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WORM-GEARS AND WORM-GEAREDAXLES1

By C H. Calkins1

ABSTRACT

After a brief historical review of the developmentof worm-gears, the author deals with worms andworm-wheels in detail, presenting the subjects of proper choice of materials, tooth-shapes, worm-gear efficiency, the stresses imposed on worm-gearing andworm-gear axles. Usually, he says, the worm is madeof case-hardened steel of S.A.E. No. 1020 grade; however,

when the worm-diameteris smaller and the stressesare greater, nickel-steels such as S.A.E. Nos. 2315and 2S20 gradee are utilized. The worm should beproperly heat-treated and carbonized to producea glass-hard

surface. Grinding of

the worm-threadis

necessaryto remove distortions. Bronze is the only materialof which the author knows that will enable the

worm-wheel to withstand the high stresses im posed by motor-vehicle axles, and three typical bronze alloysare in common use. The degree of hardnessof the bronzeis very important Duralumin,

forged and heat-treated and uaed for worm-gears,costs approximately the same as bronze andreduces the weight two-thirds; such worm-wheels havewithstood severe service. As

to tooth-shape, the common pressure-angleis 30 deg.This angle produces an included axial-angleof 60deg. and a normal included-angleof 40 or 50 deg., dependingupon the lead, and also secures proper re versibility.A properly made worm-gear is as effi cientas any other form of gearing, according to the author,and he mentions efficienciesof from 97 to 99 per cent attained by hour-glass-shaped worms under idealloads and conditions. Tooth-pressures and rub bingvelocities are the two important considerations affectingstresses on worm-gears; the relative stresses varywith the lead angle. In conclusion,it is stated thatif a worm-gear axle is unsuccessful, this is due to imperfectionsof design and of manufacture and not becausethe principle of the worm-gear drive is not practicable.1Indiana

Section paper.

Downloaded from SAE International by University of Michigan, Wednesday, October 29, 2014

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450 THE SOCIETY OF AUTOMOTIVE ENGINEERS

Worm-gears began to be used in England about 1908 by Lanchester for motor-cars and by Dennis for commercial motor-vehicles, and worm-gearing was introduced into this Country from England about 1911.Three companies in the United States began the manufacture of modern worm-gears almost simultaneously,

and machinery was imported from England to aid intheir development. Previously, no worm-gears in thisCountry were markedly efficient so far as I know, or could be called uptodate.

Regarding material and tooth shapes, the old-timeworm-gear as used in machinery previous to 1910 hadan efficiency not better than 60 per cent. In fact, someworm-gears at present used in machinery are very muchout of date. It should be realized that more advance in

the theory and practice regarding worm-gears has beenmade since 1911 than perhaps in the previous 50 years.

Until recently, worm-gears with leads from 3 to 6 in.,such as are now common on motor-truck axles, wererarely used. The grinding of the tooth of the worm wanunheard of and little was known of correct tooth-shapes

and angles and their relation to efficiency and reversi bility. Still less was known of the relation of varioussteels and bronzes to efficiency and durability. Even at present, few brass-foundries are able to produce a gear bronze which is properly cast and chilled to enable it tomeet the high requirements of the modern worm-wheel.At each foundry it is thought easy to meet the requirements, but experience has taught me that only in foundries specializing in this work and in which lengthyexperience has been acquired are the manufacturers ableto produce desirable results. I have in mind not morethan three foundries that can be depended upon to make

bronze which is properly chilled and has the proper wear ing qualities to make a worm-wheel suitable for an auto

mobile, although many foundrymen will disagree withthis statement.

In one instance, we were testing a much advertisedand highly recommended grade of bronze in our testingmachine. The speed and the load were adequately controlled. This gear had been running for a number of days on light or normal loads, but when we suddenlydoubled the load and the speed, the gear was ruined in30 min. This added speed and load was not in excess of what the gear might be subjected to occasionally in amotor-truck, but the bronze was not equal to the emer


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WORM-GEAREDAXLES 451

gency and we used no more of that grade. There is adearth of reliable literature on the modern worm-gear.Its development has been so rapid that the treatises onit are not uptodate and the worm-gear is etili the victim

of widespread fallacious reasoning that influences many people.Referring to the worm-gear axle, worm-gears of the

hour-glass type were used in an automobile axle in 1912 by the Atlas Knight Co., Springfield, Mass. These gearswere not satisfactory but, later, they were changed tothe straight type and these were fairly good. I believethe first worm-gear passenger-car axle to be made in thisCountry was assembled at Springfield, Mass., in 1912.The gears were made by the Brown & Sharpe Mfg. Co.In 1913 the Atlas Knight Co. was consolidated with theIndianapolis Engine Works, and for some time a wormdriven car was built in Indianapolis. The Jeffrey Co.,Kenosha, Wis., used in its automobiles in 1913 about 50sets of straight-type worm-gears which, according to re

ports, were very satisfactory, but they were not adoptedas regular equipment because it was feared that the public was not ready for this change, rather than because thegearing did not perform satisfactorily. All these gear'swere mounted underneath the axle. In 1909 and 1910

the H. H. Franklin Mfg. Co., Syracuse, N. Y., producedtrucks driven by worm-gears.

Choice of Materials

The worm of a worm-gear should be made of casehardened steel. S.A.E. No. 1020 steel commonly is usedfor ordinary work but, when the diameter is small andthe stresses great, nickel-steels, especially S.A.E. Nos.2315 and 2320, are resorted to. It is somewhat questionable, in many instances, whether the nickel-steels produce superior results. The worm, as it is designed for

passenger-car ratios, usually is large enough to withstand the necessary strains and the No. 1020 steel ialess costly, machines more easily, distorts less andstraightens better than the nickel-steels. In any eventthe worm should be heat-treated and carbonized properlyto secure a glass-hard surface and, the harder the sur face is, the better it is.

However, some portions of the worm, such as thethreads on the ends, should be soft. In worms of com

plicated design, the hard and the soft spots very oftenalternate throughout its length, requiring skill and in


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genuity to produce such a condition. Worms distortduring the heat-treating process and the grinding of thethreads is necessary to restore them to true form. Obviously, it is desirable to remove as little as possible of the precious "case" on the outside of the threads. For this reason it is customary, when it is found that the

threads of a particular worm unwrap or that the leadelongates in hardening, to mill or to hob this threadwith a shorter lead so that the heat-treatment will make

the threads approximately correct, thus requiring theremoval of only the minimum amount of stock by grinding. The teeth or "starts" of a worm are cut either bymilling or by hobbing. Hobbing is more economical for large production enterprises.

Suitable Bronze for Worm-Wheels

Selection of suitable worm-wheel bronze is very im portant. Bronze is the only material of which I knowthat will withstand the high stresses imposed by automobile axles, although cast iron is all right and makes afine cheap gear where the speeds are low and the stresses

are light.Three bronze alloys are in common use for automo

bile worm-gears in this Country. The first is 88.50 per cent copper, 11.00 per cent tin, 0.25 per cent lead, and0.25 per cent phosphorus. This is the familiar S.A.E.

No. 65 phosphor gear-bronze. In its chilled condition, ithas an ultimate tensile-strength of 33,000 to 40,000 lb.

per sq. in., an elongation of 4 to 8 per cent and a Brinellhardness of 75 to 90. This is perhaps the most commonly used bronze alloy for worm-gearing.

The second is an aluminum-bronze composed of 89 per cent copper, 10 per cent aluminum, and 1 per cent iron.In its heat-treated state, it has an ultimate tensilestrength of from 80,000 to 93,000 lb. per sq. in., anelongation of 4 to 10 per cent and a Brinell hardness of 170 to 200 under a 3000-kg. (6614-lb.) load. This bronzeis not chilled. It has been used extensively by one

builder of worm-geared trucks and is an exceedinglystrong bronze, but I understand that the wearing .qualities are not so good as those of the S.A. E. No. 65 phos

phor gear-bronze.A third alloy is coming into use rapidly which con

tains 88.50 per cent copper, 10.00 per cent tin, 1.00 per cent nickel, 0.25 per cent lead and 0.25 per cent phos

phorus. This has an ultimate tensile-strength of better


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than 40,000 lb. per sq. in., an elongation of around 4 per cent when cast in a three-sided chill and a Brinell hardness of 90 to 110.

Bronzes are susceptible to and can be greatly im proved by heat-treatment. They can also be cast centrifugally under varying pressures which result in considerable improvement. The teeth can be cast in placeso as to require but a small amount of finishing andthis, for large production, is extremely desirable because it saves not only metal and labor but makes thegear structure considerably better, since the chillinggets into the teeth and the wearing-surface instead of

being largely hobbed away, as is true of the ordinarysurface-chill.

In industrial work, when a worm-wheel has a hub anda web, the center portion can be made of cast iron, have

projections cast on the outside and the bronze castdirectly on the cast iron, which is first heated and then

placed in the sand. If properly done, this is a very

successful and economical method. The depth and intensity of the chilling can be varied by changing thesection of the chill.

The hardness of bronze is a very important feature.To secure the best results, a certain relative hardnessshould exist between the steel and the bronze tooth, sothat the surface of the bronze tooth will burnish down

and increase its Brinell hardness at the point of contact and highest pressure. Gear-bronze should, if over loaded, peen-out at the edges of the teeth and should notfail by granular disintegration.

Duralumin Worm-wheels

Duralumin has been forged and heat-treated and made

into worm-gears that have stood-up in a very satisfactory manner under some very hard tests, such as theservice in the Fifth Avenue motorcoaches in New York

City. The cost of duralumin worm-gears is approximately the same as that of bronze worm-gears and thesaving in weight is about two-thirds. The tensilestrength is around 55,000 lb. per sq. in., minimum. Inthe center of an axle, weight-saving is of great impor tance.

Worms and wheels are often finished by lapping themtogether or mating them with suitable masters. Thisgives and extremely fine finish that looks very well and


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perhaps improves the efficiency somewhat; however, itis not done, ordinarily. The contact between the wormand the wheel is important. It should be in the center of the wheel-tooth and should, at the beginning of itsservice, have an oval form. Changing the diameter of either the worm or the wheel will change the contact

angle and will shift the point of contact. In fact, onexact work, the last few thousandths of an inch of wormor of worm-wheel diameter are often determined byexperiment, the guide being the contact as it shows upon the testing-machine. The amount of backlash is alsoimportant and should be as small as possible, bearing inmind, however, that all worm-gears generate heat inoperation and that space must be provided for a heavylubricant. On worm-gears of passenger-car sizes, a

backlash of from 0.005 to 0.010 in., measured on thecenter dimension between the worm and the wheel, iscustomary.

Worm-Gear Tooth-Shapes

The common pressure-angle for worm-gear teeth is 30

deg., which provides an included axial-angle of 60 deg.and a normal included-angle, depending upon the lead,of around 40 to 50 deg. This angle, produces a verystrong tooth, is open enough so that a substantial wheelcan be used for grinding the worm-threads and gives proper reversibility for ordinary automobile-ratios, asreversibility is dependent not only upon the lead-angle

but upon the included angle of the tooth as well. Theoretically, the included angle of the tooth should varywith the lead so as to secure perfect reversibility; in

practice, however, with modern materials and finishes,a 60-deg. axial included-angle answers all practical requirements.

Efficiency of Worm-Gearing

Modern worm-gears are very efficient, but it is rather futile to give exact figures because they must always

be qualified by the conditions under which the tests aremade. Tests made with hour-glass worms and wormgears under ideal loads and conditions have shown anefficiency as high as 98 or 99 per cent. I am speakingnow simply of friction between the worm-teeth and donot include bearing losses or losses due to oil-splash andthe like. Other tests show a 97-per cent efficiency. Ingeneral, it can be said that a properly made worm-gear


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is as efficient as any other form of gearing. One factor entering into this efficiency is the gradual contact of theteeth which allows them to be separated by a film of oilat much greater pressures than is the case under other conditions.

An erroneous idea is that the reverse efficiency of aworm-gear is much less than the forward efficiency, but,in fact, the reverse efficiency is almost equal to the for ward efficiency and is much less than 1 per cent lessefficient.

Hour-Glass Type of Worm

The hour-glass type of worm has all the worm-teethin full contact with the wheel simultaneously, which isnot true of the straight type of worm; therefore, thetooth-pressure per square inch is less and, consequently,the distance between centers can be reduced. The toothshapes allow very good lubricating conditions. It iscommonly supposed that this type of worm cannot beground, but it can be ground commercially with a hard

emery-wheel. However, one disadvantage is that it must be mounted accurately and permanently in a fore-and-aft position and it is somewhat more expensive to make because not only the wheel but the worm as well must bemade with a hob, the worm-hob being of the same diameter as the worm-wheel.

Stresses on Worm-Gears

Worm-gear stresses can be calculated easily. Thestresses vary with the lead-angle of the worm; that is,the values of the various stresses are influenced by thelead-angle. In designing worm-gears, tooth-pressuresand rubbing velocities must be taken into consideration.I will not quote any specific allowable tooth-pressures, asthey vary according to the method of calculation and

with the amount of tooth-area which may be assumedto be in contact.

Worm-Gear Axles

The worm-gear axle is normally and inherently quietwithout requiring expensive adjustment or expensivelyaccurate machine-work. This, I believe, is not true of spiral-bevel gears. After interviewing most of the axlemanufacturers and automobile builders I find that,almost without exception, they report noise trouble intheir spiral-bevel-geared axles or, if they have overcomethis to a greater or lesser extent, they do it by expen


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456 THE SOCIETY OF AUTOMOTI VE ENGI NEERS

s i vel y accur a t e mach i ne - wo r k on t he ax l e and by r ead

j u s t ment af t e r t he c a r s

are on

t he r oad.

I n any of i ts

f o r ms t he

spi ra l - bevel gear h a s

one

d i s advant age ove r

t he wo r m- gea r i n t hat t he r i ng g ea r i s of heat - t r eat ed

steel . The

hea t - t r eat ment di s t o r t s

the

gear

and i t i s

i mp r act i cab l e commer c i a l l y to g r i nd a s pi r a l - bevel gea r

t o b r i n g t he t e et h t o t h ei r c o r r ec t s h ape agai n . R unn i n g

t h e m i n or l app i ng t hem cor r ect s t hem b u t i mpe r f e c t l y .

T hi s i s n ot t r ue of t he b r onze wo r m- gea r because i t r e

cei ves

no

he at - t r e a t ment af t e r c ut t i ng

and

consequent l y

neve r l os es i t s pe r f ec t s hape .

T he we i g ht of

a

bevel - gear axl e shoul d no t

be

di f f er ent

f r om t hat of a wo r m- gea r axl e of equi val ent des i gn. The

eng i ne- t o r que

i s t he

s ame

i n

each

case ;

t he r e f o r e

t he

t ot al be ar i n g- p r e s s ur e s

ar e t he

s ame

and

r e qui r e

a

s i m l ar t ot al f o r equ i val ent bea r i ngs . The b r onze cas t

i ngs cos t mo r e t han st eel

and

t he r ef o r e

t he

i ni t i al

ex-

pense i s per haps s omewhat mor e but t hi s i s mo r e t han

of fset

by the

el i m nat i on

of any

a dj u s t men t af t e r

t he

i ni t i a l a s s emb l y .

H Y P O I D - G E A RS

Th e hypo i d - gea r

i s

s i m l ar

to a

spi ra l - beve l gear

ex-

cept t hat t he pi ni on i s d r opped be l ow t he cent er . I t i s

i nt e r es t i ng

to

note t hat

t he

pi ni o n wh i c h

i s

n o r ma l l y

dr opped about i n . c an be d ropped or 3 i n. or mo r e ;

i n f a c t i t c an

be

d ropped s o t hat i t r uns d i r ec t l y under

nea t h t he c en t e r l i ne of t he

axl e .

Such gear s have been

made

a n d

t e st ed- out i n t hat manne r .

To go

even f a r t her

a r i ng- gea r

can be

i ns t al l ed

on

each s i de

of

t he bevel -

p i ni on t hus absol ut e l y bal anc i ng al l p r es su r es due to

s i de- t hr u st .

F U T U R E D E V E L O P ME N T

OF

WO R M- G E A R I N G

Wor m- gea r ax l es have passed the exper i ment a l s tage.

I f

any

des i gn

of

wo r m- gear axl e

is

unsuccessful

i t i s

because

of

i mper f e c t d es i g n

or

cons t r uc t i on

and

n o t b e

cause

t he

pr i nc i p l e

of

wo r m- d r i v e

i s

no t

pract i cabl e .

I

r emember t hat

i n

1896 t he f i r st aut omobi l e s u sed

bal l

bea r i n gs

and

wi r e whee l s . Ho weve r

t he

ba l l - bear i ngs

and t he wi r e wheel s gave out v e r y qui c kl y and i t was

as sumed t hat t hey we r e i mpr ac t i cabl e

f or

au t omobi l e

us e ; s o a c hange wa s ma d e t o pl ai n b ear i n gs a nd wood en

wheel s .

Lat e r howeve r whe n des i gne r s l ear ned how to

des i gn ba l l - bear i ngs

and

wi r e whee l s p r ope r l y t hese de

v i ces bec ame ent i r e l y p r ac t i cabl e. The poi n t I mak e i s

that

the

pr i nc i pl e s i nvol ved

i n t he use of

bal l - bear i ngs


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and of wire wheels were not incorrect. The trouble wasthat not enough was known about the design or aboutthe materials needed for their construction.

THE DISCUSSION

C. S. Crawford3:-Our company made exhaustive tests before it decided to use worm-gearing. We were inter ested first in a construction which would lower the center

of gravity materially. When we adopted the worm-gear drive, we burned all our bridges behind us. It would be

physically impossible for us today to change to the conventional bevel-gear type of drive without completelyremodeling our car. When a company takes a step of that kind it must be convinced that more merit exists inthe worm-gear than the public is led to believe. On atrip in the West, we coasted for 17 miles on grades thatvaried from 4 and 5 per cent to 15 per cent. Makingcomparisons with cars of well-known makes, we saw nodifference in the coasting qualities of the different typesof car; that is, in those equipped with the conventional

bevel-gears over our car equipped with the worm-gear.In addition, there seemed to be no difference of temperature between the worm-gear housing and the bevel-gear housing after those long coasts, which would naturallylead one to believe that the tooth-pressures were not anygreater in the worm-gear than in the bevel-gear.

G. H. Acker:-At the start of the present experimentwith worm-gearing, the greatest difficulty seemed to bethe maintenance of an oil-seal. A worm mounted below

the gear must run in oil, and the point of egress pf theworm-shaft from the housing is below the oil-level; so.some difficulty was expected in maintaining an oil-seal

at this point. Discussion on the various ways and meansof overcoming this difficulty would be interesting.English practice on this point indicates several solutions. One is to provide on the worm a shallow Acmethread in such a way as to cause it to return the oil tothe housing. It has been argued that the reversal ser vice has been of such slight duration that this point isnot important. However, it is customary to seal the oilat thio point and various materials are used for thiswork.

3M.aA.E.-Chief engineer. Stutz Motor Car Co. of America, Inc.,Indianapolis.


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L. R. Buckendale4:-Various types of oil-seal have been used around the worm-shaft; one is a cup made of leather, but the type used most frequently is a typicalstuffing-box. As we see it, the application of wormgearing to the passenger-car presents no engineering

problem that has not been gone over thoroughly under

different conditions.W. G. Wall5:-The motor-car engineer has always

sought to eliminate vibration and noise, and the wormgear eliminates at least 95 per cent of the noise andvibration present in the spiral-bevel gear. Although thespiral-bevel gear can be made so that it is almost noiseless, the manufacturer has great trouble to produce thiscondition. Noise comes from vibration, but often avibration exists in a rear-axle from which one can hardlyhear any resulting noise. I have often noticed that in

bevel-gear rear-axles. The worm-gear not only does notseem to have this vibration, but it seems to have a tendency to soften and deaden any other vibration resultingfrom the drive-shaft or the transmission. I think thisis one of the best reasons for using the worm-gear drive.I understand that some gears made of duralumin are

being used. How does the friction of duralumin com pare with that of bronze?

C. H. Calkins:-It is an aluminum alloy. I know itworks very well against hardened steel.

T. W. H. Jeacock6:-Our foundry supplies gear-blankefor the automotive field. Mr. Acker said that tin bronze

cannot be die-cast. It does cast satisfactorily and commercially in permanent molds. Within the last 6 monthswe have made the worm-gear blank for the Stutz car ina metal mold. This is a phosphor-bronze containing 1 per cent of nickel and has the maximum physical proper ties of the bronze alloy together with the benefits derived from the chilling. Engine and chassis design have

developed and the load the axle is required to carry hasgrown from year to year, while the alloy out of which theworm-gear blank was made had not been improved. Untila new alloy was found we were limited as to what wecould do with the worm-wheel, the teeth of which failedunder the great unit pressure. We have now worked outa process of applying a chill to all of three sides of a

4M.S.A.E.-Sales and development engineer, Timken-Detroit AxleCo., Detroit.

5M.S.A.E.-Consulting engineer, Indianapolis.6President, Buffalo Bronze Die Cast Corporation, Buffalo.


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WORM- GEARED AXLES

459

worm gear bl ank. Thi s chi l l s t he bl ank i n i ts enti rety

and gi ves

an

i ncrease

of at

l east

20 per

cent

i n the

physi

cal properti es of the same al l oy. The combi nati on of the

ni ckel -bronze and the three-sided-chi l l process has made

it possi bl e f or t he wor m gear bl ank to meet the requi re

ment s of the great uni t pressure successful l y.

MR .

B UC KE NDA L E : - Wo r m- g e a r devel opment has had

t wo phases, t he devel opment of the tooth-contacts and

the devel opment of the materi al .

MR . ACKE R: - S up pl e me nt i n g Mr . J eacock' s st atement

as to the i mprovement i n the physi cal properti es of t he

bronze he

uses

after careful anal ysi s recentl y of t he

bronze used f or the three-si ded chi l l we f ound about a

20

to

30- per cent i ncrease

i n

tensi l e-strength

but a

much

hi gher i ncrease i n ducti l i ty, about 200 per cent.

MR .

CA L K I NS : - T h e

fact that dur al um n i s stronger

than most bronzes al l owed

us to use

smal l er secti ons.

At one t i me we secured t wo For d t ruck-axl es and f as

tened t hem together i n the center w th equal brakes on

f our wheel s and put t he standard Ford al um num br onze

i n

one and

dur al um n

i n the

other.

We

f ound that w th

the normal l oads the dur al um n stood- up as wel l as the

bronze. W t h mor e l oad, i t di d not stand up as wel l as

the bronze. I n my opi ni on it i s all ri ght f or a wor m

wheel provi ded the l oad i s not too great.

V. H.

S C H N E E

7

: - T h e

physi cal properti es of the

bronze have very l i ttle bear i ng on the probl emi f the

combi nati on of the gear and the wor m materi al i s not

such that

the

oi l -fil m

can be

mai ntai ned.

We

have found

that there are certai n combi nati ons of metal s whi ch

assist

i n the

mai ntenance

of the

oi l -fi l m Steel

on

steel

does not consti tute a very good beari ng. Manganese-

bronze i s a better materi al for physi cal properti es than

gear- bronze, but i t i s not as good as bronze f or mai n

tai ni ng an oi l -fil m

A

ME MBE R: - S h o ul d

the enti re dr i vi ng surf ace show

contact ? I f not, about what percentage of the face of

the tooth does show the contact after the gear i s prop

erl y seated? Has a chassi s dynamometer- test ever been

made of the dri vi ng mount back of the axl e? Have

spi ral -bevel and wor m t ype gears been substi tuted, one

for the other, and have the comparati ve effi ci enci es of

the

i nal - dr i ve

been noted i n that way?

MR . B UC K E NDA L E : - I

know of one effi ci ency test of

7

Assi stant general manager , Cl evel and Wor m Gear

Co.

Cl eve

l and.


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that nature in which the car was equipped with two interchangeable axles, one having spiral-bevel gearing andthe other, worm-gearing. Acceleration tests were made.The first run was made with spiral-bevel gearing; then,another run was made with worm-gearing, after whichthe worm was taken off and the spiral-bevel gearing was

used again.Mr. Crawford:-Mr. Buckendale probably refers toa series of tests made on the Speedway at Indianapolis. We used for the test the largest and heaviest passenger-car we had ever built. We used what was, according to our knowledge, the best made spiral-bevelgear drive, which had a gear-ratio of 5 to 1. The car was equipped so that quick changes of the axle could bemade. The worm-drive axle had a ratio of 5 to 1. Both

of the axles were new. By using a derrick, we changedcompletely from one axle equipment to the other every16 min.

We made acceleration tests from 5 to 25 m.p.h., from5 to 60 m.p.h., from 10 to 25 m.p.h., from 10 to 50 m.p.h.and from 10 to 60 m.p.h. During the first part of the

tests, it was almost impossible to tell the difference between the bevel-gear and the worm-gear performance,on either acceleration or deceleration. What little dif ference there was seemed to be slightly in favor of the

bevel-gearing. At about test No. 50 we had completedabout 500 miles of running. In the next 500 miles of running all the figures showed that the worm-gearingwas getting better and that the bevel-gearing was getting worse. We could account for that only after noticing at the end of the test that there was a certain amountof lost motion in the pinion-shaft bearings. In somesubsequent tests we readjusted those bearings, and itwas almost impossible to tell the difference between thetwo types of gearing.

The car in which these axles were used had the engineassembly mounted so that the crankshaft was parallelwith the ground; hence, the drive-shaft for the bevelgearing was almost a straight line, but the drive-shaftfor the worm-gearing was running at an angle almostto the capacity of the universal-joints. As a result of our many tests, we have concluded that, while for thefirst 2000 or 3000 miles the worm-gearing might nothave very much advantage over the bevel-gearing, after 15,000 to 20,000 miles the worm-gear drive has a greatadvantage over the bevel-gear drive.


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Mr. Buckendale:-In the use of the gasoline-electricdrive in Philadelphia we are now operating the wormgearing on the motorcoaches there at an 11 to 1 ratio;the worm turns at 5500 r.p.m. regularly, and we know of

no definite speed-limitation so far as the worm is concerned.

A Member:-What is the power of the motors whenrun at that speed?

Mr. Buckendale:-Possibly 100 hp.

Mr. Acker:-In regard to worm-gearing at highspeed, the company I represent manufactures a line of industrial speed-reducing units for connection to motors,conveyors, and the like. We make worm-gear units thatwill handle around 200 hp. A worm of that capacity isabout 8 in. in diameter. We have such drives in service

that we know have been running satisfactorily for periods of 5 or 6 years, some of them at turbine speeds.

R. R. Teetor8:-What is the best lubricant for lubri

cating worm-gears? Has a means of forcing the oil between the gear-teeth ever been provided; that is.giving the oil a flow rather than just allowing it to sur round the gears? Since the worm turns at high speed,the tendency is to throw the lubricant from the teeth.Could not some simple device be provided by which thelubricant could be fed into the contact surface betweenthe worm and the wheel?

Mr. Buckendale:-A lubricant is needed that is unaffected by chemical contact with gear material, but weare still looking for that ideal lubricant. I think littlehas been done with automatic force-feed lubrication,

except to see that the lubricant is supplied to the gear in a freely flowing stream.

8 M. S.A.E-Chief engineer. indiana Piston Ring Con., Hagerstown.Ind.


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