PRICE ONE SHILLING

OPERATION OFMACHINE TOOLS

BY FRANKLIN D. JONES

MILLING MACHINES-PART II

MACHINERY'S REFERENCE SERIES-NO. 97PUBLISHED BY MACHINERY, LONDON

MACHINERY'S REFERENCE BOOKSThis treatise ia one unit in a comprehensive Series of Reference books originated

by MACHINERY, and including an indefinite number of compact units, each, coveringone subject thoroughly. The whole series comprises a complete working libraryof mechanical literature in which tiie Mechanical Engineer, the Master Mechanic,the Dtsienor, tlie Machinist and Tool-maker will find the special information hewishes to secure, selected, carefully revised and condensed for him. The booksare sold singly or in complete sets, as may be desired. The price of each bookis 125 cents (one shilling) delivered ;ui,v\vli<>re in the world.

LIST OF REFERENCE BOOKS

No. 1. Worm Genr-inff.—Calculating Di-mensions for Worm Gearing; l-lobs forWorm Gears; Location of Pitch Circle;Sell-Locking Worm Gearing, etc.

Ho. 9. Drafting-Boom P r a c t i c e , —Draftlng-Rocm System: Tracing, Letter-ing and Mounting; Card Index Systems.

Ho. 3. D*I11 Jiffs.—rclemfintfiry Prin-ciples nf Drill JisM: Drilling Jit." Plates;Examples of lirill Jigs: Jig Uuslilnes;Using Jigs to llest Advantage.

Wo. 4, Wiling Fixtures.—ElementaryPrinciples of Milling Fixtures; Collectionof Examples of Milling Fixture Design,f ro

No. 3. First Principle a of TheoreticalMechanics.

No. 6. PTineh and Die Work.—Princi-ples of Punch, ami rjji- Wnrlt; Surai-sUnnsfur tlie Mnkiritf find [Is« nf Dies; Examplesuf Die and Punch Design.

Wo. 7. Lathe and Planer Tools.—Cut-ting Tools for Planer aril La HIP; BoringTonls; Shape (.1 Standard Shop Tools;Forming Tools.

No. 8. Working Drawings and Draft-Ing Boom Kinks.

No. 9. Designing and Cutting Cams.—Drafting of CHiiisi Cam Cunehi Cam De-sign and (Jam Cutting; Suggestions inCam Making.

No. 10. Examples of Machine ShopPractice.—Cutting Bevel Gears with Ro-tary Cutters; Making a Worm-Gear;Spindle Construction.

No. 11. Bearings—Design of Bear-ings; Causes of Hot Bearings; Alloysfor neatinss; Friction and Lubrication;Friction of Roller Bearings.

No. 12. Mathematics of Machine De-sign.—Compiled with .special reference toshafting arid efficiency of hoisting ma-chinery.

No. 13. Blanking Dies.—Making Olank-ins Dies; Blanking and Piercing Dies;Construction of Split Dies; Novel Ideas inDie Making.

No. 14. Details of Machine Tool De-etga.—Cone Pulleys and Belts; Screngthof Countershafts; Tumbler Gear Design;Faults of Iron Castings.

No. IS. S p u r Gearing—Dimensions;Dpsign; Strength: Durability.

No. 16. Machine Tool Delves.—Speedsand TVfils nf Machine Tools: Cresired orSingle I'ulley Drives; Drives for HighSpeed OiiUiHE Tunis.

So. 17. Strength of Cylinflers—For-mulrts. Charts, and Diagrams.

No. 16. Shop Arithmetic for the Ma-chinist.—Tapers; Change Genra; Cutting

(See loalde back COY

Speeds; Feeds; Indexing; Gearing for Cut-ting Spirals; Angles.

No. 19. Use of Formulas In mechanics.•—With numerous applications.

No. 20. Spiral Gearing1.—Rulee, Formu-las, and Diagrams, etc

No. 21. Measuring Tools.—History andDevelopment of Standard Measurements;Special Calipers; Compasses; MicrometerTools; Protriu-tors. etc.

No, 32. Calculation of Element! OfMachine Desiffn.—Far tot- of Safety;Slrcngth of Bolts; Riveted Joints; Keysand Key ways: Toggle-joints.

No. S3. Theory ot Crane Design.—JibCrani's: Calculation of Shaft. Gears, andBearings; Force Required to Move CraneTrolleys; Pillar Cranes.

No. 24. Examples of Calculating De-signs.—Charts in Designing; Punch andRlvelcr Frames; Shear Frames; Billetand liar Passes: etc.

No. as. Deep Hole Drilling.—Methods.of Drilling; Construction of Drills.

Ho. 26. Modern Punch and Die Con-struction—Construction and Use of Sub-press Dies; Modern Blanking Die Con-struction; Drawing and Forming Dies.

No. 27. Locomotive Design, Part I.—Boilers, Cylinders. Pipes and Pistons.

No. 28. Locomotive Doiign, Part II,—Stephen son V:l]\i> llntion; Theory. Calcu-lation and Design of Valve Motion; TheWalschaerts Valve Motion.

No. 29. locomotive Design, Part III.—Smnkebos; Exhaust Pipe: Frames;Cross-Heads; Ouiilo Bars; Connecting-rods;Crank-pins; Axles. Driving-wheels.

No. 30. tocomotive Desigrn, Part IV.—Springs, Trucks, Cub and Tender.

No. 31. Screw Thread Tools and Gages.No. 32. Screw Thread Cutting-.—Lathe

Change Gears; Thread Tools: Kinks.No. 33. Systems s.ad Practice of the

Drafting-Room.No. 34. Care and Repair of Dynamos

and Motors.No. 35. Tables and formulas for Shop

and Drafting-Boom.—The Use i>f Formu-las; Snlution of Triangles: Strength ofMaterials; Gearinu; Screw Threads; TapDrills; Drill Sizes: Tapers; Keys: Jig

sh iNo. 36. Iron and Steel,—Principle

nt .No. 37. Bevel Oeaiine.—Rules and

Formulas; Rxamples nf Calculation;Tooth Outlines; Strength and Durability:Design: Methods of Cutting Teeth.

No. 38, grinding and Qrlndlnff Ma-chines.

r (or nddiaona.1 tides)

MACHINERY'S REFERENCE SERIESEACH NUMBER IS A UNIT IN A SERIES ON ELECTRICAL AND

STEAM ENGINEERING DRAWING AND MACHINEDESIGN AND SHOP PRACTICE

NUMBER 97

OPERATION OFMACHINE TOOLS

By FRANKLIN D. JONES

MILLING MACHINES—PART II

C O N T E N T S

C o m p o u n d I n d e x i n g — D i f f e r e n t i a l I n d e x i n g - - - 3

C u t t i n g S p u r G e a r s in a Mi l l i ng M a c h i n e 11

H e l i c a l o r S p i r a l M i l l i n g - - - - - - - 16

T h e V e r t i c a l M i l l i n g M a c h i n e - - - - - 31

L i n c o l n a n d P l a n e r - t y p e M i l l i n g M a c h i n e s - - - 43

CopyriKhU 1912. The Industrial Press. Publishers of MACHINE49-55 Lafayette Street, New York City

CHAPTER I

COMPOUND INDEXING—DIFFERENTIAL INDEXING

Ordinarily, the index crank of a spiral head must be rotated afractional par t of a revolution, when indexing, even though one ormore complete tu rns aro required. As explained in Pa r t I of thistreatise, this fractional part of a turn is measured by moving thelatch-pin a certain number of holes in one of the index circles; butoccasionally, none of the index plates furnished with the machine,has circles of holes containing the necessary number for obtaining acertain division. One method of indexing for divisions which arebeyond the range of those secured by the direct method, is to firstturn the crank a definite amount in the regular way, and then theIndex plate itself, in order to locate the crank in the proper position.This is known as compound indexing, because there are two separatemovements which are, in reality, two simple indexing operations. Theindex plate is normally kept from turning, by a s tat ionary stop-pin atthe rear, which engages one of the index holes, the same as the latch-pin. When this stop-pin is withdrawn, the index plate can be turned.

To i l lustrate the principle of the compound method, suppose thelatch-pin is turned one hole in the 19-hole circle and the index plateis also moved one hole in the 20-hole circle and in the same directionthat the crank is turned. These combined movements will causethe worm (which engages the worm-wheel on the spiral head spindle)

1 1 39to rotate a distance eiiual to 1 = — of a revolution. On the other

19 20 3SUhand, if the cranli is moved one hole in the 19-hole circle, as before,and the index plate is moved one hole in the 20-hole circle, bttt in 1he

1 1 1opposite direction, the rotation of the worm will equal =

19 20 3SI>revolution. By the simple method of indexing, it would be necessaryto use a circle liaving 380 holes to obtain Ihese movements, but byrotat ing both the index plate and crank the proper amount, either inthe same or opposite directions, as may be required, it is possible tosecure divisions beyond the range of the simple or direct system.

To i l lus t ra te tfie use of the compound method, suppose 69 divisions1

were required. In order to index the work — revolution, it is necessary69

40 40 1 40to move the crank — of a turn ( 4 0 - ^ 6 9 = — X — = — ) , and this

69 1 69 69would require a circle having 69 holes, if the simple method of indexingwere employed, but by the compound system, this division can be

p7—OPERATION OF MACHINE TOOLS

M1LUNU MACHINE INDkXING 5

obtained by using the 23- and 33-hole circles, which are found on oneof the three standard plates furnished with Brown & Sharp* spiral

1heads. The method or indexing — revolution by the compound sysiem

68Is as follows: The crank is first moved to the right 21 holes In the23-hole circle, as indicated at A in Fig. 1 and it is left in this position;then the stop-pin at the rear, which engages the 33-hole circle of theindex plate, is withdrawn, and the plate is turned backward, or tothe left, 11 holes in the E3-hole circle. This rotation of the plate alsocarries the crank to the left, or from the position shown by the dottedlines at B, to that shown by the full lines, so that after turning theplate backward, the crank Is moved from its original position a dis-

21 11 40tance J1 which is equal to — — — which is the fractional part of a

23 33 691

turn the crank must make, in order to index the work — of a69

revolution.One rule for determining what indes circles can be used for indexing

by the compound method, is as follows: Resolve into its factors thenumber of divisions required; then choose at random two circles ofholes, subtract one from the other, and factor the difference. Placethe two sets of factors thus obtained above a horizontal line. Nextfactor the number of turns at the crank required for one revolutionof the spindle (or 40) and also the number of holes in each of thechosen circles. Place the three sets of factors thus obtained belowthe horizontal line. If all the factors above the line can be cancelledby those below, the two circles chosen will give the required numberof divisions; if not, other circles are chosen and another trial made.

To illustrate this rule by using the example given in the foregoing,we have:

69 = 3 x ?A33 — 23 = 10 = 2 X 3

4 0 - J X 2 X 3 X S33'= 3 x l l23 = p, X 1

As all the factors above the line cancel, we know that the index platehaving 23- and 33-hole circles can be used. The next thing to determineis how far to move the crank and the index plate. This is found bymultiplying together all the uncancelled factors below the line; thus:

12 X 2 X 11 = 44. This means that to index — of a revolution, the

69

crank is turned forward 44 holes in the 23-hole circle; and the indexplate is moved backward 44 holes tn the 33-hole circle. The movementcan also be forward 44 holes in the 33-hole circle and backward 44holes in the 23-hole circle, without affecting the result. The move-

B No. g7—OPERATION OF MACHINE TOOLS

mente obtained by the foregoing rule are expressed in compound index-44 44

ing tables in thfi form of tractions, as for example: -\ . The23 33

numerators represent the number of holes Indexed and the denomina-tors tbe circles used, whereas, the + and — signs show that themovements of the crank and index plate are opposite in direction.These fractions can often be reduced and simplified so that it will notbe necessary to move so many holes, by adding some number to themalgebraically. The number is chosen by trial, and its sign should beoyijoaite that of tbe fraction to which it is added. Suppose, forexample, we add a fraction representing one complete turn, to eat-hof tbe fractions referred to; we than have:

23 33

23 33|_ , .

23 33

23 33

If the indexing is governed by these simplified fractions, the crankis moved forward 21 holes in the 23-hole circle and the plate is turnedbackward 11 holes in the 33-hole circle, instead of moving 44 boles, asstated. The result is tbe same in each, case, but the smaller move-ments are desirable, especially for the index plate, because it is easierto count 11 holes than 44 holes. For this reason, the fractions givenin index tables are simplified in this way. Ordinarily, tbe number o£circles to use and the required number of movements to make whenindexing, is determined by referring to a table as this eliminates allcalculations, and lessens the chance of error.

Sometimes the simple method of indexing can be used to advantagein conjunction with tbe compound system. For example, if we wantto cut a 96-tooth gear, every other tootb can be cut first by using thesimple method and indexing for 48 teeth, which would require a move-ment of 15 holes in an lS-hole circle. When half of the tooth, spaces

1have been cut, the work Is indexed — of a revolution by the compound

96method, for locating tbe cutter midway between the spaces previouslymilled. The remaining spaces are then finished by again indexing for48 divisions by the simple system.

Compound indexing should only be used when necessary, because ofthe chances of error, owing to the fact that the holes must be countedwhen moving tbe index plate. As previously explained, tbe number ofholes that the crapk is turned, is gaged by a sector. This counting alsorequires considerable time and, because of these disadvantages, thecompound system is not used to any great extent; in fact, tbe more

MILLING MACHINE INMiXINC

"ve

; Hsad ,

modern spiral heads are so arranged that divisions formerly obtainedby this system, can now lie secured in H more simple and direct way.

Differential Indexing

One of the improved indexing systems, which is applied to the uni-•rsal milling machines built by the Urown & Shunre Mfg. Co., is

known as the differen-tial method. This sys-tem Is the same inprinciple as compoundindexing, but differsfrom the latter In thatthe index plate Is ro-tated by suitable gear-Ing which connects itto the spiral-head spin-dle, as shown in Figs. 2and "• This rotation ordifferential motion ofthe index plate takesplace when the crankis turned, the platemoving either in thesame direction as thecrank or opposite to it,

as may be required. The result is that the actual movement of the cranK.at every indexing, is either greater or less than its movement wilh

relation to the index .plate. This method ofturning the index platehy gearing instead ofby hand, makes it pos-sible to obtain any di-vision liable to arise inpractice, by using onecircle of boles anfl sim-ply turning the indexcrank in one direc-tion,the same as for plainindexing. As the handmovement of the plateand the counting ofholes is eliminated, thechances of error arealso greatly reduced.

The proper sizedggars to use lor moving "- —=*.-„Hie index plate the required amount, would ordinarily be determined byreferring to a table which accompanies the machine. This table (a

8 No. 97~nPlZRAT]ON OF MACHINE TOOLS

small part of which is illustrated In Fig. 4) gives all divisions from 1 to'AH'i and includes both plain and differential indexing; that is, it showswhat divisions can he obtained by plain indexing, and also when It isnecessary to use gears and the. differential system. For example, if 130divisions are required, the 39-hole index circle is used and the crank ismoved 12 holes (see fourth column of table) but no gears are required.For 131 divisions, a 40-tooth gear is placed on the worm-shaft and a28-tooth gear is mounted on the spindle. These two gears are connectedby the 44-tooth idler gear, which serves to rotate the plate in the samedirection as the crank. To obtain some divisions, it is necessary to

Fiff. 4. Part or IndeE Table for Plain &D<J Differential Indexing

rotate the plate and crank In opposite directions, and then two idlergears are interposed between the spindle and wormshaft gears.

Fig/2 shows a spiral head geared for 271 divisions. The table callsfor a gear C haiving 56 teeth; a spindle gear E with 72 teeth an3one idler D. The sector shoulil be set for giving the craak a movementof 7 holes in the 49-hole circle or 3 holes in the 21-hole circle, either

1of which equals — of a turn. If an index plate having a 49-hole circle

7happens to be on the spindle h?ad, this would be used. Now if thespindle and index plate were not connected through gearing, 2S0 divi-sions would be ohlainod by successively moving the crank 7 holes inthe 4i!-hole circle, but the gears E, D, and C cause the index plate toturn in the same direction as the crank at such a rate that when 271indexings have been made, the work is turned one complete revolution;therefore, we have 271 divisions instead of. 280, the number being

MILLING MACHINE INDEXING 9

reduced because the total movement of the crank, tor eacii indexing,is equal to its movement relative to the index plate, plus the movementof the plate Itself when (as in this case) the crank anil plate rotate inthe same direction. If they were rotated in opposite directions, thecrank would have a total movement equal to the amount It turnedrelative to the plate, minus the plate's movement.

Sometimes it Is necessary to use compound gearing, in order to movethe index plate the required amount for each turn of the crank. Fig.3 shows a spiral head equipped with compound gearing for obtaining310 divisions- The gears given in the table are as follows: Gear Con the worm, 4S teeth; first gear if placed on the stud. f!4 teeth; secondgear G on the stud, 24 teeth; gear E on the spindle, 72 teeth; and oneidler gear D, having 24 teeth.

The following example is given to illustrate the method of determin-ing the index movements and change gears to use for differential in-dexing: Suppose 59 divisions were required, what circle of holes andgears should be used? First assume that we are to inde\ for 60

divisions by the simple method, which would require a — movement

ot the crank. Now, If the crank is indexed — of. a revolution. -v!l limes,3

•I ••

it will rotate In all, r>9 X— or 39 1/a revolutions, which is — of a

revolution less than the 41) required for one complete revolution of thework. Therefore, the index plate must be geared so that it will move

forward — of a turn, while the work is revolving once. Hence, the3

ratio of the gearing must be — to 1. Gears are next selected from those3

10 No. 07—OPERATION OP-MACHINE TOOLS

provided with the machine, which will give this ratio, as for example,gears having 32 and 48 teeth, respectively. The small gear is placed

2on the apiadle, in this case, because the index plate is to make only —

3of a turn, while the spindle makes one complete revolution. One Idlergear is also interposed between the gears, because it is necessary

2for the plate to gain — of a turn with respect to the crank; therefore,

3the movements of the index plate and crank must be in the same direc-tion.

The differential method cannot be used for helical or spiral milling,because the spiral-head is then geared to the lead-screw of the machine,as explained in Chapter III.

High-number, Reversible Index Plates

The dividing heads furnished with Cincinnati milling machines, areequipped with comparatively large index plates. This increase indiameter gives room for more circles and a larger number of holes thanthe smaller plates, and the range is further increased by making theplate reversible, each side having different series of holes. Therefore,the number of divisions that can be obtained directly from one ofthese plates is greatly increased. The standard plate regularly suppliedcan be used for indexing all numbers up to 60; all even numbers andthose divisible by 5 up to 120, and many other divisions between 120and 400. If it should be necessary to index high numbers not obtain-able with the standard plate, a high number indexing attachment canlie supplied. This consists of three special plates (seo Fig. a), whichhave large numbers of holes and different series on each side. Theycan be used for indexing all numbers up to and including 200; all evennumbers and those divisible by 5 up to and including 400. Owing tothe range of the standard plate, the high-number attachment is onlyneeded in rare instances, for ordinary milling machine work.

CHAPTER II

CUTTING SPUR GEARS IN A MILLING MACHINE

Spur gears are ordinarily cut in special gear-cutting machines, butthe milling machine i3 often used in shops not equipped with specialmachines, or for cutting gears of odd sizes, especially when only asmall number are required. Fig. e illustrates how a small spur gearis cut in the milling machine. The gear blank is first bored and turnedto the correct outside diameter and then it is mounted on an arborwhich is placed between the centers o£ the dividing head. An arborhaving a taper shank which fits the dividing-head spindle, is a goodform to use for gear work. If an ordinary arbor with centers in hoth«nds is employed, all play between the driving dog and faceplate shouldbe taken up to insure accurate indexing.

Cutter for Spur GearsThe type of cutter that is used for milling the teeth of spur gears,

is shown in Fig;. 7. This style of cutter is manufactured in various sizesfor gears of different pitch. The teeth of these cutters have thesame shape or profile as the tooth spaces of a gear of correspondingpitch; therefore, tlie cutter to use depends upon the pitch of the gearto he cut. The number of teeth in the gear must also be considered,because tha shape or profile of the teeth of a small gear is not exactlythe same as that of the teeth of a large gear of corresponding pitch.

The cutters manufactured by the Brown & Sharpe Mfg. Co. for cuttinggears according to the involute system, are made in eight differentsizes for each pitch. These cutters are numbered from 1 to 8 andthe different numbers are adapted for gears of the following sizes.Cutter No. 1, for gears having teeth varying from 135 to a rack; No. 2,gears with from 55 to 134 teeth; No. 3, from 35 to 54 teeth; Mo. 4,from 26 to 34 teeth; No. 5, from 21 to 25 teeth; No. 6, from 17 to 20teeth; N!-o. 7, from 14 to 16 teeth; and No. 8, from 12 to 13 teeth.

If we assume that the diametral pitch of the gear illustrated inFig. 6 is 12 anfl the required number of teeth, 90, a No. 2 cutter of 12diametral pitch would be used, the No. 2 shape being selected because itis intended for all gears having teeth varying from 55 to 134.

Setting- the Cutter CentralAfter the cutter is mounted on an arbor, it must be set over the

center of the gear blank, as otherwise the teeth will not be milledto the correct form. One method of centering the cutter is illustratedby the diagram, Fig. S. A true arbor is placed between the dividinghead and foot-stock centers, and the table of the machine is first.adjusted to locate the arbor in any convenient position outside of andsomewhat below the cutter as at A. The graduated dial of the cross-

Ho. 97—OPERATION OF MACHINE TOOLS

feed screw is next set to zero. The arbor is then moved to position Band it is adjusted to barely touch or pinch a thin tissue paper "feeler"/ held between the arbor and the corner of the nutter. The dial ofthe elevating screw is now set at zero, and the horizontal distance be-tween positions A and B should he noted by referring to the cross-feeddial. For convenience, this will be called dimension No. 1, as indicatedby the illustration. The arbor is next lowered and returned to positionA, horizontally, the vertical position not being particular. The arboris then raised until the elevating screw dial is again at zero, after

Fl^. e. Cutting- the Tstth al H. Spur Gear in a. Universal Milling Machine

which It is moved to position C, or until it just touches a tissue paper"feeler" as before. The horizontal dimension No. - is nexL noted byreferring to the cross-feed dial; this is added to dimension Xo. 1 andthe sum is divided by 2 to get dimension No. 3. The arbor is thenreturned to position A (as far as the horizontal location is concerned |after which it is lowered far enough to clear the cutter and then movedinward a distance equal to dimension No. 3, which is the central posi-tion. This operation can be performed more quickly than described.When making the adjustments, all dial readings should be taken at theend of the inward or upward movements, to avoid errors due to back-lash or lost motion in the elevating or feed screws.

A method of testing the location of a gear cutter, when considerableaccuracy is required, is as follows: First mill a tooth space in a

CUTTING SPUR GEARS 13

trial blank having the same diameter as tha gear blank, and then,without changing the position oC the cutter, remove the blank fromthe work arbor and turn it end for end. The blank should be looseon t ie arbor to permit feeding it back so that the cutter will eaterthe tooth space previously milled. The cutter is then revolved slowly byhand, in order to mark its position in the slot. If it is set exactlycentral, the second cut will follow the first, but if it is not central,some metal will be removed from the top of the space on one side andthe bottom on the other. In order to center the cutter, it should bemoved laterally toward that side of the tooth from which stock wasmilled at the top. Another trial cut is then taken and the test repeated.

Fig. 8. Metho

When the cutter is centrally located, the saddle should be clamped tothe lmee to hold it rigidly in position.

Setting toe Clutter to Depth—Milling toe TeetliThe next step is to set the cutter for milling tooth spaces of the

proper depth. If the outside diameter of the gear blank is accurate, thiscan be done by first adjusting the blank upward until the revolving-cutter just grazes its surface. The dial of the elevating screw is thenset at zero, after which the blank is moved horizontally, to clear thecutter, and then vertically the required amount, as shown by the mi-crometer dial. This vertical adjustment should equal the total depth ofthe tooth, space, which can be found by dividing the constant 2.1ii7by the diametral pitch of the gear. For example, if the diametral pitch

2.157is 12, the depth of the tooth space = = 0.179 inch. After the

12blank has been raised this amount, the gear teeth are formed byfeeding the hlank horizontally and indexing after each tooth space ismilled. About one quarter of (he teeth have been mi lied in the gearblank shown in Fig. G. The accuracy of the gear, assuming that the

14 o. 97—OPERATION OF MACHINE TOOLS

cutter is properly made,' will depend largely upon setting the cuttercentral and to the proper depth. When the depth is gaged from t i eoutside of the blank, the diameter of the latter should be accurate, asotherwise the teeth will not have the correct thickness. This diametercan be found by adding 2 to the number of teeth and dividing by thediametral pitch. The special vernier, gear-tooth caliper shown inFig. 9, is sometimes used for testing the thickness of the first toothmilled. This test is especially desirable if there is any doubt aboutthe accuracy of the outside diameter. A trial cut is taken at one sideof the blank and then the work is Indexed for the Bext space, after

Flfi. Q, Verniar Cal"P«r for measuring- the Thickness of Gear Tooth,at tbe PIMli Circle

which another trial cut is taken part way across the gear. The verticalscale of the caliper is then set so that when it rests on top o£ thetooth (as shown in the illustration), the lower ends of the caliperjaws will be at the height of the pitch line. The horizontal scale thenshows the thickness of the tooth at this point. The height from thetop of the tooth lo the pitch line equals the circular pitch multipliedby the constant 0.3183. The thickness of the tooth at the pitch line,for any gear, can be determined by dividing the circular pitch by 2, orthe constant 1.57 by the diametral pitch. With a diam-etral pitch of 12,

1.57the thickness would equal = 0.131 inch. The two trial cuts for

12determining the tooth thickness, should not extend across the blank,as it is better to simply gash one side; then if an adjustment is neces-sary, all the tooth spaces will be milled from the solid; whereas, if

PITCH ACIRCLE) W - a - *

\XMmtilTierif

CUTTING SPUR GEARS 15

trial cuts were taken clear across the blank, very little metal would beremoved from these spaces by the final cut and the thickness of thetacth between them would differ somewhat from the other teeth iathe gear.

When a gear tooth is measured as shown in Fig. 9 it is the chordalthickness T (see Pig. 9a) that is obtained, instead of the thicknessalong the pitch circle; hence when measuring teeth of coarse pitch,especially if the diameter of the gear is quite small, dimension T shouldbe obtained if accuracy is required. It is also necessary to find theheight x of the arc and add it to the addendum H to get the correctedheight B,, in order to measure the chordal thickness T at the properpoint on the sides of the tooth. To determine dimension T, multiply

the pitch diameter of the gear by the sineof the angle a between the center andradial lines shown. Expressing this as aformula we have T = Dsina, ia whichD equals the pitch diameter. To findangle a, divide 90 degrees by the numberof teeth in the gear. The height x of thearc is found as follows: x=:R (1 — cosa), in which R equals the pitch radius.That is, i equals 1 minus the cosine of

Ge'arTBBth^hl'ch'o""^^™ angle a multiplied by the pitch radius ofT should be delermlned t h e g e a ] , T n e c o r r e c t e d height B, 13

found by adding x lo the distance H from the top of the tooth to thepitch circle. If much gear cutting is done, it is well to secure a tablegiving the chordal thickness T and the corrected height if,, for variouspitches and numbers of teeth.

When milling .the teeth, a space is cut l)y feeding the blank insuch a direction that it moves against the rotatioa of the cutter. Aftera space is milled, the cutter is returned to its starting point and the

1blank is indexed — of a revolution (as the gear ia to have 00 teeth I

90far milling the next space. This operation is repeated until all theteeth are milled.

When milling gear teeth that are coarser than 6 or 7 diametralpitch, it is advisable to first rough mill all the teeth and then takefinishing cuts. Special "stocking" cutters are often used for roughmilling very coars« gears, preparatory to finishing by a regular cutter.The speed for cutting gear teeth depends on the pitch of the teeth,the kind of material being milled, and the rigidity of the work andmachine.

When the diameter of a gear is referred to, it is understood to moanthe pitch diameter or diameter of the pitch circle, and not theoutside diameter. The diametral pitch is the number of teeth toeach inch of pitch diameter, and the circular pitch is the distancefrom the center of one tooth to the center of the next, measured alongthe pitch line.

CHAPTER III

HELICAL OR SPIRAL MILLING

Tfie spiral heatl is not only used for indexing or dividing, but alsoin connection with the milling of spiral grooves. When a spiral Isbeing milled, the work is turned slowly by the dividing head as thetable of the machine feeds lengthwise. As the result of these combinedmovements, a spiral groove 13 generated by the milling cutter. Theprinciple of spiral milling, is illustrated by the diagrams shown inFig, 10. If a cylindrical part mounted between centers, as at A, isrotated and, at the same time, moved longitudinally at a constant rate,past a revolving cutter c. a helical or spiral groove will be milled asindicated by the curved line. Strictly speaking, a curve generated inthis way upon a cylindrical surface, is a helix and not a spiral, althoughsuch curves will be referred to as spirals in this treatise, because ofthe universal use of this term at the present time.

Evidently, the lead I or distance that this spiral advances in onerevolution, will depend upon the ratio between the speed of rotationand the longitudinal feeding movement. If the speed of rotation isincreased, the lead of the spiral will he diminished, and vice versa,provided the rate of the lengthwise travel remains the same. If thecylinder traverses a distance equal to its length while making onerevolution, the dimension I (sketch A) would equal the lead of thespiral generated, but, if the speed of rotation were doubled, the lead 1,(sketch B\, would be reduced one-half (assuming that the rate oflengthwise movement is the same in each case), because the cylinderwould then make two revolutions while traversing a distance equal toits length.

Change Gears for Spiral Milling

The method of varying the speed of rotation on a milling machine,for obtaining spirals of different leads, will be seen by referring toFig. 11 which shows an end and side view of a spiral head mountedon the table of tile machine and arranged for spiral milling. Therotary movement of the spindle S and the work, is obtained from thefeed-screw L. which also moves the table longitudinally. This feed-screw is connected to shaft IT' by a compound train of gears; 0, b, c andd. and the movement is transmitted from shaft W to the worm-shaft(which carries the indexing crank I through the spiral gears e, /,and spur gearing (not shown] which drives the index plate, crank, andworm-shaft. When a spiral is to be milled, the work is usually placedbetween the centers of the spiral head and foot stock, and changegears a. h, c and tl are selected to rotate the work at whatever speedis needed to produce a spiral of the required lead. The proper gearsto use for obtaining a spiral of given lead, are ordinarily determined

HELICAL OR SPIRAL MILLING 17

by referring to a table which accompanies the machine, although lliegear sizes can easily be calculated, as will be explained later.

As an example of spiral milling, suppose we have a cylindrical cutlerblank 3Vi inches in diameter In which right-hand spiral teeth are tobe milled, as indicated in Fig. 12, which shows the cutter after the teethhave been milled. The blank is first mounted on an arbor which isplaced between the centers with, a driving dog attached. The arborshould fit tightly into the hole of the blank so that both will rotate &aone piece, and it is also necessary to talce up all play between the driv-ing dog and faceplate. The spiral head is next geared to the feed-screw. If a table of change gears is available, it will show what gears

Vis- 'O. Diagrams illustrating the Principle ol Helical

are needed, provided the lead of the spiral is known, A small sectionof one of these tables is reproduced herewith (see Fig- 131 to Illustratethe arrangement. Suppose the lead given on the drawing is 4S inches;then this figure (or the nearest one to it) Is found in the column headed,•'Lead in Inches," and the four numbers to the right of and in line with4S, indicate the number of teeth in the four gears to be used. Thenumbers opposite 48 are 72. 24, 64 and 40, respectively, and the positionfor each of these gears is shown by the headings above the columns. As72 is in the column headed "Gear on Worm," a gear & (see also Fig.11) of this size is placed on shaft W. The latter is referred to asthe "worm-shaft," although, strictly speaking, the worm-shaft 11', is theone which carries the indexing crank and worm. The first gear cplaced on the stud E, has 24 teeth, as shown by the table, and thesecond gear 6 on the same stud has 64 teeth, whereas gear a on thescrew has 40 teeth.

After these gears are placed in their respective positions, the first

18 No, 97—OPERATION OF MACHINE TOOLS

HELICAL OR SPIRAL MILLING 19

and second gears c and f» on stud E are adjusted to mesh properly withgears u and d by changing the position of the supporting yoke Y. Asa right-hand spiral is to be milled, which means that it advances bytwisting or turning to the right, an idler gear is not used with thedesign of spiral head shown. When milling a left-hand spiral, it i3necessary to insert an idler gear in the train of gears (as at j In Fig.17) in order to rotate the work in a reverse direction; this idler hasno effect, however, on the ratio of the gearing. When the change gearsare in place, evidently any Longitudinal movement of the table effectedby turning feed-screw L, will be accompanied by a rotary movement ofthe spiral head spindle. As connection is made with the worm-shaft W,,Fig, 11, through the index plate and crank, the stop-pin O at the rearmust be withdrawn for spiral milling, so that the index plate will befree to turn.

Form of Cutter Used and its Position

The next thing to consider is the kind of cutter to use. If weassume that the grooves are to have an angle of 60 degrees, evidentlythe cutter must have teeth which conform fo this angle. The typeused for forming teeth of spiral mills, is sheW at- A in Fig. 14. Theteeth have an inclination with the axis, o£ 4S degrees on one sideand 12 degrees on the other, thus giving an included angle of 60 degreesfor the tooth spaces. This form of cutter is used in preference to thesingle-angle type shown at B, for milling spiral teeth, because the12-degree side will clear the radial faces of the teeth and produce asmooth surface. The single-angle cutter B is used for milling groovesthat are parallel with the axis. The cutter is mounted on an arbor,and it is set in such a position that when the groove is cut to therequired depth., the 12-degree side will be on a radial line, as shown bythe sketch; in other words, it should be set so that the front facesof the teeth to be milled, will be radial.

Setting the Cutter

A method of setting a double-angle cutter, for milling the teeth inspiral mills, which is simple and does not require any calculations, is,as follows: The pointer of a surface gage is first set to the height ofthe index head center and then the work is placed in the machine. Thecutter is next centered with the blank, laterally, which can be done witha fair degree of accuracy by setting the knee to the lowest positionat which the cutter will just graze the blank. The blank is then ad-justed endwise until the axis of the cutter is in line with the end ofthe work, as shown by the side and plan views at A, Fig. 15. Onemethod of locating the cutter in this position (after it has been setapproximately Ms to scribe a line on the blank, a distance from theend equal to the radius of the cutter. The blade of a square Is thenget to this line, and the table is adjusted lengthwise until the cutterJust touches the edge of the blade. The cutter can also be centeredwith end (after it is set laterally) by first moving the blank endwisefrom beneath the cutter, and then feeding it back slowly until a tissue

2U No. 97—OPERATION OF MACHINE TOOLS

paper "feeler" shows teat It just touches the corner of the blank. Therelation between the cutter and blank will then be as shown at A.

The table is next set to the angle of the spiral (as explained later)but its lengthwise position should not be changed. The surface gage,set as previously described, is then used to scribe lines which representone of the tooth spaces on the end of the blank where the cut is tostart. This is done by first drawing a horizontal line as at B. Thisline is then indexed downward an amount equal to on-e Of the tooth

E"ifl. 12. Universal Machine arranged for Spiral

spaces, and another horizontal line is drawn as at ('. Tlie last linescribed is then Indexed 90 + 12 degrees, which locates it parallel withthe 12-degree side of tlie cutter, as at D. The work is then adjustedlaterally, and •vertically by elevating tbe Knee, until the cutter is solocated that the 12-degree side cuts close to the scribed line, and, atth« same time, the required width of land w (see sketch E) is leftbetween, the top edge of the groove and the line representing the frontface ot the next tojth. After Ihe cutter is centered, as at ,-L, the longi-tudinal position of the blank should not be changed until the cutteris set as at E, because any lengthwise adjustment of the work wouldbe accompanied by a rotary movement (as the spiral head is geared to

HELICAL OR SPIRAL MILLING 21

the table feed-screw) and the position of the lines on the end wouldbe changed.

Setting the Table to Angle of Spiral and Milling1 tlie GroovesTlie table of the machine must also be set to the same angle that the

spiral grooves will make with tlie axis of the w-ork. This is done byloosening the bolts which normally hold the saddle to the clamp-bed,and swinging the table around to the right position, as shown by thedegree graduations on the base of the saddle. The reason for settingthe work to this angle Is to locate the cutter In line with the spiralgrooves which are to be milled by it. If the cutter were not in linewith the spiral, the shape of the grooves would not correspond with

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Fie 13 Part of Table sbowiug Gear CoalbtnHtlonB to use IOT obtainingSpirals of Dlllerant Ixad

the shape of the cutter. The angle to which the table should De set,or the spiral angle, varies according to the diameter of the work andlead of the spiral. As the diameter, in this case, is 3W inches and thelead of the spiral is 4S inches, the angle is 12 degrees. The directionin which the table is turned, depends upan whether the spiral Is rlght-or left-hand. For a right-hand spiral the right-hand end of the tableshould be moved toward the rear, whereas if the spiral is left-hand,the left-hand crd of the table is moved toward the rear.

After the taole of the machine is set to the required angle and thesaddle is clamped in position, the work is ready to be milled. Theactual milling of the spiral grooves is practically the same as thoughthey were straight or parallel to the axis. "When a groove is milled, itis well to either lower the table slightly or turn the cutter to such aposition that the teeth will not drag over the work, when returning foranother cut, to prevent scoring or marring the finished groove. If thework-table is lowered, it is returned to its original position by referring

22 No. 9?—OPERATION OF MACHINE TOOLS

to the dial on the elevating screw. After each successive groove is cut,the work is indexed by tu rn ing the indexing crank in the regular way.This operation of milling a groove and indexing, is repeated unti l allthe tee th ars finished. It should be mentioned that the differentialmethod of indexing cannot be employed in connection with spiral work,because with th i s system of indexing, the worm-shaft of the spiralhead is geared to the Bpindle. When mil l ing spiral grooves, the positionof the cut ter with relation to the work, should be such that the rotarymovement for producing the spiral, will be toward tha t side of the cut-ter which aas the greater angle. To il lustrate, the blank A. Fig. 14,should turn (as shown by the arrow) toward the 48-degree side of thecutter, as this tends to produce a smoother groove.

Calculating1 Change-gea r s for Spira l Milling'

As was explained in connection with Fig. 10, the lead of a spiral cutin a milling machine depends on the relation between the rotary speed

Fie. 14. Double- and Sinele-BDgle Cutters

of the work and its longitudinal movement, and these relative speedsare controlled by the change-gears a, 6. c and d. Fig. 11, which, connectthe table feed-screw L with shaft W. If the combination of change-gears is such that 20 turns of screw L are required for one revolutionof spindle S, and the screw has four threads per inch, the table willadvance a distance equal to 20 -=- 4 = 5 inches, which is the lead of thespiral obtained with that particular gearing. Now the proper gearsto use for producing a spiral of any given lead, can easily be deter-mined if we know what lead will be obtained when change-gears ofequal diameter are used. Suppose gears of the same size are employed,so that feed-screw L and shaft W rotate at the same speed; then thefeed-screw and worm-shaft IV, will also rotate at the same speed, ifthe gearing which forms a part of the spiral head and connects shaftsW and W, is in the ratio of one to one, which is the usual construction.As will be recalled, 40 turns of the worm-shaft are required for eachrevolution of spindle S; therefore with change-gears of the same diam-eter, the feed-screw will also make 40 turns, and assuming that it has

HELICAL OR SPIRAL MILLING 23

four threads per inch, the table movement will equal 40 -t- 4 = 10 Inches.This movement, then, of 10 inches, equais'the lead o£ the spiral thatwould be obtained by using cb.acge-gea.ra of the same size, and it isknown as the lead of the machine.

If we warned to mill a spiral having a lead of 12 Inches and thelead of the machine is 10, the compound ratio o£ the gears required

12 lead of spiralwould he — or — - . The compound ratio, then, may be

10 lead of machinerepresented by a fraction having the lead of the required spiral as itsnumerator and the lead of the machine or 10 as its denominator. In

16. Setting a Double-angle Cutter lor Milling T Spiral Mill

order to find what size gears to use, this ratio is revolved into twofactors as follows:

12 3 4— = — X —10 2 5

Bach factor Is then multiplied by some number which will give anumerator and denominator that corresponds to numbers of teethon change-gears furnished with the machine. Suppose both terms ofthe first factor are multiplied by 24; we would tben have,

3 24 T2

2 24 4SThe second factor is also raised to higher terms in the same way; thatis by using some multiplier which will give a new fraction, the numer-

24 .V,>. 97—0l'liIiAT10-\' OJ- MACHINE TOOLS

ator and denominator of which equals the numbers of teeth in availablegears. Suppose 8 is chosen for the second mult ipl ier ; we then have,

4 8 32

5 8 4072 32

Tho set of fractions obtained in this way, t ha t J3 — and —, represent48 40

the gears to use for milling a spiral having a lead of 12 inches. Thenumerators equal the number of teeth, in the driven gears, and thedenominators the number of teeth in the driving gears. If numbersoccurred in either fraction which did not correspond with the numberof teeth in any of the change-gears available, the fraction should bemultiplied by some other trial number until the desired result is ob-tained.

Relative Positions of the Change- gearsWhen the gears for cutting a given spiral are known, it remains to

place thorn in the proper place on the machine, and in order to do this,the distinction between driving and. drivn gears should be understood.The gear a (Fig. Hi on the feed-screw is a driver and gear 6, which isrotated by it, is driven. Similarly, gear c is a driver and gear dis driven. As the numerators of the fractions represent driven gears,one having either 72 or 32 teeth (in this instance) should be platedon shaft II". Then a driving gear with either 4(1 or 48 teeth is placedon stud E and the remaining driven gear is afterwards mounted onthe same stud. The other driving gear is next placed on the screw Land yoke Y is adjusted until the gears mesh properly. The spiral heaflwill then be geared for a lead of 12 inches, the gear on the worm having72 teeth, the first gear on the stud having 40 teeth, the second gearhaving 32 teeth, and the gear on the screw having 48 teeth. Eitherthe driving or driven gears could be transposed without changing thelead of the spiral. Por example, the driven gear with 32 teeth couldhe placed on shaft W and the one having 72 teeth could be used as asecond gear on the stud, if such an arrangement were more convenient.As previously stated, a reverse or idler gear is inserted in the trainwhen Putting left-hand spirals, but it does not affect the ratio of thegearing.

Determining' the Angle or the Hells or Spiral

When the change-gears for a given spiral have been selected, thenext step is to determine the angle to which the table of the machinemust be set in order to bring the milling cutter in line with the spiral.This angle equals the angle that the spiral makes with its axis and itdepends upon the lead of the spiral and the diameter of the cylindricalpart to be milled. The angle of a spiral can be determined graphicallyby drawing a right-angle triangle- as shown by sketch C, Fig. 10. Ifthe length r of one side equals the circumference of the cylinder onwhich the spiral is to be generated, and the base L equals the lead, the

.angle o will be tbe spiral angle. If such a triangle is wrapped around

HELICAL OR Si'lRAL MILLING 25

the cylinder, Hie hypothenuse will follow a helical curve, as the illustra-tion indicates.

Another way of determining the angle of a spiral is to first get thetangent of the angle by dividing the circumference of the work by thelead of the spiral. When the tangent is known, the correspondingangle is found by referring to a table of natural tangents. For example,if the circumference c is 12 inches, and tiie lead L Is -18 inches, the

tangent equals — — 0.25 and the angle a corresponding fo this tangent48

is about 14 degrees. Evidently, if the circumference is increased or

diminished, there will be a corresponding change in angle o providedtlie lead L remains the same. For that reason, the outer circumferenceis not always taken when calculating the spiral angle. The angle forsetting the tahle when cutting spiral gears in a milling machine, isdetermined by taking the diameter either at the pitcli circle, or atsome point between the pitch circle and the bottoms of the teeth, rathertliaa the outside diameter, in order to secure teeth of the proper shape.

Cutting1 Spiral Grooves with an End Mill

When a spiral groove having parallel sides is required it should becut with an end mill as illustrated in Fig. 16. If an attempt were madeto mill a groove of this kind by using a side mill mounted on an arbor,the groove would not have parallel sides, because the side teeth of themill would not clear the groove; in other words, they would cut away

26 No. 97—OPERATION OF MACHINE TOOLS

the sides owing to the rotary movement of the work and form a groovehaving a greater width at the top than at the bottom. This can be over-come, however, by using an end mill. Tile machine is geared lor therequired lead of spiral, as previously explained, and the work is adjustedvertically until its axis is in the same horizontal plane as the tenter ofthe end mill. With the machine illustrated, this vertical adjustmentcan be obtained by moving the knee up until its top surface coincides

Fig. IT CutlLnc tlie Teeth of a apirul Gatr in u Udlveraal Milling Machine

with a line on the column marked center; the index head centers willthen be at the same height as the axis of the machine spindle.

Cutting1 a Spiral Gear in a, Universal Milling MachineThe teeth of spiral gears are often cut in universal milling machines,

as indicated in Fig. 17, although special gear-cutting machines areused ordinarily where spiral gears are constantly heing made, becausethe special machines are more efficient. As the teeth of a spiral gearare inclined to the axis and follow helical or "spiral" curves, they areformed by milling equally-spaced spiral grooves around the peripheryof the blank, the number of the grooves corresponding, of course, to thenumber of teeth in the gear. From this it will be seen that a spiralgear is similar to a multiple-threaded screw, except that the teeth donot correspond in shape to screw threads; in fact, this type of gearingis sometimes referred to as screw gearing.

HELICAL OR SPIRAL MILLING 27

Cutter to Dae for Spiral Gears

Because of the Inclination of the teeth, the cutting of spiral gears isquite different from the method followed for spur gears, as far as thearrangement of the machine and the selection of the cutter !s concerned.The spiral head must be connected to the table feed-screw by changegears that will give a spiral of the required lead, and the proper cutterto use depends upon the number of teeth la the gear, their pitch andthe spiral angle. Just why the Inclination of the teeth to the axis ofthe gear is considered when selecting a cutter will be more clearlyunderstood by referring to the diagrammatical view of a spiral gearshown in Fig. 18. The circular pitch o[ the teeth is the distance cmeasured along the pitch circle at one end of the gear, or in a plane atright angles to the axis.

As will be seen, the circular pitch in the case of a spiral gear is notthe shortest d-lstance between the adjacent teeth, as this minimum dis-tance, n is along a line at right angles to the teeth. Hence, if a cutteris used having a thickness at the pitch line equal to one-half the circularpitch, as for spur gearing, the spaces between the teeth would he cuttoo wide and the teeth would be too thin. The distance ii is referredto as the normal circular pitch, and the thickness of the cutter at thepitch line should equal one-half this pitch. Now, the normal pitchvaries with the angle of the spiral, which is equal to angle a: conse-quently, the spiral angle must be considered when selecting a cutter.

If a gear has thirty teeth and a pitch diameter of 6 inches, wbat issometimes referred to as the real diametral pitch is a (30 -=-6 = 5)and in the case of a spur gear, a cutter corresponding to this pitchwould be used; but if a 5-pitcn. cutter were used for a spiral gear,the tooth spaces would be cut too wide, la order to secure teeth ofthe proper shape when milling spiral gears, it is necessary to use acutter of the same pitch as the normal diametral pitch.

The normal diametral pitch can be found by dividing the realdiametral pitch by the cosine of the spiral angle. To Illustrate, if thepitch diameter of the gear shown in Pig. 17 is 6.718 and there are 38teeth having a spiral angle of 45 degrees, the real diametral pitchequals 38 -=- 6.718 = 5.656; then the normal diametral pitch equals5.656 divided by the cosine of 45 degrees, or 5.656 -r- 0.707 = S. A cutter,then, of 8-diametral "pitch is the one to use for this particular gear.

This same result could also be obtained as follows: If the circularpitch c is 0.5554 inch, the normal circular pitch n can be found by mul-tiplying the circular pitch by the cosine of the spiral angle. Forexample, 0.5554 X 0.707 = 0.3927. The normal diametral pitch is nextfound by dividing 3.1416 by the normal circular pitch To illustrate.3.1416• —8, which is the diametral pitch of the cutter.0.3927

Of course, ia actual practice, it is not generally necessary to makesuch calculations, as the pitch of the gear, the lead and angle of thespiral, etc., is given on the drawing, and the work of the machinist isconfined to setting up the machine and cutting the gear according to

28 No. 97—OPERATION OF MACHINE TOOLS

(specifications. It is much easier, however, to do work of this kindwhen the fundamental principles are understood.

As previously explained in Chap. II, the proper cutter to use forspur gears depends not only upon the pitch of the teeth, but also uponthe number of teeth in a gear, because the teeth of a small gear do nothave the same shape as those of a much larger size of the same pitch.Therefore, according to the Brown & Sharpe system for spur gearshaving Involute teeth, eight different shapes of cutters (marked bynunihersi are used for cutting all sizes of gears of any one pitch,from a 12-tooth pinion to a rack. The same style or cutter can be used

Fie- 1

for spiral gearing, but the cutter is not selected with reference to theactual number of teeth in the gear, as with spur gearing.

By referring to the list of cutters given on page 11, Chapter II, itwill be seen that a No. ?, would be used for a spur gear having 3S teeth.A spiral gear with 38 teeth, however, might require a cutter of someother number, because of the angular position of the teeth. If theactual number of teeth In a spiral gear is divided by the cube of thecosine of the tooth angle, the quotient will represent the number ofteeth for which the cutter should be selected, according to the systemfor spur gears. If we assume that a gear is to have 3S teeth cut at anangle of 45 degrees, then the cutter to use would be determined as

38follows: The cosine of 45 degrees is 0.7071 and 38 ~ 0.70713 =

0.3oo5= 107. The list of cutters previously referred to calls for a No. 2cutter for spur gears having any number of teeth between 55 and

HELICAL OR SPIRAL MILLING 29

134; hence, that is the cutter to use for a spiral gear having 38 teethand a tooth angle of 45 degrees. Tt will be understood that this num-ber has nothing to do with the pitch of the cutter, which is determinedas previously explained; it is simply that one of the eight cutters(according to the B. & S. system) which is made for milling gearshaving numbers of teeth between 55 and 134.

The number obtained by the foregoing rule ia much larger than theactual number of teeth in the spiral gear. This is because a line atright-angles to the teeth, along which the normal pitch, is measured,has a larger radius of curvature than the pitch circle of the gear(although, strictly speaking, the term radius is incorrectly used, as thisline is a helix and not a circle) and the curvature increases or dim-inishes for corresponding changes in the spiral angle. Therefore, thenumber of teeth for which the cutter is selected depends upon theangle of the spiral, as well as the actual number of teeth in the gear.As the angle becomes smaller, the difference between the normal andcircular pitches also diminishes until, in the case of spur gears, thenormal and circular pitches are equal.

Gearing' Machine—Position of TableThe change gears a, b, r and d, Fig. 17, connect the spiral head and

table feed-screw and rotate the gear blank as the table feeds lengthwise.in order to produce the spiral teeth. The relative sizes of these gearsdepend upon the lead of the spiral or the distance that any one toothwould advance if it made a complete turn around the gear. Whencalculating the sizes of spiral gears, the diameter and angle of theteeth is usually made to suit conditions; consequently, the lead of thespiral is sometimes an odd dimension that cannot be obtained exactlywitli any available combination of change gears, although some com-bination of the gears furnished with a universal milling machine willgenerally give a lead which is close enough, for all practical purposes.

The gear shown in Fig. 17 has left-hand spiral teeth. Therefore it isnecessary to place an idler gear I in the train of gears in order toreverse the rotation of the gear blank. Without this idler, the rotationwould be in the opposite direction and a right-hand spiral would bemilled.

Before the teeth of a spiral gear can be milled the table of the•machine must be set to the spiral angle. This is done so that thecutter will produce grooves and teeth of the proper shape. As pre-viously explained, the angle of a spiral depends upon the lead L< see Fig 10), and the circumference e of the cylindrical surface(which may be either real or imaginary) around which the spiral isformed. The smaller the circumference, the smaller the angle a,assuming that the lead L remains the same. The angle, then, that theteeth of a spiral gear make with the axis, gradually diminishes fromthe tops to the bottoms of the teeth, and if it were possible to cut agroove right down to the center or axis, its angle would become zero.Hence, if the table of the machine is set to the angle at the top of atooth, the cutter will not be in line with the bottom of the groove, and,

30 No. 97—OPERATION OF MACHINE TOOLS

eonsequenly, the teeth will not be milled to tlie correct shape. It is acommon practice to set the table to the angle at the pitch line, winchis nearly halfway between the top and bottom of the tootli, althoughsome contend that it the angle near the bottom of the groove istaken, teeth of better shape will be obtained.

Whatever the practice may be the angle is determined by first get-ting the tangent and then the corresponding angle from a table oftangents. For example, if the pitch diameter of the gear is 4.46 and

4.46 X 3.1416the lead of the spiral is 20 inches, the tangent will equal

20— 0.700, and 0.700 is the tangent of 35 degrees, which is the angle towhich the table is set from the normal position at right angles to thespindle.

The table is adjusted by loosening the bolts which ordinarily holdit to the clamp-bed and swivpling it around until the 35-dcgree gradua-tion on the circular base coincides with the stationary zero mark.Before setting the table to the spiral angle, the cutter should be locateddirectly over the center of the gear blank. An accurate method ofcentering a cutter of this kind was described In connection with Fig.8. Chapter II.

Milling the Spiral Teeth

The teeth, of a spiral gear are- proportioned from the normal pitchand not the circular pitch. The whole depth of the tooth, that is thedepth of each cut, can be found by dividing the constant 2 157 bythe normal diametral pitch of the gear; the latter, as will be recalled,corresponds to the pitch of the cutter. The thickness of the gear at thepitch line equals l.fiTl divided by the normal diametral pitch. Aftera cut Is completed the cutter should be prevented from dragging overthe teeth when being returned for another cut. This can be done bylowering the blank slightly or by stopping the machine ana turningthe cutter to such a position that the teeth will not touch the work.If the gear has teeth coarser than 10 or 12 diametral pitch, it is wellto cut twice around; that is, lake a roughing and a finishing cut.

When pressing a spiral gear blank on the arbor, it should be remem-bered that spiral gears are more likely to slip when being cut thanspur gears. This is because the tooth grooves are at an angle and thepressure of the cut tends to rotate the blank on the arbor.

CHAPTER IV

THE VERTICAL MILLING MACHINE

When an end mill is driven directly by inserting it in the spindle ofa milling machine of the horizontal type it is often difficult to do satis-factory work, especially if much hand manipulation is required, becausethe mill operates on the rear side where it cannot readily be seenwhen one is ID the required position for controlling the machine.Moreover, it is frequently necessary to clamp the work against anangle-plate to locate it in a vertical position or at right-angles to theend mill, when the latter is driven by a horizontal spindle. In orderto overcome these objectionable features special vertical milling at-tachments are used to convert a horizontal machine temporarily intoa vertical type. These vertical attachments are very useful, especiallywhen the shop equipment ia comparatively small and a horizontalmachine must be employed for milling a great many different parts,but where there is a great deal of work that requires end milling, itis better to use a machine having a vertical spindle.

A vertical milling machine is shown in Fig, 19. The part to bemilled Is attached to table T and the cutter is driven by the verticalspindle S, so that it is always ID plain view. This la particularly desir-able when milling an irregular outline, or any part that requires closeattention.

The table of this machine has longitudinal, crosswise, and verticalmovements, all of. which eau be effected either by hand or by the auto-matic power feeds. The spindle and the slide which supports the lowerend can also be fed vertically, within certain limits, by band or power.It should be mentioned that milling machines of this type do notalways have vertical movements for both the spindle and table. Insome designs the table, instead of being carried by a sliding knee E,is mounted on. a fixed part of the base which extends forward beneathit; whereas other machines have a table that can be moved vertically,but a spindle that remains fixed, as far as vertical movement iaconcerned.

The particular machine shown in Fig. 19 is driven by a belt pulleyP, which transmits power through gears and shafts to spindle S. Thisbelt pulley is connected or disconnected with the driving shaft byvertical lever M, which serves to start and stop the machine. Thespeed of the spindle is varied by levers A, B, C. and D. Levers A andB operate a tumbler-gear through which four speed3 are obtained.This number is doubled by lever C, and lever D doubles it again, thusgiving a total of sixteen speeds. The direction of rotation is reversedby lever H,

The power feeds for the table are varied by the levers seen attached

^ .Vd. V7—<)t'l!l\'.ITW.\! OF M.-1CHLXE TOOLS'

to the feed-box F. The feed motion is transmitted to a reversing huxan the side of the knee, by a telescoping shaft, the same as with ahorizontal machine. Lever It may be used to start, stop or reverse theautomatic table feeds; lever TT controls the vertical movement of theknee and table; and lever N the cross-movement. The table is reversedby lever L at the front, the reversing lever R not being used for this

idle Ml 11 tea Macfcin

purpose. The hand wheel G is for raising and lowering the table, andthe smaller wheel E is for the transverse adjustment. By means ofhandwheel J the table can be given a fast or slow movement, or thewheel can he disconoected entirely, a clutch in the center of the hubbeing used to rnalie these changes. The handwheels E and. O can alsobe disengaged from their shafts by knobs in the center of each wheel.This is done to prevent the table from being shifted after an adjust-ment is made, in case, the workman should accidentally turn one ofthe wheels.

VERTICAL MILLING MACHINE 33

The vertical feed for the spindle head is also varied by the mechanismat F, the' required motion being transmitted to the top of the machineby a chain and sprockets which drive worm-shaft W. This worm-shaftis connected with the upper sprocket through a clutch controlled bylever I. This same clutnh is also operated by adjustable sto-ps clampedInto T-slots in the side of the spin die-head, for automatically disen-gaging the vertical feed at any predetermined point. Shaft W trans-mits the feeding movement to the spindle, through worm gearing, anda pinion shaft Q, and lever 0 engages or disengages the worm-wheelwith this pinion shaft. When the worm-wheel is disengaged, thelarge handivheel at the side of the column may'be usod to raise orlower the spindle rapidly, and, at other times, the small hand-wheelat the front gives a slow feeding movement.

Circular Milling- Attachment

The vertical milling machine is often used for milling circular sur-faces or slots. In order to do this it is necessary to Impart a rotarymovement to the piece being milled. This is done by means of a circu-lar milling attachment which is bolted to tlie main table of the ma-chine, as shown In Fig. 21. The table of the attachment can berevolved by handwheel A or automatically. Tbe power feed is derivedfrom the splined shaft which drives the longitudinal feed-screw of thetable, tills shaft being connected by a chain and sprockets to shaft Bwhich transmits the movement to the attachment. When the attach-ment is in use the table feed-screw Is disconnected from, the splinedshaft, so that the feeding movement is transmitted to the circulartable only. For adjusting the longitudinal table, when using the circu-lar attachment, a crank is applied to the squared end of the screw atthe left end of the table. The circular attachment has automatic stopsfor disengaging tlie feed at any point, which are held in a circular T-slot cut in the periphery of the table. The circumference of the tableis also graduated in degrees, so that angular adjustments can be madewhen necessary.

Vertical Milling Operations

The vertical milling machine illustrated in Fig. 19 Is shown at workin Fig. 2U. The casting C, which is being milled, is the saddle oE amilling machine, and the operation is that of finishing the dovetailways for the table. The ways on the under side Have already beenmilled and this finished part is placed against a plate or fixture F,having a slide similar to the knee upon which tbe saddle will hemounted when assembled.

The cutter used for this job has radial end teeth for milling theflat or bottom surfaces, and angular teeth for finishing the dovetail.The cutter revolves in a fixrd position, and the slide is milled byfeeding the table endwise after it is adjusted to the proper verticaland crosswise positions. The fixture is made in two parts, and the topsection can be swiveled slightly so that the dovetail can be milledtapering on one side for the gib which is afterward iuserted. The toppart of the fixture is located in the proper position when billing

34 A'o. w—OPERATION OF MACHINE TOOLS

either the straight or tappr side, by a pin which passes through theupper and lower plates.

Milling a Circular T-slot

The operation illustrated in Fig. 21, as previously intimated, re-quires the use of a circular attachment, as it is necessary to mill acircular T-slot. The casting in which this slot Is being cut, is thewheel-stand slide of a cylindrical grinder and the slot receives the

Ple. 20. Bsample ol Milling on Vertical Milling Machine

heads of clamping bolts. As the T-slot must be concentric with ahole previously bored in the casting, it is necessary to locate thishole in the center of th ircular table Thi i d b l i

a clamp and the bolts shown.The T-slot is formed by two operations: A plain, rectangular slot is

rut first by using an ordinary end-mill, and then the enlarged T-scc-tlon at the bottom is milled by a special T-slot cutter. This particularview was taken after the T-slot cutter had completed about one-quarterof the groove. The cutter rotates in one position and the circular

VERTICAL MILLING MACHINE 35

groove is milled as the casting ia slowly fed around by the circularattachment. The shape of the finished slot is clearly shown to theleft, and the plain rectangular slot cut by the first operation is shownto the right.

Examples of End and Edge Milling

Fig. 22 shows how a vertical machine is used for milling the bearingbrasses of an engine connecting-rod. These brasses are east with

flanged sides which must be finished to St tbe strap which holds thebrasses in position on the rod. An end-mill is uses for this work.The end or radial teeth finish, the bottom of the groove, while thecylindrical part o-f the mill finishes the groove to the required width.The brasses are clamped to a special box-shaped angle-plate, and foursets are milled at one passage of the tool. For finishing the oppositesides, the milled surfaces are '"bedded" on a cylindrical rod to alignthem with the table. In this way both sides are finished parallel.

"Work of this kind is often done in the shaper, but these smallbrasses can he finished more rapidly by milling, as the bottom of the

Si; No. 97—OPERATION OF MACHINE TOOLS

grooves and the aides of the flanges are milled simultaneously, where-as, with the shaiier it would be nei-essary (with a single-pointed tool)to cut down eacb side and plane the horizontal surface at the bottomof the groove, separately. Furthermore, it Is easier to mill thesijbrasses to a uniform size than to plane them in a staper. When mill-ing, the width between the flanges is governed by the diameter of thecutter, but. if a shaper were used, fills width would depend on theadjustment of the tool, which might not always be set in exactly the

3. Milling Connecting.rod Bearing Bra.aafl3 on Becker Vertical Machine

same position. The vertical milling machine used for this operation,is not the same as the one previously illustrated, although its con-struction is very similar and it is used for the same class of work.

The vertical milling machine is often used for finishing the edges ofstraight or circular parts, and irregular shapes can also be workedout by using the longitudinal and cross feeds alternately, as may barequired. Of course, if an irregular outline is to be followed, themachine is fed by hand. At A, Fig. 23, is shown an odd-shaped steelforging, the rough end ana sides of which are finished by milling, asindicated at B. The straight sides and part of the circular hub are

VERTICAL MILLING MACHINE 37

first milled as shown*in this Illustration. As the liole through the hubhas already been bored, this is used lor locating'the forging in a cen-tral position, the bored hub being placed over a close-fitting cylindricalpiece that is clamped to the table as shown. The work is held by abolt and heavy washer at the top, and it is kept from turning by asmall angle-plate which is set against tlie flanged end.

As the illustration shows, the edge is finished by a spirally-fluted end-

mill. The table of the machine is fed longitudinally for milling thestraight part, and then the circular attachment is used for finishingthe circular hub, around as far as the projecting flanged end will per-mit. The circular end of the hub is then completed (as shown in Pig.24) by using a different type of cutter which rounds that part of thehub next to the projecting end and gives a finished appearance to thework. This cutter, which is called 3 "rose mill," has a spherical tndthat forms a fillet as it feeds around.

This particular forging may require a little handwork for finishing

3S No. w—OPERATION OF MACHINE TOOLS

one or two rough, uneven spots left by milling, but this is very slightat the most. "Without a milling machine, however, it would be neces-sary to trim up this part by hand, and to make a neat job of it wouldrequire considerable time. In fact, before the milling machine cameinto use, vise or handwork was done on a much more extensive scalethan at the present time, and, incidentally, the amount of handwerkin connection with the fitting and erecting of machinery, is gradually

Fig- 24. Finishing a Circular FAllst with e. Rose Milling Cultar

diminishing, owing to the high degree of accuracy with which partscan bp finished, not only by mill ing hu t by modern machines andmethods generally.

When milling edges in the vertical machine, the depth of the cut13 sometimes limited by the spr ing of the cut ter arbor, although whenquite wide edges have to be milled, the arbor is sometimes supportedat the lower end hy a bracket which is ,a t tached to the column o£ themachine. This prevents the cut ter from springing away from thework, and enables fairly heavy cuts to be taken.

VERTICAL MILLING MACHINE 39

Surface Milling in the Vertical MachineWhile the vertical milling machine is especially adapted for milling

straight or curved edges or surfaces of irregular shape, it Is also veryefficient for finishing plain, flat surfaces on certain classes of work.Frequently the top of a easting or forging and its sides or edges, canbe milled at one setting, which not only saves time but insures accu-racy. When a flat, horizontal surface is milled in a vertical machine.

a face cutter is used, as shown in Fig. 25. This cutter, which is over12 inches in diameter, is screwed to the end of the spindle and theflange around the casting C is milled by the ends of the inserted teethor blades. This cutter is large enough to mill both sides of the castingin one cut. The over-all dimensions of this part are 12 by 36 inches,and the width of the flanges on each side is 2 inches.

The machine shown in this illustration is a powerful, rigid designespecially adapted for work of this kind. It ia similar in many re-apects to the plain horizontal machine described in Chapter I, Part 1,

40 No. 97—OPERATION OF MACHINE TOOLS

of this treatise, excepting, of course, the changes necessary on accountof the vertical location of the spindle. The part to be milled is bolteddirectly to the table, and, before milling the first casting, the knee iselevated, so that the spindle slide A will not need to extend muchbelow its bearing when the cutter is at work. The spindle and cutterare then lowered for the right depth of cut by using the fine hand-feedwhich is operated by the small wheel B at the right of the spindle.After rough milling the surface by traversing the table longitudinally,the feed is reversed and a finishing cut 0.010 of an inch deep is taken,aa the table feeds in the opposite direction.

The micrometer stop D which engages an arm B bolted to the sideof the column, makes it possible to set the cutter to the same verticalposition, when milling a number of castings of the same height. Thissame casting can also be milled by using a smaller cutter which cov-ers a flange on one side only, instead of the entire casting. When thesmaller cutter is employed, it is made to follow the rectangular flangeby using tha longitudinal and cross feeds, alternately.

The example of vertical face milling shown, in Fig. 26 illustrates amodern method o! chucking castings and operating the machine, whenlarge numbers of duplicate parts have to be milled. There are twoindependent work-holding fixtures mounted on the table, and thecutter moves from one casting to another. First a roughing cut istaken about 3/16 inch deep, with the table feeding 7% inches per min-ute. When the working side of the cutter reaches the end of the cast-ing, the feed is reversed and increased to 20 inches per minute for

VERTICAL MILLING MJC/liXE 41

the return or finishing cut. Meanwhile, another casting is placed inthe Other fixture, and when the cutter reaches it, the feed is reducedto 7% inches. While this roughing cut is being taken, a new piece ischucked in the other fixture, and so on, one casting being chuckedwhile the other is being milled, so that the milling operation is prac-tically continuous. Of course, this method of handling the work, tan-not be employed unless il is possible to clamp the part in the properposition in a comparatively short time. The fixtures shown in tinsillustration are made like milling machine vises and have special jaws

PIS. 27. Another Millios Oiieratioa Employing Two Fixtures

with angular faces which hold a casting firmly against the base ofthe vise.

Fig. 27 shows a continuous milling operation similar to the onejust referred to, as far as the method of chucking the work is con-cerned. There are two independent fixtures, as before, and the cast-ings are inserted in each fixture alternately; that is, one is beingchucked while the other is being milled. The machine is fitted withan automatic reverse, and the table travels back and forth withoutstopping. Two cuts are taken across each piece; first a roughing cutand then a finishing cut on the return movement of the table. One ofthe finished castings is shown on the left end of the table. Thematerial is malleable iron and the milled surface has an over-alldimension of G by 7 inches. From 1/16 to 3/32 inch metal is removed,and the table feeds 12*A inches per minute.

42 —OPERATION OF MACHIXP. TOOLS

Continuous Circular Milling-

The continuous method of face milling is also done in connectionwith a circular attachment. The parts to be milled are held in afixture near the edge of ths table, and, as the latter revolves, one cast-ing after another is fed beneath the revolving cutter. An example ofcontinuous circular milling is shown in Fig. 28. The operation is thatof milling sad-irons These are hold ill a fixture having a capacity forfourteen eastings. The table makes one revolution in from three tofour minutes when doing this particular work. As the finished east-

Pig. 2B Milling

ings come around to the front they are removed and replaced by roughones, without stopping the machine so that the milling operation iscontinuous. From two thousand to three thousand castings c-an hemilled per day by this method, the number depending on the kind ofmaterial. The fixture has star-shaped clamping nuts which make itpossihle to fiuichly release a finished casting or clamp a rough one inposition. This machine is not a regular vertical milling machine ofthe standard type, hut is especially designed for continuous circularmilling. The table is without cross adjustment but can be fed longi-tudinally for straight surface milling. Continuous circular milling isalso done on standard vertical machines by using the circular millingattachment, as previously mentioned.

CHAPTER V

LINCOLN AND PLANER-TYPE MILLING MACHINES

The milling machine shown in Fig. 23 is intended especially formanufacturing; that is, it is not adapted to a great variety of millingoperations but is designed tor machining large numbers of duplicateparts. The construction is very rigid but comparatively simplp, anil,

Fig 20. Bn;wii & Slimpf Plain MIUIDU Mat^me of (he Lincoln Type

therefore, this style of machine is preferable to the more complicateddesigns for work within its range. Milling machines having the samegeneral construction as the one illustrated, are often referred to as theLincoln type. As will be noted, t ie work-table A. instead of beingcarried by an adjustable knee, is mounted on the solid bed of the ma-chine and the outer arbor-support is also bolted directly to the bed.This connection gives a very rigid support both for the work and cut-

45 No. Q7—OPfifi.-1TfOX OF M.-ICHLXH TOOLS

ter. The work is usually held in a fixture or rise at tart (id to the table,and the milling Is done as the table feeds longitudinally.

The table is not adjustable vertically, but the spindle-head B with thespindle, can be raised or lowered as may be required. This verticaladjustment of. the spindle-head is effected by turning hand wheel (7which has a graduated collar reading to thousandths of an inch. Alterthf spindle has been adjusted vertically, the head is clamped to theupright by tbe four bolts shown. The spindle is driven from a pulleyat the rear which transmits the motion through shafting and gearing.

WSKJ

J1 TB i i i

A friction clutch is located in this driving pulley and provides meansfor starting and stopping the machine. This clutch is operated by thehand-lever D.

The table has a longitudinal power feed in either direction, whichcan be varied to suit requirements. This power feed can be automatic-ally disengaged at any point by setting the adjustable stops E in theproper position. The direction of the feed can also be reversed by oper-ating reverse-rod F. The large handwheel G can be used for adjustingthe table lengthwise or crosswise. Normally this handwheel is in posi-tion for traversing the table lengthwise. When a transverse movementis required in order to locate the work with reference to the cutter,the V. a nil wheel is pushed inward, which engages it with the cross-feed

L1XC0LM AMD PLANER-1YPF. MILLING VACHINIIS 4o

screw. Before using the hand traverse, the worm-gearing of the powerfeed mechanism should be disengaged by operating lover H. The varia-tions in both spindle speeds and table feeds are obtained, on this par-ticular machine, by means of change gears. As machines of this kindare frequently used for a long time on one class of work, it is not nec-essary to make speed or feed changes very often.

This machine has a maximum longitudinal feed Cor the table of 34inches; a transverse adjustment of 6 inches, and a vertical adjustmentfor the spindle of 12 inches. The variety of milling that can be doneon a machine of this type is small as compared with the column-and-knee machines, but it is intended for milling operations lhat are of the

same general character, so that a great capacity or "rangr" is notneeded. The Lincoln type is used very effectively in connection withtlie manufacture of firearms, sewing machines, electrical instrumentsand many other kinds of machinery-

Horizontal Milling Machines of the Planer Type

The machine illustrated in Fig. 30 is designed for heavy millingoperations. This style of milling machine is sometimes referred to asa planer or slab type; as the Illustration shows, it is built somewhatlike a planer. The work-table T is mounted on a long bed, and thecutter arhor C is carried by a cross-rail A which, in turn, is attachedto vertical housings. The cutter arbor is driven by gearing at the leftend, and it can be adjusted longitudinally by traversing the main sad-dle S along the cross-rail. The outer end of the arbor is supported bya bearing B, and there is also an intermediate support. Tlie work-table has an automatic feeding movement along the bed, and it can betraversed rapidly by power, in either direction, when the position

46 A'o. w~Ol'HRATlON 01-' MACHINE TOOLS

needs to be changed considerably. The power feed can be automatic-ally disengaged at the end of the cut by a tappet which is shiftedalong Ihe side of the bed to the required position. The cross-rail canbe raised or lowered to locate the cutter at the required height, and

Fig. 32- Channeling the SJ<3en of LocomotlvB Mum-rods on HorLsontnl Machine

it is counterbalanced by weights attached to wire ropes that pass overthe pulleys at the top of the housings.

Pig. 31 shows how a horizontal machine of this kind is used formilling a iarge easting. The particular part illustrated is the bed ofa turret lathe, and the operation is that of milling the V-shaped ways,

Fig. 33. Cutters ueed (or Ohannelins Wain-rofls

the Qat surfaces inside these ways and the outer sides or edges. Thearrangement of the gang of eight cutters is clearly shown by the illus-tration. The bed has been moved away from the cutters somewhat, inorder to show the shape of the milled surfaces. The V-shaped way3are milled by angular cutters and the flat innsr surfaces by cylindricalcutters, while the edges are trued by large side mills. This gang of

LINCOLN AND PLANER-TYPE MILLING MACHINES 47

flitters rotates to the right, as viewed from the operating side of themachine, and the table feeds toward the rear or against the cutterrotation.

The great advantage of machining a casting in [his way is that allthe surfaces are milled to shape at one passage of tho work. Thissame c-asting could be machined in a planer, which is true oE practi-cally all ivork done on large horizontal milling machines, but whethera planer or a milling machine should be used is a question that isoften difficult to decide. The number of parts to be milled and thegeneral character of the work, must be considered. To illustrate, it

might be possible to finish a casting hy milling much more rapidlythan by planing. It does not necessarily follow, however, that millingwill be more economical than planing. In the first place, millingcutters are much more expensive than the single-pointed planer toolswhich can be forged to shape by a blacksmith or toolsmith, and moretime is also required to set up a milling machine than a planer, espe-cially when a gang of cutters must he arranged for milling severalsurfaces simultaneously. Hence, if only a few parts are required andthe necessary milling cutters are not in stock, the cost of the cutters,and the time for arranging the machine, might much more than offsetthe time gained by the milling process. On the other hand, when alarge number of duplicate parts are required, milling is often muchmore economical than planing. It must not be inferred from this that

•IS No. 07—OPERATION OF MACHINE TOOLS

the placer should always be uaed for small quantities of work, and themilling machine when there is a large number of parts, although thequantity of work to be dono, frequently decides the question. Some-times planing is preferred to milling, because the surface left by a plan- •ing too! ia more desirable, in certain cases, than a milled surface.

When castings or forgings are quite long ani narrow, two parts aresometimes clamped side by side on the bed and milled at the sametime by separate cutters. Fig. 32 Illustrates a job of this kind. Thetwo steel forglngs on the machine are the main rods of a locomotive,the sides of which have been channeled or grooved to form an I-beamsection. This lightens the rod considerably but leaves it strongenough to resist the various stresses to which it is subjected. This"view was taken, after the channels on one side were milled. Thesechannels are milled from the solid, and the cutters used for this workare shown on an enlarged scale in Fig. 33. They have inserted spiralteeth which incline in opposite directions to neutralize the endwisethrust. They are S1^ inches in diameter and their width is 4% inches,which corresponds to the width of the channel. When milling, theseputters revolve 36 revolutions per minute, giving a peripheral speedof 82 feet per minute. The channel or groove is 1% inches deep, andit is milled in two cuts, each having a depth of % inch. A constantstream of lubricant pours on each cutter "through the hose and ver-tical pipes seen attached to the cross-rail. When setting up work foran operation of this kind, it must be held securely against endwisemovement, because the pressure of such heavy milling cuts is verygreat. In this case, the rods rest against a heavy steel block which isfastened across the end of the table to resist the endwise thrust ofthe cut.

Multiple-he ad Milling Machine

Horizontal machines are built in many different designs which aremodified to suit different classes of work. Fig. 34 shows a machinewhich, instead of having a single cutter-artoor, is equipped with fourheads. Two of these heads are carried by the cross-rail and the othertwo are attached to the right and left housings. The cross-rail headshave vertical spindles and the side-heads, horizontal spindles, so that

• the sides and top surfaces of castings can be milled simultaneously.The side-heads can be adjusted vertically on the housings, and thevertical heads laterally along the cross-rail. This particular machinewill drive face mills up to 20 inches in diameter.

Machines of the same general design are also built with threeheads, one being an the cross-rail and two on the housings, and thereare various other modifications. With the multiple-spindle machines,the number of spindles used at one time depends, of course, on thenature of the work. For some jobs it is necessary to use the hori-zontal spindles, whereas other parts are milled by using the hori-zontal and vertical spindles in combination. This type of machine isvery efficient for certain kinds of milling.

Wo. 39. Paul, Ventilation and Heating1.—Fans; Heaters; Shop Heating-

No. 40. Ply-WheBlB.—T h e i r Purpose,Calculation and Design.

Ho. 41. Jigs ana F i x t n ™ , Part I.—Principles of Jig and Fixture Design;Drill and Boring Jig Bushings; LocatingPoints; Clamping1 Devlceo.

Ho. 4Z. Ji£B anfl Fixtures, Par t II.—Open and Closed Drill Ji&s.

No. 43. JlffB anfl FlxturoB, Part III.—Boring and Milling Fixtures.

Wo. 44. Macnlne Black smithing1.—Sys-tems, Tools and Machines used.

Mo. 45. Drop forging. — Lay-out ofPlant; Methods of Drop Forging; Dies.

No. 46. Hardening- and Tempering-.—Hardening Plants; Treating High-SpeedSloel; Hardening .Gages.

Mo. 47. Electric Overhead Cranes.—Design and CiLlculatJun.

No. 48. PilBH and riling.—Types ofFli ts ; Using and Making Files,

Wo. 49. Birders for Electric OverheadCranes.

Mo. 50. Principles and Practice of As-sembling Machine Tools, Par t i.

Ko. El. Principles and Practice of As-sembling Machine TODIB. Fart II.

Wo. 52. Advanced Shop Arithmetic forthe Machinist.

Ho. 53. Use of Logarithms and Logar-ithmic Tables.

Mo. 54. Solution of .Triangles, Par t I.•—Methods, K.ules and Kx&mplcs.

Mo. 55. Solution of Triangles, Part II .—Tables of Natural Functions.

Wo. 56. Ball Bearings.—Principles ofDesign and Construction.

No. ST. Metal Spinning.—M a c l i l n e s ,Tools nnd Motliods Used.

Wo. S3. Helical and EliipUo SptingB.—Caluulation and Design.

Ma. 59. Machines. Tools and Methodsof Automobile Manufacture.

No. SO. Construction and ManufactureOf Automobiles.

Wo. 61. Blacfcamltli Shop Practice.—Model Blacksmith Shop; Welding; Forg-iriff .if Hnoki ana Chains; MiscellaneousAppliuncea and Methods.

Ho. S3. Hardness and Durability Test-Ing of Metals.

Mo. 33. Heat Treatment of Steel—Hardening, Tempering, Case-Hardening.

No. 64. Ga^e Making and Lapping.No. 65. Formulas and Constant3 for

Gas Engine Design.Mo. 66. Heating- and Ventilation of

Shop* anil Offices.Wo. ST. Bailers.No. ee. Boiler Purnaoes and Chim-

neys.No. 69. Peed Water Appliances.Ho. TO. Steam Engines.Ho. 71 Steam Turbines.No. 7B Fumps, Condensers, Steam and

Water 1-iping.No. 73. Principles and Applications of

Electricity, I'iirt 1.—static Electricity-Elccmeal Mi-uaurenifutH; liatterles.

Ho. 74. Principlea and Applications ofElectricity, r . i r l II.—llniiiii'iisin, lilec-tru-Magnctlam; Hlcctro-Plating".

No. 76. Principles and Applications ofElectricity, Part III.—Dynamos; Mulors:Klectric Railways.

wo. 76. Principleo and Applications ofElsctrlcity, Part IV.—Eleciru; Uslitjng.

Ho, 77. Principles and Applications ofElectricity, Part V.—Telegrupli :ind Tele-pljone.

No. 78. Principles and Applications ofElectricity, Part VI.—Trausmi^nm of

No. SO. Locomotive Building, Part II.—Wheels: Axles; Driving Boxes.

No. 81. Locomotive Bnlldlngr, Part III .—Cyllndorfi mill Frames.

Ho. 83. Locomotive Building, Part V.—Boiler Sli.ip I'riii Ut-«.

Ho. 84. Locomotive Building, Part VI.—Erecting.

Vo. 85. Mechanical Drawing, Part I.—Inslrumeuls; Miilri-ials; Gco metricalProblems.

Ho. 88. Mecnanical Drawing, Part II.—Projection.

Ho. 87. Mechanical Drawing, Part III.—Machina Ui-uili,.

Ho. 88. Mechanical Drawing, Part IV.—Machine Details

Ho. 30. Railway Be pair Sliop Practii

ADDITIONA1, TITLES WILL BE AMNOUWCBD IN MiOHTNERY FROM TIME TO TIME

MACHINERY'S DATA SHEET SERIESMACHINERY'S Data Sheet Books include the well-known serins'of Data Sheets|inated by MACIIIXEJIY, and issued mootlily as Hupplements to the publication;leae Data Sheets over 500 have been published, and 6,000,000 coiiioa sold. Re-

snd greatjy amplified, they are now presented in book form, kindred sub-te being' grouped together. The purchaser may secure either the bnoks onfcse BuUjects in which he is specially interested, or, if he pleases, the whole set al

Se time. The price of each book Is 25 cents (one shilllog) delivered anywherein the world. '

TITLHS AND OONTBNTS ON BACK COVHR

*f ' ,'.. "•• ' u CONTENTS Oi'n D_VI ^ SHEIJT

Nd. 1. gcri-w Threads. -ITni • ,. .-'tilesVhitwoilil, Sharp V- ami J-.rii.iMl1 ASS'ii-i.s-> si StanJuiJ Tlrreads: »rlK«!> Pip"

OU WeJtt'aa!nB.<-i: *-*; I-'..--, i l w . J»or 11. Milling Machine Indexing.

i ! 'I .j.iisr TnfJ(-r 'I inning; gfi-r- die 1-,. \ P ; Boring Bara a Of] Tnr.Js

9,; _ Acme. Ti ..:,

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;.;i:,flirfl" l i • v: t j jn R I ys ; Mi l l ing if'-* • 'jfii-( - ; Scrt-Bserf HI Kucf T r s t s r.tii n y s ; p " >'• J K-> s, - • -jo. X'J. Belt , S i p e . , i j C i ^ -.- Bt lvei .—

MO. % -aBaria.-F. C iup l ings , e j i - u H e c i ..•;,«!..->? . ,- i i t l t y - : / - . . •• ; j r-f p . ! ' -L. -Cxana CL.-m an* Hoake.- l'ij].>>. ];lo'-l(---l , i-j.. • l.,i -••\rt<\- .••->!• i i i i un . ' • : . V»1I.F-.

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I S f c t 1 M dj " VFiieela; Pins arii re

- No. 10. MoU Drive, SpeeS= aud Fet> Change Q-eaMng, and Baring- B a n . — li

r. , ;n r iv . ' f.-t- M»I-1I I IU- T c i . I s . I ' L -Sp"-d<; -u [ K—tls f a r CiLi-i.i.i, -in,l l . iRtii'M S tcP l ; 13.-i-m- V . >I>,IP S p p f ' ] 3 f, , - 0 H ; H O : . . T ' ....•••ni. nf H i g h - n

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l-fft'"..IJa,<!. Cum'.1. IJ.:I.;HK-S for Var

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'Data Sheet Scries, is publi^hi-d *l" r.n'» '.litiuns^tlii^ •'• t!w EWJivretiny EiWhm, If2.no a ypar; (.lit- ;i''i;iii'

Ftofiew Bdii'un, $3.00 a year.

MACHINERY, 27, Chancery Lane, London, W.49-55 Lafayette Street Net/ York City, U. S; Ai - "• .-lie -l.k