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