(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Tool Engineering Jigs And Fixtures"

JIGS AND FIXTURES 



TOOL ENGINEEKING 



JIGS AND FIXTUEES 



BY 
ALBERT A. DOWD 

Member American Society of Mechanical Engineers; Author of "Tools, 

Chucks and Fixtures," "Tools and Patterns," "Modern Gaging 

Practice," "Fixtures for Turning, Boring and Grinding" 

"Punches, Dies and Gages" etc. 

AND 

FRANK W. CURTIS 

Associate Member American Society of Mechanical Engineers; Western 

Editor of American Machinist; Author of "Cutting Speeds and 

Feeds," " Modern Gaging Practice " "Fixtures for Turning, 

Boring and Grinding," "Punches, Dies and Gages," etc. 



FIRST EDITION 
SEVENTH IMPBESSION 



McGRAW-HILL BOOK COMPANY, INC. 

NEW YOKK AND LONDON 
1922 



COPYRIGHT, 1922, BT THE 
McGRAW-HiLL BOOK COMPANY, INC. 



PRINTED IN THE UNITED STATES OF AMERICA 



THE MAPLE PRESS COMPANY, YORK, PA. 



DEDICATED TO THE 

MANUFACTURERS OF THE UNITED STATES 



PREFACE 

The aim and purpose of this book is to furnish information 
with respect to the science of tool engineering. Nothing has 
previously been published on the subject except in short articles 
dealing with specific examples of jigs and fixtures. Information 
of value regarding principles of design in connection with produc- 
tion tools is sadly lacking and mechanical literature contains 
only spasmodic efforts to remedy the deficiency. 

In order to cover the subject properly three volumes were 
planned, each of these being complete in itself. This volume, 
which is the first, deals with the design of jigs and fixtures, It 
covers the important points connected with the design, shows the 
reasons why certain methods are better than others, takes up 
principles and their application to design and gives many graphic 
examples which illustrate the use of the principles involved. An 
endeavor has been made to simplify the subject matter as far 
as possible and to treat it in a practical common sense manner 
which can be easily understood by the designer. A careful 
study of the illustrations and descriptive matter will enable a 
progressive man to understand both the theory and practice 
necessary for this line of work. 

The second volume takes up turret lathe and vertical boring 
mill tooling together with grinding fixtures. The third volume 
deals with punches, dies and gages. 

For a number of years the machines and tools used for pro- 
duction have been undergoing a process of evolution and although 
the development work has progressed rapidly, much still remains 
to be done. Present manufacturing methods are of the highest 
order and tooling for high production is of interest to all the 
mechanical fraternity. There are however, comparatively few 
men in this country who really know the science in all its funda- 
mentals and for this reason the tooling in many factories is 
probably not over 50 % efficient. 

A great many of those responsible for tooling are not well 
informed as to the fundamentals of design. Tools are worked 
out more or less by using ideas in vogue in the factory where the 
work is being done and the design is usually influenced by 
previous practice for work of the same character. 

vii 



viii PREFACE 

Progressive tool engineering requires first of all, a thorough 
knowledge of principles and the ability to specify the machining 
operations necessary on a given piece of work. With this as a 
basis, mechanical problems can be analyzed and the solution 
obtained by the application of known principles. For this 
reason our books take up the subject fundamentally and deal 
largely with principles although many examples of interesting 
fixtures are illustrated. Mechanical principles are fixed and do 
not change from year to year as designs often do; hence, the man 
whose knowledge of tools is firmly grounded on sound mechanical 
principles is independent, original and progressive, so that his 
designs are practical, economical and productive. 

The superintendent, factory manager, foreman and tool 
engineer will find theory and practice combined in such a way 
that the principles on which the science is based will be readily 
understood. The reasons why one design is better than another 
are graphically shown in numerous examples, dealing with actual 
cases observed during the writers' long experience in handling 
production problems both in shop and drafting room. Problems 
are analyzed; causes of trouble shown; correct and incorrect 
methods illustrated; and much valuable data are given regarding 
designs and proportions of jigs, fixtures, turret lathe tools, 
punches, dies and gages. 

M is our belief that the work will be appreciated by mechanical 
men throughout the country. We hope that the many practical 
examples will provide food for thought and eventually bring 
about a general revision and radical improvement in tooling 
methods. 

ALBERT A. DOWD. 
NEW YOKK, FRANK W. CURTIS. 

December, 1922. 



CONTENTS 

PAGE 

PREFACE v 

CHAPTER I 

OUTLINE OP TOOTJ ENGINEERING 1-17 

Effect of Design on Manufacturing- Consideration of Limits 
of Accuracy Selection of Working Points Tool Operation 
Sheets Relation of Design to Cost of Machining. 

CHAPTER II 

FUNDAMENTAL POINTS IN DRILL JIG DESIGN 18-39 

Value of Analysis Location of Rough and Finished Work 
Correct and Incorrect Location and Clamping Clearance for 
Work and ChipsProvision for Wear on Locating Surfaces 
Setting Up and Removing Work Types of Jigs. 

CHAPTER III 

DETAILS OF DRIIA JIG CONSTRUCTION 40-81 

Plain Clamps Multiple ClampsHook-Bolt and Wedge 
Clamps Equalizing Clamps Spring Plungers and Jacks V- 
Block Design Leaf Jig Design Leaf Construction Clamps 
in the Leaf Leaf Stops Leaf Locks Standard Jigs and 
Components Jig Bodies- Standardisation of Jig Posts and 
ThumbscrewsJig Foefe Locating PlugsTypes of Bushings 
Bushing Design and ProportionMethods of Holding 
Slip Bushings Standard Knobs and Thumbscrews Ejectors. 

CHAPTER IV 

OPEN AND CLOSKB JIGS 82-100 

Templet Jigs- -Plate Jigs Open Jigs for a Shaft Open Jig 
for a Pump Cover Closed Jigs Closed Jigs for Angular and 
Straight Holes- Locating and Assembling Jigs An Example 
for Practice. 

CHAPTER V 

INDEXING AND TBTONION JIGS 101-133 

Indexing Requirements- Drilling and Reaming Indexing 
Fixtures Four-Sided Jigs for Accurate Work Principles 
and Methods of Indexing Index Plungers and Latches 
Combined Index and Latch Specific Examples of Index- 
ing Jigs Roll-Over Jigs Trunnion Jigs Double Trunnion 
Jig A Difficult Drilling Problem Trunnion Jig Used 
Progressively, 



x CONTENTS 

CHAPTER VI 

PAGE 

DETAILS OF MILLING FIXTUKE CONSTRUCTION 134-181 

Types of Milling Machines Types of Cutters Important 
Details in Fixture Construction Elimination of Lost Time 
Elements Necessary in Efficient Tool Designing Locating 
Points Methods of Clamping Applications of the Lever 
Multiple Clamps Design and Use of the Hook-Bolt Sup- 
porting and Clamping Thin Castings Principles and Methods 
of Pneumatic Clamping. 

CHAPTER VII 

DESIGN OP MILLING FIXTURES 182-212 

Fixtures for Hand-Milling Form-Milling Attachments 
Design and Operation of Indexing Fixtures Semi-Automatic 
and Automatic Indexing Devices Uses of Twin Fixtures 
Fixtures for Continuous Milling. 

CHAPTER VIII 

DESIGN OF PROFILING FIXTURES 213-229 

Principles Involved Types of Profiling Machines Cam 
Milling Irregular Forms Methods of Roughing and Finish- 
ing Multiple Fixtures. 

CHAPTER IX 

VISE- JAWS AND VISE FIXTURES 230-246 

Special and Swivel Jaws Devices for Insuring Accuracy 
Quick Operation Devices for Equalizing Pressure Auto- 
matic Ejectors. 

CHAPTER X 

BROACHES AND BROACHING FIXTURES 247-267 

Principles of Design Tooth-Spacing and Chip-Clearance 
Burnishing Keyway Broaching Multiple Fixtures Index 
Broaching Spiral Broaching. 

CHAPTER XI 

DESIGN OF RIVETING FIXTURES 268-282 

Riveting Machines Types of Rivets Locating and Clamp- 
ing Use of Tables Ring-Staking Tools and Fixtures 
Ejectors. 

INDEX 283 



TOOL ENGINEERING 

JIGS AND FIXTURES 

CHAPTEE I 
OUTLINE OF TOOL ENGINEERING 

EFFECT OF DESIGN ON MANUFACTURE CONSIDERATION OF LIMITS 
OF ACCURACY SELECTION OF WORKING POINTS TOOL OPERA- 
TION SHEETS RELATION OF DESIGN TO COST OF MACHINING 

The science of tool engineering as it is now practiced dates 
back comparatively few years and very high production tooling 
is of even more recent date, A few years ago when production 
was small the majority of jigs were made as cheaply as possible, 
no great attention being paid to upkeep, because production was 
not sufficiently high to warrant it, except in the case of products 
which had been to some extent standardized, such as military 
rifles, army pistols, sewing machines, and similar work. The 
usual practice in the old days was to make a rough list of opera- 
tions which was to be followed and then give a few free-hand 
sketches to the toolmaker to show him approximately how the 
tools were to be made, leaving many of the details to the man 
himself. "When this man needed a pattern he went to the pat- 
tern maker and told him what he wanted, leaving the propor- 
tioning of the pattern to him. Then after the casting had been 
made the toolmaker "whittled" it out until a makeshift jig was 
evolved, which served its purpose in the production of so-called 
interchangeable parts. 

The tool engineer of the present day must be up to date in 
the manufacturing field ; must have a broad knowledge of ma- 
chine tools ; must understand the theory and practice of cutting 
tools, speeds, feeds and kindred subjects and should have prac- 
tical shop training of such a nature that he knows from his own 
experience just how a given machine is handled and what the 

1 




2 

requirements are for tools t l** usni HI* if, If ! *liu^ imt 
this knowledge he will not ! .'ill- t ilu th- work r-,|iiii 
him in the mast efficient wannrr, 

Listing of Operations. In nj tn ,i,iv 
first step in the process in tin* li 
necessary to machine etith umtp 
whieh is to be matmfnetttml ttt 
step in the manufacture* is MMI 
viewpoints, such an: Kconnnt> in 
suitable; tooling equipment awnl 
euraey required; ji>?s nl fixture i" 
etc. In many cases, also ttirK m*i> >*j'i < 3.,, 'h.i'n,)'?^, 
hardening, grinding nftt't fiiml* 11114*. M ; ^/ .1 *^i,>,/ i , 
other unit, poliKhiu^ bluing **r n ur IjM.it.u * 1 ' ^ * - * 
ters must be cotusidcrctl in tii* 1 li*!ut', 'f M, MM * .? || 
it is evident that the tool t'n*,!wr' tufinf i> * ^ <, > I'.un 
with the procesneK of machitnu'", liar) ?.,',* tM ^ ! ^M 
ing, but he must also tm<t<*!st;in*i fl* *M|,I ? .j ( , ^.^ . , 4 
ism as a whole in oinltr that In* if- i !^ ^^ 

for machining thin or that MirtW i ilutt i 1 % Jl l 
relation to some other hull* r 41 MI^M J 

unit will function pni|iert>% 

Points To Be Considered I*H n * j utf> f- 1 a 4 ^i** 14 5 
of a certain part in tunttd *VIT t** llir !,) i t |M tM ^ w^h 
statement that the part ifriiivinr tins liin -j j^ M,| fl .,j r )t 
for tooling. The following (ititnts niii t tt*n i ?,,^, j, im 
sideration in listing the cifii'iiitnnn, 

1. Production K^mrnL TIiK i*^ m ii.i^^if i^l ^ jt*<l*'r t 
whieh affects the methmi of t,, 4 ,, M ,| < ^.^ n 

If a comparatively smiill iitimiirr M f jrr.v. ^ t,* . j^Hj^ 
tured, the tools muM ht .snii|l* iunt *h. rtr m .., M *,,}, 
tool cost as low an pttHhihh*. It n larfr im^ 1 ^! ,'f . , -^ 
be manufactured, mnltit!t< , ( ,,| ,-, uu j ' M, M \^ j^ 

would be called for, in onli*r fn III*KJ ? |', n^ ,-: v/ ,, , jt|f 
as possible. In the latter t^iiw t|,,- ,., fi t -f *...!. v m ^i il 
tributed over mieh a R n*nf iiiimliir i,f ,,-,,, .^a* h. amf 
for took would not hi* I'xmNiv**, 

a. Material of Winch th* M'.U /i H^l* ft Ir . t . f ir a r . 
ing, a forging omtHrapin^ r if f , u> ! fM4l j,. ffNfll , , ? fi| 
stock. If a easting it may tim i fll , |M ,y r4( . ^ ^.^ , 



OUTLINE OF TOOL ENGINEERING 3 

snagged on a rough grinding wheel before machining. If it is 
a thin or irregular easting it should first be inspected both for 
quality and to wee whether it has warped out of shape KO that 
it cannot be machined to proper dimensions. 11 a forging it 
may require heat treatment before or during machining" or it 
may be hardened and afterward ground so that necessary allow- 
ances must be made during the machining to provide sufficient 
stock for grinding. If made from round stock it may be found 
best to machine it from the bar on a screw machine, or perhaps 
HM length and general shape may make handling it more profit- 




LLLU 



Fig. 1. Kxnmph* Khowhig tin* KMfahliHhmwtt* of Work lug Hurftuwti To Hi 
IWd ! Locating th* Work During Mwltitihig 

able on a manufacturing lathe after cutting it into lengths on 
a cold saw or a eutting-off machine. It IB evident from the 
foregoing that the material of which the part is made is an 
important factor in the machining. 

3. Surfaces To Be Marh-inecLln considering the various 
holes to ho drilled, ho red or reamed and the various surfaces 
to he machined, it is important first to decide 1 whether the vari- 
OUH holea can be drilled in one jig, or several jig will he re- 
quired ; next, whether several milled surfaces can bo machined 



JIGS AND FIXTURES 



in one setting or it will be more economical to make several 
operations. It is also necessary to decide whether any other 
operations that may be necessary can be handled to best advan- 
tage in combination, or by several operations. It is not good 
practice to drill small holes and large ones in the same jig, unless 
drilling machines can be so arranged as to obtain correct spindle 
speeds for the different sizes of drills required. In special cases 
it may be found profitable to do something of this kind in order 
to avoid a resetting of the wark and the cost of an extra jig. 

4. Accuracy Required. In any mechanism there are certain 
fundamental principles affecting the successful operation of the 
device. In order that it may function properly as a unit the 
various components which make it up as a whole must fit each 
other within certain limits of accuracy. These limits are usually 
specified on the drawings of each part and the tool engineer must 
keep them in mind when listing the operations as well as when 
designing the limit gages used in the production of the parts. 

The accuracy with which various machine tools will work must 
be taken into consideration and if their accuracy is not suffi- 
cient to produce the results required, a final fitting or grinding 
operation may be necessary. So it is apparent that the accuracy 
required is a factor of importance in listing operations. 

5. Selection of Working Points. In order to obtain the best 
results in production it is advisable to select working points 
which can be used for location in all of the operations on the 
work. It is difficult to give a hard and fast rule for determining 
which points are the best to work from, due to the fact that dif- 
ferent cases require different treatment and various pieces of 
work are of such widely different design that no fixed rule can 
be given to apply to all instances. A very good thought in con- 
nection with the establishment of locating points is first to ob- 
tain a flat surface and next machine two or more holes perpen- 
dicular thereto if the nature of the piece will permit it. In a 
case of this kind it is possible to work from the finished surface 
for all the subsequent operations, locating by means of pins in 
the drilled or reamed holes, and in this manner making certain 
that correct relations are kept for all the operations with the 
points established as working points. Sometimes it may be neces- 
sary to vary this procedure on account of the shape of the work, 
but the matter of establishing the working points must always 



OUTLINE OF TOOL ENGINEERING 5 

be considered very early in the listing of operations. A very 
good example which shows the establishment of working points 
is shown in Fig. 1, in which the flange A is first milled to give 
a surface to work from and in the next operation the flange 
holes B are drilled and two holes C reamed to give the other 
locations so that the work can be carried through its various 
operations by using these points from which to locate. 

6. Provision for Chucking. In the handling of work on the 
turret lathe it is frequently necessary to provide means for 
clamping or holding the work during the first operation. There 
are many cases where the shape of the work is such that it can 
be held in a chuck without difficulty, but in other instances it- 
may be found necessary to provide the work with lugs in order 
to hold it properly. A case of this kind will be noted in the 
hub, illustrated in Fig. 2. In this case it was decided to ma- 
chine the surfaces marked / in the same setting, and obviously 
it would be difficult to hold by means of the tapered portion A. 
By the addition of three lugs B the work can be readily held by 
the chuck jaws C, as indicated in the illustration. "When lugs 
of this kind are added to a easting they may be removed by a 
subsequent operation or they may be left as they are, provided 
they do not interfere with the appearance or utility of the 
finished product. 

7. Concentricity of Cylindrical Surfaces. In the listing of 
operations the importance of concentricity of the cylindrical sur- 
faces which must be in alignment should be carefully considered, 
as any variation from the truth will cause the mechanism when 
completed to cramp and not run smoothly. It is advisable wher- 
ever possible to machine concentric cylindrical surfaces in the 
same setting, but as this is not always practical, particular at- 
tention must be paid to the method of holding, when several 
operations are used, in order that the work may be true when 
completed. A very good example of a piece of work of this 
character is shown in Fig. 3. In this case the bearing seats A 
and B must be concentric to each other, and yet it is apparent 
that the two surfaces cannot be machined in the same setting 
of the work. For this reason the greatest care must be exer- 
cised in designing the tool equipment so that the first bearing 
seat B will be used as a location from which to produce the 
second bearing seat A. Many other examples could be given of 



6 JIGS AND FIXTURES 

work of this character, but the instance given is a representative 
one which will serve to illustrate the points involved. 

8. Machines Required and Available. In the selection of ma- 
chines for the work in process it is necessary that the tool engi- 
neer should be familiar with the various types of machine tools 
most suited to the work. In listing operations for an old plant 
having a considerable assortment of machine tools from which 



Chucking 




' j Section E-E 
Fig. 2. Addition of Chucking Lugs to Assist in Machining 

to choose the tool engineer must have a list of these machines 
together with necessary data on their capacities and their work- 
ing ranges. It must always be borne in mind, however, that the 
selection of a machine for high production should not be* de- 
pendent entirely upon the machine tools which are in stock, and 
it may be more profitable to purchase new equipment rather 
than to use old equipment which is out of date and does not 
give maximum efficiency. 



OUTLINE OF TOOL ENGINEERING 7 

Buy Tools as Needed. It is obvious that when listing opera- 
tions for a new plant the machine tools can be selected as they 
are needed and can be -bought as the occasion demands. In cases 
of this kind the tool engineer must be open-minded and must 
make his selection after having looked into the possibilities of 
the- newer types of machines on the market. 




Fig. 3. Concentricity Between Seats A and B Very Essential 

Plant Layout. In. handling production work the layout of 
the plant has an important bearing on the speed with which the 
work can be routed through the factory. In the case of a new 
factory it is evident that a plant layout must be made which will 
show the position of all machine tools suitably placed, so that 
there will be room for the piling up of raw material and the 
finished product. The plant engineer who understands his busi- 
ness takes all these matters into consideration. 

Some of the points which come up in the placing of machines 



8 JIGS AND FIXTURES 

are illustrated in Fig. 4. In this case the drilling machines 
shown at A and B and the tapping machine shown at C have 




Drill 



Drill Tap 

Machines Too Close 



Fig. 4. Example Showing Drilling Machines Set Too Close Together 

been placed so close together that it would be difficult to find 
space for the work both before and after machining. A much 
better arrangement is shown at D y E and F in Fig. 5. It will 




^ 
Drill Drill 

Proper Spacing 



Tap 



Fig. 5. Drilling Machines Properly Spaced 

be noted that these machines are more widely separated so that 
boxes can be placed between them for collecting the material 
as fast as it has been drilled or tapped. These boxes can be so 



OVTL1XK OF TOOL KNQINRKR1NQ 



made that they will hang on the edge of the drill-proas table, or 
they can be resting on the floor. They can be readily removed 
and replaced if desired. 

Another example of the placing of machines is given in Fig. (. 
The upper view at A, K and (! shows an arrangement of screw 
machines which is very bad because it does not make suitable 
allowance either for the stock in the machines or for the piling 
of the stock on the floor alongside of the machines. Referring 



SCREW MACHIHE 




SCREW MACHIHE, 



No Provisions For Stock 






Correct Layout 



Fig ft. Improper and Proper Spacing of Scrw Machimw 

to the lower portion of the illustration /) K and F H!HIW a much 
better arrangement, with plenty of room for finished and un- 
finished stock. 

Tool Equipment Required.When the tool engineer ban de- 
cided on his sequence of operations it will then be necessary for 
him to decide what tools will bo used in the production and also 
what gages will be necessary to bold the work within the re 

quired limits of accuracy. It in customary for the engineer to 
talk over each piece of work in a conference with bis chief drafts- 
man and possibly some others who lire intimately connected with 
the production work in the shop, At this conference* it In de- 
cided just what varieties of tools would be beat for the various 
operations, and in all probability rough sketches are made to 
indicate in a general way the kinds of tools needed* 

A decision would be reached regarding the use of mngle or 
multiple fixtures, and the inathine toolg to be used would 



10 



JWti 



be selected. As the shop Huperinti'iulmt Ls lik**Iy to IM* on* of 
the men in the conference* ho would undoubtedly have iTrtnin 
preferences in regard to the toots to iuu* for tvrtain opmitious, 
After a decision has been mulud us to ju.st h*\v arh pi*vt* is 
to be handled the list of operations nhould In* typl ami turwtj 
over to the chief draftsman, who turn tiit*ii start on tit** <t<*siti 
of the necessary tools. 

Effect of Design on the Cost of Machining. If fn*<(Ui*fit!y 
happens that in working out tlu toots Fur flit* variutis p*rittitMiH 
it is found that the shape of the work mnkt.s it itilllmilt to 







J-.f..*! 

Fig. 7. A Difficult Cant Inn 






machine, and in many camnt if inity U fniiitit to 

or change thehape of the work M^MI\ In In n/^i^t in tlii* 

handling and cheapen the wt of rnaiiiifurtur\ 

A very excellent etample of mtdt n t'tiiKitttuu in HI Fr 

7, which ahowa a small hrtww eiwfiii^ fonwtlj- iI**>aKii'ii SM fur 
so its part function in mrn^nml Wlini tin* f f w t, ttah 

started it was found to ix a wry iini|tuHifui tn 

tools that would give good rmiita, Tin* orutitial mutiny f 
operations was as follow* : (I) StrmliU** mill in%i*l^ n ti>l 

one end; (2) atraddlo-mill nitiiill unit; '> tlritl iimf mmi H f in. 
hole through both end and |^iti. holt- to w/,t*; U) turti J-m. 
endj (5) cut teeth; (6) ream holt*. 



OUTLINE OF TOOL K' 



11 



The first operation was difficult to hold, due to the two 
diameters that were to be located in V-blocks. The variation in 
the easting would throw out the work, musing the subsequent 
operations to be out of line. 

The second operation was to be held in the same manner, using 
the milled slot for location, and the small arm required a clamp 
which was very weak, due to the thickness of the portion it wan 
to clamp. 

The third operation could not be finished in such a way as to 
be certain that the holes would be in the correct relation to the 



DOWD ENGINEERING CO. 

TOOL AND OPERATION SHEET 
CUSTOMER BLANK REGISTER CO. 

ADDRESS New Ycrk 



Aim<> 
NAME 8iimntYokt 

No, PIECES PER UN IT Duo 
MATERIAL BronM 



Q|Mr, 

No. 


OacrJ|)tlon of OMrntlon and 
Mot hoc* of Holding Work 


Typo of 

Moh. 


Tools. Ga0 and 
Cixtum* 


Tool 
Number 


Dowd 
Ordor 
No. 


Mr 


No. 


1 


Drill and warn larg hol fu-o 
and turn bub on large end, cut 
off chucking stem, allowing 
i took for profiling , 


S 


Collet jawa, t,l 
bU^k, ffiHmg t<Rh, 
aut*<>n tool, drill* 

(iUl.) 


9191 


I4lf, 
141? 
1418 





1 


2 


Profile small od to length ami 
ont Eitl of fwall ann, 


Profiltr 


Profiling fixture, 


9195 


1420 


60 


f 


3 


P.m&to otbwr f j.U^ of j.uuvll arm. . 


Profiler 


Profiling flxtur* , ', 


9196 


1421 


100 


1 


4 


Drill and ream holt irt arm.. .... 


Drill 


ProfilouUor<td.) 


9197 


1411 


7$ 


1 


5 


Cut ttntlk . .. . 


urttit 


Drill (td.J 




1421 


60 






Mill kuOdi boMtt. . .,..,.,.... 


mitUr 
Plain 


i-ffi (nUU 
Milling fitur0 


9199 


1424 










inilltr 


Cutter <td.) 








1 



Fig. 8, Revised Routing for the Pit*et Bhown in Fig, 7 

milled faces. An operation of this kind w nine very difficult to 

line up to assure a hole whieh will be true with the milled 
surfaces. 

The fourth operation required a apodal arbor with an under- 
cut in order to allow the tool to face the end. 

The fifth operation uned a apecial hob which finkhed the out- 
side diameter of the teeth m well as cut them. 

The sixth operation wan very hard, to get in line with the small 
hole and the clamping WEB very difficult. 

As the tools had been planned it wan noted that Considerable 
improvement could be made if the operations were revwed, and 
after careful study the routing was changed as shown in Fig. 8. 

For the first operation a chucking stem was provided for the 
work, as shown in Fig. 9, so that by gripping the work in the 
chuck it was possible to drill, bore and ream the holes through 



1 12 

the hub and to face and turn the end at K without any mit 
; difficulty, and then before the work ww tiikrn mil if thr HiwU 

I the chucking stem was cut off with the parting tun! r, l.'uvmg 

the work clean and accurate and at tin* siiuw time providing an 
excellent location for subsequent operations. It \ull hr nnid 
f | that a "tie-piece" A was east in the work in nnlfr to prrvrnt 

too much distortion and at the same time hulil it twthrr during 
the first machining operation. It in rather Itnril to apprtTtate 
the delicacy of this pieec without it but its eotistnit*tum 




Fig, 0, Casting Itoviwd to In 

and lightness made it extremely Utdieult to tiiiirhini* without 

distortion, 

The Hecond operation wan the profiling of the enit f 

hub to the correct length and Kurfaeinp HIM*- tf flit* iiriii 
This work wan done on a profiling maehim*. it net 

for the variation in the height cif flit* tuK Tin* in tin* hub 
was used to locate from, making it eertain I lint the when 

finished would be absolutely true with tin* hole. 

The third operation, which wan that of profiling 1 flu* other fci<!i* 
of the small arm, WHH very simple ami tin* fixture wn* 
in such a way as to use the center hole from whU*h to l<**ittt% A 
suitable set block was provided. 

The fourth operation mm that of drilling and ttit* 

hole in the arm. By using the center hole to iittcl 



OUTLINE OF TOOL ENGINEERING 13 

the finished surface of the arm to "bank" on it was very easy 
to design a jig for thin operation which gave excellent results. 

The sixth operation was that of milling the inside bosses and 
cutting out the tie piece. The work was located on studs in vise 
jaws. These jaws were provided with stop pins which prevented 
the jaws from crushing or distorting the work while the milling 
operation was taking place. It was found that the work did 
not spring over (U)()03 in. when the tie piece was cut out. 

A great deal of thought was put on this particular piece as it 
was an extremely delicate one and difficult to machine. With 
the operations as originally laid out the tools would have been 
very costly and there would have been great difficulty in hold- 
ing the work within the required accuracy. As the operations 
were finally revised the tools were simple and comparatively 
cheap and the work wan held to a close degree of accuracy with- 
out difficulty. 

Another Example. A very excellent example of a change in 
design which resulted in a great saving in manufacture is shown 
in Fig, K). This may be considered an exceptional example, in 
comparing the cost of the production of piece A as shown above 
and H as shown below. The work is a yoke connection which 
was originally made from a forging bulldozed from a machine 
steel rod. The finished piece wan about 50 in. long. As origi- 
nally made, the machining necessary to complete the unit was 
as follows: (1) Htraddlc-mill bosses; (2) drill and ream holes. 
Both the drilling and nulling operations were very awkward, 
due to the length of the piece. This method was followed for 
some time until it was thought by tool engineers that consid- 
erable improvement could be made. 

After gome consideration the unit was made in two pieces as 
shown at R and ('. The* yoke end was blanked in one operation 
on a punch press with the holes pierced to the finished diameter. 
The work wan then formed an shown, thus completing the yoke. 
The next operation eonsisted of welding the yoke to a rod of 
machine teel cut to the required length. Thin operation was 
rapidly done 1 at a smaller coat, and the only remaining work 
needed to finish the piece was to dress off the welded section. 

The comparative labor costs of the two method** of manufac- 
ture showed a saving of !H) per cent in actual labor in the latter 
method. Taking the cost into consideration the new method 



14 



JIQti AX!) MM'iKKN 



does away with the milling cutters, drills ami reamer*, 

the cost of punch-press dies just ahout fiTsi'ts fin* t'urtfimj <ijr.s 

originally used, HO far an upkeep is eom'eriini, 

Threaded Work. -Very often when de*i#niiitf a pi*-* 1 *' of work 
which is to be thread oil the designer dors imf fnkr int* t'tiiKsid* 
oration the cutting 1 of the thread. lit mjmut'at'tunm: wnrk the 
majority of threads in cut hy itirniiH of flics, mill n urltr In 
have the dien work properly they KlwuM have 11 Imtl uf af Jm^t 



Fig. 10. 




Original and Kiwimi 

in Having itt 






two threads. That w to nay, tho fiwt two itr 

chamfered to allow tho die to run on to tti Kuw it $ 

evident that after two thrwub* Iti flit tlit* art* tnit likt* thm 

it would be impossible for It tci cut 11, full tip ! n 

der. ^ For this reason it in to it of 

sort in the thread if to nit it to n 

A very good example of a dlillntlt |ij mt ,f thn*ml*t| work m 
shown at A in. Fig. 11. Thin was nit t f lf * 

drawing of which called for it full tliivm! ti f to flu* 

shoulder B. It wag a produetion job iitui it wm to I* 

practically impouible to cut the rlgtif up In th* 



OVTLINK OF TOOL ENGINEERING- 15 

as shown. A concession was finally made by the customer to 
permit the thread to stop one thread away from the shoulder 
and a groove was made at the point C to allow the die to run 
out. A little forethought on the part of the designer would have 
shown him the difficulty of cutting the thread up to the shoulder 
as shown and he should have made suitable provision on his 
drawing to take care of this matter. 

Chucking Stem on a Gear Blank, In making up spur gear 
blanks such as that shown at A in Fig. 12 it may bo necessary 




f?\ f 



Fig, M. A Difficult Piece of Throidod Work, Changed 
to AHHittt in Production 

to make several settings of the work in order to machine it prop- 
erly. If, however, a chucking stem in added as shown at B in 
the illustration the work ean be held by means of the chucking 
stem in the chuck jaws C in such a way that all of the machin- 
ing can be done in one operation. After the piece has been com- 
pletely machined the parting tool I) can be run in to cut off the 
blank as indicated in the illustration. An arrangement of thia 
kind in very common and the same idea can be applied to many 
other cawes of nimilar work. 

Drilled Holes Close to a Shoulder. When drilled holes are 
called for in a piece of work it; is not only necessary to provide 
clearance for the drill but aim), if the work m to be, produced 
in quantities, sufficient clearance should be provided for the 



16 



JIGS 



. \rt'UK8 




Fig. 12, C'huc'kiiig Rtwi Atttlinl f IIi*itr 





Atftfru 9 H*f *+*,*# 

fQ iA*M IV** * ^ 


T 
' 


"...",..:... . .[ 


ft 


?0 

11 ' 'ii ; 

] 1 }'< . 





{ Q ' ' ; 

* ** ., ,,,,. , , 1 




I 






"'T:.*!!1 



Fig. 18. Insufficient Cli*aiit*t* Altifwiu! for Drill 



OUTLINE OF TOOL ENGINEERING! 17 

drill bushing. An example of this kind is shown in Fig. 13, in 
which it will be noted that the hinge hole (/ is very close to 
the shoulder B. The drawing was marked ** grind to wait" at 
point A. Evidently the intention was to grind away the canting 
slightly in order to allow clearance enough for the drill. AH a 
matter of fact, when the jig was built the bushing was cut away 
as shown at B, but even when this was done the variation in 
the casting was so great that a proper location for the hole 
could not be obtained. 

The obvious remedy for a design of this kind is to cut away 
the interfering shoulder far enough so that there will he plenty 
of clearance for the bushing. Cases of this kind are more or 
less frequent in general manufacture and it is often necessary 
to make slight changes in the design in order to drill the work 
correctly. 



rAi*Ti;ii n 

FUNDAMENTAL IN jit; 

r ALUK OF AN\IVJ"H l*Mt'U'|M\ i, II i , : 1% , \\ --u 



AM* iNYiCrttj.* i i*>" %- f % / 

ANCB FOR WoHK AM* l''<W !*< : . 

CATIMO Krttmrt^ SU-HV* l *' ' 

TfPIS OP JlttS 

There art* uumh*r *f !',', >,*.'' * 
eonsidertni in tfii* ilt*%ii*!i ! lu r ^ * f - 

design a ji^* Th** tti*i 

only a small iiniiwiiit 

ally think jf flit* ftiiin 

In taking up tlfiw i 

elementary iin*t cntft!jtt*itt fuiu , * ^f. r .- i ? , , 

clear aud reailily mwlvf^iu^lA 1 ^ \ {*>* * *> t ^, ',. i,^- 

tains a clear kmwl*tJv#* *f ih ('," '.^u^ '.!- i f , i 

the design of ii%tiifr% Ii 41 *J! ^*- -/ * * <,<, 

for hhttHelf inn! tn* lull 4!^Li^ <! ^ >'* ,. \ ^* ,, 

principle on \vhii*h li* IN ni$l/j|* si' *,' ? 

Value of Irt tit iif?t<' t < * ' i ^,-, ! 

the matter of 4 |i?^l,:'ii 4 *^f. . ,", , . * .. 

Every piwi* tif mini i* !,. ?> ,, . , - N 

fully looked over l*|nr* m^ i^-j^,^ ,, /,< 
clear undcrHtiitniiiif tif HH ^iii,f| i ri ^, - . , ,/-. k - 
various surfnf*iM mny hfMii^tr?co<| J' i -, , 
consiclemhle 1^ *f<*^i * , , . -t 

out by tht* tool fftpit^f, flwiv H<i! ! ,. ' </ * r , ,^ /, > 
the tool tli*Iiii*r mn *** t^,, <*.,/ / ? ; >f 

machine nn* fn tr f^^ , Js ,-s, - /- ,, \ 

analyak of tin* tiwt M^/,,, t ! M ^ * , ^, ^t - 

embrace also Hit* f jign .u^i !*,*,. * s> -> , * ,- , 



FUNVAMKXTAI* PO/XTti IN DRILL JIG DEMON li) 

should consider the locution of the fins, ribs or drafts, as well 
as any irregularities, in order that location points may be se- 
lected which will not be subject to variations caused by rough 
grinding, filing and chipping. It Is always advisable for the 
tool designer to make such a thorough study of the piece of 
work which he is about to tool that he can carry it in his mind 
without having to question the relations of various portions to 
each other. After this analysis has been made he should be 
ready to start his first jig or fixture, 

Points To Be Considered. -When designing a jig the follow* 
points must always be considered: the method of locating the 
work HO that it will be machined in. a uniform manner; the 
clearance between the jig body and the work; suitable provision 
for cleaning; chip clearance; accessibility in setting up and 
removing the work; distortion in clamping, etc. Various points 
in connection with those mat tern will be discussed in detail. 

In locating a piece of work in a jig when no other operation 
has been performed on it previously, the greatest care must be 
taken to select such points for locating that inequalities in the 
casting or forging will not cause the work to be thrown out of 
line in such a way that subsequent operations will not give ac- 
curate* results. The work may be a rough casting or forging 
and while the forging may be smoother and more accurate than 
the casting there in always the matter of draft to be considered. 
It is advisable wherever possible for the tool designer to obtain 
a Harnph* canting or forging from which to work. Not only does 
thin make the tool problem more simple, but at the same time it 
enables him to note when* irregularities are likely to be found 
on the work and to guard against so placing a locating point 
that it will come in contact with some irregular surface. In a 
forging, if it happens to be a complicated one, there may be an 
excessive* quantity of metal on certain parts, on account of forg- 
ing conditions. Unletw the tool designer has a forging drawing, 
a "lewd," or n rough forging, he may not be able to make suffi- 
cient allowance in his jig or fixture to take care of the exeeftH 
metal mentioned, 

A fundamental principle in tool design In, that a rough casting 
or forging mmt not ///* sup ported on more than three fixed points. 
Let us consider the work shown at A in Fig. 14, which is a rough 
easting of triangular shape to be drilled in the three corners 



where the Inmm iw* liMti 4 l N w 
jig we Hhall apply tin* pntnf^ ^ ^ j 
poiritH m a support. Th"- thp- 1 
the three holes 1), K ami I i* !j " 
bushings as illttitrtitni a! H w fb 
let us consider that 4 t^* I H '* 
we munt alno nrnko hiiri* if tH ! 
Probably the 



'.**'"<', 



! lilt if 
\4I 



Vj 




B r""Vf ' Jf f 

4 ~; 



* 



/; f 
MI*-; 



1% 14 II. X'" 1* *i 

and J ami hy n it'**l ** ! * / .i 1 I* I**, 

the work, prctiKtiri* t*wii Itr 4*j!'r4 rt t s,. j '; / fc *?j <? ,*' 

C as indfratMl by ftn* vt ti^it ^ f / 

work over Ifn* pittn II, J ii4 II 

tively, Tht* citliff ^f J^^iu5^ il,. .*. /. , ^In^n 

in the center tif tlti illtHttittiMfi, fi s a '?H^ < ** .n^ .M,M , | t}^ 

Work 18 lMfttlHl ill It If ait*! !ti- >1 ..'>M- *-/^4^ 

against the angtilar n ts<*^^n ^ ,,|,^, , * ,^ *t, .1,! f 
It is underKttKMl tlmt flu* ,f c*-t^ J( , t t ^^ *^ ** it^rr 

bushingK SH thi In i*ii) g ^ ^i 

Locating a of Itnti i**i rm It 

Eeferriiig to Fijr. 15, }>..<' ,,f ^4 >* ^^n 



JfUNHAUKXTAL MJWTti IN DRILL JIG DESIGN 



21 



has a rough hub cast on it and extending beyond the flange of 
the work A. Now this piece is also a rough easting and in order 
to obtain a true relation between the hub and the rest of the 
easting it is necessary to use the hub in setting up the work. 
By referring to the upper figure it will be seen that we do not 
depart From the three point method of setting up on the pins 
indicated at C. At the same time however the necessity for eon- 



c, 



>_ WI.___i4L 

'/ ""<> 



(o) 

{>' y, 



O" 



/ jL'cfr 
AJ *wo 



'cfrtttancf 




Fig, 15. Locating a Pirns of Hough Work Having a Hub Cant cm It 

mdering the huh makes it advisable to provide a means for lo- 
cating it on the spring V-bloeks B, By applying pressure at /) 
the work will seat itself on the three points C and will also locate 
in the spring V-blocks. In connection with the V-blocka men- 
tioned it in well to note that these should be made with a so- 
called " knife-edge. " 

Locating a Rough Forging. Very frequently rough forginga 
are made with the locations of drilled holes indicated by a 
countersunk npot. Fig. H) shows a gear blank with the center 
hole countersunk in thin manner. In canes of this kind it is com- 
mon practice to set the work up and hold it by the outside It in 
a floating chuck. When this is done the chuck is placed on a 



22 JIQ AND FIXTURES 

drilling machine and the drill centers itself in the countersunk 
hole, thus making a jig unnecessary. It is .sometimes found 
advisable where very much of this work is to be handled and 
when the drilled hole is long, to provide a supplementary bush- 
ing, supported on the column of the drilling machine in order 
to steady the drill and prevent it from "wabbling." The man- 
ner in which this is accomplished is clearly shown in the illus- 
tration. 
Another condition sometimes found in machining a rough 




floating 'ctocfi 

Fig. 16. Forging of Qar Blank with Holes Countersunk 

forging is indicated in Fig. 17. In this case a steering knuckle A 
in the part in question and it in necessary to drill through the 

center of the long hub indicated. One end of the hub m located 
in the cup bushing B while the other end eat itself in the screw 
bushing C. Now this particular ease in given as an example of 
a method which should not Ixs used. In the first place a screw 

bushing is not very good practice because it is not sufficiently 
accurate and it in likely to become clogged with chips and in 
the second place the method shown is dependent for its accuracy 
on the regularity of the two ends which themselves in the 
bushings. If these ends are not uniform the work will not be 
true in the bushings and as a consequence there will be a varia- 
tion in the relation of the hole to the arm /), such that the latter 
may be out of line and will not clean up in the subsequent opera- 



FUNDAMENTAL POINTS IN DRILL JIG DESIGN 23 

tion of turning the portions marked /. A much better way to 
locate a forging of this sort would be to locate it with a knife- 
edge V-block at each end of hub A so that when the hole Is 
drilled it will be true with the hub and in correct relation to the 
portion D. 




Fig. 17. Incorrect Method of Locating a Forging for Drilling 

Location of Finished Work. "When work has been partly 
machined it is usually necessary to locate it for subBequent oppru* 
tions from some of the finished surfaces or holes. An example 
of this kind is shown in Fig. 18, in which the connecting rot! A 
has been previously machined as indicated by the finish 




Fig. 18. Location of a Connecting Rod Forging 

marks. As these surfaces have been previously faced anil n 
it is necessary to drill the holes E and F m that they will !H 
true with each other and with the surfaces machined, the work 
must be set up with this point in mind. By allowing if to rent 
on the bushings CO the relation desired can be readily obtain*! 
It is, however, necessary to obtain a location for the hole K ami 



24 JIGS AND FIXTURES 

at the same time make sure that this location will not disturb 
the seat on the two bushings CC. This can be done by using a 
V-block as shown at B having a bearing which touches the hub 
above the parting line of the forging. When pressure is applied 
at D the effect will be to throw the hub over into the V-block 
and at the same time the angularity on the hub will tend to draw 




t 








1 

--x 


1 j" 

1 
1 

1 






] 


V 


1 
1 

1 

1 
1 

t 



B, 



.6} 



- 



Fig. 19. Location of Finished Work 

it down on to the bushing C. It is not usually considered good 

practice to drill and ream the hole E and the small hole F in the 

same operation and it is customary to locate the hole F from 

.the previously machined hole E and to do the work in another 

jiff- 
Fig. 19 shows another method of locating finished work. It 
will be noted that this piece is the same as that shown in Fig. 15, 
and the operation to be done in this case is the drilling of the 
long hole in the hub A. The holes B, C, and D have been drilled 



FUNDAMENTAL POINTS IN DRILL JIG DESIGN 



25 



and reamed in a previous operation. It will be remembered 
that we were careful to locate the work for the first drilling by 
means of the long hub and as a consequence we can now use the 
holes drilled in the previous operation for locating the piece 
when drilling the long hub. By setting the work up on pins at 
B and C we obtain the alignment and the stud D simply acts 
as a support. If there were to be other operations on this piece 
it would be advisable to use the holes B and C to locate from 
through all the subsequent operations. 
Fig. 20 shows another example of a method of locating a piece 



s 




(f 


-Tk 

y 




^J 

> 


~'~1 


A. 


j 

-S 


1 




Fig. 20. Location of a Finished Casting 

of work of which the surface / has been machined in a 
previous operation. The work is shown at A and it is located on 
the finished surfaces indicated as it is necessary to keep the holes 
square with the finished surfaces. At the same time we wish to 
make certain that the holes are drilled in the right relation to -the 
hubs E and F. Therefore we use a V-bloek 1$, slightly undercut at 
an angle of about 10 deg., in which to locate the hub F. The hub 
E will swing over against the block C which is also slightly 
undercut. Now when pressure is applied in an angular direc- 
tion as indicated by the arrow at D, the work will not only seat 
itself on the finished surface but will be forced over into the 
V-block B and against the angular "block C thus assuring a posi- 
tive and accurate location. 

Correct Side from Which to Drill Holes. There is a very 
important point which should always be considered in the loca- 
tion of holes in two adjacent pieces, when these holes pass 



26 JIQ8 &WD FIXTURES 

through both pieces ami are used as rivet or bolt noles to hold 
the two pieces together. An example of this kind is shown in 
Fig. 21. In this case the two disks ,1 and B shown m the firnt 
part of the illustration, are held together by rivets passing 
through the holes C and D. It is evident then that these holes 
must be in alignment Now let us assume that the work B is 
placed in the jig so that it Is drilled from the side E and in the 
direction indicated by the arrow. When this is done it is evi- 
dent that the drill may "run" a trifle so that the holes may take 
a slightly angular direction as indicated. Now if the upper 
pieces A were to be drilled from the side F and in the direction 
indicated by the arrow there is a possibility that these drilled 
holes might also run out a trifle. The result would bo that when 



BD-FJ .?._ 

f I Yr^y-pTr 

lb^([.d fo -M ) 

C f c ^D 



fT _f f"~: 

tirrTi 



'"o. 



Fig. 21. Correct and Incorrect M<thod of Drilling Holcu In 
Finished Adjacent Parts 

an attempt was made to assemble the two parts A and li they 
would be out of alignment and it would be impossible to put the 
rivets in place to hold the two parts together. 

Assuming that both parts A and R, m shown again in the 
other part of the illustration, are drilled in each ease from the 
sides G and H which are adjacent to eaeh other, then it is evi- 
dent that at the points where the drill starts in eaeh ease the 
holes will eoineide. 

Distortion Caused by Improper Clamping,- -The matter of 

distortion must be considered when locating and clamping any 
piece of work. Several examples of this kind are shown in 
Fig. 22. Referring to the tipper illustration the lever A is lo- 
cated on a stud B and is clamped at the end F by means of the 
clamp screw E which throws the work over against the Btud D. 
Now it will be seen that when pressure is applied in the direc- 
tion indicated by the arrow it cannot cause distortion or change 
of shape in any way. On the other hand referring to the illus- 
tration below, if the work A were to be located on a stud K with 
a eliding V-bloek used as a locator and clamper, it is evident 



FUNDAMENTAL POINTS JLV DRILL JIQ DKStQUf 27 

that the pressure applied in the direction indicated by the arrow 
might very easily tend to distort the work as shown by the dotted 
lines in the lower portion of the illustration. These are points 
which are frequently neglected by a tool designer. 

Clearance Around Work. When designing, the matter of 
clearance around the work between the walls of the jig and the 
work must be given careful consideration. An example to illus 







Fig 22. Correct and Incorrect 
Location and Clamping 



Pig. 23. Ch'nranw* Around 

Work 



trate this point is shown in Pig. 23. In this cane the work A 
is located on a stud D placed in the body of the jig, which in 
made of cast iron. Now assuming that the work A IB a canting* 
there is likely to be some variation in its outside dimension*; if 
the jig body B is also a casting there i likely to be Home vttria 
tion in its dimensions as well Therefore the clearance iw indi- 
cated at C between the walls of the jig and the work fthouUI fw 
ample to allow for variations in the eastings, AH a genera! thing 
the distance C should never he on a small work much IIH than 
f in., that is to say on a piece of work having dimension* tiltmtt 
4x 6 in. On larger work whieh may run to 18 or 20 in. or oven 
more the clearance would be correspondingly greater The writer 
has known of several eases within the last year where the clear- 
ance around rough castings of large size ha* not been 



28 JIGS AND FIXTURES 

to take care of variations. In one case the matter became so 
serious that it involved practically the rebuilding of a large part 
of an expensive trunnion jig. It is evident therefore that the 
matter of clearance around the work in a jig must be given the 
most careful consideration. 

Provision for Cleaning. Many designers do not pay enough 
attention to the matter of cleaning a jig. It is evident that when 
work is being produced on an interchangeable basis by the use 
of jigs and fixtures there is a great accumulation of chips which 
must be removed from the jig as each new piece is placed in 
position. Now, up-to-date production methods call for rapid 
cleaning and there are several methods in vogue depending on 
what material is being drilled. Some factories use air pressure 
while others depend on a can of kerosene into which the work- 
man can dip his jig from time to time, but all of them provide 
the workman with a brush to keep the jig clean. Now it is 
obvious that if a brush is to be used to keep the locating surfaces 
in a jig clean it is important to be able to reach these surfaces 
with the brush. If this is not possible the jig must be made 
open so that the chips can be washed out as they accumulate. 
Locating pads or points should be built up above the surface of 
the jig. 

A simple type of jig is shown at B in the upper part of Pig. 
24. In this case the work A rests on a stud but the walls of the 
jig surround it so that it cannot be easily cleaned. The de- 
signer, however, by coring some openings at C provides means 
of washing out the chips without difficulty. In the lower part 
of the illustration the work E is a finished piece which is located 
on a center stud F supported on four points D. These points 
are built up above the surface of the jig so that they will not- 
be apt to accumulate chips and they can also be very easily 
cleaned. Do not neglect the matter of cleaning when designing 
a jig. 

Wear on Locating Surfaces. When jigs are used for a great 
number of pieces as frequently happens in high production 
methods, the matter of wear and the accuracy depending thereon 
must always be considered. Not only should locating points on 
surfaces be so made that they can be replaced by others when 
worn, but also the manner in which they are likely to wear 
should be given attention. An example of this kind is shown 



FUNDAMENTAL POINTS IN DRILL JIO DESIGN 



29 




Fig. 24. Provision for Cleaning 




Fig. 25. Provision for Wear on Locating Surfaces 



30 JW8 AND FIXTURES 

in Fig. 25, in which the work A in a finished piece which locates 
on the stud C and rents on the hardened locater IL Xo\v if this 
locater is made slightly smaller in diameter than the work so 
as to allow the latter to overhang a little all around as indicated 
at D, there is no clanger of wearing & pocket or recess in the 
locating member. But if it should be made as shown in the 
upper part of the illustration at K it in very evident, that after 
a number of pieces has been machined a pocket might be worn 




Fig. 26, Method of Making Ix>cftting 8tud 

in the locater as indicated at F, In a ease of this kind it would 
he found that the work might take the position Hhown at and 
the inaccuracy // would result. The tool designer must always 
consider these points when designing hw jig. 

Use of Locating Studs.- Fig. 26 nhowg two methods of mak- 
ing a locating stud for use in a previously finished hole. The 
work A in example R locates on the <*ylmdrieal portion C and 
rests on I). Thin stud is made of one pieee and K shows the 
first operation in manufacture which is clone on a lathe; and F 
illustrates how the relief cuts are made by milling. The finished 
plug presents a broken surface with relief cuti so that chips arc 
not likely to accumulate on the surfaces*. The example shown 
at G illustrates another method of making the same sort of a 
locating plug, using an inserted pin instead of a solid piece, 
which is often found desirable. 



FUNDAMENTAL POINTS IN DRILL JIG DESIGN 



31 



Chip Clearance. If it were possible to break up the chips 
when drilling so that they would be in the form of dust there 
would be very little trouble caused by chips, but as this is not 
the case suitable provision must be made to take care of them 
as they are produced. Referring to Fig. 27, an example is 
shown in the work A which indicates the provision which has 




Fig. 27. Chip Clearance 

been made in the locating V-bloek B to provide for chip clear- 
ance and cleaning. If this V-block extended down the entire 
length of the work A it would be very difficult to clean out the 
chips that might accumulate around the edges of it, but by eut- 
. ting it away cus shown the trouble is avoided. 

In the upper part of the illustration several examples of bush- 
ings are shown. Let us assume that the work C is to be drilled. 
Now if the bushing is placed too close to the work as shown at I) 
there is no chance for the chips to work their way out except by 
coming up through the flutes of the drill and packing into the 
bushing. It is good practice to make the clearance between the 
bushing and the work about one diameter of the drill as shown 



32 



JWM AM) JFL\TUltKti 



at E. Care must be taken however not to go to extremes and 
place the bushing so far away from the work that inaccuracy 
may result as shown at F. In this case the bushing is so far 
away from the work that the drill may run off and produce an 
angular hole as Indicated. 




Pig. 28. Peculiar Condition HhiHt rating Trouble Oatiwd by Chips 

A peculiar case in connection with chip clearance is shown in 
Fig. 28. In this ease the work which was drilled was of Ktccl 
and the chips working up through the flutes of the drill became 
entangled in the thumbscrew A in such a way as to loosen it, 
thus releasing the work and causing inaccuracy. It in evident 
that this could have been avoided by making the screw A a left- 




-^. :f l 



Fig. 20. Burr Clearance in a Cottar Fin Jig 

hand serew, but this would not be good practice as a left-hand 
screw is awkward to use, 

Burr Clearance. A matter which is frequently neglected by 
young designers is the making of provision for the burr which 
is thrown up by a drill as it passes through the work, Tn many 
eases this can be neglected as there is no burr to speak of on 
cast iron or malleable iron. It in particularly noticeable how- 
ever on jigs for small steel pins, cotter pin jigs and the like. An 
example of this kind is shown in Pig. 29 in which the work A 



FUNDAMENTAL POINTS IN DRILL <//(? 



33 



is to be drilled at the point B and a very simple jig has been 
made to hold it. The jig is a plain block of steel C having a 
strap D across it which contains a stop screw E that acts as ail 
end locater. Now it will be seen that when the hole B is drilled 
burrs will be thrown up around the hole at E and F and if no 
provision is made for these burrs it will be very difficult to get 
the work out of the jig after it has been drilled because the burnt 
will prevent it. The remedy for this is to cut a groove slightly 
larger than the drill diameter at the top and bottom of the jig 
as shown at G. When this is done the piece can be removed 
without difficulty. 




Fig. 30. Size of Holes To Be Drilled in 8am t Retting 

Size of Holes To Be Drilled in Same Setting. It is not 

advisable to attempt to drill holes of large and small diameter** 
in the same jig unless conditions are such that the jig in very 
expensive and it would be costly to make other jigs. In amen 
of this kind it might be possible to arrange two machine* Ride 
by side so that the jig can be moved from one to the other in 
drilling the holes. An example of this kind is shown in Fig, SO 
in which there is a series of reamed holes f in. in diameter all 
around the edge of the casting, aa shown at A. It will be een 
that there are also a f-in. reamed hole and a 1-in. reamed hole 
in the work. It would be better praetiee to drill all of the 
holes A in one jig and then to build another jig for the holeH U 
and C. This point should always be considered by the tool engi- 
neer when laying out his operations, but occasionally it is over- 
looked so that the jig when made is not practical. 



34 JIQ& A AW I 

Setting up and Removing Work, it happens occasionally 
that an inexperienced designer will design a jig and after he 
has worked it up very nearly to completion lie will discover 
(or some one else will discover) that he cannot get the work 
into or out of the jig. Naturally this is somewhat embarrassing, 
so that the point may be brought up at this time that it in well 
for the designer to bear continually in mind throughout the 




Fig. 31. Sit-On 0r Plate Jig 

design of his jig that it is neceHHary to put Urn work into the 
jig and to remove it therefrom. Suitable provision xhould be 
made so that the operator can reach in ami remove Ilia work 
without difficulty or eke an ejector ttbould bo provided to take 
eare of the matter. 

Types of Jigs. There are various typoi of in common 
use and these will bo dealt, with in detail in their proper frequence. 
It is not easy to make a broad diHtinction brtwwn nomo of the 
types of jigs, but speaking generally they may bo divided into 
the following: Plate and templet jigs; cart jig open arid dosed; 



FUNDAMENTAL POINTS IN DRILL JIG DESIGN 



35 



built-up jigs; trunnion and indexing jigs, and standard jigs. 
A brief discussion will be given of each of these types. 

Plate and Templet Jigs. One of the simplest types of jigs 
is a "set-on" or plate jig, illustrated in Fig. 31. Jigs of this 
kind are used on heavy castings where one end is to be drilled 
with a few holes and when the other end is finished so that it 
can be used as a surface on which to set up the work. In the 
illustration shown A is the work and B is the jig. This par- 
ticular jig is made of cast iron and has a steel V-block located 



Punch 

Templet 




U 20' 

Fig. 32. Templet Jig for a Large Ring 

as shown at C which is used to locate the jig in relation to a 
boss on the easting. A thumbscrew D is provided at the oppo- 
site side in order to make the jig fast to the work and draw it 
up tightly into the locating block. We might easily imagine 
a condition in which the hole E had been previously machined, 
thus allowing a plug to be dropped -.down into the hole to use 
as a locator instead of working from the outside bosses with a 
V-block as shown. 

A templet jig is generally imed with a prick punch to locate 
a series of holes on some pieces of machine work where only a 
few are required. An example of this kind of jig is shown in 
Pig. 32. In this ease the work A is a large ring which has a 
number of holes B drilled in it here and there on the surface 
of the ring. The templet jig is made of sheet metal and Is lo- 
cated in the work by means of several lugs such as those shown 
at C. A special punch like that indicated at D is used to mark 



36 



J7M* AA7> F1XWRK8 



the centers of the holes by placing it in the templet and striking 
it a blow with a hammer. After the work has been completely 
marked the templet is removed and the drilling is done on a 
drilling machine. 





\LJ 



Fig, 33, Open Jig Tyjw* 

Open Jigs. A very simple type of open jig in shown in Fig. 
33. Jigs of this kind are used for simple pierm which can be 
easily clamped and which have only a few holes to 1m drilled. 
In the ease shown the work A in ItK'ated by meaiw of a center 
stud C and is clamped down by the 0- washer D. After this has 




Fig. 34. Closed or Box Jig 

been done the jig body B is turned over and the work is drilled 
from the other side. 

Closed or Box Jigs. The type of jig shown in Fig. 34 is 
usually termed a box jig. The body of the jipr may be all steel 
or east iron but in the ease shown it is east iron, TUwhinga are 
inserted as at A and B and a hinge or leaf G w provided which 



FUNDAMENTAL POINTS IN DRILL JIG DEMON 37 

sometimes acts as a clamp to hold the work in place, hut mure 
frequently it simply provides means for removal of the work 
after it has been drilled. Jigs of this kind are commonly used 
for small parts and light drilling. 




'Work A 
Fig. 35. Built-Up Jig 

Built-up Jigs. Fig. 35 shows quite a different type 1 of jik r iw 
this is made up of separate pieces of stock which are Here wed 
and doweled together. The advantages of this type of jig art* 
that it can be readily made and that it 1ms many advantages 
from the viewpoint of replacements when worn. In the particular 
jig shown, the work A rests on the steel base K and in held in 




Fig. 36. Trunnion Jig 

place by means of the thumbscrew Cl The leaf D has a btwhinj? 
at E and it is located and held in plaee by the quart<r-turn 
thumbscrew F. A jig of this kind can be canily cleaned In uddi 
tion to its other advantages. 

Trunnion Jigs. In the drilling of automobile cylinders traiw- 
mission cases, housings and many other large <-a8tinH having 
holes drilled from several sides and posmbly at varioun aiitfii% 
a trunnion jig is usually found the mast desirable, beeiuw ftr 



38 J1G8 AND FIXTURES 

the work has once been placed in the jig all of the holes can be 
drilled before it is removed and as a consequence correct rela- 
tion between the holes will always be assured. A simple type 
of trunnion jig is shown in Fig. 3ti. In this case the work A is 
located in the cradle B which in its turn Is mounted on the trun- 
nions at E. As the various holes are drilled the index pin D is 




Fig. 37, Indexing Jig 

removed and the portion It is turned over into such positions 
that the desired bushings come uppermost. 

The correct location is awmrecl by means of the index pin 
which is generally inserted in a bushing in order to insure ae- 
curacy. Trunnion jigs are made in great variety and the exam- 
ple shown to illustrate the type is a very simple one, 

Indexing Jigs. An indexing jig is somewhat different from 
a trunnion jig in that the work is indexed into different posi- 
tions for drilling a series of holes usually through the same 
bushing. A ease of this kind is shown in Fig. 87 in which the 



FUNDAMENTAL POINTS IN DRILL JIG 

work A is located by means of some previously drilled holes in 
the surface B. In this ease there are four holes to be drilled 
at C and one bushing located in the bracket I) in the eorreet 
relation to the center of the work. A jig of this kind in .sup- 
posed td be strapped or clamped to the drilling maehine table 
and the work is indexed by pulling it around until the index 
pin E enters the various holes in the revolving member F* 

Occasionally index jigs are made when two or more holes art* 
close together and a series of the.se holes is required at equally 
spaced intervals around the parts. Many methods of Indexing 
are in use and the example shown is a very elementary type, 
Other instances will be given under their proper heading. 



CHAPTER III 
DETAILS OF DRILL JIG CONSTRUCTION 

PLAIN CLAMPS MULTIPLE CLAMPS HOOK BOLT AND WEDGE 
CLAMPS EQUALIZING CLAMPS SPRING PLUNUKRS AND JACKS 
V-BLOCK DESIGN LEAF JIG DESIGNLIMP CONSTRUCTION 

CLAMPS IN THE LEAF LEAF STOPS LEAF LOCKS STAND- 
ARD JIGS AND COMPONENTS JIG BODIES -STANDARDIZATION 
OF J I G POSTS AN D T HUM USO RE WS J I ( J V E ET~T X )C ATI N G 
PLUGS TYPES OF BUSHINGS HUSHING DRSIGN AND PROPOR- 
TIONMETHODS OF HOLDING SLIP HUSHINGS STANDARD 

KNOBS AND TnUMBaCREWS~.KjE(JT()RS. 

In locating a piece of work in a jig there are several points 
which must be looked after very carefully, in order that the 
piece may seat itself properly, may locate against portions of 
the easting which are not likely to vary and may be clamped 
securely without any danger of distortion. We have gone very 
thoroughly into the principles of locating the work in a previous 
chapter and we have taken up the various points which influence 
the design of a satisfactory jig. It must be borne in mind that 
there are numberless varieties of clamps which are used for 
various conditions found in jig work in many factories through- 
out the country and that it is the selection of the proper type 
of clamp which shows the skill of the designer. 

It is of primary importance that the clamp should not tend 
to force the work away from the locating points when pressure 
is applied to it. It very frequently happens that the bearing 
which the clamp obtains on the work m not quite what it should 
be and as a consequence the work is forced away from its bear- 
ing and locating points so that inaccuracy is the result. In 
handling delicate work it is important that the clamp should 
not be applied to any portion which m likely to spring out of 
shape or to be distorted, making the finished product inaccurate. 

40 



DETAILS OF DRILL JIG rOAVSTATT'/'/OA -H 

Great care must be exercised when several damps are applied 
on different portions of a piece of work. When a condition of 
this kind arises the clamps must be designed in such a way that 
they will equalize and distribute the pressure so that, the work 
will not be tilted out of its true position. 

Plain Clamps. In Fig. 38 are shown both correct ami in- 
correct methods of clamping. With the work A set up on lugs t 
C and D, the clamping action should be directly over these points 
as shown at E and F. Pressure should never he applied at point 
for the reason that it would be apt to distort the* work so that It 
might take the position B. This is a principle in designing; hut 
it does not apply to every case. We might easily imagine u 




Fig. 38. Correct and Incorrect McthodH of (MampttiK W*rk 



heavy piece of work which could be clamped at (I without eauw 
ing any trouble. On light work the principle mentioned muM 
be very carefully adhered to. 

Several types of plain clamps which are commonly uwd in 
jig design are shown in Fig. 39. These clamps may lit* varied 
to suit particular conditions; that Is they may be bent into dif- 
ferent shapes and they may be operated by means <f a 
in the middle or at the end, or they may be pivoted, They may 
be shaped to conform to a peculiar canting and thiy may lv** 
a very narrow bearing point where they come in contact with 
the work. In fact they may bo changed to Kiilt itn inflnitt* 
number of conditions. There is shown at A a clump commonly 
called a U-elamp which is made of a Ringte piece of ntccl \w\\\ 
into a U-shape. This type of clamp is frequently usid in fn*t. 
plate work, and on milling machines or boring milk, tininn 
T-bolt as indicated. The clamp shown at /I \\m a puidi* mid 
support at G which prevents it from turning and Kelt in* out 
of position with the work when it m not twed. The Htot it! /* 
allows the clamp to be pulled back away from the wr!c nfti*r 



42 



JIGS AND FIXTURES 



the piece has been machined. This type of clamp is in common 
use for many varieties of jig work. 

The clamp shown at E is similar to B but it is operated and 
guided in a different manner. The operator applies pressure 



,,-A 



-Worfr 




C 




-Worft 




Fig. 39. Types of Plain Clamps 

to the clamp by means of the thumb-knob F on the end of the 
screw G. When releasing the work the screw slides along in the 
groove at H. This groove also serves to keep the clamp in align- 
ment with the work when clamping. 

Hook-Bolt and Wedge Clamps. At A in Fig. 40 is shown 
a hook-bolt damp, frequently found very convenient for work 
not easily reached with the ordinary form of clamp, or when 
there is not room enough to permit the use of a plain clamp. In 
using a hook-bolt the heel B of the hook-bolt should be "backed- 



DETAILS OF DRILL JIG CONSTRUCTION 



43 



up' 7 so as to take the pressure resulting when the clamp is 
tightened. Unless provision is made for taking up pressure 
there is a possibility that after continued use the hook-bolt may 
become bent so as to be practically useless. There is a tendency 
on the part of tool engineers to avoid the use of hook-bolts for 
this reason. We consider however that a hook-bolt is too useful 
an adjunct to be cast away. There is no objection whatever to 




Fig. 40. Hook-Bolt and Wedge Clamps 

a hook-bolt when it is backed up as shown by the upper view 
at C, as the strains of clamping are taken by this backing up 
lug so as to prevent any bending of the hook-bolt. When used 
in this way it will be found that many problems in clamping 
are simplified. 

A wedge clamp is shown at D and although this form of clamp 
is not recommended for all work there are certain cases where 
it can be applied to advantage. The wedge is likely to distort 
the work or the jig, but in certain eases suitable provision can 
be made to counteract this distortion in the fixture and when 
this is properly done no difficulty should be experienced in its 
use. There are certain factories in the country which use jigs 
with wedges to a considerable extent. Sometimes a wedge is 
hung by a piece of closet chain and fastened to the jig so that 
it will not be lost. At other times the wedge is made extra long 
and pins are inserted at each end to prevent its being lost or 
falling out of the jig. 



44 



JIGS AND FIXTURES 



Suggestions for Clamping. Fig. 41 shows a group of repre- 
sentative clamps which can be applied to many varieties of work. 
These illustrations are diagrammatic and serve to show prinei- 




Fig. 41. Group of Representative Clamps 

pies rather than careful details. The clamp B should not be 
used except when the work is located over pins or in some other 
way which prevents it from moving when the clamp is applied. 
This particular clamp is operated by a lever C and slides for- 



DETAILS OF DRILL JIG CONSTRUCTION 46 

ward on the work as the stud D rides up on the angular hard- 
ened block E. A pin or nut on the end of the stud F takes the 
pressure of the clamp. 

A somewhat similar arrangement is shown in the clamp G. 
It is somewhat more elaborate but has the advantage of being 
made up in unit form so that it can, if necessary, be stand- 
ardized and made up in quantities when the occasion warrants. 
The section A-A shows another view of the block with the slid- 
ing clamp in position in the block H. In operation the clamp 
is slid forward until it comes to rest over the pin /, after which 
pressure is applied by means of the thumbscrew. It is an excel- 
lent clamp which is easily operated and a form similar to it is 
used in great quantities by one very large manufacturing con- 
cern in the Middle West. 

In order to avoid throwing a piece of work out of alignment 
when clamping, the scheme shown at K can be used. The work 
locates in a V-block and the pin K is adjusted by means of the 
collar screw L. This type of clamp applies the pressure directly 
to the work without any turning action. 

The clamp shown at M is not used frequently, but there are 
occasions when a piece of work like that shown at N can be held 
to advantage by this type of clamp. The objection to it is that 
it must be loosened considerably in order to remove the work 
unless it is possible to slide the piece out of the jig end-wise. 

The C-washer clamp shown at is too common to need much 
description. In its simplest form it is a washer, cut out on one 
side so that when the nut P is loosened it can be slipped out 
readily. After this the work can be removed without difficulty 
and without removing the nut. 

The clamp shown at Q is very useful on small light work. It 
is rapid in its action and serves to clamp the work at R and S 
at the same time. When the thumbscrew T is operated equal 
pressure is brought to bear in the directions indicated by the 
arrows. Particular attention must be paid to the position of 
the points of contact in relation to the pivot pin or more pres- 
sure will probably be applied in one direction than in the other. 

The clamp shown at U is commonly called a " button " clamp. 
It is useful for small work and is so made that the portion 17 
does not revolve but is hung loosely on the end of the screw so 
that when pressure is applied it adjusts itself to the work. The 



46 JIGS AND FIXTURES 

button may be made large or small according to conditions. It 
is a useful clamp and is found in many varieties of light jig 
construction. 

A somewhat peculiar type of clamp is shown at V whose use 
is limited to finished work. Furthermore the work must be 
positively located in order that it may not be forced out of posi- 
tion by the action of the clamp. The operation in clamping is 
a swinging one as indicated by the arrow and the clamp is so 
made at the point shown in section AA, that a wedging action 
takes place between the clamp and the top of the pin W. 




-Work 




Fig. 42. Multiple Clamps 

Another type of clamp, with a " button " end as shown at JT, is 
similar to that shown at U except that the screw which operates 
it has a ball-end as indicated, in addition to which the clamp 
itself is made with three points T separated 120 deg. so that the 
three points will bear with uniform pressure on a regular sur- 
face. A clamp of this kind is frequently used for holding the 
round end of a piston in automobile work, but other applica- 
tions may frequently be found in the general run of jig work. 
Multiple Clamps. It is frequently necessary in clamping a 
piece of work to apply pressure simultaneously at two points 
which are widely separated. Sometimes the clamp is applied to 
two pieces at the same time while at others it may be at two 
points on the same piece of work. The example A shown in 
Fig. 42 is of a plain clamp spread out at the end so that the 
points B and C bear on the work. If the work has been ma- 
chined it is unnecessary to provide anything more than a plain 
nut for clamping, but when the work is "in the rough " it is 



DETAILS OF DRILL JIG CONSTRUCTION 



47 



advisable to provide for inequalities by making the portion D 
in the form of a ball so as to permit the clamp to float enough 




Fig. 43. Correct and Incorrect Method of Using Double End Clamps 

to take care of the inequalities in the casting. The clamp E is 
commonly used to hold two pieces of work at the same time as 
indicated at F. It can be swung around side- wise after the work 
is machined to allow the pieces to be removed. 

Fig. 43 shows correct and incorrect methods of using the 
double end clamp. When clamps of this kind are to be used 
the two points which bear against the work should be as nearly 
the same distance from the center as possible. In the exag- 
gerated example shown at A the clamp is so proportioned that 
it would be apt to dislocate and force the work out of its cor- 
rect location. The example E shows a properly designed clamp 
for the same piece of work. 

Equalizing Clamps. When it is necessary to hold several 
pieces at the same time or to apply pressure equally to three 
or four pieces at the same time, an equalizing clamp must be 
used. It is difficult to illustrate all of the various types of 
equalizing clamps which are used in jig work, but the principles 
underlying the design can be simply shown as in Fig. 44. In 
the first part of the illustration, the work consists of two pieces 
set up and clamped uniformly with the same screw at the same 
time. When pressure is applied by means of the screw E, there 
is a reaction through the lever C on the end of the pin D so as 
to force the clamp E down on the work. At the same time the 
reaction of the screw forces the clamp F down on to the work 
on that side of the jig with an equal amount of pressure. 



48 



JIGS AND FIXTURES 



In clamping four pieces of work a similar principle can be 
applied as shown at G. An equalizing lever is provided at H, 
pivoted at J where the leverage is applied. The pressure will 
be equal on the rods K and L and also on the clanip M and N 
so that the four pieces of work will be held with uniform pres- 




Fig. 44. Equalizing Clamps 

sure. The piece Q is clamped at both ends at the same time by 
means of the clamps R and S when pressure is applied at T. 
By the addition of various levers which must be properly 
pivoted it is possible to hold a number of pieces at the same 
time with equal pressure. It must always be remembered how- 
ever that the power which is applied must be in direct propor- 
tion to the number of pieces which are to be clamped. An odd 
number of pieces is more difficult to clamp than an even num- 
ber. In order to clamp three pieces at G instead of four, it is 
necessary only to provide a fulcrum at X in place of the work. 

It is sometimes necessary to locate a piece of work from a 
certain position with respect to the clamp. An example of this 
kind is shown in Fig. 45 in which the work A locates against 
an adjustable stop B directly in the clamp. The screw C holds 
the work down as shown. 

Spring Plungers and Jacks. In supporting a piece of work 
in a drill jig or a milling fixture some of the points of support 



DETAILS OF DRILL JIG CONSTRUCTION 



49 



must be made adjustable when the work is a rough, casting. 
There are also a number of cases where jacks and spring 
plungers are used not only as a support but also to throw a 
piece of work over into a certain position. As a general thing 
spring jacks are made in such a way that they can be positively 
locked after they have reached a given position, so that there 
will be no chance of their moving under the pressure of a drill 
or milling cutter. The locking device used to hold the jack in 
position is of primary importance. Whatever method of lock- 




Fig. 45. Clamp for Holding and Locating Work 

ing is employed it must be such that there- is no tendency to 
produce in the jack a hole or depression that might make it 
likely to assume after a time one position regardless of the posi- 
tion of the work against which it acts. Many ingenuous ar- 
rangements are used. 

There is shown at A in Fig. 46 a common type of spring jack. 
Common as this type is, it is open to some objections. The 
plunger or jack B is usually pack-hardened so that it has a soft 
core. Therefore the action of the round end screw C has a tend- 
ency, after considerable use, to make a depression or pocket as 
indicated by the dotted lines at D. It is important that the 
angular surface against which the screw acts should not be too 
great. As a general thing about 5 deg. is sufficient. Speaking 



50 



JIQ8 AND FIXTURES 



generally, we do not favor this type of jack on account of the 
objection mentioned. 

The jack shown at E is very similar in general construction 
except that it has a pocket for the spring, so that it can be used 
In more confined situations. There is an added improvement also 
in that the locking pressure is applied through the soft brass 
member F acted upon by means of the screw G. There is no 
turning movement to the plug F as it comes against the jack, 
therefore it is not likely to wear a perceptible depression. 




Fig. 46. Spring Plungers and Jacks 

The jack shown at H is practically the same in construction 
but it is provided with a shield J in order to guard against chips 
and dirt working down into the bearing and causing it to become 
loose. A protecting cover can be applied to almost any type 
of jack, but it is necessary only where the jacks are to be used 
for a very great number of pieces. 

Another type of jack, shown at K, is milled on one side to 
form a support as shown at L and is also provided with angular 
surface M against which the plug N acts. The plug is made with 
a tongue so that it enters the slot L and prevents the jack from 
turning. The plug 7 is also cut so that its angular surface bears 
against the angularity of the jack. There are cases when a jack 
of this kind may be found very useful. 



DETAILS OF DRILL JIG- CONSTRUCTION 



51 



In Fig. 47 an entirely different type of jack is shown at A. 
Such jacks are used extensively on light work such as type- 
writer and cash register parts. In the hands of a careful work- 
man they will give good results but they can be made to distort 
the work considerably unless properly used. The jack is oper- 
ated by pushing the plunger B forward by means of the knob C. 
The workman must know by the "feeling" that he has applied 
all the pressure necessary after which he turns the knob C 
slightly which causes the taper pin D to expand the end of the 



Work 




Fig. 47. Adjustable Jacks 

plunger B so that it locates firmly. The end of the plunger B 
is flatted off at E and a plate F is provided to prevent it from 
turning. 

An excellent type of ja^ck is shown at G. The binding or 
locating action is produced by drawing up on the plunger H 
by means of the knob K. Thehole L shown in the upper view 
is usually made about %2 in. larger than the jack. A jack of this 
kind will exert a great deal more pressure, but it is somewhat 
more expensive to make than some of the others mentioned. It 
is apparent that when considerable pressure is required the 
knob K can be replaced by a nut that can be tightened by a 
wrench. 

Another type of jack is shown at M. It is similar in general 



52 



JIGS AND FIXTURES 



construction to the one just described, but the location action is 
somewhat different. The plunger N is concave at to the same 
radius as the jack so that when pressure is applied by means of 
a nut at P the friction against che jack is sufficient to keep it 
from slipping. There are other designs which can be used for 
spring plungers and jacks but the ones illustrated are more com- 
monly used in jig work. 
Fig. 48 shows a method of clamping two jacks simultaneously. 



" t tf*T~~^~' 



Work 




Fig. 48. Locking Two Jacks at One Time 

Assuming that the jacks are bearing on the work at A and B in 
such a way that it is necessary to lock them at the same time in 
one operation, the method shown can be used to advantage in 
many cases and other developments can be made to suit par- 
ticular conditions. In the case shown the locking devices con- 
sist of two sleeves at C and D. These sleeves are tapered slightly 
on one side at the points E and F to engage with the tapered 
portions of the jacks A and B. Rod G extends through both of 
the sleeves and is threaded at the end H so that when the knob K 
is turned the two sleeves approach each other and bring equal 
pressures to bear on the angular portions of the jacks. A nut 
can be used in place of the knob. 

V-Block Design. Many types of V-blocks for locating and 
clamping are found, several of which are shown in Fig. 49. 



DETAILS OF DRILL JIG CONSTRUCTION 



53 



The type shown at A is found in every toolroom and is used for 
various jobs on the milling or drilling machine. Clamping ac- 
tion in setting up a piece of work, such as shown at B, should 
be in the direction indicated by the arrow. It is not, however, 
necessary to have the pressure of clamping through the center 
of the V-bloek as it may be a trifle to one side or the other 
without causing any inaccuracy in the work. Another type of 
V-block, shown at C, is very useful in jig work. The angle is 
slightly less than a right angle and as a consequence pressure 
applied in any direction indicated by the arrows will force the 




Fig. 49. Types of V-blocks 

work D directly into the block. This type is commonly used for 
small work. 

An adjustable V-block is shown at E. The blocks F and G 
are pivoted on the studs indicated and may be adjusted by 
means of the headless screws H and K. After the adjustment 
the cheek nuts must be tightened to make the location per- 
manent. 

Still another type of adjustable Y-block, shown at L, will need 
two round pins cut at an angle at the point M. This type of V 
can be adjusted by means of the check nuts. The objection to 
this type, and also to that shown at E, is that there is always 
a possibility of the nuts loosening so as to cause variation in the 
location. 

The principle of a sliding V-block is shown at N. The block 
has a slot at which permits adjustment. Pressure can be ap- 
plied through the screw P to adjust the block. An arrangement 
of this kind is not good on account of the opening at the slot 



54 JIGS AND FIXTURES 

which allows chips to accumulate, causing considerable trouble. 
Furthermore, practically all of the pressure applied by the an- 
gular jaws is taken on the head of the screw Q. If it becomes 
necessary at any time to use a block of this type it should be 
tongued as shown at R and a suitable sheet metal cover should 
be placed over the slot to protect it from chips and dirt. When 
a V-block is made like that shown at R there is always a possi- 
bility of chips accumulating under the sliding portion so that 
after a while it can be operated only with difficulty. For locat- 




Section A-A 




Fig. 50. Sliding V-block Design 

ing several V-blocks in line with each other when they are not 
adjustable they may be tongued as shown. Occasionally a piece 
of work is located in a V-block and it is at the same time de- 
sirable to hold the work down by means of the V-block. An 
example is shown at S, where the work is located by means of 
the sliding V-block T. The block may be undercut to an angle 
of about 10 or 15 deg., so that it will not only locate the work 
but will hold it down as well. 

At B in Fig. 50 is shown an approved method of locating 
sliding V-blocks. The block is fitted on the sides to the slot 
at G and is held down by means of gibs at D. The block is 
operated by means of a screw at E. This is the best method of 
making a sliding V-block, but it is sometimes desirable to make 
the gib D in the form of a flat plate extending completely across 



DETAILS OF DRILL JIG CONSTRUCTION 



55 



the V-bloek. Naturally these points may be varied to suit and 
do not affect the fundamental features of design. Another type 
of block is shown at F. There may be cases when a block of 
this kind has advantages but in general it is expensive to make 
and has no practical advantage over the design shown at B. 
The plate G is expensive and difficult to fit. 

The method of fitting a slide as shown at H is not to be com- 
mended as it is much more difficult and expensive than the de- 
sign shown at B. We have seen V-bloeks made in this way but 
have not approved of the design. It is usually considered good 




Fig. 51. Swinging V-block Design 

practice to keep a design as simple as possible so as to avoid 
unnecessary machining and fitting. 

In Fig. 51 is shown at A a type of swinging V-block which 
is quite useful on small work. Blocks of this kind are useful 
where the work is located by a central stud on the jig. The 
work shown would be difficult to locate in a regular sliding 
V-block. Blocks of this kind can be made up in quantities for 
small work and to a certain extent standardized so that they can 
be used by simply drilling and tapping a hole for the screw 
shown at B and applying the block G which carries the backing- 
up screw. 



56 



JIGS AND FIXTURES 



Another type of swinging V-block is shown at D. The V-bloek 
is made in two parts, E and F, controlled and adjusted by means 
of the thumbscrew G. The thumbscrew has a shoulder at B 
which engages with two supports on the swinging members. 
This type is used to a considerable extent by a large manufac- 
turer in this country. 

Leaf Jigs. In the design of leaf jigs there are many points 
to be considered. In the example shown in Fig. 52 the jig A 



.Work 




Fig. 52. Leaf Jig of Simple Design 

was designed for holding the work B, while being drilled 
through the portions indicated at C. The work is fastened into 
the jig in one position, after which the jig is turned over until 
it assumes the position shown, in which position the drilling is 
done. There is no particular objection to this type of jig and 
it is in common use in many factories. However, a leaf jig 
design is shown at D for comparison. The leaf E is swung back 
against the leaf stop indicated while the work B is being loaded 
on to the stud. The leaf is then swung down into position 
carrying the work with it until it takes the location shown by 
the dotted lines. A quarter-turn screw F is used to locate the 
leaf in position. The advantages of this type over the one at A 
are that it is much more convenient to operate and if a multiple 
drill-head is used, it can be clamped firmly to the correct loca- 
tion on the table. 

Leaf Construction. In the construction of jig leaves the 
hinge is an important factor. Several methods are in vogue. 
There is a straight pin such as that shown at A in the upper 



DETAILS OF DRILL JIG CONSTRUCTION 



57 



part of Fig. 53. In this construction it is considered good prac- 
tice to make the pin so that it will be a drive fit in the leaf B 
and a running fit on the two end bearings. Probably the best 
construction obtained is by making the pin a standard taper 
like that shown at (7. When this construction is used the ad- 
justment for wear can be made very easily and any amount of 
freedom can be made in the leaf by simply giving an additional 
turn to the taper reamer. 

It is sometimes desirable to make a leaf like that shown at D 




Harden arid ground 

Wear Ploifes 
Fig. 53. Jig Leaf Construction 

in order to obtain a slightly equalized action on the leaf when 
it is used for clamping or for some other purpose. In the con- 
struction of jigs which are to be used for thousands of pieces, 
it is advisable to make proper provision for wear in the leaf in 
order to preserve the accuracy. A construction such as that 
shown at E is excellent and is in use by a number of manufac- 
turers. The wear plates shown at F are hardened and set into 
both the leaf and the jig body. It will be seen that they can 
be readily replaced when worn. 

Clamps in the Leaf. In connection with leaf construction 
we must also consider the instances when clamping action is ap- 
plied through the leaf. There is an important point which 
should always be thought of when clamps are to be inserted in 



58 



JIGS AND FIXTURES 



a jig leaf, and that is that the leaf must be made heavy enough 
so that it will not buckle when the pressure is applied. I n 
Fig. 54 several types of clamps which can be applied to the leaf 
of a jig are shown. The leaf A should be made heavy enough 
to takethe pressure of the screw B so that it will not tend to 
buckle and take the position indicated by the dotted lines, as 
this would make the bushing C out of alignment with the work. 
Attention should also be paid to the position of the screw B in 




Fig. 54. Clamps in Jig Leaves 

relation to the bushing C. The amount of space required at D 
will be dependent upon the general condition and size of 
the jig. 

Another method of clamping through the leaf of a jig is shown 
at E. Pressure is applied through the clamp F by means of the 
screw G so that the ball-portion H comes in contact with the 
work as indicated. One end of the clamp is rounded at K where 
it bears against the leaf. It is prevented from falling out of 
the leaf by the pin at L and the guard pin M. This con- 
struction was used in order to allow free UvSe of the bushing N, 
and at the same time clamp very close to it. It is evident that 
a hole in the clamp is necessary as indicated. 

A very useful type of leaf clamp for small work is indicated 
at 0. It is a type that is used preferably on finished work be- 
cause its action is limited. The movement of the pin is con- 



DETAILS OF DRILL JIG CONSTRUCTION 



59 



trolled by the screw P acting- on the angular cut in the pin 
through the plug Q, also cut to an angle on the end which en- 
gages with the cut in the pin. 

There are some eases where the clamp is used in a leaf when 
the leaf does not carry any bushings. Referring to Fig. 55, the 
sketch at A shows a leaf of this sort having a rocking clamp B 
pivoted on the leaf. There are no bushings in the leaf and it is 
used principally for clamping. The clamp pressure is applied 
through the eye-bolt and hand knob C and D. The end of the 
leaf must be slotted so that the bolt can be swung out of 





Work 







Fig. 55. Leaf Construction Fig. 56. Details of Jig Leaves 

place in order to lift the leaf. This form of construction is very 
common and will be found useful in many cases. 

When a leaf contains several t bushings as at E the form of 
construction shown is commonly used. The end of the leaf is so 
slotted that the quarter-turn screw F passes through it when 
the leaf is lifted. When it is locked in position the head of the 
thumbscrew binds it firmly in place. 

Tn Fig. 56 several kinds of leaves are shown. Two methods 
of making a hinge are indicated at A and B. In the case A the 
hinge swings at A and therefore has a short bearing, while 
in the other case the hinge hangs from the points C and D, 
which are much further apart so that greater accuracy is 
assured. 

A leaf like that shown at E is sometimes useful in jig con- 
struction when it is necessary to place a bushing close to the 



60 



JIQS AND FIXTURES 



work and at the same time get it out of the way while the work 
is being removed. It is a good idea to provide some means of 
clamping the leaf while drilling. A quarter-turn screw or some 
other approved method can be used. 

It is often necessary to lighten a large jig in order to expedite 
the handling of it Sometimes it is advisable to make a leaf out 
of aluminum as shown at F. It is a good idea to provide bush- 
ings at the hinge point G and hardened plates at the end H in 
order to avoid having the wear on the soft metal. 




Fig. 57. Leaf Locking 

Leaf Locking,. Jig leaves may be locked in a variety of ways, 
several of which are shown in Fig. 57. The leaf A is fastened 
by means of a quarter-turn screw B, the end of the leaf being 
slotted. Wear plates at the bearing points should be pro- 
vided if the jig is to be used for a great number of pieces. 
Sketch C shows provision to simplify the toolmaker's work in 
putting in the pin D by leaving the finished support / from 



DETAILS OF DRILL JIG CONSTRUCTION 



61 



which to locate the jig leaf while drilling the pin hole. This 
support can be machined when planing up the jig. An eye- 
bolt lock for a jig leaf is shown at E. "When such a lock is 
used the end of the leaf should be rounded off at F in order to 
facilitate the opening. The cam lever fastening shown at G 
can be used to advantage in many cases for fastening the leaf 
in position. Care must be taken to make sure that the radius 
E is not too small to prevent the proper locking on the pin K. 
As a general thing tool designing departments have a set of 
standard cam levers which give the important dimensions. Two 
other types of leaf lock levers are shown at L and M. Speaking 
generally the writers do not favor these forms of construction. 
It must be admitted, however, that they are in use in a number 




Fig. 58. Leaf Supports 

of factories with more or less success. The principal objection 
to their use is the fact that there is very little adjustment for 
wear and they are therefore likely to become inaccurate after 
they have been used a short time.* 

Leaf Stops. When a jig is being used it is important to pro- 
vide a rest for the leaf when it is thrown back in loading or 
unloading the jig. If some provision is not made there is a 
chance that the operator may throw the leaf over and break or 
strain it. Several types of leaf stops are shown in Fig. 58. The 
one indicated at A is a simple type which is fastened to the wall 
of the jig B so that the leaf, when swung up, comes against it 
at C. Another type, shown at D, is somewhat similar, but very 



J2 JIGS AND FIXTURES 

much better, because the point of leverage E is farther away 
from the hinge. 

Another type of leaf support is shown at F. The leaf is held 
up by means of an arrangement similar to a trunk lid support. 
This construction is "trappy " and possesses no particular advan- 
tages. There may be 'cases, however, in a very large jig where 
a similar application may be found useful. 



Leaf 



fcfj U 




p/crfes 


T 


A 


^ 


B 




o| Fee j. m .u o I 




Fig. 59. Standard Angle and Channel Iron Jig Bodies 

Standard Jigs and Components. There are many parts of 
jigs and fixtures in common use that can be standardized either 
to obtain uniform design or to enable a factory to make them 
up in quantities. There are some parts that are seldom used 
but the general design and proportions of these are so well 
established that drawings can be made of various sizes to cover 
practically all conditions. There are also many accessories such 
as thumbscrews, hand knobs, ejectors, jig bodies and jig leaves, 
which can be made in certain sizes and carried in stock so that 
the toolmaker can use them whenever they are shown on a tool 
drawing without having to make up each one as he requires it. 
In addition to the parts mentioned it is possible to standardize 



DETAILS OF DRILL JIG CONSTRUCTION 



63 



bushings so that they also can be made up in quantities. How- 
ever, this is not frequently done as there are so many sizes to 
take into consideration. 

Standard Jig Bodies. There are two varieties of standard 
jig bodies, the angle-iron form and the channel-iron form; of 



fir 



.f 



r-ii 




Oi 



11 




Fig. 60. Standard Type Jig Body 

these varieties the angle-iron form is the more common and is. 
frequently found both in steel and cast iron. The channel-iron 
jig body is less common except in certain classes of work where 
a great many parts of small and comparatively uniform sizes 
are to be jigged, Eeferring to Fig. 59 a standard steel angle- 
iron jig body is shown at A. The usefulness of such a jig body 
is very apparent and it has the advantage of being made up 
cheaply for a variety of usages. For small parts requiring leaf 
jigs, many combinations can be made with angle irons of this 



JIGS AND FIXTURES 



1/-X 

variety It is easily possible to build up a post like that shown 
at B and fit a leaf with thumbscrew and wear plates, as indi- 
cated to suit a great number of conditions. The jig feet can 
be screwed into place as shown and can be put in wherever they 
are needed Another advantage of this type of jig is that the 
an-le iron can be made in a long strip and planed up accurately 
and then cut up into sections which may or may not be stand- 
ardized for width according to the requirements. A great many 
factories carry angle iron in stock ready for use when needed. 
On certain classes of work a channel-iron body may be found 
a great advantage. For example, the channel-iron body C may 
be made up in a number of sizes and may be standardized for 




Fig. 61. Angle Iron Jigs Made of Cast Iron 

width, depth and length. Assuming that three or four sizes are 
carried in stock it is evident that a leaf may be fitted in; a 
V-block or locating pin inserted; clamps put on; or other appli- 
ances fitted to suit a great number of cases. In the standardiza- 
tion of jig bodies the manufacturer must be governed by the 
relative size of the components in his product. 

It may be well to state in passing that it is advisable to pro- 
vide good fillets on all angle-iron and channel-iron castings or 
forgings as shown at D, E and F, to make the sections as strong 
and serviceable as possible. If it is necessary at any time to 
fit blocks or other parts around the fillets, it is advisable to 
chamfer the block rather than to cut out the fillet,- so as not to 
weaken the fixture. 

A standard type of jig body without dimensions is illustrated 
in Fig. 60. This is a very good design which can be used on many 
classes of small work. Dimensions can be given on the various 



DETAILS OF DRILL JIG CONSTRUCTION 



65 



parts so that the tool designer can obtain a better understanding 
of the requirements In designing a standard jig body. 

The utility of an angle-iron jig is indicated in Fig. 61. The 
angle irons are of east iron. There is shown at A an angle plate 
made into a simple jig by applying the bushing plate B and a 
locating stud on which the work C is held. This is a very sim- 
ple form of jig in which the work is held in place by hand while 
drilling. 

Another application of the angle-iron jig is shown at D. A 
bushing of similar form is to be drilled in such quantities that 



-Mark 




Fig. 62. Well Designed Jig with Hocking Clamp 

it is advisable to provide a means of clamping the work. The 
clamp E is pivoted at F so that it will swing out of the way 
when not in use, thus allowing the work to be removed from the 
stud without difficulty. Other applications of angle-iron jigs 
will be mentioned in a subsequent article. 

We have made mention of the importance of proportioning 
a rocking clamp so that the clamping points are about the same 
distance from the center. An example which illustrates the ap- 
plication of a clamp of this sort is shown in Fig. 62. The body 
of this jig is made of cast iron and the clamp is of such a nature 
that it swings free of the work on a swiveling arm. In this 
application the work is held in a V-block and the clamp holds 
it firmly against the shoulder and carries it down into the block 
at the same time. 



66 JIGS AND FIXTURES 

Advantages of Standard Jigs. Another advantage of a 
standard size and form of jig is in the location of the jig when 
in use on the drilling machine. Let us assume that a number 
of different jigs are used from time to time and we know that 
it takes a little time for the operator to arrange the machine so 
that each jig will be conveniently handled. By the use of 
standard jigs it is possible to clamp or screw down guides, as 
indicated at A and B in Fig. 63, so that jigs of a standard size 




Fig. 63. Standard Jig Used Between Guides 

can be readily slipped between the guides when changing from 
one part to another. In the standardization of jigs other appli- 
cations will be found which will prove profitable in the actual 
processes of manufacture. 

The same idea of using guides can be applied on large cast- 
iron jigs providing the sides of the jig are finished so they will 
pass between the guides. In progressive drilling an arrange- 
ment of this sort will be found to be a great advantage. 
^ In taking up the various components which are used in built-up 
jigs we must not forget the jig post and the frequently used 
quarter-turn screw. Several examples are shown in Fig. 64. 
Example A is not generally considered good practice because 
there is no locating provision made to take care of abuse or wear 
m the leaf. The quarter-turn screw B does not assist in loatin" 



DETAILS OP DRILL JIG CONSTRUCTION 



67 



the leaf, and the accuracy is entirely dependent upon the hinge 
constraetion. 

Jig Posts and Thumbscrews. It is much better to make a 
jig post as shown at C and to allow the leaf to locate on the sides 
D and E. Provision for wear may be made as indicated at F, 
in which the same type of jig post is used as that shown at C, 
but provided with wear plates of hardened steel at and H so 
that the accuracy of the leaf fitting is assured. The post can be 





/v 


N/< 


.eerf 




Jt 








1 


A 






00 


<2>o 






Lear 



Fig. 64. Jig Posts and Quarter Turn Screws 

turned and threaded at its lower end as indicated at K and a 
suitable dowel provided at L to make location positive. 

A type of jig post sometimes used, shown at Q, can readily 
be made so that it will screw onto the body and it can be fur- 
nished with wear plates at R and 8 if desired. In addition the 
leaf can be provided on the sides at T and U with plates that 
can be hardened and ground to an accurate fit. 

Quarter-turn screws are frequently used in leaf jigs; several 
varieties are shown in the figure. When screws of this kind are 
used it is necessary to turn them so that they are in alignment 
with the slot in the leaf when loading or unloading the jig. A 
refinement which makes it possible for the operator to turn the 



68 



JWti AND FJXTURE8 



screw the right amount every time is shown at M. The under- 
side of the thumbscrew is cut away and the pin N acts as a stop 
for the screw. Another method which gives the same result is 




Fig. 65. Examples of Jig Feet 

shown at where the stop pin P is fitted to the leaf instead of 
in the jig post. 

Jig Feet There are several things to be considered in the 
design of jig feet. They should be made long enough so that 
there will be room to take care of an accumulation of chips 
under the jig body, yet not long enough to be fragile. They 



DETAILS OF DRILL JIG CONSTRUCTION 



69 



may be screwed to the jig body, a hole being provided, as indi- 
cated at A y Fig. 65, in which a pin can be placed to assist in the 
operation. Occasionally it is desirable to force in the jig feet, 
instead of screwing them in place, and when this is done it is 





Fig. 66. Locating Plugs 

advisable to use a construction similar to that shown at B in 
which flats are provided to assist in assembling. 

A very excellent method of fastening jig feet in place is shown 
at (7, a system frequently used when a jig has to be turned or 
if feet are provided on each side. The nut D can be used to 
draw the foot tightly into position and its location and accuracy 
can be assured by the squareness of the face E and the accuracy 



70 JIGS AND FIXTURES 

of the fit on the shank of the foot at F. It is advisable to pro- 
vide means for locking the nut, consequently the thread on the 
shank should be of fine pitch. 

When jig feet are of cast iron it is well to make the thick- 
ness T of the foot equal to the wall of the jig and the length L 
about two and one-half times the thickness. 

It is well to make jig feet for cast-iron jigs in the form of an 
angle as indicated at 0. Attention should be paid to the pro- 
portions of this angle, if the jig is a small one, in order that it 
may be large enough to overlap any hole in the drilling machine 
table. A construction such as that shown at H is recommended 
when work is to be drilled from two sides of a cast-iron jig ; ft, 
will be noted that a pad is placed at K at right angles to the jig 
foot, yet on this side of the jig the foot is not built up high be- 
cause it would make an awkward construction and one that 
might very easily be broken. When jig feet come opposite each 
other it is well to make the design similar to that shown at L, 
a construction that is strong and that gives ample clearance 
for chips. 

Locating Plugs. Several designs of locating plugs are shown 
in Fig. 66. In sketch A the plug B is made of one piece of 
steel, a construction requiring considerable labor. It is much 
better to use a construction similar to that shown at C in which 
the plug D is used in connection wtih a hardened and ground 
washer E. The locating plug is drawn up tightly by means of 
the nut at F. 

Care must be taken when a piece of work rests on a flat sur- 
face to furnish little space for dirt and chips to accumulate. 
In sketch (? a plug is shown at H and the work rests on K, cut 
out in four places to give less bearing surface and to provide 
clearance for the drill after it has run through the work. The 
slots could be made somewhat larger and thus leave less chance 
for dirt and chips to accumulate. In making up locating plugs 
for use in a round hole it is advisable to relieve them so that 
they will not completely fill the hole. They can be relieved as 
shown at L, M or N, depending upon circumstances. The 
methods shown at L and N are much to be preferred to that 
shown at M. The latter tends to weaken the plug so that it is 
easily broken. All plugs that are made a drive fit in a jig or 
fixture must have sufficient stock that they will not loosen easily 



DETAILS OF DRILL JIG CONSTRUCTION 



71 



when In use. The length of drive should be from two and one- 
half to three times the diameter as shown at P. 

In chamfering the top of a plug which is to receive a piece of 
work the angle of the chamfer should be as long as can con- 
veniently be made. It can be from 45 to 15 deg. on the side, 
but it is much better to approach the 15-deg. angle rather 
than the 45-deg. angle, as the work will assemble much more 
easily and will not tend to i4 coek." A diagram showing a 
method used in locating a piece of work on two plugs is shown 
at Q. This is a connecting rod in which the holes at the ends 
ai'e held within limits of ztO.OOl in. The two plugs shown are 
relieved but not correctly. The plug E can remain as it is, but 




Fig. 67. Types of Bushings 

that at S should be turned around 90 deg. in order to allow for 
possible variations in the work. 

Types of Bushings. Fig. 67 shows a number of types of 
bushings used in jig construction. Bushing A, a common type 
having no head, is used almost exclusively by some factories, 
but the majority prefer bushings with heads and we believe this 
type to be better in the majority of eases on account of the 
abuse to which bushings are subject. The bushing shown at B 
is undercut at the shoulder. This is not good practice; it is 
much better to round the bushing slightly as shown at C and 
chamfer the casting a trifle as in this way a bushing is obtained 
that is stronger and is less likely to crack or break either in use 
or when hardening. 

In the design of slip bushings the knurled form shown at D 
is frequently used. It is well to state at this point that all slip 



72 JIGS AND FIXTURES 

bushings should be provided with hardened liners as indicated 
at E. A screw bushing, as shown at F, is very bad and should 
never be used. When it is necessary to make bushings so that 
they will screw into a jig a hardened liner should be provided 
as indicated at G. The head of the liner bushing is on the in- 
side of the jig so that when pressure is exerted on the bushing 
there will be no tendency to force out the liner. 

Screw bushings are used in some cases where a clamping action 
is needed on the work at the point where the bushing is used. 
If it is found that no other means of clamping can be used, a 
much better form of construction is that shown at H in Fig. 67. 
The accuracy of location in the slip-bushing is assured by the 
cylindrical bearing at K and the threaded portion is made a 
loose fit. An additional refinement is found in bushing L which 
has a cylindrical bearing at M and N and a thread in the mid- 
dle. This type insures as high a degree of accuracy as is pos- 
sible for screw bushings. 

Provision should always be made to insert a pin in bushings 
of this kind in order to facilitate removal. The matter of spring 
in the jig leaf must also be considered when a screw bushing is 
used, as it generally is, for clamping. The jig leaf should be 
reenforeed sufficiently to take care of the strain incurred. 

Bushing Design and Proportion. Various methods of mak- 
ing bushings, of which some are good and some bad, are shown 
in Fig. 68. The bushing shown at A is too short and does not 
give proper alignment for the drill, so that it is likely to cause 
inaccuracy as indicated at B. It is well to make a bushing from 
two to three times the length of the drill diameter if possible so 
that it has an appearance similar to that shown at C. So doing 
keeps the drill in good alignment and does not tend to produce 
angular holes. A bushing should have sufficient stock in contact 
with the hole into which it is pressed that it will not tend to 
loosen when in use. The bushing shown at D has only about 
one diameter in contact with the hole into which it is pressed 
whereas the bushing C has over two diameters. It is sometimes 
possible to use a construction like that shown at E where the 
jig wall is thin, and it is not possible to obtain great depth for 
the bushing. A screw such as that shown at F can be used to 
hold the bushing in position. 

In regard to the relieving of the inside of the bushing, the 



DETAILS OF DRILL JIG 



73 



form shown at G is tapered for a part of its length, a construc- 
tion much better than if counterbored as shown at H because 
in the latter ease the drill lip may strike the edge of the counter- 
bore and cause trouble. Jig bushings are usually rounded to 
facilitate the entrance of the drill as indicated at K. It is ad- 




Fig. 68. Bushing Design and Proportions 

visable to use a large radius in the mouth of the bushing wher- 
ever possible. Data relative to the distance between the work 
and the bushing have been given in a previous chapter. 

Methods of Holding Slip Bushings. Slip bushings are used 
in many eases where it is necessary to drill and ream the same 
hole in the same jig. The first bushing is made to the drill size 
and the second bushing to the reamer size. When slip-bushings 
are used provision must be made to prevent the bushing from 



f! 



iff! 



74 



JIGS AND FIXTURES 



pulling out of the jig when the drill is being removed. Several 
varieties of locks or clamps are shown in Fig. 69. There is shown 
at A a very common type which has a pin B with a shoulder 
which locks the bushing in place, a type used in the majority 




Fig. 69. Methods of Holding Slip-bushings 

of shops. A bail-bushing is indicated at C. There are advan- 
tages to this type of bushing for large work in that it is con- 
veniently removed, as the bail acts as a handle and the bushing 
is locked in position by snapping the bail down over the pin 
at D. Another form of lock for a slip bushing is shown at E, 
embodying the same principle as that used at B. Instead of 
using a pin for locking, a steel block as shown at F is screwed 
to the jig body. Another form of clamp for holding a slip bush- 



DETAILS OF DRILL Jia CONSTRUCTION 



75 



Ii]g is shown at G. The lever is clamped around the bushing by 
means of the pinch-binder at H and the bushing is prevented 
from pulling out of the jig by means of the retaining pin K 
which is shouldered so that the lever passes under it. The action 
of the drill tends to throw the lever against the pin K. In re- 
moving the bushing the lever takes the position shown by the 
dotted line. 




Work 



Fig. 70. Locating of Bushings 

Location of Bushings. The shape of the work to be drilled 
influences to some extent the location of the bushings. There 
are cases where a piece of work is so designed that it is difficult 
to place the bushings so that accuracy will be assured in the 
drilling operation. In the first chapter of this book the effect 
of design on the machining process was commented upon to 
quite an extent, and it was pointed out that the design of the 
work is an important factor which influences the efficiency of 
jigs and fixtures. There are some tool designers who are very 



ip- 



76 JIGS AND FIXTURES 

harsh in their criticism of the pieces for which they are called 
upon to design tools and are continually suggesting changes in 
their design. Changes in design are costly, especially if they 
cause the changing of expensive patterns, and should not be 
made unless there is something worth while to be gained. 

However, it has been pointed out that there are numerous 
instances when a change in design would result very profitably 
to the manufacturer. 

A piece of work is shown at A, Fig. 70, having an extended 
hub B. The inexperienced designer would be very apt to locate 
his bushings as shown at C and D, without sufficient support in 
the jig body. Either of two methods can be used to avoid the 
difficulty. In the method indicated at E the jig body is cut out 
at F to allow the hub to pass up into it so that the bushings 
G and H can be so made that they will have sufficient contact 
with the jig body. Another method is indicated at K, where 
the body of the jig is carried down in the form of bosses L and M 
to give stock for the bushings. Provision is made for drilling 
the center hole through the bushing 0. 

Standard Knobs and Thumbscrews. The ability of the tool 
designer is frequently shown in small ways such as the appli- 
cation of thumbscrews or knobs to operate various moving parts 
in the jig. It is well to consider the fact that the workman who 
handles a jig or fixture has to use his hands all day long. Speak- 
ing generally, a knob or thumbscrew should be so arranged that 
the operator can use it without "skinning his knuckles" on some 
surrounding part of the jig. The form of the knob should be 
such that it will not make an operator's fingers sore. 

It is advisable to avoid the use of knurled screws as far as 
possible, because they tend to make an operator's fingers tender 
if used frequently. The knob shown at A, Fig. 71, can be made 
with as many points as desired and it can be of steel or cast 
iron. If it is standardized, a number of sizes can be made up 
and carried in stock to suit various conditions. The hole may 
be drilled so 'that it can be readily fitted to standard sizes of 
screws or studs, as shown at B. A pin C is generally used to 
fasten the knob in position. 

Another type of knob, shown at D, can be used to advantage 
in numerous cases. The knob itself may have as many notches 
as seem desirable, th'is being a matter for individual decision. 



DETAILS OF DRILL JIG CONSTRUCTION 



77 



In this case the knob is made with a long hub tapped out at E 
so that it can be used to pull up on a stud or down on a clamp ; 
in fact it can be used in a number of ways which will suggest 
themselves to the tool designer. These knobs also can be made 
up in several sizes and carried in stock. A very common method 
of providing a means of adjusting a screw is shown at F, where 
a pin G is driven into the end of the screw to act as a handle. 




Fig. 71. Standard Knobs and Thumbscrews 

In the writer's opinion this construction should be used very 
seldom, except when very light pressure is to be applied. The 
objection to this method is that it is hard on an operator's 
fingers and that he is frequently tempted to use a wrench in 
order to tighten the screw ; as a result the pins very soon become 
bent and practically useless. 

A general form of pin knob is shown at H in which the pins 
are four in number and are set in at an angle. Even in this 
case however there are objections to the form used for much 
the same reasons as previously stated. 

A very excellent form of knob or thumbscrew is shown at K. 



If 



/ 

I 

IX 



-o JIGS AND FIXTURES 

lo 

This form has become a standard in many shops and is excellent 
both from the viewpoint of economy and convenience of opera- 
tion The knob has three points which accommodate themselves 
to the operator's fingers and do not make them sore. It is a 
form that can be used as a nut when drilled and tapped, or in 
a manner similar to that shown at A. 

A diagram which indicates the importance of clearance for 
the operator's fingers is shown at L. The knob M has been so 
placed that there is very little clearance for the workman's 
fingers between the screws and the walls of the jig N and 0. The 
amount of clearance necessary is shown by the dotted lines. It 
is a very good idea for a tool designer to imagine that he is 




Fig. 72. Handwheels and Large Hand Knobs 

operating the jig himself, making sure that his finger clearance 
is ample. At the same time he must remember that the shop 
man's hands are somewhat larger than his own and he should 
therefore make considerable allowance for finger clearance. The 
writer has frequently seen jigs, considered good by the drafting 
room, that caused the operator untold trouble, due to improper 
provision for his fingers. 

It should be remembered by the tool designer that the amount 
of pressure to be exerted influences the size of the knob to be 
used and it is sometimes found desirable to use a knurled screw 
in order to prevent the application of pressure enough to distort 
the work or spring it out of its true position. 



DETAILS OF DRILL JIG CONSTRUCTION 



79 



Handwheels and Large Knobs. On large fixtures it is fre- 
quently necessary to use handwheels or large knobs in order to 
provide pressure sufficient to operate the mechanism. The be- 
ginner is very apt to be "stingy" in the details of his design 
whereas the experienced designer is "generous" and makes a 
*' comfortable" jig which can be used with satisfaction by the 
operator. 

A form of hand knob which has found a great deal of favor 
with manufacturers in general is shown at A in Fig. 72. This 




Fig. 73. Simple Ejector for Drill Jig 

form of knob is usually made up in one or two sizes, the exam- 
ple shown being the 4-in. size. A knob of this kind is used only 
on large fixtures and jigs where considerable pressure is needed. 
It is generally made of cast iron and the hub is left solid so 
that it can be drilled or tapped to suit particular conditions. 
The advantage of this knob is that it fits the palm of the hand 
and the fingers can go down between the points which enables 
the operator to get a good grip. 

On large fixtures it is often desirable to use handwheels such 
as that shown at B. Handwheels of various sizes can be pur- 
chased cheaply and can be drilled or tapped in the hub C to suit 
any particular job. It is also possible to provide the wheel 
with a handle, as shown by the dotted lines at Z>, if desirable. 

There may be cases where it is an advantage to notch a hand- 
wheel as shown by the dotted lines at E so that an operator can 



80 



JIGS AND FIXTURES 



get a little better grip. A handle can be put in as indicated by 
the dotted lines at F to provide more leverage. 

Ejectors for Drill Jigs. There are many cases when it is 
essential to provide a means for removal of a piece of work 
from a jig or a fixture. It is not good practice to make up a 
jig in such form that the operator must use a hammer or screw- 
driver to get the work out after it has been machined. A simple 
form of ejector may be used, such as shown in Fig. 73. The 



Wor/<'\ 



Locating 
block 




* Turn eccentric- 



Fig. 74. Ejectors Operated by Eccentric and Wedges 

work A has been placed on the locater B which it fits snugly. 
To remove the work the operator would be obliged to use a 
screwdriver to pry it off from the locating plug B unless pro- 
vision was made for ejection. It is a very easy matter to insert 
the pins as shown at C and to operate them by means of the 
lever D. 

There are many eases where a somewhat simpler form of 
ejector can be used. The pins C could be held by a retainer and 
the lever D left off entirely. The operator could provide a 
wooden block on his drilling machine table and operate the 
ejector by striking the pins on it. 



t f 



DETAILS OF DRILL JIG CONSTRUCTION 81 

There are occasional cases where the removal of a piece of 
work from the jig requires that considerable attention be paid 
to the method of removal. A case of this kind is shown in 
Fig. 74 in which the work A is located on a central stud B which 
it fits closely. Ejectors are formed in this instance by two pins 
C and D which extend through the locating block as indicated 
and rest on eccentric portions of the shaft E. When the lever F 
is operated the eccentric causes the pins to rise and push tlie 
work from the plug. Another method of operating a similar 
mechanism is shown in the upper part of the figure. The ejector 
pins G and H are operated by means of the angular surfaces 
K and L on the rod P. A pin or hand knob can be provided 
at Q or as conditions require. 

Speaking generally, the use of ejectors would be required on 
any piece of work that could not be easily removed by hand. 
It is advisable to consider the conditions and the necessity for 
ejectors when designing any jigs in which the location is by 
means of finished surfaces, pins, or plugs. When ejectors are 
used the pressure must be distributed in such a way that it will 
not cause a "cramp" or li cock" in the work. 



r 



I ! 

n 



CHAPTEE IV 
OPEN AND CLOSED JIGS 

TEMPLET JIGS PLATE JIGS OPEN JIGS FOB A SHAFT OPEN JIG 
FOB A PUMP COVER CLOSED JIGS CLOSED JIGS FOR ANGULAR 
AND STRAIGHT HOLES LOCATING AND ASSEMBLING JIGS 
AN EXAMPLE FOR PRACTICE. 

In the previous chapters we have taken up a number of points 
in connection with the design of drill jigs. We shall now apply 



Work: 




Fig. 75. Templet Jigs 

some of the principles which have been described. It is not our 
intention to apply every principle or each mechanism which has 
been mentioned, but rather to give a few examples of jigs of 

82 



OPEN AND CLOSED JIGS 



83 



various types to illustrate the general procedure in jig construc- 
tion. From the examples given the tool designer can note vari- 
ous features of importance and by careful study he can doubt- 
less see other ways in which the same piece of work can be 
jigged. As a matter of fact the studious designer will find it 
to his advantage to consider each jig shown and endeavor to 
handle the work in as many different ways as he can, applying 
the principles which have been carefully explained in the pre- 
ceding chapters. 




Fig. 76. Use of a Templet Jig with Locating Plug 

As explained previously, the templet jig is the simplest form 
that can be made. In elementary form it is sometimes nothing 
more than a thin plate of steel with holes located to suit the 
condition. This plate is often set on the work and marked with 
a prick-punch or scriber. Templet jigs of this kind would be 
made up only in cases where there were a dozen or so pieces 
to be drilled and also when the location of the holes did not 
require very great accuracy. 

Going a step further in the design of templet jigs let us con- 
sider the ones shown in Fig. 75. The work A is a cast-iron 
frame of large size; there are a number of holes to be drilled 
on the upper surface, and there are only a few pieces to be 
machined. In order to drill these cheaply and to have uni- 
formity for the various pieces, the jig A is made up of sheet 
metal and is furnished with three J.ocaters shown at B, C and D. 



84 



JIGS AND FIXTURES 



The templet is placed in the position shown and clamped in 
place by some convenient method, using the locaters to bring it 
into the correct position. The holes are then prick-punched with 
a punch similar to that shown at E, after which the templet is 
removed and the work drilled according to the locations marked 
Another templet jig is shown at F in which the work is an 





Fig. 77. Plate Jig for a Large Casting 

automobile frame. The hole G in the front spring hanger is 
used as one locater for the jig and the pin H acts as the other 
stop against the side of the frame. This jig is a little more 
elaborate than the one previously shown as it is furnished with 
a thumbscrew at K to clamp it in position. Jigs of this kind 
may be furnished with bushings if desired, or they may be used 
with a prick-punch to locate the holes before drilling, as in the 
previous instance. It is evident that this type of jig could be 



OPEN AND CLOSED JIGS 85 

made much longer and carried farther along the frame to allow 
for the drilling of the other holes if necessary. A method of 
using a templet jig is shown in Fig. 76, the work being shown 
at A and the jig at B. Let us assume that the templet has been 
clamped to the work and that one hole has been drilled at C. 
A convenient method of making sure that the templet does not 
shift, is to use a plug like that shown at D in the first hole 
drilled. After this another hole can be drilled at some distance 
away as at E and a second plug inserted after which the re- 
maining holes can be drilled without danger of disturbing the 
location of the templet. An electric drill, indicated at F, is 
convenient for work of this sort. 

Plate Jigs. There is a strong family resemblance between 
plate and templet jigs, yet there is a distinct difference, in that 
the plate jig is often used for high production while the templet 
jig is never used except when production is small. There are 
many cases where a large piece of work requires a few holes to 
be drilled accurately in relation to other holes which have been 
previously bored and reamed and it may frequently prove to be 
more economical to design a plate jig than to attempt to do the 
work in a very large jig in connection with other holes. An ex- 
ample of this kind is shown in Fig. 77, in which the work A is a 
large casting which has been machined on the base B and on the 
upper surface at C and in which the holes D and E have been 
bored and reamed. It would not be economical to make a large 
jig to drill the holes at F and G, especially as it is necessary to 
locate them in relation respectively to the reamed holes D and E. 
It will be found more economical to make up a plate such as 
that shown at H, which has bushings provided at F and G and 
which locates by means of the studs K and L in the reamed 
holes. It is evident that a large jig of this sort would need 
nothing to hold it in place as it would be quite heavy. There- 
fore a handle is provided at M by which to lift it off the work 
after the drilling has been done. Jigs of this kind are in com- 
mon use in many factories. 

In Fig. 78 is shown another application of a plate jig which, 
like that in the previous instance, is located by means of a 
stud A in the center hole of the work B. This stud is provided 
with a key at C in order that the location of the holes D may 
be in a given relation to the keyway. The location of the holes 



86 



JIGS AND FIXTURES 



D is such that it would be difficult to support the work prop- 
erly unless particular provision were made. In order to assist 
in drilling, a support E is made up of cast iron so that the work 
rests on it. There are occasional cases where a support of this 
kind may be used in order to avoid designing an expensive jig. 
Jig for a Dovetail Slide. A simple plate jig, which will give 
very accurate results, is indicated in Fig. 79. The work A is 





Core for Chips 
Fig. 78. Plate Jig with Accessory Support 

a dovetail slide which has been finished all over and in which 
it is necessary to drill the four holes shown at B. These holes 
must be drilled in correct relation to the dovetail and it is there- 
fore necessary to locate the plate jig in the dovetail slide as in- 
dicated. The jig is provided with a binder at C, operated by a 
thumbknob D. The binding member is so made that it fits a 
circular recess in the plate and it is evident that this forms an 
excellent clamp to hold the plate in position. The end location 
of the jig is obtained by means of the stop-screw shown at E. 

Open Jigs. In the design of open jigs the general construc- 
tion of the work to be drilled must be first considered. As a 
general thing jigs of this kind are made for work which does 



OPEN AND CLOSED JIGS 



87 



not have a great depth. Occasionally they are so arranged that 
the whole jig must be turned over and the drilling done from 
the side opposite that in which the piece is loaded. This usually 
necessitates drilling against the clamp and while not always 
objectionable, it is considered better practice to drill against a 
solid surface. In the example shown in Fig. 80 the piece of 
work A has been previously reamed at B and has been milled 





Fig. 79. Jig for a Dovetail Slide 

on the surfaces marked /. It is necessary to locate the work so 
that the hole C is in a fixed relation to the hole B which must 
therefore be used as a locater. The work is set up on a stud 
at B and clamped by means of a swinging C-washer D through 
the nut E. It will be noted that the C-washer is pivoted so that 
it will swing clear of the work. By making the washer in this 
way loose pieces in the jig are avoided, which is always an 
advantage. The other end of the work is located under the 
bushing C by means of the sliding V-block F, operated by means 
of bayonet-lock and screw-bushing shown at G. This construc- 
tion allows for variations in the boss on the work at the point C 
and at the same time a quarter turn of the knob H releases the 
V-block and allows it to be pulled back sufficiently so that the 
work can be removed from the jig. There are many cases where 



S3 



JIGS AND FIXTURES 



If 



I I 



this construction is extremely valuable as it permits rapid action 
and the mechanism is at the same time simple and easy to manu- 
facture. This is a very good example of an open jig for a piece 
of high production work and the principles illustrated can be 
applied in numerous cases. 

Open Jig for a Shaft. Fig. 81 shows an open jig of excel- 
lent construction. The shaft A has been completely machined 
before the work is drilled. It is necessary to locate the drilled 
hole B at 90 deg. from the keyway in the taper at C. The work 





Section Through "V Block, Bushing 
cmcTC" Clamp 



mp 
Fig. 80. Open Jig for a Lever Arm Bracket 

is placed in V-blocks and located against the stop D at one end. 
The sliding member E is arranged so that it will locate in the 
keyway. A cam lever shown at F is used to clamp the work. 
The clamp is so made that it bears at (7 and H simultaneously. 
A slot at K allows it to be slid back away from the w r ork when 
loading or unloading. A suggestion is made in regard to the 
construction of the pin at L. Two methods can be used, the 
one shown in the drawing being the cheaper. The enlarged 
view at $/ shows an improved method which is more substantial 
but also more expensive. The designer must be governed by the 
size of the stud at L and if it is found that the pin is not suffi- 
ciently strong to withstand the pressure of the cam lever, the 
improved construction M can be used. A jig of this kind is 
rapid and its operation makes it very convenient to handle. 
The jig shown in Pig. 82 is an open jig which, however, is 



OPEN AND CLOSED JIGS 



89 



close to the border line between the open and closed types. The 
work A is a pump cover which has been machined on the sur- 
faces marked /. It is to be drilled at B, C, D and E in this 
operation and it is necessary that these holes should bear a cor- 
rect relation to the outlet F as well as to the previously ma- 
chined surface and also to the outside diameter of the work. The 



Work 




Elevation Showing Clamp 




Fig. 81. Open Jig for a Shaft 

method of locating the piece is rather out of the ordinary. The 
casting rests on four hardened bushings directly under the holes 
B y C, D and E and the spout F is located against the hardened 
locating pin G through the action of the bevel spring plunger H. 
It is also given another location, with respect to its outside 
diameter, by contact with the locating pins K and L, which are 
fixed in the body of the jig. After the operator closes the lever 
M y when the work is in position, the clamp N Is screwed down 
on the work by means of the thumbscrew 0. It will be seen 
that this clamp is not directly above the locating bushings on 
which the work rests, yet there is no danger of distortion on 
account of the stiffness of the casting. The portion of the work 
opposite the points K and L and mid-way between them strikes 



JIQ8 AND FIXTURES 

the angular surface of the spring plunger P which depresses 
and at the same time insures a positive location against the 
two pins K and L. 

The locking of the leaf is by means of a quarter-turn screw 
shown at Q. This jig is rather exceptional in its general con- 
struction and may be considered as an excellent example of 
modern jig design. 



L-i 

>=>*? ^ r^x 

V-'t. /-.vd 




Fig. 82. Open Jig for a Pump Cover 

Importance of Chip-Clearance in Closed Jigs. In closed 
jig design particular attention must be paid to the clearance 
around the work in order to have plenty of room for chips to 
accumulate, for cleaning, and for setting up and removing the 
work. Wherever possible in closed jig design it is a good idea 
to core openings in the side of the jig in order to allow for 
cleaning. A very good example of a closed jig of simple con- 
struction is shown in Fig. 83. The work A is a casting which 
has been finished at / in a previous operation. There are three 
blind holes to be drilled at B, C and D and it is necessary to 



OPEN AND CLOSED JIGS 



91 



locate the work from the finished side of the casting, from the 
boss around the hole D and to provide another loeater which 
will come in contact with the rough casting on the side as indi- 
cated at E. In the design of the jig it is well to note that the 
stud E could be so made that it would be adjustable, but in this 
case it has not been done because the casting is known to be a 
good one and not subject to variations at this point. The boss 
around the hole D locates in an adjustable V-block, the con- 




Pig. 83. Closed Jig with Clamp in Leaf 

struction of which has been mentioned in a previous article. The 
work is clamped in position by means of the screw at the corner 
adjacent to the hole C. It is advisable to set this thumbscrew 
at an angle of 10 or 15 deg. so that the action will tend to force 
the work down on the finished surface / as well as to carry it 
into its correct location. The work rests on the heads of the 
three hardened bushings at B, C and D. These bushings are 
slightly different from the regular type in that they are counter- 
bored slightly to allow for chips while drilling. The method 



92 JIGS AND FIXTURES 

of clamping the work is by means of an equalizing clamp F f 
which is mounted in the leaf G. Attention is called to the fact 
that the clamping action is not directly over the points in which 
the work rests, but it can easily be seen that the thickness of 
the casting is such that there is little likelihood of its being dis- 
torted by the pressure of the clamp. The leaf is clamped by 
means of the swinging eyebolt H and the thumbknob K. Care 
must be taken to allow plenty of clearance at L so that there 
will be no chance that the screw will strike the drilling-machine 
table before the leg does. The eyebolt is so made that it will 
not revolve completely on account of the end H, which strikes 
the wall of the jig as the eyebolt is thrown open. When in use 
this jig is turned over so that the work is drilled from the side 
opposite the leaf. The jig feet N and should not be made 
too long as they might interfere with the drill chuck. There 
are several important points of general construction involved 
in the design of this jig. 

Closed Jigs for Angular and Straight Holes. "When large 
castings are to be drilled from several sides, the jig is frequently 
made in trunnion form, but when the work is comparatively 
small it is customary to provide for drilling the holes from 
various directions, by making it possible to set the jig up in 
different positions as required. "When some holes are to be 
drilled straight and others at an angle in the same jig, care 
must be taken that projecting knobs, setscrews or other pro- 
tuberances, do not strike the surface on which the jig is resting. 
In Fig. 84 a closed jig is shown for the work A which has been 
previously machined in a turret-lathe operation at B, C, D 
and E. There are four holes to be drilled at F, arranged at the 
four corners of a rectangle. There is also an angular hole to 
be drilled at G. The work is located on the fixed plug H at one 
end of the jig and rests on the hardened ring K. At the other 
end a plug L is used as a locater. It will be noted that this 
plug is arranged so that it can be operated quickly. The method 
used is an application of the familiar form of bayonet-lock, the 
plug being slotted at M, and the slot having an angularity at N 
to provide for locking by means of the teat screw which en- 
gages with the slot. 

As it is necessary to locate the finished pad containing the 
four holes F in such a way that the holes mentioned will be 



OPEN AND CLOSED JIGS 93 

square with, the finished surface, a locater must be provided. 
The form of locater used is shown in an enlarged section. The 
plug P is made with a double end at Q and R so that these two 
points bear against the casting and straighten it up in relation 
to the finished surface. The plug is mounted in a bushing and 
is controlled by a spring. The end of the bushing is slotted to 




Enlarged Section Showing Locater 
Fig. 84. Closed Jig for Angular and Straight Holes 

receive a pin 8 which keeps the locater in its correct position, 
provides a means for withdrawing it when inserting the work, 
and acts as a restrainer to prevent it from coming out of the 
bushing. It can be seen that the action of the locater is prac- 
tically automatic after the work is placed in the jig and tends to 
straighten out the finished surface and thus- bring it in to its 
true position while the plug L is being operated. 

As originally designed four feet were provided at T and U 
in order to give support while drilling the angular hole G. The 
construction would be much improved by extending these feet 



94 JIGS AND FIXTURES 

and separating them farther, as indicated by the dotted lines, 
in order to give greater stability. 

Simple Type of Closed Jig. A conventional form of closed 
jig is illustrated in Fig. 85. The work A locates on a hardened 
plate B which is set in the body of the jig. The bushings C are 
carried in the leaf. The work locates on a central stud D and 
is clamped by means of C-washer E. Provision is made in the 




, i 

} ' 

f ? 

1 f 

I 
'> 



V 




Fig. 85. Simple Type of Closed Jig 

leaf for the nut on top of the C-washer in order to bring the 
leaf as close to the work as possible. The leaf is changed by 
means of a quarter-turn screw shown at F and a stop-pin is 
provided at G. 

Attention is called to the leaf stop indicated at H. It is also 
well to note the manner in which the stud D, on which the work- 
is located, is arranged and that the wall of the jig is opened up 
on two sides at K in order to provide for cleaning. It will also 
be seen that the work does not get a bearing on the stud D for 
its entire length as it is relieved at the lower portions, yet it 
gives ample surface for accurate location. 

A very good example which shows the application of a swing- 



I 



OPEN AND CLOSED JIGS 



95 



ing V-block to a jig is shown in Fig. 86. The work A locates 
in a block B at one end of the jig while the other end is locked 
and clamped by means of the two arms, C and D, operated by 
a thumbscrew at E. This application can be used in many 
cases, and the example will give the designer a number of good 
ideas in regard to the details of construction. 




u 



Fig. 86. Design of Jig with Swinging V-block 

Built-up Jigs. A number of units frequently used in the 
construction of built-up jigs have been illustrated and described 
in an earlier article. In the example shown in Fig. 87 some of 
these principles and units are illustrated. 

The work A has been finished all over in a previous operation 
and it is located on the central stud B and also in the four 
pins C, D, E and F. The holes to be drilled are a blind hole 
at G and three smaller holes H, K and L. The depth of the 
blind hole is important and for this reason the leaf is provided 



n 



'* ' 



90 JIGS AND FIXTURES 

with two hardened and ground stop-pins at M. The enlarged 
view shows the type of gage used for determining the depth 
of this blind hole. The hardened pins M act as stops for the 
gauge block A T and the point gauges the depth of the hole. If 
the hole is not deep enough the gage will not come down on 
the pins, while if it is too deep the gage can be turned around 
so that it will pass between the pins and strike on the sides. 




Fig. 87. Built-up Jig of Representative Type 

This jig is provided with a leaf stop of standard form shown 
at P and the leaf is fastened by means of the quarter-turn 
screw Q and bears on the wear plates indicated at R. Provi- 
sion is made for stopping the quarter-turn screw by means of 
the pin S. The construction of the hinge is of the approved 
method previously described, in which a taper pin T and wear 
plates at U are employed. The work is held firmly in position 
on the locating studs by means of a special equalizing clamp 
in the leaf. A sectional view of the construction is shown at V. 
It will be seen that the pins W are cut on an angle at the end X 



OPEN AiVD CLOSED JIGS 97 

so that they exert a downward pressure on the pins which clamp 
the work. The action of the operating pins is limited by the 
slots at so that they do not disengage completely from the 
angular slot X. 

This jig is built up from a standard angular plate Z and a 
number of units previously described have been used in its con- 
struction. It is an excellent form of jig because it can be made 
up from standard units to some extent, is very easily cleaned, 
quickly operated, and has every provision for adjustment and 
replacement to take care of wear. It may be argued that the 
clamping does not take place directly over the locating studs 
but it has been pointed out that this principle cannot always be 
followed, and in the case shown the work is sufficiently stiff 
that no danger of distortion need be apprehended 

Locating and Assembling Jigs. It is often necessary to 
assemble a number of pieces on a shaft in a certain relation to 
each other both radially and longitudinally. "When this is 
necessary it is advisable to make use of a locating jig, an exam- 
ple of which is shown in Fig. 88. The work consists of a shaft 
A to which are applied several collars at B, C and D, fastened 
to the shaft by means of taper pins. The jig is of cast iron 
and the various units necessary are mounted on it. The shaft A y 
with collars B, C and D loosely assembled on it, is forced up 
-, against the hardened stud E by means of the thumbscrew F. 
Each of the collars is held in position and prevented from turn- 
ing by means of a screw G mounted in a block H. The screws 
force the shaft over into V-blocks and longitudinal location of 
the various collars is assured by the space between the various 
blocks. 

The principle shown at G is also used at B and D, but the 
position of the unit is shown in dotted lines in order to make 
the illustration more clear. The leaf K is provided with bush- 
ings at L, M and N by means of which the holes are properly 
located. The work being clamped independently of the leaf, a 
tapered reamer can be used to finish the holes after the leaf 
has been thrown back into the position shown. Applications of 
the principles shown can be used for other work of similar 
character. 

It is frequently necessary to locate gears, cams, levers, or other 
parts on a shaft in a certain relation to each other. In cases of 



98 



J1G8 AND FIXTURES 



M 
ii. 



this kind it may be possible to use a jig similar to that shown 
but with different schemes for locating. The gear shown at 
is to be assembled on a shaft and it is necessary that the gear 
teeth should have a certain relation to other members on the 




Fig. 88. Locating and Assembling Jig for Shaft and Collars 

shaft. The pawl P, used to give this location, is operated by 
means of a thumbscrew Q. A spring can be applied to throw 
the pawl out of location when the screw is released. 

Another example is shown at R. This is a lever which must 
be located on the shaft at S' and in the correct angular relation 
to the hole at T. It is a simple matter to provide a pin at T to 
give the desired position, the pin being cut away as indicated 
in order to provide for slight variations between the center dis- 
tances of the two holes. When pressure is applied in the direc- 



OPEN AND CLOSED JIGS 



99 



tion indicated by the arrows the shaft will be forced into the 
V-block and the lever will be held in its correct position. 

There are some eases where a pin is assembled in the lever 
arm as indicated at U. When this is the case a locating block 
may be slotted as at V to receive the pin. The angularity of 
this slot should be at right-angles to a center line passing 
through the two holes in the lever. 

A method which can be used for locating work in a V-block 
is indicated at W. A swivel block X is mounted on the end of 




Fig. 89. Examples for Practice in Designing Locating Jigs 

a stud Y and operated by means of a collar screw Z. This type 
of clamp has an advantage when it is necessary to guard against 
any turning action which might change the position of the work 
when clamping. Occasionally a collar must be located on a 
shaft in relation to a previously drilled hole such as that indi- 
cated at A A. The work can then be located in a Y-block and 
a plug can be pushed into the collar at BE. This sketch also 
illustrates the slotting of a single V-block to provide for loca- 
tion instead of using several blocks as indicated on the jig. 
CC is also slotted but in a direction different from that in the 
example just mentioned. 

Example for Practice. When a series of parts is to be as- 
sembled such as the cams shown at A, B, C and D in Fig. 89, 



100 JIGS AND FIXTURES 

it is common practice to provide the cams with a driving hole 
sucll ^ that shown at E in each cam. This hole is carefully 
located and is used in cutting the cam and in assembling. The 
parts are generally set over a small plug similar to that shown at 
F and are located by means of the pin G. A jig of suitable size 
is made, either cast or built up, in such a way that the pieces 
are all located one over the other on the plug mentioned. A 
suitable clamp must be provided to hold the four pieces firmly 
in position. After they have been assembled the rivet holes // 
are drilled. It sometimes happens that the pin G is weak and 
is likely to be bent when in use. It is better to provide the jig 
with bushings as indicated at K and L. After this is done a 
plug M can be placed through all of the holes one after the other 
to give the correct location. 

A good problem suggested here is the designing of a jig for 
drilling the rivet holes H in these cams. 

Another example which offers a good problem is afforded by 
the parts 0, P and Q. sets over P and P over Q, and a locat- 
ing jig is desired so that the rivet holes 72 and 8 can be drilled 
in their correct location. As an alternative we suggest that a 
locater similar to that shown at T can be used in the teeth U 
but if this appears too expensive a paddle gauge or plug such 
as that shown at X can be used. 

On certain classes of work assembling and locating jigs are 
of extreme importance and it is therefore a good idea for the 
designer to note the construction of the examples given very 
carefully and put into practice the various principles which 
have been illustrated and described. He will find it a decided 
advantage to design several jigs of this kind, using examples 
from his own practice and taking cases which are of particular 
interest rather than those which appear simple and easy to 
work out 



CHAPTEE Y 
INDEXING AND TRUNNION JIGS 

INDEXING REQUIREMENTS DRILLING AND REAMING IITDEXING 
FIXTURES FOUR-SIDED JIGS FOR ACCURATE WORK PRIN- 
CIPLES AND METHODS OF INDEXING INDEX PLUNGERS AND 
LATCHES COMBINED INDEX AND LATCH SPECIFIC EXAM- 
PLES OF INDEXING JIGS ROLL-OVER JIGS TRUNNION JIGS 
DOUBLE TRUNNION JIG A DIFFICULT DRILLING PROBLEM 
TRUNNION JIG USED PROGRESSIVELY. 

When a piece of work is to be drilled from three or four sides 
it may often be desirable to locate it in some form of indexing 
or trunnion jig. Speaking generally, the necessity for a trun- 
nion jig is indicated when the work is of large size or when the 
angularity of the holes would not permit the use of a closed 
jig. It is evident that a large closed jig, say 20x18x15 in., 
would be very cumbersome and difficult to handle when turning 
it over to drill the work from the various sides. Also if the 
holes in the work were to be so located that the angles did not 
diverge greatly from each other, it would be practically impos- 
cible to drill the holes unless the pieces were located in an index 
jig of some kind. 

The tool engineer in making a decision as to the type of jig 
to be used for the work must analyze the conditions under which 
the jig is to be used and must also pay attention to the fol- 
lowing points which affect the design. 

Points To Be Considered. (1) The ultimate production for 
which the jig will be required. This is an important factor in 
the design, as it is evident that it would not be economical to 
design an indexing jig for a piece of work on which the 
production is small. It would be better to make several simple 
and cheap jigs rather than to design one expensive trunnion 

jig- 

(2) The number of sides from which the work must be drilled. 

101 



102 JIOS AND FIXTURES 

It is difficult to give a fixed rule as to when a trunnion jig may 
be called for and it should be noted that the number of sides 
from which the work is to be drilled does not, necessarily, settle 
the matter. We can easily assume that a piece of work having 
holes in four sides might be of such form or size that it would 
no t need to be handled in an indexing or trunnion jig. On the 
other hand if the work were very large and difficult to handle 
it might even be necessary in some cases to design a trunnion 
jig ? even if the holes were drilled from only one side of the 
piece, in order to facilitate loading and unloading. 

(3) The machines on which the various drilling operations 
w ill be done. This factor is an important one and must always 
be given early consideration. There are many cases where mul- 
tiple spindle drilling machines can be used in connection with 
trunnion and indexing jigs, provided the holes are more or less 
uniform in size. There may be other conditions which would 
| indicate that a radial drilling machine must be used. There may 

| also be cases where a light sensitive drilling machine with only 

I one spindle or with several spindles carrying drills of different 

* diameters arranged in gang-form may be necessary. 

i (4) Loading and unloading: In placing the work in the jig 

I and removing it after it has been drilled attention must be paid 

i to the convenience of operation. If the work is heavy it is evi- 

i dent that the operator must be considered to some extent so that 

I he will not be obliged to load the work from an awkward posi- 

I tion. For the sole purpose of making the method of loading 

1^ and unloading as easy as possible, it is often desirable to make 

a trunnion jig with a special loading position. "When the work 
is small such provision is not necessary in the majority of cases. 
It is sometimes a great convenience to the operator if the jig 
is provided with ejectors of some form and when this is done 
care must be taken that the pressure of the ejectors is exerted 
in such a direction that there is no possibility of a cramping 
action when in operation. 

(5) Locating and clamping: In the location of the work and 
in the clamping thereof the weight of the work which is to be 
drilled is an important factor. For very heavy and large cast- 
; ings the matter of leverage which must be exerted on the work 

to force it into a correct position must be carefully thought out 
by the tool designer. Cam levers, handwheels, bayonet lock 



INDEXING- AND TRUNNION JIGS 103 

plugs and other devices may often be necessary to Insure the 
correct location. In clamping the work in a large trunnion jig 
the clamps should be so proportioned that when they are set up 
they will not cause distortion and thus interfere with the proper 
working of the jig. 

(6) Clearance when indexing: This is an important point 
which is likely not to be given the consideration w r hich it re- 
quires. When large work is being handled on a trunnion jig it 
may often be found desirable to clamp the jig to the table of 
the drilling machine. It is evident that when the jig is indexed 
it should not interfere with the setting of the machine spindles, 
nor should it strike the column of the machine. The writers 
know of a large trunnion jig, designed to be used on a heavy 
drilling machine with a special multiple drill head, which when 
swung interfered with the column of the machine. It was found 
necessary to provide a special mounting for the base of the jig 
so that it could be moved away from the column each time it 
was indexed. Such mistakes can be avoided if the tool designer 
will provide himself with data showing the various clearances 
on the machine to be used for the work. 

Having considered the various points mentioned in connec- 
tion with the design of indexing and trunnion jigs let us now 
proceed to a discussion of the design of various types of jigs 
which come under this heading. "We may have (a) a number 
of holes which are drilled so close together that it is not pos- 
sible to arrange the spindles of a drilling machine to drill all 
of the holes at the same time; (b) a number of holes in a cir- 
cular plate at the same distance from the center; (c) several 
holes in line with each other which must be drilled separately 
on account of the spindle spacing on the drilling machine; (d) 
a number of holes equally spaced in the periphery of a cylinder ; 
(e) angular holes arranged in various ways. 

Indexing Requirements. It is obvious that both the shape 
of the work and the relation of the various drilled holes to each 
other are factors important in determining the type of indexing 
jig most suitable for a given piece of work. There are given in 
Fig. 90 several examples of work showing a variety of condi- 
tions: A is a circular plate having four holes B equally spaced 
and at the same distance from the center. There are several 
ways in which this piece of work can be drilled. One way is 



104 



JI08 AND FIXTURES 



to make a drill jig with four bushings and move it about on the 
table of the drilling machine so as to bring each bushing under 
the spindle. Another way is to use the same jig, drilling with 
a four-spindle head. Still another way is to make an indexing 
jig, a suggestion for which is given in the illustration. A drill 




Fig. 90. Several Examples of Work Requiring Indexing Jigs 

bushing of the proper size would be fixed as shown at C and the 
work would be placed on an indexing table or disk. 

At D there is shown a drum in which four holes E are to be 
drilled. This operation can be done in either an ordinary four- 
sided jig or an indexing jig. 

The plate F offers the rather exceptional problem of drilling 
96 holes, J in. in diameter and \ in. c. to c. in each direction, a 
problem with which we had to deal quite recently. It would be 
impossible to arrange a series of drill spindles close enough to- 



INDEXING AND TRUNNION JIGS 105 

gether to drill all the holes at the same time, but it would be 
entirely practicable to drill alternate holes in one or two lines 
at the same time. Hence the logical method is to mount the 
work so that it can be indexed in two directions in a horizontal 
plane. Suitable provision for carrying the bushings would be 
made in the jig and the required stops or indexing points on 
the two slides G and H would give the various positions. The 
piece K would be clamped to the table of the machine. 

A number of combinations of drill spindles could be made 
when drilling a piece of this character. If the machines were 
to be multiple-spindle drilling machines, the heads could be 
spaced to drill alternate holes in the first line and the corre- 
sponding holes in the third line. The plate could be indexed 
in one direction only so that the intermediate holes could be 
drilled. Several indexing operations all in one direction would 
complete half of the drilling. After this the other slide operat- 
ing in the other direction could be indexed progressively to com- 
plete the work. It is possible to handle a piece of work of this 
kind by means of automatic attachments through which the 
indexing mechanism is operated by the action of the drill head 
when it is lifted from the work. 

Index Boring and Reaming Jig. In Fig. 91 is shown an 
example of an indexing jig in which the two holes A and B are 
to be bored and reamed without removing the work. Bushings 
could be carried on the sliding member C or a permanent bush- 
ing could be supported on the column of the machine. The work 
is of large size and as a consequence indexing is done by means 
of lever D which operates pinion E meshing with rack F on the 
sliding member C of the fixture. Location bushings are pro- 
vided at G and H. The slide is shown in the neutral position. 
Attention is called to the adjustable stops K and L which ap- 
proximate the location as the slide is indexed from one position 
to the other, thus making it easier for the operator to insert a 
pin in the location bushings. This example is not intended to 
show details of construction but rather the application of a 
principle. 

In designing a jig of this character it is advisable to make 
the lever D long enough to afford easy operation. Care must 
be taken that the pinion E is large enough to index the work 
without too great radial motion of the lever. If the holes A 



106 



JIGS AND FIXTURES 



and B are spaced so far apart that a very large pinion would 
be required it is better to make the pinion small and provide 
the lever with a reversible ratchet. Both ratchet and pinion 
should as a rule be covered to exclude chips. 

Swivel Index Jig. A simple form of indexing jig is indi- 
cated in Fig. 92, in which the work A has two holes at B and C. 
The jig itself consists of a box D pivoted at the point E. It is 
indexed by means of the handle F. Hardened studs G and H 
are provided to bear against the adjustable stops 7 and J. Bush- 





r 


C H 








. V- 




AJ 


t^g? 
"TO 


B 




\ i} 


-% 


P 














' 








Fig. 91. Index Jig for Boring and Reaming 

ings could be provided to give more accurate location, but for 
light work the method shown would give good results. 

The same principle could be applied if there were three holes 
instead of two, but another method of indexing would be re- 
quired. It would be necessary to find the common center for 
the three holes and pivot the swinging member at that point in 
order that the bushings would come directly under the drill 
spindle. There are certain isolated cases where such a jig would 
be found very useful. A rapid indexing device could be used 
and various modifications made to suit particular conditions. 

It frequently happens that a piece of work similar to that 
shown at A in Fig. 93 is to be drilled at two or more points 
such as B and C, the holes to have an angular relation to each 



INDEXING- AND TRUNNION JIGS 



107 



other. When the two holes are to be close together and drilled 
from the same side of the piece, it would not always be ad- 




11 




GD 


Q 


J 



^ 



Fig. 92. Swivel Indexing Jig 

visable to build an indexing jig, on account of the cost. Assum- 
ing then that the holes are to be drilled in a simple jig having 
the form shown at D, it would not be difficult to make up a 



Work 




Jjg 



Pig. 93. Angular Plate Used in Connection with a Simple Jig 



special angular plate such as shown at E, on which the jig could 
be located at the proper angle for drilling the hole B/ after this 
hole had been drilled the jig could be taken from the plate and 
placed on the drill table to drill hole C, as shown in the second 
position. 



108 



JIGS AND FIXTURES 



If the production required on the work were considerable 
the angular plate could be clamped under one spindle of a two- 
spindle machine for drilling one hole and the jig could be trans- 
ferred rapidly to a position on the machine table under the 
second spindle for drilling the second hole. Occasionally on 
very large work an angular plate, such as that shown, will save 
the cost of a trunnion or indexing jig. 

Four-Sided Jig for Accurate Work. The requirements of 
certain classes of work are such that it is not always desirable to 
use an indexing jig or fixture, especially when great accuracy 




Fig. 94. Four-Sided Jig for Accurate Work 

is necessary. In the majority of cases an indexing jig will give 
results well within the limits of accuracy necessary, but there 
are occasional instances when some other method may be pre- 
ferred. There is always the possibility of a slight inaccuracy 
resulting from the use of any indexing mechanism,, caused by 
chips or dirt working into the indexing members or by wear, 
misuse or neglect. 

An example of very excellent construction to be used when 
great accuracy is required is shown in Fig. 94, the piece of work 
A being a cross which carries four gears on the arms. It is im- 
portant, not only that these arms be at right angles but that 
the locations of the center-holes in the ends of the arms should 
be of the same depth and the same distance from the center hole 
on which the work is located. The work is located on a center 
stud and clamped by means of the C-washer, one of the arms 
being located in a spring V-bloek shown at B. The jig is pro- 



INDEXING AND TRUNNION JIGS 109 

vided on four sides with feet which can be very accurately ma- 
chined. The bushings G, D, E and F also can be located with 
great accuracy and can be faced so that they are exactly the 
same distance from the central locating plug. The depth of the 
countersinking is determined by the collar G which strikes the 
head of the bushing. 

Simple Index Jig. It Is sometimes necessary to design a jig 
for drilling a series of holes which are equally spaced in the 
periphery of a shaft or some other part of a similar kind. An 
example is shown in Fig. 95 in which the holes shown in the 




^Section Through 
Hole 3 



Fig. 95. Simple Index Jig 



sectional view at A are to be drilled in the shaft B. The method 
illustrated here is not recommended for use except in rare cases ; 
it may be found useful when a simple and cheap method is re- 
quired for a comparatively small number of pieces. The ac- 
curacy obtained will be found to be very satisfactory. The work 
B is located in V-blocks at G and D and the jig E is provided 
with a bushing at F located centrally over V-block C. The upper 
surface G of a hardened block H is ground to a fixed distance 
below the center line of the V-blocks. A supplementary block 
K, which has been accurately squared up, is clamped to the end 
of the shaft by means of the setscrew L. By loosening the clamp 
operated by the thumb nut M and pushing the clamp back out 
of the way the shaft can be turned until the block K has rested 
on each of its four sides and the work has been drilled in each 



110 



JIGS AND FIXTURES 



of the four positions. The block K can be made with three, 
four, five, six, eight or more sides. 

In quantity production it is often desirable to drill a piece of 
work and ream it in the same jig. Many times when this is to 
be done slip bushings are employed in the jig and the drill is 
replaced by a reamer in the drilling machine. A method which 
can be used is illustrated in diagram form in Fig. 96. Briefly 



Ream 




Loading 




Fig. 96. Index Drilling and Reaming 

stated the principle employed is that of an index table A on 
which are mounted three jigs that are indexed from loading 
position B to drilling position C, to reaming position"!) and 
back to loading position. A method like this is suitable only 
for high production. But it will be found to be an advantage 
in many ways when the nature of the work will permit. Chang- 
ing from drilling to reaming bushings can be done by pivoting 
a plate containing four bushings of each kind or it can be done 
by using an outside bracket for the bushings. 

Principles and Methods of Indexing. In discussing the 
methods used in indexing various fixtures for drilling we must 
first consider the matter of accuracy. It must be remembered 
that indexing surfaces, plugs, bushings, wedges or any other 
members which are used to locate from in the process of index- 
ing should be kept as free from chips and dirt as possible in; 
order that the indexing may be accurate. This is a fundamental; 



INDEXING AND TRUNNION JIGS 



111 



point which must always be thought of by the designer. Let 
us refer to Fig. 97, in which two indexing plugs are shown at 
A and B. The design shown at A has a plug which is located 
radially so that it will enter the index plate D as far from the 
center E as possible. It may even be advisable to make a very 
large index plate for a comparatively small index jig if the 
accuracy required is great. In example B the plug F is quite 
close to the center G so that any errors in indexing would be 
multiplied in the work in direct proportion to the distance of 
the surface being drilled from the center G. 
It may be taken as a general principle that the further away 




Good 




R, 



Bad 



Fig. 97. Examples of Good and Bad Methods of Locating the Index Pin 

from the center the indexing pin can be located the more ac- 
curate the work will be. 

Index Plungers and Latches. When an indexing jig is ro- 
tated into its various positions there must be a positive method 
of location provided for each position. There are a number of 
methods in common use, some of which are illustrated in Fig. 98. 
The simplest type of indexing pin is shown by the first sketch. 
A is the indexing member and B is the fixed member. Each 
of them is provided with a hardened bushing, at C and D re- 
spectively, in such alignment that the plug E can be pushed into 
them to form a lock as the various indexing positions are used. 
An objection to this form of indexing is that the plug is a loose 
piece which may be easily lost; it may, however, be attached to 
a piece of closet chain, and fastened to the fixed member. It 
can also be arranged with a special bushing and a spring to 
keep it in place. 

Another form of indexing plunger, shown at F, is used by 



112 



JIGS AND FIXTURES 



many designers and has much to recommend it. The plunger 
is tapered at the end and seats itself in the tapered end of the 
bushing ff. It has a long bearing in the bushing K and is pro- 
vided with a spring to hold it in position. Some designers pre- 




Fig. 98. Index Plungers and Latches 

fer a straight pin instead of a taper, as indicated at L. The 
writers- believe that this is a matter of personal preference 
although it is claimed that a taper plunger will adjust itself for 
wear when the straight plunger will not Care must be taken 
in designing a tapered plunger, and the sides should not taper 
more than 10 or 12 deg. on each side of the center line. 
In some cases it is necessary to use a heavy spring for holding 



INDEXING AND TRUNNION JIGS 113 

a plunger in position ; a construction that requires considerable 
pulling on the part of the operator. This can be remedied by 
inserting a pin in the stem of the plunger as indicated at M and 
then cutting a cam-path on the end of- -the bushing at N. The 
insertion of a rod handle at the end makes it possible to pull 
out the plunger by a turning action, much easier than a straight 
pull. 

A form of index which is much in use on large work and which 
ha^ the advantage of placing the pin as far as possibls from the 
center, is shown at P. There is no particular comment to be 
made on this method except to say that it is good. 

On large trunnion jigs it is often difficult to operate a pull-pin 
by means of a knob and it is much more convenient for the 
operator to provide a lever. An example is shown at Q. A lug 
K is attached to the base of the fixture to act as a fulcrum for 
the lever 8. The fulcrum should be so placed that the length 
of the lever w r ill permit the operator to withdraw the pin easily. 
It is evident that an elongated slot must be provided in the 
lever or the index pin to take care of radial movement when a 
spring is used. Many times it is desirable to use a steel plate 
instead of a bushing as an index plate, as shown at T. In one 
of two methods that are common practice, the lever, as shown 
at U, is formed at Y, so that it w r ill seat itself in the angular 
slot in the steel disk T. When an arrangement of this kind is 
made the designer must be careful to position the center W so 
that the distances X and Y will be equal in order that the angles 
on the lever will coincide with the angles on the disk. 

The other method is shown at Z. The plunger is mounted in 
a slide and is operated by a lever. The second method is to be 
preferred on account of its greater accuracy but space will not 
always permit its use. Care should be taken that the plunger 
is given a long bearing in the slide in order to obtain 
accuracy. 

Combined Index and Latch. In indexing fixtures for high 
production work and in other designs of indexing fixtures it is 
desirable to make a very quick operating index and latch, one 
which will be so nearly automatic that a man can operate it 
rapidly and without giving it much attention. Such a latch is 
shown in Fig. 99. This form can be used in many cases and 
can even be arranged so that the movement of the drill press 



112 



JIGS AND FIXTURES 



many designers and has much to recommend it. The plunger 
is tapered at the end and seats itself in the tapered end of the 
bushing H. It has a long bearing in the bushing K and is pro- 
vided with a spring to hold it in position. Some designers pre- 




Fig. 98. Index Plungers and Latches 

fer a straight pin instead of a taper, as indicated at L. The 
writers believe that this is a matter of personal preference 
although it is claimed that a taper plunger will adjust itself for 
wear when the straight plunger will not. Care must be taken 
m designing a tapered plunger, and the sides should not taper 
more than 10 or 12 deg. on each side of the center line. 
In some eases it is necessary to use a heavy spring for holding 



INDEXING AND TRUNNION JIGS 113 

a plunger in position ; a construction that requires considerable 
pulling on the part of the operator. This can be remedied by 
inserting a pin in the stem of the plunger as indicated at M and 
then cutting a cam-path on the end of -the bushing at N. The 
insertion of a rod handle at the end makes it possible to pull 
out the plunger by a turning action, much easier than a straight 
pull. 

A form of index which is much in use on large work and which 
ha the advantage of placing the pin as far as possible from the 
center, is shown at P. There is no particular comment to be 
made on this method except to say that it is good. 

On large trunnion jigs it is often difficult to operate a pull-pin 
by means of a knob and it is much more convenient for the 
operator to provide a lever. An example is shown at Q. A lug 
R is attached to the base of the fixture to act as a fulcrum for 
the lever 8. The fulcrum should be so placed that the length 
of the lever will permit the operator to withdraw the pin easily. 
It is evident that an elongated slot must be provided in the 
lever or the index pin to take care of radial movement when a 
spring is used. Many times it is desirable to use a steel plate 
instead of a bushing as an index plate, as shown at T. In one 
of two methods that are common practice, the lever, as shown 
at U, is formed at Y, so that it will seat itself in the angular 
slot in the steel disk T. When an arrangement of this kind is 
made the designer must be careful to position the center W so 
that the distances X and T will be equal in order that the angles 
on the lever will coincide with the angles on the disk. 

The other method is shown at Z. The plunger is mounted in 
a slide and is operated by a lever. The second method is to be 
preferred on account of its greater accuracy but space will not 
always permit its use. Care should be taken that the plunger 
is given a long bearing in the slide in order to obtain 
accuracy. 

Combined Index and Latch. In indexing fixtures for high 
production work and in other designs of indexing fixtures it is 
desirable to make a very quick operating index and latch, one 
which will be so nearly automatic that a man can operate it 
rapidly and without giving it much attention. Such a latch is 
shown in Fig. 99. This form can be used in many eases and 
can even be arranged so that the movement of the drill press 



114 JIGS AND FIXTURES 

spindle as it passes up after drilling the work will index the 
fixture A steel disk A, having a number of index slots B, is 
mounted on a center plug C to which the body of the jig to be 
indexed is attached. The lever D has a cam cut on it at E, this 
cam being used to control the movement of pin F in the latch 0. 
The lever is provided with a dog H which engages with the edges 
of the various index slots. ' The lever itself swings freely on the 




WmJ%%%^^ 



Fig. 99. Combined Index and Latch 

bearing K which is a part of the stud L, fixed in the member G 
by means of the pin M. 

In operation, when the lever is moved in the direction indi- 
cated by the arrow, the pin rides up on the cam thus pulling 
the latch out of the slot until restrained by the shoulder of the 
cam at N. At this point the dog drops into the slot and the 
lever is moved in the opposite direction until the latch drops 
into place once more, thus completing the indexing. This prin- 
ciple 'can be applied on both large and small jigs, preferably 



INDEXING AND TRUNNION JIGS 



115 



for indexing from four to eight stations. All of the working 
parts should be hardened to insure long life and accuracy. 

Index Table for Drilling. In Fig. 100 is shown a form of 
indexing table which can be made up and carried in stock. It 
can be used for many purposes requiring a rapid and accurate 
index. Frequently, indexing of a number of holes is desirable 
and yet the number of pieces to be made is small, or for some 
ether reason it does not seem advisable to make up an indexing 
fixture. In cases of this kind an index table can be used to 




Fig. 100. Indexing Table for Drilling 

advantage. A circular cast-iron base A has been faced on the 
upper surface and fitted with a table B, having a center bearing 
by means of the plug C to which it is firmly screwed. The plug 
has a flange D fitted to run freely against the surface E. A 
hardened shoe F is attached to the fixture at one side. The 
lower part of the bearing plug is slotted to receive the index 
rocker G which is pivoted loosely on the pin H. The upper 
surface of the rocker is beveled to the form shown at I. This 
bevel surface acts as the index for the plate when acted on by 
the spool K. The form of this spool is shown clearly in the 
diagram L, and it will be noted that the flatted side allows clear- 
ance for indexing. A great advantage in this type of indexing 
mechanism is the fact that there is clamping action of the rocker 
against the hardened block. 



116 



JIG 8 AND FIXTURES 



In the particular instance illustrated, the device is made for 
indexing to 180 deg., but the same principle can be used for 
various numbers of index spacing by making suitable modifica- 
tions in general construction. The cam K can be operated from 
outside the fixture by means of a simple lever attached to the 
pin M. An approximation of the indexing used can be deter- 
mined by reference to the pointer at 0. The advantages of this 
device are that it is accurate, very rigid in construction and all 
the working parts are protected from dirt and chips. 

Index Fixture for Holes in a Circle. We referred to a con- 
dition in Fig. 90 in which a number of holes were drilled so 
close together that drill spindles could not be spaced close 




Through Center 



Fig. 101. Indexing Jig for a Number of Holes Close Together in a Circle 

enough to drill them all at once, and we showed a method of 
handling such a condition. The holes were arranged in rec- 
tangular form. We will now consider indexing jigs arranged 
for a group of holes so spaced in a circle that it is not possible 
to set the spindles of a drilling machine close enough together 
to drill them all at one time. 

Such a condition is shown in Fig. 101, the work being shown 
at A and the holes indicated at B. In this jig the work is set 
up and located on a central plug C and clamped in position by 
means of a C-w r asher D. It rests on the three pins E, F and (?. 
The bushings are spaced for alternate holes as indicated at E. 
The stud on which the work is located is mounted in a revolving 
plate K, supported by the base L. Indexing is done by means 
of the lever M which engages with the slots N and in a hard- 
ened plate. Another lever P is used to swing the index plate 



INDEXING AND TRUNNION JIOS 



117 



from one position to the other. This is a very good example 
of an index jig to take care of a condition such as that fre- 
quently found in the main driving shaft clutch gear of an auto- 
mobile. There are many other cases when a jig of similar form 
can be used, as the general simplicity of the construction makes 
it readily adaptable to a variety of conditions. Any one of the 
several methods could be used for indexing instead of the one 
shown. It is advisable to provide some means of fastening the 
jig down to the drilling-machine table. 



Clearance 




Fig. 102. Index Fixture for Angular Holes 

Index Fixture for Angular Holes. The fixture shown in Fig. 
102 is an indexing drill jig for a series of blind holes drilled at 
an angle in the work A. Great accuracy in the location of the 
holes is not of supreme importance, and therefore a method of 
indexing can be used which will give approximate locations but 
not to exact dimension. The index plate has a series of notches 
cut in it at B, spaced in such a way as to give the correct spac- 
ing for the drilled holes. A spring plunger C with a rounded 
end is mounted in a block so that the plunger engages the 
notches in the index plate. A weak spring should be used when 
a design of this kind is made in order that the indexing may 
be as easy as possible. 



116 



JIGS AND FIXTURES 



In the particular instance illustrated, the device is made for 
indexing to 180 deg., but the same principle can be used for 
various numbers of index spacing by making suitable modifica- 
tions in general construction. The cam K can be operated from 
outside the fixture by means of a simple lever attached to the 
pin If. An approximation of the indexing used can be deter- 
mined by reference to the pointer at 0. The advantages of this 
device are that it is accurate, very rigid in construction and all 
the working parts are protected from dirt and chips. 

Index Fixture for Holes in a Circle. We referred to a con- 
dition in Fig. 90 in which a number of holes were drilled so 
close together that drill spindles could not be spaced close 




Section Through Center 



Fig. 101. Indexing Jig for a Number of Holes Close Together in a Circle 



enough to drill them all at once, and we showed a method of 
handling such a condition. The holes were arranged in rec- 
tangular form. We will now consider indexing jigs arranged 
for a group of holes so spaced in a circle that it is not possible 
to set the spindles of a drilling machine close enough together 
to drill them all at one time. 

Such a condition is shown in Fig. 101, the work being shown 
at A and the holes indicated at B. In this jig the work is set 
up and located on a central plug C and clamped in position by 
means of a C-washer D. It rests on the three pins E, F and (?. 
The bushings are spaced for alternate holes as indicated at H. 
The stud on which the work is located is mounted in a revolving 
plate K, supported by the base L. Indexing is done by means 
of the lever M which engages with the slots N and in a hard- 
ened plate. Another lever P is used to swing the index plate 



INDEXING AND TRUNNION JIGS 



117 



from one position to the other. This is a very good example 
of an index jig to take care of a condition such as that fre- 
quently found in the main driving shaft clutch gear of an auto- 
mobile. There are many other cases when a jig of similar form 
can be used, as the general simplicity of the construction makes 
it readily adaptable to a variety of conditions. Any one of the 
several methods could be used for indexing instead of the one 
shown. It is advisable to provide some means of fastening the 
jig down to the drilling-machine table. 



Cfoarqnce 




Fig. 102. Index Fixture for Angular Holes 

Index Fixture for Angular Holes. The fixture shown in Fig. 
102 is an indexing drill jig for a series of blind holes drilled at 
an angle in the work A. Great accuracy in the location of the 
holes is not of supreme importance, and therefore a method of 
indexing can be used which will give approximate locations but 
not to exact dimension. The index plate has a series of notches 
cut in it at B, spaced in such a way as to give the correct spac- 
ing for the drilled holes. A spring plunger C with a rounded 
end is mounted in a block so that the plunger engages the 
notches in the index plate. A weak spring should be used when 
a design of this kind is made in order that the indexing may 
be as easy as possible. 



118 



JIGS AND FIXTURES 



The index plate can be mounted in either of two ways: As 
shown at D it is held in place by the two locknuts E and F, 
which are adjustable to permit regulation of the pressure on 
the bearing and adjustment for wear. A more common method 
of mounting is shown at G, where the stud is fitted so that it 
comes through the hole a few thousandths and is fastened by 
one or two nuts as shown at H and by the dotted lines K. If 
the work is to index in one direction only, one nut might be 




Fig. 103. Indexing Jig for Angular Holes in a Piston 

sufficient, providing the direction of the indexing is such as to 
tend to tighten the nut rather than to loosen it. If the index- 
ing is likely to be in both directions two nuts are necessary. 

In Fig. 103 is shown another angular jig for drilling a series 
of angular holes in an automobile piston. The work A is lo- 
cated on a stud B and drawn down against its shoulder by the 
pull back rod C which is tightened by the hand knob Z>. In 
tightening this rod a clamping action takes place on the pin E 
inserted in the wrist-pin hole. 

As the angular-drilled holes need not be particularly accurate 
in their spacing, the indexing is done by means of the ball F 
which snaps into notches cut around the plug G. The bushing 



INDEXING AND TRUNNION JIGS 



119 



In this jig is carried in an overhanging arm K which forms a 
part of the jig body L. The designer should pay attention to 
the stability of jigs of this character and should provide a base 
of sufficient dimensions so that it will be well supported. 

When several holes are to be drilled in a ring such as that 
shown at A in Fig. 104, two methods can be used. If there is 
available a multiple drill of capacity suited to the work, a sim- 
ple jig can be made so that all the holes can be drilled at one 
time. If, however, such a machine is not available, one solution 
of the problem is to use an indexing jig. The type shown 
here is exceptionally good from the indexing point of view, 



L< !ft"tffQm. 




s^ 
Fig. 104. Indexing Jig for an Annular Ring 

because there is very little chance for dirt or chips to get Into 
the' mechanism and thus cause errors in indexing. 

The work is clamped on the locating ring B by the sliding 
clamps shown at C and a bushing D is so placed that the holes 
will be located the correct distance from the center of the ring. 
Sufficient clearance must be allowed between the work and the 
bottom of the bushing at the point E so that there will be no 
difficulty in the removal of the work. The indexing mechanism 
consists of a circular plate F, in the underside of which are 
located the bushings G. The index plate is centered in the base 
H and is held in place by the two locknuts K and L. 

The index plunger M is operated by means of the lever N 
which projects out through the side of the fixture in a location 
convenient for the operator. The work can be indexed either 
by pulling it around, by grasping the ring or by means of holes 
in the index ring F. This type of jig is excellent for many pur- 



fr JIGS AND FIXTURES 

f poses and the principles shown can be applied not only to driL 
jigs but to other indexing fixtures for various machining opera- 
tions. It should be borne in mind that the class of work for 
which an index fixture is designed and the amount of pressure 
which it is called upon to withstand will affect to a large extent 
the general design and proportions of the fixture. 
Fig. 105 shows a large jig designed for use in drilling a series 




Fig. 105. Indexing Jig for Radial Rivet Holes 

of holes A and B equally spaced around the periphery of an 
automobile brake band. This jig is quite different in construc- 
tion from any of those shown previously and it may be consid- 
ered in the nature of a u horrible example." In other words it 
is something which is neither practical nor well designed, yet it 
is expensive and much unnecessary work is involved in its con- 
struction. The entire construction is very clumsy and heavy. 
A very large bearing is given to the index plate C. The index 
plate and the casting E which carries the bushing, have been 
made separate, for no apparent reason except the possibility of 
breakage while machining the casting or on account of replace- 
ment in the event of serious wear in the index plate. In addi- 
tion to these points a series of bushings A and B have been lo- 
cated around the periphery of the jig when two bushings that 
would have answered all purposes could easily have been car- 
ried on the stationary member. The only really good feature 
about the fixture is the indexing mechanism which is designed 
so that it can be operated by a foot pedal. 



INDEXING AND TRUNNION JIGS 



121 



It is suggested to the student of this book that he make 
an alternative design of an indexing jig for the same piece of 
work, employing some of the principles which have been illus- 
trated. The brake drum diameter was 14 in. and the face 3 in. 

A decided improvement on the jig shown in Fig. 105 is that 
illustrated in Fig. 106. A series of six slots containing three 
holes each, A, B and C, are spaced equally around the periphery 
of the work D. Previous to the drilling operation the work has 
been bored, turned and faced and a keyway has been cut 
at E. It is necessary to locate the various holes in relation 




Fig. 106. Indexing Jig for a Clutch Drum 

to the keyway mentioned, so the jig is made with a locater 
to provide for this. The work is slipped over the locating plug 
F and is drawn back against the hardened locating plate G by 
means of the rod H operated by the handwheel. 

Rapid removal is assisted by means of the C-washer K. The 
base L is of substantial construction and has a bearing of large 
diameter in which the locating member M revolves. The correct 
location of the various holes is obtained by means of the index 
lever N which engages in a series of notches in the outside 
diameter of the plate. The construction of the lever is some- 
what similar to one of those shown in Fig. 98. 

In general construction this jig embodies some good features 
in design and should be studied carefully. Some of the advan- 
tages are that it can be cheaply made, and can be easily ad- 



122 



JIGS AND FIXTURES 



justed for wear by simply " papering up" under the locating 
ring G and making suitable adjustments on the bearing M. 

High Production Indexing Jig. In Pig. 107 is shown an 
excellent example of a high production indexing jig for a small 
hub A which has a series of eight small holes drilled radially in 
its outside diameter. It will be noted that the indexing mechan- 
ism is similar to the one illustrated in the earlier part of this 
chapter. The base of the fixture B carries a spindle C which is 
provided with a taper plug D so designed that it will expand 
the split end of the arbor E on which the work locates. The 



Washer 



Spring 




Fig. 107. Rapid Production Indexing Jig for a Small Hub 

plug is actuated by the rotation of the threaded plug F which 
is operated by means of the hand knob G. 

Due to the fact that the work is of a nature making removal 
from the arbor difficult, the two ejectors H and K are provided. 
When the operator loosens the taper plug by means of the knob 
G a slight blow of the hand on the knob in the direction indi- 
cated by the arrow will force the work from the arbor. A slid- 
ing member is provided for the knob which permits it to act 
after the screw is tightened to the taper plug. This is done by 
means of a setscrew L which engages with a longitudinal slot 
in the outside of the plug. An additional refinement can be 
made on the ejector by using the construction shown at M. A 
coil spring is interposed between the collar N and the face so 



INDEXING AND TRUNNION JIGS 



123 



that it tends to pull the plungers back after they have been 
operated. A hardened washer also can be fastened against the 
face of the knob G as indicated at P. For small work produced 
in large quantities variations of this design will be found to 
give excellent results. 

Roll-Over Jigs. A piece of work may require drilling from 
several sides and it may be of such a size that the jig cannot 
be handled easily. The conditions may not warrant the use of 
an indexing or trunnion jig and yet the production required 
may make it necessary to design a fixture that can be operated 
conveniently and rapidly. When a jig approaches a size 8 or 10 




Fig. 108. Designs for Roll-overs 

in. square and it is necessary to drill holes from several sides it 
is often desirable to make provision for rolling over so that the 
operator will not be obliged to lift the jig or drop it on each 
side in succession. Several methods of applying "roll-overs" 
are shown in Fig. 108. A is a cast form which is made as a 
part of the jig itself, the corners B and C being rounded to 
permit rolling the jig over on either of these sides. A flat por- 
tion is provided at C to assist in loading so that the jig will not 
be wobbling from side to side when the piece is being locked in 
position. 

D shows a roll-over of practically the same form except that 
it is made as a separate piece which can be applied to the jig 
body by means of screws E. A third form, shown at F, is prob- 
ably the most useful and cheapest of all the varieties illustrated. 
It is made from a steel strip bent to the shape shown and 



124 



JIGS AND FIXTURES 



screwed to the body of the jig by means of TOO or more screws 
<?. There is very little to be said in regard to the design of roll- 
overs and the illustrations given are sufficient to cover prac- 
tically all cases. The points which should be borne in mind are 
that the roll-over must be so constructed that it will operate 
easily and at the same time not interfere with any extensions 
or lugs on the jig or interfere with loading in any way. 

In Fig. 109 is shown aa outline example of a roll-over jig of 
simple construction embodying the principles just mentioned 
The work A is located on a central stud B and by a nut and 
C-washer C. The requirements of the work are that it must be 




Fig. 109. Roll-over Jig 

drilled from the direction indicated by the two arrows. The 
bushings are shown at D, E, F and G. "When being loaded the 
jig rests on the table on the flat portions H and K. It will be 
seen that it can be readily rolled over on the curved surfaces 
L and M . 

Design of Trunnion Jigs. The tool designer should now 
have a very good idea of jig construction so that he should be 
able to decide when a trunnion or indexing jig is necessary. We 
will give here a word of caution in regard to the consideration 
of the machine capacity on which the trunnion jig is to be used. 
Be sure to select a machine of sufficient size so that there will 
be no difficulty in indexing the jig. Another matter which 
should be thought of is the balance of the trunnion when it is 
loaded. In all cases the pivot points on which the jig swings 
should be approximately at the center of gravity of the cradle 



INDEXING AND TRUNNION JIGS 



125 



when it has been loaded with the work. This brings up another 
point which should be taken into consideration, namely, the 
material from which the work is made. For example, large cast- 
ings may be made of a light metal, such as aluminum, or a 
heavy metal, such as cast-iron. 

In the design of very large trunnion jigs gearing is occasion- 
ally used to revolve the work. The gearing is operated by means 
of a crank which may be either fastened permanently to the 
fixture or made so that it can be slipped off when not in use. 




Fig. 110. Trunnion Details 

The placing of the work in the jig is an important point that 
should not be neglected and every provision should be made so 
that the operator can load the work without a great amount of 
difficulty. 

There are several well-defined types of trunnion jigs as fol- 
lows: Open or cradle type, in which the work is loaded into a 
receiving cradle and clamped in place, after which the jig is 
indexed so that the work can be drilled from the opposite side ; 
closed or box type, in which the work is drilled from several 
sides in succession ; the double trunnion type, a rather uncommon 
form, built when it is desired to revolve the work in two direc- 
tions in order to drill it from the ends as well as from the sides. 

Details of Trunnions. In Fig. 110 are shown some details 



12 e JI08 AND FIXTURES 

of trunnions in common use. Form A is a simple type having 
two trunnion bearings at B and C, the base and the two trun- 
nion bearings being cast in one piece. This type is used where 
removable plugs act as shafts on which the jig swings. In rare 
cases the shaft may extend through both holes. The use of this 
form is limited by the nature of the work and it possesses some 
disadvantages in that it must be replaced entirely in case any 
part of it should be broken. It can be used sometimes to ad- 
vantage where a cheap method of construction is desired. The 
holes at B and C can be rebored and supplied with bushings 
when they become worn ; or they may be supplied with bushings 
in the first place which would improve the construction some- 
what. 

The bearing shown at D is a common form with a cap E. It 
may be cast iron or furnished with half bushings as indicated 
at F. The bushings may be made of bronze or steel or they may 
be babbitted. All bearings on trunnion jigs should be made of 
generous proportions with plenty of stock allowed for reboring. 
An excellent way to design trunnion bearings is shown at G. 
The general form of the bracket indicated can be followed in 
many cases. Attention is called to the tongue H and the groove 
K for aligning the two brackets when they are assembled on 
the base K. In proportioning a bracket of this kind it is well 
to make the thickness of the hub L not less than half the diameter 
of the hole M, and it is usually better to exceed these propor- 
tions slightly in order to make the construction more reliable 
and to provide for emergency. 

Trunnion Jig with Cradle. In Fig. Ill is shown a very 
good example of an open trunnion jig with a cradle. The work 
A is a large casting which has been previously finished on the 
side B and is to be drilled from the same side. It would be 
difficult to load the work in an upside-down position if a plain 
jig were used. We see here the reason for the trunnion design 
as it is evident that the work can be readily placed in the cradle 
and can be clamped by a method similar to that indicated at G. 
The jig cradle is of cast iron with an index flange at D in which 
the bushings E and F are located. The trunnion is located so 
as to distribute the weight of the cradle and the work equally 
and thus make the indexing easy. The trunnions are supported 
in bearings F and (?, which have removable caps. Following the 



INDEXING AND TRUNNION JIGS 



127 



procedure shown in Fig. 103 the base G is grooved so that the 
two brackets carrying the trunnions will be in alignment. An 
end view of the bracket used is shown at H. The index pin 
K is of the removable type. It may be attached to the jig with 
a piece of closet chain. Another form of bracket which can 
sometimes be used is shown at L. This form is not as strong 
as that shown at H but for light work it will give satisfaction. 




w^%^^^ 





Fig. 111. Open Trunnion Jig with Cradle 

The trunnion jig described is very simple, yet of a form which 
is frequently used. A more elaborate method of indexing can 
be used if desired. 

Trunnion Jig with a Peculiar Index and Clamping Device. 
The example shown in Fig. 112 is diagrammatic only and is 
rather unusual in the principle of indexing and clamping. When 
drilling the work at A and B considerable pressure would be 
exerted by the drills at some distance from the center on which 
the jig is supported and it would ordinarily require a large 
index plate to give the accuracy required. Assuming that the 
work can be drilled from two sides only, the indexing portion 
or box in which the work is held as shown at C can be provided 



128 



JIGS AXD FIXTURES 



with hardened and ground parts at D, E, F and G. These 
parts must be accurately located in relation to the center H, 




W%%%%%2^^ 



N 



Fig. 112. Unusual Type of Trunnion Jig 

At one side of swinging support K, shown in detail at L, bears 
against the underside of the hardened plate D. On the other 




w/////////////////m^^ 

Fig. 113. Trunnion Jig for Cam Drum 

side the cam lever M is used. When it is desired to index the 
fixture the two levers K and M are thrown out of the way. 
After indexing, support K is thrown up into position and the 
cam lever is operated by means of the handle P thus forming an 



INDEXING AND TRUNNION JIGS 

accurate index and locking the entire mechanism securely. The 
supporting latches and cams must be of sufficient size to give the 
necessary stability to the structure. 

An example of a good trunnion jig for a large cast-iron drum 
which has a series of holes half way around the outside is shown 
in Pig. 113. The work is located by means of the finished hubs 
A and B, which rest in bearings as shown and are clamped by 
means of hinges and leaf clamps. The work is located sidewise 




VY 



Fig. 114. Trunnion Jig Requiring a Sliding Movement when Indexing 

by being forced against the stop C by the thumbscrew D. 
The index part of this jig is in the form of a cradle. The 
base of the casting E supports the trunnion brackets F and G, 
in the latter of which the index pin H is located. A connecting 
plate K carries the two bushings L and M. In locating the work 
in the jig the cradle is revolved about 45 deg. from the position 
shown which permits the work to be rolled into position without 
difficulty. 

Trunnion Jigs Requiring a Sliding Movement when Index- 
ing. Fig. 114 illustrates the trouble which may be caused by 



130 



JIGS AND FIXTURES 



not carefully considering the machine on which the work is to 
be produced. When indexing, the jig will follow the path in- 
dicated by the dotted circle, which would mean that it would 
strike the drills. The minimum height above the table to which 
the drill head can be raised is indicated at A while the clear- 
ance necessary to swing the jig is shown at B. 

One method of remedying the difficulty would be to provide 
a slide that would permit the jig to be moved out into the posi- 
tion shown by the dotted lines. Interference might take place 
in some other point, for example on the face of the column, in 
which case the same remedy would prove efficacious. 




///r///////^^^ 

Fig. 115. Principles of Double Trunnion Jig 

The diagram shown in Fig. 115 is given in order to illustrate 
the principles of a double trunnion jig and is not by any means 
intended to illustrate an actual working jig of this character. 
The wor~ can be mounted in the indexing member A, supported 
in trunnions at B and provided with a suitable indexing device 
so that it can be swung around in the direction indicated by 
the arrows. The bracket C is mounted on a cradle D which in 
turn is carried by trunnions E and F. This also is provided 
with an indexing mechanism in one or the other of the brackets 
6 or H. 

A great deal of care must be taken in the design of a double 
trunnion jig, but before designing it at all it is well to give 
a great deal of thought as to whether or i ot it is advisable to 
design such a cumbersome mechanism. Generall. speaking it 
is better to avoid using a device of this kind whenever possible. 
The principles which have been mentioned in the general de- 



INDEXING AND TRUNNION JIGS 



131 



serlptlon of trunnion jigs can be applied with, equal favor to 
the double trunnion type, but it must be remembered that there 
are movements in each direction to take care of, and there is 
considerable danger of interference when indexing from one 
position to another. However, there are a number of double 
trunnion jigs in use here and there throughout the country 
which have given satisfaction. 




Fig. 116. Example of a Difficult Drilling Problem 

A Difficult Drilling Problem. The work shown at A in Fig. 
116 is a gasoline tank filler flange which must be drilled with 
eight %6-in. holes E. The second view indicates the accuracy 
required. It is suggested that the tool designer use this example 
for practice and design a trunnion, cradle or indexing jig in 
which the various holes can be drilled. 

It is a difficult piece of work to handle efficiently and it will 
serve as a very good brain stimulus to the tool designer. He 
should be able after a review of the various points and exam- 
ples given under indexing and trunnion jigs to design a 



132 



JIGS AND FIXTURES 



creditable jig for this piece of work. It is practically impos- 
sible to design a roll-over jig or a jig with, feet at various angles 
for this piece of work due to the close approach to each other 
of the various angles. 

A condition frequently found when locating a piece of work 
which has been previously machined is shown in Fig. 117. The 
work A is located by the outside of the flange B in a locating 
ring C. Therefore, if the casting is of large size, it may be dif- 
ficult to remove the work from the ring after it has been drilled. 




"Fig. 117. Ejector for a Large Casting 

In order to assist in the removal two pins D and E are placed 
opposite each other in the indexing member F. These two pins 
are acted upon by the cams G and H which are pinned to the 
shaft K. They are locked when in position shown at L and 
take the position shown at M when in action. 

It will be seen that if the member F is the indexing member 
it is necessary to provide a means of operating the ejectors from 
outside the swinging member. This is done by pinning a collar 
N to the end of the shaft and cutting a slot across this collar as 
shown at 0. The pin P, controlled by the lever Q, is flatted 
at E so that it loosely fits the slot in the collar N. When the 
jig is indexed this slot and pin will come into alignment so that 
the pin can be revolved by means of the lever thus raising the 
ejector pins and forcing the work up out of the seat. A suitable 
stop such as that indicated at 8 is suggested in order that the 



INDEXING- AND TRUNNION JIG8 



133 



lever may always regain a certain position to make the engage- 
ment of the pin with the slot absolute. 

Trunnion Jig Used Progressively. Let us assume that a 
piece of work, held in the trunnion jig at A in Fig. 118, is to 
be drilled from three sides in sequence. It is possible to mount 
the trunnion jig on wheels and to provide a track on which the 
jig can be rolled, so that it will come successively under the 




T 






///7/////////WW 

Operation 3 Operation 1 Operation I 

Fig. 118. Trunnion Jig Used Progressively 

spindles of the three single spindle machines equipped with mul- 
tiple heads. It may be found advisable to provide suitable stops 
for the positions of the jigs. Arrangements of this kind would 
be made only when high production was desired. 

The use of the trunnion jig for progressive machining is very 
common in the modern automobile shop, however, for drilling 
cylinder and crankcase castings. Frequently as many as half 
a dozen different operations are performed on as many ma- 
chines, the jig passing along the track from one machine to the 
next as the successive operations are performed. 



CHAPTER VI 
DETAILS OF MILLING FIXTURE CONSTRUCTION 

TYPES OF MILLING MACHINES TYPES OF CUTTKIIS IMPORTANT 
DETAILS IN FIXTURE CONSTRUCTION ELIMINATION OF LOST 
TIME ELEMENTS NECESSARY IN EFFICIENT TOOL DESIGNING 
LOCATING POINTS METHODS OF (CLAMPING APPLICATIONS 
OF THE LEVER' MULTIPLE CLAMPS DESIGN AND USE OF THE 
HOOK-BOLT SUPPORTING AND CLAMPING THIN CASTINGS- - 
PRINCIPLES AND METHODS OF PNEUMATIC CLAMPING. 

As a factor in high production of interchangeable parts, the 
milling machine is of the greatest importance. With the excep- 
tion of the turret lathe and screw machine there IN no other 
machine tool which approaches it in importance to manufactur- 
ing. On account of its value as a producer, the fixtures used 
in connection with it should be of the most up-to-date character 
and should be so designed as to obtain the greatest efficiency 
from the machines to which they are applied, 

Types of Milling Machines. In order to understand thor- 
oughly the requirements of milling fixtures, it. is necessary first 
to know the various types of milling machines in order that 
their adaptability for different classes of work may be fully 
appreciated. There are a number of forms of machines* among 
which are hand-milling machines, Lincoln type, plain and 
universal, duplex, multiple spindle, vertical, continuous and 
some other varieties more or less specialized either in general 
mode of operation or in their application to particular kinds of 
work. Among the latter class are spline milling, profiling, cam 
cutting, automatic form-milling, rack cutting gear cutting and 
bobbing machines. There is also the thread milling machine 
for milling screw threads and worms. In fact, the process of 
milling is adapted to so many kinds of work that new machines, 

134 



DK'rA/l.ti OF MIUJNO PlXTVJtK CONSTRUCT fON 135 

which employ milling- as a means for removing stock, are eon- 
tinually being- developed to assist in the solution of production 
problems. 

Considered as a, machine type, there are more varieties of 
milling machines on the market than any other machine tool in 
use to-day. The engine lathe IB frequently used in small shops 
as a milling machine and many horizontal boring mills are 
arranged so that they can be used for milling as well as for 
boring. In reality, any machine having a spindle to which a 
milling cutter can be applied has possibilities in the line of 
milling, and can be adapted to this kind of work by the use of 
a sliding fixture arranged to operate at right angles to the 
spindle. 

However, we shall take up the application of milling fixtures 
to only those types of milling machines that are commonly used 
for product ion. 

Selection of Machines. The efficiency of a milling fixture 
may often be affected by the type of machine on which it is 
used. Hence it is well to consider the adaptability of the vari- 
ous machines used in milling operations in order that a judicious 
selection may be made for a given piece of work. In order to 
f am ilinrao the 1 designer with the adaptability of the various 
types of milling machines a series of diagrams Is given here- 
with* a reference to which will be of assistance in reaching a 
decision, 

These* diagrams are intended to show the particular class of 
work for which the machines are beat adapted, yet it must be 
remembered that there in no hard and fast rule, which will abso- 
lutely determine the* placing of a certain kind of work on a given 
type of machine, Many f actors have an influence in the mat- 
ter; for example, a form milling operation may be most suited 
to it Lincoln type of milling machine, yet on occasion it may be 
accomplished Hatlsfactorily on a plain milling- machine if the 
Lincoln type machine In not available. So also a key-way may 
be cut on a hand milling 1 machine or on a plain machine, and 
a Htraddlo milling operation may be clone on a hand milling 
machine. In the wleetion of machines, then, the designer must 
b governed not only by each machine's adaptability to the work 
in quwtion but ttlc> by the machines which are available. In 
an old factory thi8 matter must be carefully considered, as the 



136 



JIGS AND FIXTURES 



machines are already installed, but in planning operations for 
a new factory, where new machinery is to be bought, it is im- 



//g Ma 




Fig. 119. Type of Bench Milling Machine 

portant to select the machine most suited to the work and pur- 
chase it. 

/ Tape 

/ r 




Longitudinal Travel 
of Tabte is 4" 



Fig. 120. Another Type of Bench Milling Machine 

Bench Milling Machines. A type of bench milling machine 
which is very useful for small work is shown in Pig. 119. Ma- 
chines of this kind are often made and used for production work 



IWTAIl.ti OF MILLING P/XTUKK CONSTRUCTION 137 

various kinds, and their accuracy and compactness make them 
ry useful when groat numbers of small parts are to be milled, 
10 eoiustruetion of the machine will he clearly understood from 
i* illustration. 

Another type of bench milling 1 machine is shown in Fig. 120. 

10 arrangement of this is slightly different from the one previ- 

sly described, but it serves to show the field of such machines. 

10 feeding mechanism in this case is by means of a hand lever 

hieh operates a sector meshing with a rack on the under side 

the dovetail slide. Fixtures can be applied to the table, 

hieh is provided with a T-slot for convenience. 

Hand Milling Machines. Referring to the diagram at A in 

ig. 121, two views of a standard type of hand milling machine 

e shown. Machines of this kind can usually be purchased in 

vo sizes, both of which are driven by an open bolt without back 

wiring. They are usually provided with a two- or three-step 

we pulley in order to obtain a suitable range* of speeds. In 

>mo types the head II which carries the spindle is mounted on 

vertical slide, HO arranged that it can he moved up or down 

y means of the lover (\ to which a weight /) is often attached 

;i order to provide a gravity food. The table E has a cross 

lovemenf operated by a lever. An over-arm F is arranged HO 

hut the arbor can he given an outboard support when desired. 

Vnothor type* of hand milling machine has a spindle mounted 

n n fixed head, the table being arranged so that it can be fed 

ip and down by one lever and crosswise by another. This type 

s not hown in the diagram, but its construction will be readily 

uidorHtom!. 

The eliwH of work to which those machines are most suited 
ww'wts of key-wiiy cutting, slotting, light-facing or forming 
:-ut % ligbt strmldlo milling operations, or any other light work 
f it similar ohnruotor. The machine, not being equipped with 
hack geiitx in not nulled for any kind of heavy cutting nor is it 
adaptable to long surface cuts on account of its being a hand 
feed marbine. For work on brans or aluminum parts, which 
require high surface Bpeedn, thus type of machine is a wonderful 
producer, rapid in operation and economical in upkeep. It is 
frequently utilised for light facing cuts by using an end mill. 
Plain Milling Machines. The diagram at (I shows a plain 
milling nmohim* whieh m made, in a number of sixes suitable 



138 



JIGS AND FIXTURES 



for both light and heavy work. The smaller sizes are sometimes 
made without back gears while the larger machines are heavily 
geared and suitable for very heavy cutting. The same general 
type of machine, when adapted to very heavy cutting, is vari- 
ously termed a " manufacturing milling machine" or a "heavy- 
duty milling machine," according to the manufacturer's fancy. 
In this type of machine the spindle H is tapered at the end 



YttJb/e 




Fig. 121. Hand and Plain Milling Machine Diagrams 

to receive the arbor K, and oftentimes a cross slot in the end of 
the spindle is provided to give additional driving power to the 
cutter arbor. The over-arm L is adjustable so that it will sup- 
port the end of the cutter arbor as indicated. Additional arbor 
supports can be used midway on the over-arm to give additional 
rigidity for very heavy cutting. The table on machines of this 
type is arranged so that it has three movements: 

1. Adjustment or power feed in and out in the direction in- 
dicated by the arrows M. 

2. Hand and power feed at right angles to the cutter arbor. 



DKTA/l.N OF MllJ.lXtl FIXTURK VONtiTkUCTION 139 

;L Hand aiul sometimes power feed vertically hi the direction 
of the arrows at A". 

The table () is provided with two or more T-slots used for 
locating fixtures and clamping work. 

Machines of this type are used for slotting, straddle milling, 
face milling, gang milling, form milling, etc. The larger sizes 




r, "7?^7,m?fflffi 

Cufter 







Fig, liS'Jt, Unc'uhi Typt* and Duplex Milling Machine Diagrams 

are chiefly used in mtmufacturing in connection with milling 
fixture* for heavy cutting, and can be adapted for many kinds 
of work, Tin 1 over-arm can lie dispensed with for work when 
an end mill IK nwul like that nhown at V. Also a large inserted 
tooth mill can ho applied to face a piece of work as at Q. 

Lincoln Type of Milling Machine. One of the oldest forms 
of millmK mwhiwH in the Lincoln type, a diagram of which is 
nhown in Fig. 12*2. Thin machine is quite different from the 



140 JIGS AND FIXTURES 

others mentioned, as the table has no vertical adjustment. An 
adjustment to the spindle permits this to be set vertically within 
certain limits. Referring to the illustration, the cutter arbor A 
is held by a taper in the end of the spindle B and is drawn back 
tightly by means of a threaded rod passing through to the other 
end of the spindle. The cutters must be set in relation to the 
work by means of spacing collars on the cutter arbor A except 
when the table has longitudinal adjustment. Machines of this 
kind are built in several sizes, all of which are provided with 
back gears and power feed. They are intended principally for 
forming cuts, gang milling, heavy straddle milling and slotting. 
Their general construction adapts them for use on long work of 
such a character that the cut is continuous from start to finish. 
Vises with special jaws are frequently used on machines of this 
kind for military rifle parts, sewing machine parts and many 
other conditions requiring continuous and formed cuts. 

Duplex Milling Machine. In general manufacturing it is 
often necessary to face off two or more surfaces on opposite sides 
of a casting or forging. For conditions of this kind the duplex 
milling machine, a diagram of which is shown at C in Fig. 122, 
is of great value. Machines of this type are provided with two 
spindles, D and E, which are adjustable towards each other and 
sometimes vertically. Provision is made for heavy cutting by 
means of back gears in some types, while others are driven by 
an open belt on a two- or three-step cone pulley. The machines 
are made in several sizes for both light and heavy work. 

The class of work to which machines of this kind are best 
adapted is shown by the work F in the illustration, but in the 
smaller sizes they are useful for slotting or facing bosses on oppo- 
site sides of light castings and other work of a similar nature. 
Many cases are encountered when work can be done by their 
assistance which would require two operations on some other 
type of machine. 

Vertical Milling Machines. Machines having a vertical spin- 
dle, adapted to hold milling cutters, are made in several sizes 
by a number of manufacturers. We are not particularly inter- 
ested in the various types, as these are much the same in gen- 
eral construction, although some have more refinements and con- 
veniences than others. Generally speaking, the spindle is driven 



N OF Mll.LlXU FIXTURK CONSTRUCTION 



141 



by means of gearing except in the machines intended for very 
light work, la some types an accurate vertical adjustment to 
the spindle with a convenient method of setting makes it pos- 
sible to mill .several heights of work one after the other without 
disturbing the height of the table during- the process. By the 
use of size blorks and the adjustment mentioned very accurate 
work can he produced in this way. 

Fig. 12:! shown a diagram of a vertical nulling machine at A, 



Cutter. 




Fig, llJtt. Wrtlrtd, C'ntttimiouH arid Multi Hpimllo Milling Machines 

with n largo uwrrted tooth cutter It, in use for surfacing the 
work ('. The* tithie /> is provided with power longitudinal feed 

and occasionally with power cross and vertical feeds also. Ma- 
chines an* arranged to give it variety of feeds in both directions 
on mte imtchimH, while in others the longitudinal feed to the 

table is the only one. Adjustments are always provided, how- 
ever, for rawing and lowering the table and moving it in and 
out. The tonjdtucUnal feed is the most used, although the others 
are occasionally required and are very useful at times. 

The work to which thene tools are best adapted is the facing 

of large ciwtingH, such a flange's, transmission cases, etc., al- 



142 JIQS AND FIXTURES 

though in addition to this work they are suitable for cutting 
shoulders, some kinds of forming, undercutting flanges and 
many other operations. They can be run at high speed and 
as a consequence are often used for aluminum and brass 
work. 

Circular Milling Attachments. The vertical type of milling 
machine can be supplied with a circular table having power 
rotary feed, which is useful for continuous or circular milling 
operations. A diagram showing the application of this attach- 
ment is shown at E in Fig. 123. The table can be furnished 
with multiple fixtures to hold a number of pieces which are to 
be milled. In the case shown the table revolves as indicated by 
the arrow, and the work F is loaded and unloaded by the 
operator without stopping the machine so that the cutting opera- 
tion is practically continuous. The economy effected by the use 
of multiple fixtures of the rotary type is dependent upon the 
shape of the work to be milled, the method used in setting up 
the work and the amount of space between the pieces. In other 
words, as the rotary feed of the table is continuous, the cutter 
should be producing chips practically all of the time. Conse- 
quently it is not profitable to make continuous rotary fixtures 
for work of such shape that the pieces cannot be set close to- 
gether or when the cutter will be "cutting air" a good part of 
the time. 

Multiple Spindle Milling Machines. When one or more 
spindles of a milling machine are arranged horizontally and 
others are set vertically, the machines are called "multiple 
spindle." The common form shown at G has two spindles, E 
and K, in a horizontal plane and opposite to each other and two 
additional spindles, L and M, arranged vertically. The hori- 
zontal spindles usually can be adjusted vertically and towards 
each other within certain limits, while the vertical spindles are 
provided with both lateral and vertical adjustments. The work, 
N and 0, can be faced on top and at the sides in the same set- 
ting, and fixtures can be so arranged that a number of pieces 
can be set up so as to make the operation very nearly continu- 
ous. The table P may be fed by rack and pinion, screw and 
nut or angular worm and rack, according to the practice of the 
various machine tool makers. Machines of this type are very 
powerful, are suited to heavy manufacturing and may have as 



DETAIL** OF MILLING FIXTURK CONSTRUCTION 143 

many as seven spindles in some eases. The table P is often very 
long so that it will contain a number of fixtures if desired. 

Machines of this kind are generally used for facing the top 
and sides of castings. They are high production tools for which 
it is customary to make multiple fixtures holding a number of 
pieces. 

Indexing Milling Machines. In order to facilitate the mill- 
ing of certain kinds of work and to make the operation very 
nearly continuous and thus avoid loss of time both for the op- 
erator and the machine, an indexing milling machine has been 
developed, as shown in outline in Fig. 124. This machine 




^ 
Fig, 124. Indexing Milling Machines 

fa provided with a rotary table indicated in the diagram at A. 
On the table two slides are mounted at B and C in such a way 
that they can be indexed if desired. Assuming that a piece of 
work shown at /> is to be machined, it would be loaded into the 

fixture* in the loading position as indicated in the diagram. 
While the loading operation is going on another piece of work K 
in being 1 machined. It will be seen that the only time lost on 
a machine of this kind is the amount necessary for indexing 
from otii* pomtion to the other, so that the operation is very 
nearly continuous. 

The machine is of rigid construction and is provided with 
feeds suitable for heavy cutting. There are many eases when 
machines of this kind can be used on straddle milling work, 
grooving, or surfacing in order to increase production. 

It is advisable for the tool designer to provide himself with 



144 



JIGS AND FIXTURES 



data showing various dimensions of importance on milling ma- 
chines. These diagrams can be made up in a form like that 
shown in Fig. 125. There is practically all the information 
given that the tool designer needs when designing a milling fix- 
ture for use on this particular type of machine. It is not neces- 





f 




. 




4 








\ 








Fig. 125. 



Ore raff Length 

Working Length of 7ab/e-< 

LongitadfnaJ Feed of Table -471% 

Diagram of Milling Machine Showing Dimensions 
Necessary for Designing Fixtures 



sary to make diagrams of this kind in great detail, but maximum 
and minimum dimensions are important, as they show the range 
of the machine. Dimensions of T-slots and spacing of the same 
together with table dimensions are important. 

Selection of Milling Cutters. Various kinds of work require 
cutters of different kinds in order to produce the work to the 
best advantage. In the selection of these cutters the tool engi<- 



1>KTA/LN OF MILLING FIXTURE CONSTRUCTION 



145 



neer must be governed by the kind of material which is to be 
cut as well as the* form of the cut. Fig. 126 shows a number 
of milling operations with the cutters most suitable for each par- 
ticular piece of work. The work A is made from steel, and it is 






sfl 



*.' 



L 





*-' s, 

LN 







1 


* 1 


t 
\ 

\ 




\ 




' 


^^^^Ju^ 






-r^nr7TT-fpr77 








,' ' '< 


tumaam 
**-*. 







Fig, lii. Application of Milling Cutters 

to bet HurfamL AHHumitig it to bo a forging, a spiral cutter 
like that nhown t K would le suitable, for the work. This cutter 
would him* tlu* variotw teeth nicked alternately in order to 

4 *brcak the chip* 1 if the cut were to be a very heavy one. 
This work (J m of <*at.-iron arid is to be slotted at D. For work 



146 JIGS AND FIXTURES 

of this kind a side milling cutter should be used, such as that 
indicated at E. The work shown at F is of cast-iron and is to 
be faced as indicated. This work, being of large size, can be 
cut to best advantage with an. inserted tooth cutter like that 
shown at G. Another method of milling a slot in cast-iron is 
shown at H. This work might be done by using an end milling 
cutter K. In connection with the use of this type of cutter for 
machining a slot it is well to note that the cutter should be 
smaller than the slot which is to be machined, and two cuts 
would usually be necessary to finish the slot to the required 
width. 

The work shown at L may be of cast-iron, bronze, aluminum, 
or steel, but in any one of these cases the straddle milling cut 
shown would probably be done by means of the two side milling 
cutters, M and N. For the shoulder work shown at two side 
milling cutters, P and Q, would be found suitable. It would be 
necessary to relieve the face of the cutter Q so that cutter P 
would lie close against it and slightly within the edge of the 
teeth on the Q cutter. 

For forming a piece of work such as that shown at R a form 
milling cutter 8 would be required. Cutters of this kind are so 
made that they can be ground on the edges of the teeth without 
losing their form. The T-slot shown at T must be machined by 
what is termed a T-slot cutter as shown at U. The slot V is 
machined first by means of a cutter similar to that shown at If, 
after which the T-slot cutter is used. 

Other Forms of Milling. Fig. 127 shows several other va- 
rieties of milling cuts for which special machines are used. The 
work A is a shaft in which it is required to cut two splines of 
the form shown at B. These splines must be directly opposite 
each other and in the center of the shaft. For work of this kind 
a double head machine with adjustable spindles at C and D is 
commonly used. This machine is termed "a spline milling ma,- 
ehine." The type shown can be so adjusted that both cutters 
are working to the same depth, or they can be adjusted so that 
one cutter is withdrawn while the other continues to cut until 
it has passed by the center of the shaft being milled. In this way 
a slot can be readily produced entirely through a given piece of 
work. Machines of this kind are semi-automatic in their action, 
the work being reciprocated to a length determined by the length 



IWTMI.N Of Mll.MXd FIXTURE CONSTRUCTION 147 

of the spline, the cutter he ing fed into the work at the end of 
each stroke. 

Another type of machine for cutting splines is shown at E. 
The work F has a single spline cut at which is machined by 
means of an end mill in the head //. This type of machine is 




x 




k~B~ 




Fig, 1*27, 



Application* of Milling Cutters 



provided with a iwi profit ting motion and an automatic feed 
for the Hitter at the end of eah stroke, 

In the prndut'tum of th waded work a special type called a 
thread milling miifhine w frequently iwod. 'For some varieties 
of titrc*a(!M a holt <titter can he HKCH! like that shown at K while 
in other ^nmm a single cuttor like that at L may he utilized* In 
using the hob cutler cue revolution of the work M will produce 



148 



JIGS AND FIXTURES 



a completed piece. In the other case the work A T would need to 
be revolved as many times as there are threads. 

For very heavy Acme or square threads the thread milling 
machine is very useful, and it is utilized also for threading shafts 
such as lead screws. The work obtained by this method is very 
accurate and uniform in quality. 

Spur and spiral gears are often cut on gear cutting machines 
or gear hobbing machines. Splined shafts like that shown in 




Fig. 128. Contour Cutter Sizing Chart with Teeth Set Off 6 Degrees 

the section at are also made on a hobbing machine of this type. 
The work P, which is a spur gear, would be mounted on an arbor 
Q in a gear hobbing machine, and the teeth would be cut by 
means of a hob as indicated at R. In operation the gear is con- 
tinually revolving, and the hob cutter gradually passes through 
one or more gears according to the size and general shape of 
the blanks. Suitable feeds are provided, and the machine is also 
furnished with a knock-off which can be set so that the machine 
will be stopped after the work is finished. 

There are many other milling machines of more or less spe- 
cialized forms, some of which are used in the manufacturing of 



DETAILS OF MILLING FIXTURE CONSTRUCTION 149 

certain kinds of work. As these machines are so highly spe- 
cialized, it is not advisable to attempt a description of them be- 
cause they are seldom required by the tool engineer when work- 
ing out production problems. 




Dia.ofCuiier 


NaofTeeth 


A 


B 


C 


D 


E 


F 


G 


Dia.ofPi'ns 


5 


14- 


*h 


.156 


1% 


.261 


% 


'/4 


7t 


S /I6 


6 


16 


5k 


.209 


? 7 /l6 


.314 


% 


>/4 


% 


5 /i6 


7 


i8 


&k 


.230 


2 7 /8 


.366 


3 /4 


% 


/ 


% 


8 


20 


l ! /z 


.282 


3 3 /8 


.418 


% 


% 


/ 


% 


3 


22 


8% 


.334 


3% 


.470 


3 /4 


% 


/ 


% 


JO 


24 


9 3 /8 


.355 


4 9 /3? 


.523 


% 


% 


l r /8 


7/6 


II 


26 


10% 


.408 


4 ?5 /32 


.575 


% 


% 


l f /8 


7 /iB 


12 


28 


11% 


.460 


5%2 


.627 


% 


% 


l'/8 


7/6 



Fig. 129. Inserted Tooth Milling Cutter with Staggered Blades 

Cutter Sizing Chart. A contour cutter sizing chart is shown 
in Fig. 128. This chart is convenient for use in designing mill- 
ing cutters. The number of teeth varies according to the diam- 
eter of the cutter, and in this example all teeth are set off 6 
deg. Variations can be made to suit conditions, but the chart in 
itself will be found useful as a guide in obtaining properly pro- 
portioned cutters. 



150 



JIGS AND FIXTURES 



Fig. 129 shows a chart for inserted tooth milling cutters hav- 
ing staggered blades. In this example the blades are set over 
alternately as indicated. This makes it useful in sizing a slot 
or something of this sort. The various dimensions given will 
be found useful in proportioning cutters of this kind. 




OiajrfWer Ho-ofTeeUt 



& 



IG 



5k 



ToSuif 



.3/4 



18 



Vk 



ToSuit 



? 7 /8 



?0 



ToSuit 



3% 



.418 



8% 



ToSuit 



.470 



3/4 



3 /8 



10 



?4 



ToSuit 



.523 



J!/i_ 



26 



To Suit 



4% 



.575 



7 /l6 



1? 



Zd 



ToSuit 



.627 



Fig. 130. Inserted Tooth Milling Cutter with Solid Body 

Fig. 130 shows another type of inserted tooth milling cutter 
made with a solid body as shown. This type of cutter is de- 
signed primarily for face milling, and the body screws directly 
on to the spindle. The proportions and various dimensions 
given will be found useful in proportioning cutters of this kind. 

Fig. 131 shows a chart of straight side inserted tooth milling 
cutters. This type of cutter is designed for use on an arbor. 

Fig. 132 shows another type of inserted tooth cutter designed 



DETAILS OF MILLING FIXTURE CONSTRUCTION 



151 



for face milling. This can be made up in solid form as shown 
and applied to the spindle in some convenient manner. The 
blades are set at an angle in this example. 
Important Points in Design of Milling Fixtures. In the 



D/a. 




Dia.ofPfns 



14 



.136 



Ityie 



.261 



16 



5 l /2 



.JQ9 



2% 



,314 



18 



.210 



2 7 /8 



.366 



20 



.262 



3% 



418 



22 



.3/4 



.470 



10 



24 



9% 



.335 



.523 



/'/* 



7/6 



26 



10% 



.388 



.675 



12 



29 



11% 



.440 



.27 



Fig. 131. Standard Straight Side Inserted Tooth Milling Cutters 

design and construction of milling fixtures, the following points 
should be carefully considered: 

1. Production Required. This is an important factor, as the 
number of pieces to be machined should influence the design of 
the fixture to a great extent. Simple fixtures should be made 
for work which is machined only in small quantities, while for 
high production work the best type of fixture should be de- 
signed. 



152 



JIGS AND FIXTURES 



2. Dead Tim 3 on the Machine. In analyzing a production 
problem in which the milling machine is to be used, the dead time 
on the milling machine should be reduced to a minimum in order 
to obtain the maximum efficiency of the machine. The milling 
fixtures should be so designed that there is as little time lost as 
possible during the loading and unloading of the fixture. In 
very high production work it is frequently desirable to make up 




%a.of&rHer 


MatfTeefh 


A 


B 


c 


D 


I 


F 


G 


D\a.oi?ms 


2 l /2 


d 


?'/8 


ToSui+ 


/3 //6 


.131 


'/2 


l /4 


3 /4 


l /4 


3 


10 


?'/? 


ToSuit 


/ 


.158 


'I? 


r /4 


3 /4 


f /4 


3fc 


10 


3 


ToSufr 


l'/4 


J84 


'I? 


'k 


3 /4 


74 


4 


IZ 


3fe 


ToSuft 


iViB 


.210 


'k 


l /4 


7 /8 


'/4 


4k 


12 


4 


ToSuit 


/% 


.236 


'k 


'/4 


% 


'/4 


5 


14 


4'/ 2 


To Suit 


/'% 


.263 


% 


y+ 


% 


% 



i Fig. 132. Standard Inserted Tooth Face Mills 

fixtures that permit one piece of work to be inserted and clamped 
while the other is being machined. 

3. Accuracy Required. When work is to be milled within a 
tolerance of 0.001 in., it is frequently necessary to make provi- 
sion for both roughing and finishing cuts. As a rule two fixtures 
should be made for work of this kind, each one being provided 
with suitable set blocks for setting the cutters to the required 
sizes. 

4. Rigidity of Fixtures. There is no operation in manufac- 
turing in which rigidity is as important as in milling. Weak- 



DETAILS OF MILLING FIXTURE CONSTRUCTION 153 

ness tends to develop "chatter," which is injurious both to the 
cutters and to the machine. Care must be taken in the design 
of milling fixtures to make sure that there are no weak points 
and that all portions are well ribbed to withstand cutting strains. 

5. Safety of the Operator. The importance of designing 
milling fixtures so that the operator will not be endangered 
during the process of loading and unloading the work cannot 
be over-emphasized. The operator's hands should not approach 
the cutters closely. The position which the operator is required 
to take when using the fixture must be studied so that there is 
no chance for injury due to lack of attention. 

6. Chips. As the milling machine is a great producer of 
chips, attention should be paid to the cleaning of the fixture, 
and clamps, locating surfaces, and other important parts should 
be so designed that chips will not interfere with their proper 
functioning. 

7. Set Blocks. All milling fixtures should be provided with 
set blocks so arranged that the cutters can be set in correct re- 
lation to the work. A size block or "feeler" can be interposed 
between the cutter and the set block when making adjustments. 
If all fixtures for milling are provided with set blocks the ac- 
curacy of the work is assured, and resetting after grinding the 
cutters is very easily done. 

8. Selection of Machines. The selection of the machine best 
suited to work requires judgment, knowledge of conditions, and 
a list of machines which may be used, as well as an understand- 
ing of the best type of machine for the work in the event that 
new tools are be purchased. Although the choice of machines 
may be limited, the selection should always be made with a view 
to economy in production. 

,9. Upkeep of Fixtures. Fixtures for high production work 
should be so designed that replacement of locating parts, studs, 
clamps and other parts can be readily made. It is very neces- 
sary to provide a suitable method of fastening the various units 
to the fixture in order to facilitate their removal and replace- 
ment when worn. 

10. Material To Be Cut. The kind of material to be ma- 
chined affects the design of the fixture to some extent, due to 
the fact that cast-iron or other cast work such as aluminum 
and brass can usually be cut faster than such material as alloy 



154 



JIGS AND FIXTURES 



steel. Therefore, the kind of material and the speed and feed at 
which the job will run have to be considered in planning mill- 
ing fixtures. 

Cutter Action on the Work. A piece of work being milled 
is subject to two forces, viz., the feed and the cutting action. 
The combined result of these two forces tends to move the work 
out of its position, hence it must be resisted by the fixture and 
the clamps which hold the work. Due consideration must there- 




Wrong Right 

Fig. 133. Diagrams Illustrating Cutter Action 

fore be given to the manner in which the work is held in relation 
to the feed and also to the cutter. 

Fig. 133 shows a piece of work at A in which a slot B is being 
machined. The feed of the table is in the direction of the arrow 
C, while the cutter revolves as shown by the arrow D. The 
action of the cutter tends to pull the work toward it, which is 
very bad practice for the reason that any lost motion in the 
feed screw of the table will cause " chatter" in the work; also 
the work tends to "crowd" into the cutter teeth so that the 
cutting action is not good. "When the work is fed in the same 



/<' MILUSU 



u CONSTRUCTION 



155 



direction (' with the cutter revolving in the direction F, there 
Ls no "chatter" and the teeth of the eutter attack the work in' 
the proper manner. 
The work (! Is being fed in the direction of the arrow If, while 



V^Wy-a 


D "*t ;> 


/^J7\ 


'**\ / 

4 ,.*v 




'**"" 


<- A > 



an 



Work 



\ 

V, 

\ X 




Fig, 134. Action of Cutter Teeth 

the eutter in revolving a.s at K. This is incorrect because the 
cutter action tends to lift the work and may therefore be acting 
atfttmut the damps which hold it down on the fixture. It may 
even lift the table itaelf unless the gibs are adjusted tightly. 




Wrong 
* 



R0ht 



Fig. Kir. CuUi*r Action in Relation to Clamps 

When the* cutter h revolving in the direction M, the pressure? 
of th cut in rwite<i hy the* ntability of both the fixture and 
the table, 

Fife. 1W flhows n IHJJT A which in to be slotted as indicated 
at /I. Vnlmn i-iire in imecl in the selection of the cutter, a con- 
dition like that rthowii In the cutter C may be found. This eut- 
ter has teeth /> ipiiced RO far apart that not more than one tooth 



156 



JIGS AND FIXTURES 



is in action on the work at the same time. If the feed is coarse, 
"considerable "chatter" and poor work may result. 

It is much better to select a cutter having teeth spaced closer 
together as indicated at E, so that there will be several teeth in 
action on the work at the same time. 

In designing milling fixtures it is not generally considered 



DE 




Fig. 136. Trouble Caused by Chips 

good practice to clamp the work in such a way that the cutting 
action is against the clamp. Fig. 135 shows the work A held in 
a fixture B, by means of a clamp screw C. The direction of the 
feed D and the rotation of the cutter E both force the work 
against the clamp screw. This is very bad indeed and should 
be avoided. 

At F the work (? is firmly clamped against a solid shoulder 
of the fixture H by means of a rocking clamp K operated through 



Il^ OF MILLING FIXTURE CONSTRUCTION 157 

the threaded rod L. The thrust of the cut is then taken by a 
solid wall of metal and there is no possibility of "chatter." 

Provision for Chips. Milling' cutters produce chips very 
rapidly and in largo quantities. Therefore milling fixtures 
should be designed so that locating surfaces, clamps, screws and 
other devices will not become elogged with chips so as to inter- 
fere with their proper working. Fig. 136 shows an equalizing 
lever A, eonneeted to two rods K and C which pass through the 
holes /> and K in the body of the milling fixture F. The open- 
ings around the rods 'permit chips to fall through and accumu- 
late at <) and //, resulting eventually in interference with the 
action of the* levers. The holes should be covered in order to 
prevent this accumulation or else the fixture should be arranged 
o that it can be readily cleaned. As a milling 1 fixture is always 
bolted down to the 1 table in a fixed position, provision for clean- 
ing should not necessitate 4 its removal from the table. Openings 
in the side of the* fixture can be made but it is better to prevent 
the chips from entering and thus do away with the necessity 
for cleaning. 

At K i shown a locating stud with a groove at / into which 
chips or dirt may drop so that work located on the plug will 
seal itself properly. This is very bad indeed as after a time 
the groove fills up with chips and dirt which have to be cleaned 
out frequently to allow the work to locate properly. M is an 
adjustable, threaded member in a fixture base. This also should 
be avoided as far IIH possible because chips will eventually work 
into the thread and make it difficult to operate. 

The locating block N is relieved at in order to ensure cor- 
rect location of the work /*. This design is open to the same 
object ions an the example K. 

The type of adjustable V-block shown at Q is most annoying 
to an operator, as the chips get in to the elongated slot and also 
under the block causing it to rise us shown at R. 

Design of Milling Fixtures. There is some difference of 
opinion as to whether a well-ribbed milling fixture will give as 
satisfactory results as OIK* which is made of very heavy section 
cant iron without ribbing. Those advocating heavy sections 
without ribbing claim that the solidity of the metal in a heavy 
milling fixture tends to lemen vibration and thus give better 
results than a ribbed milling fixture. The writers believe that 



158 



JIGS AND FIXTURES 



a well-ribbed milling fixture of substantial section will answer 
the purpose in nearly all eases although for extremely heavy 
cuts a good body of metal is desirable. 

Fig. 137 shows at A a solid base plate of cast iron on which 
a built up fixture can be placed. The illustration B shows a 
similar, though heavier plate. The latter would be better de- 
signed as shown at C, with the mass of metal reduced and the 
sections strengthened by the use of ribbing. The view at D 
indicates the position of the various ribs. The ribs of a fixture 





! 



Fig. 137. Design of Fixture Bases 

of this type should be so proportioned that there will be no 
tendency to "buckle" and thus cause vibration while a cut is 
in progress. 

Details of Construction. Fig. 138 shows a corner wall A 
which has been made to a large radius in order to give maximum 
strength. Square corners on castings and sections of unequal 
thickness should be avoided. B shows a square corner which is 
likely to crack at the points shown, due to strains set up by 
unequal cooling in the foundry. 

The diagram at C is given in order to emphasize the fact that 
all castings should be so designed as to allow for "draft." Draft 
is not necessary to the casting, but the pattern has to be tapered 



IWTAILK QF MILLING FIXTURE CONSTRUCTION 159 

so that lifter the mold is made, the pattern can be removed from 
the sand without injuring the moid. And as the pattern is a 
duplicate of the fasting, the necessary draft is included in the 
design of the casting. The amount of draft necessary varies 
from 4 in. to \ in. per foot. It is advisable to show the draft on 
deep Hustings as indicated at I) and E. 

Where bosses are provided on castings it is well to make them 
larger in diameter than appears necessary, in order that the 




' Strength 




>jf ff 

hi 






J 


1 




-J 
sBtjshincf 










*" " / 


H 


I 

f 


t 




j ^ 


" " 



Fig. 1*18, 




of Construction 



location of holes in tin? bcmaen may not be seriously affected by 
variations in the canting. Also when bosses are used as bear- 
ing^ it is advisable to mako them large enough so that they may 
be* bushed for wear as indicated at I<\ There is nothing much 
more annoying to a toolmaker than to find insufficient allowance 
for stock on a boss, so that the hole is not central with the boas, 
allowing a shouldered stutl to lap over the edge. 

Uniformity of Ribs and Walls. In order that the castings 
used for fixture* work may bo sulwrtantial and not subject to 
cracks due to unequal cooling, uniformity in the sections should 
be preserved an far as possible. Fig, 139 shows a section A in 



160 



JIGS AND FIXTURES 



which the walls B, C, D, E and F are all of uniform thickness. 
A fixture designed in this manner will be free from, defects or 
cracks in the metal which are often caused by unequal cooling. 
The correct design of ribs is an item which should be given 
the most careful attention. It is not uncommon to see an an- 
gular rib like that shown at G when there is no good reason for 
making it so light A rib like that shown at H -ill withstand 
pressure very much better than the other one. 




Fig. 139. Uniformity of Kibs and Walls 

In the case shown at K, the rib L has very little value; yet if 
it were to be made as at M it would give stability to the con- 
struction and add to the general rigidity of the fixture. 

U-Lug Design. A milling fixture must be bolted to the table 
on which it is used, therefore a means of fastening must be 
provided so that it can be quickly adjusted when removing or 
replacing it. In Fig. 140, A shows a good construction for 
U-lugs. Lugs made to the outline shown by the dotted line at 
B develop a very weak section at C. By designing the lugs as 
indicated by the full lines at D and E, greater strength is ob- 
tained and there is less likelihood of breakage. U-lugs are 



DKTAlLti OF MILLING FIXTURE CONSTRUCTION 



161 



usually cored at F and the cored dimensions should be not less 

than ho larger than the T-bolt used to hold the fixture down. 

A key slot (t is provided for locating the fixture on the table. 

In proportioning the outlines of the boss //, it is well to make 




Ing. 140, Il-Lug Doaign 

each aide of the finished portion at least one-half the distance F 
and even more than this Is not objectionable. The depth K 
should always h from one and one-half to two times the dimen- 
sion F. 




Fig, 141. T-Blots and Keys 

IMugH shoultl not be net in too close to the body of the fixture 
HH hulicatccl by the dotted lines at L. It in much better eon- 
Htructicin to inako the distance M at leaat as much as the dimen- 
Hion F. When this IH clone a large fillet can be used at JV thus 
giving additional strength to the fixture. 



162 



AND FIXTURES 



T-Slots and Keys. Milling fixtures are located on the tables 
of milling machines by means of rectangular keys which fit the 
T-slot A in Fig. 141. A common form of key is shown at B. 
The dimension C is made to the size of the slot in the milling 
machine table. The length of the key D is generally from 2 to 3 
times its width. 

As milling machine table slots vary from -} in. to -J in. with in- 
termediate sizes, it is often desirable to make fixtures transfera- 




Fig. 142. Set Blocks 

ble from one machine to another. To provide for such a condi- 
tion, the keys can be made as shown in the illustration at E. 
This type of key is so proportioned that it can be used to fit a 
slot having a width as shown at F and it can also be reversed 
and used to fit another slot like that indicated at G. An ar- 
rangement of this kind is of great advantage where a number of 
milling machines having different size slots are to be used in 
production. 

Set-blocks. In order to make sure that cutters are set in the 
correct relation to the work on a milling fixture, it is essential 
that each fixture be provided with suitable set blocks. 



IWTA11.K OF A! UMNO FIXTURE CONSTRUCTION 163 



ng that the work A shown in Fig. 142 is to be ma- 
chined at , a hardened net block C should be provided. In 
setting the cutter to the correct depth a "feeler" D is inter- 
posed between the cutter and the set block C. The thickness of 
"feeler" can lie standardized and suitable allowance made be- 
tween the top of the set block C and the depth of the cut de- 
sired. 

In the example # the work is to be finished on the surfaces 
F and (} and it is, therefore, necessary to provide set blocks 
at // and A" HO that the feeler L ean be interposed *us indicated 
in order that the cutter may be accurately set, both vertically 
and horizontally. 

In considering methods iLsed in the location of work in mill- 




Fig. 143. Mftthod* of Bracing Work 

ing fixtures attention must be paid not only to the position of 
the locating: 8urfae, but also to their accasnibility for the pur- 
pOHe of cleaning. In addition to these points the thrust of the 
cutterH and their action on the work must also be given con- 
siderable attention HO that proper provision will be made for 
remitting thm aetion. 

Fig. 14! *ihowH a piece of work A which is being fed in the 
direction denoted by the arrow against the milling cutter B 
which IH revolving w indicated. The work locates on a plate C 
and against a block I) but it will be noted that the portion which 
i being cut lien in a plane considerably above the block D which 
takt8 tin* thruHt. Thw IH not good practice and much better re- 
sults would be obtained by making the block as shown at E. 
Hero the work in supported directly in line with the thrust of 
the cutter* 



164 



JIGS AND FIXTURES 



Locating and Supporting Work. It is often necessary to 
locate a piece of work from a finished surface such as that shown 
at A in Fig. 144, and also by means of a hole in the same plane 
but higher up as shown at B. When a condition like this is 
found it is essential to provide a "float" to one member or the 
other in order to take care of slight inaccuracies in machining. 
In the particular case shown the work locates on a central stud 



^,' 

^////////>7//^///fa'-'Work. 




Work 




Fig. 144. Locating and Supporting Work 

C, on the plate A, and by means of a plug D mounted in a ver- 
tical slide E. 

If no provision were made for errors in machining it might 
easily be possible to set up the work and obtain a result similar 
to that shown at F in which the work locates on the plug but 
does not seat itself properly on the plate at A. As cases of this 
kind are frequent, provision should be made for variations either 
in the manner shown or by some other means equally good. 

The work G is a thin collar mounted on a locating stud H in 
order to mill the. slot across the top as indicated at K. It is 
very easy to support the work while milling so that the slot on 



!.** OF MILLING FIXTURE CONSTRUCTION 



165 



the side at L will be backed up well, but the opposite side M 
will have a tendency to open up when the cutter machines it, 
with a result like that nhowu at N. The designer should always 
hear this in mind when making a fixture for a similar piece of 
work and .should provide support at the points where the eutter 
finishes its work. 

Clamps Used in Milling. In the chapter on the design of 
drill jigs, various elamps are shown which are used to some ex- 
tent in all kinds of fixtures. Exceptional cases may require 
slightly different methods of clamping due to the requirements 




Fig. 1-15. VarlwiH TypOH of MilliiiK-C 



of ihtf work. The method of holding a piece of work for a mill- 
ing operation is one of the most important things in connection 
with the design of the fixture, and HA a consequence the elamps 
nhoutd be very Hulwluntial and should be applied at the proper 
pointH in order to obtain the boat reaultH. 

Several varietioH of clumps are shown in Fig. 145. The work 
A is loeated on a hardened plata B and is clamped down by 
meaiiH of thf ntriip dump Bhown at 0. This clamp is slotted 
at I> to permit it being withdrawn from the work by means of 
the pin K which net* an a handle, A Blotted clamp of this sort 
w likely to become* clogged with chips and, therefore, a suitable 
cover fihould be placed over the Blot, A braMng V can be made 
so that it fills thcs hole ff occupied by the spring Tl thus pre- 



166 JIGS AND FIXTURES 

venting the chips from accumulating around the spring and 
interfering with its action. 

The clamp K is used for holding the work down when a clamp 
on the top of the work would interfere with a cutter used on 
the entire upper surface. This type of clamp thrusts against 
a solid shoulder L and the action of it in clamping tends to sink 
the point M into the edge of the work and at the same time hold 
it down. It is advisable to make the point M rather " stubby " 
so that it will not become dulled too easily. A clamp of this 
kind is useful when it is difficult to clamp the work in the 
ordinary way. It is possible to adapt it to a number of condi- 
tions to suit particular cases. 

A swinging leaf clamp can be used to advantage in holding 
a piece of work such as that shown at 0. The work locates on 
a hardened plate P and is clamped by means of the screw Q 
which is held in a swinging clamp R. A leaf -type of clamp is 
sometimes found necessary in milling fixture design and the 
principle shown here can be applied if needed. 

A rather peculiar type of clamp for work which cannot be 
clamped in the regular way, is shown at 8. This clamp has a 
knife-edge at T which sinks into the work and at the same time 
clamps it down. The thumbscrew U has a wear plate under the 
point as shown at V. It is of the greatest importance in de- 
signing a clamp of this sort that the pivot W be located con- 
siderably lower than the point T so that the clamping action 
will be down in the direction indicated by the radial line X. 

Special Forms of Clamps. Work of peculiar or irregular 
shape which has not been provided with clamping lugs often 
calls for the design of special clamps in order to hold it prop- 
erly and without distortion or dislocation. Considerable in- 
genuity is sometimes required in order to devise a suitable 
method. A number of clamps designed to suit peculiar condi- 
tions of holding, are shown in Fig. 146. The casting A has an 
overhanging flange C which is to be machined as indicated by 
the / mark. The work rests on locating plugs, one of which is 
shown at B. The ordinary type of clamp would be difficult of 
access if used for a condition of this kind, therefore a device 
must be used which will give satisfactory results and which will 
be readily accessible. Several methods are shown which may be 
adapted to work of this kind. 



DETAILS OF MILLING FIXTURE CONSTRUCTION 



167 



The clamp D is slotted at E to allow it be moved back out 
of the way when, placing the work in position, or removing it. 
The clamping is accomplished by means of the cam G which is 
pivoted to the end of the clamp. The cam bears on the wear 
plate F and is operated by the thumbscrew H. This type of 
clamp is open to several objections, among which are the cost 
of manufacture and its limited range. If the eastings should 
vary considerably in thickness at the clamping point the clamp 




Fig. 146. Special Forms of Milling-Clamps 

might not hold the work at all as the adjustment is somewhat 
limited. 

Another type of clamp is shown at K for the same piece of 
work. In this case a projecting lug is provided on the fixture 
at L so that the thumbscrew M can be used to operate the clamp 
from beneath. This form can be frequently used on fixtures, 
providing the extra depth of fixture needed is not objectionable. 
Ample clearance for the operator's knuckles should be provided 
when designing this form of clamp. 

Another form of sliding clamp is shown at N, for holding the 
same piece of work. This type is operated by means of the 
sliding wedge which is forced under the end of the clamp by 



168 JIGS AND FIXTURES 

the action of the thumbscrew Q. The wedge may be given a 
bearing on a hardened plate P if desired. Of the three clamps 
shown for this piece of work the one illustrated at K is the sim- 
plest and most practical. 

An excellent method of clamping small work of certain kinds 
is shown at R. The work rests on a support T and is clamped 
against the knife-edge locater 8 by means of the sliding clamp 
U. It will be seen that the latter is set at a slight angle so that 
the pressure is partly downward. This form of clamp may be 
made up in units of several sizes and standardized. The block W 
carries the slide which is adjusted by the thumbscrew X acting 
in the nut "P. This clamp can be utilized for many varieties of 
small work when clamping space is restricted. 

Lever Operated Clamps. In order to make a clamp self- 
contained it is often desirable to operate it by means of a lever 
and thus avoid the use of a wrench. If there is plenty of room 
on the fixture so that the handle can be revolved completely 
without interfering with the cutter or any part of the fixture, 
a lever can frequently be used to good advantage. Levers can 
be used on nearly all types of clamps which are operated by 
means of a nut, provided there is room enough so that they can 
be operated without interference. 

Fig. 147 shows a piece of work A which is being milled by 
the cutter B. It is clamped in place by the slotted clamp C 
operated by lever Z>. It can be seen that if the thickness of the 
work should vary, the clamping lever might take the position 
indicated by the dotted lines at E, thus interfering with the 
cutter. If the work is finished on both locating and clamping 
surfaces, the variation would be very slight and the lever could 
be fitted so that it would not interfere with the cutter. 

A special form of lever which pulls the clamp away from the 
work when it is loosened is shown at N. The work F locates on 
points set in the fixture base. It is clamped down by the two 
points K in the equalizing clamp H, which is controlled by the 
lever. A cam path is cut on the lower side of the hub as indi- 
cated at P, the pin O in the clamp being controlled by the cam 
in such a way that when the lever is operated in loosening the 
clamp, a continuation of the movement causes the pin to 
strike the end of the cam path at Q thus pulling the clamp 
back from the work. The pin L acts as a guide for the clamp. 



DETAILS OF MILLING FIXTURE CONSTRUCTION 



169 



In using this form, suitable allowances must be made for 
variations in the work in order that the clamp may work prop- 
erly under all conditions. It is well to make the thread M of 
coarse pitch or even a multiple thread if the occasion warrant 
it. This type of clamp will be found more satisfactory on 
finished work where the variations are very small. 



*WorkA 




Fig. 147. Clamps Operated by Levers 

Locating and Clamping Odd Shaped Work. Work which 
is to be milled almost in line with a normal clamping surface is 
difficult to locate and clamp firmly, at the same time keeping 
the clamps below the end of the cutter so that there will be no 
interferences. A case in point is shown in Pig. 148, in which 
the work A is to be milled on the two bosses indicated. The 
surface B has been machined and is to be used for location. By 



170 



JIGS AND FIXTURES 



setting it on this surface, on a hardened locating plate in the 
fixture C, it can be brought up against the knife-edge locater D 
by means of the swinging clamps on the opposite side at F. 

The locater D is well backed-up by the lug on the casting at E. 
The operation of the swinging clamp F is controlled by the 
thumbscrew H so that the knife-edge point forces the piece 
over against the locater D and at the same time holds it down 
on the locating plate B. The pivot K on which the swinging 



Work A 





Ct R->f 



^'Oi 1 


(O. 






p) l 


i /**\ 



Fig. 148. Locating and Clamping Odd-Shaped Work 

clamp moves should always be set well back of the knife-edge 
6r, so that the action in clamping will be downward. 

Another piece of work requiring a method somewhat out of 
the ordinary for locating and clamping, is shown at Q. Here 
the surface L is to be machined and the work must be located 
not only in relation to the under-side of the surface mentioned 
but also in such a way that it will bear a certain relation to the 
hub M. The method used is to locate each end of the hub in 
a knife-edge V-block such as that shown at R. This gives a 
location on two of the three points necessary. It can then be 
tipped until it strikes the fixed locating point shown at N, after 
which the three spring-jacks indicated at can be released until 
they strike the under-side of the flange, after which they should 
be locked. This work could be clamped with an arrangement 



DETAILS OF MILLING FIXTURE CONSTRUCTION 



171 



similar to that previously described, using knife-edges at P and 
Q. Conditions similar to this are frequently found in general 
manufacturing and a careful analysis must always be made to 
make sure that the work does not locate on more than three 
iixed points. 

Special Form of Finger Jack. Pig. 149 shows a type of 
linger jack which is very useful in supporting work for pro- 
filing or milling. The principle on which this jack is based is 
a wedging action produced by the tapered member A in con- 
tact with the under-side of the plug B. The operator grasps 
the knurled screw (7 and pushes the plunger forward until the 
end of the jack D supports the work. A turn of the finger locks 
it in place by means of the plug shown at E. 



u, t ? ." rvv ^* 




Fig, 149. B'inger Jack for Milling Fixtures 

Equalising Clamps. It is often necessary to hold two or more 
parts at the* same time. When this condition arises, the clamps 
should he made in such a way that they will exert a uniform 
pressure on the work. An equalizing type of clamp must there- 
fore he used, 

Fig, 150 shows two pieces of work at A and B winch are to 
be machined on the upper surface. The work locates on the 
blocks C and I) and there is a locater on each side as shown 
at F. The base of the fixture E contains a spring plunger If, 
on the upper end of which is mounted a rocker (7, so formed 
that the angular surfaces will come in contact with the edges of 
the work. The lower part of the plunger is slotted to receive 
a wedge K which may be operated in any convenient manner. 
The action of the wedge draws the plunder down and the 
rocker & equalizes the clamping action so that it is distributed 



172 



JIGS AND FIXTURES 



evenly on both parts A and B. The sectional view at L makes 
the construction easily understood. A clamp of this kind is 
useful when the work is of such a nature that it can be put into 
the fixture without difficulty, but if this cannot be done, this 
type should not be used because it requires too much movement 
of the plunger in order to remove and replace the work. 

The two pieces of work shown at M and N are to be machined 
at the points and P, therefore clamps should be provided 
which can be operated simultaneously, thus equalizing the pres- 




ITig. 150. Applications of Multiple Clamps 

sure. The clamps Q and E are slotted so that they can be pulled 
back when removing and replacing the work. The clamps are 
operated by means of the eye-bolts T and V and their action is 
equalized by the lever S. When the thumb-knob X is screwed 
down, the same amount of pressure is applied on both clamps 
Q and E so that the pressure on the work M and N is the same. 

This form of equalizer is very commonly used and can be 
applied to a variety of conditions. It is of course important 
that the pivot point Z be mid-way between the two operating 
eye-bolts T and U in order that the pressure may be uniform. 

Clamping Work in Groups. The greatest care must be used 
in clamping several pieces of work against each other so that 



DKTAIL8 OF MILLING FIXTURE CONSTRUCTION 173 

slight erroivs in locating will not cause inaccuracies in the fin- 
ished product. A ease in point is .shown in Fig. 151. The work 
consists of four bars A, B, C and D on which a small flat sur- 
face is to be milled as indicated. The bars are located in the 
fixture E so that the bar D is clamped against the under cut 
portion F on one side of the fixture. It will be seen that when 
the thumbscrew K is operated, the swinging clamp II strikes 




Fig. 151. Clamping Work in Groups 

against the bar A throwing it over against 7? which in turn 
moves the angular rocking clamp HO that it forces the bar 
against /> thus holding the entire group of bars. 

For the condition shown this method of clamping is not ob- 
jectionable*, but assuming that the bars were to be located for 
a key-way as shown at L, If, N and 0, it is evident that accumu- 
lated variations would be found in the positions of all of the 
slots with the exception of /*. If the bans chanced to be a trifle 
large the slot Q would be slightly off center, B would be a little 
more HO and 8 still more out of alignment. 



174 JIGS AND FIXTURES 

This point must always be remembered in designing fixtures 
for holding a number of pieces, as a condition like that shown 
would be very serious, in that the errors in the key-ways would 
make it impossible to obtain a fit on the corresponding female 
member. 

Another method useful in clamping work in groups, is shown 
at T. This is a connecting rod in which a pin has been inserted 
in the small end U so that it may be used to locate from during 
the progress of the work. The work is located at the large end 
by means of another pin which rests on the hardened block V 
where it is securely held by the sliding clamp W. The fixture X 
must be so arranged that the clamp W can be dropped down in 
the direction indicated by the arrow far enough so that the work 
can be easily removed. The machining on the rod consists of 
straddle milling the two sides of the bosses and saw cutting it 
at the same time as indicated. 

It is common practice to set up work of this kind in groups, 
the number of pieces to be machined at the same time being 
governed by the capacity of the machine and the dimensions of 
the connecting rod. It is evident that when one side has been 
cut, the work can be removed and turned over in the same 
fixture so that the other side can be machined. 

Design of Hook-Bolt Clamps. Some data have been given 
in one of the chapters on drill jigs regarding the design of hook- 
bolt clamps in their application to drill jigs. Similar clamps 
may be used for milling fixtures, although they should be much 
heavier than those used for drilling. Pig. 152 shows a piece of 
work A located on the plug B, and which must also be held 
firmly on the rectangular end. A special form of combined 
hook-bolt and jaw is used in this case. The member D is a 
bushing having a jaw cut on it at E against which one side of 
the work locates. The rod F has a jaw G at one end and passes 
entirely through the bushing D, being operated by the thumb- 
knob at the other end H. This entire mechanism will "float," 
and when the thumb-knob is operated, the work is firmly 
gripped between the jaws E and G after which the thumb- 
screw K can be tightened, locking it positively. A teat screw L 
prevents the rod jP from turning. Attention is called to the 
manner in which the jaw G is supported at P. 

A somewhat similar device is shown holding the work M . This 



OF MILLING JP1XTUHK CONSTRUCTION 175 

piece is also gripped between jaws at N and and the hook- 
bolt is released by means of the spring indicated. In this par- 
ticular ease it is necessary to swing the hook-bolt out of position 
in order to remove the work, and the method used is clearly 
shown in the end view, the movement of the hook-bolt being 
indicated by the arrow and the dotted lines. The same careful 



Locating 



> H 

Mr- '"Wll 




Fig. 152, Designs of Hook-Bolt Clamps 

provision has been made here for supporting the heel of the 
hook-bolt at Q. 

An application of a similar principle is shown in the method 
of holding the work R. The jaw T grips the work on one side 
while the hook-bolt S draws it down and also clamps it. Suitable 
beating points must be provided on which the casting may be 
supported. This may be done at the point Z by the insertion 
of a stud or by some other convenient method. Attention is 
one more called to the support of the heel of the hook-bolt at X. 

Special Application of Hook-Bolt Clamps. For thin work 
that is likely to be distorted either in the cutting or the holding, 



176 



J1W8 AND 



the hook-bolt may frequently be utilized to good advantage. 
An application of this kind to a very difficult piece of work 
is shown at A in Fig. 153. The work locates on a central stud 
B and on hardened ring at C. The arms of the bracket are 
straddle milled at D and E and are also finished at F and G. 
The material is manganese bronze and the two arms of the 
bracket D and E are very frail. Therefore, the method of hold- 
ing during the process of machining must take into considera- 




Section 
Fig. 153. Special Applications of Hook-Bolt Clamps 

tion the spring of the material and clamps of special form must 
be used. The work must be held close to the points where the 
cutting is to be applied and the clamping device must be of a 
" floating" nature in order that the location of the work on the 
stud B and the surface C may not be disturbed. 

A pair of hook-bolts using a principle similar to that applied 
to the work A in Fig. 1 52 were used for the first operation while 
holding the work for the milling of the inside surfaces F and G. 
The section taken along the line OP shows the two sides of the 
work N gripped at the top by the hook-bolts H and K and at 
the bottom by the jaws L and M. The floating action of the 



I>KTA1I.N OF AULMNO FIXTURE CONSTRUCTION 177 

hook-bolts allows the work to be securely gripped in such a way 
that the cutter can machine the piece without distortion. 

For the second operation, which consisted of milling the out- 
Hide surfaces K and 1), a similar arrangement was used. The 
work locates on a central plug X through which the hook-bolt 
Z passes. The lower part of the work is held by a floating col- 
lar F. .Both the end of the hook-bolt and the collar are cut 




Fig, 154. Method of Supporting and Clamping a Thin Casting 

away on a slight angle so that the clamping action draws the 
work tightly against the central locating plug X and gives great 
rigidity during the straddle-milling operation. It may be well 
to state that both of these fixtures were made for work requir- 
ing great accuracy and that they were operated by girls, 

Holding a Large Piece of Thin Work. In milling thin work 
it is important that it be held in such a way that vibrations will 
not be mi up during the cutting operation. An efficient method 
of holding a piece of this kind rigidly, yet without distortion, 
JB shown in Fig. 154. The work A. is a deep, thin bronze cast- 



178 JIGS AND FIXTURES 

ing which is to be milled along the upper part of the flange B. 
The work is located on suitable supports under the flange, in 
the V-block at C and against the locating block D. It is clamped 
as indicated by the arrows at E and F. The clamping action 
will obviously tend to distort the sides of the casting and as 
there are no lugs on the work to which clamps can be applied, 
the results would be very unsatisfactory. The writers have seen 
a fixture of this kind in which it was impossible to machine the 
work without distortion; in fact it was difficult to machine it 
at all on account of the "chatter" induced by the vibrations 
of the thin metal walls. 

A remedy which was suggested and applied successfully is 
indicated at G. This is a "spider" of aluminum having two 
supporting studs P which rest on the bottom of the casting. 
At H, K, L and AT, screw jacks are located, directly opposite 
the outside locating and clamping points. 

When setting the work in this fixture the outside clamps are 
first set up very lightly and locked in position. The spider G 
is then set inside the work and the screw jacks set up tightly 
by means of the nuts at N and 0. As the jacks are directly 
opposite to the outside holding and locating points a metal-to- 
metal contact is obtained which does not distort the work, yet 
holds it firmly so that all vibrations are "killed" and the piece 
can be milled with speed and precision. 

The principles illustrated in this example can be applied in 
many similar bases. It is well, however, to note that a much 
better way of finishing 1 a casting of this sort would be 
by using a surface grinding machine instead of a milling 
machine. 

Equalizing Hook-Bolts. An excellent fixture, which was de- 
signed for holding the work A while milling the circular form 
D, is shown in Fig. 155. The work has been previously finished 
in the hole B and also on the sides E. It is evident that the 
action of a large form cutter such as that used in milling the 
contour D necessitates exceptionally rigid support for the work 
in order to eliminate "chatter" during the operation. The 
work is located on a stud at B so that it rests against a solid 
surface at E and is located in the other direction by the pin C. 
It is clamped back against the shoulder E by means of the hook 
bolts F and G, these being operated by the equalising bar H 



/>A?7 f .4//,tf OF MILLING FIXTURE CONSTRUCTION 179 

through the action of the hand wheel M and the screw K. The 
latter works against a hardened block at L. 

The hook belts are provided with camslots at and P which 
are so located that when the pressure of the spring at Q and R 
is exerted after the handwheel is loosened, the hook bolts turn 
90 (leg 1 - nd are thus out of the way so that the work can be 
readily removed. In other words, when the hook bolts are 




Fig, I. Fixture with Equalizing Hook Bolts 

piiRhed out away from the work by means of the springs, a pin 
in the campath maktn* them revolve in the manner noted. An 
additional refinement can he wed as shown at F, if conditions 
warrant It, by mounting 1 the hanclwheel on the shaft X in which 
a bayonet lock Z In cut. A method like this would make the 
operation of the mochanwrn somewhat faster than the example 
previously dew-ribed. The advantages of this type of fixture 
are the extreme rigidity that IB obtained and the fact that the 



180 



JIGS AND FIXTURES 



operator is not obliged to put his hands near the cutter. It is 
rapid in operation and the construction is such that the upkeep 
is very economical. The use of air-operated chucks and other 
clamping devices is becoming more and more general for work 
requiring careful holding or rapid operation. The majority of 
present day factories are equipped with air compressors and 

Work 




Fig. 156. Principles of Pneumatic Clamping 

pipe lines extending to the various departments of the shop. 
With such equipment, advantage should be taken of the oppor- 
tunities for using air pressure to operate fixtures of various 
kinds. 

Principles of Pneumatic Clamping. Pig. 156 shows a few 
diagrams which will assist the designer in understanding the 
principles of pneumatic clamping. The work shown at A is being 
held for the milling operation indicated between the jaws B 



DETAILS OF MILLING FIXTURE CONSTRUCTION 181 

and C of a pneumatic holding fixture. The air cylinder E is 
a part of the fixture itself. The air enters the chamber at the 
port F and acts upon the head of the piston D, which is coupled 
to the sliding jaw C. The operation of the mechanism is very 
simple as it only requires the turning of a lever to admit or re- 
lease the air. The amount of power developed is determined 
by the pressure carried in the pipe line F and the diameter of 
the piston D. Increased power can be readily obtained by the 
use of compound levers, bell cranks or similar appliances. 

In another example the air enters the cylinder through a pipe 
at G and acts against a piston connected to the lever H. This 
lever operates a sliding rod at L, applying pressure in the direc- 
tion indicated by the arrow. The amount of leverage obtained 
is dependent on the position of the fulcrum pin K. 

Another diagram shows the piston connected to a hook-bolt N 
in order to clamp the work against the locating surface P. The 
air enters the cylinder at M 9 acting against the piston 0. 

A point of great importance in connection with the use of 
air pressure for operating various devices, is the matter of 
packing to prevent the escape of the air and consequent loss of 
holding power. Lubricated asbestos packing is frequently used 
in connection with suitable glands as shown at Q and R, the 
packing being drawn tightly around the shaft S. A method of 
packing a piston is shown at T, the packing being compressed 
by means of an annular ring-nut U. It is evident that air must 
frequently be applied in both directions in order that the piston 
may operate effectively. The diagram shows two ports at V and 
W which can be closed and opened alternately as required, by 
means of a valve. 

Pneumatic clamping can be applied through equalizing de- 
vices of various kinds ; one of which is shown in diagrammatic 
form. Here the air acts on the equalizing lever Z through the 
air cylinder in such a way that the pressure acts uniformly at 
the points X and Y, thus operating the clamps. To the designer 
of high production tools the possibilities of air clamping should 
be given the most careful consideration, and in particular cases 
where it is desirable to operate a number of clamps simultane- 
ously with a uniform pressure it may often be possible to adapt 
pneumatic methods to advantage. 



CHAPTER IX 
VISE- JAWS AND VISE FIXTURES 

SPECIAL AND SWIVEL JAWS DEVICES FOR INSURING ACCURACY 
QUICK OPERATION DEVICES FOR EQUALIZING PRESSURE- 
AUTOMATIC EJECTORS. 

The use of vises with plain or special jaws oftentimes makes 
it possible to hold small work advantageously for milling, shap- 
ing and drilling operations. Generally speaking vise-jaws are 
used more often for milling than for other operations. Vises 
can be adapted and used with special jaws to hold irregularly- 
shaped work which would be difficult to hold in any other way. 
It is unfortunate that tool engineers do not specify the use 
of vises more frequently, for their advantages are so evident 
and their adaptability so great that they can be used profitably 
in many cases which would otherwise require expensive fixtures. 
The standard type of milling machine vise used for manufac- 
turing in many shops is not adapted for very heavy cutting. It 
was designed originally for toolroom work to provide a means 
of holding flat and round stock for light cuts. It is theoretically 
wrong in principle as the thrust of the cut is taken by the 
t> movable jaw instead of by the solid jaw. 

I' Fig. 197 shows a vise of this kind at A. Note that the movable 

J jaw B is intentionally made long and heavy in order to make 

':' it as rigid as possible. In reality, although the vise is not de- 

,\ signed for very heavy cutting, good results may be obtained 

;1 from it and many factories use no other type. The jaw is 

| operated by means of a screw. 

| The vise shown at C is designed especially for manufactur- 

| ing- This type takes the thrust of the cut on the solid jaw D. 

| The movable jaw E is a unit with the slide F on which the levers 

jjj G and H are mounted. By loosening the binding lever G and 

I moving both levers along in the slot of slide F various openings 

P of the jaws can be easily made according to the capacity of the 

* 230 



VISE-JAWS AND VISE FUTURES 



231 



vise. In operation the cam lever H is set until the jaws grip 
the work firmly, after which the binding lever is tightened. As 
the latter is slightly eecentrie to the cam lever, the locking action 
is improved and greater leverage obtained. Both of the vises 
illustrated can be furnished with special and swivel jaws. 






Fig. 197. Examples of Milling and Manufacturing Vises 

In addition to the two types of vises shown there are special 
forms for toolroom use. The vise principle used is generally 
like that shown at A, the difference in design being in the method 
of mounting the vise so that it can be swiveled in either a horizon- 
tal or vertical plane. A manufacturing vise operated by com- 
pressed air was described in a previous chapter. 

Special vises can be made up for extraordinary conditions if 
it is found that standard vises cannot be used. If it is impos- 
sible to grip the work properly with special jaws in a standard 



23a JIGS AND FIXTURES 

vise, the designer can apply the same principles to his design 
and' make a special vise to suit the conditions. When the ca- 
pacity of a standard vise is not great enough to take in the 
work, a special vise can be designed providing the production 
required warrants the expenditure. Vises that are made up 
specially are apt to be costly, yet if they are to be used for 
high production the expense will be saved many times. 

Design of Vise- Jaws. Vise- jaws are apparently very simple 
from the designers' standpoint, yet their importance is appre- 
ciated more as a better understanding of their adaptability and 
possibilities is gained. A few points of importance are given 
here in connection with the use of vise-jaws. 

(1) Selection of vise. Most factories use several styles and 
sizes of vises in their production work. Data should be pro- 
vided regarding the capacities of the various types in order that 
a selection may be made with discriminating judgment. The 
predominating factors which influence the selection are: (a) 
The depth of the jaw: (b) the maximum opening; (c) the 
length of the jaw. 

(2) Depth of the work. As most vise-jaws are made shallow, 
the depth of the work to be held is an important factor in de- 
termining whether a vise can be used for a given operation or 
not. Within certain limits it is possible to design the jaws for 
a special piece of work so that they will extend above the jaws 
of the vise, but when this is done they should be made substan- 
tial enough to withstand the thrust of the cut and the pressure 
of the vise screw without vibration. 

(3) Length of the work. The length of vise- jaws varies ac- 
cording to the type and size of machine vise selected and it is 
often desirable to hold a piece of work that is considerably 
longer than the jaw. It may also be necessary to provide some 
means of location beyond the end of the jaws. It should not 
be decided that a piece of work is unsuitable for holding in 
vise-jaws simply because the work is longer than the jaws. 

(4) Vise opening. When vises are screw operated, special 
jaws should be so designed that very little movement of the 
screw is necessary to release the work, allowing it to be taken 
out of the jaws without difficulty. In cases where the work 
locates on pins in one or the other of the special jaws, it is 
frequently necessary to provide a filler or clamping plate which 



VISE-JAWS AND VISE FIXTURES 



233 



can be thrown out of the way when the jaws are released In 
order to avoid too much movement. This matter will be taken 
up in detail later in this article. 

(5) Formed jaws. Irregular work such as small forgings, 
castings and other parts which require milling operations are 
frequently held by means of special jaws which are 4k formed 
out" by the toolmaker to fit the contour of the work. "When 
jaws of this kind are designed, a clamping action must be ob- 
tained on the work close to the point where the cut is to be 
made. For example, in a forging having a ball end, the jaw 




Fig. 198. General Diagrams of Vise- Jaws 

would be formed to hold the ball loosely in order to obtain the 
location, while the work would be gripped at other points where 
the cutting action is to take place. There are so many varieties 
of formed jaws that it has not been deemed essential to take 
up their design in this article. Each individual case must be 
treated differently according to the shape of the piece and the 
general requirements of the work. 

General Diagram of Vise- Jaws. Fig. 198 shows a standard 
type of vise-jaws, such as are usually supplied with a milling 
machine vise. Attention is called to the fact that the dimensions 
A and B are fixed, according to the style and size of the vise 
used. It is necessary therefore to ascertain these dimensions 
before proceeding with the design of any special jaws. The 
dimension C is also important as it determines the maximum size 



232 JIGS AND FIXTURES 

vise, the designer can apply the same principles to his design 
and' make a special vise to suit the conditions. When the ca- 
pacity of a standard vise is not great enough to take in the 
work, a special vise can be designed providing the production 
required warrants the expenditure. Vises that are made up 
specially are apt to be costly, yet if they are to be used for 
high production the expense will be saved many times. 

Design of Vise- Jaws. Vise-jaws are apparently very simple 
from the designers 7 standpoint, yet their importance is appre- 
ciated more as a better understanding of their adaptability and 
possibilities is gained. A few points of importance are given 
here in connection with the use of vise-jaws. 

(1) Selection of vise. Most factories use several styles and 
sizes of vises in their production work. Data should be pro- 
vided regarding the capacities of the various types in order that 
a selection may be made with discriminating judgment. The 
predominating factors which influence the selection are: (a) 
The depth of the jaw: (b) the maximum opening; (c) the 
length of the jaw. 

(2) Depth of the work. As most vise-jaws are made shallow, 
the depth of the work to be held is an important factor in de- 
termining whether a vise can be used for a given operation or 
not. Within certain limits it is possible to design the jaws for 
a special piece of work so that they will extend above the jaws 
of the vise, but when this is done they should be made substan- 
tial enough to withstand the thrust of the cut and the pressure 
of the vise screw without vibration. 

(3) Length of the work. The length of vise- jaws varies ac- 
cording to the type and size of machine vise selected and it is 
often desirable to hold a piece of work that is considerably 
longer than the jaw. It may also be necessary to provide some 
means of location beyond the end of the jaws. It should not 
be decided that a piece of work is unsuitable for holding in 
vise-jaws simply because the work is longer than the jaws. 

(4) Vise opening. When vises are screw operated, special 
jaws should be so designed that very little movement of the 
screw is necessary to release the work, allowing it to be taken 
out of the jaws without difficulty. In cases where the work 
locates on pins in one or the other of the special jaws, it is 
frequently necessary to provide a filler or clamping plate which 



VISE-JAWS AND VIBE FIXTURES 



233 



can be thrown out of the way when the jaws are released in 
order to avoid too much movement. This matter will be taken 
up in detail later in this article. 

(5) Formed jaws. Irregular work such as small forcings, 
castings and other parts which require milling operations are 
frequently held by means of special jaws which are "formed 
out" by the toolmaker to fit the contour of the work. When 
jaws of this kind are designed, a clamping action must be ob- 
tained on the work close to the point where the cut is to be 
made. For example, in a forging having a ball end, the jaw 



r. 1 -J 




Movable 
jaw ~ 

r 

p 

/i- 

sr rv 


. 
1^, 

'^- 

H 

>r/. 


,<^r ^j Minimum 
I ax/mt/m t 
i Stationary 
J |^'_/c?w 


A H 


V&\ B X^ 


\ 


Drill holes * Chamfer 
in jig 


"1 

*c 




Fig. 198. General Diagrams of Vise- Jaws 

would be formed to hold the ball loosely in order to obtain the 
location, while the work would be gripped at other points where 
the cutting action is to take place. There are so many varieties 
of formed jaws that it has not been deemed essential to take 
up their design in this article. Each individual case must be 
treated differently according to the shape of the piece and the 
general requirements of the work. 

General Diagram of Vise- Jaws. Fig. 198 shows a standard 
type of vise-jaws, such as are usually supplied with a milling 
machine vise. Attention is called to the fact that the dimensions 
A and B are fixed, according to the style and size of the vise 
used. It is necessary therefore to ascertain these dimensions 
before proceeding with the design of any special jaws. The 
dimension C is also important as it determines the maximum size 



234 

of the work that can be properly gripped between the jaws 
of the vise. 

It frequently happens that the work is higher than the height 
of the jaws, in which case care must be taken to see that the 
pressure is resisted by designing the jaws so that they will 
have additional support near the point where the cutting action 
is applied. An example of this kind is shown at D in which it 
will be noted that the jaws extend considerably above the body 
of the vise as shown at E and F. Support is provided by the 
"heel" at and H. 

The example at K indicates a method used for locating the 
work L on one jaw M; the other jaw N is cut away as shown at 
to prevent trouble from an accumulation of chips. The prin- 
ciple used here is applicable to many kinds and shapes of small 
work, the location always being on one jaw only. 

A good method of holding round work is shown at P. The 
work Q lies in a "vee" which is slightly undercut at R so that 
the pressure of the jaw S tends to draw it down against the sur- 
face T thus holding it firmly in position. This principle can 
be used to advantage in holding many kinds of round work. 

Assuring Accuracy in Location. When work is to be milled 
accurately in relation to some previously finished surface it is 
oftentimes advisable to provide vise-jaws with an accurate means 
of location. This is particularly desirable when the vises used 
are old and more or less worn, but whether this is the case or not 
a very high degree of accuracy can only be obtained by making 
some provision in the jaws so that they will always register 
exactly the same. If the tolerances on the work are very close, 
this point must be kept in mind when designing special jaws. 

Fig. 199 shows a very good method of registering vise- jaws 
accurately. A and B are the two jaws, one of which is provided 
with hardened guide pins at C and D while the other contains 
bushings E and F. The pins act as dowels and thus preserve 
the correct relation of the jaws at all times. In such a case the 
work might be located on suitable pins at 0, the positions of 
these pins being determined by the nature of the work and the 
general requirements. The length of the dowel pins is deter- 
mined by the thickness of the work and the method of location. 
The side view of the jaw gives a clear idea of the relative posi- 
tions of the screw holes H and K and the dowel pins mentioned. 



VISE-JAWS AND VISE FIXTURES 235 

Two other methods are shown in the same illustration. In 
one of these the work M rests on the shoulder of a special jaw 
while it is gripped by the other jaw N. A support Is provided 
at P which acts in a somewhat similar manner to the dowels 
previously mentioned by preventing the movable jaw from lift- 
ing when it is tightened. These jaws would be improved by 
giving them a shoulder at Q and R similar to the ease shown 
previously. One objection to this design is that the spaces at 
T and 8 are narrow and therefore they form an excellent place 
for chips to accumulate and cause trouble in closing the vise. 

Another example of an attempt to provide an accurate means 





Fig. 199. Assuring Accuracy in Location 

of location is shown in the jaws holding the work U. In this 
case the work rests on the shoulder V and a tongue is provided at 
W which is intended to prevent the jaw from lifting and thus 
obtain greater accuracy than would be otherwise possible. The 
objection to this type is that it is more or less expensive; there 
are bad pockets for chips and it is generally impractical. 

In analyzing the methods of location shown in this illustra- 
tion it is obvious that the guide pin method is the best on account 
of its adaptability, simplicity in construction, and the ease with 
which the jaws can be cleaned. The cost of construction and 
the accuracy obtained are additional points in its favor. 

Quick Removal of Work. When making up a set of vise- 
jaws it must be remembered that the rapidity with which the 



236 



JIGS AND FIXTURES 



vise is operated is dependent to a great extent on the amount 
of opening- necessary to remove and replace the work. When 
the latter is of such a nature that it must be located on a stud 
and removed from the stud after the operation, a considerable 
opening to the jaws may be required. When a cam operated 
vise is used a certain amount of opening can be made rapidly, 
and this may serve to take care of many conditions, but 
when the regular type of milling machine vise is used, every 
half revolution of the screw means that the operator is obliged 
to remove his wrench and replace it again. This takes time 
and is a decided objection if the jaws need to be opened rapidly. 
In order to obviate this trouble it is customary to provide a 




Fig. 200. Provision for Quick Removal of Work 

filler block to lie between the work and one jaw. By taking out 
this filler block the work can be removed and replaced readily 
and not more than a half turn of the screw is required to pro"- 
vide sufficient opening. The filler can be made in the form of 
a loose piece or it can be pivoted to one jaw so that it can be 
swung out of the way when not in use. 

Fig. 200 shows a pair of jaws at A and B, the jaw A holding 
four collars C by means of the locating block D. If no provi- 
sion were made for rapid removal of the work it would be neces- 
sary to open the jaws the distance shown at E in order to allow 
all four collars to be removed at once. To provide against such 
a contingency, the jaw B is provided with a swinging block F 
which acts as a clamp against the work and yet is quickly re- 



VI8E-JA.W8 AXD YJ8E FIXTURES 



237 



movable. The designer is advised to make provision of this kind 
in all cases where similar work is to be handled. Although it is 
permissible to use a loose piece for the same purpose, it is not 
nearly as good as a swinging member. 

Swivel, Multiple and Floating Jaws. When rough work is 
being held by being gripped on two or more surfaces, it is ad- 
visable to provide a swivel jaw in order to hold it properly. 
Also when several pieces are being held at the same time there 
is a possibility of slight variations in thickness or diameter of 






/^ 


L 


*VOf~n 


LJ 






T 




I 


\ 

ft 


i 


j( 


I 








Q 


* 


'3&"i 


I 

rv 



/"toor ting join 
Fig. 201. Swivel, Multiple and Floating Jaws 

these pieces which makes it necessary to provide some means of 
distributing and equalizing the pressure. 

Fig. 201 shows a piece of work at A, being held for a milling 
operation. The lugs at B and C are likely to vary somewhat in 
height, therefore provision must be made for this by means of 
a swivel jaw as shown at D. 

An example of a swivel jaw arranged so that it will hold four 
pieces is shown at E. In this case the work consists of four 
bars F, located in the V-block jaw G. The other jaw H is made 
in the form of a swivel block having two supplementary swivels 
at K and L. 



238 



JIGS A1?D FIXTURES 



The designer should remember that all of the pressure of the 
jaws will come upon the pins at M, N and if made like the 
illustration. It would be much better practice to make the pins 
mentioned a loose fit in the swivel and let the pressure come 
against the radius at the back of each of the blocks. The pins 
should only act as retainers and not take any pressure. 

A supplementary or floating jaw is sometimes used to hold 
several pieces, as shown at P. This method is useful where sev- 
eral pieces are to be milled at one time. The block lies between 
the two jaws and R and is located by means of a pin in an 
elongated slot shown at S. In operation, the work is loaded by 
removing the floating jaw P and placing the piece on it after 



/^operation 




Cutter 



\ 



i Cutter 



cJc 


.0. 


.0, 




operatic* 
Fig. 202. Method of Locating and Holding Long Work 

which it is set in position between the jaws and clamped in 
place. This method is useful for handling small pieces of work 
when a number of them are to be located at one time. If there 
is likely to be a variation in the length of the pieces, the jaw Q 
can be made in swivel form to take care of the variations. 

It is sometimes possible to use the same set of jaws for more 
than one operation on the same piece of work, and when this 
can be done without interfering with the production schedule 
it is obviously an advantage. Occasionally jaws can be provided 
with two sets of pins or other means of location and cutters 
can be arranged on the arbor so that both operations can be 
done at the same time ; one piece being finished while the other 
is being rough-milled. When bar work is to be milled it is often 
possible to use the same jaws for several operations. An exam- 
ple of this is shown in Fig. 202, in which the work A is a bar 



VI8E-JAW8 AXD VltiE FIXTURE 



239 



somewhat longer than the jaws in which it is being held. The 
bar is located endwise by the stop at B, this stop being a part of 
the extension C which is fastened to one jaw. An end view of 
the jaws is shown at D and E, where it will be seen that the 
jaw E is slightly undercut to assist in holding the work. The 
locating bar C is fastened to the jaw E and acts as a support 
for the work as indicated. 

The first operation consists in cutting a slot in the end of the 
bar at F. The locater B is made so that it will fit this slot, 




Hfor* 




Work 



Work 





Fig. 203. Examples Showing Methods of Location 

therefore not only can the work be set up for the second opera- 
tion with the same set of jaws, but the second operation will be 
properly located in relation to the first The second operation 
consists of milling a longitudinal slot in the bar as shown 
at H. 

Location of Small Work. In locating small work in vise- 
jaws, a great deal depends upon the shape of the piece. Fig. 
203 shows an excellent example of a production job on a small 
piece of work on which two operations are being performed at 
the same time. The work A is located on pins at B, and D 



240 J108 AND FIXTURES 

in the jaw E while the slot is cut at F. This is the first opera- 
tion on the work after it has been cut off. In the same set of 
jaws the piece is held in another position as shown at G and 
located by the milled slot F, using locating pins at E, K and L. 
This operation mills the slots at M and N and also cuts the work 
into two pieces by means of the slotting cutter 0. As it is pos- 
sible that the work might not be located firmly against the two 
pins at B and H, provision is made to insure their contact at 
these points. By using a pair of fiat springs at P and Q the 
work will be automatically forced over against the locating pins 
without particular attention on the part of the operator. 

The work shown at R must be located from the shoulder 8. 
This brings up a point in design which is frequently neglected 
when vise-jaws are made and that is the alignment of the jaws. 
It is always advisable to make the shoulder location on one jaw 
only as shown at T, rather than to attempt to line up two shoul- 
ders on opposite jaws. Another example of a shoulder location 
is shown at V, in which case it will also be noted that the loca- 
tion is on one jaw only. There are occasional cases when this 
rule can be overlooked, for example, when dowel pins are used 
in the jaws to insure accuracy as shown in Fig. 199. However, 
it is safer to follow the rule of locating on one jaw only. 

Vise- Jaws Designed for Several Consecutive Operations. 
It is interesting to note the adaptability of vise-jaws for hold- 
ing small parts which have several consecutive milling opera- 
tions. An example which illustrates this point is shown in Fig. 
204. The consecutive operations are shown on the rectangular 
block in the illustrations 1, 2, 3 and 4. The work is first cut 
off from a rectangular bar so that it takes the form 1. The next 
operation is the forming of the radius shown at 3, and the fourth 
operation is the profiling of the circular cut shown at 4c-A. In 
the first operation the bar B is placed in the jaws shown until 
it strikes the end stop C. The jaws are then tightened and the 
portion D is cut off. "When the jaws are loosened the piece 
slides down the inclined plane E into a box provided for it and 
the bar B is pushed forward again until it strikes the stop C, 
after which the eutting-off operation is repeated. 

In the next operation the work is held by means of the jaws 
F and G while the straddle milling cut is made at H and K. 
This operation machines the piece to length, a suitable allow- 



V18E-JAW8 AND VISE FIXTURES 



241 



anee having been made for this operation while cutting off the 
work. 

The next operation is the cutting of the radius as shown at L. 
The work is held by suitably formed jaws and is located against 
the pins If, A r and by means of the thumbscrew P, which is 
so placed that it is outside of the milling machine vise and can 
therefore be easily manipulated. These three examples have 



LZG di Q 




Saw - 



o 





h 













H --p> 




r 


K 




O 




P 






O 





Fig. 204. Vise-Jaw Design for Several Consecutive Operations 

been given to familiarize the designer with the methods used for 
progressive operations on small parts. Many applications can 
be made of the principles shown here. 

Equalizing Pressure by Means of Beeswax Jaws. There 
are instances when a number of pieces are to be held at the same 
time in a set of vise- jaws and yet it is difficult to make sure 
that all of the pieces are held firmly, due to slight variations 
in the work. There are also irregular forms which have to be 
supported at several points while cutting, and which must in- 



242 



JIGS AND FIXTURES 



corporate some method of equalizing the supports to take care 
of slight inaccuracies in the work. The principle shown in Pig. 
205 can be applied to a variety of conditions, and it has been 
used successfully for holding work which would be difficult to 
support by any other known method. In the example shown 
there are five parts A, B, C, D and E, located in V-blocks in the 
jaw F. The other jaw is equipped with a series of plungers G 
which are lapped to an accurate sliding fit in the jaw jff. The 
chamber K in this jaw is filled with beeswax or heavy grease. 
When this mass is compressed by means of the screw at L the 
vise pins G are forced out until they all come in contact with 




Work 



Fig. 205. Equalizing Pressure by Means of Bees-Wax Jaws 

the work. After the first adjustment has been made by means 
of the screw the pins will automatically equalize themselves so 
that a positive contact will be assured on each one. In making 
up a set of jaws of this sort care must be taken that the various 
fits for the pins and the screw are carefully made in order to 
prevent leaks when the pressure is applied. 

Vise Fixture for Small Work. Occasionally a milling opera- 
tion has to be performed on a piece of work which is difficult 
to locate in vise-jaws. When a condition of this kind arises it 
is sometimes possible to design a vise fixture in which the work 
can be located and clamped and then the fixture itself placed 
between the vise- jaws for the milling operation. A case in point 
is shown at A in Fig. 206. This piece of work has previously 
been drilled and reamed at B and C and faced on both sides. 
It is located on two pins in the holes and clamped by means of 



VISE-JAWS AND VISE FIXTURES 



243 



the strap clamp D. This clamp is so arranged that it swings 
away from the work until the pin E strikes the stop pin F in 
the body of the fixture, thus permitting the work to be removed. 
When the work is clamped the point of the screw G rides up on 
the angular surface of the block H and a wedging action takes 
place which makes the operation very rapid. The fixture K 




-0J 



K 

Jtork 




'Cuff 



^ Jaws- 





El ev. Showing Fixture Clamped m Vise Sect ron Shoeing Screw 
Fig. 206. Vise Fixture to Hold Small Work 

locates between the jaws of a standard vise which clamps it at 
the points L, M, N and 0. Provision is made at some convenient 
point so that end location in the vise- jaws will be assured. The 
operation to be done in this fixture is the cutting of the slot 
at P. Obviously this method of holding is convenient and at 
the same time the fixture is cheap and can be operated rapidly. 
Cases are found now *nd then when a fixture of this kind can 
be used to advantage. 



244 



JIGS AND FIXTURES 



Special Vises with Equalizing Jaws. As a vise of suitable 
dimensions to handle the work A shown in Fig. 207 could not 
be obtained, a special vise was designed. The work is located 
by means of two pins at D in the solid member of the vise. The 
work to be done is the cutting of the two slots B and C. 

The swivel block E fits the radius at F in the sliding member 
which passes under the rigid block 0. The pin H acts as a re- 
tainer only and is a free fit in the hole. In operation the cam 
lever K acts against the hardened block L, clamping the work 
firmly. The body of this vise is made of cast iron and the slid- 




Fig. 207. Special Vise with Equalizing Jaw 

ing parts are all carefully fitted to insure the necessary ac- 
curacy. It will be noted that construction of this vise is such 
that the cutting action comes against the solid member and not 
against the movable jaw. 

There are occasional cases when special vises can be made up 
to suit a particular condition but unless the conditions are such 
that the expense of a special vise is warranted, it is better to 
use a standard vise. 

^ Ejectors for Vise Jaws. As a refinement in the design of 
vise-jaws it is often necessary to provide means for removing 
the work after the milling operation has been done. Many times 
the shape and position of the work is such that it can only be 



V18E-JAW8 AXD TIKE FIXTURES 



245 



removed with difficulty. For eases of this kind ejectors can be 
provided which will facilitate the operation. Several examples 
of ejectors are shown in Fig. 208. The work A is to be located 
on the stud B in the vise-jaw C. As it would be difficult to 
locate this work easily it is placed on the movable jaw D so that 



Ejectors,, 






Fig. 208. Various Types of Ejectors for Vise Jaws 

it rests on the two pins at K and L, which locate it approxi- 
mately. Then, as the jaw is moved up into position the beveled 
end of the stud B enters the hole, thus locating the work cor- 
rectly. After the work has been done, the ejectors F and 6 
pull the work away from the stud, making it easy for the op- 
erator to remove it. This method precludes the necessity of 
using a screwdriver to pry the piece off from the stud, which 



246 JW8 A-ND FIXTURES 

might result in damage to the work or spring the stud out of 
alignment. 

The form of ejector shown at M can be used either by itself 
or in connection with a piece of work like that at A. Assuming 
that this work is the same as the other piece except that it is 
smaller and thinner, it would be difficult for the workman to 
get his fingers into position to remove the work. Ejectors similar 
to those shown at F and could be used here to pull the work 
off from the locating stud, but after it had been removed it 
would still lie in the jaw in such a position that the workman 
could not get hold of it easily. By making use of the lever N, 
however, the piece could be raised so that it would be easily 
accessible. 

Attention is called to the construction of the plungers 
which provide the spring pressure for the ejector. This method 
is entirely different from the other and it has some advantages, 
although it is a little more expensive in construction. There is 
no danger of this type of spring plunger being clogged up with 
chips or dirt. 

The work P is located on a button at Q and it will be seen 
that such a piece might be difficult to remove after it had been 
machined. Using the lever S to operate the plunger JR makes 
the operation much easier and the work can be removed with- 
out difficulty. 

In the design of vise-jaws, particularly when small and thin 
pieces are to be handled, the ejector is an important factor as 
it assists greatly in cutting down the operating time. In addi- 
tion to this, the work can be removed readily and without injury 
and as there is no necessity for hammering or otherwise injur- 
ing the fixture, a better product is assured. 



CHAPTEE X 
BROACHES AND BROACHING FIXTURES 

PRINCIPLES OP DESIGN TOOTH-SPACING AND CHIP-CLEARANCE 

BURNISHING KEYWAY BROACHING MULTIPLE FIXTURES 
INDEX BROACHING SPIRAL BROACHING. 

The process of broaching is very old and dates back several 
hundred years when holes of various shapes were made in metal 
by forcing one or more tools of the required shape through the 
work by driving with a hammer or other means. Later on, short 
broaches with teeth were made and pushed through the work 
by means of hand presses or those operated by power. It was 
not until 1901, however, that the present process of pulling 
broaches through the work was developed. Before this time 
broaches were pushed through the work; now they are pulled 
through it in the majority of cases. 

Push broaches are short while pull broaches are long and it 
is evident that the latter types possess distinct advantages over 
the former, in that a greater number of teeth can be used, and 
as a consequence the cutting action is more uniform and sizes 
can be held mucti more easily. In addition to this, broaches that 
are pulled through the work do not tend to "run" or crowd 
to one side or the other, which fact is also a decided advantage. 
We must qualify this statement somewhat, because a dull broach 
will run out of alignment more or less. If the pull broach is 
sharp, however, it should run true if properly used. 

Important Points in Design. There are a number of factors 
which influence the design and general construction of broaches 
and broaching fixtures. The tool engineer who attempts the de- 
sign of tools of this sort must first familiarize himself with the 
important features and method of operating a broaching ma- 
chine. There are several types on the market, the general fea- 
tures of which are more or lass similar. Different methods of 
centralizing the broach in relation to the work are used, but 

247 



248 JIGS AXt> FIXTURES 

other than this the construction is much the same in all types. 
In the horizontal types of machines, the work rests or is held 
by a fixture of some sort against a vertical faceplate through 
which the broach passes while in operation. Some types of 
broaching machines have only one spindle while others have two. 
In the two spindle variety one spindle is operating while the 
other is returning so that the lost time in setting up is reduced 
to a minimum. 

Let us now consider the various points of importance in con- 
nection with the design of fixtures for broaching and also some 
pertinent matters regarding the broaches themselves: 

(1) Material To Be Broached. As in other machining opera- 
tions, the material to be broached is an important factor in deter- 
mining what tools are best adapted for the work. So, in broach- 
ing, the material affects not only the design of the broach but 
the fixture that is to be used as well. The shape of the broach 
teeth and the amount of material that each tooth will have to 
remove are important factors which influence the production. 

(2} Thickness of the Metal. This matter is of great impor- 
tance in broaching operations as it affects the spacing of the 
broach teeth. It is difficult to cover the situation in a general 
note but detailed information will be given on the subject later 
on in this article. 

(5) Production Required. This matter must always be taken 
into consideration in designing a fixture as the cost of tools 
should be as nearly as possible in proportion to the amount of 
work that is to be produced. In broaching fixtures, this factor 
may easily affect the design of both broach and fixture and also 
determine the type of machine on which the work should be 
done. 

(4) Preparation of Work Before Broaching. Unlike many 
other operations, work that is to be broached usually requires a 
certain amount of preliminary machining. A hole must be pro- 
vided in which to insert the broach and a square surface should 
be provided on that side of the work which locates against the 
faceplate of the broaching machine. This point is of importance 
and, unless due consideration is given to it, may affect the ac- 
curacy of the work to an appreciable extent. 

(5) Accuracy Required. It is seldom that a broached hole is 
required within an accuracy greater than from 0.001 to 0.002 in. 



BROACHES AND BltOACHIXti FIXTURES 249 

and as it is not particularly difficult to keep within these limits 
it is evident that the broaching process can be applied to many 
kinds of work in general manufacturing. If very close toler- 
ances are required both roughing and finishing cute can be taken 
as in other machining processes. In some cases it is necessary 
to locate a broached hole in relation to another one which has 
been previously machined, in which case it may be found de- 
sirable to use the outboard sliding support with which broaching 
machines are provided in order to support the end of the broach 
and keep it in correct alignment while in operation. 

(6) Lubrication. All broaching machines are provided with 
means of directing a stream of cutting lubricant into the hole 
while it is being broached, and this must be considered in mak- 
ing up a fixture in order that the lubricant may reach every 
part of the broach. For example, a square hole should be 
broached with a corner upward and not "flat, so that the lubri- 
cant will reach all four sides of the broach and will not spatter 
off as it might otherwise. In broaching spiined work, the channel 
between two of the splines should be at the top, so that it will 
retain the liquid and serve to carry it into the hole with the 
broach. The kind of lubricant used depends upon the material 
that is to be cut. 

(?) Rigidity. It is highly important that all work that is 
to be broached should be supported properly in order to pre- 
clude the possibility of " chatter" or of the material springing 
away from the broach during the process, which would cause 
inaccuracies and tend to injure the broach. When several pieces 
are to be broached together or when the work is thin, particular 
attention must be given to the method of holding. Suitable sup- 
ports or jacks must be provided for work which is irregular in 
shape in order to avoid any of the troubles mentioned. 

(8) Clamping. Various types of clamps have been described 
in previous chapters so that it is only necessary to refer to some 
of these to cover practically all conditions of clamping such as 
may be required in broaching fixtures. Particular attention 
should be paid to any work which is thin or of irregular shape 
so that there will be no distortion due to improper methods of 
clamping. 

(9) Cost of Tools. Usually the fixtures used for broaching 
are simple in design and inexpensive to make. There are cases, 



250 JW8 ^ ND FIXTURES 

however, when something more elaborate is needed in order to 
decrease the setting up time or when the work is of such a char- 
acter that it cannot be supported and clamped properly in a 
simple type of fixture. 

Broaching Methods. In considering the design of broaching 
fixtures, the designer must first realize that there are two meth- 
ods in use. Fig. 209 illustrates diagrammatically both forms of 
broaching processes. The work shown at A is set up on the table 
of an arbor press at 5. The broach C is short and is pushed 
through the work by means of the press spindle. Attention is 
called to the fact that all push broaches must be short and that 
the usual method is to push several of them through the work, 
one after another, each one being so proportioned that it will 



^Push brooch 

Work. 




LSr 



Pull Broach 



Fig. 209. Types of Broaching 

remove a little more stock than the one which preceded it. The 
end D should be so made that it will act as a pilot when enter- 
ing the work. The teeth are so proportioned that each tooth is 
slightly larger than the preceding one. The amount of this 
variation is dependent upon the material to be cut and the shape 
and size of the hole. 

The piece of work shown at E is broached by pulling the tool 
through the work instead of pushing it as in the first instance. 
This work is done on a horizontal broaching machine designed 
strictly for the broaching process. In contrast with the other 
example shown, the broach F is long, usually from 24 to 36 in., 
depending on the capacity of the machine and also upon the 
amount of stock to be removed. It will be noted that the pull- 
ing action of this broach is resisted by the faceplate G on the 
machine itself. The portion H acts as a pilot and centers the 
broach in the hole, as in the preceding example. 

Broaching an Oil Groove. A bushing which acts as a shaft 
bearing is often provided with an oil groove. When the work 



BROACHES AXD BROACHING 



251 



is manufactured in small lots a cold chisel of the proper form 
is frequently used and the operation is done by hand. If the 
production is large, other methods can be used according to the 
depth of the groove, the material which is to be cut, and the 
machines which are available. 

Fig. 210 shows a piece of work A in which an oil groove is 
cut at B y this groove being shallow as indicated in the illustra- 
tion. In this case the work rests on a bushing C and the ma- 




Work- 



Fig. 210. Simple BroaeMng Operation 

chine used can be an arbor press or other similar machine. It 
might be possible to use a drill-press spindle to apply the pres- 
sure if no other machine were available. The cutter or broach 
bar D is a sliding fit in the bushing and an adjustable cutter 
is provided at E. By means of the screw and binding shoe F 
the cutter can be held in any position, desired. 

The bar itself is located in the bushing by means of the teat 
screw (7 which enters the slot H in the bar. It is evident that 
the depth of the groove is controlled by the position of the cut- 
ter, and there may be cases when two or three cuts are needed 
in order to produce the desired results. Oil grooves are usually 



252 



JIGS AND FIXTURES 



shallow so that a single cut will often be found sufficient. In 
the event of a deep cut being required, it would be better to 
run the work through several times, adjusting the cutter a little 
more for each successive cut, rather than to attempt an adjust- 
ment several times on each piece of work. It would be pos- 
sible, however, to make a bar with rapid adjustment features if 
this seemed desirable. 




Broach' 
Work Locctfer- 

Fig. 211. Examples of Plain Broaching and Methods of Setting Up 

A method of this kind may be found useful occasionally for 
work that is being rushed, or when production is such that the 
expense of a broach of the regular form is not warranted. This 
process can also be used for high production if the cut is very 
shallow, in which case certain refinements may be found ad- 
visable. A bar can be made in such a way that the upper end 
is held in a drill press spindle, and the cutter L mounted in an 
adjustable block If, as shown in the sectional illustration at K. 
The block can be held by setscrews as at and P in the upper 



BROACHES AND BROACH IS a FUTURES 253 

view. After the cutting has been done the drill press spindle 
is raised. The cutter rubs lightly against the groove during the 
movement, but does not, in jure the work. 

Plain Broaching. Certain varieties of -work that are to "be 
broached do not require fixtures of any kind, although occa- 
sionally bushings may be necessary if the work is small. In 
Fig. 211 are shown several examples of work which require 
nothing but a bushing large enough to admit the broach. Ex- 
ample A is a cylindrical piece in which the round hole is to be 
broached after it has been drilled ; B is a square hole broaching 
proposition ; C is a four key way ; D is a collar having a number 
of inside serrations. 

Each one of these pieces can be broached without fixtures by 
using the method shown in the diagram. The work E may be 
any one of the pieces illustrated above, and it may be seen that 
the only thing which must be provided except the broach itself, 
is the bushing F. Even this is unnecessary if the work is of 
sufficient diameter so that it will rest firmly against the face- 
plate on the machine. The broach is so made that the portion G 
acts as a pilot in the work, thereby centering it so that as soon 
as the first tooth strikes the work it is drawn back against the 
faceplate and held there during the cutting action. 

A number of matters must be taken into consideration in the 
designing of broaches for various purposes. Some of these 
points have been taken up under another heading in the first 
part of this chapter. There are others, however, which cannot 
be properly covered in a general w r ay, therefore these will be 
mentioned specifically. 

A few examples are given in Fig. 212 in order to make some 
of these points clear to the tool designer. The work A has been 
properly prepared for the broaching process by drilling a hole 
and facing one side square with the hole. It will be seen that 
this piece of work is not very thick so that if a broach were to 
be used such as that shown, only one tooth of the broach would 
be cutting at a time. In other words, the distance between B 
and C is too great so that the work may drop down off center 
and thus either break some of the broach teeth or produce 
work which is off center or otherwise inaccurate. Two or more 
teeth of the broach should always be in the hole at the same 
time, and yet there should not be too many to allow for clear- 



254 

ance for chips. As there is no way in which chips can get out 
from hetween the teeth until they reach the end of the hole it 
is evident that an accumulation is likely to clog the broach, 
causing breakage or rough work. 

The example D shows a long hole and it can be seen that there 
are too many teeth engaged in the work at the same time. It 
is advisable therefore in designing broaches for long holes, to 



Work*. 







Fig. 212. Principal Points in Broach Design 

space the broach teeth farther apart than when the work is 
thin. The example F shows a good arrangement in which there 
are always two and sometimes three teeth in the hole at the 
same time as indicated at (?. There is plenty of chip clearance, 
however, so that the cutting action is good and the work pro- 
duced will be both accurate and smooth. 

It can reaHily be understood from the foregoing discussion 
that a broach of the same diameter may not always be suited 
to two different pieces of work if one happens to-be thick and 



BROACHES AND BROACHING FIXTURES 255 

the other thin. This objection can be overcome if the work can 
be arranged or stacked two or three pieces at a time. If the 
condition is similar to the one shown at A 9 suitable provision 
must be made for clamping the various pieces together so that 
they cannot drop down on the broach during the operation. 

Spacing of Teeth and Chip Clearance. The diagram of the 
broach at L illustrates the points that are of importance in de- 
signing broaches. The pitch of the teeth is the distance between 
them as indicated at H; the amount of variation being deter- 
mined by the material to be cut and the length of the hole. A 
formula which is often used for determining the correct dis- 
tance, is here given. Assuming P as the pitch and L as the 
length of the hole, then: P^V^XO.35. This formula can 
be considered as reliable for average conditions and it will serve 
as a basis on which the designer can determine the correct pitch 
for any given condition. As a general thing, very large broaches 
which will permit a deep space for chips can be designed with 
a decreased pitch, while those broaches which are to be used 
for tough or hard materials may require a slightly increased 
pitch. 

The variation in the size of successive teeth is indicated at 
K and L; this amount, ranging from 0.001 to 0.003 in. for steel 
and sometimes double this amount for soft cast Iron and brass, 
is influenced by the length of the hole to be broached so that 
too great an amount of metal may not be removed by a number 
of teeth in engagement at the same time. The land on the teeth 
is indicated at If, the amount usually being about %2 in. for 
medium sized broaches. The land on the teeth is sometimes 
ground straight but ordinarily there is a back taper of from 
2 to 3 deg., as indicated at 0. 

N indicates the clearance, which depends largely on the length 
of the hole to be broached and the amount of metal which each 
tooth is to remove. It is also affected by the diameter of the 
hole as previously mentioned. An Important point in this con- 
nection is the fillet at the root of the tooth. This should be 
made as large as possible, both for strength and also so that there 
will be less likelihood of cracks during the hardening process. 

Plain Broaches. Plain broaches are usually made with the 
last few teeth the same size in order to assist in the upkeep of 
the tool. After grinding a few times the number of teeth of the 



256 J108 AND FIXTURES 

same size will be gradually reduced until finally there is only 
one sizing tooth left, after which nothing further can be done 
and the broach must be discarded or used for a smaller size 
after re-grinding. Some forms of broaches can be made up in 
a series of units as indicated at P, Q and B 9 and mounted on 
an arbor 8. It is evident that the units can be provided with 
a keyway for location and they can be held on the arbor by 
means of check nuts as shown at T. If the size of the broach 
permits, it is as well to put the nuts on the forward end and 
provide a shoulder at the rear for the various cutters to be 
drawn against. The size and method of coupling used have an 
effect on this part of the design. 

Broaching Round Holes. When round holes are to be 
broached, a good finish can be given to the work by burnishing 
it or swaging it as shown at J7. In this case a burnishing broach 
W of rounded form is drawn up against the shouldered por- 
tion V by means of the nut at X. After the cutting has been 
done the rounded portion is pulled through, thus producing a 
very fine finish and also compressing the metal so that a hard 
wearing surface is obtained. 

Broaches having considerable area often can be made to cut 
more freely by nicking the teeth as shown in the diagram at Y. 
The nicks must be so arranged that they overlap each other as 
at Z. An arrangement of this kind breaks up the chips and 
assists in cases where hard metal is encountered or on broad 
surfaces. 

Broach Couplings. The method of connecting the broach to 
the pulling member of the broaching machine permits the opera- 
tion of coupling and uncoupling the broach to be done rapidly. 
Provision of some sort must also be made so that either the work 
may be adjusted vertically in relation to the broach, or that 
the broach itself can be adjusted in relation to the work. Some- 
times the faceplate is adjustable up and down and in other cases 
the broach coupling is provided with adjustment. 

In Pig. 213 is shown a piece of work A and a broach B, the 
latter being connected to the pulling member of the broaching 
machine by means of the taper pin D. 

The coupling slide F is mounted on the ways of the machine 
and suitably fastened to the screw E. The holder C screws 
into slide G, which can be adjusted by means of screw H, so as 



BROACHES AND BROACB1XG FIXTURES 



257 



to bring the broach into the correct position with relation to 
the work. 

Methods for Slotting the Ends of the Broach. The detail 
at K shows a common method of slotting the end of the broach 
when ?. pin coupling is used like that shown above. Another 
method is indicated at If, this arrangement consisting of a 
milled slot on each side of the bar. There are occasional in- 
stances when it is desirable to pull more than one broach at a 
time in a horizontal plane and when this becomes necessary it 
is obvious that some other form of coupling must be used. A 
case in point is shown at the lower left-hand corner of the illus- 




fff Machine'' 



Fig. 213. Methods of Broach Pulling 

tration, the coupling member X being mounted on the ways of 
the machine at and P. The screw portion Q fits the pulling 
member of the machine, while the broaches are held in the usual 
manner at R and 8. In such a case care must be taken by the 
designer to see that the pulling action is distributed equally on 
both broaches so that there will be no chance of cramping dur- 
ing the operation. 

Keyway Broaching. Several examples of keyway broaching 
are shown in Fig. 214. The ordinary method is illustrated in 
the example A, which is being cut by broach D. The work is 
located on a bushing B which is fastened into the faceplate of 
the machine. This bushing is so made that the broach fits a slot 
in it at C, thereby guiding and supporting it at the same time. 



258 



JIGS AND FIXTURES 



This method is generally used for ordinary keyway cuttting as 
the only fixture required is the guide bushing. Standard 
broaches can also be used, which is obviously economical. 

When a taper hole has a keyway cut in it as shown at E, the 
method used is the same except, that the guide bushing F is 
made to fit the taper and it is also tilted so that the keyway 
will be parallel to the side of the tapered hole as indicated. 
Care must be taken by the designer to see that the work fits the 
tapered portion E yet does not strike against the surface G. 
Sufficient clearance must be provided so that there will be no 




Double Keyway 

Fig. 214. Various Methods of Broaching Keyways 

chance for this to happen; %e or even % in. is none too much, 
depending on the angularity of the taper. 

An excellent idea which can be applied to certain kinds of 
work is shown at P. This is a guide bushing in which the broach 
Q is operating. It is evident that as the broach or bushing 
wears, the keyway will become shallower and eventually will 
not be deep enough to pass inspection. By providing a shim 
at R, adjustments can be made as desired by placing paper or 
thin metal between the shim and the body of the bushing, thus 
raising it up and prolonging its usefulness. 

Referring to the work shown at L, attention is called to the 
two keyways at 11 and N. In broaching a piece of work like 
this two methods are possible ; a bushing can be made like that 
at and two separate broaches used at M and N, in connection 



BROACHES AND BROACHING 



259 



with a coupling; like the one illustrated in Fig. 213, or a broach- 
ing bar can be made up with two inserted broaches in their 
correct positions, and the work done without resorting to a guide 
bushing. Either of these methods will produce good work. 

Broaching Square Holes. In broaching square holes the 
work must first be prepared for the operation by drilling a hole 
and facing one side square with the hole. As a general thing 
the corners are not quite square, as a sharp corner would be 
hard to keep up and also it might cause trouble in hardening 




Fig. 215. BroacMng Square Holes 

if the work were to be heat-treated. The sides of the hole are 
also relieved slightly in order to obtain a better bearing on the 
shaft and likewise to relieve the cut somewhat while broaching. 
This is clearly shown in the work A in Pig. 215. Starting with 
the hole at B, the work when about half finished would appear 
like the diagram at C. The illustrations at D and E show the 
general form of broach used for this kind of work. The method 
used for setting up the work is the same as those mentioned and 
shown under the descriptions of broaches which do not require 
guide bushings. 



260 



JIGS AND FIXTURES 



When a square tapered hole is to be broached the work must 
be set up so that the taper of the corner of the hole is parallel 
with the spindle of the machine as shown at F in the same illus- 
tration. An indexing fixture must be made for work of this 
kind and the broach itself must be so designed that it is of the 
form shown at G. The cut should extend slightly beyond the 
center of each side. It is of the greatest importance for the 
designer to remember that the angle at the corner of a square 
taper hole is not the same as the angle of the sides. It is a 



-- -/Broaches 




Fig. 216. Double Broaching Fixture for Two Different Size Holes 

compound angle which is not usually given on the blue print 
of the part; therefore it must be figured out by trigonometry. 
Broaching Fixture for Connecting Rod. The crank pin and 
piston pin holes in connecting rods for automobiles are fre- 
quently finished by broaching. A fixture for this purpose is 
shown in Fig. 216. The fixture itself is very simple and yet it 
is effective and accurate. The two connecting rods A and B 
are located on studs at their upper and lower ends, one large 
end and one small end of each rod being broached at the same 
time as indicated at C and D. The locating plugs are correctly 
located in the faceplate E which is positioned by means of the 
plug F against the faceplate on the machine. A large and small 



T 



BROACHES AND BROACHING FIXTURES 



261 



broach are used simultaneously, after which the connecting rods 
are transposed while the other two holes are broached. 

Broaching Fixture for a Ratchet Sector. Fixtures for 
broaching use many of the devices which have been previously 
illustrated and the principles of holding and clamping can be 




Fig. 217. Broaching Fixture for Ratchet Sector 

applied to this type of fixtures as well as to the others. There 
are, however, peculiar conditions to be met in the design of 
fixtures for broaching and these can best be appreciated by citing 
suitable examples. The matter of removing and replacing the 
broach after each operation sometimes takes time which can be 
avoided by a little thought on the part of the designer. An 
example of this kind is given in Fig. 217, the work A being a 



262 JIGS AXD FIXTURES 

ratchet sector of which four pieces are to be broached at a time 
as indicated. The work is set up in the swinging locater B 
which rests on a lug 0, and is pivoted at D in such a way that 
it can be swung over into the broaching position when desired 
and located by a pin at F which corresponds to G on the face- 
plate as shown. In the loading position, the clamp is pulled 
back as shown by the dotted lines at K while the work is being 
placed on the two pins at X and Y. The clamp is then tight- 
ened and the work is ready to be swung into place when the 
other pieces are finished. While the loading of one group of 
pieces is proceeding the other set is being machined, being held 
in the other swinging member G and located by the dowel pin 
at H. The clamp L holds the f6ur pieces firmly and the broach 
M cuts the serrations shown. A bracket N is mounted on the 
face of the plate to act as a guide and support for the broach. 
After the pieces have been machined the swinging member C is 
turned over until it rests on lug P where the pieces can be re- 
moved and replaced by others. 

As the broach used for this operation is a heavy one it is ad- 
visable to support the outer end on the sliding support which 
can be obtained as a part of the broaching machine equipment. 
"With a fixture like the one shown, however, it is unnecessary 
to remove the broach at all and consequently the only time lost 
is in the return stroke of the broach and the swinging into place 
of a fresh group of pieces. Arrangements of this kind are some- 
times possible when work does not have a hole in it through 
which the broach must pass. 

Broaching Fixture for Timing Gear. Certain kinds of work 
must be located in a fixed relation to each other when they are 
installed in the mechanism of which they form a part. It is 
therefore a decided advantage to take this into consideration 
when designing tools for these parts. An example of this kind 
is given in Fig. 218, the work A and B consisting of two auto- 
mobile timing gears. A definite relation must be kept between 
the keyways which are to be broached and the teeth which have 
been previously cut In addition to this each gear must be 
properly marked in a particular place so that when the two 
gears are assembled in the car the gears can be meshed at these 
points, thus assuring the correct position of the cams on the 
camshaft in relation to the throws of the crankshaft 



BROACHES AND BROACHING FIXTURE!* 



263 



The work is located on two studs, the locating pins at C and D 
being provided to determine the relation of the key way with a 
given tooth. The method used is apparent from the illustra- 
tion. The marking of the teeth is done by the swinging arms 
H, each of these having in it a pointed pin K which, when struck 
with a hammer, makes a mark on the gear. After the marking 




Fig. 218. Broaching Fixture for Timing Gears 

has been done the arms are swung out of the way so that the 
gears can be readily removed. The principles illustrated here 
can be applied in other cases where the location of the keyway 
must be kept in relation to some other part. 

Examples of Index Broaching. Index broaching is of vari- 
ous kinds and the requirements are also varied. In one case 
accuracy may not be of the greatest importance, while another 
may require the greatest care to produce it within the necessary 



264 



JIGS AND FIXTURES 



limits. These points must be considered when designing fixtures 
for any kind of an operation. So far as the fixtures are con- 
cerned the indexing devices which have been described in pre 
vious articles cover the situation quite thoroughly, so there is 
no necessity for repetition. Several examples of work which 
may require an indexing device of some kind are shown in Fig. 
219. The work A, for example, is of such large diameter that 




Finished Work 



Fig. 219. Examples of Index Broaching 

it would hardly be desirable to make up a four spline broach, 
both on account of its weight and also the expense. It is evi- 
dent therefore that an indexing device would be of assistance 
in a case of this kind. A method is illustrated in order to point 
out the errors into which a tool designer may fall unless he 
analyzes a situation carefully. Let us assume that the work is 
set up on a guide bushing so that a broach can be used as at F. 
If then the guide bushing has a slot G located at 90 deg. from 
the one which is used as a guide for the broach, it would appear 
that the work could be turned around on the bushing to take 
another position and located with a plug as at K. Witt this 



BROACHES AXD BROACH ISO FIXTURES 265 

plug in place a broach cut could be made as at H, and the opera- 
tion could be repeated to finish the other keyways. If the work 
A is to be machined at E 9 C, D and E it is apparent that any 
slight error in location of the plug K would cause an error 
which would become more and more as the work is turned 
around, so that the piece when completed might be valueless. 
Hence, it is seen that a method of this sort is not good practice 
and will not produce accurate work. 

An index fixture of simple design could be used with much 
more satisfactory results, and although it might be a little more 
expensive than the method illustrated, the product obtained 




Fig. 220. Outboard Support for Heavy Broaching 

would pass inspection. Another example of work which requires 
indexing is shown at L, w r hieh is an internal gear of large 
diameter. The work is to be done by the broach N which is so 
designed that it will cut a number of teeth at one time. The 
work can be located on pins in the holes M on a simple index 
plate so that the successive broaching operations will produce 
a finished gear. Any good method of indexing can be applied 
to a piece of work like this, although it is essential to use a 
method which will not multiply the error as in the instance 
just mentioned. An indexing fixture should be made up with 
the indexing bushings or slots as far away from the center as 
possible in order to insure accurate work. 

When the use of a heavy broach is necessary the weight of 
the overhanging portion of the broach is likely to be a matter 
of serious moment. It is evident that if it is to be supported 



266 MG8 AND FIXTURES 

at all it must be done by some arrangement whieh will permit 
it to be aligned properly, or else the work produced may be 
inaccurate. When one hole is to be broached in accurate rela- 
tion to another accurate alignment is also necessary, so that 
in each of these two cases it is well to" use the outboard support. 
An example which shows the application of this device is 
illustrated in Fig. 220 ? the work A being similar to the internal 
gear shown in the preceding illustration. In this case, how- 




Broach 



Fig. 221. Method of Spiral Broaching 

ever, the broach is so made that all of the teeth are cut at the 
same time, and as a consequence the broach is both large and 
heavy. The support E is provided with a slide D on which is 
mounted the member C which holds one end of the broach as 
indicated. Provision is made so that proper alignment can be 
obtained without difficulty. 

Spiral Broaching. When it is necessary to broach a spiral, 
two methods are possible; the broach may be arranged so that 
it will revolve while cutting, or the work may revolve while the 
broach is passing through it. In Pig. 221 two examples of 



BROACHES AND BROACHING FIXTURES 267 

spiral work are shown at A and B and one method of broaching 
is shown. The work A is mounted on the broach C so that the 
pulling action comes against the face of the bushing E. This 
bushing is adjusted by the two check nuts at G so that it will 
revolve freely and all of the thrust is taken on the thrust "bear- 
ing F. The fixture D is mounted on the faceplate of the ma- 
chine and fastened by means of screws. 

In operation the angularity of the broach teeth causes the 
work to revolve so that the spiral is cut without other assistance. 



CHAPTER XI 
DESIGN OF RIVETING FIXTURES 

EIVETING MACHINES TYPES OF RIVETS LOCATING AND CLAMP- 
US^ USE OF TABLES RING-STAKING TOOLS AND FIXTURES- 
EJECTORS. 

The process of riveting is used extensively in many classes of 
work, both small and large. For example, adding machines, 
typewriters, cash registers, etc., have many small parts made up 
from two or more units, assembled and riveted together to make 
a single component of the mechanism. Automobile frames, steel 
girders for buildings, ship plates, bridges and many other forms 
of structural work depend largely on the process of riveting to 
locate and hold together the various structural members. Rivets 
in structural work are usually heated before driving but for 
small parts cold rivets are used and it is here that riveting 
fixtures are used to advantage. 

Methods of Riveting. Rivets are headed over either by hand 
or machine. In some cases the rivets are in such a position that 
it is very difficult to head them over on a machine, necessitating 
a hand operation. Hand riveting as a rule does not require a 
fixture. 

The machines used for riveting are of two general types, one 
of which heads the rivet by spinning the metal over to form a 
head; the other peins the metal by striking successive blows. 
Both types are extensively used, the selection being dependent 
upon the kind of work that is to be done. 

Riveting machines are made in several styles, both horizontal 
and vertical ; single, double and multiple spindle ; operated me- 
chanically or by pneumatic power. In some machines work is 
placed on an anvil and the spindle is moved up to it; in others 
the anvil itself moves toward the spindle. In the reciprocating 
type of machine the spindle is arranged to hold a pein of suit- 
able form, while in the rivet spinning machine hardened rolls 

268 



N OF RIVETIXG FIXTURES 



269 



are used. In either machine the action is very rapid and work 
is produced much more quickly than by hand riveting 1 . 

Machine riveting produces sharp, quick blows which are ren- 
dered elastic by springs or rubber cushions. In the pneumatic 
type the air acts as a cushion. The force of the blow can be 
regulated by the operator. The application of riveting fixtures 
covers such a wide field that it will be understood better by re- 
ferring to the various examples given in this article. The facility 
with which work can be handled generally governs the produc- 
tion, as the actual time consumed by the riveting operation is 
very small. 

The kind of work to be riveted affects the shape and form of 




c 






B 






A 







Toper I ** Oper 



Toper 2!? Oper 







*M 






H 






K 


-~-mmvx. 




L 



L 






K 






H 








Tl Blind Rivet 



Straight- l^Oper Straight - 2" Oper. 

Fig. 222. Types of Rivets and Riveting 

rivets used. Straight rivets with round heads are often used 
when the appearance is important and when there is plenty of 
room in the mechanism so that projecting rivet heads will not 
interfere with some other part. Straight rivets with flat or 
countersunk heads are also much used for plain work. Taper 
rivets are valuable when correct relation of several parts to each 
other is required. 

Fig. 222 shows several types of rivets and methods of riveting. 
Pieces A, B and C are to be riveted together with taper rivets 
as shown at D. Before the riveting operation the parts are 
reamed in a locating jig and rivets are inserted to act as dowels 
and keep the parts together. The form of locating jig men- 
tioned has been described under the head of drill jig design. 

In riveting these parts together a taper rivet D is used. The 



270 JIGS AND FIXTURES 

first operation heads over the large end of the rivet and it is 
important that clearance should be provided in the riveting 
fixture at E so that the rivet will not bottom. After the large 
end has been headed the work is turned over so that the small 
end comes uppermost as at G. The other head of the rivet rests 
on the anvil at F. Care must be taken to see that work does 
not rest on the block in this ease as the rivet head might be 
somewhat lower than the surface of the work which would allow 
it to be forced out during the riveting process. This would 
cause a loose fitting rivet and inaccurate work. It is important 
that taper rivets should be made of uniform length and the 
holes must always be carefully reamed. 

Straight Riveting. When straight rivets are used in fasten- 
ing several pieces together as shown at H, K and L, the anvil 
used must be cut away to allow the end of the rivet to seat itself 
as shown at N. The depth of the recess should be sufficient to 
allow for a head on this end of the rivet when the work is 
turned over. After the head M has been formed the work is 
reversed and the head takes the position 0. The other end N 
can then be riveted taking care that the head rests firmly on 
the anvil. 

Round Head Rivets. This is the most common type of rivet- 
ing, as the rivet is always provided with one head. This head 
rests in a special anvil E which is cupped at 8 deeper than the 
rivet head and slightly smaller in diameter. This supports the 
rivet and also prevents it from turning. Riveting of this kind 
is often done on a punch press as well as a riveting machine 
and several rivets may be headed at the same time, providing 
the work is uniform. 

Blind Rivets. When rivets do not go through the piece of 
work they are called blind rivets and are generally made in 
taper form as shown at U. When a case of this kind is found, 
the taper of the hole should be slightly different from that of 
the rivet in order that a wedging action will be produced due 
to the difference between the two tapers. This wedging action 
is sufficient to hold the rivet in place. 

Method of Riveting Rollers. If a roller such as that shown 
at C in Fig. 223 is to be held in place in a piece of work A by 
means of the special rivet B, provision must be made so that 
the roller will be free to move on the rivet. Suitable allowance 



DESIGN OF RIVETING FIXTURES 271 

must be made so that the shoulder E is slightly longer than the 
roller. When the rivet is headed on the upper end there will 
be sufficient clearance to allow the rolls to revolve. In setting 
up work of this kind a special anvil can be made as at Z>. This 
anvil is smaller than the rivet head in order to prevent up- 
setting the head. The bushing E serves to locate the rivet and 
roll. 

The method of riveting a hinge is shown at F and G. The 
anvil K is made so that it wiH hold the round head rivet H. 






n 




N \ZiAo 



Fig. 223. Forms of Riveting Tools 

A shoulder is provided at L which gives the proper allowance 
between the two parts. The operation of riveting can be done 
in the regular way. 

Several forms of peins are shown at M, N, and <?. The 
form M is used for flat and countersunk rivets. N is somewhat 
similar but being cupped slightly has a greater spreading action 
on the rivet. The form has a series of points which tend to 
pein the rivet rapidly. In the rivet spinning machine a hard- 
ened roll Q is used to form a rivet head as indicated at P. 
There are many other forms of peins used in riveting, the shape 
of these depending on the work to be done and somewhat upon 
the material of which the rivet is composed. 

General Notes on Design. Rivets often act as dowels in lo- 
cating several parts with relation to each other when great 
accuracy is not important. The design of fixtures for this class 



272 JW8 AND FIXTURES 

of work is not at all difficult. "Work having a center hole and 
in which rivets are located radially should be provided with a 
location hole unless the shape of the piece is such that it can 
be easily set up in the desired position. For instance, if two 
washers are to be riveted together so that the center holes will 
be in alignment, a stud can be used as a locater ; whereas if the 
outside diameters are to be in alignment the work should be 
nested and located from the outside. In riveting two gears to- 
gether so that the teeth will bear a certain relation to each other, 
pins or pawls should be used between the teeth. 

The location points for work that is to be riveted should be 
as near to the outside as possible, in order to obtain maximum, 
accuracy. Clamps are not always required in riveting work 
together but they are frequently used in order to prevent 
spreading of the work when the pressure of the hammer is ap- 
plied. A rivet spread out between two pieces of work is the 
ordinary result unless clamps are used, the vibration of the 
machine causing the two pieces to separate. Various types of 
rivets require special forms of anvils in order to avoid the pos- 
sibility of bad rivets. Several points in this connection have 
been brought out in Figs. 222 and 223. 

The position and location of the fixture on the riveting table 
must be so arranged that the rivet will *be directly over the 
anvil and in contact with it. The production required on any 
riveting proposition does not necessarily affect the design of the 
fixture as there are not many ways of riveting work. Positive 
and rapid clamping are important, however, and the accuracy of 
the product is dependent upon the location and the use of proper 
rivets. 

Vibration should always be considered. All loose parts of 
fixtures should be well screwed down so that the excessive vibra- 
tion cannot loosen them and cause trouble. 

.Riveting Several Pieces Together. In Fig. 224 is illus- 
trated a method for locating and clamping several pieces to- 
gether for riveting. This is an example which makes plain 
the importance of proper locating and clamping, in order to 
prevent trouble due to vibration and also to insure accuracy. 
Unless the work is held properly it is likely to open up 
and separate so that the rivet may bulge out as shown at C 
between the plates A and B. Rivets should not be used as 



DESIGN OF RIVETING FIXTURES 



273 



dowels to locate work If great accuracy Is required ; other means 
should be provided. In the example shown the four pieces 
D, E, F and G are slipped over the center stud H and clamped 
by means of the nut shown. The locating plug K Is a loose 
piece which is pushed through all the pieces and Into the bush- 
ing L which locates It. This is better than a station locating 
stud similar to the center one, because it is less likely to be 
sprung out of its true position. The locating plate is slotted in 
three places to allow for the rivets N. For riveting the othei 
side of the work another fixture is necessary. 




Fig. 224. Locating and Clamping for Riveting 

Method of Locating and Clamping. The type of fixture 
shown in Fig. 225 is very good for a number of kinds of work 
and it can easily be standardized. In the example given, the 
work A is to be furnished with a pin B which Is to be riveted 
in place. The center distance from G to B is very important. 
The work is located on the stud C and the riveting is done over 
the anvil shown. The anvil is directly over the portion H which 
fits the riveting machine. The work is nested between the fixed 
member E and the movable pin F, the latter being arranged so 
that it does not turn as it is moved by the screw. This clamping 
arrangement has been previously described. 

Attention is called to the location of the pin C in the bush- 



274 



JIGS 



FIXTURES 



ing D. This provides for easy replacement of the pin when 
worn and thus preserves the accuracy. Clearance should be 
allowed at G so that the work will not rest on anything except 
the rivet. 




Tig. 225. Riveting Fixture Showing Methods of Locating and Clamping 

Swinging Type of Riveting Fixture. To assist in the rapid 
handling of work a swinging fixture is often an advantage. An 
example of this kind is shown in Fig. 226. The work A has two 
rivet studs as indicated at D, these being located at B and C as 
indicated. As they operate in a face cam in the completed 
mechanism their location is important and they must be firmly 
riveted into position. The work locates on a central stud E and 



DEFIGN OF RIVETING FUTURES 



275 



is held firmly in position by the pawl F operated by the thumb- 
screw G. The swinging member of the fixture is pivoted at // 
so that in operation the rivets can be brought into position 
under the hammer by swinging the lever I/ until it strikes the 
pins at K and L. When in the riveting position ample support 




Fig. 226. Swinging Type Riveting Fixture for Two Holes 

is given by the fixture at N, this portion being clamped in place 
in the riveting machine. The dotted lines indicate the two posi- 
tions of the fixture when riveting. This is a clean cut example 
of a simple riveting fixture involving principles which can be 
applied to other work of similar character. Tables axe ^ of ten 
used on riveting machines in order to simplify the location of 
fixtures which are to be used for several operations. Also when 



276 



JIGS AND FIXTURES 



fixtures are large and when rivets are so spaced that they can- 
not easily be located on an anvil, a table permits easy location 
and makes the operation of riveting more convenient. A few 
points in connection with the use of tables are illustrated in 
Fig. 227. It is important that the table should be so located 
that the stem A will be in positive contact with the anvil on 
the machine. There must never be a space between them as 
indicated at B as this would not give proper support. The 



Locating pfnS" 



t 




Turn fixture 180 
* fbr this hole 



O 



.Table 



JUL 



U 
w&M 



.Tcrb/e 



Anvif 




l_ 



'%%%%0^///W/////^^^ Anvil"* 

Fig. 227. Use of Special Table with Locating Pins 

fixture which may have an anvil of its own, must also always 
be made so that the under side of the anvil is in contact as at 
C. It should never be made as shown at D as this would not 
give good results and would buckle as indicated by the dotted 
line. 

In locating any fixture on the table an arrangement of pins 
can be provided so that several locations can be easily made. 
If a number of pieces of a similar kind are to be riveted it is 
often possible to standardize the tables and the relation of the 
pins so that fixtures can be built which will all be usable on the 
same table. The work E for example is to be riveted at F, G 



DESIGN OF RIVETING FUTURES 



277 



and H and it is located for the operation on the riveting fixture 
K. Locating pins are provided at M 9 N, and P so that by 
moving the fixture along as indicated by the dotted lines, all 
three rivets can be brought into position over the center line of 
the riveting machine. Other fixtures for work of similar shape 
and size can be so made that the same table can be used in 
each case. 




Table 



Finish flush 
with feef* 



Work*. ,C 







Fig. 228. Example of Riveting Fixture Using Special Table 

In Fig. 228 is shown another example of a fixture used on a 
special table A. The plug B must rest on the anvil of the rivet- 
ing machine. The work C is to have the two pins D and E 
riveted in place and the method of location here is the same as 
that previously described. The ends of the bushings at F and G 
must be ground so that they are flush with the feet of the fixture 
in order that they will be in contact with the plug E during the 
riveting operation. The locating pins on this table are arranged 
in similar fashion to those previously described. 



278 



JIGS AND FIXTURES 



Riveting Fixture Used for Both Sides of Work. The de- 
signing department can often help in simplifying the design of 
riveting fixtures by paying attention to the location of rivet 
holes, and placing them in such positions that the same fixture 
can be used for riveting both sides of the work. An example 
which illustrates the advantages of this forethought is shown 




Table, 



Fig. 229. Riveting Fixture for Both Sides 

in Fig. 229. The pieces A and B are riveted together at three 
points C, D and E, these points being 120 deg. apart and the 
same distance from the center. The pieces are assembled on 
the center plug at F, resting on six plugs as indicated. Three 
of these plugs are cut away to allow for the heads of the rivets, 
while the other three are plain on the top. For the first riveting 
operation the slotted pins are used successively; but for the 
second the plain pins are used, the work being turned over. 
Two pins G and H are used in the riveting machine table to 



DESIGN OF RIVETING FIXTURES 27S 

act as locaters for the fixture. It will be noted that the edge of 

the fixture is notched in several positions so as to give correct 
locations for the various rivets. The notch acts as one locater 
against the pin H, while the other location is fixed by a contact 



Locating 

-' pins 




Section A-B-C-D -E 
Fig. 230. Riveting Fixture for Two Spur Gears 

of the outside of the fixture with the pin G. A pin L is placed 
in the fixture to locate the two pieces and attention is called to 
the manner in which it is cut away so that it will not interfere 
with the flange indicated. All of the six studs used for riveting 
are flush with the legs of the fixture thus assuring proper sup- 
port when they are brought into position for riveting. This 
fixture is built high in order to make it easier to turn over; it is 



280 JIG8 AND FIXTURES 

dirt proof and easy to clean. The design being so made that 
both operations can be done in the same fixture cheapens the cost 
considerably and also expedites the operation. 

Riveting Fixture for Two Spur Gears, When gears are to 
be riveted it is often necessary to locate each of them by the 
teeth in order to preserve the correct relation. Riveting fixtures 
for this class of work should be carefully designed in order to 
make sure that no inaccuracies will result from imperfect loca- 
tion. An example of this kind is given in the two pieces F and G 




Fig. 231. Example of Ring-Staking and Types of Ring-Staking Tools 

in Fig. 230, in which there are four rivets to be driven as indi- 
cated. The rivets used are tapered, therefore provision must 
be made to prevent the small end of the rivet from bottoming 
in the slot during the first riveting operation. The work is 
located on a central stud and the pawl H engages with a tooth 
in the part F; the pawl K is used similarly with the gear 0. 

A swinging clamp of special design is used to hold the work 
as indicated at L. This clamp swings on a stud M into the posi- 
tion shown by the dotted line so that the work can be easily 
removed. The stop pin N limits the movement. The riveting 
table has three pins 0, P and Q, which serve to locate the rivet- 
ing fixture m the manner previously described. For certain 
classes of work fixtures of this kind are very much used and by 



DESIGN OF RIVETING FIXTURES 



281 



using a standard plate a number of fixtures can be handled on 
the same table without difficulty. 

Ring Staking Operations. Ring staking is the process of 
peining over or swaging two pieces of work together by means 
of a circular tool having a sharp edge which swages or forces 
the metal on one piece of work over into a countersunk portion 
on the other. A ring staking operation is often used when work 
is to be riveted, as it prevents the parts from coming apart or 




Fig. 232. Ring-Staking Fixture with Ejector 

separating, the rivets serving to keep the pieces from turning 
in relation to each other. The machine used for ring staking 
is a punch press. 

Fig. 231 shows a few examples of work requiring ring staking, 
and the tools used for the operation. The cam A and the bush- 
ing B are to be fastened together by staking with the tool C. 
The enlarged sectional view shows at D the effect of the staking 
operation, the metal being upset and forced over into the 
countersunk portion. King staking tools are frequently piloted 
to assist in preserving accuracy. In the example E the locating 
stud in the fixture is carried up far enough to act as a pilot in 
the staking tool. The pilot F is in the staking tool itself so that 



282 JIGS AND FIXTURES 

it centers the work as it enters the hole. In another example 
the pilot G in the staking tool enters a bushing on which the 
work locates, the bushing being relieved slightly at H so that if 
the metal is contracted by the staking tool it can still be removed 
from the bushing without difficulty. 

Ring Staking Fixture with Ejectors. Fig. 232 shows a com- 
plete fixture for ring staking the two parts A and B. The fixture 
fits in a shoe C on the bed of the punch press, being located 
and held in place in some approved manner. The counterbored 
portion of the shoe D can be standardized so that a number of 
fixtures can be used with the same shoe. The staking tool E 
fits the ram of the punch press as indicated. The work locates 
on a stud F which extends above it and acts as a pilot for the 
tool. 

Work of this kind sometimes clings to the tool and rises with 
it, in which case a stripper like that shown at G may be found 
an advantage. Work may also stick on the locating plug so 
that it is not easily removed without using an ejector. It is 
advisable to provide for both contingencies by using both 
stripper and ejector. The form of ejector used in this instance 
has been previously described so that further comment is un- 
necessary. It is important to know the stroke of the press when 
designing ring staking fixtures, in order that the height oif the 
fixtures may be kept within the required limits. 



INDEX 



Accuracy in milling operations, 

importance of, 152 
of vise- jaws, 234 
required, consideration of, 4 
Accurate work, four-sided jig for 

obtaining, 108 
Adjustable jacks, 51 

v-blocks, 53 

Advantages of duplex milling, 188 
Air operated clamps, 180 

pressure for cleaning fixtures, 28 
Aluminum jig leaves, 59 
Analysis, value of, in laying out 

operations, 18 
Angle iron jig bodies, 62 
Angular and straight holes, drill 

jigs for, 92 
holes, drill jig for, 92 

index fixture for drilling, 117 
plates, use of, 107 
work, method of drilling, 107 
Applications of milling cutters, 145, 

147 
of step blocks to profiling 

fixtures, 221 

Assembling and locating jigs, 97 
Attachment for form milling, 184 
Automatic cam cutting machines, 

216 

form milling attachment, 184 
indexing, device for hand mill- 
ing machine, 201 
for milling, 200 
drill jig, 114 
jig, 122 
profiling, 227 

fixtures for, 227 

B 

Bearing seats, importance of con- 
centricity in, 6 



Bearings for jig leaves, 57 

Beeswax vise-jaws, 241 

Bench milling machines, various 

types of, 136 
Blind rivets, 270 

Boring and reaming index jig, 105 
Box or closed jigs, 36 
Brake band, indexing jig for, 120 
Broach couplings, 256 
fixture, double, 260 
pulling, methods of, 257 
slotting for coupling, 257 
supporting and aligning, 265 
Broaches and broaching fixtures, 247 
important points in design 

of, 247 

chip clearance for, 255 
design of, 257 
important points in design of, 

254 

lubrication of, 249 
spacing of teeth in, 254H255 
Broaching an oil groove, simple 

method of, 251 
examples of work suitable for, 

252 

fixture cost of, 249 
double, 263 

for connecting rod, 260 
for ratchet sector, 261 
for timing gear, 262 
with locaters, 263 
fixtures and broaches, 247 
clamping methods used in, 249 
important points in design 

of, 247 

rigidity of, 249 
importance of outboard support 

in, 265 
important points in design of 

fixtures for, 248 
index, 264 

keyways, methods used in, 258 
283 



284 



INDEX 



Broaching, methods of, 250 
of setting up for, 252 

plain, 252, 253 

principles of, 248 

round holes, 256 

spiral, method of, 266 

square holes, 259 
tapered holes, 260 

types of, 250 

Bronze casting, continuous circular 
milling fixture for, 210 

ring, milling fixture for cutting, 

197 

Built up jigs, 37, 96 
Burr clearance in drill jigs, 32 
Bushing design, 73 
Bushings, insufficient clearance for, 
16 

design and proportion of, 72 

knurled, 71 

liner, 72 

location of, 75 

methods of holding, 74 

screw, 71 

slip, 71, 74 

types of, 71 
Button clamps, 44 



Cam clamp for shaft, 89 
cutting machines, 216 
drum trunnion jig, 128 
lever method of locking jig 

leaves, 60 

Cast iron angle jigs, 64 
Castellating nuts, index fixture for, 

196 

Castings, finished, location of, 25 
thin, method of supporting and 

clamping, 177 
Channel iron jig bodies, 62 
Chart of inserted tooth milling 
cutters with solid bodies, 
150 

Chatter in milling fixtures, 152 
Chip clearance in closed jigs, im- 
portance of, 90 
in drilling, 30 



Chip troubles in drilling, 32 

in milling fixtures, 156 
Chips in milling fixtures, 153 
provision for, 153, 157 
for washing out, 28 
Chuck jaws, serrating fixtures 

for, 207 
Chucking lugs added to casting, 5 

stem, advantage of, 15 
Circular profiling, 223 
Clamp, cam operated, 89 

for holding and locating work 

in jig, 49 

in leaf of closed drill jig, 91 
plain, s'mple type of, 41 
Clamping, correct, 47 

correct and incorrect, 27 

importance of, 40 

improper, distortion caused by, 

26 

incorrect, 47 
pneumatic, 180 
pressure, direction of, 25 
suggestions for, 44 
thin castings, method of, 177 
work, correct and incorrect 

methods of, 41 
work in groups, 173 
Clamps, air operated, 180 
button, 44 
double end, 47 
equalizing, 44, 47 
air operated, 180, 181 
principles of, 48 
for milling, equalizing, 171 
special forms of, 166, 167 
hook-bolt, 174, 176 
in jig leaf, 58 
in the leaf, 57 
knife edge, 170 
lever, 44 

operated, 168 
multiple, 46 

for milling, 172 
operated by lever, 168 
pivot, 44 

representative group of, 44 
sliding, 44 
used in milling, 165 



INDEX 



285 



Clamps, wedge, 42 
Cleaning, provision for jig, 28 
Clearance around work, importance 

of, 27 

for burrs in drilling, 32 
for chips in drilling, 30 
for operator's hand, 77 
when indexing jigs, 103 
Closed drill jigs, 91 

jigs, simple type, 94 

with clamp in leaf, 91 
or box jigs, 36 

Clutch drum, indexing jig for, 121 
Combined index and latch for 

drill jig, 114 

Concentricity, importance of, 6 
Connecting link, spline milling 

fixture for, 191 
rod broaching fixture, 260 
forgings, location for drilling, 

23 

index fixture for miling, 202 
Consecutive operations in vise-jaws, 

240 
Construction details of milling 

fixtures, 158 
of jig leaves, 57 
of leaves in drill jigs, 56 
Continuous circular milling fixture 

for bronze casting, 210 
milling fixture for chuck jaws, 

207 

for cylinder heads, 206 
for pump body, 209 
fixtures, principles of, 205 
machine, diagram of, 141 
method of locating work 

economically for, 205 

special machines for, 212 

slot and straddle milling fixture, 

208 

Correct and incorrect methods of 
drilling holes in adjacent 
parts, 26 

Cotter pin jigs, 32 
Couplings for broaches, 256 
Cradle trunnion jig, 126 
Cup bushings, location of work in, 
22 



Cutter action, diagram showing, 154 
in relation to clamps, diagram 

illustrating, 155 
on the work, 154 
teeth, action of, 155 
Cutters, milling, action on work, 154 
inserted teeth with staggered 

blades, 149 
sizing chart of, 148 
standard straight side in- 
serted tooth, 151 
Cylinder heads, continuous milling 

fixture for, 206 
C-washers, use of, 44 



Delicate operation, profiling fixture 

for, 222 
Design, changes in, consideration of, 

4,5, 6 

of broaches, 254 
of drill jigs, 18 
of hook-bolts, 175 
of index plungers and latches, 

111 

of sliding v-blocks, 54 
of swinging v-blocks, 55 
of trunnion jigs, 124 
of u-lugs, 160 
Details of jig leaves, 59 

of trunnions, 125 

Diagram of milling . machine show- 
ing dimensions , 144 
Difficult casting to machine, 10 

drilling problem, example of a, 

131 

Direction of clamping pressure, 25 
Distortion caused by improper 

clamping, 26 

Double broach fixture, 260 
broaching fixture, 263 
end clamps, 47 
indexing fixture for a forked 

lever, 204 
trunnion jig, 130 
Drill bushing, insufficient clearance 

for, 16 

index jig for reaming and bor- 
ing, 105 



286 



INDEX 



Drill jig, built up, 96 
bushings, 72 
design, 18 

double trunnion, 130 
ejectors, use of, 79 
feet, casting, 68 
examples of, 68 
inserted, 68 

method of fastening, 68 
for a clutch drum, indexing, 

121 

for a radial rivet hole, index- 
ing, 120 

for annular ring, indexing, 119 
for pistons, 118 
for pump cover, 90 
for shaft, open, 89 
indexing, for holes in a circle, 

116 

for rapid production, 112 
locating and assembling, for 

shaft and collars, 98 
open trunnion, 127 
plate for dovetail slide, 86 
roll-over, 123, 124 
simple index, 109 
swivel index, 106 
templet, design of, 82 
trunnion, for cam drum, 128 
used progressively, 133 
with cradle, 126 
with angular plate, 107 
with swinging v-block, 95 
jigs, cast iron, 64 
closed, 90, 91 

simple type, 94 
for angular and straight holes, 

92 

for rivet holes, 100 
indexing and trunnion, 101 
locating and assembling, 97 

examples for practice, 99 
open, 86 

for lever arm bracket, 88 
plate, 84 
trunnion, 124 
details, 125 

Drilled holes close to a shoulder, 15 
in forgings, 21 



Drilling and reaming in same jig, 110 

method of, 110 
holes in adjacent parts, 26 
index table for, 115 
machines, spacing of, 8 
problem, difficult, 131 
Duplex milling, continuous milling 

fixture for, 211 
fixtures, 188 
machine, 140 

diagram, 139 
multiple fixture for, 189 



E 



Effect of design on cost of machin- 
ing, 10 
Ejector for a large casting, 132 

used on ring staking fixture, 281 
Ejectors, 79 

eccentric, 80 
for drill jigs, 80 
for vise-jaws, 244, 245 
wedge type, 80 
Elementary points in design of drill 

jigs, 19 

Equalizing clamps, 44 
for milling, 171 
principles of, 48 
hook-bolts, 178 

milling fixture with, 179 
pressure by means of beeswax 

jaws, 241 
vise-jaws, 244 
Example of a difficult drilling 

problem, 131 
Examples of jig feet, 68 

of shapes suitable for profiling, 
224 

F 

Feeler, use of, in milling, 162 
Feet, jig, examples of, 68 
Finger jacks, 51, 171 
Finished work, location of, 23 
Fixture clamped in vise, 243 
for use in vise-jaws, 243 
Fixtures for broaching, 247 



INDEX 



287 



Floating vise-jaws, 237 

Forging, location in cup bushings, 22 

Forgings, location of, 21 

Form milling attachment, auto- 
matic, 184 
plate for profiling use, 225 

Formed vise-jaws, 233 

Forms of riveting tools, 271 

Four-sided drill jig for accurate 
work, 108 



Gear blank chucking, 15 

forging with countersunk 

holes, 22 

Guides, standard jig used between, 
66 



H 



Hand clearance, importance of, 77 
knobs, 78 

milling machine, automatic in- 
dexing device for, 201 
diagram, 137 
work suitable for, 138 
wheels, 78 
High production straddle milling 

fixture, 186 
Hinges for jig leaf, 59 
Holes, square, broaching, 259 
Hook-bolt clamps, 42 
backing up, 43 
for milling, 174 
special applications of, 175 
Hook-bolts design of, 175 
equalizing, 178 

milling fixture with, 179 



Importance of clamping work prop- 
erly, 40 

Important points in connection with 
broaching, 248 

Improved design of parts, 13 

Improvements in machining ob- 
tained by change in design, 
10 



Index and latch combined, 114 
broaching, 264 

methods of, 264 
drilling and reaming, 110 
fixture for angular holes, 117 
for castellating nuts, 196 
for connecting rod, 202 
for cutting bronze ring, 197 
for holes in a circle, 116 
head, use of, 193 
jig for boring and reaming, 105 
simple, 109 
swivel, 106 

milling fixture, twin, 195 
pin, location of, 111 
plungers and latches, 111, 112 
table for drilling, 115 
Indexing and trunnion jigs, import- 
ant points in, design of, 102 
attachment for milling, semi- 
automatic, 200 

automatic device for drill jig, 114 
fixture, double, for connecting 

rod, 202 
semi-automatic, for milling 

spline shaft, 198 
jig, 38 

for a clutch drum, 121 
for annular ring, 1 19 
for radial rivet holes, 120 
rapid production, 122 
jigs, clearance necessary for, 103 
for angular holes in a piston, 

118 
for multiple holes in drilled 

plate, 104 

interferences in, 103 
requirements of, 101 
milling fixture, 192 

machines, 143 

principles and methods of, 110 
requirements, 103, 104 
Inserted tooth face mills, standard, 

152 

milling cutter chart, 149 
with solid body, 150 
Interfering shoulder, 17 
Irregular work, locating and clamp- 
ing, 169 



288 



INDEX 



Jacks, 48 

adjustable, 51 
and spring plungers, 50 
finger, 51, 171 
locking, 51 
Jig bodies, angle iron, 62 

channel iron, 62 

standard type, 63 
boxed or closed, 36 
leaf clamps, 58 

construction, 57 

details, 59 

locking, 60 

posts and thumbscrews, 67 
Jigs, built up type, 37 
cast iron angle, 64 
indexing, 38, 101 
leaf, 56 
open type, 36 
standard, 62 
trunnion, 37 
types of, 34 
with rocking clamps, 65 

K 

Kerosene for cleaning, 28 
Keys, design of, 162 

and T-slot proportions, 161 
Keyway broaching, 258 
Knife edge clamps, 170 

for milling, 165, 166 
Knobs and thumbscrews, standard, 

76 
hand, 78 



Light work clamps, 44 
Lincoln type milling machines, 139 
Liner bushings, 71 
Locating and assembling jigs, 97 
for shaft and collars, 98 
and clamping for riveting, 273 

odd shaped work, 169 
and holding work by clamping, 

49 
and supporting work for milling, 

164 
jigs, 97 

examples for practice in de- 
signing, 99 
pins for indexing, 112 
studs, use of, 30 
surfaces, wear on, 29 
two spur gears for riveting, 279 
Location, correct and incorrect, of 

work, 27 
of bushings, 75 
of connecting rod forging, 23 
of finished work, 23 
of rough forgings, 21 

work, 19 

of small work in vise- jaws, 239 
of work, 4 
for riveting, 272 
in vise-jaws, 234, 235 
pins used in riveting, 276 
Locking jacks, 51 
plugs, 69, 70 

spring plungers in jacks, 50 
two jacks at one time, 52 
Lubrication of broaches, 249 
Lugs, chucking, 5 



Large casting, ejector for, 132 
Layout of plant, 7 
Leaf clamps, 57 

construction, 56, 59 

jigs, 56 

locking jig, 60 

stops, 61 

supports, 61 
Lever clamps, 44 

index milling fixture for, 204 

operated clamps, 168 



M 

Machine tool, avoiding dead time on, 

152 

placements, 8, 9 
tools available, 6 
purchase of, 7 
selection of, 7 

Machined surfaces, location of, 24 
Material to be considered in listing 

operations, 2 
to be cut in milling fixtures, 153 



INDEX 



289 



Method of clamping work, 155 
of locking leaf, 59 
of making locating studs, 30 
Methods of bracing work, 163 
of broaching, 250 
of clamping work in groups, 173 
of ring staking, 280 
of riveting rollers, 270 
Milling continuous, 205 

cutters, action on work, 154 
application of, 145 
selection of, 144 
sizing chart of, 148 
special application of, 147 
spline, action of, 190 
standard, straight size in- 
serted tooth, 151 
fixture basis, design of, 158 
chip troubles, 156 
clamps, 165 

special form, 166, 167 
construction details, 158 
continuous for bronze casting, 

210 

for chuck jaws, 207 
for cylinder heads, 206 
for pump body, 209 
design, important points in, 

151 

for castellating nuts, 196 
for cutting bronze ring, index, 

197 

piston ring, 183 
for duplex milling, 188 

machine, continuous, 211 
for facing and splitting boss, 

182 
for slot, multiple under-cut, 

187 

hand, 182 
index, for connecting rod, 202 

for square shaft, 193 
indexing, 192 

for forked lever, 204 
reciprocating, principles of, 

185 

set block, 153 

spline for connecting link, 191 
straddle, 186 



Milling fixture, with equalizing 

hook-bolts, 179 
fixtures, design of, 157, 182 
of fixture bases for, 158 
details of construction, 159 
multiple for duplex milling, 

189 

reciprocating, use of, 186 
rigidity of. 152 
straddle, 186 
uniformity of ribs and wails 

159, 160 
up keep of, 153 
machine diagram, continuous, 

141 

duplex, 139 
multi-spindle, 141 
showing dimensions, 144 
vertical, 141 
duplex, 140 
indexing diagram, 143 
selection of, 153 
vises, 2SO, 231 
machines, bench, 136 

diagram, Lincoln type, 139 
diagrams, hand and plain, 137 
indexing, 143 
Lincoln type, 139 
multiple spindle, work suit- 
able for, 142 
plain, 138 
selection of, 135 
types of, 134 
vertical, 140 
operations, accuracy required, 

152 
spline, 189 

principles of, 147 
thread, application of, 147 
with hob cutter, 147 
with single cutter, 147 
various forms of milling cute, 

146 

work accurately, 162 
Multi-spindle milling machine dia- 
gram, 141 

Multiple clamps, 46 
for milling, 172 
locking, 172 



290 



INDEX 



Multiple milling, 192 

fixture under-cut for slot, 187 
fixtures for duplex milling, 

189 
spindle milling machine, work 

suitable for, 142 
vise-jaws, 237 







Odd shaped work, locating and 

clamping, 169 
Oil groove broaching, 251 
Open drill jig, 86 

for pump cover, 90 
jig type, 36 

Operation sheet typical, 11 
Operations, listing of, 2 
Operator's safety, 153 
Outboard support for broaching, 265 



Peins for riveting, 271 

Pinch binder slot, milling fixture for, 

182 
Piston, indexing jig for angular 

holes, 118 

ring, cutting milling fixture, 183 
Pivot clamps, 44 
Placement of machine tools, 8, 9 
Plain clamps, 41 

type of, 42 
milling machine, 138 

diagram, 137 
machines, work suitable for, 

139 

Plant layout, 7 
Plate and templet jigs, 35 
jig for dovetail slide, 86 
for large casting, 84 
large, 84 
jigs, 34, 84 
Plugs, locating, 69 

locking, 70 
Plungers, spring, 48 
Pneumatic clamping, 180 

principles of, 180 
Posts, jigs, 67 



Principles and methods of indexing, 

110 

of drill jig design, 18 
of pneumatic clamping, 180 
Production required in listing of 

operations, 2 
in milling operations, 151 
Profiling, accuracy required, 217 
automatic, 227 
chip accumulation, 218 
circular, 223 
cuts, forms of, 218 

various kinds of, 218 
fixture, design of, 213 
examples of, 222 
multiple, 227 
well designed, 225 
fixtures, application of step 

block, 221 
circular, 228 
design of, 217 
location of work for, 217 
machine, bench, diagram of, 213 
machines, bench, 213 

one and two spindles, dia- 
grams of, 215 
use of, 213 
position of work, 217 
roughing and finishing methods 

of, 226 

shape of work, 217 
shapes suitable for, 224 
slot, 222 
step, 219, 220 
surfaces, 219 
use of form plate, 225 
Progressive use of trunnion jig, 133 
Proportion of bushings, 72, 73 
Proportions of u-lugs, 161 
Protection for spring plungers and 

jacks, 50 
Pump body, continuous milling 

fixture, 209 
cover jig, 90 
Punch used with templet jig, 35 



Quarter-turn screws, 67 



INDEX 



291 



R 



Ratchet sector broaching fixture, 261 
Reciprocating milling fixtures, 186 

principles of, 185 
Removal of work from jigs, 81 
Removing and setting up work, 34 
Requirements for tools, 9 
Ribs and walls, uniformity of, 159, 

160 
Rigidity of broaching fixtures, 249 

of milling fixtures, 152 
Ring staking, 280 

fixture with ejector, 281 
holes, 280 
methods of, 280 
operations, 281 
Rivet hole, indexing jig for, 120 

holes, drill jigs for, 100 
Riveting fixture for several pieces, 

273 

for two holes, 275 
spur gears, 279 
on special table, 277 
showing method of locating 

and clamping, 274 
swinging type, 275 
fixtures, design of, 268 

important points in design of, 

272 

swinging type, 274 
locating and clamping for, 273 
machines, 268 
methods of, 268 
process of, 268 
rollers, method of, 270 
several pieces, 273 
straight, 270 
table, special, 276 

with locating pins, special, 

276 

tools, 271 

work from both sides, 278 
Rivets as dowels, 271 
blind, 270 

important points in, 272 
plain, 269 
round head, 270 
types of, 269 



Rivets, various kinds of, 269 
Rocking clamps in drill jigs, 65 
Roll-over jigs, 123, 124 
Roll-over design for, 123 
Rollers, method of riveting, 270 
Rough work, location, of, 19 

for a hub, 21 
Round head rivets, 270 
hole broaching, 256 
Routing sheet, 11 

S 

Safety of operator, 153 
Screw bushings, 71 

machines, spacing of, 9 
Screws, quarter turned, 67 
Selection of milling cutters, 144 

machines, 135, 153 
Semi-automatic indexing device for 

milling, 200 

Serrating fixture for chuck jaws, 207 
Set blocks, 162 

on milling fixtures, 153 
Set-on or plate jigs, 34 
Setting up and removing work ? 34 

work from hub, 21 
Shoulder, drilled holes close to, 15 
Simple leaf jig, 56 
Size of drilled holes, 33 
Sliding clamps, 44 

for milling, 165 
trunnion jig, 129 
v-blocks, 53, 54 
Slip bushings, 71 

methods of holding, 73 
Slot and straddle miling fixture, 

continuous, 208 
milling fixture, multiple or 

under-cut, 187 
profiling, 222 

Small work, vise-jaw fixture for, 243 
Solid body, inserted tooth milling 

cutter, 150 
Special applications of hook-bolt 

clamps, 175 

machines for continuous mill- 
ing, 212 
table with riveting fixture, 277 



292 



INDEX 



Spider support for milling, 178 

supporting jack, 178 
Spiral broaching, methods used for, 

266 

Spline and slot milling, explanatory- 
diagram, 190 
nulling, 189 
action of cutters, 190 
fixture for connecting link, 

191 

principles of, 147 

Splined shaft, semi-automatic index- 
ing fixture, 198 
Spring plungers, 48 

and jacks, 50 
v-blocks, 21 
Spur gear blanks, chucking, 15 

gears, riveting fixture for, 279 
Square hole broaching, 259 

shaft, indexing fixture, 193 

milling fixture straddle, 193 
tapered hole, broaching, 260 
Standard inserted tooth face mill, 

152 

jigs, advantages of, 66 
and components, 62 
used between guides, 66 
knobs and thumbscrews, 76 
straight side inserted tooth 

milling cutters, 151 
Step block, application of, 221 

profiling, 219, 220 
Stops, leaf, 61 

Straddle milling fixtures, 186 
Straight riveting, 270 
Strap clamps for milling, 165 
Studs, locating, method of making, 

30 

Support for rough casting, three- 
point, 20 

of work in miUing, 155 
work by spring plungers and 

jacks, 48 

Supporting and aligning broach, 265 
and locating work for mill ing, 

164 

Supports, leaf, 61 
Surface profiling, 219 
Surfaces to be machined, 3 



Swinging clamps for milling, 165 
type of riveting fixture, 274 
v-block design, 55 

Swivel index jig, 106 
vise- jaws, 237 



Templet jig, sheet metal, 83 

with a locating jig, 83 
jigs, 35 

design of, 82 
use of, 83 
Thin castings, method of supporting 

and clamping, 177 
Threaded work, 14 
Three-point support, 20 
Thumbscrews, 67 

and knobs, 76 

Timing gear broaching fixture, 262 
Toe clamps for milling, 165 
Tool and operation sheet, 11 
engineering, outline of, 1 
equipment required, 9 
Tools used in ring staking, 280 
Trouble caused by chips, 32 
Trunnion details, 125 
jig, double, 130 
ejector for, 132 
for cam drum, 128 
on track, 133 
open, with cradle, 127 
requirements, 101 
requiring sliding movement, 

129 

unusual type, 128 
used progressively, 133 
with cradle, 126 
jigs, 37, 101, 124 
T-slot and key proportions for 

fixtures, 161 

Twin index milling fixture, 195 
Two-holes, riveting fixture for, 275 
Two jacks, locking at one time, 52 
Types of broaching, 250 

of milling machines, 134 
of rivets, 269 
of v-blocks, 53 



INDEX 



293 



U 



U-lug design, 160 
details, 161 
proportions, 161 
Under-cut milling fixture for spline 

shaft, 198 
v-blocks, 53 

Upkeep of milling fixtures, 153 
Use of feeler with, set block in mill- 
ing, 162 
of index head for milling square 

shafts, 193 
of knife edge vees, 169 



Various methods of locking jig 

leaves, 60 

V-block design, 53 

swinging, 55 

sliding, trouble with chips, 53 
swinging, in jig, 95 
types of, 53 
V-blocks, design of, 54 
knife edge, 169 
location of work in, 53 
protection from chips, 53 
sliding, 53, 54 
spring, 21 
under-cut, 53 
Vertical milling machine diagram, 

141 

machines, 140 
Vise fixture, 242 
Vise-jaws, accuracy of, 234 
and vise-fixtures, 230 
beeswax, 241 
depth of work, 232 
diagram of, 233 



Vice-jaws, ejectors for, 244, 245 

equalizing^ 244 

floating, 237 

for long work, 238 

for small parts, 240 

form of, 233 

of ejectors for, 245, 246 

important points in design of, 
232 

multiple, 237 

quick removal of work from, 236 

swivel, 237 
Vises, cam operated, 231 

for milling, 230, 231 

selection of, 232 

special, 231 

W 

Wear on locating studs, 29 

plates for jig leaf, 57 
Wedge clamps, 42 
Work, changes in design of, 4 ? 5, 6 
clearance around, 27 
ejectors, 79 

in groups, clamping, 173 
light, clamps for, 44 
locating and supporting for 

milling, 164 
location of, 4 

in v-blocks, 53 
long, held in vise- jaws, 238 
methods of bracing, 163 
removal from vise-jaws, 235 
of, 81 

from vise-jaws, 245 
riveted from both sides, 278 
small, location in vise-jaws, 239 
support, 48 

Working surfaces, establishment of 
in listing operationSj 4