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外文翻译1LATHESANDGRINDINGLathesaremachinetoolsdesignedprimarilytodoturning,facingandboring.Verylittleturningisdoneonothertypesofmachinetools,andnonecandoitwithequalfacility.Becauselathealsocandodrillingandreaming,theirversatilitypermitsseveraloperationstobedonewithasinglesetupoftheworkpiece.Theaccountsforthefactthatlathesofvarioustypesaremorewidelyusedinmanufacturingthananyothermachinetool.Lathesinvariousformshaveexistedformorethantwothousandyears.Modernlathesdateformabout1797,whenHenryMaudsleydevelopedonewithaleadscrew.Itprovidedcontrolled,mechanicalfeedofthetool.ThisingeniousEnglishmanalsodevelopedachange-gearsystemthatcouldconnectthemotionofthespindleandleadscrewandthusenablethreadstobecut.LatheConstruction.Theessentialcomponentsofalathearethebed,headstockassembly,tailstockassembly,carriageassembly,quick-changegearbox,andtheleadscrewandfeedrod.Thebedisthebackboneofalathe.Itusuallyismadeofwell-normalizedoragedgrayornodularcastironandprovidesaheavy,rigidframeonwhichalltheotherbasiccomponentsaremounted.Twosetsofparallel,longitudinalway,innerandouter,arecontainedonthebed,usuallyontheupperside.SomemakersuseaninvertedV-shapeforallfourways,whereasothersutilizeone外文翻译2invertedVandoneflatwayinoneorbothsets.Becauseseveralothercomponentsaremountedand/ormoveonthewaystheymustbemadewithprecisiontoaccuracyofalignment.Similarly,properprecautionshouldbetakeninoperatingalathetoassurethatthewaysarenotdamaged.Anyinaccuracyinthemusuallymeansthattheaccuracyoftheentirelatheisdestroyed.Thewaysonmostmodernlathesaresurfacehardenedtooffergreaterresistancetowearandabrasion.Theheadstockismountedinafixedpositionontheinnerwaysatoneendofthelathebed.Itprovidesapoweredmeansofrotatingtheworkatvariousspeeds.Itconsists,essentially,ofahollowspindle,mountedinaccuratebearings,andasetoftransmissiongear——similartoatrucktransmission——throughwhichthespindlecanberotatedatanumberofspeeds.Mostlathesprovidefromeighttoeighteenspeeds,usuallyinageometricratio,andmodernlathesallthespeedscanbeobtainedmerelybyfromtwotofourlevers.Anincreasingtrendistoprovidetocontinuouslyvariablespeedrangethroughelectricalormechanicaldrives.Becausetheaccuracyofalatheisgreatlydependentonthespindle,itisofheavyconstructionandmountedinheavybearings,usuallypreloadedtaperedrollerorballtapes.Alongitudinalholeextendsthroughthespindlesothatlongbarstockcanbefedthroughit.Thesizeofthisholeisanimportantsizedimensionofalathebecauseitdeterminesthemaximumsizeofbarstockthatcan外文翻译3bemachinedwhenthematerialmustbefedthroughthespindle.Theinnerendofthespindleprotrudesfromthegearboxandcontainsameansformountingvarioustypesofchucks,faceplates,anddogplatesonit.Whereassmalllathesoftenemployathreadedsectiontowhichthechucksarescrewed,mostlargelathesutilizeeithercam-lockorkey-drivetapernoses.Theseprovidealarge-diametertaperthanassurestheaccuratealignmentofthechuck,andamechanismthatpermitsthechuckorfaceplatetobelockedorunlockedinpositionwithoutthenecessityofhavingtorotatetheseheavyattachments.PowerissuppliedtothespindlebymeansofanelectricmotorthroughaV-beltorsilent-chaindrive.Mostmodernlatheshavemotorsoffrom5to15horsepowertoprovideadequatepowerforcarbideandceramictoolsattheirhighcuttingspeeds.Thetailstockassemblyconsists,essentially,ofthreeparts.Alowercastingfitsontheinnerwaysofthebedandcanslidelongitudinallythereon,withameansforclampingtheentireassemblyinanydesiredlocation.Anuppercastingfitsontheloweroneandcanbemovedtransverselyuponitontypeofkeyedways.Thistransversemotionpermitsaligningthetailstockandheadstockspindlesandprovidesamethodofturningtapers.Thethirdmajorcomponentoftheassemblyisthetailstockquill.Thisisahollowsteelcylinder,usuallyabout2to3inchesindiameter,thatcanbemovedseveralincheslongitudinallyinandoutoftheuppercasting外文翻译4bymeansofahandwheelandscrew.TheopenendofthequillholeterminatesinaMorsetaperinwhichalathecenter,orvarioustoolsasdrills,canbeheld.Agraduatedscale,severalinchesinlength,usuallyisengravedontheoutsideofthequilltoaidincontrollingitsmotioninandoutoftheuppercasting.Alockingdevicepermitsclampingthequillinanydesiredposition.Thecarriageassemblyprovidesthemeansformountingandmovingcuttingtools.ThecarriageisarelativelyflatH-shapedcastingthatrestsandmovesontheoutersetofwaysonthebed.Thetransversebarofthecarriagecontainswaysonwhichthecrossslideismountedandcanbemovedbymeansofafeedscrewthatiscontrolledbyasmallhandwheelandagraduateddial.Throughthecrossslideameansisprovidedformovingthelathetoolinthedirectionnormaltotheaxisofrotationofthework.Onmostlathesthetoolpostactuallyismountedoncompoundrest.Thisconsistsofabase,whichismountedonthecrossslidesothatitcanbepivotedaboutaverticalaxis,andanuppercasting.Theuppercastingismountedonwaysonthisbasesothatitcanbemovedbackandforthandcontrolledbymeansofashortleadscrewoperatedbyahandwheelandacalibrateddial.Manualandpoweredmotionforthecarriage,andpoweredmotionforthecarriage,andpoweredmotionforthecrossslide,isprovidedbymechanismswithintheapron,attachedtothefrontofthecarriage.Manualmovementofthecarriagealongthebedis外文翻译5effectedbyturningahandwheelonthefrontoftheapr