主講人：趙慧、楊國星TianjinLightIndustryVocationalTechnicalCollegeTechnicalRequirementsonthePartDrawing——DimensionalTolerancesandGeometricalTolerancesIntroductionMainContent01TolerancesandFits02

GeometricalTolerancesPartITolerancesandFitsPARTIConceptofTolerancesandFits

1.Interchangeability

Inmassproductionandassemblyofmachinery,therequirementisthatabatchofmatingparts,whenprocessedaccordingtothedrawings,canbeassembledwithoutselectionandstillmeetthedesignandusagerequirements.Thispropertybetweenpartsiscalledinterchangeability.2.DimensionalToleranceAchievingabsoluteaccuracyinthedimensionsofpartsduringmanufacturingispracticallyimpossible.However,toensuretheinterchangeabilityofparts,theallowablevariationindimensions,definedduringthedesignprocessbasedontheusagerequirementsofthepart,iscalleddimensionaltolerance,orsimplytolerance.ConceptofTolerancesandFits01.

StandardTolerances

Standardtolerancesrefertoanytolerancethatdefinesthesizeofthetolerancezone.Thereare20grades:IT01,IT0,IT1throughIT18.02.FundamentalDeviationFundamentaldeviationreferstotheupperorlowerlimitdeviationofthetolerancezonerelativetothezeroline.Nationalstandardsdefine28differentfundamentaldeviationsforholesandshafts,representedbyuppercaseletters.ConceptofTolerancesandFits

3.FitsAfitreferstotherelationshipbetweenthetolerancezonesofaholeandashaft,whichhavethe

samebasicdimension、andareintendedtobeassembledtogether.Duetotheactualdimensionsoftheholeandshaftbeingdifferent,differenttypesoffitsmayoccurafterassembly.Theseareclassifiedintothreetypes:

(1)ClearanceFit–Thetolerancezoneoftheholeisabovethetolerancezoneoftheshaft.Whentheholeandshaftareassembled,thereisaclearance(whichcanincludeaminimumclearanceofzero)betweenthem.ConceptofTolerancesandFits

3.Fits(2)InterferenceFit–Thetolerancezoneoftheholeisbelowthetolerancezoneoftheshaft.Whentheholeandshaftareassembled,thereisaninterference(whichcanincludeaminimuminterferenceofzero)betweenthem.ConceptofTolerancesandFits

3.Fits

(3)TransitionFit

–Thetolerancezonesoftheholeandshaftoverlap.Whenanypairoftheholeandshaftareassembled,thefitmayeitherhaveclearanceorinterference.ConceptofTolerancesandFitsMarkingthetolerancezonecodeMarkingthelimitdeviationsMarkingboththetolerancezonecodeandlimitdeviations1.DimensionToleranceMarkingonPartDrawingsConceptofTolerancesandFits

Basicdimension,tolerancezonecodeofthehole/tolerancezonecodeoftheshaft2.

DimensionToleranceMarkingonAssemblyDrawings(1)FitMarkingBetweenGeneralPartsConceptofTolerancesandFits2.DimensionToleranceMarkingonAssemblyDrawings(2)FitMarkingBetweenGeneralPartsandStandardComponentsWhenageneralpartfitswithastandardcomponent(suchasabearing),becausethetoleranceofthestandardcomponentfollowsitsownnationalstandards,onlythetoleranceofthegeneralpartismarkedintheassemblydrawing.Thetoleranceofthestandardcomponentisnotmarked.PartIIGeometricalTolerancesPARTII1.

ConceptofGeometricalTolerancesWhenmachiningparts,notonlythedimensionsmayhavedeviations,butalsothegeometricshapeandrelativepositioncanhaveerrors.Geometricaltolerancesrefertotheallowabledeviationsintheactualshape,orientation,position,andrunoutofapart.ConceptandTypesofGeometricalTolerancesConceptandTypesofGeometricalTolerances2.

TypesofGeometricalTolerancesandTheirCharacteristicSymbolsNotationofGeometricalTolerances1.GeometricalToleranceBoxandItsContentsThegeometricaltoleranceboxisdrawnwithfinesolidlines,placedhorizontallyorvertically.Theheightoftheboxis

twicetheheightofthedimensionnumbersinthedrawingandtheboxitself.NotationofGeometricalTolerances(2)Whenthemeasuredfeatureisacenterline,centersurface,orcenterpoint,thearrowheadoftheguidelineshouldalignwiththedimensionarrowforthatfeature.2.

MeasuredFeaturesWhenannotatinggeometricaltolerancesonthedrawing,guidelinesareusedtoconnectthemeasuredfeaturesandthetolerancebox,withtheguidelineendinginanarrowhead.(1)Whenthemeasuredfeatureisacontourlineoracontoursurface,thearrowheadshouldbeplacedonthecontourlineoritsextension,ensuringthatitisclearlyoffsetfromthedimensionline.

NotationofGeometricalTolerances(1)Whenthedatumfeatureisacontourlineorcontoursurface3.

DatumThedatumrelatedtothemeasuredfeatureisrepresentedbyan

uppercaseletter.Theletterisplacedinthedatumbox

andisconnectedtoafilledorblanktriangletoindicatethedatum.NotationofGeometricalTolerances(2)Whenthedatumfeat