>> P.535
ScrewPitchDiameterMeasurementThree-wiremethodThescrewpitchdiametercanbemeasuredwiththethree-wiremethodasshowninthegure.Calculatethepitchdiameter(E)withequations(1)and(2).RootTangentLengthMetricthreadorunifiedscrew(60°)E=M-3d+0.866025P………(1)Whitworththread(55°)E=M-3.16568d+0.960491P…(2)Spindled(x3)PScrewEMSm=Wirediameter=ScrewpitchdiameterdEM=MicrometerreadingincludingthreewiresP(Convertinchestomillimetersforunifiedscrews.)=ScrewpitchAnvilThreadtypeOptimalwiresizeatDMetricthreadorunifiedscrew(60°)Whitworththread(55°)0.577P0.564PFormulaforcalculatingaroottangentlength(Sm):Sm=mcos(Zm-0.5)+Zinv0{0}+2XmsinFormulaforcalculatingthenumberofteethwithintheroottangentlength(Zm):Zm'=Z·K(f)+0.5(ZmistheintegerclosesttoZm'.)Here,K(f)=1{sec0√(1+2f)2-cos20-inv0-2ftan0}However,f=XZMajorMeasurementErrorsoftheThree-wireMethodinv20°・=・0.014904inv14.5°・=・0.0055448ErrorcausePrecautionsforeliminatingerrorsPossibleerrorErrorthatmightnotbeeliminatedevenwithprecautionsMicrometers0mα0ZχSmZm:Module:Pressureangle:Numberofteeth:Addendummodificationcoefficient:Roottangentlength:NumberofteethwithintheroottangentlengthdpMicrometersdm90゜Zdm(a)(b)Foragearwithanevennumberofteeth:•m•cosα0zm=dp+cosφ=dp+cosφdgd±3µmGearMeasurementOver-pinmethoddpPitcherror(Workpiece)Errorofhalfangle(Workpiece)ErrorduetoanvildifferenceWirediametererrorCumulativeerror1.Correctthepitcherrorδp=δE2.Measureseveralpointsandadopttheiraverage.3.Reducesinglepitcherrors.Pitcherror±18µmat0.02mm1.Usetheoptimalwirediameter.2.Nocorrectionisneeded.±0.3µm±0.3µm1.Usetheoptimalwirediameter.2.Usethewirewhichhasadiameterclosetotheaverageattheonewireside.1.Usethepredeterminedmeasuringforceappropriateforthepitch.±8µm±1µm2.Usethepredeterminedwidthof-3µm-1µmmeasurementedge.3.Useastablemeasuringforce.theworstIncase+20µm-35µmWhenmeasuredcarefully+3µm-5µmOne-wiremethodThepitchdiameterofodd-utedtapcanbemeasuredusingtheV-anvilmicrometerwiththeone-wiremethod.Obtainthemeasuredvalue(M1)andcalculateMwithequation(3)or(4).M1=Micrometerreadingduringone-wiremeasurementD=Odd-flutedtapdiameterTapwiththreeflutes:M=3M1-2D···························(3)Tapwithfiveflutes:M=2.2360M1-1.23606D······(4)Then,assignthecalculatedMtoequation(1)or(2)tocalculatethepitchdiameter(E).AnvilSpidle(orPlunger)Odd-flutedtapNeedle(orhand)Foragearwithanoddnumberofteeth:dm=dp+cosφ•cos=dp+cosφ•cos(z)90°z•m•cosα0(z)90°dgHowever,χdpinvφ=dg-2=z•m•cosα0-(2z-invα0)+z•χdp2tanα0πObtainø(invø)fromtheinvolutefunctiontable.zα0mχ:Numberofteeth:Pressureangleteeth:Module:Addendummodificationcoefficient13-8
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