>> P.161
•One-wiremethodThepitchdiameterofodd-utedtapcanbemeasuredusingtheV-anvilmicrometerwiththeone-wiremethod.Obtainthemeasuredvalue(M1)andcalculateMwithequation(3)or(4).M1=Micrometerreadingduringone-wiremeasurementD=Odd-utedtapdiameterTapwiththreeutes:M=3M1-2D···························(3):M=2.2360M1-1.23606D·······(4)TapwithveutesThen,assignthecalculatedMtoequation(1)or(2)tocalculatethepitchdiameter(E).AnvilSpindleRootTangentLengthOdd-flutedtapWireSmFormulaforcalculatingaroottangentlength(Sm):Sm=mcos(Zm-0.5)+Zinv0{0}+2Xmsin0Formulaforcalculatingthenumberofteethwithintheroottangentlength(Zm):Zm'=Z·K(f)+0.5(ZmistheintegerclosesttoZm'.)where,K(f)=1{sec0√(1+2f)2-cos20-inv0-2ftan0}m:Module:Pressureangle0:NumberofteethZ:AddendummodificationcoefficientX:RoottangentlengthSm:NumberofteethwithintherootZmtangentlengthForagearwithanoddnumberofteeth:dm=dp+cosø·cos=dp+cosø·cosz·m·cos90°dg0z()however,dpinvø=dg–dpX2=z·m·cos(0–2z–inv2tan0+z·X0)Obtainø(invø)fromtheinvolutefunctiontable.02-800zmX:Numberofteeth:Pressureangleteeth:Module:Addendummodificationcoefficientdm90ºZdp(b)(90°z)and,f=XZinv20°inv14.5°0.0149040.0055448GearMeasurementOver-pinmethoddpdm(a)Foragearwithanevennumberofteeth:z·m·cosdm=dp+cosø=dp+cosødg0MajorMeasurementErrorsoftheScrewMicrometerErrorcauseMaximumpossibleerrorPrecautionsforeliminatingerrorsErrorthatmightnotbeeliminatedevenwithprecautionsMicrometerfeederror3μmAnvilangleerror±5μmassumingtheerrorofahalfangleis15minutesMisalignedcontactpoints+10μmInuenceofmeasuringforce±10μmAngleerrorofthreadgage±10μmLengtherrorofthreadgageWorkpiecethreadangleerror±(3+L25)μmJIS2gradeerrorofhalfangle±229minutes-91μm+71μmCumulativeerror(±117+40)μm1.Correctthemicrometerbeforeuse.±1μm1.Measuretheangleerrorandcorrectthemicrometer.2.Adjustthemicrometerusingthesamethreadgageastheworkpiece.1.Useamicrometerwithalowmeasuringforceifpossible.2.Alwaysusetheratchetstop.3.Adjustthemicrometerusingathreadgagewiththesamepitch.1.Performcorrectioncalculation(angle).2.Correctthelengtherror.3.Adjustthemicrometerusingthesamethreadgageastheworkpiece.1.Performcorrectioncalculation.2.Adjustthemicrometerusingthesamethreadgageastheworkpiece.1.Minimizetheangleerrorasmuchaspossible.2.Measuretheangleerrorandperformcorrectioncalculation.3.Usethethree-wiremethodforalargeangleerror.±3μmexpectedmeasurementerrorofhalfangle+3μm+3μm+3μm±1μm±8μmassumingtheerrorofhalfangleis±23minutes+26μm-12μmScrewPitchDiameterMeasurement•Three-wiremethodThescrewpitchdiametercanbemeasuredwiththethree-wiremethodasshowninthegure.Calculatethepitchdiameter(E)withequations(1)and(2).E=M-3d+0.866025P.......(1)Metricthreadoruniedscrew(60°)Whitworththread(55°)E=M-3.16568d+0.960491P.......(2)Spindled(×3)PScrewd=WirediameterE=ScrewpitchdiameterM=MicrometerreadingincludingthreewiresP=Screwpitch(Convertinchestomillimetersforuniedscrews.)AnvilEMThreadtypeMetricthreadoruniedscrew(60°)Whitworththread(55°)OptimalwiresizeatD0.577P0.564PMajorMeasurementErrorsoftheThree-wireMethodErrorcausePrecautionsforeliminatingerrorsPossibleerrorErrorthatmightnotbeeliminatedevenwithprecautions1.Correctthepitcherror(2.Measureseveralpointsandadoptp=E)theiraverage.3.Reducesinglepitcherrors.1.Usetheoptimalwirediameter.2.Nocorrectionisneeded.1.Usetheoptimalwirediameter.2.Usethewirewhichhasadiameterclosetotheaverageattheonewireside.1.Usethepredeterminedmeasuringforceappropriateforthepitch.2.Usethepredeterminedwidthofmeasurementedge.3.Useastablemeasuringforce.Pitcherror(workpiece)Errorofhalfangle(workpiece)DuetoanvildifferenceWirediametererrorCumulativeerror±18μmassumingthatthepitcherroris0.02mm.±3μm±0.3μm±0.3μm±8μm±1μm-3μm-1μmIntheworstcase+20μm-35μmWhenmeasuredcarefully+3μm-5μm
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