CHAPTER 13

GEAR_CT,-TTIN G N{ACHINES

I3-1. Gear-Cutting Methods

The two principal methods ernploved at present in the manufacture oft,-,othed gears are: form cutting and generating.

Form-cutting process. This methocl makes use of a cutting tool whosecutting edges have been formed to the shape of the tooth space to be cut.Eramples of such tools are gear-tooth milling cutters of the disk or end-millirpe (Fig. 246a and b) and form tools (Fig.246c).

If a single tool is employed, the cutting of the spaces alternates withindexing, i.e., turning the blank to the next tooth space or 1 revolution,;;here z is the number of teeth on the gear being cut. The production capacity,-f this method is low since each tooth space is machined separately, andtime is lost in returning the tool to its initial position and in indexing thegear blank.

Iloreover, since the tooth profiIe depends upon the module, pressure angleand number of teeth, it is theoreticall_v necessary to have a tool with a specialpr,rfile (milling cutter or form tool) for each gear rvith a different number,-i teeth or module. In actual practice, hower,er, sets of gear-tooth millingcrrtters are used (B cutters per set or. for more accurate gears, 15 and, lessfiequently, 26 cutters) for each module of gear. Each cutter in the set isd,tsigned for cutting a limited range of numbers of teeth. Gears cut by thisr,ethod are not very accurate since, in addition to the errors associated withi:.accurate operation of the indering mechanism, there are inevitable errorsirirerent in the cutting tool. In consequence, this gear-making method is

Fig. 246. Gearlvith a gear-tooth cutter; (b)

g@

ll__,_+_-(8)

LluWHt"/ IVJc4

(r)

manufacttrrc by thc form-cutting process:with an end-mill type gear milling cutter; (c) r/ith a lorm 10()1

23*

-

356 GEAR.C UTTIN G 1 MACHINES

Fig. 24i. Principle of the multiple-tool shapirrg cutter head:'

I-gear blank; g-form tools; 3-bodyol the heaal

Fig, 248. Generation of involuteprofiles:

J-gear blank; z-cutting tool

resorted to in regular production only if a gear-cutting machine is noavailable. It is used, horvever, in repairs, in making single gears, in scimrcases for cutting herringbone gears, and in roughing the tooth spaces (irroughing operations).

In mass production the forrn-cutting principle is applied in the multiple.tool shaping cutter head (Fig. 247) used to cut all the tooth spaces of a gearat the same time. This cutter head has as many radially arranged form toolsas there are spaces (or teetii) on the gear being cut. The profile of the tooisis exactly of the some shape as the gear-tooth spaces. During each full stroke(cutting and leturn) of the cutter or gear blank (in a directi-on perpendicularto the plane of the drarving) each tool is fed radially toward the blink, by anarnount equal to the infeed, prior to each cutting stroke. AII the tools aresimultaneousiy retracted from the rvork on the return stroke to avoid rubbingof the tool clearance surfaces against the machined surfaces. All the tootirspaces are cub simult,aneously, and the gear is finished rvhen the tools reachtheir {ul} depth of cut.

lhe prociuction capacity of this gear-cutting method is verv high andthe accuracy of the cut gears ciepencis only upon the accuracy of tlie cuttcrrhead rvhich may be sufficiently high. Drawbacks of this methrid are thecomparativeLy comple-x manufacture of the cutter heads and the necessitvof having a separate head for each size of gear.

Another high-production forur-cutting process used in gear naking isbroaching which is economically justified only in the mass production ofidentical gears. Broaching produces highly accurate gears wit[ an ercellentsurface finish.

The generating proccss. This method is based upon the meshing of thecuLter rvith the gear being produced to develop the tooth b)'the relative

-l

T3-3. GEAR-HOBBING ]\IACHINES

rolling motion of the cutter and the work. For this purpcse the cutter isshaped like a gear, gear rack or \\-orm, i.e., a parl rhich could mesh withthe gear being cut, or the tool is made so that its cutting edges descriLe inspace the surfaces of the tooth profiles of a certain imaginary gear or rack.knorvn as the generating gear or rack. In this meshing action of the work anci.

tcol, to nhich an additional cutting notion is imparted, the cutting edgesof the tool, gradually removing material lrcn the tocth spaces' shape thegear teeth to profiles that are the enr-elope of the consecutive positions of thccutting edges of the tool (Fig. 248).

Though the generating methcd canrrot compare in output with form cut-ting, as used in the multiple-tool shaping cutter heads cr in broaching,it is much more universal. A tool of a certain mcdule, operating by thegenerating principle, can cut gears with any numter of teeth of the samemodule, including modified gears.

35?

13-2. Gear-Cntting Machine Glassification

Gear-cutting machines can be classified according to the following fea-t ures:

(1) The type of machining and tool used: into gear hobbers, gear shapers,gear planeri, gear-broaching machines, gear-shaving_machines, gear grind-ets, gear lappers, gear-tooth honers, and gear-tooth _rounding machines.

(2)'-Purpose: into machines for cuttingspur and helical gears, worm'$heels,herringbone geals, gear lacks, straight bevel gears, and curved-tooth bevelqears." (3) The finish of the machinedthe teeth, for finishing the teelh'of the teeth.

tooth surfaces: into machines for roughingand for microfinishing the active surfaces

l3-3. 0ear-Hobbing Machines

Se miautomatic gear'-hobbing machines are the most commonly used ma-chines in gear manufacture. This is due mainly to their ccmparatively high,production capacity, versatility and sufficiently high accuracy.-

Figure 249 illustrates a universal semiautcrnatic gear hobber. Gear hob-tersian cut external spur and helical gear-s, as l-el} as \rolm I'hcels. Cer-tain mcdels permit the cutting of spline shafls, as well a.s other parts having;projections, recesses or flats of identical shape, equally spaced ab-out theperiphery of the part, at the same distance frcm the centre (Fig. 250):--

Gear irobhers can also cut internal gears of sufficiently large size. Thisrequires a speciall attachment operating by the fornn-cutting method and

GEAR.CUTTING TIACHINES

SiR#

/

Fig- 249' Univcrsal semiautomatic gear-hobbing machine, model 5KB2[I:r-bed; z-tabre saddre; r-circ"t* T3ii"L:l?;"i;:tl5;tii,*upport with a,m 4ai 5-work arbori

a,

a mechanism for manual indexing of the blank fromgetrc arer very rarely cut in-gear hobbers; they canancl much faster in a gear shaper.. Notwithstanding the great variety of types andhave the same elementary gear trai; (Fig."i51).

tooth to tooth. Internalbe cut more accurately

sizes, all gear hobbers

j

I

13.3. GEAR-HOBBING TIACHINES

ffiwffiFig. 250. \,'arious l-orlipieces that can be hobbed

6izt

359

i-hob;:2-*orm wheel

J,I

)

Elementary hobbing-machine gear train:blank; 3-index worm; 4-index rvorm wheel; 5-change gears

360 GEAR-CUTTING }IACHINES

vr rp

W(o) cu,*irc 3 wor'r ."n*,,=*,,Ili;*i?:i*"j.':d;l;1..l,i.1il'":t'J;:;-

wheer with ransenria, feedof rhe hob; (c) cutrins a spur sear rvith axiaiieed; iirl;i;i",?; i,iii""^i"g!"" with axiaIfeed

. Gea.r hobbers operate on the generating principre. The rotary motionsimparted to the gear blank and cutting iooi ftoli) are ihu .u*, as thoseof the worm wheel and worm in worm"geurils. TtrgLJ rru"r. i"ligiJivattached to the index worm wheel which'is drii'en ry ?n*-i"aux rvorm. Thelatter-is linked kinematical_lV to the hob fy -."". ;i ;h;;g. gears. The re_quired ratio of hob and blank sp_eeds is estabiist.o ly trr" .rrunge gears in sucha manner that during one revolution of the hob tnb ilant< tJrnI through asmany teeth as there are starts (threads) on the hob, i.;:, the blank mustmake I revolutions per revolution of the hob, where k is the number ofstarts on the hob and z is the number of teeth on the gear being cut. In aclcli-tion to the continuous indexing motion, it is neceis;;y to obtain on theTachine the primar-y cutting motion, feed motion anJ"motions for tenta-tivelysettingthetoolandblankintheinitiatworr<ingposiir"".. c;;*q";;;i;,the actual gear train of a -gear hobber includes meJhanisms-lvhich determinethe kinematic features of-the various moders "f g.;; [;bers (for

" ,oo*detailed discussion se_e Vol. 2, part Three, Sec. 5_5i.'-- """"

In c^utting worm wheels the axis of the nol i. J.t perpendicurar to theaxis of rotation of the blank (Fig. 251). The following pli"-.ip"r motions are

k,r

r3-3. GEAR-HOBBING IIACHINES

required for tiris operation (Fig. 252): principal rolary q.U$!-+g_!S_Stion u-,f the hob, rotaryrmotion u. of the gear blank (continuous ind-xing motion),and feed mo,t-io_grvhich can be either radial infeed s; (Fig. 252a) or tangentialieed-T1

'@x-nSZUl. naaiat infeed ceases when'tie"full depth of"cut is

reached. If tangential feed is employed, the hob is set at the beginningto the full depth of cut and it feeds into the blank by an axial feedir otion.

Th" tudiul$ed-gqlbpd has a higher production capacity. However,a cornparatively few hob teeth cut each tooth on the gear, producing more,,r less visible llats that reduce the tooth profile accuracy. Furthermore, inradial infeed only a small part of the hob length is actually doing the cut-ting. As a result, the hob \ryears nonuniformly. This also has an unfavourableeffect on the tooth profile accuracy.

If multiple-start hobs are employed, or if high gear accuracy is required,tire tangential feed method is used. It can be used, however, only whena special hob slide is available to transmit power axial travel to the hob.Single-tooth fly-cutting hobs (Fig. 253a), or tapered hobs (Fig. 253b), orcvlindrical hobs with a tapered entering end are used in tangential feedlear cutting.

Fly-cutting hobs (also called fly cutters) are used in piece production sincethey are considerably cheaper than hobs. Cylindrical hobs with a taperedentering end and tapered hobs wear uniformly since they cut along theirfull length. The high tooth profile accuracy attainable in tangential feedgear cutting is due to the large number of hob teeth that cut each tooth ofthe lvorm r,vheel.

To cut spur or helical gears the hob is set so that the threads of thelhobon the side facing the gear blank are directed along the axes of the toothspaces when spur gears are being cut (vertically in the most common typeof gear hobber), and at the helix angle B of the teeth when helical gears arebeing cut. This is done by setting the hob axis, in the first case, at an angle

361

i

Fig. 253. Fly-cutting-hobs (a) and tapercd hobs (b)

F-*:-

Type of machine

Maximumdi ameterof blank,

mm

TABI,E 38

L 200 to 2,000{ 63 to 400

2.5 115 to 500

330 to I,930 0.(i Ilorizontal blank axis.Travelling hob slidecarriage

Vcrtical travel of blank.Radial infecrl of hobslide saddle

Powcr ofdrivc

motor,kw

Netweight,

approx.

Semiautomaticgear hobbers

53OII53OBA

5K30tB

5306K5307K5K324A5K32TI

3501 ,500I,300

5080

125

0.5I1.7

5.57.57.57.5

200 5

320 6500 8800 10

12

2030304040

90 to 450100 to 40040 to 31040 to .310

3,000 Vertical blank axis. Mov-4,500 ing table type6,2007,200

{2,800 Vertical blank axis. Mov-22,800 ing stanchion type

9,800tB, 600

200,000200,000

5K328II I,2505A342rr 2,0005343II 3,2005345 5,0005346 8,0005348 12,500

40 to 200

18 to 100

10 to 60

t0 to 60

10 1o 60

l0 to 60

t41.4

25

25

25

25

Strrr iir tt l,orrlt l, ichorizontal splinehobber

IIori zontalhobbers

I ) il rnc l,rr t' I 5( ) ,

length 700 to 2,000

Diameter 500,length 2,000

to 3,000Diameter 800,length 4,000

Diamctcr 1,21-r(),

Icrrgtlr 5,(i0{)

8 l,o 250 7.5

5A37OTI

5373A

5A375

16 to 100

l0 to 60

10 to flO

3 ,1)00to

4,600

22,000

49,000

{ift, ir00

Ilorizontal blank axis.Travelling hob slidecarriage

20

ITobbers for mak-ing globoiclworms and wormwheels

(E3-57)548549NI

Ccnt re-to-cerr tledistancc y maxi-

rrrum modulc, rnm320x12800 x 26

1,600x50

11 to 189

0.01 to 450.002 to 25

7.5t317

6,900 ltadial infecd of stan-30,000 chion in roughing60,000 Ilotary feed of tablo in

finishing

JU4 GEAR-CUTTING MACHINES

o to the horizontal, equal to the helix angle of the hob (Fig.252c). In thesecond case, the hob isiet at an angle ? : 13 -F a, where B is the helix angleof the helical gear being cut (Fig. 252d). If the hand of the helical gear andthat of the hob are different (one right-hand and the other left-hand), theplus sign should be used in the above equation; if the hand is the same, theminus sign should be usecl.

The feed motion s in cutting spur and helical gears is the travel of the hobalong the axis of the gear blanli (Fig. 252)- In cutting helical geals an incre-rnenl motion is impaited to the table rvith the gear blank, with a! angulqrvelocity that rvouid provide one full_ additional revolution of the blankdurirrg vertical feed of the hob through a distance equal to the lead of thehelical teeth on the gear.

The principal dimensions of a geql hobber are the maximum diameterand module of guut that can be cut (Table 3B)'

Depending upon the disposition of the blank axis, geat hobbers may be

eithei vertiCal or horizontal models'Horizontal hobbers are intendedj chiefly for cutting pinion shafts (in

which the gear is integral \\,ith its shaft) and spline shafts.. The hob is set

to the depti of cut andlhe feed in these machines is accomplished by motionsof the cutter head.

Vertical hobbers have either a moving worl< table or a moving hob slidestanchion. In the moving table models, the hob is set to the depth -of

cutunJ f"a into the blank 6y travel of the table with the gear blank' In themoving stanchion models, positioning-motions and radial infeed are accon]-plishei by travel of the stanchion with the hob slide and hob.

13-4. Setting Up and Holding

the Gear Blanks in Hobbing

The accuracy rvith which gear teeth. ale cut depends_for the most-partupon the accuracy with rvhich-the gear blank-is-set-lp i-n the machine' There-

#t;; i-h; iocating hole axis or shift axis of the blank must coincide' and

lfr" io*ii"g faceif the blank must be square, with the axis of rotation of the

*otf. i"nf""*ithin specifie.l iolerarrces *hett the blank is set up on the hobber

table.In cto-ping the blanks, they must be supported as near.as possible to the

point of appli"cation oi t[" cutt"ing for_c-e. This provides for depen-dable clamp-

i;t; p;;;l"ting all shifting of ine blank under the action of the cuttincforce.

The setting-up accuracy is checked with a dial indicator, the contacipoi"i of

'*triri ir upplied either to the a1611ting (locating) hole of "the blarrk

I

li

I3-4. SETTING UP AND'.HOLDING THEf,GEAR BLANKS IN HOBBING 365

or shaft journals, or to the outside surface of the blank (to measure radialrunout), as well as to the locating face of the blank.

Radial runout of the gear blank may be due to a lack of concentricityhetween the locating and outside surfaces, or misalignment of the axis ofthe locating surface and the axis of table rotation. The first of these caseshas no significant effect on the accuracy of the gear being cut since the pitchcircle will be concentric rvith the locating surface.

Radial runout, due to misalignment of the axis of the locating surfaceand that of table rotation, should be maintained at a minimum value andshould not exceed the values listed in Table 39'

TABLE 39

Ilaximum permisslble radial runout,of diameter,

microns, in hobbing a blankmln

Grade ofacc u racyof gear

b0i ngcut accrrrd-

ing toUSSR

Std GOST1643-56

up to 200 up to 800 up to

0

7

8o

20

50

4,t0

.):

60

80

180

50

80

100

220

up to 2,000

70

130

150

300

up to 4,000

100

200250500

Si{e runout of the gear blank, due to inaccurate setting up on the hobbertable (misalignment of the rvork supports, dents on the locating or seatingsurfaces, chips or dirt under the locating surface of the blank' etc-), shouldnot exceed the follolving permissible values (where f : permissible radialrunout of the outside diameter, microns; Dro: diameter of the circle onwhich the side runout is checked, mm; and b : face width of the gear, mm):

Grade of accuracy ofgear being cut accord-

ing to USSRstd GosT 1643-56

Permissible side runouto.r5 F D;

0.2 F D;. os F D{oa.25 F+

The method used toand required accuracy

hold the blank depends uponof the gear to be cut. Figure

the size, construction254 illustrates typical

366 GEAR-CUTTING MACHINES

Fig. 254. Methods of holding the gear blanks in hobbing machines

methods of holding gear blanks in hobbing machines. small gear blanks l'X,lh l_tgg.uting hole can be held either seplrately (Fig. 214a)"or in a stack(Fig. 254b) on a rigid arbor, or mandrel, 2, which -Jy nuu.'a pilot at the,upper end that is supported in the bushing of the work-support arm. Largeand.medium-siz-e.gears -/ are held on cast-iion supports z inine form of feEtor rings (Fig. 254c ul+_d).- I{ pinion shafts 1 are iut in the horizontal typeof hobher, one end of blank I il secured in fixture z (Fig. 2b4e) and the ot"hiris supported in bushing { qt the support bracket. tne nta"ti is rotated byfaceplate 4 through the body of the fixture and detachable driving dog ;"..

13-5. Gear Shapers

Semiautomatic and automatic gear shapers cut external and internalspur and helical gears, cluster gears, flanged gears, toothed clutches, gearracks, ratchet wheels, cams, etc.

. In this general_ type of gear-cutting machines, the cutting tool resembleseilhel a gear rack and is called araik-type cutter (Fig. zbb;), or a gear, inrvhich case it is called a rotary gear shalper cutter (ni[. zsBaj. G.;rlh;p;

-f

I3-5, GEAR SHAPERS Jhl

(a) w*h " "".o-1;?;

?il;.ll:lTi,flT"lliJ'I^. shaper cutrer

".jlg, a rotary cutter har.e found much wider application because they have.a higher output (the _cutting process is not inteirupted to index the "biank)and can perforrn all the operafions done in hobbers, except for cutting rvormwleels..They can additionally cut internal gears b), the ginerating prlnciple.I'he, output of gear shapers is less than that of hobbers. They are indispen-sable, holever, for such jobs as cutting internal gears of practically'anydiameter, as rvell as cluster gears in wiirch the diitance beilveen the gearrims is not suf-frcient for the required overtravel of a hob.'r\ geal shaper (operating witli the rotary-type cuLter) has the folrorvirrgprincipal .motions (Fig. 256): A. straight-iin;- primary cufling motion r,iaccomplish.4 !v ,travel of the cutter only in on. dit"ciion (cut"ting strokeiand return of the?ii'ttei to the initial position u" (return stro)ie). B]Continluous rotation of the_shaper cutter (ulfand of the'gear blank (u2l to obttrinthe circttlar feed (indexing motion). The speeds of Jutter ancl blank rotatiolare co-ordinated by means of change ge_ars in such a manner that in one

revolution of the cutter the blank makes 19 revolutions, lvhere zc : numberof teeth on the cutter and z : numbbr of teeth on the gear to be cut. c. Feed-in Ilotion sii (radial or circular infeed) of the cutter"is obtained bv travelof tlie cutter axis in a direction torvard thg _bl_q4k u*i. lr;itii ,l.ipi"*Ii""of the cutter and circular feed. \\hen the cutlei't us fe-f in-to the'requireclrlepth, i.e., to the rvhole depth of the teeth, the feed-in -oiioo ceases auto-maticalll' rvhile the circular feed and the cutting motion continue untilthe gear blank makes one full revolution. This crits all ihe teeth and themachine is automatically stopped. A gear can be cut in one, two or threepasses. D. \\rithdrawal of the iable wilh the blank from the cutter, or tliecutter from the blank takes place during each return stroke. Its purpose

7a

368 GEAR-CUTTING MAC}IINES

,, l'rl I'" q"%

,6"lll">t tn*L)

Cear biank

,d Lta*lo)

,.\Fig.756. Principle of the gear shaper:

V l-saddle; p-rail; r-rrbte

is to prevent rubbing.and conseqqelt intensive yrear of the cutting edgesl"'1 ;; ;##;from the cu*er during Thu ""tu"'" .ti'"r.r o"il" ;0). iii; #ilr,ir"*i'g motion

h

:t,ii.)i{r;Jl

\jii

iI

I(

'fAltLlt 4{}p

I

Nunrber offull strokes

of cutterpcr min

Power oldrivc

motor,kw

Nctwcigh t,

ligapprox.

400 to 2,000 0.6

nemarks

Cutter ram 'withdrawalon return strokc

Typc of gcar slrapcr

Operating rvith a sin-gle rotary cuttcr:Automatic shapcr

Scmiautornaticshapers

51074 85080

1.72005M12 200 to 700 1,900 Tablc rvithtlras'al on rc-turn stroke

51zr0ll 500

58 15011 800

5616111 1,2'-.t0

It3-{58 2,000

to 550 1.5-4.5 4,400to 1il0 7.5 10,000

to 150 7.5 t0'400to 210 7 .5 {0,800

Cutter ram withdra*'alon return strol<e

TJ

t212

12

90

30

25

40

Operating rvitlt a mul-tiplc-tool shapi ng

cuttcr lroad

5A{105A1205A130

t25200320

5

6

10

60 to 120 14

1r0 l,o 120 17

i]2 to 1(X) 20

1l,800 All the tcct'h oI tlre gear

13,7(X) arc cut simultancouslYt 5,700

:J70 GEAR-CUTTING MACHINES

is imparted to the ram rvith the cutter i' the heavier machines (moclels El40B,58150fI, etc.).Gear shapers are available rvith either

'ertical or horizo'tal spindles.The horizontal spindre shapers ur"uiiy operate r,r,ith trvo rotary shapingcuLters travelling torvard each c,ther. tn.v .u,i #;;,;i;.tl l.or e.rternaland inIernaI spur and helical gears, ^..unif ,;;;;;";;"1-ii,-,h herrirrgbonegears (rvithoul, a clearance gop-;.

The vertical type of geaishaper is more rvidely used. In acldition to themachines using a rotary gear- siraping cutter, operating on tno generatingprinciple, rnodels a.u urrullubte rvhicfr operate Lv tn* f-ormlcutting processan$,lse a,mu.lriple-rool shaping cutter head (see Fic. i4ii"'^^

-the.outpur, of this lasr typc of gear-cutti'g maJhine is B_ 1o l0_folri rhatof ordinary gear shapers, un,i rrori" thuo 4-f;ld ir." ,rtp"i of gcar-hobbingmachines. The most serious drarvbacri of trroru ;,;.d;;.- is that a specialcomplex cutter head must be avairable for each,iru ot:g"* lo be rnacre (eachmodule and number of teeth).The kinematic chains of gear shapers is tar<en up in cletail in part Three,Vol. 2, Sec. 5-4.

t3-6. Bevel 0ear Generators

Bevel gears'can be cut, as mentioned previously (see Sec. g-3), in univer-sal miiling r'achines or shapers. Horvever,_ the accuracy of bevel gears, cutby this rnethod, is so lorv that such rnethods u",r;;;irlir*,i-.un be emproyedonly in extreme cases rvhel no special gear_-cutting machines for level gearsare available. rforer'e., t"hu output of "millers

^rd;h;;;; i'. u".y lorv rvhenthey are used for cutting bevel gears.. . At the present time, 6evel g.ito urn manufacturecr both by trre form cut-l::g^el^{.^q"lnllting p.ocesses."The form-c.utting_ pri'crp1.-i, ,,s.a in cutringIarge ile\-el gears up to 5,000 mn i' diameter and ivith a rlodule up to s0;;(Tq.lle 41) rvith a iingle toor o. "'ii[-iiuo tools_rvhjch operate ro a temprate.The.generating principle is basecl on reproducing ttie-slaes of the teeth::_ul tTucinary crorvn ge.ar in space_by meins of th"e c'tting edges of rotatltng cutlers or rcciprocarirg tools iFig. 252). The profiler"or _itru .r,:.igh-tcutting edgcs coincjde rvith tlrt,oppo.irig sides of Lrr.o leetS ol' tlrc imasirrr'vcro\yn, or generating, gear rvith rvhichihu grur, b;;g-;;i ;. ;;;;f.'Thiprimary culting motion' either rotation oi reciprociation. is transmittedl: "tl::::."ll-:^q :gg"r. X{otion of the Ii.rs^t typc ('r"i"ii""i'i, accomptis}red:l^S^,i1iqll bevel gear generators clesigned for cutting bevel gears u,ith a shortrace \rroilr. these generators use rotating _circular critters operating b1'thegenerating principle (for erample, modeli230, see fufri" ZfJ.

13-tt. REVEL (;l'l-\R (ill\ERATOFS ?,7 I

i

I

I

l

l

d

f is. !i7 . T,ruls rr itlrslririglrt lul tirrq t'rlqlsIlrul lorrrr iltr0 l,rutll SnuCO

of tlrc irnaginarY clorvtrgL\tlll:

t-be\.el sear l)larlk; .?-im-aginar-\ clo\\:11 gear; i-tools

Fic. l5S. L,r'trct';ttittga strriqlrl hotoI gt'arrvilh tirlirlirrg cit'crtlar

t:r rttcis

The rotating cuttels (Fig. 258) IeYol\-e about lheir a\es to pTo\,ide the

.";ti"g otiioii(", ""T tiltr".il i' planes pa-ssing through the sides of the

teeth o' the i'raginary t'orvn gear io shape the teet!,.alongtheir.length'ancl at the same tinclde'-partic-ipate i1 the relative rollilg motion betl'een

the cutbers antl blarrli to ,,btain the retluirecl tooth profile (u1 and u2)'":Sti.uigf.f

linc cutting i-q 'r.cle

use _of in the slraight b-e'el

^gear generators

that lave trvo recipru.loling toof. rvliich ,lrape thc pI9!.i... of the beeth 5eing

cut. In t1 rlachine oiliiir;yp., geal bla'li ? 1Fig.':;rr) is rotated (n1 rpm)'

,ur,,, r;"L"t.d is cradie Z 1rr, tpittj rvith the recipiocatirrg bools rvhich repre-

.",'l i.inrnralicalll, tt," uap.int siclcs of a tooth in an irnaginary crown

*ott,,o, _slidcs 3 rvith toois 4 reciprocate (r) along \\.il).s arrangg$ o" the l:c,:

of crarlle 2. Ihe l.ools cut in their tnotiolt tc,rx'ard the ape-t oI tlre gear pllcrl

cone.'fhe tools clo iiot cut on tlie leturn stroke, rvhen thel' are \Yithdlawn

irorn the blanji to oi.oia clamaging the n'rachined surfaces of the teeth'

Fl g*re 260 shor.i s thc succei-*i'e positiotrs of the tools antl gea' blauli

ilurirg goneration. .fi'iJr. beel;";ng'ot the tooth cutting process, tlie tool

1rr rnacirining o1e ni t,tr" sirie slrtacei of the teeth starts to cgt into lhe blank

ielg. :AO, po-.itio', Z or.a 2). The'. the secr,rn4 tool, rle-signetl to -shape the

,,rh.r sirle surfaces oith" teeth, begins to cuL the gear (Fig' 260' positions 3

,,,,,iij.',it ifrir pltirt, iile lirst to,ith_ has been coiipletely gcnerat'ed' Upon

i".if*. totuii""'(r"ili'of the cradlc the tools rutr otrl oI rnesh wit'h the gear

lrltrrrlt. silce the trvo tools represetit only one Iooth-space of t]re irnaginary

.;;rr.;' g"nr. ff."t.f;t;; nh;ir-ihe tooth'has beeu shaped, both l:rlank and

21+*

v-?----

lr=- I

Type of machine

Straight bevel geargencrators

'tl:'oTiJ' | *:io.lt,'.?:"cut, mm

I

Netweight,

kgapprox.

3,000 Operate with tvo rc-

8,000 ciprocating tools12,000

Iuodel

5T23B5A25OII5282|

l\Iaximumdi ameterof blank,

mm

Powcr ofdri vc

motor,kw

125500

800

1..5

8

t6

0.6

7.5

FulI strokesper minup to 800

75 to 472

30 to 307

TABLE dl

Tcrnplatc-t,ypcstraight bevcl gcar:

plancrs

Operates rvith t\Yo

tools5.,\ 283

52Tr,r2(5285)

1 ,6003, 200

5,000

Lo 727

to 80to 15

7.5l0t4

19,0(X)40,00050 ,000

30 1.7

40 3.580 :1.5

Operate rvilli a singletool

Spiral bcvel gcarplaning generalor

Straiglit bcvel geargcnerator

1 ,600

m pcr mlnup to 80

27 to 180

l7 35 ,000 Gcnerates gear n'itlr a

single tool. Illarikinclexes ono tooth ilfull stroke of tool

7 ,000 Opotatis rvith tn'orotating cllItcrs

Spiral bevel gear gelr-

erltors5T2345T244527852BTI

1+3 to 51t0

200 to 500

25 to 32;t

21 to 300

12it 2

250 0

500 10

800 15

0.83.54.'-,'t

10

3,000 Opetatc r,ith farle-mill5,000 type cttttcrs

10,50014 ,000

Fig, 259. Principle of tbe straight bevel gear generator

straight

- l> ,--^ --f=1 .V-,'-fffi)'(fld) ,#f,e))\ \:z \5/ "\i7

\v123

,@,reD,=@456

Successive positions ot,n. ,331-.it#" gear blank in generating a260.

tz

1

/

Fig. 261. Curved-tooth bevel gear being cut on a generating-type machine

614 GD..\IT-(] i]1'TIN IIi [I,\OHINES

n,

t\

(o) t0J

face-rnil.l t)'pe cutter irr rclatiorl to tht'!'ig. 262. '\rrangornctrts of tho qcar blanh.arrd the, rirrllu aris

cradle are rcversed. At thc cld of this reverse rolatiou. the lllauli is inderedio tfr" nert tooth (Fig.260. posilions 5 ancl 6). This procedure is rcpeated

for cac[ toot]r of the gear in tlie same scquerrce. 'I'he brvo tools are not subject-ed to the same loacl-in opcratiorr since one o[ l,hern cuts into the blank fc'r

each tooth and wears f;i-qter than the other tool. To eliminate the effect

of this nonuniforn wear on the profile accuracy, the tceth arc linish cut

after roughing the tooth spaces' -\Iost of the stocli i-q removerl in the roughinroperation.-Roughing

i-q done either rvith siuglc incie-ting in rvhich tooth spac-es a_t'e

cut in'sircc-ession, or by corttinuous irrtle\ing to eYery other l,ooth. In tlielatter case, both l,ools operate urtdcr ideritical conditiorl-q'

Curvecl-tootli bevel genrs of the spiral bevel, zerol and hl,poid types al'e

cut in rtrachines using the face-lnill t,vptl of cubters ancl operatirtg on tlitgenerating principle (motlel rT23r\ and others). In the cutting pr:ocess.

[Le guur 6eing cit meshes l'it]r an imaginarl' crow1. or geleratillg' geal'

of rvf,ich the ictive surfacc of tlie rolating cufter represents one tooth-'Iltttooth forrn is olttained as a re'sult of a rclat,ive rollirig motion betrveen tliecutter and the blanl<.

Spiral bevetl gear generators havo the foilorving principal tnoLiotr:(Fig.261): (a) piimarl' cuttirrg nrotion drreto independenI rotation of cttt-ier"l (nl iprn); (b) roll motion corrsisting of rotation o1 of cradle 3 rvith thtimaginarv crown gcar arrcl rotation ro of gear blanl< 2 rvhich is co-ordinatetirvitf, crarile roll tlirough change gears (not -qhorvn in the diagram); (c) *'ith-clrawal of the blank from thc cutter aftcr cuttirrg each tooth; and (d) inderins

e\-l|iuei

il

l:

iiI

I

l

I

h

t

II

IfI

t

l

L 3-7. G EAT:i.!.INISIII\ 'i

\I.A.CH{N I]S D/J

Illolioll $ltich is transrnittcd to the blanh rvhen the cradle returns to itsirriiial position after cutting each tootli.curverl-Looth bevel gears may be crrt either rvith tlie aid of a crown gear.irr rvhich case the aris of the cutler is parallel 1o thc craclle aris fs in

I:ig-,262a (rnoticl oT23A), or rvith a ber-el gcnerating gcar trig. ziizrrl.In tlre latter ctrse. the blank aud the crrtter ian be siviiettea'tniougtr a'narrglc z1.q_in-reference to the plane ol rotation of the craclle (this priiclpieis applied, for erarnple, in rnoclel ol7]l).

. I'he kinematic principles involvecl in cutting bevel gears an{ the gearingtliagrarn-s of the mac]rines used for tliis purpoie rvill ije consiclereci ln pariThree, Vol. 2, Sec. 5-6.

13-7. Gear-Finishing Machines

. .hi the great rnajority of cases. the tectli cif machinecl gears urrclergo a fin-isirilg operation since after cutling 1[e gear the surface"finish on tiie toothproflles or the meshing errors do nut coniply rvith the requirernents speciiieclirr the gears. Gear-Iinishing methocls inclucle: burnishin[. shar.ing. llpping,erinding and honing.

"({olllg,tlt!9. As-the result of plastic cieformation of the surface la)rer

"I tttetal. the sirle surfaces oI the teeth of uriharclened gears are compresieclbr- burnishing. This operation consists es-qenbially in rilling the rvork gearu'ith one or several burnishing gears ri'ho-.e teethire very hird, smooth"andaccurate' 'Ihe latter gears are driven bv a rnotor. The requirecl load is applieJb1- a rveight.or by means of electric. pneunratic c,r hjdraulic der.ice-"...The capacity of a gear-burnishing liachine j-q speciliecl hy the maximum

rliameter of gear it accornrnodates. Trie capacit-r' of geariburnishing ma-chin^es procluced in the soviet Union tangcs fr,om 12ito 5,000 rnm"(Tab-le 42).

.Qear sltari\g is based on tlre cutiing o[ fine clrips fr,rrn 0.00j to 0.1 mmtLick {ronr the gear-tooth profiles by the cutting eclges of the tool duringtho_ relatir-.e sljding rnotion of the tooih profrles on t"he me-.liing ruort geoi,rrtcl tool. The latter is called the gear-shaving cutter. The forrns of tne c.r"tte,t.rrrr€Spond to thc trvo methods of -.liaving, rotary anci linear (rach). Ther'ltary metho_d employs a gearlilie cutter; the rtrck method uses a cutting toolhaving. the shape of a rack arrd is employed to a les.qer ertelt than thi firstrnetl'rocl. The cuttcr teeth are scrratecl to form a series of cutting edges (Fig.Itj3). To obtain the rela.tive sliciing action betrveen the tooth'ptofitn., ttLl-orh gear ancl the shaling cuttcr are sct up in the gear,-shar,ing machine'.r'ith crossed ares in thc form.of spiral gearing. Tlie mo_qt efficiint anglesi,et\\'een the axes are betrvee'10" aid t;d. ttre"teast perrnisslbte ang.le iE i.'*'hich i-q used in shaving gears having a flange or shoulcler that iiterferes.i'ith tlie cutter at a larger angle.