Carbide RehobbingA New Technology

That Works!Fried Young

F,orlest ICity GearRoscoe, IIIL

Many people in the gear industry haveheard of skiving, a process wherein solidcarbide or inserted carbide blade hob with15 - 600 of negative rakeare used to recutgear to 62 Rc. The topic of this article is theuse of neutral (zero) rake elid carbide bobsto remove heat treat distortion, achievingaccuracies of AGMA 8 to AGMA 14. DIN10-5 and improving urface finish on gearsfrom 8 DP - 96DP (.3 module - ..26 rn.),

Early technology developed with Azurniskiving hobs yielded encouraging result .However, few people seemed to adeptthisprocess in lieu of gear grinding. Among thedrawbacks were [he necessity of havingextremely rigid bobbing machines and workflxruring. expensive tooth timing, centeringdevices. expensive cutters, and the difficulty of

[p EXcept CIR, J015 MalfllPl' eIIG•• :r: .spur

I Pr..,,,ur •• nl/I.: 21"Oil m.tr.IIIP~ch: 12·Numblr 01T,Ith: 14Pia:hIDilltlllM:l.tM1 l'UJ.oolllA-B1 PJD.Mu AIlowabl. Eec,~ncl!'f.TmICo"'0Irtl' &~f .cm~t. '0 tu!" P.=B1 wch Mull.IBlckluh .IXl4 Mm• .996 PILl<WIIhlJi"'.lulMating IG.lr: PIN J02Q..I88 OD. Min. Min,

He,alTlm 14IlAmlr Dimnc., Min ..1.1_,

H.lix An;'.: R.II. or Il. H.l.1 d: NDminalMin. Rom Fitl.t IRadiLl': !D131Cll" ol'IGnt liP,,, SS·I&1l: e," li I[l:>8u.' Cif,cl" !ll1Ii1!l': !l1,SIT"", InvoIyt' I'onn, lIiamWier 1T.1.1F.1: I.C6lIlInvolUlllloll' Arlgl, to T.U: Di,.: 14" ,e1"11'IY1J1llt1 RolliAngl.tD Outside Di.~~·1·Root 011.;9q5 M;n.I.o111 Mu.[)"m,rqion (lv" Pirq 1,.3569 -131mM".ur·ing Piu Oi.mltlr: .144

I

Hob blJrrthisside,

Usa d~btmIIttachmentto remeve.

UlC FROM GROUND SmE

Fijl.l- Case]

116 GE .... R TE CH NOLOGY

.765

1.'6321'(.163U

re-sharpening the cutters properly to raaintainthe correct involute.

Some of these problems have been eliminat-ed by using zero-rake solid carbide hob whichare available from ma.ny of the major hob man-ufacturers, This elim.inate the need to offsetthe diamond wheel when resharpening on ahob sharpener. reduces the initial. cost of pro-ducing the cutter and increase cutter life.Another improvement i the common use ofnon-contac], electro-magnetic sensor whichautomatically divide the stock on the toothflanks with extreme accuracy, lfthe quality ofLhegear is excellent initiaUy and heat treat di -tortion i minimal. it is possible to recut gearswith as little as .0015 - .003" over wires as asalvage method for gears which grew unex-pectedly during heat treat.

Ideally gear should be roughed with protu-berance hobs which have any desired profilemodification built in, If the part i, crowned, itmay be beneficial to crown during roughing 0

that an even amount of lock: is removed fromthe flanks, leaving a uniform case hardnessdepth. Helical gears often unwind during healtreat, and accommodation may be made toincrease the helix angle. For fillle pitch, we startwith approximatel y 0° [5' as an offset.Remember that if a protuberance rougher isused. it generally only produces the correctinvohne in a sometimes narrow range of teeth.

Our experience is limited to the carbide

rehabbing of gears ranging from 8DP - 96DPand less than 4" 000 mID.) in diameter,although many people have skive-bobbedmuch coarser. larger gears to 40 mm module.In fact a number of manufacturers skive coarsepitch gears to reduce finish grinding times.

Remember that. proper gear blank finishingis crucial for achieving high quality levels forcarbide rehabbing. just as it is vital to geargrinding. Bore-type blanks should be honed. ortD.-ground, and faces should be parallel. andperpendicular to the bore. Similarly. shaftsshould be cylindrically ground to provide truelocating diameters to the centers for cuttingand later inspection.

Since carbide can be susceptible to crack-ing. tater vintage bobbing machines withbacklash-eliminating features, power tailstockdamping and CNC controls multiply dramati-cally achievable production rates ami accura-cies as wellas prevent. hob damage. As report-ed in a January. L993 •.paper, "Skive HobbingHardened Gears" by Hans Glatzeder, rigidmachines can carbide rehob to 2/3 their capaci-ty diameter and module (Ref. 1).

Cutting tools should be A or AA quality andpreferably titanium carbo-nitride (TiCN) coat-ed to improve lubricity. Either face 0[ borekeys are suggested to increase drive rigidity.Typical carbides are ISO KlO, K05, MIS, MIOand P20 (Tables I - IV). Depending on pitch.stock removal, hardness and whether protuber-ance halos were used to rough, surface speedsrange from 90 - 340 m/rnin. Recommendedstock removal is .002 - .006" (.05 - .15 mm.).Required quality may dictate a finishing pass.In this case it is beneficial to climb-cut on onepass and conventionally cut the other toreduce cutter wear and improve quality.Experimentation on helical gears is warrantedto determine if opposite-hand hobbing; i.e.,left-hand hob, right-hane! gear or vice versa.will yield better results. Close observation ofthe cutter and gear quality will help determineshift and sharpening intervals. On fine andmedium pitch gears, we expect at least 2000'pieces per hob or more. depending on hob sizeand part hardness. unless suffering a crash,Microfini. h is determined by the number offlutes in the cutter versus the number of teethin the gear. the pressure angle, feed rates,

Values In Tan-Tho-us:andl 0'1: In Inch

LEAD ... PIROIFILIE TESTCl'1? ,.28- Il'n"

R.qd. Pr. 8/ L.: 8 Att 1'1:101L.: 13

h. ~ --';"Il'"O'O-

F W.J"· lmill'R.od PrBlt.O:8Ac!PrTCilLe I~

3 LoftflaM. Z I I 2 RJ~h!flink 3------- ---------~.------

II

Du"lit\<TIP

I: I

~o

10 I,- ..,-I-~-' - --, --11---,'----...1\.. -, -,--

~ ! iE+ +

~ 10 ft t=t=='===f!:=.l" =-""=- =- ., 11=' -=-:;=1:' '=~-=i=:_=':!::;' -~-:::I:::=-=.~::!="

I ,'I :1 I~~~~--'~..-r---r~'~~~i_-~JROOT

~ ~ ~ 2 UmitValult , 1 4TOI1.5 2.3 2 2.9 .. i; ·011:5 • I•

F=t~ 1,3 2:1 i. G -I- -, --,-.- I. !.~,,-I- -1.5 ~i -1.4 c,- 5 -I- ~~.-~)C _II -

,.1.9

-1.3

1 I 2 Ri hI Flank 3- . - 1 Tooth Nr I ,~ S I . 9

-, i-!_ ....- - .... ' '" -, j ~ • I I

+- -. - - -:..~-=- I • .- _r -

jt - .

t - 1 - . t.f: .. - .: I' - I- -- - I .~~--4----1r-~~~--~--~I~--I-~-~~I----~, ~

'.I . ,I

BonOM~

W4.9F-I-

4.,-,. 3 Limit V81ue I

U 1.1 LI U/4, 1.0.6 8 10 ,8 --{- :8

4 .7

21.2,)

~,' 13 4

1.2 ., 1.1,1 .7

A-/-

Fig.2 - Case 1

material cut, hardness and coolant. Surpris-ingly. carbide-nabbed finishes approachground finshes, often around l 6 microinches.Flank wear of .002 - .006" (.05 - .15 mm.) perhob flank is a suggested starting point in fineand medium pitches before shifting and sharp.ening, Because TiCN does not lend itself torecoating, and regrinding the hob profile is noteasily done. we have not used recoating.

So far only recutting has been mentioned. Itshould be noted that many manufacturers arecarbide hobbing from solid. In fine to mediumpitches. this is practical in the 40 - 50 Rc range.especially where small quantities are involved,and hob spindle rpms may be reduced to under100. Hobbing from the solid. is generally morecostly than carbide rehobbing rough hobbedgears due to tooling and machine time costs.

Most of our carbide rehobbing has beenclone on mechanical bobbers which realign thehob tangentially after the machine has beeninitialized with the home position for nob and

Fred Youngis tirepresident of ForestCi/), Gear Co, a fine andmedium pitch gear jabshop, He was IheChairman of AGMA 'sSmall BusinessCommittee and theauthor of several paperson gearing subjects.

'MAY/JUNE 1994 11

PITCH + IRUNOUT TESTPilI1ND. Din M! TVl3t Sp~r 0111'12112194/1<.21T= '4 O'.12JOl H~~O'O'R Rc_l1

Pnch TIP ~~UI1i 5.1/8 P.,h T T' Accul1'l S 1)\ fI,u"'DiII'Flqd.a..I .l1li • 1! B Bu..tV_ ell d! 6J 'IllAct V ..... ~ UI 12 U IS lin II I' U 1.1Arto..l ~ 13 ii: 13 I.

~ GMuT~ 12Duality Levels [0 AGMA 3111:03,•

fO ~ VlluBS In TBIl-'Thouunds of an inch."'''If"""i! -~- ~~..

GM,n.'1 N".I~PITCH - 'G--'n.T.~,. -- -- -- - ~•

l' , ,~.~

~~ ~ I I'10

I __ I

<r GMu.T.No. '10 ~ - -- -- --~--,

.°'·'''1 , ! ,

I~ ct,,

I

I.

~1"'9"" I -----r' • I

, ,~

t ;, ,I

8Mo1.T.N<>;I

~

i ~i.' IACClU- 810,1... T 1'10"1 ,,7, I

I,

I' i_I iT~ 1~ I - " 1 !ID i I I

-V- -- , -T =r ~~ I !: ~IG]UIIi(. T NG. I

IGULI< T 1'10 3

j -t I , ,I

RUNDUT 1 I I I 1, I I I i I....!I.... CU uu i I ,

10 I jI I"Q - ! . I

GM,nTNo"I !

Fig,.3- Case 1

PITCH + RUNOUTTESTPartN.: s.r. Rem ..

= I,m!.I

[.10 D~'2BDDD H _IB 30'0' LPrteh TtT • A-m

00

~ Pne ~ T T • Accum sp.n, \moulon.

DO

Ilu.lity Ltv.ls to AGMA 3!IO-.03-::-;-;;-:--:-;---:--t----i--,- V.lues in Ten-Thousands 01 an Inch..

El M,.. T. No" 6

I

--'---__;:-- i ' 'j- -=1 .:- - -t- ~ +!

m Max.T, NDC5.J .- .' - .:t' - 1--- '.J

RunolJ1

.JL

10

()

,El fIIlln. T. 'No,; l

. -,-,......., ,-'t -:- '--I - ... ;I-_. - - ,t· '"

Fig.5 - Case 2

!lead + Profile TestD P 28 AGMA P A. 20"0'0"

Iluillty Lallol, to AGMA m.o:t n.lo H.llJ'3Ir0" LValues ~nTilin-Thous.l!lndl or ,nlnc:tI F.W..Y' BCll. .ilSlf'Quality A.qd. Pr 10 I Le 10 A«Pr 10 I Le: 10 nlq<\. Pc 10 I lI: 10 Ac- Pe 10 /lI.l0

TIP 4 3 LtttRlnk 2 I 1 !R"ht FIonk J !

I

I . IW ~ -- : I w I

16 1" -- - v , I ,

--'-- 1,

~:.il~ -I_:.il .1.1131 - 1-'·; -

--I - - -I-:r- ~+ , =-- - l-I- 1::1-·... -'.I L ,-

~:I e 1 _-I - -=-~--::--- , - - ,- --. , -,"r 10 ~

_. J -- ---'- =\1---- -- - ,-1-=1¥ H-:~

~:. --r- t= - ----.- ,

1,9 .------' =± I- -I -j--t. t:::::::::0 l.r1

ROOt I--

l'lIm.vliiii • -' Unoi VII .. 1-'--

3 2 1 ,rWH I B 11 U U u b'U 17 IA_ 1.3 i s UiF+ U J 1J 1.0 I u 1+-_ . .l. 12 lJ 1a J 11A+ -J -5 -9 -s -1 !+ ~, -I I -I -11 -10

!

4 J LoItR.nI; ,1 I 1 211oJ1h1_J 4 -TOP

G~ • =f=:" L ==fta:...GI --'--- 4 ..!.T_NoI-4- __+-- -",,-,-j--

J11 - -1 : r--- t-.I1 ',~:I

:{ ~ ---+-, - ~'. ~r 1=lt .-I :F-r- I::'~.125 - 1- li==

-r- .,-1'-i -.' -11 • ~~:1"

~::-'!l - ,... - - r-

rIO 1 -, - :::::j -:: - f--, - - t-.- , --\' - 1-1- '.-- -~r----= t:\ ---+-. _'f-:: ;-= I=~ -- '----In--; <r-r- , oi, .-r-, -+---- 1- I-AIr---'-

1--1:::-:-1-' I~80l1Olol 1---1 1-- .-"-",.V.lul 4 J 1 1 lmlllV.lul I 2 3 4T CI':L3 1lI l.i 1.9 12 1 2.S ~. 2.2 U 3.1 U J UF+ 1.5 1.1 1.& 111 IS !+ 11 1.2 1.lI 15 UA+ -1 I -2.2 -11 -10 1 -15 H:- -.1 -12 -u -.8 I -U1C"III Ii3 M '5l 5.6 5_ W 41 50 49 SOO •. 9

Fig.4 - Case 2

HardnessTransitionZone{must not fall in groove]Material 41l50

Item Spur or Helical Gear :Data SpecifiC8tion Insp.1 TYlle Hehcal X2 Normaldja metra I pitch 283 Number of teeth 10 X4 Normal, pressure ,angll! 2D~ !

5 H'elj~angle 1'8'30'00·6 Hand 0' helix Left7 Standard pitch diameter ,3766,8 Wholedeptlt .0803 X9 AGMA,quality number 10

10 Total composite tolerance .001031 X11 Tooth'lo-moth composite tolerance .000712. X12 l Mastel part number13

,Meas, over .06857 dis. [21wires .4965- .4935 X

14 Lead 3.53602615 Lead toleranc II I .000323 X16 Profile tolerance .000216 X17 !Rollangle {functional profilel 1.1I94JO X

19 OutSide dia. of gear .s. .A715 ±.oooI.006 X

20 Center dlstancatfunctlonall .960J421 Circular tooihtfi ie kness .0677 - .065822 Backlash .003 - .000323 Tooth form (see detail " ")

25 Modilication .011526 Base dis. .3516 I

27 Mating gear 699607 'I28, Min root dis, .30529' Pinion must have .000410 .0008 crown I X

Fig.6 - Case 2

work piece stored from a setup part. Hob shiftlimits areestablished over a circular pitchrange, shifting the hob in and out to realignfrom the timed position established by theproximity device located over the top of theworkpiece. When the hob is thoroughly wornin a given area, the hob is shifted a full circularpitch ami continues across the hob face. Caremust be taken to cut reasonably good parts inroughing and to insure that no severe damageoccurs in heat treat. If a CNC hobber can beused, better profile results are possible becausethe workpiece is rotated rather than shifting thehob, which may degrade the profile.

Following are some histories which shouldmake a strong case for the cost-effectiveness ofcarbide rehobbing as a substitute for geargrinding. In fact, many applications would beimpractical to grind because of wheel diameterand cost. Keep in mind this hobbing was doneon non-CNe, mechanical hobbers, costing$250,000 - $350,000, versus gear grinders,which usually cost $1,000,000.

Case History .1. Aerospace high pressurepump gear (Figs. 1-3). Fourteen teeth, 12 DP,28° PA, .765" face width, spur, hardened to55 - 60 Rc,

A. Rough cut-double cut, .0501..030" (1.27 -.76 mm.) feed at 350 rpm with a 2" (50 mm.)diameter hob-331m. Normal tooth thickness,.1301.132 (3.3 mm.).

B. Finish-cut 400 rpm, feed .015" (.38mm.), 2" (50 mm.) diameter cutter, TiCn coat-ed, production 141hr. auto-loading.

Case History 2. Power tool application(Figs 4-6). Ten teeth, 28 DP, 200 PA, 18.58°,.68" (17.3 mm.) helical face width, hardened to48 - 53 Rc, material41L50.

A. Rough hob bed 800 rpm, .045" (1.14mm.) feed, .0701.072" (1.6 mrn.) Normal tooththickness, 1OO{hr.

B ..Finish crown bobbed 500 rpm, .025" (.63mm.) feed, ..0642/.0625" (1 .6mm.) normaltooth thickness, 601hr.

Case History 3. Aerospace application(Figs. 7-9). Forty teeth, 32 DP, 20,0 PA, .325"face spur material 431 cres, heat treat210/245,000 PSI, AGMA io.

A. Rough hob 900 rpmf.050 (1.27 mm ..)feed, 1 7/8 diameter M42 bob TiN, production1OOlhour.

B. Finish carbide TiCll, 530 RPM, .025"

LEAD ... PROFILE TESTQUIlIft) Levii'll! to AGMA 390.~3,Valu.aii: in Ten-Thousands: of-lIrflnc~-.

f'UO ".1" ,','rlual Roll [I, Pr; 10 Le: 10 Act p~:ID j La: II Re ~,Pr; 1C le: HI A~I Pr: 12 le. II

TIP -----.,-4~ _ ~e~~ _ 2 ' J~ I 2 RllJhlR.nk 3

a·, 11r: -r -r---r- --~

II

--. -

~+,

--'

l.JmitValu~ 1orf5 1.3

Z2.0

21.3

31.2

41,3 13

F-I-A-I

.9-.3

1.0.4

'1.0-1.l

,9.9

-I- 1.l-I- -,6

1.0-,8

1.0-,5

1.3-1

1,1-.S

3 Luftfla-nk 2. 21 11

.. I-..., - -

1 P.lghtFlal"lk J11 _ ,_ 21, -, .1--"~ '---1

: .'. -, ..• -t-_ -

I

,!l_TQ~th Nr 1 1~ ,.---1-,}:_" -, -I .:

'031Tap

• I

1·'1

:~ j: r'

"

, r :'~_'_ "I: r-,

" !.:" ,1-----=-,

lJmitVlJlue l 2 3 4Of,!.2 ,,' .1 is ilia" 2,1 2,1 1.2 ,9 1:1

F-/A

" ,1 ,. 1.1 ,9 -I- J ,9 .9 s .8

Fig.7 - Case 3

PITCH + IRUNOUT TESTPart No. DEln: Type: SpurT-4O 0 =3.1 HIlIO"~'U~ R 8e:;; 1150

T1P' ACl:um S.ll8Pitch Pitch TtT'" Accum S l/a PiUr1CHII~ 10 10<.£ 2.5 5,6

" 1.0 11 3,9 '.9 2.6E 12 12

R~d_ QUJ;!I ....: 10LJmltVa~ue ii '2.5ActValue ~ 1.2Art (lliaL !; 12

1.9 3,9

-lL GM,L..!N.c' 33 ~*~_~_-' ~_10 ~~{tj ~~~~=:;:~~~~=_Quality Levels 10 AGMA 390,03,= ~Values in Ten-Thousands of an tnch,

gMiii, T. No" 15P1TC~ G Min,T,: No" 21 '

-I I .-- I ~.-'--+i---f-----t.l- f----t----

c 1 'I " il-lL~~~~~~~~~, ., =-= .! ..

10 3 .: i ,. ililM ax. T.No,3lJ I

[!]Max.T.No.:l0 - ·11

!

. 'I . ,1-..:... 1 _. - - -. .':'I~I",',"

I.i': I _

I' - .! - -I ' -.I "-:.J -::::. - ,:. ',' .

A.CUM. GMlo,T. No,c29ElM,n. T. No" 11 I.

,II-I .

RUNCUT lilM",Y:,NO:1S: - !'" -. I' -:C'3'~ :,.'r. -, ::-=2'.::--:- =~~-',......,-...,.......I·-"-· '"7'--+--:-:1.~-.· ~::-::'::±-::-:::-- t-:-.:-.-:-:-: : -. "":-F- :~~

IQ

Fig.8 - Case 3

MAY/JUNE 1994 1'9

AGMAW32 DP 20"40 Teeth

.1101rCE .0005 nCE32 Micra

.001 A mlxorCham4 Pl

.005 R Max4PL

.779 ± .002 Oia

Hcne if necessary

-L A 8 .0015 I

Option I Blink per p,m!

Option 2 Op1ional ,processing. Screw machine blank, double disc grind. Bore10.L hone to final sIn.

T. 'Heartrelt rAW MIl-H·6874 WIth rhe exc.poon rhat til, range shall be210,000 ID 245,000 psi and the impact valua shall be 18 ftIlllilmin.

Fig.9 - Case 3

PITCH + IRUN'OUT TESTP r R m ~• II 0 IUIJO H. IS '0'0' R

PJtcfL Tt c urn _SDi!ln ...., PRe"" ., Accum SpIn unout

p' • .9:82

-L. 8MIlI.T.No:I __ ...J',--;o.,.J:I...-_-I-,_f"_-·_I.- "j' .. ~.,.,101 _- --L._+._+I_·, t- 1 '

-oi. _-~---~~~ __ -_l'""-__ , Qual!\, LavelSlo AGMA 390.00.ii. 1 Values in Ten-Thousands of an inch.

8 Min. T. Nil.: 10 __ +-_-1-e_I---t-_-I--_:"", -+---;,--+--P'tch - 8 M". 'r.~.:3 __ +-----:" ~r_+-_r'[-.;.:•._=+---=-::~ 11''::'-''':--+'.:....~•• I!--.:..I--:.:-:....

-~-+_,,---!-:.... ..+-I-I---I.-- ~1 .,.1 ~l 1 • 1· . r:.: i ., - -

10 .jj I =-l .. L t,·. -"t' 1.1 - ...= 1 '~.,. ,,-~; - -.j

0- ElMoLT.'! •. t I l' L. -1-- ,-- .1 -

t I - -. --.: ,,'=... '.- ----.::==-...--.A-10 I . ~ ,- .-:-:.:- ~ -_ • - -- -_. - - .' . --

t +- 1-- 1--- '1--- - 1-- 1----, _. -.8Min.T No.:) T -'.::- -- - .._.!"1-0

Fig.n-eo~4

Lead + Profile TestQ"t'" ~tIt '" AfiMII :I!iD.b3 D P ,4 AGMA jp II.lII"O'O"Vlklu.' __~Df.~ I~Pi Th ,3 Hot ,goa II" It

FW" SCO .'el'Iluthl¥ IItqd.Pr.-llt.1 AclPr- /lr, 10 Roqd.I'I:- Ilt:. A<lPr-Ilr,'O

np • 3 ltItFlonl<2 , , 2 RiO"' RonI< 3 •, ,'!.1

I -,-J 1i t -~ n - -" 4J,lI70 IV 1 :1 ~.~ "'0 , I

~+I t ,-.-

I j , . - . t~- - •!OIl' 11', : - - - -- ,I)~I,

~ '0 ~

f--, -I-~

1: . illi - - . : ,A11.! 4 11 ;' ,,n- -r= -:~- ...:l- • t -:.. >--. i --

I~Vt" • 3 'i I ,,,-~Voluo ,'-'7 '<3 •T+ u II ~O .. <l + 5.1 1.1 SoD 1.2 53f+ ·~ ,~ 51 5., U + U U ~O ~O SO11+ • -, .s 1 .z -/- ,~ -1.8 -Z5 -1.0 -llK-d\," ..I. +1+ ++ +1+ +1+ ++ +1+ ++ -

010 • 3 ltltA .... 2 1 1 2ItovlnA''Il.30TOP r=:'-'- !--------1 . ., 'J_Nol , -t--T _'0

. - t- - - t---

2:1_. - L_~'" r--::::: 1--

~ cr --=-;- ......L-

88 ~, -1'\1 IfiI

.I ,--- - .. j=-1 I- '. [IS' -1- -_..25 - I.":::.-; - - c--.- ,,1 >~ >'1 . :-= ;R..,

.~ !-t..: --=tt f-=r I-- '::trill· 'I ..' F3 I

~ 10 1 .\ i- i- .-<1\ ~.2\.. f-=::l+L ~-i) .- '7'-

.1 r\ ,- r-l=- r\... "r - !-- .~ -=~..:: I~-- ==/=-.:..;:::: f~- -t I:""':::;: -- . I:=:::BOnDM ,,, :-- - - l--. --I--- - - 1-

GM'V.,.. • J 1 1 lIn1.V.lue I 2 3 •T W<lS U 30 U 2.! II bu 11 zs z.r ,U 2.5 ,

F+ 11 IT 13 11 ,1 1+ 'S 2.0 U ,IJI I

II-/- 11 IJ I ~ , 1.3 I-/- I -u 1~ -.' .JI ,UII[:118 l' l~ It II U JIll 1.l U n 1.5 61

Fig.W - Case 4

PIT'CH t RUNOUT TES,TPAnNn: .,.13 D .'1.000 ,'S-0'0 R = !182

Prtch T' Accum ISi'iM .M Phch TIT' c m span ul'1'oult-qd QiJl ,"!~ ~ 8

L.JmftVllul .l! 5!I~

5.8 IS.O~~!!h!. ~ 8 ] U 1.J .1 .1.3 2.B 1.3 .0

IDulL 13 I"" 11 I~

-L. [!]M .. TNo,. I

:Ilol '.I0Il:

1!M1 -:1 !L_ a ~:;'naI

• J10 'I --'- J j I- 1 ,I,-~ -- ... GuslIly !levels to AGMA 390.00.

I oi , Values in Ten- Thousands of 10 inch. I,I- -r - - "

6MIO.1 N.:la

1 .-'Pl!<:h - I --

I8 M,n.T.~ •. 3 1 I; ~. I, .' j -:.= --F'-I- I- I-Ll 1 - I-, . 1 -

I10 ! ~ 1 L_ --'f-- . T - rm M.~ TN e.

t"I0- .- ! ..1 1 _I • -

13M .. T N.'9 I -- r~ . ] .. 1- 1:-: - .:-->

ID J , - y*-~ :.::: ,~- 1- _ •

1 - --- ~ .:::f~l==': h I-=--J , c __.r: :I-~- ~==~-=r~ .- -

t I I --~ ,. .=EM.. ~~2' --;-:- --=-= r= - ,-..:-~ .--= !. .-~ I':;~F- ~-lAc,,,,,, "l ~ J e-= ~ t 1-8"'" T !io.:'11 .~

, I 1. . i ,.1=

..:lL - ---=- t10 J .....,..I~ -

-' ~'1 I -

I I I 1- - .,-~I -,- -i--I-S-Lr=r.:: _ .:t- =. -:"1 -1-:[!lMtLTNo.:' I _ - ~-=: 'J _ _. -:

[!l Mox.T.No·' -=: !:~;:~~r.:::::r..=:"= ..::"E::I;:"'"~' -RunQilt :;:;1:'-:;t..:- •. - _. • - I: .' 1.--

·1 1 - .. ;::.. - .-=:- --- I- I~-::;- rr 1--::1 - - -:- .~ 7.:.: - .L-" 1::-...L.

10 'j i- ~.==::- 1-' ..-- - -:.... j..::.....:...: '1"- ' .-I-- .t-=- ~ 1=-'

El Min. T loIo.:T t ,.:;'::I'=-_. ..

Fig.12- Case 5

(..64 mm.) feed, 1 7/8 hob diameter, 281hr.Case History 4. Lift truck motor armature

(Figs. 10-1 I). Thirteen teeth, 14 DP, 20°PA, 18.83° helical, .97 (24.6 mm.) facewidth, 86L20 material, induction hardenedgear 58 - 63 Re.

A. Rough hob 1" diameter hob, 800 rpm,.040 feed, 6711u. Normal tooth thickness,.1406/.1387.

B.. Finish hob 350 rpm, .025 (.64 mm.) feed,crowned, .0002/.001" (.005 - .025 mm.) 24/hr.

Case History 5. Lift truck armature shaft(Figs. 12-13). Thirteen teeth, 14 DP, 20oPA,14.7SoheIi.x. face 1.3" (33 mm.), crown-bobbed to AOMA 8..

A. Rough hob 600 rpm .. OS5" (1.4 mm.)feed, ]-7/8" (47.6 mm.) diameter hob TiCn,45/hr.

B. Finish hob 325 rpm,.025" (.64 mm.)feed, I-7/8" (47.6 mm.) diameter cutter TiellI7/23/64. Normal tooth thickness •. [233/.1208(3.Imm.).

C. 14T, 16/32DP, 300PA spline, 2.12" (53.8mm.) face-finish splined, 22/48 Rc core hard-ness with carbide TiCN 1-7/8" (47.6 mm.)diameter hob. 341hr.

For variation. Fig. 14 depicts a cast toothform pump gear re-hobbed in alloy C

+;000-;001

Involute FormNumber QfTeeth 11Pite h Oiarneter 1.375Pressure Angle 28"Circular Tooth Thickness .2104Root Diameter 1.Z3ll ApprOM.Center Distance With Similar Mate 1.5008 acklash Per Pair .003Dimensions Over Two .375 Oia. P.ins2.153

Fig.l4

PITCH ... IRUNOUT TESTPori No: S.,· B Rem.:!

>15

!~13 Dp= 14.000 H. = 15"0'0' RPitch TH. • 'Accum.. Span. ~ Pilch TH, • Ace""', Span, Runou!

~eqd.au.al ~ 8 I ~ 8I ,m~V.I", I.: 5,8 I 10 5.8!"OLV.I." 'ii 6 ,7 1,6 .5 I~ 4~.L!lu.!' ~'14 115

lS.0.7.1 .7

U~.

~ccum. '-,

~I10 't

~--u:;~_ __:1::: -

--r--- ... +- ..4- -

I!I Max. T. No.: 1 _=t==-- f-.

Runoul

Fig. 13 - Case 5

TabID I

Rockwell DeflectionISO Hardness Resistence W Co Ti fa C

I

I 60 5 5 0 '6P20 901 90 83 10 15 15 9

I

70 4I

3 0 6M10 91.5 100 86 9 11 11 8

89.5 120 75 '5 0 0 5M15 I 93 220

I95

I 9 10 12 7 I

89 150 85 3I

a a :5K05 93 230 9'7 8 3 7 7

, SA 4

I

0 0 , :5KmI

90.5, 120 90 7 1 2 I 6

Table ill

Feed Module IOPt Flaugh mm (in) Finish mm (in)

! III II

>12 3-4mm/rev 2-3mm/rev(<2J II 1.120- .160"/rev) [.080 - .120"/rev)

> 12 I 2.- 3.5mm/rev 11.5- 2.5mm/rev[<2J i (.008 - .140"/rev) (.060 - .1OO"rev}

!

'MAY/JUNE, 1994 :2,1

ADVERTISERS INDEXI

Reader Service No. Page No.

I AfW SystemsI

7 23I

ASM International 37 47

American Pfauter, L.P. 1 !FC

I American Metal Treating Co. 34 48I,I

I Bourn & Koch Machine Tool Co. 10 11I

I

Contour Hardening 16 47

I Detroit Broach Co. 17 47I

I

Diagrind Inc. 8 39

Diamond Black Technologies, Inc. 26 46

Eltech, Inc. 32 48

Fair/ane Gear, Inc. 11 12I

Forest City Gear 18 6

GM1-FHUSA 36 5

I High Noon 4 4

INfEX Information Export 8

I M & M Precision Systems 3 2I

I Mstrscope Corp. 14 47I

I

National Broach & Machine Co. 30 BC

! Normae, Inc. 12 42!

Parker Industries 9 II

Pfauter-Maag Cutting Tools L.P. 2 I

Prentice-Hal!

I

47I

IProfile Engineering, inc. 33 48

I Pro-Gear Co., Inc. 31 48I

I Starcut Sales, inc.I 5 4

Sunnen Products Co. 19 47

United Tool Supply 35 42

Winter & Son, Ine., Ernst 13 47

22 GEAR TECHNOLOGY

Table IIII

Hardness HeRI

Speed mm/min (in/min)

50-55 70+90(220-2901

'55-60 160 + 70! (190- 220) I

I60-65 50 + 60

I(160-190)I

Table IVSpeed' mm/min (in/min)

I

Module DP

1 +5 60 + 90(5-25) (190 - 290)

6+ 12 50 + 70(2-4) (160 - 220)

I

> 12 30 + 50«2) 96 -160)

Hastalloy. This presented a problem for theelectromagnetic sensor, since this material isnon-magnetic.

Tables I-IV (Ref. 2) define typical carbidegrades, liberal feed rates for roughing and fin-ishing and suggested speeds versus hardnessand speed versus module. We tend to be moreconservative with our speed and feeds to savehob wear and improve quality ..

In conclusion, carbide rehobbing is anextremely economical approach to removingdistortion caused by heat treatment. Besidesapproaching gear ground quality levels and fin-ishes, carbide rehobbing can be used withsmall hobs capable of approaching blend-cutshoulders, which larger grinding wheels,including double belicals, cannot reach.Hardware cost is fractional, since the samemachine can be used for roughing and finish-ing and mass production is readily obtainablewith automatic loading. This process isaviable alternative to gear grinding. I.References:1. Glatzeder, Hans. "Skive Hobbing HardenedGears," Liebherr Versahntechnik ,GMBH.2. McElroy, William E. "Using Hobs forSkiving: A Pre-Finish and Finishing Solution."Gear Technology, May/June, 1993.

Acknowledgement: This article was first pre-sented at the AGMA Gear ManufacturingSymposium in Detroit, MI, Oct. 10-15,1993.