严肃党内政治生活,永葆先进性纯洁性

F4vTq-news 发布时间: 2020-07-07 05:33:34

“优秀员工分享工作经验”

Itisnowproposedtoreviewthestandardtoolsofafittingshop,noticingthegeneralprinciplesoftheirconstructionandespeciallyoftheiroperation;notbydrawingsnordescriptionstoshowwhatalatheoraplaningmachineis,norhowsomeparticularengineerhasconstructedsuchtools,butupontheplanexplainedintheintroduction,presumingthereadertobefamiliarwiththenamesandpurposesofstandardmachinetools.Ifhehasnotlearnedthismuch,anddoesnotunderstandthenamesandgeneralobjectsoftheseveraloperationscarried[121]oninafittingshop,heshouldproceedtoacquainthimselfthusfarbeforetroublinghimselfwithbooksofanykind.

Incastingandforgingoperationsthematerialistreatedwhileinaheatedandexpandedcondition;thenatureoftheseoperationsissuchthataccuratedimensionscannotbeattained,sothatbothforgingsandcastingsrequiretobemadeenoughlargerthantheirfinisheddimensionstoallowforshrinkageandirregularities.Finishingasaprocessconsistsincuttingawaythissurplusmaterial,andgivingaccuratedimensionstothepartsofmachinerywhenthematerialisatitsnaturaltemperature.Finishingoperationsbeingperformedassaiduponmaterialatitsnormaltemperaturepermitshandling,gaugingandfittingtogetherofthepartsofmachinery,andasnearlyallotherprocessesinvolveheating,finishingmaybecalledthecoldprocessesofmetalwork.Theoperationsofafittingshopconsistalmostentirelyofcutting,andgrindingorabrading;apropositionthatmayseemnovel,yettheseoperationscomprehendnearlyallthatisperformedinwhatiscalledfitting.

Artisticdrawingisaddressedtothesenses,geometricaldrawingisaddressedtotheunderstanding.Geometricaldrawingmay,however,includeartisticskillnotinthewayofornamentation,buttoconveyanimpressionofneatnessandcompleteness,thathasbycommoncustombeenassumedamongengineers,andwhichconveystothemindanideaofcompetentconstructioninthedrawingitself,aswellasofthemachinerywhichisrepresented.Artisticeffect,sofarasadmissibleinmechanicaldrawing,iseasytolearn,andshouldbeunderstood,yetthroughadesiretomakepictures,abeginnerisoftenledtoneglectthatwhichismoreimportantinthewayofaccuracyandarrangement.

CHAPTERII.MECHANICALENGINEERING.

Thisprincipleissomewhatobscure,andthenatureofpercussiveforcesnotgenerallyconsidered—amatterwhichmaybeillustratedbyconsideringtheactionofasimplehand-hammer.Few[103]people,inwitnessingtheuseofahammer,orinusingonethemselves,everthinkofitasanenginegivingouttonsofforce,concentratingandapplyingpowerbyfunctionswhich,ifperformedbyothermechanism,wouldinvolvetrainsofgearing,levers,orscrews;andthatsuchmechanism,ifemployedinsteadofahammer,mustlackthatimportantfunctionofapplyingforceinanydirectionasthewillandhandsmaydirect.Asimplehand-hammerisintheabstractoneofthemostintricateofmechanicalagents—thatis,itsactionismoredifficulttoanalysethanthatofmanycomplexmachinesinvolvingtrainsofmechanism;yetourfamiliaritywithhammerscausesthisfacttobeoverlooked,andthehammerhasevenbeendeniedaplaceamongthosemechanicalcontrivancestowhichtherehasbeenappliedthenameof"mechanicalpowers."

Thefirstoftheseoperationsincludesallthreadingprocessesperformedonlathes,whetherwithasingletool,bydiescarriedpositivelybysliderests,orbymilling.

1.Themosteconomicalandeffectualmechanismforhandlingisthatwhichplacestheamountofforceandrateofmovementcontinuallyunderthecontrolofanoperator.

Steamandothermachineryappliedtothetransportofmaterialandtravel,innavigationandbyrailways,comprisesthegreatershareofwhatmaybecalledengineeringproducts;andwhenweconsiderthatthisvastinterestofsteamtransportislessthanacenturyold,andestimateitspresentandpossiblefutureinfluenceonhumanaffairs,wemayrealisetherelationthatmechanicalsciencebearstomoderncivilisation.

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  • 雨花郡主zSlx0

    Nextinorderarestrains.Asthecuttingactionisthesourceofstrains,andastheresistanceofferedbythecuttingtoolsisasthelengthorwidthoftheedges,itwillbefoundinthepresentcasethatwhileotherconditionsthusfarhavepointedtosmallproportions,thereisnowanewonewhichcallsforlargeproportions.Indisplacingthemetalbetweenteethofthree-quartersofaninchpitch,thecuttingedgeortheamountofsurfaceacteduponisequaltoawidthofoneinchandahalf.Itistrue,thedisplacementmaybesmallateachcut,butthestrainisrathertobebaseduponthebreadthoftheactingedgethantheactualdisplacementofmetal,andwefindherestrainsequaltotheaveragedutyofalargeplaningmachine.Thisstrainradiatesfromthecuttingpointasfromacentre,fallingonthesupportsoftheworkwithatendencytoforceitfromtheframing.Betweentherackandthecrank-shaftbearing,throughthemediumofthetool,cutterbar,connection,andcrankpin,andinvariousdirectionsanddegrees,thisstrainmaybefollowedbymeansofasimplediagram.Besidesthiscuttingstrain,therearenoneofimportance;thetensionofthebelt,thesidethrustinbearings,thestrainfromtheangularthrustofthecrank,andtheendthrustofthetool,althoughnottobelostsightof,neednothavemuchtodowithproblemsofstrength,proportion,andarrangement.

     CHAPTERXV.PNEUMATICMACHINERYFORTRANSMITTINGPOWER.

  • 雪灵芝icwlN

  • 如萱紫儿DXonC

    Asremarked,everyattempttogenerateanythingnewinmachineryshouldbecommencedbyascertainingawantofimprovement.Whensuchawanthasbeenascertained,attentionshouldbedirectedfirsttotheprinciplesuponwhichsuchwantorfaultistoberemedied.Propermechanismcanthenbesuppliedlikethemissinglinksinachain.Propositionsthusstatedmayfailtoconveythemeaningintended;thissystematicplanofinventingmaybebetterexplainedbyanexample.

  • 但法国rUtnM

    Theeyefailstodetectvariationsinsize,evenbycomparison,longbeforewereachthenecessaryprecisionincommonfitting.Evenbycomparisonwithfiguredscalesormeasuringwithrules,thedifferencebetweenaproperandaspoiledfitisnotdiscerniblebysight.

     

  • 大笨蛋goWuo

    v

  • 扒皮成GvToT

    Inusingrulingpens,theyshouldbeheldnearlyvertical,leaningjustenoughtopreventthemfromcatchingonthepaper.Beginnershaveatendencytoholdpensatalowangle,anddragthemontheirside,butthiswillnotproducecleansharplines,norallowthelinestobemadenearenoughtotheedgesofsquarebladesorsetsquares.

     Second.Inamachinewheretwoormoreoperationsarecombined,thecapacityofsuchamachineisonlyasasingleoneoftheseoperations,unlessmorethanonecanbecarriedonatthesametimewithoutinterferingonewithanother.

  • 草莓果gZCVL

    1.Aconceptionofcertainfunctionsinamachine,andsomedefiniteobjectwhichitistoaccomplish.

     MillingtoolsareemployedatCreweforroughingouttheslotsinlocomotivecrankaxles.Anumberofdetachabletoolsaremountedonastrongdisc,sothatfourtosixwillactatonetime;inthiswaythedisplacementexceedswhatalathecanperformwhenactingcontinuouslywithtwotools.Rotaryplaningmachinesconstructedonthemillingprinciple,havebeentriedforplanesurfaces,butwithindifferentsuccess,exceptforroughwork.

  • 绿卡纸yft87

    Thesubjectofsteam-power,asidefromitsmechanicalconsideration,isonethatmayaffordmanyusefullessons,bytracingitshistoryandinfluence,notonlyuponmechanicalindustry,butuponhumaninterestsgenerally.Thissubjectisoftentreatedof,andbothitsinterestandimportanceconceded;butnoonehas,sofarasIknow,fromstatisticalandothersources,venturedtoestimateinamethodicalwaythechangesthatcanbetraceddirectlyandindirectlytosteam-power.

     Betweenarunningmotionofthedies,orarunningmotionoftheblanks,therearethefollowingpointswhichmaybenoticed.

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