MreSiu has limited error-detectingcapabilitie For example it will tell youif the calculated mea urement everwire is larger than the out ide diameterof the gear

In addition the program give instruc-tion to enable the per on on the simpfloor to make a second cut if th inilialmea urernent over wires is bigger limnth computed value Simply enter lbectual measured valueOIId the program

will return the required depth of cut toachieve the correct me surement

VireSizti a DOS-ba d program f rlBMcompaiible PC available n eilh r35 or 525 diskette It co 125According to the Worrall Grinding CoInternet page found at hl1pllwwwsnowmiddotcrestrletlwgcl~middotoftwareJllJn the Windowversion should be available around thetime ef this printing

Geal SharewareIt eem everyone has Web page

the e day In fact mo t of the oihvarepackages in this ankle were found by

Gear Software YouDidnt Know About

invented a magic wand to lake awaysome of the drudgery

The computer revolution promi edcalculation at the touch of at button anddesign by menu For many ppiicationthat promise has been fulfilled Howeverif youve e er gone shopping forgeillsoftware youve probably found thatth -re iSII ( much to choose from

The gear market is so smalleha main-

sjream software developers have largelyignored it But gear software is out thereif you know where to look Most of it basbeen de igned by gear hopre earchinstitution independent con ultantsandIlni varsities for their own use We suspectthai many more hop have de ignedtheirown oftware but dont offer it for sale

What we found comes in a variety ofprice rangesand performs a variety offunctions Some packages use te~t-onlydl plays while others have very detailedgraphic and animation We make nojudgments about how u eful any of lill

oftware is We lea e thai [Q youFor the Shop Floor

Sometimes the simple tprograms cansave time and make employees more pro-ductive Caleularing a gear correct The ~Bphle dlsplay or lARI shows gearleelh In mesh

m esigningand manufacturinggear requires the skills of amathernatician the knowledge ofan engineer and the experience of

a precision machinist For good measureyou might even includethe art of a magi-cian because the formulas 000eI calcula-tion involved in gear manufacturing areo obscure and the prooesses 0 little

known thal only members of an elitecadre of profe ionals can perform them

While il may seem like magic to Ihre t of us 110 gear engineer can pull aninvolute out of hi haL 1be fact is that m t

of gear design and manufacturing illardwork attention to detail and trial and error

But wouldnt it be nice if omeone

William RStolt

measurement over wire with a calcula-Lor and involute charts isa tedious pro-ject that no one enjoys

Worra]] Grinding Company Ander-on CA Cleated a program called

WireSile (Version 10) to make the calcu-lation fast and simple

We wrote it out of necessity sayGeorge Worrall president Its reallyhandy Ito use in the shop If you doitona calculator it takesabout an hour and ahalf With this program you could havethe ecretary do it

WireSize uses the Zahor ki longmethod to calculate wire sizes for puror helical gears Ising informarion thatcan be taken directly from specificationson a drawing

For example after you enter the num-berofteeih diametral pitch pre sureangjeOIId amount of backlash the program willgive you values for involute check pitchdiameter and wire size as well as theoreti-cal measurement over wire OIIdmeasure-menl over wires with backl h

JANUARVFEBRUAR( au 29

-

WHERE TO GETTHE SOFTWARE

ATS SoftwareP08ox388Gouverneur NY 13642AIao available athttpJJwwwsharewarecom

COSMICUniversity of Georgia3B2 East Broad StreetAthans GA 30602-4272(708)542-3265Fax f708l542-4807E-mail serviceOcossackcollllicugaedu

ESDUInternationalpic11 Corsham StreetLondon Nl 6UAUnited Kingdom(44) 171-490 5151Fax (44) 171-4112701E-malt esduOesducom

GearSoft DesignPO Box 1362 Lane Cove8128 Huxtable AvenueLane Cove NSW mAUSTRAUAf811294111282Fax (8112 94111282

Hexagon Industriesoftware GmbHStittelstrlase 8Dmiddot73230 KirchheimTeckGermeny149)7021 59518Fax (49) 7021 59986httpiJwwwh8xagondeindexhtm

Mechanical a Structural Design aSoftware4275-29 Rose Or I1I1JPleasanton CA 94588(510) 134-6701Fax (S10) 443-3995http20518624511msds

UNIKAssociates4Oamp5A N Calhous RoadBrookfield WI 530051414) 781-3334Fax 1(141781-5335E-mail softwareunikcomhtlpJwwwunikcomunikenghtmI

WorraD Grinding1639 South StreetAnderson CA 96007(916) 365-4565Fax (916) 365-9560ht1pilwwwsnowcrestnetWgcIoftwIrehtm

30 GEAR TECHfOLOGV

GearCAD Includes modules for cutter designand measurement over rollers

doing research on the Internet Howeverwe were able to find only one piece ofgear shareware

GEARGEN from ATS SoftwareGouverneur NY was created as an aidfor designing and manufacturing elec-trodes to cut the molds for die-cast gearsIt has developed into software that can beu eful in designing the gears as well

The user call enter the number ofteeth diametral pitch and pressure angleto specify the gear he or she wantsPressing the Generate Gear buttoncauses the program to mathematicallyhob the gear form using the valuesentered The program will return valuesbased on ANSI B61-1968 and otherstandards for pitch diameter outsidediameter root diameter fillet radius andnormal circular tooth thickness

After the gear form is generated theuser can plot it on a printer or view it onscreen to see the effects of changing theroot radius pressure angle or addendum Inaddition the form can be saved to disk inXY format or DXF format which can beread by most CAD programs Also avail-able is a G-Code format which can be usedas toolpath instructions for a machine tool

GEARGEN can also calculate themeasurement over wires and wire sizesto be used for a given gear

After calculating a gear form the usercan generate a second form which cor-responds to a mold cavity to be used to

create the gear This step includes anoption that allows the user to compensatefor shrinkage From the meld cavity youcan generaze a cut plot which can beused to create the EDM electrode thaiwit] cut the cavity of the mold

GEARGEN assumes a working know-ledge of gear forms and machining oper-ations In many cases the user is requiredto perform calculations and enter appro-priate values For example the programoffers pressure angles of 145 20 and 25degrees from the menu While you canenter other values for the pressure angleyou have to calculate the responses your-self However from there you can stillhave the program calculate wire sizesand mold and electrode forms

GEARGEN is shareware whichmeans you can download the program inits entirety from the Internet We fount itat httpllwwwshareware com If you trythe program and like it a licensed versionis available from ATS Software for $79

Engineering AidsWhile software can certainly help

gear manufacturers by performing rou-tine calculations 011 the shop floor it Canalso save umeand improve accuracy byhelping the gear engineer perform someof the more complex calculationinvolved in design

The Engineering Toolbox from UNlKAssociates Brookfield wm is an electron-ic library of 101 programs for engineers

The gear-related calculation modulesincluded in the package are for helicalbevel and worm gear forces involutespur gears gear outside diameter three-gear drives and worm lead

For the helical gear force program theuser enters the input torque pitch radiushelix angle and pressure angle The pro-gram gives tangential force radial forceand force parallel to the axis The resultscan be printed

In addition users call view helpscreens that show the formulas used aswell as sample input and output

Also in the package are many genericengineering modules including frustrumof a cone fluid pressure on a piston tor-sional stress on a shaft and Ohms Law

Engineering Toolbox costs $295 Youcan download a free demonstration ver-sion at lutplwwwunikcomiunikenght1lli

-

WHERE TO GETTHE SOFTWARE

ATS SoftwareP08ox388Gouverneur NY 13642AIao available athttpJJwwwsharewarecom

COSMICUniversity of Georgia3B2 East Broad StreetAthans GA 30602-4272(708)542-3265Fax f708l542-4807E-mail serviceOcossackcollllicugaedu

ESDUInternationalpic11 Corsham StreetLondon Nl 6UAUnited Kingdom(44) 171-490 5151Fax (44) 171-4112701E-malt esduOesducom

GearSoft DesignPO Box 1362 Lane Cove8128 Huxtable AvenueLane Cove NSW mAUSTRAUAf811294111282Fax (8112 94111282

Hexagon Industriesoftware GmbHStittelstrlase 8Dmiddot73230 KirchheimTeckGermeny149)7021 59518Fax (49) 7021 59986httpiJwwwh8xagondeindexhtm

Mechanical a Structural Design aSoftware4275-29 Rose Or I1I1JPleasanton CA 94588(510) 134-6701Fax (S10) 443-3995http20518624511msds

UNIKAssociates4Oamp5A N Calhous RoadBrookfield WI 530051414) 781-3334Fax 1(141781-5335E-mail softwareunikcomhtlpJwwwunikcomunikenghtmI

WorraD Grinding1639 South StreetAnderson CA 96007(916) 365-4565Fax (916) 365-9560ht1pilwwwsnowcrestnetWgcIoftwIrehtm

30 GEAR TECHfOLOGV

GearCAD Includes modules for cutter designand measurement over rollers

doing research on the Internet Howeverwe were able to find only one piece ofgear shareware

GEARGEN from ATS SoftwareGouverneur NY was created as an aidfor designing and manufacturing elec-trodes to cut the molds for die-cast gearsIt has developed into software that can beu eful in designing the gears as well

The user call enter the number ofteeth diametral pitch and pressure angleto specify the gear he or she wantsPressing the Generate Gear buttoncauses the program to mathematicallyhob the gear form using the valuesentered The program will return valuesbased on ANSI B61-1968 and otherstandards for pitch diameter outsidediameter root diameter fillet radius andnormal circular tooth thickness

After the gear form is generated theuser can plot it on a printer or view it onscreen to see the effects of changing theroot radius pressure angle or addendum Inaddition the form can be saved to disk inXY format or DXF format which can beread by most CAD programs Also avail-able is a G-Code format which can be usedas toolpath instructions for a machine tool

GEARGEN can also calculate themeasurement over wires and wire sizesto be used for a given gear

After calculating a gear form the usercan generate a second form which cor-responds to a mold cavity to be used to

create the gear This step includes anoption that allows the user to compensatefor shrinkage From the meld cavity youcan generaze a cut plot which can beused to create the EDM electrode thaiwit] cut the cavity of the mold

GEARGEN assumes a working know-ledge of gear forms and machining oper-ations In many cases the user is requiredto perform calculations and enter appro-priate values For example the programoffers pressure angles of 145 20 and 25degrees from the menu While you canenter other values for the pressure angleyou have to calculate the responses your-self However from there you can stillhave the program calculate wire sizesand mold and electrode forms

GEARGEN is shareware whichmeans you can download the program inits entirety from the Internet We fount itat httpllwwwshareware com If you trythe program and like it a licensed versionis available from ATS Software for $79

Engineering AidsWhile software can certainly help

gear manufacturers by performing rou-tine calculations 011 the shop floor it Canalso save umeand improve accuracy byhelping the gear engineer perform someof the more complex calculationinvolved in design

The Engineering Toolbox from UNlKAssociates Brookfield wm is an electron-ic library of 101 programs for engineers

The gear-related calculation modulesincluded in the package are for helicalbevel and worm gear forces involutespur gears gear outside diameter three-gear drives and worm lead

For the helical gear force program theuser enters the input torque pitch radiushelix angle and pressure angle The pro-gram gives tangential force radial forceand force parallel to the axis The resultscan be printed

In addition users call view helpscreens that show the formulas used aswell as sample input and output

Also in the package are many genericengineering modules including frustrumof a cone fluid pressure on a piston tor-sional stress on a shaft and Ohms Law

Engineering Toolbox costs $295 Youcan download a free demonstration ver-sion at lutplwwwunikcomiunikenght1lli

Beyond CalculotionAt some point a gear engineer needs

more IibWII a program that plugs valuesinto formulas and spits out results He orshe needs something that win belp designstronger quieter or longer lasting gears

One source of such gear design soft-ware is ESDU International plc inLonden The companys Data Itetasare comprehensive handbooks on a vari-ety of engineering disciplines which arecompiled from the latest standards andfield data Most of the data items are preseraed as printed handbooks but manyare supplemented by computer programsThe data items are available onan annu-al subscription basis

Part of the companys sub-series ontribology Dimensions Deflections andStresses for Hertzian Contacts underCombined Norma] WIld TangentialLoading is the title of one computerizedData Item that would be of interest togear engineers The program locate crit-ical stress points on rolling bearingscams and gears for failure prediction

The cost of the data item is $875 pervolume per year with a minimum orderof $2625 which is the equivalent of threevolumes for one year or one volume forthree years

ESDU also offers third-party softwarefor the design of spur and helical gearsaccording to AGMA lSOIDIN Of Britishstandards These program are sold out-right for pound950 each

Mechanical amp Structural Design ampSoftwarellas about a dozen gear andspline design programs that will providecomplete manufacturi~g and inspectiondata stress analy is and life ratings

Thecompany started writing gear soft-ware about 25 years ago says LaszloKeves director of engineering Originallyprogrammed in FORTRAN all programsare now written in BASIC and can be runon ffiM-compatiblecomputers

Gear-related programs include pack-ages for Spill helicaJbaightbevel spiralbevel and hypoid gears In additionMSDS offers programs for simpleepicyclic spur and helical gear trainsinvolute splines ronerbeari~gs threadedfasteners and helical compression springs

The programs have very limitedgraphics capabilities buraie company

plans to put more graphics into its soft-ware Keves ays

MSDS software costs between $500and $]()OO per module depending on theexact modules the customer requires

Space Age GearsFor almost 30 years the USgovem-

ment has released computer software tothe public through COSM[C NASAsSoftware Technology Trans-fer Centerlocated at the Univen ity of Georgia

Software developed for use in thespace program and software written atthe NASA-run armed forces researchcenters around the country Ilave beenreleased over the years In the pasl fiveyears or so some gear-related softwarehas become available

TUFE - Spur Helical and SpiralBevel Transmission Life alld ReliabilityModelestimares life dynamic capacityand reliability of aircraft tnmsmi sions

High EHiciencyOil Mist CollectorCleans oil mist and fumes

from your faciility

GARDNER ENVIRONMENTAL PRODUCT

1201 WLAKE STREET- HORICON WI

Gardner EnvironmentallProducts has designed ahigh efficiency oil rnlstcollector that will captureoil mist at the sourceThe GA BOO is Iightweight and easily adaptsto most equipmentThe GA 800middot is ideal foruse in machine centerswet and dry grindingapplications

bull High Velocity Intake

3Year limited Warranty

bull Low Maintenance

-aoo CFM

bull Static Pressure Gauge

CIRCLE 141 or call11middot8I1o34()1160 X9141

OTHER GEARSOFTWARE AVAILABLEFor a full discussion of software not men-tioned in this article see -How Many MiceDoes it Take ToDesign a Gearmiddot in theJanuaryFebruary 1995 issue

OisengCIATEQCalz del Ratablo 1150Col Fovisste76150QueretaroMexico++ 52142-163429

Grlar Design SoftwareFairfield ManufacturingPOBox 7940lafayette IN 47903(317) 474-3474

GearCalc AGMA2fS Scoring+Geartech Software100 Bushbuck RoadTownsend MT 596444061266-4620

GearpackSoftware Enginaering Services2801 Ridge AvenueRockford IL 6110318151963-1760

peGearsPC Enterprises115Vonder laneSedona a 86336

Power TransmissionCIMlogic2 Wellman AvenueNashua NH 00060(6031881-9918

Program 1500 TK SolverUniversal Technical Systems1220 Rock StreetRockford Il61l01(815) 963-2220

Van Gerpen-Reece SoftwareVan Gerpenmiddot A eeee Engineering1502Grand BoulevardCedar Falls lA 50613(319)m-7673

32 GEAR TECHNOLOGY

Sereens [rom GearCAD (above and beloW lell) show -car geomlr) clements in diJJeren1 eolorsZARJ+ eome witb a materials database (below right)

enabling optimization of transrnis ionduring the design stage

The analysis provided by the programis based on the two-parameter Weibulldistribution lives of me component gearsand bearing Input and result can befonnatted in either metric or Engli hmeasurement units

YOucan analyze spur helical and spi-ral bevel reductions as well as combina-tions of these reductions Basic spur andhelical reductions included in the pro-gram are single mesh compound meshand planetary gear trains A variety ofreduction types is also available for piralbevel gear sets

TUFE was just released for publicpurchase in 1996 nis3vailable for avariety of platforms and systems II habeen succes fully implemented on 18Mmiddotcompatible PCsand UNIX workstationsCost i $50000 Documentation includ-ing u er instructions and method of solu-tion can be purchased separately for $40for evaluation purposes

IlIIiiiiIiiiIftii0__

I-IIIIIL IIIIiiIIII

O1iiIIiIIiI0 _

0 0 --00 __

~~-I---~- HIIIL~

--[J__ In_I

--~(]-0-Oiiii0_~

o~0_0_o ~0___

DANSI (Dynamic Analysiso SpurGear Transmissiolls)another NASArelease was developed in 1993 It can beused for parametric studies to predict theeffect on dynamic load and tooth bendingstress for spur gears due to operatingspeed torque stiffness damping inertiaand tooth profile

DANST calculate the properties ofsystem components and substitutes theminto the governing equations to solve fordynamic tooth loads and tooth bendingsire ses The model includes driving anddriven gears connecting shafts motorand load The equations of motion werederived from ba ic gear geometry andelementary vibration principles Thedynamic olution1 found by integratingthe equauon of motion

DANST allow u ersio choose from avariety of gear materials basic geargeometries and operating condition Users can al 0 choo e from a number ofcombinations of tooth profile variationsand user-digitized profile modifications

Three standard forms of tip relief areincluded among the tooth profile options

The program is available from COS~MC for $500 n i provided in sourcecode format so you can make changes Itruns on workstation-level computersYou may purchase the program docu-mentation seprucately for $]8 This willgive you user instructions and anoverview of tbe method of solution aswell as ample input and output

Information about the NASA programs

is available on the Internet at the COSMJCweb site httpllwwwcosmicugaedu

Gear Design SystemsIf youre looking for a complete gear

design package it might pay toextendy01l1 search outside the United StatesWe turned to Au tralia and Germany fortwo fairly comprehensive gear designpackage

GearCAD by GearSoft Design Lane

Cove NSW Australia is a completegeardesign y tem written for IBM-compati-ble PCs It includes calculations associat-ed with the geometry of involute gears forthe design of pur and helical gearsetsSome of the advanced features of the pro-gram include adjustable addendum non-standard center distance seleejable back-lash tooth sizing and load checking

When de igningpur gears GearCADallows the user to choose moduleFeUows tub Looth or diametral pitch for-mals in external internal or planetaryconfigurations The gears are graphicallydisplayed on screen and changing one ormore basic parameters will cau e the gearto be redrawn instantly

Users can also u e the zoom commandto check for interference Pre sing a keywin cau e the gears to rotate in meso The(lisplay identifies each of the following bya different color piniongear pitch circleoutsideiaside diameter circles root circlebase circle trochoidal fillet line of actionstart of involute profile circle undercutcircle stan of active profile and maximumallowable outside diameter

Our goal in developing GearCADwas to adopt the visual design conceptsays Stan Koci manager of GearSofiDesign We wanted an easy-to-use pro-gram imple enough for the occasionalgear de igner bUI with the power for thevery experienced designer

Sub-windows include cutler selectionpreliminary estimation of tooth size cen-ter distance amp gear ratio approximationpermissible load approximation measur-ing roller calculation and AGMA geome-try factors J and I

The visual design concept makes theprogram an ideal teaching aid says KociFor example if the user changes from anob cutter to a IS-tooth pinion-type cut-ter the designer can visually examine theeffects Oil tile SIP root diameter filletradius and interference

GearCAD includes many warningmessages in case certain geometry para-meters go outside permis ible rangesFor example if interference existsbetween the tips of the pinion teeth andthe internal gear teeth as tile teeth go outof mesh the program will bring up awarning message that tip interference ispresent Likewise GearCAD will let youknow if the operating pres UTe angle orthe backlash is too large or too small

Designs created can be printed orsaved to disk in DXF or XY file formatfor u e in CADCAM programs Thesoftware comes with a detailed manualincluding gear terminology formulasused for calculations and examples ofspecific design problems and how theyare solved with the software

GearCAD Release 28 sells forapproximately $Uoo It is written forDOS but can be run under Windows 31Windows 95 or Windows NT A modulefor spiral gears is not yet completed

Anothercomprehensi ve gear designpackage ZARl Gearing CalculationSoftware comes from HexagonMechanical Engineering Software inGermany The program calculates geom-etry and trength of external andinternalspur andhelical gears with involute teethin conformance with DIN 3960 39613967 and 3990

Once the user has entered the pressureangle helix angle normal module num-ber of teeth face width addendum mod-ification and center distance ZARl cal-culates complete gear geometry tooldimensions and contact ratio factors

Antr the basic gear design has beencalculated the user can enter a gear qual-ity level and tolerance zone to determinethe final gear data tootll thickness back-

4UU ~UUU1UClI ~JJlll1ALCU

with hobbing teeth in metalblanks Plastic gears usuallycan be used as-molded andrequire no finishing COIl-

sequently they have II sig-nificant cost advantage inproduction quantities Thecost of plastic alternativescan be one-half to one-tenththat of stamped machined orpowder metal gears depend-ing on the manufacturingtechnique For example the

VVVlY tilt are middotllUSC 10 l

Differences in pecific gravityalone however are not directindicators of weight savingamong other reasons becauseto transmit the same powerplastic gears must usually belarger than meta] gears Yetonce trade-offs in size andpower are made plastics lendthemselves to innovative geardesigns and smaller lighterdrivetrainsv For examplecompact split-path planetary

WUett me use OI grease mustbe avoided such Eli Ia erprinters or motorized toy

Unlubricated gears cansimplify drive design butplastic gears can also operatewith and benefit from lubri-cant when nece sary Amajor automotive supplierfor instance elimi aatedsqueaks and wear in motor-ized car seats by replacingmetal seat adjuster gears withthose molded in acetal

JANUARyFEBRUARY leR7 35

Payoff and Potenti-l1Typically gears are a

means of positively transmit-ting uniform motion withconstant drive ratios Ther-moplastic and thermosettingpolymers have long providedalternatives to metals in low-powered unlubricated geartrain Gears machined fromphenolics and other ther-mosets can be used at higheroperating temperatures and

lash and measurements over balls orpms In adcHtion ZARI willi calculatethe load-bearing capacity with respect totooth root fatigue fracture and pitting

ZARI tomes with special windowsfor designing planetary gear train andspecial profiles [t comes with a databaseinterface that allows the u er to electmaterials used for makingihe gears Theextended version ZARl+ comes with amaterials database built in Otherwiseusers can develop their own dBase~ lyledatabase of materials

The graphic display of ZARI draws

the gear form on screen Users can seethe tooth form as generated bya slmula-tion of the cutting tool action In addi-tionthe gear in mesh can be shown inanimation

ZARI can be integrated with mostCADCAM programs through its DXfand IGBS interfaces The program gener-ates drawings of the front and side eleva-tions of the gears calculated as well astables containing the gear data anddimensions

ZARl run on IBM-compatible PCsusing MS-DOS 31 or higher The price is$1J06~or ZARI or $[450 for ZARJ + withthe materials database included A demoversion can be downleaded onlhe Internetat huplwwwllexagorl delzarl_fhtmThere you can also find informationabout distributors of the ottWate andadditional programs available includingZAR2 a similar program for bevel gearsthat ells for $10330

Til Us MIll YouTllII If you found this article of Interest andloruseful please circle 210

For more information on the foHowingcompanies please circle the appropriatereader service numberAlI n_CiroIt InCOMC_n CinIIe III

ESDU I nnCIroIIZ13asaft 0 CInIldlHUIIIOIISaftwIre- cn1I1MIDL _a1I1UNIK AaooIellll CIroIIII7Wornll GrllId _bull Cin II

OTHER GEARSOFTWARE AVAILABLEFor a full discussion of software not men-tioned in this article see -How Many MiceDoes it Take ToDesign a Gearmiddot in theJanuaryFebruary 1995 issue

OisengCIATEQCalz del Ratablo 1150Col Fovisste76150QueretaroMexico++ 52142-163429

Grlar Design SoftwareFairfield ManufacturingPOBox 7940lafayette IN 47903(317) 474-3474

GearCalc AGMA2fS Scoring+Geartech Software100 Bushbuck RoadTownsend MT 596444061266-4620

GearpackSoftware Enginaering Services2801 Ridge AvenueRockford IL 6110318151963-1760

peGearsPC Enterprises115Vonder laneSedona a 86336

Power TransmissionCIMlogic2 Wellman AvenueNashua NH 00060(6031881-9918

Program 1500 TK SolverUniversal Technical Systems1220 Rock StreetRockford Il61l01(815) 963-2220

Van Gerpen-Reece SoftwareVan Gerpenmiddot A eeee Engineering1502Grand BoulevardCedar Falls lA 50613(319)m-7673

32 GEAR TECHNOLOGY

Sereens [rom GearCAD (above and beloW lell) show -car geomlr) clements in diJJeren1 eolorsZARJ+ eome witb a materials database (below right)

enabling optimization of transrnis ionduring the design stage

The analysis provided by the programis based on the two-parameter Weibulldistribution lives of me component gearsand bearing Input and result can befonnatted in either metric or Engli hmeasurement units

YOucan analyze spur helical and spi-ral bevel reductions as well as combina-tions of these reductions Basic spur andhelical reductions included in the pro-gram are single mesh compound meshand planetary gear trains A variety ofreduction types is also available for piralbevel gear sets

TUFE was just released for publicpurchase in 1996 nis3vailable for avariety of platforms and systems II habeen succes fully implemented on 18Mmiddotcompatible PCsand UNIX workstationsCost i $50000 Documentation includ-ing u er instructions and method of solu-tion can be purchased separately for $40for evaluation purposes

IlIIiiiiIiiiIftii0__

I-IIIIIL IIIIiiIIII

O1iiIIiIIiI0 _

0 0 --00 __

~~-I---~- HIIIL~

--[J__ In_I

--~(]-0-Oiiii0_~

o~0_0_o ~0___

DANSI (Dynamic Analysiso SpurGear Transmissiolls)another NASArelease was developed in 1993 It can beused for parametric studies to predict theeffect on dynamic load and tooth bendingstress for spur gears due to operatingspeed torque stiffness damping inertiaand tooth profile

DANST calculate the properties ofsystem components and substitutes theminto the governing equations to solve fordynamic tooth loads and tooth bendingsire ses The model includes driving anddriven gears connecting shafts motorand load The equations of motion werederived from ba ic gear geometry andelementary vibration principles Thedynamic olution1 found by integratingthe equauon of motion

DANST allow u ersio choose from avariety of gear materials basic geargeometries and operating condition Users can al 0 choo e from a number ofcombinations of tooth profile variationsand user-digitized profile modifications

Three standard forms of tip relief areincluded among the tooth profile options

The program is available from COS~MC for $500 n i provided in sourcecode format so you can make changes Itruns on workstation-level computersYou may purchase the program docu-mentation seprucately for $]8 This willgive you user instructions and anoverview of tbe method of solution aswell as ample input and output

Information about the NASA programs

is available on the Internet at the COSMJCweb site httpllwwwcosmicugaedu

Gear Design SystemsIf youre looking for a complete gear

design package it might pay toextendy01l1 search outside the United StatesWe turned to Au tralia and Germany fortwo fairly comprehensive gear designpackage

GearCAD by GearSoft Design Lane

Cove NSW Australia is a completegeardesign y tem written for IBM-compati-ble PCs It includes calculations associat-ed with the geometry of involute gears forthe design of pur and helical gearsetsSome of the advanced features of the pro-gram include adjustable addendum non-standard center distance seleejable back-lash tooth sizing and load checking

When de igningpur gears GearCADallows the user to choose moduleFeUows tub Looth or diametral pitch for-mals in external internal or planetaryconfigurations The gears are graphicallydisplayed on screen and changing one ormore basic parameters will cau e the gearto be redrawn instantly

Users can also u e the zoom commandto check for interference Pre sing a keywin cau e the gears to rotate in meso The(lisplay identifies each of the following bya different color piniongear pitch circleoutsideiaside diameter circles root circlebase circle trochoidal fillet line of actionstart of involute profile circle undercutcircle stan of active profile and maximumallowable outside diameter

Our goal in developing GearCADwas to adopt the visual design conceptsays Stan Koci manager of GearSofiDesign We wanted an easy-to-use pro-gram imple enough for the occasionalgear de igner bUI with the power for thevery experienced designer

Sub-windows include cutler selectionpreliminary estimation of tooth size cen-ter distance amp gear ratio approximationpermissible load approximation measur-ing roller calculation and AGMA geome-try factors J and I

The visual design concept makes theprogram an ideal teaching aid says KociFor example if the user changes from anob cutter to a IS-tooth pinion-type cut-ter the designer can visually examine theeffects Oil tile SIP root diameter filletradius and interference

GearCAD includes many warningmessages in case certain geometry para-meters go outside permis ible rangesFor example if interference existsbetween the tips of the pinion teeth andthe internal gear teeth as tile teeth go outof mesh the program will bring up awarning message that tip interference ispresent Likewise GearCAD will let youknow if the operating pres UTe angle orthe backlash is too large or too small

Designs created can be printed orsaved to disk in DXF or XY file formatfor u e in CADCAM programs Thesoftware comes with a detailed manualincluding gear terminology formulasused for calculations and examples ofspecific design problems and how theyare solved with the software

GearCAD Release 28 sells forapproximately $Uoo It is written forDOS but can be run under Windows 31Windows 95 or Windows NT A modulefor spiral gears is not yet completed

Anothercomprehensi ve gear designpackage ZARl Gearing CalculationSoftware comes from HexagonMechanical Engineering Software inGermany The program calculates geom-etry and trength of external andinternalspur andhelical gears with involute teethin conformance with DIN 3960 39613967 and 3990

Once the user has entered the pressureangle helix angle normal module num-ber of teeth face width addendum mod-ification and center distance ZARl cal-culates complete gear geometry tooldimensions and contact ratio factors

Antr the basic gear design has beencalculated the user can enter a gear qual-ity level and tolerance zone to determinethe final gear data tootll thickness back-

4UU ~UUU1UClI ~JJlll1ALCU

with hobbing teeth in metalblanks Plastic gears usuallycan be used as-molded andrequire no finishing COIl-

sequently they have II sig-nificant cost advantage inproduction quantities Thecost of plastic alternativescan be one-half to one-tenththat of stamped machined orpowder metal gears depend-ing on the manufacturingtechnique For example the

VVVlY tilt are middotllUSC 10 l

Differences in pecific gravityalone however are not directindicators of weight savingamong other reasons becauseto transmit the same powerplastic gears must usually belarger than meta] gears Yetonce trade-offs in size andpower are made plastics lendthemselves to innovative geardesigns and smaller lighterdrivetrainsv For examplecompact split-path planetary

WUett me use OI grease mustbe avoided such Eli Ia erprinters or motorized toy

Unlubricated gears cansimplify drive design butplastic gears can also operatewith and benefit from lubri-cant when nece sary Amajor automotive supplierfor instance elimi aatedsqueaks and wear in motor-ized car seats by replacingmetal seat adjuster gears withthose molded in acetal

JANUARyFEBRUARY leR7 35

Payoff and Potenti-l1Typically gears are a

means of positively transmit-ting uniform motion withconstant drive ratios Ther-moplastic and thermosettingpolymers have long providedalternatives to metals in low-powered unlubricated geartrain Gears machined fromphenolics and other ther-mosets can be used at higheroperating temperatures and

lash and measurements over balls orpms In adcHtion ZARI willi calculatethe load-bearing capacity with respect totooth root fatigue fracture and pitting

ZARI tomes with special windowsfor designing planetary gear train andspecial profiles [t comes with a databaseinterface that allows the u er to electmaterials used for makingihe gears Theextended version ZARl+ comes with amaterials database built in Otherwiseusers can develop their own dBase~ lyledatabase of materials

The graphic display of ZARI draws

the gear form on screen Users can seethe tooth form as generated bya slmula-tion of the cutting tool action In addi-tionthe gear in mesh can be shown inanimation

ZARI can be integrated with mostCADCAM programs through its DXfand IGBS interfaces The program gener-ates drawings of the front and side eleva-tions of the gears calculated as well astables containing the gear data anddimensions

ZARl run on IBM-compatible PCsusing MS-DOS 31 or higher The price is$1J06~or ZARI or $[450 for ZARJ + withthe materials database included A demoversion can be downleaded onlhe Internetat huplwwwllexagorl delzarl_fhtmThere you can also find informationabout distributors of the ottWate andadditional programs available includingZAR2 a similar program for bevel gearsthat ells for $10330

Til Us MIll YouTllII If you found this article of Interest andloruseful please circle 210

For more information on the foHowingcompanies please circle the appropriatereader service numberAlI n_CiroIt InCOMC_n CinIIe III

ESDU I nnCIroIIZ13asaft 0 CInIldlHUIIIOIISaftwIre- cn1I1MIDL _a1I1UNIK AaooIellll CIroIIII7Wornll GrllId _bull Cin II

Three standard forms of tip relief areincluded among the tooth profile options

The program is available from COS~MC for $500 n i provided in sourcecode format so you can make changes Itruns on workstation-level computersYou may purchase the program docu-mentation seprucately for $]8 This willgive you user instructions and anoverview of tbe method of solution aswell as ample input and output

Information about the NASA programs

is available on the Internet at the COSMJCweb site httpllwwwcosmicugaedu

Gear Design SystemsIf youre looking for a complete gear

design package it might pay toextendy01l1 search outside the United StatesWe turned to Au tralia and Germany fortwo fairly comprehensive gear designpackage

GearCAD by GearSoft Design Lane

Cove NSW Australia is a completegeardesign y tem written for IBM-compati-ble PCs It includes calculations associat-ed with the geometry of involute gears forthe design of pur and helical gearsetsSome of the advanced features of the pro-gram include adjustable addendum non-standard center distance seleejable back-lash tooth sizing and load checking

When de igningpur gears GearCADallows the user to choose moduleFeUows tub Looth or diametral pitch for-mals in external internal or planetaryconfigurations The gears are graphicallydisplayed on screen and changing one ormore basic parameters will cau e the gearto be redrawn instantly

Users can also u e the zoom commandto check for interference Pre sing a keywin cau e the gears to rotate in meso The(lisplay identifies each of the following bya different color piniongear pitch circleoutsideiaside diameter circles root circlebase circle trochoidal fillet line of actionstart of involute profile circle undercutcircle stan of active profile and maximumallowable outside diameter

Our goal in developing GearCADwas to adopt the visual design conceptsays Stan Koci manager of GearSofiDesign We wanted an easy-to-use pro-gram imple enough for the occasionalgear de igner bUI with the power for thevery experienced designer

Sub-windows include cutler selectionpreliminary estimation of tooth size cen-ter distance amp gear ratio approximationpermissible load approximation measur-ing roller calculation and AGMA geome-try factors J and I

The visual design concept makes theprogram an ideal teaching aid says KociFor example if the user changes from anob cutter to a IS-tooth pinion-type cut-ter the designer can visually examine theeffects Oil tile SIP root diameter filletradius and interference

GearCAD includes many warningmessages in case certain geometry para-meters go outside permis ible rangesFor example if interference existsbetween the tips of the pinion teeth andthe internal gear teeth as tile teeth go outof mesh the program will bring up awarning message that tip interference ispresent Likewise GearCAD will let youknow if the operating pres UTe angle orthe backlash is too large or too small

Designs created can be printed orsaved to disk in DXF or XY file formatfor u e in CADCAM programs Thesoftware comes with a detailed manualincluding gear terminology formulasused for calculations and examples ofspecific design problems and how theyare solved with the software

GearCAD Release 28 sells forapproximately $Uoo It is written forDOS but can be run under Windows 31Windows 95 or Windows NT A modulefor spiral gears is not yet completed

Anothercomprehensi ve gear designpackage ZARl Gearing CalculationSoftware comes from HexagonMechanical Engineering Software inGermany The program calculates geom-etry and trength of external andinternalspur andhelical gears with involute teethin conformance with DIN 3960 39613967 and 3990

Once the user has entered the pressureangle helix angle normal module num-ber of teeth face width addendum mod-ification and center distance ZARl cal-culates complete gear geometry tooldimensions and contact ratio factors

Antr the basic gear design has beencalculated the user can enter a gear qual-ity level and tolerance zone to determinethe final gear data tootll thickness back-

4UU ~UUU1UClI ~JJlll1ALCU

with hobbing teeth in metalblanks Plastic gears usuallycan be used as-molded andrequire no finishing COIl-

sequently they have II sig-nificant cost advantage inproduction quantities Thecost of plastic alternativescan be one-half to one-tenththat of stamped machined orpowder metal gears depend-ing on the manufacturingtechnique For example the

VVVlY tilt are middotllUSC 10 l

Differences in pecific gravityalone however are not directindicators of weight savingamong other reasons becauseto transmit the same powerplastic gears must usually belarger than meta] gears Yetonce trade-offs in size andpower are made plastics lendthemselves to innovative geardesigns and smaller lighterdrivetrainsv For examplecompact split-path planetary

WUett me use OI grease mustbe avoided such Eli Ia erprinters or motorized toy

Unlubricated gears cansimplify drive design butplastic gears can also operatewith and benefit from lubri-cant when nece sary Amajor automotive supplierfor instance elimi aatedsqueaks and wear in motor-ized car seats by replacingmetal seat adjuster gears withthose molded in acetal

JANUARyFEBRUARY leR7 35

Payoff and Potenti-l1Typically gears are a

means of positively transmit-ting uniform motion withconstant drive ratios Ther-moplastic and thermosettingpolymers have long providedalternatives to metals in low-powered unlubricated geartrain Gears machined fromphenolics and other ther-mosets can be used at higheroperating temperatures and

lash and measurements over balls orpms In adcHtion ZARI willi calculatethe load-bearing capacity with respect totooth root fatigue fracture and pitting

ZARI tomes with special windowsfor designing planetary gear train andspecial profiles [t comes with a databaseinterface that allows the u er to electmaterials used for makingihe gears Theextended version ZARl+ comes with amaterials database built in Otherwiseusers can develop their own dBase~ lyledatabase of materials

The graphic display of ZARI draws

the gear form on screen Users can seethe tooth form as generated bya slmula-tion of the cutting tool action In addi-tionthe gear in mesh can be shown inanimation

ZARI can be integrated with mostCADCAM programs through its DXfand IGBS interfaces The program gener-ates drawings of the front and side eleva-tions of the gears calculated as well astables containing the gear data anddimensions

ZARl run on IBM-compatible PCsusing MS-DOS 31 or higher The price is$1J06~or ZARI or $[450 for ZARJ + withthe materials database included A demoversion can be downleaded onlhe Internetat huplwwwllexagorl delzarl_fhtmThere you can also find informationabout distributors of the ottWate andadditional programs available includingZAR2 a similar program for bevel gearsthat ells for $10330

Til Us MIll YouTllII If you found this article of Interest andloruseful please circle 210

For more information on the foHowingcompanies please circle the appropriatereader service numberAlI n_CiroIt InCOMC_n CinIIe III

ESDU I nnCIroIIZ13asaft 0 CInIldlHUIIIOIISaftwIre- cn1I1MIDL _a1I1UNIK AaooIellll CIroIIII7Wornll GrllId _bull Cin II

Not Permanently Of Coursejust For 4 Days To Attend

GEAR EXPO 97October19~22 1997

Cobo CenterDetroit Michigan

Theres only one place togo ifyoure buyingl gearingl equipment prod-ucts supplies or services-GEAR EXPO 97 the only internationalltrade show devoted exclusively to the gear industiY

fig 2- In middottbe middotWorld Washer manufactured ln SIlvera IcountriesWhidpooIIICorporationl lintroduced I spUlledl cllrtJb Of middotsplutcbt contain-ingl a spline and glirsl molded tn Icetlll copolymer The low-wearepicyclic gelll assemJlly lasts four times IDormaIIwishIng machine lifeallil reduces the lIumber of movillg PIIIlSlIy 2D

learance

Center Disllmce

Internal Gear amp Pinion

IFig3- Int rnal gears - re as ellsy to mold in pmiddotlastic as external gearsTbey pJOVidmiddot II means to redoc center distances nd Ipack bighl powerdensities in B small spaIIcopolymer compatible withlubricants Oil bath lubrica-lion also enables designers toexploit the added strength ofglass-fiUedplastic gearswithout excessive wear

PI8StiCgears provide theopportunity to cut drive noiseby reducing dynamic load-ing Gear misalignmentandmal] toolh errors create tiny

impacts resulting in runningnoise However lower mod-ulus plastic gear teeth deformto compensate for the inaccu-racies and their softer rnateri-al absorbs impact makingplastic gears quieter thanmetal Depending on theapplication plastic gears canbe quiete r than expensivemetal gears which are one ortwo AGMA classes higherin quality

36 QEAR TECHNOLOGV

Powerful Potentialhe mo t powerful

advantages of plastic gearsmay be the design opportu-nities they afford Geargeometries overlooked bydesigners accustomed tometal are easy to mold inplastic and they can reducedri ve ize weight and costFor exampfe a commonarrangement of two externalspur gears with a large ratiodemands a wide center dis-ranee The ame ratio can beachieved ina smaller spaceby replacing an externalgear with an internal gear(Fig 3) Internal gearstough to machine in metalare easy to mold in plastic

Low cost low wear plas-tic gears may also allowdesigners to reconsider the

old axiom The fewer partsthe better Split-power pathsin parallel or non-parallel axisdrives can indeed have moreparts butthey afford advan-tages ill space weight effi-ciency and co t Plastic gearsimpose no special restrictionson gear ratios and therequired accuracy can beachieved with todays mold-ing machine and material

The more powerful thedrive the more complicatedwill be the up-front de igneffort required to make plas-tic gears work The state ofthe gear art has advanced towhere plastic gears are nowin drives from 14 to 34 hp Future applications may takethem between 1 and 10 hp inthe near-term and up to 30hpin the long term Horsepowerlimits for plastic gears varywith the polymer dependingupon tne modulus strengthand creep characteristicswhich all change with tern-perature Nevenhele s plas-tic gear limits can be definedbroadly by K-factor1gtand unitloads ar ambient temperiltureDepending on the polymerreinforcement and lubrica-tion plastic gears are broadlycompatible with K-faCIors of30-200 psi and unit loads of400-2000 psi

Plastic gear trains are gen-erally built around involutegear technology This systemis very forgiving of the centerdistance shifts inherent illplastic gears bur non-involutesystem which are center-distance ensiuve are notgood candidates for plasticgears In particular manynon-parallel axi systems arenot ba ed on involute technol-ogy and aredifficult to manu-facture with plastic gears

Bevel gears are an excep-tion They are non-involute

but often made of plastic The low modulus of plasticsmakes them relatively forgiv-ing of the alignment errorsinherent in mass-producedbevel gears Crossed-ax]helical worm gear whichmake point-contact whennew are good candidates forplasticat low loads Theircapacity is increased by lni-tial wear which produces aline contact Involute facegears have a line contact andare preferred to worm drivesat higher power levels

To Lubricate Or NotAs engineering resins now

move into drives with higherhorsepower and greater preei-sionthe drive designer facesth choice of oil- or grease-lubricated or unlubricatedgearboxes This decision amithe choice of a hibricant arekey factors for the drivde igner to consider

For plastic gears runningin an oil bath the oil facili-tates removal of frictionalheat and allows higher loadcapacity Unlubrieated andgreased gears are aerody-narnieally cooled and there-fore run hotter with lowerloadcapacity Unlubricatedgear sets are often molded indifferent materials forreduced coefficient of frie-tion (COF) Acetal copoly-mer gears are often matedwith those made of nylon 66or polyurylene ~erphLhalateas these combinations havemuch lower COFs than setsof any of these materialsworkingaJone Unlubricatedplastic gears often havelubricants uch asPTFE sili-cone or graphitecompound-ed into the polymer Whilethese additives reducethecoefficient of friction (COF)Ihe COF is still higher thanthat of greased gears

bullbullbullbullbull _ T1ECHNDLOGY FOCUS 1 bullbullbull _

Generally the load capac- ~ the modulus and trength ofity and life of hibricated pias- mot plastics and acceleratetic gears is gaverned by i creep The e effects must bebending fatigue at th tooth considered in tbe designroot Unlubricated gear process and tudie to quan-which run hottest with the tify them areju t beginninglowest load capacity often ~ Gear also usually de-fad by wear or overheating i mand more preci ionthanon the tooth flanks Greased l commonly molded parts sogears win occasionany fai] ~ their tooling can be expen-by wear if the grease doe ive A good plastic gear de-not stay in the mesh sign however saves money

While engineering resins by reducing trial-and-error

can resist oils and grease mold i~eriltions For the pro-lubricants mu t be carefully 1 ject engineer building a drivechosen because orne can ~ with pia tic gears ideallycause dramatic changes in should start with a teamgear properties and dimen- 1 including a de igner molderion For example extreme i tool builder and rein suppli-

pres ore oilsare unnecessary 1 er all expenenced with gearswith the low contact pre ures ~ The team need the mostfound in plastic gearing and complete application infer-orne can auack pia ics mation available to create the

chemically Likewise the j rna t detailed gear specifics-choice of resin for liIe appli- l lion possible Ambient tem-cation i important PIFEand ~peralllLrelubrication and dutyother lew-friction additives 1 cycle all impact gear life andcompounded in tile materia] l drive performance A hous-

of plastic gears may have lit- ling material wlticb matchesLIevalue or negative value if i the thermal and moisturethe gears are oiled or greased 1 expan ion of plastic gears

In TbeKnow can help maintain precisePlastics are naturally

more prone to dimensionalcreep than metal and creepin plastic gears depends 011

their duty cycle and tempera-lure Consequently moldedgears are best used in appli-cations without static loadsIf tauc Joads cannot beavoided plastic gears mustbe designed to operate prop-erly after teeth have deflect-ed due to creep

The operating speed ofpia tic gear obviouslyimpact operating tempera-ture However rapid loadingroles can aJ 0 affect materialpropertie For orne materi-als the fa IeII a tooth iload d the liIjgher the effec-tive modulus and strengthHigll r temperature reduces

center distance Howeverpla tic hou iogs cannot dissi-pale hear a wen a metalGear welling due to moistureabsorption inome re ins canalso stall tight-me hedgearsComputer-aided design toolscan help designers allow forworslcase tolerances

Driving DesignPlastics also change the

rule ef gear and drivedesign The designer of ameta] pinion gear would nor-mally limit the aspect ratio toone or less With plastics ana pect ratio of two or threemay be acceptable as funtooth contact may beachieved Plastic gear canrequire tip relief unneces aryin metal gears The lowermesh tiffness of plastic teeth

ModeIIGHM U5-35Gear IHoningl Machine

127995(Shavers 111511 Ivailable)

ModelGS32-132 x StrokeGear Shapingl MachineS1m995

IModel1 GH50-1775lings Gear Hobber

$149995

CIRCLE 1111or call 1-8110-340-11611 d111

JANUARYF BRUAmiddotRY 11187 37

_------------TECHNOLOGYFOCUS------------requires more backlash thanfound in metal gears A hunt-ing ratio considered desirablein many metal gear trains toequalize wear may acceleratewear with pla tic gears Theguidefiaes for metal gearde ign must be examinedcarefully before applyingthem 10 plastic gears

The rack tooth formremains a convenient way todefine and generate gearteeth in metal or pla ticStandard metal gear profilescan provide a starLing pointfor plastic gearsahhoughthere are some pIa tic pro-files which are preferred

Most profile are based ona 20deg pressure angle and aworking depth of two overthe diametral pitch or twotimesthe module Howeverthe profile needs to be opti-mized for a material with alower modulus greater lem-perature sensitivity and dif-ferent coefficients of frictionand weal than metal

Plastic gears commonlyhave greater working depthsthan metal gears sometimesup to 35greater Thisaltcws for variationsineffecti ve center distancecaused by thermal chemical

and moisture expansion Thedesigner of plastic gearsshould strive for 8 full rootradius not only to reducestre ses at the root but also toenhance resin flow into theteeth during injection mold-ing which reduces molded-instresses and removes heatmore uniformly from the plas-tic during solidification Amore stable geometry results

The designer of plasticgearsah 0 hould pay pedalattention to haft attachmentBore tolerance naturallyimpact true center distancessometimes resulting in loss ofproper gear action A simplepress-fit demands extra mold-ing precision for a securemount witltout over-stressingthe plastic A press-fit knurled01 sphned shaft can transfermore torque but also putsmore stress on the gear hubInsert-molded hubs grip bet-ter but during molding asthe plastic shrinks onto theshaft they can induce resid-ual stre e Ultrasonicinser-tion of a knurled shaft pro-duces the lowest residualstres es A single- or double-D keyed shaft prevents slip-page and minimizes distor-tion wi assembly in some

Tahle 1 - Tvpical Print Data for A Molded Spur Gear

Pan NoMating Gelr iPart NaMaterial

NUlllber 01TeelllDiametral PilchModulePressure AngleBase PtiehReference Pitch DiallllierlffHtiwe Tooth TIIicLrlelS RalPDhceWidth

OdSld DiameterEHedive ODIJide Diameter

Roll Angle Elective ODNonnal Tooth Tip RadiulTllHIlRYOlute Fonn Diamalar

RolIAngle TIP

Root DiamelerBale Diamat8J

38 GEAR TECHNOLOGY

InspectionllDatIAGMA nullity NoMeasured Tooth ThielLn WPinsSizi over II Pins of OXmiddot DiameterRadial Aunout [TIll)Pitch VlriationTooth Alignment

Master Gear NoIO Teet--CIIIS 1AGear rest RadiusTmLolldTooth-to- Toatll CompositeIComposite IMinimum Fillet Radius

Blsic Generating IRickFlank AngleTip tomiddot IReference UnaTooth 1IIicknui al RlteranceTip Rldill1

cases However if torque ishigh these can becomeloose For high torque appli-cations splined assembliesare preferred

Molded In WhatThe choice of a gear re in

also demands careful studyLess expensive commodityresins generally lack thefatigue life temperatureresistance lubricant resis-tance and dimen ional stabil-ity required for quality plas-tic gearsin al1 butthe mostprimilive applicalion How-ever many of todays engi-neering resins provide thenecessary performance forworking gear trains

Itis generally easier tomold higl1qualiay gears withresin containing minimaladditi yes than with highlyfilled blends The pecifiershould call for only a muchglass or mineral fiUeror lubri-cant additives as are actuallyneeded If external lubricationis required the drive designerresin supplier and lubricantsupplier hould work togetherto select an appropriate lubri-cation system

Most gear apphcationsuse the crystalline resinsnylon and acetal becausethey have better fatigue resis-tance than amorphous plas-tics Nylon both with andwithout glass reinforcementcontinues to serve in manygear and housing applica-tions However it is moistureabsorption prone and conse-quemshifts in properties anddimensions have pushedmany designers to acetalAcetal copolymer does notabsorb moi ture and there-fore provides long-termdi mensional stabHity andexceptional fatigue andchemical resistance over abroad temperature range

Other resins have foundlimited gear success ADS hagood dimensional stabilityand low shrink out of themold but its fatigue charac-teristics make it suitable onlyfor light load and short ser-vice life Liquid CrystalPolymer (LCP) has excep-tional dimen lonai stabilityand fills the most intricatemolds To date LeI has beenused for only mall precisiongearsunder light loads suchas tiny wristwatch gear Linear poly-phenylene sulfide(PPS) has exceptional temper-ature and chemical re istanceand good fatigue life It hasbeen effective in other highlyloaded parts molded with finedetails and hould prove to bea high-performance gearmaterial As plastic gearmove into higher loads withlarger gears in lubricatedenvironments the improvedfatigue resistance and dimen-sional stability of long fiber-reinforced plastics shouldmake these materials leadinggear candidates

Specify and MoldGear re in selection reo

quires the designer to focuson resin performance at thehigh end of the operating tem-perature range planned for thedrive Heat deflection temper-atures for engineering resinrange from 170Ffor unfillednylon and 230degF for acetalcopolymer to 500degF for rein-forced lineal PPS at 264 psiHowever higher temperatureslower both the modulus andstrength of gear resinsTheyincrease creep rate and mtro-duce thermal expansion intoprecision paris Fortunatelythe temperature response ofengineering resins is wellunderstood allowing design-ers to predict the effect ontheir gears

_----TECHNOLOGY FOCUSbullbullbull _For the gear molder uni-

form mold flow and coolingis essential to the fabricationof accurategears Uniformcooling from cavity to cavityis also critical for consistentquality gears The best ap-proach for precision gears isa single-cavity mold but it israrely cost-effective tor pro-duction Multi-cavity moldscan create minor differencesin flow pattems and majorvariations from part to partThe more mold cavities thegreater the potential varia-tion Four cavities i general-ly the maximum allowablefor molding precision gears

Three-plate tooling withsmall pin gales on the gearweb is common for moldingmost small gears Howeverlarger gears with heavierteeth can require centerdiaphragm gating for betterdimensional control andhigher quality

Whatever the mold gearteeth should be cut in aninsert not integral to themold cavity Gear designersand molder are alma t guar-anteed to replace the toothprofile once or twice in thegear prOtotyping evohmon toget it right Interchangeablering inserts make refiningthe tooth profile faster andless expensive

Smooth MeshTile initial engineering

effort to de ign plastic gearsis greater than that requiredwith metals if only to copewith changing properties anddimensions The most com-mon errors of plasticgeardesigners start with insuffi-cient application specifica-tions The specifics of theapplication must be factoredinto detailed drawings beforeprototyping The drawingsmust contain sufficient

information to manufacturethe gear (See Table L)

Problems with prototypescan also tempt gear designersto change resins a middotcostlymistake given the differentshrink characteristics of vari-au plastics It is better torework the tooth profile thanswitch the materiaiunles itis clear that the wrong mater-ial was chosen

Expertise to avoid the pit-falls of plastic gears is avail-able from gear consultantssoftware and resin suppliers

With careful design and mate-rial selection the power trans-mitted by plastic gears can besignificant andthe potential

lceI81copolymer Igelrs in bull dualdrin wasber Iransm issionl daval-oped IbY Maytag

Zan Smith is a sla engineerwith Hoechst Technical Polymersworking with customers 10 developgear applications with the compa-nys resins He holds a doctoratein mechanical engintering and isthe author of numerous books andarticles 011 plastics and gearing

market program development exec-urill with HTP She is responsiblefor bringing new acetal copolymerapplieations to wIIter

TIIUs yenAll You TIIInk bullIf you found this article ofinterest andor useful please01211

For more Infonnation aboutHoechst Technical Polymersplease circle 221

SPIRAL BEVEL IGEAIRS

I

Spirall amp ~Straigh BevellGearanufacturingCommercial to aircraft quality gearing

Spur helicall spli1nedshafts internallamp lexternalshavedl amp ground gears Spirallbavalgrinding

Mil-1-45m- Mil~-Sm-45662SPC

MIDWEST GEAR8 TOOL INC

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CIRCLE 113 or call111aoo341)1160 x911li

Inspects toAGMA orDINstandarcis withcomputer analiysisGear analysis is now simple andaccurate with our DoublemiddotFlanK

Gear Roller and IBM compatible software Inset shows MasterGear rolling with helical parallel axis componentbull Perform total composlle tooih-io-tcom nick

ana runout analySiSbull Display component tolerances and analysis resultsbull Computer indicates out-ot spec valuesbull AnalysiS with AGMA or DIN StandardFor FREE brochure circle reader service numberFor FAST action call 937859middot8273 or FAX 937859-4452

MampM PFlECISltJNSYSTEMS~

The Metrology and Motion People~ reg

JANUARYFEBRUARY 1997 39

bullbullbullbullbull _ T1ECHNDLOGY FOCUS 1 bullbullbull _

Generally the load capac- ~ the modulus and trength ofity and life of hibricated pias- mot plastics and acceleratetic gears is gaverned by i creep The e effects must bebending fatigue at th tooth considered in tbe designroot Unlubricated gear process and tudie to quan-which run hottest with the tify them areju t beginninglowest load capacity often ~ Gear also usually de-fad by wear or overheating i mand more preci ionthanon the tooth flanks Greased l commonly molded parts sogears win occasionany fai] ~ their tooling can be expen-by wear if the grease doe ive A good plastic gear de-not stay in the mesh sign however saves money

While engineering resins by reducing trial-and-error

can resist oils and grease mold i~eriltions For the pro-lubricants mu t be carefully 1 ject engineer building a drivechosen because orne can ~ with pia tic gears ideallycause dramatic changes in should start with a teamgear properties and dimen- 1 including a de igner molderion For example extreme i tool builder and rein suppli-

pres ore oilsare unnecessary 1 er all expenenced with gearswith the low contact pre ures ~ The team need the mostfound in plastic gearing and complete application infer-orne can auack pia ics mation available to create the

chemically Likewise the j rna t detailed gear specifics-choice of resin for liIe appli- l lion possible Ambient tem-cation i important PIFEand ~peralllLrelubrication and dutyother lew-friction additives 1 cycle all impact gear life andcompounded in tile materia] l drive performance A hous-

of plastic gears may have lit- ling material wlticb matchesLIevalue or negative value if i the thermal and moisturethe gears are oiled or greased 1 expan ion of plastic gears

In TbeKnow can help maintain precisePlastics are naturally

more prone to dimensionalcreep than metal and creepin plastic gears depends 011

their duty cycle and tempera-lure Consequently moldedgears are best used in appli-cations without static loadsIf tauc Joads cannot beavoided plastic gears mustbe designed to operate prop-erly after teeth have deflect-ed due to creep

The operating speed ofpia tic gear obviouslyimpact operating tempera-ture However rapid loadingroles can aJ 0 affect materialpropertie For orne materi-als the fa IeII a tooth iload d the liIjgher the effec-tive modulus and strengthHigll r temperature reduces

center distance Howeverpla tic hou iogs cannot dissi-pale hear a wen a metalGear welling due to moistureabsorption inome re ins canalso stall tight-me hedgearsComputer-aided design toolscan help designers allow forworslcase tolerances

Driving DesignPlastics also change the

rule ef gear and drivedesign The designer of ameta] pinion gear would nor-mally limit the aspect ratio toone or less With plastics ana pect ratio of two or threemay be acceptable as funtooth contact may beachieved Plastic gear canrequire tip relief unneces aryin metal gears The lowermesh tiffness of plastic teeth

ModeIIGHM U5-35Gear IHoningl Machine

127995(Shavers 111511 Ivailable)

ModelGS32-132 x StrokeGear Shapingl MachineS1m995

IModel1 GH50-1775lings Gear Hobber

$149995

CIRCLE 1111or call 1-8110-340-11611 d111

JANUARYF BRUAmiddotRY 11187 37

_------------TECHNOLOGYFOCUS------------requires more backlash thanfound in metal gears A hunt-ing ratio considered desirablein many metal gear trains toequalize wear may acceleratewear with pla tic gears Theguidefiaes for metal gearde ign must be examinedcarefully before applyingthem 10 plastic gears

The rack tooth formremains a convenient way todefine and generate gearteeth in metal or pla ticStandard metal gear profilescan provide a starLing pointfor plastic gearsahhoughthere are some pIa tic pro-files which are preferred

Most profile are based ona 20deg pressure angle and aworking depth of two overthe diametral pitch or twotimesthe module Howeverthe profile needs to be opti-mized for a material with alower modulus greater lem-perature sensitivity and dif-ferent coefficients of frictionand weal than metal

Plastic gears commonlyhave greater working depthsthan metal gears sometimesup to 35greater Thisaltcws for variationsineffecti ve center distancecaused by thermal chemical

and moisture expansion Thedesigner of plastic gearsshould strive for 8 full rootradius not only to reducestre ses at the root but also toenhance resin flow into theteeth during injection mold-ing which reduces molded-instresses and removes heatmore uniformly from the plas-tic during solidification Amore stable geometry results

The designer of plasticgearsah 0 hould pay pedalattention to haft attachmentBore tolerance naturallyimpact true center distancessometimes resulting in loss ofproper gear action A simplepress-fit demands extra mold-ing precision for a securemount witltout over-stressingthe plastic A press-fit knurled01 sphned shaft can transfermore torque but also putsmore stress on the gear hubInsert-molded hubs grip bet-ter but during molding asthe plastic shrinks onto theshaft they can induce resid-ual stre e Ultrasonicinser-tion of a knurled shaft pro-duces the lowest residualstres es A single- or double-D keyed shaft prevents slip-page and minimizes distor-tion wi assembly in some

Tahle 1 - Tvpical Print Data for A Molded Spur Gear

Pan NoMating Gelr iPart NaMaterial

NUlllber 01TeelllDiametral PilchModulePressure AngleBase PtiehReference Pitch DiallllierlffHtiwe Tooth TIIicLrlelS RalPDhceWidth

OdSld DiameterEHedive ODIJide Diameter

Roll Angle Elective ODNonnal Tooth Tip RadiulTllHIlRYOlute Fonn Diamalar

RolIAngle TIP

Root DiamelerBale Diamat8J

38 GEAR TECHNOLOGY

InspectionllDatIAGMA nullity NoMeasured Tooth ThielLn WPinsSizi over II Pins of OXmiddot DiameterRadial Aunout [TIll)Pitch VlriationTooth Alignment

Master Gear NoIO Teet--CIIIS 1AGear rest RadiusTmLolldTooth-to- Toatll CompositeIComposite IMinimum Fillet Radius

Blsic Generating IRickFlank AngleTip tomiddot IReference UnaTooth 1IIicknui al RlteranceTip Rldill1

cases However if torque ishigh these can becomeloose For high torque appli-cations splined assembliesare preferred

Molded In WhatThe choice of a gear re in

also demands careful studyLess expensive commodityresins generally lack thefatigue life temperatureresistance lubricant resis-tance and dimen ional stabil-ity required for quality plas-tic gearsin al1 butthe mostprimilive applicalion How-ever many of todays engi-neering resins provide thenecessary performance forworking gear trains

Itis generally easier tomold higl1qualiay gears withresin containing minimaladditi yes than with highlyfilled blends The pecifiershould call for only a muchglass or mineral fiUeror lubri-cant additives as are actuallyneeded If external lubricationis required the drive designerresin supplier and lubricantsupplier hould work togetherto select an appropriate lubri-cation system

Most gear apphcationsuse the crystalline resinsnylon and acetal becausethey have better fatigue resis-tance than amorphous plas-tics Nylon both with andwithout glass reinforcementcontinues to serve in manygear and housing applica-tions However it is moistureabsorption prone and conse-quemshifts in properties anddimensions have pushedmany designers to acetalAcetal copolymer does notabsorb moi ture and there-fore provides long-termdi mensional stabHity andexceptional fatigue andchemical resistance over abroad temperature range

Other resins have foundlimited gear success ADS hagood dimensional stabilityand low shrink out of themold but its fatigue charac-teristics make it suitable onlyfor light load and short ser-vice life Liquid CrystalPolymer (LCP) has excep-tional dimen lonai stabilityand fills the most intricatemolds To date LeI has beenused for only mall precisiongearsunder light loads suchas tiny wristwatch gear Linear poly-phenylene sulfide(PPS) has exceptional temper-ature and chemical re istanceand good fatigue life It hasbeen effective in other highlyloaded parts molded with finedetails and hould prove to bea high-performance gearmaterial As plastic gearmove into higher loads withlarger gears in lubricatedenvironments the improvedfatigue resistance and dimen-sional stability of long fiber-reinforced plastics shouldmake these materials leadinggear candidates

Specify and MoldGear re in selection reo

quires the designer to focuson resin performance at thehigh end of the operating tem-perature range planned for thedrive Heat deflection temper-atures for engineering resinrange from 170Ffor unfillednylon and 230degF for acetalcopolymer to 500degF for rein-forced lineal PPS at 264 psiHowever higher temperatureslower both the modulus andstrength of gear resinsTheyincrease creep rate and mtro-duce thermal expansion intoprecision paris Fortunatelythe temperature response ofengineering resins is wellunderstood allowing design-ers to predict the effect ontheir gears

_----TECHNOLOGY FOCUSbullbullbull _For the gear molder uni-

form mold flow and coolingis essential to the fabricationof accurategears Uniformcooling from cavity to cavityis also critical for consistentquality gears The best ap-proach for precision gears isa single-cavity mold but it israrely cost-effective tor pro-duction Multi-cavity moldscan create minor differencesin flow pattems and majorvariations from part to partThe more mold cavities thegreater the potential varia-tion Four cavities i general-ly the maximum allowablefor molding precision gears

Three-plate tooling withsmall pin gales on the gearweb is common for moldingmost small gears Howeverlarger gears with heavierteeth can require centerdiaphragm gating for betterdimensional control andhigher quality

Whatever the mold gearteeth should be cut in aninsert not integral to themold cavity Gear designersand molder are alma t guar-anteed to replace the toothprofile once or twice in thegear prOtotyping evohmon toget it right Interchangeablering inserts make refiningthe tooth profile faster andless expensive

Smooth MeshTile initial engineering

effort to de ign plastic gearsis greater than that requiredwith metals if only to copewith changing properties anddimensions The most com-mon errors of plasticgeardesigners start with insuffi-cient application specifica-tions The specifics of theapplication must be factoredinto detailed drawings beforeprototyping The drawingsmust contain sufficient

information to manufacturethe gear (See Table L)

Problems with prototypescan also tempt gear designersto change resins a middotcostlymistake given the differentshrink characteristics of vari-au plastics It is better torework the tooth profile thanswitch the materiaiunles itis clear that the wrong mater-ial was chosen

Expertise to avoid the pit-falls of plastic gears is avail-able from gear consultantssoftware and resin suppliers

With careful design and mate-rial selection the power trans-mitted by plastic gears can besignificant andthe potential

lceI81copolymer Igelrs in bull dualdrin wasber Iransm issionl daval-oped IbY Maytag

Zan Smith is a sla engineerwith Hoechst Technical Polymersworking with customers 10 developgear applications with the compa-nys resins He holds a doctoratein mechanical engintering and isthe author of numerous books andarticles 011 plastics and gearing

market program development exec-urill with HTP She is responsiblefor bringing new acetal copolymerapplieations to wIIter

TIIUs yenAll You TIIInk bullIf you found this article ofinterest andor useful please01211

For more Infonnation aboutHoechst Technical Polymersplease circle 221

SPIRAL BEVEL IGEAIRS

I

Spirall amp ~Straigh BevellGearanufacturingCommercial to aircraft quality gearing

Spur helicall spli1nedshafts internallamp lexternalshavedl amp ground gears Spirallbavalgrinding

Mil-1-45m- Mil~-Sm-45662SPC

MIDWEST GEAR8 TOOL INC

26069 Groesbeck HwyWarren MI48089

CIRCLE 113 or call111aoo341)1160 x911li

Inspects toAGMA orDINstandarcis withcomputer analiysisGear analysis is now simple andaccurate with our DoublemiddotFlanK

Gear Roller and IBM compatible software Inset shows MasterGear rolling with helical parallel axis componentbull Perform total composlle tooih-io-tcom nick

ana runout analySiSbull Display component tolerances and analysis resultsbull Computer indicates out-ot spec valuesbull AnalysiS with AGMA or DIN StandardFor FREE brochure circle reader service numberFor FAST action call 937859middot8273 or FAX 937859-4452

MampM PFlECISltJNSYSTEMS~

The Metrology and Motion People~ reg

JANUARYFEBRUARY 1997 39

_------------TECHNOLOGYFOCUS------------requires more backlash thanfound in metal gears A hunt-ing ratio considered desirablein many metal gear trains toequalize wear may acceleratewear with pla tic gears Theguidefiaes for metal gearde ign must be examinedcarefully before applyingthem 10 plastic gears

The rack tooth formremains a convenient way todefine and generate gearteeth in metal or pla ticStandard metal gear profilescan provide a starLing pointfor plastic gearsahhoughthere are some pIa tic pro-files which are preferred

Most profile are based ona 20deg pressure angle and aworking depth of two overthe diametral pitch or twotimesthe module Howeverthe profile needs to be opti-mized for a material with alower modulus greater lem-perature sensitivity and dif-ferent coefficients of frictionand weal than metal

Plastic gears commonlyhave greater working depthsthan metal gears sometimesup to 35greater Thisaltcws for variationsineffecti ve center distancecaused by thermal chemical

and moisture expansion Thedesigner of plastic gearsshould strive for 8 full rootradius not only to reducestre ses at the root but also toenhance resin flow into theteeth during injection mold-ing which reduces molded-instresses and removes heatmore uniformly from the plas-tic during solidification Amore stable geometry results

The designer of plasticgearsah 0 hould pay pedalattention to haft attachmentBore tolerance naturallyimpact true center distancessometimes resulting in loss ofproper gear action A simplepress-fit demands extra mold-ing precision for a securemount witltout over-stressingthe plastic A press-fit knurled01 sphned shaft can transfermore torque but also putsmore stress on the gear hubInsert-molded hubs grip bet-ter but during molding asthe plastic shrinks onto theshaft they can induce resid-ual stre e Ultrasonicinser-tion of a knurled shaft pro-duces the lowest residualstres es A single- or double-D keyed shaft prevents slip-page and minimizes distor-tion wi assembly in some

Tahle 1 - Tvpical Print Data for A Molded Spur Gear

Pan NoMating Gelr iPart NaMaterial

NUlllber 01TeelllDiametral PilchModulePressure AngleBase PtiehReference Pitch DiallllierlffHtiwe Tooth TIIicLrlelS RalPDhceWidth

OdSld DiameterEHedive ODIJide Diameter

Roll Angle Elective ODNonnal Tooth Tip RadiulTllHIlRYOlute Fonn Diamalar

RolIAngle TIP

Root DiamelerBale Diamat8J

38 GEAR TECHNOLOGY

InspectionllDatIAGMA nullity NoMeasured Tooth ThielLn WPinsSizi over II Pins of OXmiddot DiameterRadial Aunout [TIll)Pitch VlriationTooth Alignment

Master Gear NoIO Teet--CIIIS 1AGear rest RadiusTmLolldTooth-to- Toatll CompositeIComposite IMinimum Fillet Radius

Blsic Generating IRickFlank AngleTip tomiddot IReference UnaTooth 1IIicknui al RlteranceTip Rldill1

cases However if torque ishigh these can becomeloose For high torque appli-cations splined assembliesare preferred

Molded In WhatThe choice of a gear re in

also demands careful studyLess expensive commodityresins generally lack thefatigue life temperatureresistance lubricant resis-tance and dimen ional stabil-ity required for quality plas-tic gearsin al1 butthe mostprimilive applicalion How-ever many of todays engi-neering resins provide thenecessary performance forworking gear trains

Itis generally easier tomold higl1qualiay gears withresin containing minimaladditi yes than with highlyfilled blends The pecifiershould call for only a muchglass or mineral fiUeror lubri-cant additives as are actuallyneeded If external lubricationis required the drive designerresin supplier and lubricantsupplier hould work togetherto select an appropriate lubri-cation system

Most gear apphcationsuse the crystalline resinsnylon and acetal becausethey have better fatigue resis-tance than amorphous plas-tics Nylon both with andwithout glass reinforcementcontinues to serve in manygear and housing applica-tions However it is moistureabsorption prone and conse-quemshifts in properties anddimensions have pushedmany designers to acetalAcetal copolymer does notabsorb moi ture and there-fore provides long-termdi mensional stabHity andexceptional fatigue andchemical resistance over abroad temperature range

Other resins have foundlimited gear success ADS hagood dimensional stabilityand low shrink out of themold but its fatigue charac-teristics make it suitable onlyfor light load and short ser-vice life Liquid CrystalPolymer (LCP) has excep-tional dimen lonai stabilityand fills the most intricatemolds To date LeI has beenused for only mall precisiongearsunder light loads suchas tiny wristwatch gear Linear poly-phenylene sulfide(PPS) has exceptional temper-ature and chemical re istanceand good fatigue life It hasbeen effective in other highlyloaded parts molded with finedetails and hould prove to bea high-performance gearmaterial As plastic gearmove into higher loads withlarger gears in lubricatedenvironments the improvedfatigue resistance and dimen-sional stability of long fiber-reinforced plastics shouldmake these materials leadinggear candidates

Specify and MoldGear re in selection reo

quires the designer to focuson resin performance at thehigh end of the operating tem-perature range planned for thedrive Heat deflection temper-atures for engineering resinrange from 170Ffor unfillednylon and 230degF for acetalcopolymer to 500degF for rein-forced lineal PPS at 264 psiHowever higher temperatureslower both the modulus andstrength of gear resinsTheyincrease creep rate and mtro-duce thermal expansion intoprecision paris Fortunatelythe temperature response ofengineering resins is wellunderstood allowing design-ers to predict the effect ontheir gears

_----TECHNOLOGY FOCUSbullbullbull _For the gear molder uni-

form mold flow and coolingis essential to the fabricationof accurategears Uniformcooling from cavity to cavityis also critical for consistentquality gears The best ap-proach for precision gears isa single-cavity mold but it israrely cost-effective tor pro-duction Multi-cavity moldscan create minor differencesin flow pattems and majorvariations from part to partThe more mold cavities thegreater the potential varia-tion Four cavities i general-ly the maximum allowablefor molding precision gears

Three-plate tooling withsmall pin gales on the gearweb is common for moldingmost small gears Howeverlarger gears with heavierteeth can require centerdiaphragm gating for betterdimensional control andhigher quality

Whatever the mold gearteeth should be cut in aninsert not integral to themold cavity Gear designersand molder are alma t guar-anteed to replace the toothprofile once or twice in thegear prOtotyping evohmon toget it right Interchangeablering inserts make refiningthe tooth profile faster andless expensive

Smooth MeshTile initial engineering

effort to de ign plastic gearsis greater than that requiredwith metals if only to copewith changing properties anddimensions The most com-mon errors of plasticgeardesigners start with insuffi-cient application specifica-tions The specifics of theapplication must be factoredinto detailed drawings beforeprototyping The drawingsmust contain sufficient

information to manufacturethe gear (See Table L)

Problems with prototypescan also tempt gear designersto change resins a middotcostlymistake given the differentshrink characteristics of vari-au plastics It is better torework the tooth profile thanswitch the materiaiunles itis clear that the wrong mater-ial was chosen

Expertise to avoid the pit-falls of plastic gears is avail-able from gear consultantssoftware and resin suppliers

With careful design and mate-rial selection the power trans-mitted by plastic gears can besignificant andthe potential

lceI81copolymer Igelrs in bull dualdrin wasber Iransm issionl daval-oped IbY Maytag

Zan Smith is a sla engineerwith Hoechst Technical Polymersworking with customers 10 developgear applications with the compa-nys resins He holds a doctoratein mechanical engintering and isthe author of numerous books andarticles 011 plastics and gearing

market program development exec-urill with HTP She is responsiblefor bringing new acetal copolymerapplieations to wIIter

TIIUs yenAll You TIIInk bullIf you found this article ofinterest andor useful please01211

For more Infonnation aboutHoechst Technical Polymersplease circle 221

SPIRAL BEVEL IGEAIRS

I

Spirall amp ~Straigh BevellGearanufacturingCommercial to aircraft quality gearing

Spur helicall spli1nedshafts internallamp lexternalshavedl amp ground gears Spirallbavalgrinding

Mil-1-45m- Mil~-Sm-45662SPC

MIDWEST GEAR8 TOOL INC

26069 Groesbeck HwyWarren MI48089

CIRCLE 113 or call111aoo341)1160 x911li

Inspects toAGMA orDINstandarcis withcomputer analiysisGear analysis is now simple andaccurate with our DoublemiddotFlanK

Gear Roller and IBM compatible software Inset shows MasterGear rolling with helical parallel axis componentbull Perform total composlle tooih-io-tcom nick

ana runout analySiSbull Display component tolerances and analysis resultsbull Computer indicates out-ot spec valuesbull AnalysiS with AGMA or DIN StandardFor FREE brochure circle reader service numberFor FAST action call 937859middot8273 or FAX 937859-4452

MampM PFlECISltJNSYSTEMS~

The Metrology and Motion People~ reg

JANUARYFEBRUARY 1997 39

_----TECHNOLOGY FOCUSbullbullbull _For the gear molder uni-

form mold flow and coolingis essential to the fabricationof accurategears Uniformcooling from cavity to cavityis also critical for consistentquality gears The best ap-proach for precision gears isa single-cavity mold but it israrely cost-effective tor pro-duction Multi-cavity moldscan create minor differencesin flow pattems and majorvariations from part to partThe more mold cavities thegreater the potential varia-tion Four cavities i general-ly the maximum allowablefor molding precision gears

Three-plate tooling withsmall pin gales on the gearweb is common for moldingmost small gears Howeverlarger gears with heavierteeth can require centerdiaphragm gating for betterdimensional control andhigher quality

Whatever the mold gearteeth should be cut in aninsert not integral to themold cavity Gear designersand molder are alma t guar-anteed to replace the toothprofile once or twice in thegear prOtotyping evohmon toget it right Interchangeablering inserts make refiningthe tooth profile faster andless expensive

Smooth MeshTile initial engineering

effort to de ign plastic gearsis greater than that requiredwith metals if only to copewith changing properties anddimensions The most com-mon errors of plasticgeardesigners start with insuffi-cient application specifica-tions The specifics of theapplication must be factoredinto detailed drawings beforeprototyping The drawingsmust contain sufficient

information to manufacturethe gear (See Table L)

Problems with prototypescan also tempt gear designersto change resins a middotcostlymistake given the differentshrink characteristics of vari-au plastics It is better torework the tooth profile thanswitch the materiaiunles itis clear that the wrong mater-ial was chosen

Expertise to avoid the pit-falls of plastic gears is avail-able from gear consultantssoftware and resin suppliers

With careful design and mate-rial selection the power trans-mitted by plastic gears can besignificant andthe potential

lceI81copolymer Igelrs in bull dualdrin wasber Iransm issionl daval-oped IbY Maytag

Zan Smith is a sla engineerwith Hoechst Technical Polymersworking with customers 10 developgear applications with the compa-nys resins He holds a doctoratein mechanical engintering and isthe author of numerous books andarticles 011 plastics and gearing

market program development exec-urill with HTP She is responsiblefor bringing new acetal copolymerapplieations to wIIter

TIIUs yenAll You TIIInk bullIf you found this article ofinterest andor useful please01211

For more Infonnation aboutHoechst Technical Polymersplease circle 221

SPIRAL BEVEL IGEAIRS

I

Spirall amp ~Straigh BevellGearanufacturingCommercial to aircraft quality gearing

Spur helicall spli1nedshafts internallamp lexternalshavedl amp ground gears Spirallbavalgrinding

Mil-1-45m- Mil~-Sm-45662SPC

MIDWEST GEAR8 TOOL INC

26069 Groesbeck HwyWarren MI48089

CIRCLE 113 or call111aoo341)1160 x911li

Inspects toAGMA orDINstandarcis withcomputer analiysisGear analysis is now simple andaccurate with our DoublemiddotFlanK

Gear Roller and IBM compatible software Inset shows MasterGear rolling with helical parallel axis componentbull Perform total composlle tooih-io-tcom nick

ana runout analySiSbull Display component tolerances and analysis resultsbull Computer indicates out-ot spec valuesbull AnalysiS with AGMA or DIN StandardFor FREE brochure circle reader service numberFor FAST action call 937859middot8273 or FAX 937859-4452

MampM PFlECISltJNSYSTEMS~

The Metrology and Motion People~ reg

JANUARYFEBRUARY 1997 39