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gR8Wu-news 发布时间: 2020-07-12 02:03:42

“幸运飞艇聊天室安卓”Theadvantagesgainedbymilling,asstated,arespeed,duplication,andaccuracy;thedisadvantagesaretheexpenseofpreparingtoolsandtheirperishability.

Thedifferencebetweenhowmachineryisconstructedandwhyitissoconstructed,isawideone.Thisdifferencethereadershouldkeepinmind,becauseitistothesecondquerythatthepresentworkwillbemainlyaddressed.Therewillbeanattempt—animperfectone,nodoubt,insomecases—todeducefrompracticethecauseswhichhaveledtocertainformsofmachines,andtotheordinaryprocessesofworkshopmanipulation.Inthemindofalearner,whetherapprenticeorstudent,thestrongesttendencyistoinvestigatewhycertainproportionsandarrangementarerightandotherswrong—whytheoperationsofaworkshopareconductedinonemannerinsteadofanother?Thisisthenaturalhabitofthought,andthenaturalcourseofinquiryandinvestigationisdeductive.Millingrelatestometalcuttingwithserratedrotarycutters,anddiffersinmanyrespectsfromeitherplaningorturning.Themovementofthecuttingedgescanbemorerapidthanwithtoolswhichactcontinuously,becausetheedgesarecooledduringtheintervalsbetweeneachcut;thatis,ifamillingtoolhastwentyteeth,anysingletoothoredgeactsonlyfromafifteenthtoatwentiethpartofthetime;andasthecuttingdistanceortimeofcuttingisrarelylongenoughtogeneratemuchheat,thespeedofsuchtoolsmaybeone-halfgreaterthanforturning,drilling,orplaningtools.Anotherdistinctionbetweenmillingandothertoolsistheperfectandrigidmannerinwhichthecuttingedgesaresupported;theyareshortandblunt,besidesbeingusuallycarriedonshortrigidmandrils.Aresultofthisrigidsupportofthetoolsisseeninthelengthofthecuttingedgesthatcanbeemployed,whicharesometimesfourinchesormoreinlength.Itistruetheamountofmaterialcutawayinmillingismuchlessthantheedgemovementwillindicatewhencomparedwithturningorplaning;yetthedisplacingcapacityofamillingmachineexceedsthatofeitheralatheoraplaningmachine.Theoreticallythecuttingordisplacingcapacityofanymetalorwoodcuttingmachine,isasthelengthoftheedgesmultipliedintothespeedoftheircuttingmovement;arulewhichappliesveryuniformlyinwoodcutting,andalsoinmetalcuttingwithincertainlimits;butthestrainsthatariseinmetalcuttingaresogreatthattheymayexceedallmeansofresistingthemeitherinthematerialactedupon,orinthemeansofsupportingtools,sothatthelengthofcuttingedgesislimited.InturningchilledrollsatPittsburg,[141]toolstosixincheswideareemployed,andtheeffectproducedisasthelengthoftheedge;butthedepthofthecutisslight,andtheoperationisonlypossiblebecauseoftheextremerigidityofthepiecesturned,andthetoolsbeingsupportedwithoutmovablejointsasincommonlathes.

Thismakesastatementinbriefofwhatcomprehendsaknowledgeofpattern-making,andwhatmustbeunderstoodnotonlybypattern-makers,butalsobymechanicalengineerswhoundertaketodesignmachineryormanageitsconstructionsuccessfully.

(1.)Whatshoulddeterminethesocialrankofindustrialcallings?—(2.)Whyhavethephysicalsciencesandmechanicartsachievedsohonourableaposition?—(3.)Howmaythegeneralobjectoftheengineeringartsbedescribed?—(4.)Whatisthedifferencebetweenscienceandartasthetermsaregenerallyemployedinconnectionwithpracticalindustry?

Inrespecttorepairingalone,theconsiderationofhavingthepartsofmachineryfittedtostandardsizesisoftenequaltoitswholevalue.

Chuck-boringisemployedinthreecases;forholesofshallowdepth,taperholes,andholesthatarescrew-threaded.Aspiecesareoverhunginlathe-boringthereisnotsufficientrigidityneitherofthelathespindlenorofthetoolstoadmitofdeepboring.Thetoolsbeingguidedinastraightline,andcapableofactingatanyangletotheaxisofrotation,thefacilitiesformakingtaperedholesarecomplete;andasthetoolsarestationary,andmaybeinstantlyadjusted,thesameconditionsanswerforcuttinginternalscrew-threads;anoperationcorrespondingtocuttingexternalscrews,exceptthatthecrossmotionsofthetoolslidearereversed.

Forpulleys,gearwheels,orotherstandardpartsofmachinerywhicharenotlikelytobemodifiedorchanged,ironpatternsarepreferable;patternsforgearwheelsandpulleys,whenmadeofwood,asidefromtheirliabilitytospringandwarp,cannotbemadesufficientlystrongtowithstandfoundryuse;besides,thegreatestaccuracythatcanbeattained,evenbymetalpatterns,isfarfromproducingtruecastings,especiallyfortoothwheels.Themoreperfectpatternsare,thelessrappingisrequiredindrawingthem;andthelessrappingdone,themoreperfectcastingswillbe.

Aninterestingstudyinconnectionwithmodernshapingmachinesistheprincipleofvariousdevicescalled'quickreturn'movements.Suchdevicesconsistofvariousmodificationsofslottedlevers,andwhatisknownasWhitworth'squickreturnmotion.

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网友评论

  • 雨花郡主diqL7

     

  • 雪灵芝0SltZ

  • 如萱紫儿KjSph

  • 但法国ZvEbP

    Thisimportanceofshopprocessesinmachineconstructionisgenerallyrealisedbyproprietors,butnotthoroughlyunderstoodinallofitsbearings;anapprenticemaynoticethecontinualeffortthatismadetoaugmenttheproductionofengineering-works,whichisthesamethingasshorteningtheprocesses.

     

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  • 扒皮成5ldXs

    Allthesethingsconstitutetechnicalknowledge,andtheprivilegeoftheiracquirementisanelementofvalue.Thecommonviewtakenofthematter,however,isthatitcostsnothingforamastertoaffordtheseprivileges—theworkmustatanyratebecarriedon,andisnotretardedbybeingwatchedandlearnedbyapprentices.Viewedfromanypoint,theprivileges[22]ofengineeringestablishmentshavetobeconsideredasanelementofvalue,tobeboughtataprice,justasatonofironoracertainamountoflabouris;andinacommercialsense,asanexchangeableequivalentforlabour,material,ormoney.Inreturnamasterreceivestheunskilledlabourorserviceofthelearner;thisserviceispresumedtobegivenatareducedrate,orsometimeswithoutcompensation,fortheprivilegesoftheworksandtheinstructionreceived.

     

  • 草莓果yYsoE

    (1.)Whyaremachineframesconstructedinsections,insteadofbeinginonepiece?—(2.)Whymustpartswhichhavecontactonoppositesideshavespecificdimensions?—(3.)WhatarestandardsofmeasurebaseduponinEngland,America,andFrance?—(4.)Howcanweightbemeasuredbytime?—(5.)HastheFrenchmetreprovedastandardadmittingoftestreference?

     Itisneverenoughtoknowthatanypieceofworkiscommonlyconstructedinsomeparticularmanner,orthatapropositionisgenerallyacceptedasbeingcorrect;areasonshouldbesoughtfor.Nothingislearned,inthetruesense,untilthereasonsforitareunderstood,anditisbynomeanssufficienttoknowfromobservationalonethatbeltsarebestforhighspeeds,thatgearingisthebestmeansofforminganglesintransmittingpower,orthatgearingconsumesmorepower,andthatbeltsproducelessjarandnoise;theprincipleswhichlieatthebottommustbereachedbeforeitcanbeassumedthatthematterisfairlyunderstood.

  • 绿卡纸EB8km

     Intreatingofmachineryfortransport,asaclass,thesubject,asfarasnoticedhere,willbeconfinedtomovingandhandlingmaterialasoneoftheprocessesofmanufacturing,andespeciallyinconnectionwithmachineconstruction.Iftheamountoftime,expense,labour,andmachinerydevotedtohandlingmaterialinmachineshopsisestimated,itbecomesamatterofastonishmenttoasmanyashavenotpreviouslyinvestigatedthesubject;asanitemofexpensethehandling,oftenexceedsthefittingonlargepieces,andintheheavierclassofworkdemandsthemostcarefulattentiontosecureeconomicalmanipulation.

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