>> P.465
AiryandBesselPointsWhenalengthstandardbarorinsidemicrometerlieshorizontally,supportedassimplyaspossibleattwopoints,itbendsunderitsownweightintoashapethatdependsonthespacingofthosepoints.Therearetwodistancesbetweenthepointsthatcontrolthisdeformationinusefulways,asshownbelow.aaAirypoints(a0.577)Theendsofabar(ormicrometer)canbemadeexactlyhorizontalbyspacingthetwosupportssymmetricallyasshownabove.Thesepointsareknownasthe‘AiryPoints’andarecommonlyusedtoensurethattheendsofalengthbarareparalleltooneanother,sothatthelengthiswelldened.05459401DV0.05mmaBesselpoints(a0.559)Thechangeinlengthofabar(ormicrometer)duetobendingcanbeminimizedbyspacingthetwosupportssymmetricallyasshownabove.Thesepointsareknownasthe‘BesselPoints’andmaybeusefulwhenusingalonginsidemicrometer.aReferencePointSetting•Referencepointsettingwithasettingringorcylindricalmastergage.Insertaboregageintoasettingringorcylindricalmastergage.Oscillatetheboregage.Thereferencepointiswherethecontactpointispisheddeepest.0AB0102030(2)100545Thimble(1)Outersleeve35406789(1)Outersleeve(2)ThimbleReading35mm0.015mm35.015mmIHowtoReadtheScaleHowtoReadtheScaleGraduation0.005mm05459401DV0005mmWhenHoltestisused,themeasuredvaluediffersbetweenmeasurementacrosstheanvilandthemeasurementonlyatthetipoftheanvilduetotheproductmechanism.Performthereferencepointsettingunderthesameconditionbeforemeasurement.ChangesinMeasuredValuesatDifferentMeasuringPointsWhenyouusethetipoftheanvilformeasurement,setthereferencepointbyusingthetipoftheanvil.WorkpieceSettingofreferencepointMeasurementErrorDuetoTemperatureVariationofTubularInsideMicrometersHeattransferfromtheoperatortothemicrometershouldbeminimizedtoavoidanysignicantmeasuringerrorduetotemperaturedifferencebetweentheworkpieceandmicrometer.Ifthemicrometerishelddirectlybyhandwhenmeasuring,useglovesorholdtheheat-insulator(iftted).EffectofMisalignmentonAccuracy(InsideMicrometer)XFigure1Figure2X0102030ABInsidediametertobemeasuredLengthmeasuredwithaxialoffsetX:L:X:OffsetinaxialdirectionInsidediametertobemeasuredLengthmeasuredwithradialoffsetX:L:X:OffsetinradialdirectionLL60.0008-58IftheInsideMicrometerismisalignedintheaxialorradialdirectionbyanoffsetdistanceXwhenameasurementistaken,asinFigures1and2,thenthatmeasurementwillbeinerrorasshowninthegraphbelow(constructedfromtheformulaegivenabove).Theerrorispositiveforaxialmisalignmentandnegativeforradialmisalignment.ℓ=200mmℓ=500mmℓ=1000mm12345678910Misalignment(offset)ofoneendofmicrometer(mm)0.100.090.080.070.060.050.040.030.020.01misalignment)(mm)andnegativeforradial,Error(positiveforaxial,△△:L-:Errorinmeasurement=√2+X2-△:Errorinmeasurement△:L-2–X2-=√
| < 
| 
> | 
>>
