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EngineeringDrawings:GeometricTolerancing
AshortseriesoflecturesonEngineeringDrawingasPartofMECH24005400:MechanicalDesign1ByPaulBriozzo
DistortedObjectsbySuzyLelievre
ScaleTransformSALOMEGeometryUsersGuide:ScaleTransform
GeometricTolerancing
GeometricTolerancingWhatisit?
GeometricTolerancing UnlikeDimensionalTolerancethatconcernsitselfwithsizecontrol,
GeometricTolerancing concernsitselfwithshapecontrol
GeometricTolerancing influencesthemanufacturingandinspectionprocesschosen
GeometricTolerancing isrequiredinfeaturesinindustriessuchas Aerospacecomponentmanufacture Automobilecomponentmanufacture Precisionmachinerymanufacture Biomedicalcomponentmanufacture
GeometricTolerancing isusedwherehighinterchangeofpartsisrequired
GeometricTolerancing andDimensionalTolerancing arelinked
BasicConceptsofGeometryTolerancing
GeometryTolerancesarespecifiedaccordingtofunctionalrequirements:Useitifitisneeded,ifnotDONOTasitaddstotheexpenseofthemanufacture,inspectionofacomponentandclarityofanengineeringdrawing.
Dependingonthefeaturetobetoleranced andthewayinwhichitisdimensioned,thetolerancezonewillbeoneof: Thespacebetweentwoparallellines Thespacewithinacircle Thespacebetweentwoconcentriccircles Thespacewithinacylinder Thespacebetweentwocoaxialcylinders Thespacebetweentwoequidistantsurfaces Thespacewithinasphere
GeometryTolerancing SymbolicStructure
InterpretationofGeometryTolerancingFlatness
AFlatnesstoleranceisusedtocontroltheflatnessofasurface.Thetolerancezoneisaspecifiedspaceseparatingtwoparallelplanesbetweenwhichthesurfacetobecontrolledmustlie.
Straightness Astraightnesstolerancemaybeusedtocontrol:
1.Straightnessofaline 2.Straightnessofanaxisinasingleplane 3.Straightnessoftheaxesofsolidsofrevolution
Perpendicularity Aperpendicularity toleranceisusedtocontrol:
1.alinewithrespecttoadatumline 2.anaxiswithrespecttoadatumplane
3.asurfacewithrespecttoadatumaxis 4.asurfacewithrespecttoadatumplane
Position Apositiontoleranceisusedtocontrolthelocationofafeatureby
limitingitsdeviationfromaspecifiedtrueposition. 1.aholeaxis 2.asurface
Position(Concentricity) Aconcentricitytoleranceisusedtocontrolaconditioninwhich
twoormorefeaturessuchascircles,spherescylinders,conesorhexagonsarerequiredtoshareacommoncentreoraxis
CaseStudy QantasA380OilStubPipeLatein2010,aQantasA380sufferedacatastrophicfailureofoneofitsfourmainRollsRoyceengines.Investigationspointtoafailureinanoilstubpipecausedbyamanufacturingdefect.
Position(Symmetry) Asymmetrytoleranceisusedtocontrolaconditioninwhichoneormore
featuresaresymmetricallydisposedeithersideofacentreline(axis)orcentreplane(median)ofanotherfeaturewhichisspecifiedasthedatum.
Cylindricity Acylindricity tolerancespecifiesatolerancezoneconsistingofanannularspacebetween
twocoaxialcylindershavingadifferenceinradiiequaltothespecifiedtolerance.
Angularity Anangularitytoleranceisusedtocontrolangularrelationshipsofanyanglebetween
straightline(axes)orsurfaceswithstraightlineelementssuchasflatorcylindricalsurfaces
Circularity Acircularitytolerancespecifiesthewidthofanannulartolerancezone,boundedbytwo
concentriccirclesinthesameplanewithinwhichthecircumferenceofthefeaturemustlie.
Parallelism Aparallelismtoleranceisusedtocontroltheorientationoffeaturesrelatedtooneanother
byanangleofzerodegrees.
Example(ABadOne)
EffectsofCombiningLinearandGeometricTolerances
Intolerancing featuresofsizeonmatingcomponentswhereeaseofassemblyisimportant,itshouldberealisedthattheleastfavourableconditionforassemblyoccurswhenmatingsizesarethemaximummaterialsizeallowablebytheindividualtoleranceofeachcomponent.
Greatervariationsinshapegeometrycanbeacceptedasthematingsizesapproachtheirleastmaterialsize.
VirtualSize Virtualsizereferstothedimensionoftheoverallenvelopeofperfectformwhichtouchesthe
highestpointsofafeature.
Forashaft,itisthemaximummeasuredsizeplustheactualeffectofformvariationssuchasflatness,straightness,roundness,cylindricity andprofile.
Forahole,itistheminimummeasuredsizeminustheactualeffectofformvariationssuchasflatness,straightness,roundness,cylindricity andprofile.
InterpretthisExampleofGeometricTolerancing