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1、螺纹的画法、螺丝的选用、紧固件的画法（Thedrawingmethodofscrewthread,theselectionofscrewsandthedrawingmethodoffasteners）First,thebasicelementsofthethread(1)threadshape;Onthecrosssectionofthethreadaxis,theoutlineshapeofthethreadiscalledthethreadshape.Ithastriangle,trapezoid,zigzagandrectang
2、le.Differentthreadshapeshavedifferentuses.(2)threaddiameter;Thebigdiameter(nominaldiameter)isthemaximumdiameterofthethread,thatis,thediameteroftheimaginarycylindricalsurfacethatcoincideswiththeouterorinnerthreadoftheouterthread,andisexpressedbyD(externalthread)orD(inter
3、nalthread).Thepathisthesmallestdiameterofthethread,thatis,thediameteroftheimaginarycylindricalsurfacethatcoincideswiththebottomoftheouterthreadortheinsideoftheinternalthread.Itiscalledthepath,andisrepresentedbyD1(externalthread)orD1(internalthread).Themiddlediameterhasa
4、nimaginarycylinderbetweenthebigdiameterandthesmalldiametercylindricalsurface,andthewidthofthetoothshapedgrooveandthewidthofthebulgeareequalonthebus.Theimaginarycylinderiscalledamiddlediametercylinder,anditsdiameteriscalledthemiddlediameter.Itisoneofthemainparameterstoco
5、ntrolthethreadprecision.(3)thenumberofthreads(n)withasinglethread(commonlyused)andmultiline,threadformedalongahelicallineforsinglethread;threadformedalongtheaxialdirectionofuniformdistributionoftwoormorethantwohelixformultiplethread.(4)thedistancebetweenthepitch(P)andth
6、elead(Ph)threadadjacenttothetwoteethatthemiddlediameterlinecorrespondstothetwopoints,whichiscalledpitch.Thesamethreadlineoftwoadjacentteethintheaxiallineofthecorrespondingdistancebetweentwopoints,knownasthelead,fromFigure7-5showsthattherelationshipbetweenthepitchandpitc
7、h:singlethreadP=Ph;multithreadPh=nP(5):threadturningpointsright-handedandleft-handedtwo.Whenturningclockwise,thescrewthreadiscalledtheright-handthread.Whenscrewingcounterclockwise,itiscalledaleft-handthread.Right-handedthreadisoftenusedinengineering.Onlyinternalandexter
8、nalthreadsofthesameshape,diameter,pitch,line,androtationcanbescrewedtogether.Two,theprovisionsofthreaddrawingT
