle need not be equal.
Area = product of two adjacent sides.
Short side = area divided by long side.
Long side = area divided by short side.
Diagonal = V sum of squares of adjacent sides.
A plane figure of four sides, two of
which are parallel.
Area = sum of parallel sides X one-
half the altitude.
A regular plane figure of six sides.
All the sides are equal and all the
angles are equal. The sum of all the
angles equals 720.
Area = square of side X 2.598.
Area = square of radius of circum-
scribed circle X 2.598.
Area = square of radius of inscribed
circle X 3.464.
Side = radius of circumscribed circle.
Side = radius of inscribed circle X 1.155.
Radius of inscribed circle = side X .866.
A plane figure bounded by a curved
line, every point of which is equally
distant from a point within called the
center.
A diameter is any straight line pass-
ing through the center and touching the
CIRCLE circumference at each end.
Two circles having equal radii are equal.
Two circles with unequal radii vary in area as the
squares of the radii the circumferences are propor-
tional to the radii.
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THE STARRETT BOOK
A chord is a straight line intersecting or touching the
circumference, but not passing through the center.
A chord at right angles to a diameter is divided into
two equal parts by the diameter.
Circumference = diameter X 3.1416.
Area = square of radius X 3.1416.
Area square of diameter X .7854.
Radius = circumference -H 6.2832.
Radius = V area -*- 3.1416.
A plane figure included between two
circumferences having the same center.
Area = 3.1416 X (large radius
squared -- small radius squared).
Area = .7854 X (large diameter
squared small diameter squared).
A plane figure included between two
radii and the arc.
Area = one-half the radius X length
of arc.
Area = .008727 X radius squared X
angle in degrees.
57.296 X length of arc
Angle = -
radius
57.296 X length of arc
Radius =
degrees in angle
Length of arc = .01745 X radius X degrees in angle.
A plane figure bounded by a curve,
of which every point is the same dis-
tance from two points on the longest
axis; that is, the sum of the distances
from any point to the foci is equal to
the sum of the distances from any other
point to the foci.
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THE STARRETT BOOK
Area = 3.1416 X the product of its semi-axes.
Area = .7854 X product of axes.
Circumference (approx.) = 3.1416
sum of square of axes
A cycloid is a curve formed
by a given point on a circumfer-
ence of a circle rolling on a
straight line.
Length of curve = diameter of circle X 4.
Length of curve = radius of circle X 8.
Area = 3 X 3.1416 X radius squared.
Area = 9.4248 X radius squared.
Area = area of circle X 3.
An involute is a curve traced
by the end of a string as it un-
winds from a cylinder and is kept
taut. The string is always tangent
to the cylinder. To draw the curve,
divide the circumference into any
number of equal parts, the smaller
the number, the more accurate the
curve. Through these points on the
circumference, draw lines at right
angles to the radius and make the lengths of these tan-
gents equal to the actual length of the arcs. The curve
drawn through these points is an involute.
SOLIDS
A solid having six faces, each a
square. All faces and edges are equal.
Volume = cube of edge.
Edge = \/ volume.
Total area = square of edge X 6.
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THE STARRETT BOOK
SQUARE PRISM
HEXAGONAL
RIGHT
PRISM
REGULAR PYRAMID
FRUSTUM OF PYRAMID
A solid having a rectangular base
and rectangular sides. All opposite edges
are equal and parallel.
Volume = product of the three
edges.
Any edge = volume -*- product of
other two edges.
Total area = area of base and top
+ area of sides.
Total area = sum of areas of the six
faces, all rectangular.
A prism having for its base a regular
hexagon, and bases at right angles to
faces.
Volume = 2.598 X square of side of
base X vertical edge, or altitude.
Lateral area = side of base X ver-
tical edge X 6.
Total area = lateral area + (5.196 X
square of side of base) .
A right pyramid is a solid having a
base a regular polygon and faces isos-
celes triangles.
Volume = one-third altitude X area
of base.
Lateral area = perimeter of base X
one-half slant height.
Slant height = altitude of triangular
face.
Slant height = V vertical edge
squared one-half side of base squared.
A frustum of a regular pyramid has
parallel bases; that is, it is the lower
portion of a pyramid cut by a plane
parallel to the base.
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RIGHT CONE
THE STARRETT BOOK
Volume = sum of areas of the two bases and mean
proportional between them X one-third altitude.
The mean proportional is equal to the square root
of the product.
Lateral area = the sum of the perimeters of the
two bases X one-half slant height.
Slant height = V square of edge ' square of one-
half difference of side of bases.
A right cone has a circular base and
vertex in a line perpendicular to the
center of the base. It is a solid of revo-
lution; that is, it is a solid figure formed
by revolving a right triangle on its verti-
cal side as an axis.
Volume = 1.0472 X
of base X altitude.
Volume = .2618 X
eter of base X altitude.
Conical area = 3.1416 X radius of
base X slant height.
Slant height = V square of radius + square of altitude.
Altitude = V square of slant height square of radius.
The frustum of a cone has parallel
bases. It is the lower portion of a cone
when cut by a plane parallel to the base.
Volume = one-third altitude X sum
of the areas of the two bases and the
mean proportional between the two
bases.
The mean proportional is equal to the square root
of the product.
Lateral area = sum of perimeters (circles) of two
bases X one-half slant height.
Slant height = V square of altitude + square of
difference in radii.
square of radius
square of diam-
FRUSTUM OF CONE
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THE STARRETT BOOK
A right cylinder is a solid having
circles for bases and lateral surface per-
pendicular to bases. It is a solid of revo-
lution; that is, it is generated by revolv-
ing a rectangle about a side as an axis.
Volume = 3.1416 X square of radius
X altitude.
Volume = .7854 X square of diam-
eter X altitude.
Cylindrical surface = 6.2832 X radius X altitude.
Cylindrical surface = 3.1416 X diameter X altitude.
Total surface cylindrical surface + twice area of
(circle) base.
Hollow cylinder; axis of hole coin-
ciding with axis of cylinder.
Volume = difference in volume of
two cylinders.
Volume = 3.1416 X altitude X (square
of large radius square of small radius).
Volume = 3.1416 X altitude X thick-
ness X (large diameter thickness).
A sphere is a solid bounded by a
curved surface every point of which is
equally distant from a point within, called
the center. It is a solid of revolution;
that is, it is generated by revolving a half
circle on the diameter as an axis.
4 X 3.1416 X cube of radius
HOLLOW CYLINDER
SPHERE
Volume =
Radius =
= 4.1888 X cube of radius
T/ volume
4.1888
= .6204 X \j/ volume.
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THE STARRETT BOOK
Area = 4 X 3.1416 X square of radius,
= 12.5664 X square of radius.
Radius =
area
12.5664
= 3.5447 X V area
Hollow sphere.
Volume = difference in volumes of two spheres.
Volume = 4.1888 X (cube of large radius cube of
small radius).
A spherical segment is formed by
passing a plane through a sphere. If the
plane passes through the center, the seg-
ment is one-half the sphere. If it does
not pass through the center
Volume = 3.1416 X square of height
X (radius one-third height).
Radius of segment = V height X (dia-
SPHERICAL SEGMENT
SPHERICAL ZONE
meter of sphere height of segment).
Surface of spherical segment = 2 X
3.1416 X radius of sphere X height.
Surface of spherical segment =
6.2832 X radius of sphere X height.
A spherical zone is formed by pass-
ing two parallel planes through a sphere.
Volume = volume of sphere vol-
ume of segment.
Area = 2 X 3.1416 X radius of
sphere X height.
Area = 6.2832 X radius of sphere X
height.
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THE STARRETT BOOK
MECHANICS
A FORCE is any cause which tends to produce or
modify motion. It is measured in pounds, usually. Force
has three characteristics direction, place of applica-
tion, magnitude.
WORK is the product of force and distance. It is
measured in foot-pounds or in inch-pounds. Work does
not involve the element time.
POWER is the amount of work done in a given time.
It is the product of force and distance divided by time;
and is expressed in foot-pounds per minute, or foot-
pounds per second. The element of time is always
included.
Power should not be given the same meaning as force,
although some carelessly refer to an applied force as
being a power.
VELOCITY is rate of motion. It is distance divided
by time, and is expressed in feet per minute or feet per
second. Velocity does not include force nor weight.
MOMENT OF FORCE. The moment of a force is
the force multiplied by the perpendicular distance from
the fixed point to the direction of the force. The fixed
point is called the center of moments, and the perpendic-
ular distance is called the lever arm of the force. Moment
of force is measured in foot-pounds or inch-pounds.
GRAPHICAL REPRESENTATION OF FORCES. A
force may be represented graphically by a straight line,
the length being proportional to the magnitude. That is,
the line is drawn to some scale. One end of the line
represents the point of application, and an arrow head
at the other end represents the direction.
Two or more forces may act together on a body.
To find a single force which produces the same effect
as two or more forces, is to find the RESULTANT. The
operation is called the COMPOSITION OF FORCES.
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THE STARRETT BOOK
To find two or more forces which combined are
equivalent to a given force is to find the COMPONENTS.
The operation is called the RESOLUTION OF FORCES.
PARALLELOGRAM OF FORCES. When two forces
acting at a point can he represented in
direction and magnitude by the adjacent
sides of a parallelogram, the resultant
will be represented in direction and mag-
nitude by the diagonal of the parallelo-
gram. A B and A C are the forces and
A R the resultant.
If two forces act in the same direction, the resultant
is equal to their sum.
If two forces act in opposite directions, the resultant
is their difference.
PARALLEL FORCES. When two
forces are parallel and act in the same
direction, but not from the same point,
their resultant is parallel to both, and is
equal to their sum. The resultant is
located between the forces at a point that
divides the line joining the points of
application inversely as the magnitudes.
CD : AB = AE : E C
If the forces act in opposite direc-
tions, the resultant is parallel to both,
but is located outside of them on the
line (produced) joining the points of
application. It is nearer the greater force
and takes the same direction as the
greater force, but in intensity it is equal
to the difference between the compo-
nents. The point of application of the
resultant is:
AB : CD = CE : AE
-^B
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THE STARRE'TT BOOK
LEVERS
Moments of forces are very important factors in
machines. They may be illustrated in levers.
A lever is an inflexible rod, which may move about
a fixed, point called the fulcrum. The lever arms are the
portions between the weights or forces and the fulcrum.
To solve all problems relating to the lever, it must
be remembered that the moments are the weights or
forces multiplied by the distances from the fulcrum;
that is, by the lever arms.
As the lever is considered in balance, the product of
the weight and length of weight arm is equal to the
product of the power and length of power arm.
^ When the fulcrum is between the
f L A * ~"1 weight and the force, and both weight
(w) [ and force act in the same direction :
W X L = F X /
or W : F = / : L
FX I FX Z
W=
L W
WX L WX L
/
i
Z F
When the weight or load is between
the fulcrum and the point at which the
force is applied, the" same principles
apply; in fact, the same formulas are
used.
j Z-* In the third form of lever, the force
* A i is applied at a point between the fulcrum
I (w) and the weight. The same formulas are
used.
If the weight of the lever itself is to be considered,
the moment of force (F X Z) remains the same, but there
153
THE STARRETT BOOK
are then several moments of weight. The additional
moments of weight are found by multiplying the weight
of the lever arm by the distance of its center of gravity
from the fulcrum. In a lever of the first class there will
be two moments of weight due to the weight of the lever,
one will act with the moment of force and the other act
with the moment of weight. With levers of the second
and third class, the additional moment of weight will
act with the original moment of weight, and, therefore,
is added to it.
THE WINDLASS. The moment of
force and the moment of weight are the
means for finding the force required to
lift a weight by a rope wound on the
drum of a windlass.
F X L = WX /
WX I
p __ _
PULLEYS OR BLOCKS. The force
required to lift the weight is equal to
the weight divided by the number of
ropes that are shortened.
W
F =
N
If there are five ropes and the weight
is 300 pounds, the force is:
300
F = -- = 60 pounds
o
The velocity with which the weight
is raised is equal to the velocity of the
force divided by the number of ropes
shortened.
Velocity of F
Velocity = -
N
154
THE STARRETT BOOK
PULLEYS
A simple way to transmit power, either at the same
speed, or a change of speed, is to place a pulley on the
driving shaft and another on the driven shaft and pass
an endless belt over them. It is evident that the linear
speed of the pulleys is the same; that is, one revolution
of the driving pulley pulls the belt through a distance
equal to its circumference, and a point on the periphery
of the driven pulley will be pulled through this distance
whether or not the periphery is equal to the circumfer-
ence of the driving pulley.
To change the rotative speed of shafts it is only
necessary to place on them pulleys of unlike diameters.
The revolutions are inversely proportional to the
circumferences and, therefore, to the diameters. The
smaller pulley runs at the higher rotative speed.
D = diameter of driver,
d = diameter of driven.
Revs, of driven : Revs, of driver = D : d.
Revs, of driven X d = Revs, of driver X D.
The product of the revolutions and diameter of one
pulley is equal to the product of the revolutions and
diameter of the other pulley.
From Revs, of driven X d = Revs, of driver X D
Revs, of driver X D
we have d =
Revs, of driven
Revs, of driven X d
and D = -
Revs, of driver
To find the diameter of the driven pulley, multiply
the revolutions of the driver by its diameter and divide
by the revolutions of the driven.
156
THE STARRETT BOOK
Example: The driving shaft makes 150 revolutions
per minute and the driving pulley is 12 inches in diam-
eter. The driven shaft is to make 600 revolutions; what
diameter pulley should be selected?
150 X 12
d = = 3 inches
600
The driving shaft makes 200 revolutions and the
driven shaft is to make 150 revolutions per minute.
With a driven pulley of 24 inches diameter, what size
driver pulley should be used?
150 X 24
D = - - = 18 inches
200
To find speeds when sizes of pulleys are known :
Revs, of driver X D = Revs, of driven X d.
Revs, of driven X d
Revs, of driver =
D
Revs, of driver X D
Revs, of driven = -
d
Example: The driver pulley is 16 inches diameter
and the driven is 18 inches diameter. When the driver
runs at 270 revolutions per minute, what will be the speed
of the driven pulley?
156
THE STARRETT ROOK
Revs, of driver X D
Revs, of driven =
270 X 16
-=240
18
Example: Two pulleys, one of 14 inches diameter
and the other of 18 inches diameter, are available. The
driven shaft is to run at 120 revolutions per minute. If
the 14-inch pulley is placed on the driven shaft what
should be the speed of the driver?
Revs, of driven X d
Revs, of driver =
D
120 X 14
18
= 93 1-3
FORMULAS FOR PULLEY DIAMETERS AND
REVOLUTIONS
When three factors are known the fourth can be
found by using one of the following formulas:
Dia of driven X Revs, of driven
Dia. of Driver =
Revs, of driver
Dia. of driver X Revs, of driver
Dia. of Driven =
Revs, of Driver =
Revs, of Driven =
Revs, of driven
Dia. of driven X Revs, of driven
Dia. of driver
Dia. of driver X Revs, of driver
Dia. of driven
167
THE STARRETT BOOK
The same principles apply to more complex belting.
Suppose two pulleys are on the same shaft; we then
have a combination that resembles a train of gears.
This arrangement is often desirable when it is im-
practicable to get the speed reduction with one belt;
that is, when the larger pulley would have to be very
large as compared with the smaller.
In the above illustration the high rotative speed of
pulley A (on a motor shaft for example) is reduced to
a much lower figure at pulley D.
Revs, of A X diameter of A = Revs, of B X diameter
of B and Revs, of C X diameter of C = Revs, of D X diam-
eter of D. But pulleys B and C are on the same shaft and
have the same rotative speed.
Revs, of B = Revs, of C.
Combining these equations we may express the rela-
tion as follows:
The speed of the first driver multiplied by the
diameters of all the drivers is eqaal to the speed of the
last driven pulley multiplied by the diameters of all
driven pulleys. Or
Revs, of A X diameter of A X diameter of C =
Revs, of D X diameter of B X diameter of D.
If five of the above quantities are known the sixth
is easily found.
168
THE STARRETT BOOK
Example: Pulley A runs at 1200 Rev. per minute,
and is 4 inches in diameter. Pulley B is 12 inches in
diameter, C is 5 inches, and D is 16 inches. What is
the speed of D?
1200 X 4 X 5 = Revs, of D X 12 X 16
24,000 = Revs, of D X 192
24,000
Revs, of D =
192
= 125
In the above we have found the rotative speed of D
without finding the rotative speed of B, but we had given
the diameters of B and C.
Suppose we had given the speed of D. J>ut do not
know what pulleys to use in place of B and G.
Revs, of first driver product of diameters of all drivens
Revs, of last driven product of diameters of all drivers
Revs, of A diameter of B X diameter of D
or
Revs, of D diameter of A X diameter of C
The two unknown quantities are diameter of B and
diameter of G; but the RATIO can be found. Using the
data in the above example we have
1200 16 X diameter of B
125 diameter of C X 4
Diameter of B 4 1200
Diameter of G 16 125
- 12
~!>
169
THE STARRETT ROOK
Then the ratio of the diameters is 12 : 5, and any
pulleys having diameters in this ratio will give the desired
speeds. The pulleys may be 12 and 5 inches, 18 and 7V 2 ,
or 24 and 10.
Example: The shaft of 3-inch pulley D is to make
900 revolutions; what pulleys must be placet as B and
C if A is 14 inches in diameter and
makes 150 revolutions? The available
pulleys have these diameters 8, 9,
10V 2 , 11, 12, 13y 2 inches.
The formula to use is
Revs, of first driver product of diameters of all drivens
Revs, of last driven product of diameters of all drivers
150 diameter of B X 3
900 14 X diameter of C
1 3 diameter of B
^ Tijn _ vv
6 14 diameter of C
Diameter of B 1 14
__ vx f _
Diameter of C 6 3
_14_ 7
~18~ "9"
160
THE STARRETT BOOK
Then multiply the ratio 7 : 9 by any number which
will make 7 and 9 equal to the diameters of pulleys on
hand. Multiplying by 1% gives 10% and 13y 2 .
To prove that the calculation is correct, place these
values in this expression:
The speed of the first driver (150) multiplied by the
diameters of all drivers (14) and (13%) is equal to the
speed of the last driven (900) multiplied by the diam-
eters of all driven pulleys (10%) and (3).
150 X 14 X 13% = 900 X 10% X 3
28,350 = 28,350
LENGTH OF BELTS
Open Belt. Pass a tape, preferably a steel tape,
around the pulleys. This will give the length direct, if a
single belt; but if a double belt is to be used add to the
measurement twice the thickness of the belt. The length
of small belts may be obtained by passing the belt around
the pulleys and straining with hand pull.
New belts stretch and become slack after a short
time, and the slack should be taken up. With long belts
stretching may be anticipated by cutting the belt one
inch shorter for every ten feet.
Rule for Length of Open Belt
Add diameters of pulleys in inches and multiply the
sum by 1.57, then add to this product twice the distance
between centers in inches.
Formula for Length of Open Belt
(R-r) 2
L = 3.14 (R+r) +2D + -
D
R = Radius of large pulley, inches.
r = radius of small pulley, inches.
D = Distance between centers of shaft, inches.
L = Length of belt, inches.
161
THE S-TARRETT BOOK
Formula for Length of Crossed Belt
(R + r) 2
L = 3.14 (R + r) + 2D +
D
The letters have the same values as above.
Example: Two pulleys are 11 feet apart and are 24
and 16 inches in diameter. Length of belt? Open and
crossed.
(12- 8)*
L = 3.14 X (12 + 8) + (2 X 132) + -
132
16
= 62.8 + 264 + -
132
= 326.8 + .12
= 326.92 inches, open belt.
-(12 + 8) 2
L = 3.14 X (12 + 8) + (2 X 132) + -
132
400
= 62.8 + 264 + -
132
= 326.8 + 3
= 329.8 inches, crossed belt.
GEARS
CONSTANT VELOCITY RATIO. Belts over pulleys
and plain rolling cylinders cannot be depended upon
to give a constant velocity ratio there is always some
loss of speed due to slip. But when two gears are in
mesh a point on the pitch circle of one moves at the
same linear velocity as a point on the pitch circle of
the other, and the number of revolutions is always a
constant ratio for these two gears.
162
THE STARRETT BOOK
Two gears in mesh have the same pitch; that is, the
distance from the center of a tooth to the center of the
next tooth, measured along the pitch circle, is the same
for both gears. Therefore, two gears of the same pitch,
but of different diameters, must have an unequal number
of teeth.
It may be said that the space occupied by a tooth
and the space between two teeth is the same in both
gears if they have the same pitch. This fact shows
immediately that the linear velocity of the pitch circles
must be equal and the rotative speeds can be found in the
same way as with belts. The pitch diameter or the num-
ber of teeth is substituted for the pulley diameter, for
the numbers of teeth are proportional to the pitch diam-
eters in the same way that the peripheries of pulleys are
proportional to the diameters.
A gear having twice as many teeth as the gear mesh-
ing with it will make but one-half as many revolutions
in a given time. Or, the speeds (rotative) are inversely
as the number of teeth; the gear with the smaller number
of teeth runs at the higher speed.
As in belts and pulleys, one gear of a pair is the
driver and the other the driven or follower.
The number of revolutions of the driver multiplied
by the number of teeth on the driver is equal to the
number of revolutions of the follower multiplied by the
number of teeth on the follower.
Revs, of driver X T = Revs, of follower X t, if
T = number of teeth on the driver and t = number of
teeth on the follower:
"Revs, of follower X /
T =
and t =
Revs, of driver
Revs, of driver X T
Revs, of follower
163
THE STARRETT BOOK
To find the number of teeth (T) on the driver, mul-
tiply the revolutions of the follower by its number of
teeth and divide the product by the revolutions of the
driver.
Example: The follower has 64 teeth and makes 30
revolutions per minute. The driver makes 80 revolutions
per minute. How many teeth has the driver?
30 X 64
T = - - = 24
80
Example: The driver makes 160 revolutions per
minute and has 40 teeth. The follower makes 100 revo-
lutions. How many teeth?
160 X 40
/ = - - = 64
100
Revs, of follower X /
Revs, of driver = -
Revs, of follower =
T
Revs, of driver X T
Example: The follower has 90 teeth and makes 110
revolutions per minute. If the driver has 44 teeth, how
many revolutions per minute?
110 X 90
Revs, of driver = - = 225
44
Example: A driver having 63 teeth makes 800 revo-
lutions per minute. If the follower has 42 teeth, what
will be its speed?
800 X 63
Revs, of follower = = 1200
42
164
THE STARRETT BOOK
FORMULAS FOR SPEED OF GEARS
When three factors are known the fourth can be
found by using one of the following formulas:
Revs, of follower X teeth on follower
Revs, of Driver =
Revs, of Follower =
teeth on driver
Revs, of driver X teeth on driver
teeth on follower
Revs, of follower X teeth on follower
Teeth on Driver =
Teeth on Follower =
Revs, of driver
Revs, of driver X teeth on driver
Revs, of follower
As in the case of pulleys, great speed changes are
made by trains of gears in place of a pair. Examples
are found in hoists, clocks, lathes, etc. Each pair in the
train has its driver and follower, and if the shafts are
parallel it is usual to get the speed change by keying
two gears of unequal size on every shaft, except the first
and last.
The velocity ratio of the first to the last is found
as follows:
The product of the number of teeth on all the drivers
divided by the product of the number of teeth on all the
followers is the velocity ratio.
Suppose the train has three drivers, A, B, and C and
three followers, L, M, and N.
A has 14 teeth and drives L having 70 teeth. Pinion
B on same shaft with L has 13 teeth and drives M hav-
ing 104 teeth. Pinion C has 15 teeth, and is on the same
shaft with M; C drives N having 75 teeth. What is the
velocity ratio of A to N?
165
THE STARRETT BOOK
Velocity ratio =
teeth on A X teeth on B X teeth on C
teeth on L X teeth on M X teeth on N
14 X 13 X 15
70 X 104 X 75
1
~ 200
Knowing the velocity ratio of the train, it is easy to
find the speed of N if the speed of A is known. If A
runs at 1800 revolutions per minute, N will make only
9 revolutions for 1800 4- 200 = 9.
When the speed of the first driver or the last fol-
lower is also known, the speed may be figured from the
following:
Multiply the revolutions per minute of the first driver
by the continued product of the number of teeth on all
drivers, and divide by the continued product of the
teeth on all followers. The quotient will be the revolu-
tions per minute of the last follower.
LATHE GEARING
The apprentice who wishes to figure change gears
for screw cutting should understand the principles, as
166
THE STARRETT BOOK
already explained, rather than be dependent upon formu-
las. There is but one statement to be memorized.
The continued product of the speed of the first
driver and the number of teeth on all drivers, is equal
to the speed of the last follower multiplied by the con-
tinued product of the teeth on all followers.
In figuring change gears, the number of threads per
inch to be cut corresponds to the revolutions of the
driver, and the number of turns on the lead screw to
move the carriage one inch corresponds to the speed of
the follower.
Then the number of threads to be cut multiplied by
the teeth on the spindle stud equals the number of
threads on the lead screw multiplied by the teeth on
the lead screw gear. Or
threads to be cut teeth on lead screw gear
threads on lead screw teeth on spindle stud
Suppose there are 6 threads on the lead screw and
46 teeth on the lead screw gear how many threads will
be cut if a 24-tooth gear is placed on the spindle stud?
threads to be cut 40
6 " 24
40
threads to be cut = X 6
24
= 10
The above assumes that the lathe is geared 1:1; that
is, the lathe screw constant is equal to the number of
threads per inch on the lead screw. If the lathe is not
so geared, the lathe screw constant should be used in
place of the threads per inch on the lead screw.
167
THE STARRETT BOOK
The foregoing example shows how the figuring can
be done when the gears are on the spindle stud and lead
screw; but the problem is usually one of finding out what
gears to use.
Suppose seven threads are to be cut, and there are
five threads per inch on the lead screw. What gears
are to be used?
threads to be cut teeth on lead screw gear
threads on lead screw teeth on stud gear
7 teeth on lead screw gear
5 teeth on stud gear
The ratio of the gears is as 7 : 5.
By multiplying both 7 and 5 by any number, such
as 6, we get
42 teeth on lead screw gear
30 teeth on stud gear
Using the formula as above may aid in disposing of
that troublesome question, "Which gear goes on the
stud?"
In some cases it may seem easier to assume one
gear and go through the calculation to find the other,
there being then one unknown quantity and three known
quantities.
168
THE STARRETT BOOK
Table 13
Specific Gravity and Properties of Metals
Metal or Composition
Specific
Gravity
Weight per
Cubic Inch,
Pounds
Melting
Point.
Deg. F.
Linear Ex-
pansion per
Unit Length
per Deg. F.
Aluminum
Antimony
Barium
Bismuth
Boron
Brass: 80 C., 20 Z
70 C., 30Z......
60C..40Z
50C..50Z
2.56
6.71
3.75
9.80
2.60
8.60
8.40
8.36
8.20
885
0.0924
0.2422
0.1354
0.3538
0.0939
0.3105
0.3032
0.3018
0.2960
03195
1200
1150
1560
500
1700-1850
1675
0.00001234
0.00000627
0.00000975
0.00000957
00000986
8 60
03105
610
1 57
0567
1450
Chromium
Cobalt
Copper
Gold
Iridium
Iron, cast
Iron, wrought
Lead
6.50
8.65
8.82
19.32
22.42
7.20
7.85
11.37
1 74
0.2347
0.3123
0.3184
0.6975
0.8094
0.2600
0.2834
0.4105
0628
2740
2700
1940
1930
4100
2300
2900
620
1200
0.00000887
0.00000786
0.00000356
0.00000556
0.00000648
0.00001571
Manganese
742
2679
2200
Mercury (60 F )
13 58
04902
39
Molybdenum
Nickel
Platinum, rolled
Platinum, wire
8.56
8.80
22.67
21.04
87
0.3090
0.3177
0.8184
0.7595
00314
4500
2600
| 3200
144
0.00000695
0.00000479
Silver
1053
3802
1740
00001079
Sodium
Steel
Tellurium
0.98
7.80
625
0.0354
0.2816
02256
200
2500
840
0.00000636
Tin
729
02'632
446
00001163
Titanium
354
1278
3360
18 77
6776
5400
Vanadium
Zinc, cast
Zinc, rolled
5.50
6.86
715
0.1986
0.2476
02581
3200
| 785
0.00001407
169
THE STARRETT BOOK
Table 14
Average Specific Gravity of Miscellaneous Substances
Substance
Specific
Gravity
Asbestos 2.8
Asphaltum 1.4
Borax 1.75
Brick, common 1.8
Brick, fire 2.3
Brick, hard 2.0
Brick, pressed 2.15
Brickwork, in motor 1.6
Brickwork, in cement 1.8
Cement, Portland 3.1
Chalk 2.6
Charcoal 0.4
Coal, anthracite 1.5
Coal, bituminous 1.27
Concrete 2.2
Earth, loose 1.2
Earth, rammed 1.6
Emery 4.0
Glass 2.6
Granite 2.65
Gravel 1.75
Gypsum 2.2
Ice 0.9
Ivory '. 1.85
Limestone 2.6
Marble 2.7
Masonry 2.4
Mica 2.8
Mortar 1.5
Phosphorus ( 1.8
Plaster of Paris 1.8
Quartz 2.6
Salt, common 2.1
Sand, dry 1.6
Sand, wet 2.0
Sandstone 2.3
Slate 2.8
Soapstone 2.7
Soil, common black 2.0
Sulphur 2.0
Trap 3.0
Tile 1.8
170
THE STARRETT BOOK
Table 15
Specific Gravity of Gases
(At 32 degrees F.)
Gas
Sp.
Gr.
Gas
.?:
Air.
1.000
Hydrogen . .
0.069
Acetylene .
0.910
Illuminating gas . . .
0.040
Alcohol vapor
1.601
Mercury vapor
6.940
Ammonia
0.592
Marsh gas
0.555
Carbon dioxide
1.520
Nitrogen
0.971
Carbon monoxide
0.967
Nitric oxide
1.039
Chlorine
2.423
Nitrous oxide .
1.527
Ether vapor
2.586
Oxygen
1.106
Ethylene
Hydrofluoric acid
Hydrochloric acid
0.967
2.370
1.261
Sulphur dioxide
Water vapor
2.250
0.623
1 cubic foot of air at 32 degrees F. and atmospheric pressure weighs 0.0807 pound
Table 16
Specific Gravity of Liquids
Liquid
fe
Liquid
Sp.
Gr.
Acetic acid
1.06
Muriatic acid
1.20
Alcohol, commercial
0.83
Naphtha
0.76
Alcohol, pure .
0.79
Nitric acid .
1.22
Ammonia
0.89
Olive oil
0.92
Benzine
Bromine
0.69
2.97
Palm oil
Petroleum oil
0.97
0.82
Carbolic acid
096
Phosphoric acid
1.56
Carbon disulphide
1.26
Rape oil
0.92
Cotton-seed oil
0.93
Sulphuric acid
1.84
Ether, sulphuric
0.72
Tar ...
1.00
Fluoric acid
Gasoline
Kerosene
1.50
0.90
0.80
Turpentine oil
Vinegar
Water
0.87
1.08
1.00
Linseed oil
0.94
Water, sea
1.03
Mineral oil
0.92
Whale oil
0.92
171
THE STARRETT BOOK
Table 17
Composition of Miscellaneous Alloys
Alloys
Antimony
Bismuth
1
|
I
1
c
H
H
N
Brass, common yellow
61.6
2.9
0.2
35.3
Brass, to be rolled
32
1.5
10
Brass castings, common
20
2.5
1.25
Gun metal
8
1
Copper flanges
9
026
1
Bronze Statuary
91.4
1.37
1.7
5.53
German Silver
2
6.5
7.9
6.3
Britannia metal
50
25
25
Chinese white copper
20.2
15.8
1.3
12.7
Pattern letters
15
15
70
Bell metal
4
1
Chinese gongs
40.5
9.2
White metal, ordinary
28.4
3.7
14.2
3.7
Spelter
1
1
Type metal
1
3-7
172
THE STARR ETT ROOK
Table 18
Average Specific Heats of Various Substances
Substance
Specific
Heat
Substance
Specific
Heat
Alcohol (absolute)
700
500
Alcohol (density 0.8)
0.622
0214
Lead....
Limestone
0.031
217
Antimony
Benzine
0.051
450
Magnesia
Marble
0.222
210
Brass
0.094
Masonry, brick
0200
Brickwork
0.200
0057
Mercury
Naphtha
0.033
310
Charcoal
Chalk
0.200
0215
Nickel
Oil machine
0.109
0400
Coal
0.240
Oil, olive
0350
Coke
Copper 32 to 212 F
0.203
0094
Phosphorus
Platinum
0.189
032
Copper, 32 to 572 F
0.101
Quartz ,
188
Corundum
0198
Sand
195
Ether
0503
Silica
191
Fusel oil
Glass
0.564
194
Silver
Soda
0.056
0231
Gold
0.031
Steel, mild
116
Graphite
0201
Steel high carbon . ...
117
Ice
0504
Stone (generally)
0200
Iron, cast
0.130
Sulphur
178
Iron wrought, 32 to 212 F .
110
Sulphuric acid ....
0330
32 to 392 F
115
Tin
0056
32 to 572 F
0.122
Turpentine
0472
32 to 662 F
126
Water ...
1 000
Iron, at high temperatures :
Wood, fir
0650
1382 to 1832 F
1750 to 1840 F
0.213
0218
Wood, oak
Wood pine
0.570
0467
1920 to 2190 F
0.199
Zinc
0.095
173
THE STARRETT BOOK
Table 19
Templets for Drilling Standard and Low Pressure Flanged
Valves and Fittings American Standard
V
N
to
*l
s=
Thickness
of Flange
Diam. of
Bolt Circle
"SI2
|2
"S
I
c^
S|
II
5^
Thickness
of Flange
Diam. of
Bolt Circle
o
l
0.2
Va
&&
1
4
7 A
3
4
H
42
53
2%
49H
36
VA
1%
4^
H
3H
4
7 /ie
44
55%
2%
51%
40
IX
1H
5
%6
SK
4
*Ji
46
57%
2^6
53%
40
1A
2
6
M
4%
4
M
48
59H
2%
56
44
1 5 A
2H
7
^6
SM
4
K
50
61%
2%
58%
44
1%
3
7H
M
6
4
H
52
64
2K
60H
44
1%
3H
8H
15 ft6
7
4
5^
54
66%
3
62%
44
1%
4
9
15 Ae
7^
8
H
56
68%
3
65
48
1%
4^
9%
!%6
7%
8
%
58
71
3H
67%
48
1%
5
10
!%6
8M
8
%
60
73
3K
69%
52
1%
6
11
i
9H
8
%
62
75%
3%
71%
52
IH
7
12 H
l^le
10%
8
%
64
78
3%
74
52
IH
8
13 M
m
11%
8
%
66
80
m
76
52
1%
9
15
1%
13%
12
%
68
82%
VA
78%
56
IK
10
16
1%6
14%
12
K
70
84^
m
80^
56
IK
12
19
Hi
17
12
J^
72
86H
3M
82^
60
IK
14
21
iH
18%
12
l
74
S8 1 A
3H
84^
60
IK
15
22^
IK
20
16
l
76
90%
m
86H
60
IK
16
23^
l%a
21%
16
1
78
93
3%
88%
60
2
18
25
lAe
22%
16
1H
80
95%
3%
91
60
2
20
27H
1^6
25
20
1H
82
97H
3K
93%
60
2
22
293^
l 18 Ae
27%
20
1%
84
99%
3Ji
95H
64
2
24
32
IK
29H
20
1%
86
102
4
97%
64
2
26
34%
2
31%
24
1%
88
104%
4
100
68
2
28
36^
2^6
34
28
1%
90
106^
4^
102%
68
2K
30
38%
2K
36
28
1%
92
108%
4H
104^
68
2K
32
41%
2%
38>i
28
1H
94
111
4%
106%
68
2K
34
43%
2%6
40^
32
1H
96
113%
4%
108^
68
2%
36
46
2K
42%
32
1H
98
115H
4M
110%
68
2%
38
48%
2K
45%
32
1H
100
117%
4M
113
68
2%
4.0
CAS./
?V4
47 \
36
154
4U
OU/4
^/2
**( 74
A/ 8
Bolt holes are drilled K inch larger than nominal diameter of bolts.
174
THE STARRETT BOOK
Table 20
Templets for Drilling Extra Heavy Flanged Valves and
Fittings American Standard
Size
Diam. of
Flange
Thickness
of Flange
Diam. of
Bolt Circle
No. of
Bolts
Size of
Bolts
1
4^
>#
3K
4
H
in
5
%
3%
4
/4
6
13 /16
4
%
2 2
6M
I/fa
5 2
4
5 /8
2^
71^
1
57^
4
3
8K
1/^8
6^
8
%
3/^
9
1 8 /16
7K
8
%
4
10
IK
7%
8
%
4/^
103^
1 5 /16
8
%
5
11
9K
8
%
6
12H
1 7 /1 6
10^
12
%
7
8
14
15
3H
13 8
12
12
7 /8
7 A
9
16K
14
12
10
17J^
15K
16
1
12
20^
2 8
17%
16
l/^
14
23
2/'8
20K
20
1^8
15
24^
2%6
21/^
20
IK
16
25^
2K
22^
20
IK
18
28
2^i
24%
24
IK
20
30^
2^
27
24
if!
22
33
2/^
29K
24
24
36
2%
32
24
i/^
26
38K
34^
28
i/^
28
40%
2^5/16
37
28
i/^
30
43
3
39 K
. 28
1%
32
45K
33^8
41^
28
1/^8
34
47^
3K
43^
28
1J/8
36
50
3^g
46
32
IJ/g
38
52K
3^16
48
32
1%
40
54^
3%6
50K
36
l/^
42
57
3 1 ^io
52%
36
\1/o
44
59K
3%
55
36
2
46
61^
3%
57K
40
2
48
65
60%
40
2
Bolt holes are drilled
inch larger than nominal diameter of bolts.
175
THE S T A R RETT BOOK
Table 21 Tap Drills
For A. S. M. E. Standard and .Special
Machine Screw Taps
The diameter given for each hole to be tapped allows for a
practical clearance at the root of the thread of the screw and will
not impose undue strain upon the tap in service.
Size
of Tap
No. of
Threads
Size of
Drill
Size of
Tap
No. of
Threads
Size of
Drill
80
.0465
9
32
.1405
1
64
.055
10
24
.140
1
72
.0595
10
30
.152
2
56
.0670
10
32
.154
2
64
.070
12
24
.166
3
48
.076
12
28
.173
3
56
.0785
14
20
.182
4
36
.080
14
24
.1935
4
40
.082
16
20
.209
4
48
.089
16
22
.213
5
36
.0935
18
18
.228
5
40
.098
18
20
.234
5
44
.0995
20
18
.257
6
32
.1015
20
20
.261
6
36
.1065
22
16
.272
.6
40
.110
22
18
.281
7
30
.113
24
16
.295
7
32
.116
24
18
.302
7
36
.120
26
14
.316
8
30
.1285
26
16
.323
8
32
.1285
28
14
.339
8
36
.136
28
16
.348
9
24
.1285
30
14
.368
9
30
.136
30
16
.377
NOTE : Special Taps are in Bold Face Type.
176
THE STARRETT BOOK
Table 22 Tap Drills for Machine Screws
Size of
Tap
American
Standard
Diameter in
Inches
Size of Drill
for Outside
Diameter of
Screw
Size of Drill
for Tapping
Hole
Size of
Tap
American
Standard
Diameter in
Inches
Size of Drill
for Outside
Diameter of
Screw
H|
2x48)
50
13x20)
17
2x56
.25763
44
49
13x22
.071961
*%4
17
2x64]
48
13x24]
15
3x40)
49
14x20)
15
3x48
.22942
39
47
14 x 22
.064084
V*
11
3x56]
45
14x24]
10
4x32)
46
15x18)
12
4x36
4x40]
.20431
33
44
43
15 x 20
15 x 22
.057068
F
10
8
15x24]
7
5x30)
5x32
5x36
5x40]
.18194
tt
43
42
41
38
16x16)
16 x 18
16x20]
.05082
I
12
7
6x30)
6 x 32
6 x 36
.16202
28
38
37
36
17x16)
17 x 18
17x20j
.045257
L
8
4
3
6x40J
35
18x16)
2
7x28)
7x30
.14428
24
34
33
18 x 18
18x20]
.040303
19 /64
2
1
7x32]
32
19x16)
1
8x24)
8x30
.12849
19
31
31
19 x 18
19x20]
.03589
*;
B
8x32]
30
20x16)
c
9x24
9x28
9x30
9x32
.11443
16
30
28
28
26
20 x 18
20x20]
22 x 16 \
22 x 18 /
.031961
.025347
p
s
E
F
H
10x24)
26
24 x 14 )
L
10 x 30
10x32]
.10189
11
24
24
24 x 16
24x18]
.0201
%
M
N
11x24)
11 x 28
.090742
6
21
20
26 x 14 \
26 x 16 /
.01594
18 /82
p
11x30]
19 '
12x20
24
28 x 14 \
28 x 16 /
.012641
fti
R
12x22
20
12x24
.080808
%2
19
30 x 14 \
u
12x28
18
30 x 16 /
.010025
2%4
V
177
INDEX
Abbreviations for Drawings 12
Abrasives, Grain . , . . 43
Adjusting Toolmakers' Buttons with Micrometer . . 104
Algebraic Signs 132-136
Aligning Shafting 119
Alloys, Composition of , 172
Angle, Measurement of 140
Bench Work 35
Bolt and Screw Lists . .- 7
Boring Holes in Jig Body 103
Buttons' Toolmakers' 104
Calipering over a Flange 27
Calipers, for Testing Screw Threads 85
Calipers, Hermaphrodite 69
Calipers, Inside and Outside 27
Calipers, Micrometer 19
Calipers, Spring 26
Calipers, Vernier 16
Carbon Steel 75
Carbon Steel Drills, Speed of 51
Center Gage 67
Center Punches 56
Change Gears 79
Chipping 38
Chisels for Chipping 38
Chucking 93
Chucking Tools : 96
Coefficient (Algebra) 127
Composition of Alloys 172
Compound Gears for Thread Cutting 82
Contact Measuring 15
Counterboring : 62
Cup Wheels 117
Cutting Compounds for Drills 53
Cutting Lips of Drills 47
Cutting Screw Threads 77
Deep Hole Drilling . 02
Detail Drawings 7
Dividers, Spring 28
Draw Filing 42
Drawing the Drill 55
Drill Grinding . 48
Drill Speed . 51
Drilling 48
Drilling Deep Holes 62
Drilling, Drawing the Drill . . . . ' 55
Drilling for Reamer "... 57
Drilling for Tapping 58
Drilling, Holding Work 56
Drilling Large Holes 61
Drilling, Starting Drill 55
Drilling, Templets for Extra Heavy Flanged Valves and Fittings . 1J5
178
THE STARRETT BOOK
Drilling, Templets for Standard and Low Pressure Flanged Valves
and Fittings 174
Drills, Cutting Compounds 53
Drills, Cutting Lips 47
Drills, Kinds 47
Drills, Letter Sizes of 59
Drills, Making ' 97
Drills, Testing Cutting Lips 49
Eccentric Turning 91
Elementary Algebra 126
Emery, Grades of 43
Equations 134
Equivalent Tables 60
Expansion of Metals 169
Exponent 127
Extra Heavy Flanged Valves and Fittings, Templets for Drilling . 175
Files, Kinds . 40
Filing 40
Filing, Testing Surface 42
Fits, Amounts to Leave 30
Flanged Fittings, Templets for Drilling . . . 174
Forced Fits 29
Forces 151
Gear Speeds, Formulas for 165
Gears for Thread Cutting 79
Gears, Speed of 163
Gears, Trains 165
Grades of Emery 43
Grading Grinding Wheels Ill
Grinding 109
Grinding, Allowances for 110
Grinding, Amounts to leave 113
Grinding Cylindrical 113
Grinding Flat Surfaces 116
Grinding Wheels, Grade and Grain 115
Grinding, Measuring Work 116
Grinding Milling Cutters 100
Grinding Speeds for 114
Grinding Wheels 109, 111
Grinding Wheels, Grades Ill
Grinding Wheels, Mounting 116
Hack Saw Machine 45
Hack Saws 43
Hack Saws, Cutting Speed 44
Hack Saws, What One to Use . 46
Hand Chipping 38
Height Gage 17
High Speed Steel Drills, Speed of 51
Holding Drill in Spindle 56
Holding Work for Drilling 57
Holding Work in Chucks 95
How to Read a Micrometer 21
How to Read a Vernier 22
How to Read a Vernier Micrometer . 23
Involute 146
179
THE STARRETT BOOK
Jig Bushings 107
Jig for Drilling Cylinder Flange 108
Jigs and Fixtures 101
Jigs, Locating Bushing Holes 102
Jigs, Types 101
Knurling '..... 96
Lapping 117
Lathe 65
Lathe Centers 65
Lathe Gearing 106
Lathe Tools 70, 75
Lathe Tools, Clearance 72
Lathe Tools, Grinding 73
Lathe Tools, Rake 72
Lathe Tools, Setting 73
Lathe Tools, Testing Cutting Angles 74
Lathe Work, Measuring 85
Laying Out for Drilling 53
Length of Belts, Formulas for 161, 162
Level for Aligning Shafting 119
Leveling Instrument 119
Leveling Instrument, How to Set Up 124
Levels, Finding Difference 125
Levers 153
Limits of Accuracy , 29, 32
Locating Bushing Holes in Jigs 102
Locating Jig on Face Plate 103
Locating Machinery 123
Low Pressure Flanged Fittings 174
Lubricant for Thread Cutting 84
Mandrels, Use of 76
Measuring Lathe Work 85
Measuring Screw Threads 84
Measuring Tools 13
Measuring Work, Grinding 116
Mechanics 151
Melting Point of Metals 169
Mensuration 140
Micrometer, Adjusting Buttons with 104
Micrometer as a Gage 25
Micrometer Calipers 19
Micrometer, for Measuring Screw Threads 86
Micrometer, How to Read 21
Micrometers, Adjustment for Wear 25
Micrometers, Quick Adjustment . . 25
Milling Cutters 99
Milling Cutters, Grinding 100
Plane Figures 142, 146
Plate for Laying Out 37
Plumb Bobs 121
Polishing 43
Preparing Surface for Laying Out 35
Protractors 37
Pulley Diameters and Speeds, Formulas for 157
Pulleys 155
180
THE STARRETT BOOK
Pulleys, or Blocks . . 154
Quick Adjustment of Micrometers 25
Radical Sign 128
Reamers, Making 97
Screw Threads 77
Screw Threads, Measuring ." 84
Screw Threads, Pitch 77
Screw Threads, Properties of U. S. Standard 78
Scribing Lines for Laying Out 35
Section Lines 11
Shop and Engineering Formulas 137
Signs (Algebra) 132
Sliding Pit . 29
Solids 146
Specific Gravity of Gases 171
Specific Gravity of Liquids . ' 171
Specific Gravity of Metals 1G9
Specific Gravity of Substances 170
Specific Heat of Substances 173
Speed of Drills 52
Speed of Gears, Formulas for 165
Standard Flanged Fittings 174
Starting Drill 55
Stellite 76
Surface Plates 38-
Table 1 Allowances for Different Classes of Fits 31
2 Speeds and Feeds for Drilling 51
3 Speed of Drills 52
4 Letter Sizes of Drills 59
5 Sizes of Tap Drills 59
6 TJ. S. Standard Screw Threads 78
7 Brown & Sharpe Taper Shanks 87
8 Morse Taper Shanks 88
9 Tapers 92
10 Allowances for Grinding . 110
11 Grinding Wheel Speeds 114
12 Grinding Wheels for Different Materials 115
13 Specific Gravity and Properties of Metals 169
14 Specific Gravity of Substances 170
15 Specific Gravity of Gases 171
16 Specific Gravity of Liquids 171
17 Composition of Alloys 172
18 Specific Heat of Substances 173
19 Templets for Drilling Standard and Low Pressure Flanged
Valves and Fittings American Standard 174
20 Templets for Drilling Extra Heavy Flanged Valves and
Fittings American Standard 175
21 Tap Drills, A.S.M.E. Standard . . . 176
22 Tap Drills for Machine Screws 177
Tap Drills, Sizes of ... t 59, 78, 176, 177
Taper in Given Length 90
Taper Shanks 87, 88
Taper Turning 86
Taper Turning, Offset of Centers, Amount 90
Tapers, Testing 91
181
THE STARRETT BOOK
Targets 123
Testing Cutting Lips of Drills 4!)
Testing Flat Filing 42
Test Indicator . . . . 67
Testing Turned Taper 91
Thread Tool, Form of 82
Thread Tool, Setting 84
Tolerance, Limits of 32
Tool Holders 75
Tool Making 97
Toolmakers' Buttons 103
Train of Gears 165
Transferring Measurements 26
Truing Work in Chucks 95
Turning, Work Centers 69
Universal Dial Test Indicator 07, 103
Vernier Calipers . . . .- 16
Vernier Height Gage 17. 10r>
Vernier, How to Read 22
Vernier Micrometer, How to Read 23
Vitrified Wheels 109
Wear of Micrometers 25
Weight per Cuhic Foot of Substances 170
What Hack Saw to Use
Windlass
Work Centers
Work Centers, Locating , - ,
Working Drawing Abbreviations
Working Drawings
46
154
69
89
12
182
THE STARR E T T BO Q K
SETS OF TOOLS
FOR APPRENTICES AND STUDENTS
SET NO. 900
IN FOLDING LEATHER CASE
Size of case folded, 7" x 4%" x l%*
Set No. 900 consists of the leather case and the
following tools:
No. 11, 6" Combination Square, com- No. 390, Center Gage
plete No. 241, 4" Caliper
No. 117B, Center Punch No. 79, 4" Outside Caliper with solid nut
No. 321, 6" Flexible Steel Rule in pocket No. 73, 4" Inside Caliper with solid nut
case No. 83, 4" Divider with solid nut
PRICE, set complete
$6.00
183
THE STARRETT BOOK
SETS OF TOOLS
FOR APPRENTICES AND STUDENTS
SET NO. 901
IN NICELY FINISHED WOODEN CASE
Size of case, 12"x7"xl^
Set No. 901 consists of the wooden case and the
following tools:
No. 11, 6" Combination Square, com-
plete
No. 321, 6" Flexible Steel Rule in
pocket case
No. 117B, Center Punch
PRICE, set complete
No. 390, Center Gage
No. 77, 5" Divider with solid nut
No. 79, 6" Outside Caliper with solid nut
No. 73, 6" Inside Caliper with solid nut
$6.15
184
UNIVERSITY OF CALIFORNIA LIBRARY
BERKELEY
Return to desk from which borrowed.
This book is DUE on the last date stamped below.
Allgl7'48JL
.RY U>E
i
Due end of WINTER Quarter M AB 1 5 9 flQ 3 *
subject to redall after-
WR 1 "7'
'IS STACKS
REC'OLO
21-100m-9,'47(A5702sl6)476
M51G983
