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主讲人：赵慧、杨国星TianjinLightIndustryVocationalTechnicalCollegeDimensioningthepartdrawingPartIDimensionalDatumsPARTIDimensionalDatumPointLineSurfaceThestartingpointformeasuringthedimensionsofapartduringdesign,manufacturing,andinspectioniscalledtheDimensionalDatum.TheDatumPoint

designdatumprocessdatumDimensionalDatuma.DesignDatumTypesofDimensionalDatums

01

Fromthedesignperspective,adesigndatumisselectedtomeetthestructuralandperformancerequirementsofthepartwhenitisinstalledinamachineorcomponent.D---DesignDatumintheWidthDirectionC--DesignDatumintheLengthDirectionB--DesignDatumintheVerticalDirectionDimensionalDatumb.ProcessDatum

TypesofDimensionalDatums

01AxialProcessDatumChuckDatumProcessDatum车刀

Fromtheperspectiveofthemanufacturingprocess,aprocessdatumisselectedtofacilitatethemachiningandmeasurementofthepart.Thesearespecificreferencepointschosentoassistinthemanufacturingandmeasurementprocessofthecomponent.DimensionalDatumSelectionofDimensionalDatums

02Thedesigndatumandtheprocessdatumshould,asfaraspossible,coincideinordertoreducedimensionalerrorsandensureproductquality.SelectionPrinciplesMostpartshavedimensionaldatumsinthreedirections:length,width,andheight.However,forpurelyrotationalbodies,onlytwodirectionsofdimensionaldatumsareused:radialandaxial.Three-PointDatums

Apartmayhavetwoormoredatumsinonedirection.Typically,thereisonlyoneprimarydatum,andtheothersaresecondaryorauxiliarydatums.Themostimportantgeometricfeaturesofthepartshouldbeselectedastheprimarydatum.PrimaryandSecondaryDatumsPartIIIssuestoConsiderWhenProperlyAnnotatingDimensionsPARTIIIssuestoConsiderWhenProperlyAnnotatingDimensionsDirectlyannotatefunctionaldimensions

01Thefunctionaldimensionsofapart,alsoknownastheprimarydimensions,refertothedimensionsthataffectthemachinespecifications,performance,workaccuracy,andtheprecisepositioningofthepartwithinanassembly,aswellasdimensionsthatrequirefits.Thesedimensionsshouldbedirectlyannotatedandnotderivedbycalculation.SlotFitsUnreasonableReasonableIssuestoConsiderWhenProperlyAnnotatingDimensionsGenerally,closeddimensionchainsshouldbeavoided.

02Closeddimensionchain

Theleastimportantdimensioninthedimensionchainshouldnotbemarked.IncorrectCorrectIssuestoConsiderWhenProperlyAnnotatingDimensionsConsiderationofeaseandfeasibilityofmeasurement

03DifficulttomeasureEasytomeasureIssuestoConsiderWhenProperlyAnnotatingDimensionsDimensionsfromthesameprocessshouldbegroupedtogetherforannotation.03PartIIICommonHoleDimensioningMethodsonPartsPARTIIICommonHoleDimensioningonPartsCommonHoleDimensioningonPartsRecessedHoleStraightHoleCountersunkHole

"6×φ7"meansthatthereare6holes,eachwithadiameterofφ7.Thediameterofthelargeendoftheconicalpartisφ13,andtheconeangleis90°.CounterboreHoleFortherecessedplaneφ20,thedepthdoesnotneedtobemarked.Duringprocessing,therecessedareaisgenerallymachineduntilnoburrsarepresent.Foursmallcounterboredholeswithadiameterofφ6.4,andalargeholediameterofφ12,depthof4.5.DescriptionSideAnnotationMethodGeneralAnnotationMethodStructuralTypesCommonHoleDimensioningonPartsSummaryofthisLectureDimensioningDat

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