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1. Machine element design
Introduction

2. Analyze Problem
Designmeanstocreateaplanorsketchofsomethingthatisgoing
tobemadelater,especiallyaplanthatdetailswhatthefinished
thingwilldoandlooklike.
ClassificationsofMachineDesign:Themachinedesignmaybeclassifiedasfollows:
1.Adaptivedesign.Inmostcases,thedesigner’sworkisconcernedwith
adaptationofexistingdesigns.Thistypeofdesignneedsnospecialknowledgeorskilland
canbeattemptedbydesignersofordinarytechnicaltraining.Thedesigneronlymakesminor
alternationormodificationintheexistingdesignsoftheproduct.
2.Developmentdesign.Thistypeofdesignneedsconsiderablescientific
traininganddesignabilityinordertomodifytheexistingdesignsintoanewideaby
adoptinganewmaterialordifferentmethodofmanufacture.Inthiscase,thoughthedesigner
startsfromtheexistingdesign,butthefinalproductmaydifferquitemarkedlyfrom
theoriginalproduct.
3.Newdesign.Thistypeofdesignneedslotofresearch,technicalabilityandcreative
thinking.Onlythosedesignerswhohavepersonalqualitiesofasufficientlyhighordercan
takeuptheworkofanewdesign.

3. Analyze Problem
Designmeanstocreateaplanorsketchofsomethingthatisgoing
tobemadelater,especiallyaplanthatdetailswhatthefinished
thingwilldoandlooklike.
ClassificationsofMachineDesign:Themachinedesignmaybeclassifiedasfollows:
3.Newdesign.Thistypeofdesignneedslotofresearch,technicalabilityandcreative
thinking.Onlythosedesignerswhohavepersonalqualitiesofasufficientlyhighordercan
takeuptheworkofanewdesign.
Thedesigns,dependinguponthemethodsused,maybeclassifiedasfollows:
(a)Rationaldesign.Thistypeofdesigndependsuponmathematicalformulaeofprincipleof
mechanics.
(b)Empiricaldesign.Thistypeofdesigndependsuponempiricalformulaebasedonthe
practiceandpastexperience.
(c)Industrialdesign.Thistypeofdesigndependsupontheproductionaspectsto
manufactureanymachinecomponentintheindustry.

4. Analyze Problem
Designmeanstocreateaplanorsketchofsomethingthatisgoing
tobemadelater,especiallyaplanthatdetailswhatthefinished
thingwilldoandlooklike.
ClassificationsofMachineDesign:Themachinedesignmaybeclassifiedasfollows:
3.Newdesign.Thistypeofdesignneedslotofresearch,technicalabilityandcreative
thinking.Onlythosedesignerswhohavepersonalqualitiesofasufficientlyhighordercan
takeuptheworkofanewdesign.
Thedesigns,dependinguponthemethodsused,maybeclassifiedasfollows:
(d)Optimumdesign.Itisthebestdesignforthegivenobjectivefunctionunderthespecified
constraints.Itmaybeachievedbyminimizingtheundesirable
effects.
(e)Systemdesign.Itisthedesignofanycomplexmechanicalsystemlikeamotorcar.
(f)Elementdesign.Itisthedesignofanyelementofthemechanicalsystemlikepiston,
crankshaft,connectingrod,etc.
(g)Computeraideddesign.Thistypeofdesigndependsupontheuseofcomputersystemsto
assistinthecreation,modification,analysisandoptimizationofadesign.

5. Analyze Problem
THEELEMENTOFMACHINEDefinitionofkeyterms
Elementisanelementarypartofmachinethatisproducedwithoutanyassembling
operations.
Machineisatechnicaldeviceinwhichmechanicalmotionsareperformedinorderto
replaceorfacilitatehuman’sphysicalandmentalwork.
Machineisadeviceconsistingofvariouselementsarrangedtogether,soasto
performtheprescribetasktosatisfyhumanneeds.
E.g.:Apump-setisamachineinwhichtheinputiselectricalenergy,thepump-setutilizes
theelectricalenergytoperformtheprescribedtaskofliftingwatertothedesired
location(output).

6. Analyze Problem
THEELEMENTOFMACHINEDefinitionofkeyterms
Elementsaredividedinto:
Simple(screws,nuts,keys,ball,etc.)
Elaborateinshape(crankshaft,gearbox,toothedwheel,etc.)
Subassemblyisacombinationofassemblyunitsandelementswhichperformthe
identicalfunctions(bearings,clutches,speedreducers).
Serviceabilityisabilityofanelementormachinetoperformitsfunctionaccording
tospecifications.

7. Analyze Problem
Machineelementdesign

8. Analyze Problem
GeneralapplicationofMachineelement
1.Machineelementsusedforholdingthecomponents:-Thesetypeofmachine
elementsincludenutsandbolts,screw,cotters,keys,couplings,pins,revettes.
2.Machineelementsusedfortransmittingthepower:-Machineelementslikegears,
shafts,clutchesandbrakes,pulleys,belts,chain,sprocket,areusedtotransmit
powerfromoneplacetoanother.
3.Machineelementsusedforsupportofothercomponents:-Machineelementslike
bearings,axles,brackets,hangersetc.areusedtogivesupporttorotatingor
stationarymembers.

9. Analyze Problem
GeneralapplicationofMachineelement
TRANSMISSIONS SYSTEM
Transmissionis a mechanism intended to transmit power from the prime mover (an
engine or a motor) to the driven machine.

10. Analyze Problem
GeneralapplicationofMachineelement
CLASSIFICATION OF TRANSMISSIONS
Transmissionbyfriction:apowertransmissionsystemutilizingasetoffrictiongearsso
arrangedthatvaryingtheirpositionsrelativetooneanothergivesawiderangeofspeed
ratios.
Africtiondriveorfrictionengineisatypeoftransmissionthatutilizestwowheelsinthetransmission
totransferpowerfromtheenginetothedrivingwheels.Thesystemisinherentlyacontinuously
variabletransmission;byadjustingthepositionsofthetwodisks,theoutputratiochanges
continuously.

11. GeneralapplicationofMachineelement
CLASSIFICATION OF TRANSMISSIONS
Forexample,inamanualtransmissionsystemforavehicle,engagementreferstothe
connectionofgearswhenthedriverselectsaspecificgearusingthegearshifter.This
engagementallowspowertobetransmittedfromtheenginetothewheels,determiningthe
speedanddirectionofthevehicle.

12. GeneralapplicationofMachineelement
CLASSIFICATION OF TRANSMISSIONS
Theefficiencyandeffectivenessofatransmissionsystemwithdirectcontactdependon
thedesign,materials,andlubricationusedtominimizewearandensuresmoothoperation.
Itcontrastswithsystemsthatuseindirectmethodslikefluidcouplingsor
electromechanicalsystemswherethereisnodirectphysicalcontactbetweentransmission
components.

13. GeneralapplicationofMachineelement
CLASSIFICATION OF TRANSMISSIONS
Transmissionbyflexibleconnectiontypicallyreferstoamethodoftransferringpoweror
motionbetweentwocomponentsusingflexibleelements.Unlikerigidconnections,
flexibleconnectionsallowforsomedegreeofmovement,misalignment,orvibration
isolation.Therearevarioustypesofflexibleconnections,eachsuitablefordifferent
applications.Somecommonexamplesinclude:
Fastenings These type of machine elements include nuts and bolts, screw, cotters, keys,
couplings, pins, revettes are used for holding the components.

14. MachineElementDesign
Classification of Engineering Materials
Theengineeringmaterialsaremainlyclassifiedas:
Metalsandtheiralloys,suchasiron,steel,copper,aluminum,etc.
Non-metals,suchasglass,rubber,plastic,etc.
Metalsandnonmetalsaretwobroadcategoriesofelementsontheperiodictable,and
theyexhibitdistinctcharacteristics.Herearesomekeydifferencesbetweenmetalsand
nonmetals:
PhysicalProperties:
Metals:Typicallyhaveashiny,lustrousappearance.Theyaregoodconductorsofheat
andelectricity.Metalsareusuallysolidatroomtemperature(withtheexceptionof
mercury)andaremalleable(canbehammeredintothinsheets)andductile(canbe
drawnintowires).
Nonmetals:Oftenhaveadullappearance.Theyaregenerallypoorconductorsofheat
andelectricity.Nonmetalscanexistinvariousstatesatroomtemperature(solid,liquid,
orgas)andareoftenbrittle.
StateatRoomTemperature:
Metals:Mostmetalsaresolidsatroomtemperature.Mercuryisanexception,beinga
metalthatisliquidatroomtemperature.
Nonmetals:Nonmetalscanexistinvariousstatesatroomtemperature.Forexample,
oxygenandnitrogenaregases,bromineisaliquid,andsulfurisasolid.

15. MachineElementDesign
Classification of Engineering Materials
Theengineeringmaterialsaremainlyclassifiedas:
MalleabilityandDuctility:
Metals:Metalsaremalleable(canbehammeredorrolledintosheets)andductile(can
bedrawnintowires).Thesepropertiesarisefromtheabilityofmetalatomstoslidepast
eachother.
Nonmetals:Nonmetalsaregenerallynotmalleableorductile.Theytendtobebrittle
andcanbreakorshatterwhensubjectedtostress.
ElectricalConductivity:
Metals:Metalsaregoodconductorsofelectricityduetothepresenceoffreeelectrons
thatcanmoveeasilythroughthemetallattice.
Nonmetals:Nonmetalsaregenerallypoorconductorsofelectricity.Theymaybecome
conductiveundercertainconditions,butthisconductivityisusuallymuchlowerthan
thatofmetals.
ChemicalProperties:
Metals:Tendtoloseelectronsandformpositivelychargedions(cations)inchemical
reactions.Theyoftenreactwithacidstoproducehydrogengas.
Nonmetals:Tendtogainelectronsandformnegativelychargedions(anions)in
chemicalreactions.Theymayreactwithmetalstoformioniccompoundsorwithother
nonmetalstoformcovalentcompounds.

16. MachineElementDesign
Classification of Engineering Materials
Density:
Metals:Generallyhavehighdensities.
Nonmetals:Generallyhavelowerdensitiescomparedtometals.
The metals may be further classified as:
(a)Ferrous metals, and (b) Non-ferrous metals.
The primary distinction between ferrous metals and nonferrous metals lies in the presence of
iron.Here are the key differences between ferrous metals and nonferrous metals:
Composition:
FerrousMetals:Containironasasignificantcomponent.Commonexamplesincludeiron,
steel,andcastiron.Stainlesssteel,whichcontainsironbutalsoincludeschromiumand
nickel,isalsoconsideredferrous.
NonferrousMetals:Donotcontainironasamajorcomponent.Examplesincludealuminum,
copper,lead,zinc,andpreciousmetalssuchasgoldandsilver.

17. MachineElementDesign
Calculation of loads applied on machine part.

18. MachineElementDesign
Calculation of loads applied on machine part.
Hooke'sLawisafundamentalprincipleinphysicsandmaterialssciencethatdescribes
thebehaviorofelasticmaterials,particularlyinthecontextofstretchingor
compressing.Thelawisnamedafterthe17th-centuryEnglishscientistRobertHooke,
whofirstformulatedit.

19. MachineElementDesign
Calculation of loads applied on machine part.
Hooke'sLawisafundamentalprincipleinphysicsandmaterialssciencethatdescribes
thebehaviorofelasticmaterials,particularlyinthecontextofstretchingor
compressing.Thelawisnamedafterthe17th-centuryEnglishscientistRobertHooke,
whofirstformulatedit.Hooke'sLawcanbestatedmathematicallyas:
F=−k⋅ΔL
Hooke'sLawiscommonlyappliedtothebehaviorofspringsandelasticmaterials,butit
alsoservesasastartingpointforunderstandingthemechanicalpropertiesofmaterialsin
general.ItisimportanttonotethatHooke'sLawhaslimitationsandmaynotaccurately
describethebehaviorofmaterialsunderextremeconditionsorbeyondtheirelasticlimits.

20. MachineElementDesign
Application of machine parts
DESIGNOFPOWERSCREW
Powerscrewisamechanicaldeviceusedtoconvertrotarymotionintolinearmotioninorder
totransmitpower.Powerscrewsareusedtoobtainhighmechanicaladvantage.Unlike
thethreadedfastenerswhichareusedtoclampthemachinemembers,powerscrews
areusedtotransmitpower.
Apowerscrewisamechanicaldevicethatconvertsrotarymotionintolinearmotionandvice
versa.Itconsistsofathreadedshaft(screw)andamatingnut,anditsdesignallowsforthe
efficienttransmissionofpowerandmotion.Powerscrewsarecommonlyusedinvarious
engineeringapplications,suchasinmachinery,automotivesystems,andmanufacturing
equipment.
Common applications of power screws are:
Screw jacks: to move large loads with minimum effort.
Lead screw of lathe: for axial movement of tool and its precise positioning.
Tensile testing machine: to exert large force.
Vice: to clamp the work piece
Power screw comprises of two main components: screw and nut, and can operate in
following three ways

21. MachineElementDesign
Application of machine parts
DESIGNOFPOWERSCREW
Power screw comprises of two main components: screw and nut, and can operate in
following three ways:
Screw rotates in bearings and nut moves axially
Screw rotates and also moves axially while nut is kept fixed
Nut rotates and screw moves in axial direction
Summary:Powerscrewshavelargeloadcarryingcapacity,arecompact,providelarge
mechanicaladvantage,provideveryaccurateandpreciselinearmotion,havesmoothand
noiselessoperation,arereliableandhavelessercost.Disadvantagesarethatpower
screwshavepoorefficiencyandhighrateofwear.

22. MachineElementDesign
Application of machine parts
TypesofScrewThreadsusedforPowerScrews
Squarethread:isadaptedforthetransmissionofpowerineitherdirection.Thisthread
resultsinmaximumefficiencyandminimumradialorburstingpressureonthenut.The
squarethreadsareemployedinscrewjacks,pressesandclampingdevices.
Trapezoidalthread:isamodificationofsquarethread.Theslightslopegiventoits
sideslowerstheefficiencyslightlythansquarethreadanditalsointroducesome
burstingpressureonthenut,butincreasesitsareainshear.Itisusedwhereasplitnutis
requiredandwhereprovisionismadetotakeupwearasintheleadscrewofalathe.
Buttressthread:isusedwhenlargeforcesactalongthescrewaxisinonedirection
only.Thisthreadcombinesthehigherefficiencyofsquarethreadandtheeaseof
cuttingandtheadaptabilitytoasplitnutofacmethread.Itisstrongerthanotherthreads
becauseofgreaterthicknessatthebaseofthethread.Thebuttressthreadhaslimitedusefor
powertransmission.Itisemployedasthethreadforlightjackscrewsandvices.
(a) Square thread (b) Trapezoidal tread (c) Buttress tread

23. MachineElementDesign
Application of machine parts
MultipleThreads:Thepowerscrewswithmultiplethreadssuchasdouble,tripleetc.are
employedwhenitisdesiredtosecurealargeleadwithfinethreadsorhighefficiency.Such
typeofthreadsareusuallyfoundinhighspeedactuators.
Types of Screw Threads used for Power Screws

24. MachineElementDesign
Application of machine parts
TorqueRequiredtoRaiseLoadbySquareThreadedScrews
Thetorquerequiredtoraisealoadbymeansofsquarethreadedscrewmaybedetermined
byconsideringascrewjackasshowninFig.(a).Theloadtoberaisedorloweredisplaced
ontheheadofthesquarethreadedrodwhichisrotatedbytheapplicationofaneffortatthe
endofleverforliftingorloweringtheload.

25. MachineElementDesign
Application of machine parts
TorqueRequiredtoRaiseLoadbySquareThreadedScrews
Alittleconsiderationwillshowthatifonecompleteturnofascrewthreadbeimaginedtobe
unwound,fromthebodyofthescrewanddeveloped,itwillformaninclinedplaneasshown
inFig.(a).
From the geometry of the Fig. (a), we find that

26. MachineElementDesign
TorqueRequiredtoRaiseLoadbySquareThreadedScrews

27. MachineElementDesign
TorqueRequiredtoRaiseLoadbySquareThreadedScrews
Whentheaxialloadistakenupbyathrustcollarasshowninbelow,sothattheload
doesnotrotatewiththescrew,thenthetorquerequiredtoovercomefrictionatthe
collar,
CollarCommonlyfoundinpowertransmissionapplications,shaftcollarsarering-shaped
plasticormetaldevicesthatclamparoundashaft.Thepurposeofthecollarisusuallyto
holdmotorcomponents,gearassemblies,sprockets,bearings,andotherpartsinplaceand
sometimesfacilitatetheirpropermovement.

28. MachineElementDesign
TorqueRequiredtoRaiseLoadbySquareThreadedScrews
Where:
:outside and inside radius of collar
IfaneffortP1isappliedattheendofaleverofarmlengthl,thenthetotaltorquerequired
toovercomefrictionmustbeequaltothetorqueappliedattheendoflever,i.e.

29. MachineElementDesign
TorqueRequiredtoRaiseLoadbySquareThreadedScrews

30. MachineElementDesign
TorqueRequiredtolowerLoadbySquareThreadedScrews
Alittleconsiderationwillshowthatwhentheloadisbeinglowered,theforceoffriction
(F=µ.RN)willactupwards.Alltheforcesactingonthebodyareshown
Resolving the forces along the plane,

31. MachineElementDesign
TorqueRequiredtolowerLoadbySquareThreadedScrews
Torque required to overcome friction between the screwand nut,
Efficiency of Square Threaded Screws
Theefficiencyofsquarethreadedscrewsmaybedefinedastheratiobetweentheidealeffort
(i.e.theeffortrequiredtomovetheload,neglectingfriction)totheactualeffort(i.e.theeffort
requiredtomovetheloadtakingfrictionintoaccount).
Theeffortappliedatthecircumferenceofthescrewtoliftthe
loadis
Note that If there would have been no friction between the screw and the nut, then φ will be
equal to zero.

32. MachineElementDesign
TorqueRequiredtoraiseLoadbySquareThreadedScrews
This shows that the efficiency of a screw jack, is independent of the load raised.
In the above expression for efficiency, only the screw friction is considered. However, if
the screw friction and collar friction is taken into account, then

33. MachineElementDesign
TorqueRequiredtoraiseLoadbySquareThreadedScrews
Note that : The efficiency may also be defined as the ratio of mechanical advantage to the
velocity ratio.
We know that mechanical advantage,

34. MachineElementDesign
TorqueRequiredtoraiseLoadbySquareThreadedScrews
Maximum Efficiency of a Square Threaded Screw
Multiplying the numerator and denominator by 2, we have,

35. MachineElementDesign
OverHaulingandSelfLockingScrews
The effort required at the circumference of the screw to lower the load is
Intheaboveexpression,ifφ<α,thentorquerequiredtolowertheloadwillbenegative.In
otherwords,theloadwillstartmovingdownwardwithouttheapplicationofanytorque.
Suchaconditionisknownasoverhaulingofscrews.Ifhowever,φ>α,thetorquerequired
tolowertheloadwillbepositive,indicatingthataneffortisappliedtolowertheload.Such
ascrewisknownasselflockingscrew.Inotherwords,ascrewwillbeselflockingifthe
frictionangleisgreaterthanhelixangleorcoefficientoffrictionisgreaterthantangentof
helixanglei.e.µortanφ>tanα.

36. MachineElementDesign
EfficiencyofSelfLockingScrews

37. End