rodney katz - prototype design and manufacturing manual

7/25/2019 Rodney Katz - Prototype Design and Manufacturing Manual

1/64

PROTOTYPEDESIGNAND

MANUFACTURINGMANUAL

DEPARTMENTOF

MECHANICAL

ENGINEERING

RODNEYKATZ, MICHAELLEWIS Rev.0


2/64

PrototypeDesignandManufacturingManual Rev.0

i

TABLEOF CONTENTS

Introduction...................................................1

PARTI Design...............................................2

1 FirstSteptoDesign.............................2

2 Prototyping.........................................3

2.1 ExamplePrototypeDevice..........6

3 TopDownMachining..........................7

4 Alignment!..........................................9

4.1 AlternateMethods....................13

5 Bearings.............................................17

6 Motor................................................17

7 Orings...............................................18

8 PipesandTubes................................21

8.1 Fittingsforpipes........................21

9 Materials...........................................22

9.1 RawMaterials............................22

9.2 Aluminum....Error!Bookmarknot

defined.

9.3 Steel...........................................23

9.4 PVC.............................................23

9.5 Delrin.........................................24

9.6 Plexiglas.....................................25

10 Drawings........................................26

10.1 CommonDrawingmistakes.......27

10.2 Dimensioning............................27

10.3 Tolerances.................................35

10.4 AnilamCNCMill........................35

PartII Manufacturing................................39

1 Posts.................................................39

1.1 ImportantNotesforposts........43

2 CNCMilling.......................................44

2.1 Setupmethods..........................44

3 ORings.............................................48

3.1 AxialOrings..............................48

3.2 RadialOrings............................51

4 DrillingandTapping.........................54

4.1 Tapping......................................54

Appendices.....................................................I

References......................................................I


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INTRODUCTION

The purpose of this manual is to present best practices for the design and

manufacturingofprototypedevices,lowvolumemachinedpartsandassemblies.

Itisimportanttonotethatmanyofthemethodsandtechniquesoutlinedinthemanual

arespecifictotheUVicMech.MachiningFacility.

Figure1.1Mixerdevice

The manual is structured around the design and manufacturing of a single device

(shown above in Figure 1.1) which encompasses many typical characteristics of

mechanicalfeaturesfoundintheDept.MechanicalEngineeringresearchapparatus.

Thisdesign is very efficient tomachine, incorporates inherent alignment,uses stock

materialreadilyavailableinthemachineshopandisfamiliarwiththeshopmachinists.

Themanualwillalsoincludecomparisonexamplesoflesseffectivedesignsofthesame

device.These

methods

are

often

initially

thought

tobeeasier

tofabricate

but

donot

lend thesameadvantagesoftherecommendedsampledesignshownabove

Designmethodologyisaverybroadsubject;thismanualonlycoversthebasics.

Extendedtopicslikehighvolumemanufacturing,rapidprototypingandtechniquesused

outsidetheMech.Eng.Shoparenotcoveredinthismanual.


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2

PARTI DESIGN

1 FIRSTSTEPTO DESIGN

Designofadeviceshouldalwaysbeginwithopeningcommunicationwiththespecific

shoporfacilitywherepartswillbemanufactured.

Thecapabilitiesoftheshoporfacilityneedtobecarefullyconsideredinordertodesign

economicallyfeasibledevices orequipment:

o Machineryandshopspecificexpertise,CNCmilling,lathecapability,sheetmetal

capabilities,welding capabilities,heavymachining,precisiongrinding,waterjet

cutting, EDM,rapidprototyping,etc.)

o Shoppreferredmanufacturingmethodsandmaterials.

o Machine tool (lathe, mill) capacity. What is the largest or smallest size

workpieces and cutting tools the shops machines can comfortably

accommodate.

o Timelinerequiredtodeliverparts.

While inthedesignphase,continuallycommunicatingwithshoppersonnelwillalways

leadtodesignswhicharelessexpensiveandmoreefficienttobuild.

Whenever possible, design parts in inches. The rationale being the machine shops

cuttingtool andmaterialinventoryareintheimperial(inch)system.Designinginmetric

then converting to inches leads toodddimensions thus complicating thedesign and

machiningprocess,resultinginamorecostlyandtimeconsumingpart

Alwayskeep inmind stockmaterial sizeswhendesigningparts.This isparamount to

achievinganeconomicallyfeasibledesign.Oftenthestockmaterialsizewillbesufficient

to accommodate yourdesignwith little additionalmachining required. InCanadawe

stillworkwith stockmaterial sizes in the inch systemasmostofourmaterial comes

fromU.S.suppliers.


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3

2 PROTOTYPING

Generallyprototypepartsshouldincorporatethefollowing:

o InherentAlignment. Partsautomaticallyfitintoplace.Thiseliminatestheneed

forpostmachiningandhandtoolmodificationinordertofitpartstogether.

Bosses and other features should be incorporated in the design to assure

alignmentoffinalassemblies.

o Abilitytobeadjustedwith littlerework.Thiscouldmeanaddingextraholesor

elongating holes for unforeseen additions orwhen youmay feel adjustability

couldberequired.

o Theuseofeasilymachinablemateriali.e aluminum,acetyl(Delrin),PVC(plastic)

whereeverpossible.Eventhoughthesematerialsmaybetwiceorthreetimes

thecostofsteel, their fabricatingandmachiningcostswillbedrastically lower

resultinginalessexpensivepart.

o Reduce thenumberofpartswith tight tolerances (to lower costand increase

machiningefficiency).

o Sizepartswithaconsiderationformaterialyield.E.g.aluminumsheetcomesin

48X96sheets.Ifyourequirefourpieces12X12thiswillresultinmuch

wastematerial. Reconsider the design toworkwith 12 X 12 pieces. Sheet

metaldoesnot consumematerial for cutswhereasplatematerial (3/16and

thicker)willconsumeapproximately3/16percutduetothesawingandclean

upprocess.Platematerial isalso supplied in12 increments.Therefore if four

12X12platesarerequiredthiswillproducealargeamountofexcessmaterial.

Trytoworkthedesignwithpartsizesof11.75X11.75

o Tappedholes#632andlargershouldbedrilledallthewaythroughinmaterials

up to thick ifpossible asopposed toholesdrilled to specificdepths. It is

alwayseasiertotapathroughholeopposedtoablindhole(holethatdoesnot

penetrate). Theholemayonlybetappedpartiallythrough.

o Whendesigningaholeforapressfitdowelpin, incorporateasmallerdiameter

throughholewhichcanbeusedtopushorknockthedowelpinoutifrequired.


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Thiswilloftenbethecase.(SeeFig.2.1below). Ifnothroughhole ispresent it

willbeverydifficulttoremovethedowelpinandremovalmethodswillresultin

damagingthepinandthemaybethehole.

Figure2.1Thruholeinshafttoallowremovalofdowelpin

o

Tabs or marks for realigning parts if they are going to be placed back in a

machine for postmachining operations. This is often the casewhen the part

needsholesalignedtoeachotherfrombothends. Anotherreasonforalignment

markswouldbeorifthepartneedstobeorientedinaspecificrotationalangle

atassemblytime.(SeeFigure2.2).

Figure2.2Circularpartandfixturewithgroovesforrealignment

o Flatson roundparts.Thisallows for thepart tobe replaced intoavisewitha

knownorientationforpostmachiningormodificationsatalaterdatefrom(See

Figure2.3)

DowelpinShaft

Thruholetopushoutdowel

Scratchmarks

forrealignment


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Figure2.3Roundpartwithflatselfalignsinvise

Avoidweldingparts together.Weldingdoesnot allow formajor changes if required.

Separatingpartscanbevery labour intensiveandsometimescloseto impossible. It is

alsoverydifficulttoaccuratelyalignweldedparts.

Design theassemblyofsufficientsizetoavoidworking inconfinedspaces.Alsoavoid

theuseoftinyscrewsi.e. #256andsmaller.

Trytokeepthefastenerthreadtypeselectiontoaminimum.#1032isaverypractical

size for much of the metal work performed in the shop and is easily tapped.

(use a #1024forplastics)

Utiliseasmanyofftheshelfitemsaspossible.Thesewillsavemanyhoursofdesignand

machining work, paying for themselves many times over. Often offtheshelf

componentsmaynotmeetalltherequirementsbutcanbemachinedtoaccommodate

thedesignrequirements.


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2. 1 EXAMPLE PROTOTYPEDEVICE

ThemixerdeviceshowninFigure2.4isthe exampleprototypeassembly.

Keycomponents,whichwillbediscussedinthemanual,arenotedonthediagram.

Figure2.4MixerDevice

Motor

(gearsdrivemainshaft)

Post

NPTThreadedHole

(Cylindersurfaceisspotfaced)

ControlPanel

TopPlate

(Topdownmachined)

NPTandISOFittings

Oringseals

Bearings


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3 TO PDOWNMACHINING

Flat parts (Top and Bottom plate)machined using amanual or CNCmill should be

designed inorderthattheyaremachinedononeortwosidesonly.This iscalledTop

Down. Trytoavoidhavingfeaturesmachinedinthesidesofplates.

o The actual process of cutting material is relatively quick. It is the setup and

positioningof materialandpartsthattakesmajorityofthetime.

o Ifapartcanbesetuponceand thencutwithout rotatingor repositioning the

partmachiningefficiencywillincreaseexponentially.

o Figure 3.1 shows an example of a part which requires multiple setups to

machine.Thispartwillneedtoberepositioned inthevisefourtofivetimesto

drill all the required holes in the sides consumingmuch time and effort. The

more often a part is repositioned (clamped) in the machine the greater the

possibilityofmisalignmentofthefeatures.

o Alsothelonglengthofthispartcreatestwopossibleproblems:

ThemillingmachinebeingusedmaynothavetherequiredtravelintheZ

axisneededtodrilltheendholes(showninthethirdsetupofFigure3.1).

Rememberthedrillchuckisextendsapproximately 3inches,thedia.

drill extends 4 and the part on end extends approximately 6 high,

resultinginaconsumptionof 13ofthemillingmachinesZaxistravel.

Ifthepartismachinedwhileonendthestabilityofthepartmaynotbe

enoughtopreventmaterialflexandresultininaccurateholepositioning.

Thepartclampedonend(Fig3.1C)willalsoaccentuatethedeviationof

the hole positioning ( 0.1degreeoffperpendicularon a 6protruding

clampedpartinthevisewillcauseapositioningerrorofthedrilledhole

by0.010)Trying toensuring thepart isclampedperpendicularby this

amountorbetterisverytimeconsuming).


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Figure3.1MultiplesetupsrequiredforapartthatcannotbemachinedTOPDOWN


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4 ALIGNMENT!

Alignmentofparts and features isoneof themost important aspectsofmechanical

design.

Ifpartsaredesignedwithalignmentinmindatalltimesitwillpreventmuchfrustration

andaddedcostinthefinalassembly.

Figure4.1PostwithendbossesandextraholesinOD

Onebasicmethod toalignparts is tousepostswithbossesonbothends.Figure4.1

showsanexampleofapostwhichincorporatesbossestoaidalignment.

Incorporatingabossoneachsideoftheposthastheaddedadvantageofallowingthe

posttobeheld inthe lathechucksothecritical lengthcanbemeasuredoffthefront

faceofthechuckjaws(the Zdatum).

Theprocedureusedintheshopforaccuratelymachiningthistypeofpostdesignisvery

efficient.

Figure4.2showshowpostswithintegralbossesareusedintheassembly.


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Figure4.2Alignedplatesandpostsassembly

Oncethepartsareassembledthetwoplateswillbealignedsufficientlyinorderthatno

fussingorfiddlingwillberequiredtoattainthedesiredresult.

Thismethod allows theplates tobeefficientlymilledanddrilledTopDownwithone

setup.Norepositioningisrequired.

Thismethod canbe altered to suitmanydifferent applicationswhile stillmaintaining

alignmentofplatefeatures(eg.centreholes,shaftholes,bearingboresetc.):

o

Platescanbedifferentshapesifrequired(Fig.4.3)

o 2or3postscanbeusedinsteadof4(Figure4.3)

o Notallpostsneedtobethesamediameter

o Platethicknessescanbedifferent

ThemachiningprocessforpostsisinPartII Manufacturing,Section1(Page39).


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Figure4.3

3post

design

with

difference

shaped

plates


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Carchassis TappingMachine

Table SubmersibleChassis(fitsintube)

Winch 3postdesign

Figure4.4Examplesofhowpostscanbeused

Figure4.4showsexamplesofhowpostscanbeused.(eg.Carchassis,table,ROV,etc.)


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4. 1 ALTERNATE METHODS

This sectionpresents someof the alternatives tousing roundpostswithbosses.The

alternativesmayappeareasiertofabricatebutareoftenmuchmoretimeconsumingto

machineandassembleandtheydonotincorporateinherentalignmentfeatures.

Figure4.5showsadesignsimilartotherecommendedmethod

o Thesquarepostsaredifficulttomachine.

o Multiplesetupsarerequiredtomachinetheposts.

Figure4.5Plateassemblyusingsquareposts


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Figure4.6andFigure4.7showthetwoplateassemblywithanglebrackets

Anglebracketsareappealingbecausetheyseemsimpletomachine(justcutto length

anddrill).Anoteof caution!Oftenwhatappears simple to fabricate results inbeing

ratherdifficultandcumbersome.Themethod inFigure4.6 isvery timeconsuming to

machine as the top andbottomplates cannotbemachined topdown.A totalof 64

holesmustbedrilled.Halfoftheholesalsoneedtobetappedinthesidesoftheplates.

Figure4.6Plateassemblyusinganglebrackets

Unstable


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Thesecondanglebracketmethoduseswelds.

o This assembly requires16welds . Considerable time is required to setup and

weld.Properalignmentoftheplateswillbevirtuallyimpossibleoftenrequiring

somepostmachiningorhandwork.

o Intermsofprototypingweldingdoesnotallowpartstobeeasilymodified.

Figure4.7Plateassemblyusingweldedanglebrackets

Figure4.8showsaweldedversionofawinchframe.ThewinchinFig4.8wouldtakea

considerableamountof timeandefforttoconstructdueof thenumberofweldsand

therequirementthattheframebeaccuratelyalignedforbearingsblocks.

Figure4.8WeldedWinchFrame


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NOTE:ThereisatimeandplaceforweldingbutinmostassembliesusedintheMech.Eng.

Dept.itisnotappropriate.Weldingofsmallaluminumpartsisverydifficultandshouldbe

avoided.

Figure4.9belowshowsthetwoplateassemblyusingCchannel.Thismethodisappears

relativelyquicktomachinebuthassignificantalignmentlimitations:

o Cchannel comes in standard sizes therefore spacingof theplateshas limited

options. Spacersmustbeusedtoadjustplatespacing.

o ThesizeofextrudedcchannelisnotalwaysaccurateandtheCchannelsidesare

oftennotperpendicular.

o Ensuringtheholesaredrilleddirectlyoppositeoneanother intheCchannel is

verydifficult.

o SecurelyholdingtheCchannelpartsinthevicefordrillingiscumbersome.

Figure4.9Plateassemblyusingcchannelforposts


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5 BEARINGS

Bearings of many varieties are often used in mechanical design and are of utmost

importancetothefunctionalityoftheassembly.

Machinedfeaturesthatacceptbearingsmustusuallybemadetotightertolerancesthan

otherfeatures.

Ifaboreholeforabearingistoosmallrequiringexcessforcetoseatthebearingitwill

oftencausethebearingtorunroughandleadtoprematurefailure.

Ifaboreholeistooloosethebearingwillsloparoundandreducethealignmentofthe

shaft.

Alwaysincludetolerancesindrawingsfordimensionsrelatedtobearings.

Ifpossiblehave thebearingsavailableat timeofmachining.Thiswillgreatlyhelp the

machinistcorrectlysizethebearingborehole.

6 MOTORMOUNTING

Mostsmallandmidsizemotors incorporateabossandboltholesontheirface(Figure

1.1).

The motors boss assures concentric alignment of the motorshaft to the mounting

surface.

Correct tolerancingof theboss receivingbore is very important. Ifpossiblehave the

motoravailabletothemachinisttochecktheboresizeandfitattimeofmachining.This

willoftenavoidtimeconsumingreworkofparts.


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Figure6.1Motorwithbossandboltholes

7 ORINGS

Oringsareoneofthemostcommontypesofsealsused.Theyareextremelyefficient

and very inexpensive. Themachiningprocesses required to accommodateOrings is

oftensimpleifthepartisdesignedwithconsideration.

SealingusingOringsallows foreasydisassemblyof theapparatus ifmodificationsor

cleaningisrequired.

Figure7.1Orings

Boss

Boltholes


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TypesofORingSealingConfigurations

o Axial:oringsealisonthefaceofapart.

o Radial:oringseal isontheouteror innerwallofapart.Radialsealsonsmall

shaftscansignificantlydecreasethestrengthoftheshaft.Inthiscaseitisbetter

togroovetheinnerdiameteroftheparttheshaftwillfitinto.

o AvoidtheuseofRadialOringconfigurations ifpossible,theyaremoredifficult

tomachineand requiremuch tighter tolerances inall respects. Note that the

PlexiglasOringcontainerconfigurationinthesampleMixerdeviceusesanaxial

seal.Thereareseveralreasonsforthischoice:

o It iseasiertomachinevs.aradialseal. Ifaradialsealwereused,thePlexiglas

container

I.D.

wouldhave

tobeaccurate

and

concentric.

This

is

often

not

the

caseinstocktubularmaterial.InordertoattainanaccurateandconcentricI.D.

onatubeitmustbeboredonalathewhichisverytimeconsuming.Foranaxial

sealonlytheendsofthecontainerneedtobemachinedwhichisaquickprocess

o A radial seal is often makes it difficult to remove the end caps especially in

oceanographicinstruments.

Figure7.2 AxialORingseal RadialORing seal


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Figure7.3 Axialgland Radialgland

ThegrooveinwhichtheORingsitsiscalledthegland(fig7.3)

AppendixVandVIshowtablesforglandsizes.

ThemachiningprocessforOringglandsisinPartII Manufacturing,Section3

(Page48).


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8 PIPES AN DTUBES

Pipes:Pipesizesarereferredtobasedontheirnominalinnerdiameters,nottheirouter

diameters.i.e.a schedule40 pipewillhaveanO.D.of 1.050

o

Note:Thenominal innerdiameterofpipeusuallydoesnotmatch thephysical

inner diameter. This is due to the different wall thicknesses (referred to as

schedulesizesi.esched.40orsched.80).Differentpipematerialshavedifferent

O.D.sizesi.e.copperpipehasanO.D.of0.875vs. steelandaluminum

pipehavinganO.D.of 1.050.

Tubes: Tube sizes are referred to based on their actual physicalO.D. i.e. 1 tube is

physically1.00O.D.

Pipe isoften lessexpensive than tube therefore it isusedwhen largerquantitiesare

requiredinthedesignorwhenfluidtransportisrequired.Tubeisusedwhenaspecific

diameterisrequired.

8. 1 PIPEAN DFLUIDFITTINGS

ThefollowingarethemostcommonfluidfittingsusedintheMech.Eng.Dept.research

apparatus

NPT (NationalPipeThread) isa standard forpipe fittings.NPT fittingsare tapered to

produceaneffectivefrictionsealwhenscrewedintothematingfitting.

Note:A NPTfittinghas threadO.D.ofapproximately1/2.

NPT fittingsarenotused in thinmaterialor sheetmetal.Aminimumof four threads

mustbeengagedtoproduceareliableseal.

ISOfittingshavestraightthreadsandincorporateanOringinthebasetocreateaseal.

Themating surface for theseoringsmustalwaysbe spotfaced toproducea reliable

seal.Seetheoffsetholeinthetopcapofthesampledevice.Thespotfaceisrequiredto

produceasurfacewithmachiningmarksconcentricwith theOringseal. If this isnot

donethestriationsoranyscratches intheplasticplatewouldallowa leak.Whenever

OringsareusedanymachiningmarksorscratchesmustbeconcentricwiththeOring.


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9 MATERIALS

This section lists some of themore commonmaterials used in theUVicMech. Eng.

Machine Shop. Consult McMasterCarr (www.mcmaster.com) for more detailed

informationonthematerialsizes,characteristicsandcost.

9. 1 STOCKMATERIALS

Whendesigningkeepinmindthestandardsizesofstockmaterials.

o In most cases stock materials cannot be depended on for accurate sizes or

geometrictolerances(perpendicularsides,parallelism,etc.)

o An example exception is precision ground steel rod which is ground to tight

tolerances.

o Ifhighprecisionalignmentisrequiredthestockmaterialmustoftenbemachined

onthesignificantmatingsurfaces.Aluminumplatehasgoodsurfaceflatnessas

opposedtoaluminumextrusionandisapproximatelytwicetheprice.Useof

aluminumplatecanoftenreducetheamountofmachiningrequiredpayingfor

itselfinthe

final

result.

9. 2 ALUMINUM

AluminumismostoftenthematerialofchoiceintheMech.Eng.MachiningFacility.

AluminumCharacteristicsandAdvantages

o Lightweight

o Largesizeselection

o

Goodstrength

o Goodcorrosionresistance

o Easytomachine

o

Cleantowork

o Goodesthetics


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o Highheatconductivity

o Easilyrecyclable

o Readilyavailable

o Difficulttoweldproperly

o Canbeanodizedtoachieveaveryhighlycorrosionresistantsurfaceandcoloured

surface.

9. 3 STEEL

MildSteel Characteristics

o

Highstrength

o Heavy

o Corrodeseasily(rust)

o EasytoWeld

o Certaintypesofsteelprovedifficulttomachine

o Lowcost

o Considerablymorecostlytomachinethanaluminum

Mild steel isnotusedextensively in theMech.Eng.Machining facility. It is generally

usedforshafts,heavyweldedstructures,axelsetc.

StainlessSteelcharacteristics

o Verygoodcorrosionresistance(Oceanographicapplications)

o Hightemperature

o Veryhighstrength

o Veryheavy

o

Expensive

o Weldseasily

o Costlytomachine,useonlywhereabsolutelynecessary

9. 4 PV CPLASTIC


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PVCcharacteristics:

o Good corrosionresistance

o Easytomachine

o Lightweight

o Can be bonded easily.Note: Amechanical interconnectivity of the two parts is

alwaysrequiredwhenbondingPVC.ItisnotadvisabletobuttjointPVC.

o

Notrecommendedforwearapplicationsduetohighfrictioncoefficient.

9. 5 DELRIN(ACETAL)

Delrin(Acetal) isoftenusedasareplacementforaluminumparts.Dueto itsexcellent

machinability try to implement it into designswhere possible.Onemajor advantage

being that itdoesnotneed any coating tobe corrosionproof. It alsoproduces very

estheticallypleasingpartsdueitssheenandcolour.

Delrin(Acetal)hasthefollowingcharacteristics:

o Excellentmachinability

o Corrosionproof

o Goodrelativestrength

o

Lightweight

o Toughandwearresistant

o Verylowfrictioncoefficient

o Solventandfuelresistant

o Whiteorblackincolour

o Commonlyavailableinroundrod/bar,sheet,andplate

SomeapplicationsofDelrin:

o

Bushingsforlowspeedapplications

o Wearpads

o Fluidfittings

o Gears,pulleys,idlers

ImportantNotes:


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O Delrincannoteasilybebondedtoitselforothermaterials.

9. 6 PLEXIGLAS

Plexiglascharacteristics:o Lightweight

o Opticallyclear

o Brittle

o Scratcheseasily

o Lowoperatingtemperatureband

o Commonlyavailableinsheet,tubeandsolidround

o

Bondstoitselfveryeasily

Plexiglascanbebentusingheat.

o Bending Plexiglas is not recommended for prototype design because changes

andadjustmentscannotbemade.

o AccuratelyheatbendingPlexiglasiscanprovetobedifficult.

Plexiglas canbeeasilybonded togetherwithabuttjoint resulting in relatively strong

bond(Figure9.1).

o

SurfacesmustbesmoothandflatforbondingPlexiglasi.e. routedormilled.

Figure9.1Plexiglasbondedbuttjoint


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10 DRAWINGS

Trytoalwaysincludeanassemblyviewwithasetofsubmitteddrawings.

o Thiswillhelptheshopunderstandthepurposeofthepartsandwhereextracare

shouldbetakenwhenmachining.Iftolerancesordimensionswereomittedina

drawing itwilloftenallowtheshoptomakean informedjudgment iftheyare

notabletocontactyou.

Makesurethedrawingscaleisnotedsoifdimensionsneedtobecheckedoraremissing

theycanbemeasuredoffthedrawing.

Whenprototyping,printingdrawingswitha1:1scalecanbeusefultoseetheaffectsof

changesonthepart.

General information should be included in the drawing title block. An example title

blockisshowninFigure10.1.

o Detailstoinclude:scale,quantity,material,part#,contactinfo,tolerances

Figure10.1ExampleTitleBlock


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10.1 COMMONDRAWINGMISTAKES

Toomanydecimalsplaces

Dimensionsreferencedfromwrongsideofpartedge

Fonttobigortoosmall(shouldbe12pt. 14pt.)

Arrowheadstoobig

Toomanyhiddenlinesshownmakingdrawingdifficulttointerpret(useasectionviewif

neededtoshowhiddendetails)

Toomuchinformationononedrawingsheet(usemorethanonedrawingsheettoshow

partmoreclearlyifthisisthecase)

10.2

DIMENSIONING

Useordinatedimensioningtomakedrawingseasiertoread.

Mark the origin of a part based on the origin which will be used when the part is

machined.

Draw ordinate lines on the side of the part which is closest to the detail they are

showingthepositionof.

The following pages show examples of drawingswhich are cluttered and difficult to

understandfollowedbyadrawingwhichusesbestpracticesfordimensioningdrawings.

Dimensiondrawing features according to the shoppreferredmethodor specificCNC

millthatwillbeused.(Seesection10.4AnilamCNCMill,page35)


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Figure10.2OrdinateDimensioning

3.000

2.625

0 1.0

00

.375

1.6

25

2.8

75

3.0

00

3.1

88

.500

4.7

50

5.0

00

0

.250

.500

1.000

2.000

3.2

50

1.250

1.635

.260

.375 THRU 3PL

.250 THRU 3PL

1.000 THRU

R.300 TYP

.250 NOM


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3.000

2.625

0 1.0

00

.375

1.6

25

2.8

75

3.0

00

3.1

88

.500

4.7

50

5.0

00

0

.250

.500

1.000

2.000

3.2

50

1.250

1.635

.260

.375 THRU 3PL

.250 THRU 3PL

1.000 THRU

R.300 TYP

.250 NOM


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PrototypeDesignandManufacturingManual

30

4.750

3.188

5.000

.250

1.000 THRU

2.875

.260

1.635.500

1.000

.375

1.000

1.625

3.000

THRU 3PL.250

3.250

.500

THRU 3PL.375

2.000

1.000

2.625

.25

1

3.000

Figure10.3Exampleofbaselinedimensioning


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Notesaboutdrawing(Figure10.3):

Useofbaselinedimensionsmakesdrawingtooclutteredandhardtoread

Elevationviewshownwithhiddenlinesisconfusing.Shouldhavehiddenlinesremoved.

Slotlengthdimensionshouldbedonetothetotallengthofslot(asshownbelow).

.260

1.375

.2

Undesirableslotdimensioning

.260

1.635

.2

Preferredslotdimensioningstyle

Figure10.4Dimensioningofaslotlength


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Notesaboutdrawing:

Dimensionlinesaredifficulttofollow.Ordinatedimensionsshouldbeonthesideofthe

partclosesttothefeaturetheyaredefining(showninFigure10.7).

Elevationviewofpartshouldbeshownwithouthiddenlines(Figure10.5).

.250 NOM

.250 NOM

Figure10.5Elevationviewwithandwithouthiddenlines

Dimensionlinesshouldnottouchthepart.

.260

.260

Figure10.6Dimensionlinespacing


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PrototypeDesignandManufacturingManual

33

1.25

0

3.250

1

.000

4

.750

5

.000

3

.188

0

.250

1.001.000

2.000

2.625

3.000

.375

1.6

25

2.875

.500

3

.000

.500

1.635

1.000 THRU

.375 THRU 3PL

R.3

.250 THRU 3PL

.250 NOM

Figure10.7Easytoreaddrawingusingordinatedimensions


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Desirabledrawingcharacteristics:

Thedrawingaboveusesthepreferredstyleofdimensioning.

Dimensionlinesarespacedaparttoavoidclutteringthedrawing.

Dimensionsareclosetothefeaturetheydescribe.

Theslotscentrepositionisdimensionedandthewidthandtotallengthareshown.


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10.3 TOLERANCES

Tolerancesareaveryimportantaspectofdrawingswhichareoftenoverlookedandare

notgiventheattentiontheyrequire.

Alldimensions

should

have

an

associated

tolerance.

An

efficient

tolerancing

method

includes

asection

to

the

includesasectiontothedrawingsheetstitleblockwhichdefinesthestandardtolerancesbasedonnumberof

tolerancesbasedonnumberofdecimalplaces(shownin

Figure10.8).

Tolerances

.xxx 0.003

.xx 0.01

.x 0.015

Unlessotherwisenoted

Figure10.8DrawingBlockforStandardTolerances

Ifcertaindimensionscanaccommodatewider tolerance then removetheappropriate

decimals. Whenspecificallyneededaddtolerancestoindividualdimensionstohighlight

theprecisionrequired.

10.4 ANILAM CN CMILL

TheCNCMillingmachineusedextensively intheMech.Eng.MachineShoputilisesan

Anilamcontrolsystem.

Thefollowingfiguresshowthecontrolsystemsdifferentinputscreens(conversational

programming)forvariouscannedcycles.

o

Acannedcycleisasetofmachineoperationsinitiatedbyasinglelineofcode.It

usesafillintheblanktypeinterface.

Usethescreensshownbelowtodeterminetheappropriatemethodtodimensionpart

featureswhichwillbeCNCmilled(diagramsarespecifictoAnilamcontrolsystem).


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Figure10.9Inputscreenforboltholecircle

Figure10.10Inputscreenforrectangularprofile


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37

Figure10.11Inputscreenforcircularprofile

Figure

10.12

Input

screen

for

rectangular

profile

Figure10.13Inputscreenforcircularpocket


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Figure10.14Inputscreenforframepocket

10.4.1 ANILAMCANNEDCYCLEDEFINITIONS

Profile:CircularorRectangular.CNCmillcutstheoutlineoftheshape.Cuttercanbeon

the insideoroutsideof the shape.Profilesareused formilling theoutside contours,

slotsandholes.

Pocket:CircularorRectangular.CNCmillcutsallofthematerialinsideoftheshapetoa

specifieddepth.

Frame: CNC mill cutsa rectangular groove. This can have any radius on the corners

(commonlyusedforrectangularoringgrooves).

Note:Allthesecycles requiretheshapescentreposition, length,width ordiameter,

thereforeitismosthelpfultodimensiondrawingswiththeserequirementsinmind.


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39

PARTII MANUFACTURING

1 POSTS

The drawing below (Figure 1.1) shows the best practices for dimensioning a postdrawingwhenusingthemachiningmethodoutlinedonthefollowingpages.

3.7

5

0.25

3.5

00

.5

.750-.002

+.000

2 PL

1/4-20

1.0 NOM

UVic Fac ulty of Engineering

Hole Tapper

Drawn by REV.

SCALE: 1:1 MATERIAL:

MLDate:

SHEET 1 OF 1

Part: Qty.

A

1

7/22/2009

Comments:

Dimensions in inchesunless noted.

Tolerances:

.xxx .003

.xx .010

.x .015unless otherwise stated

Project:

Standoff

Break all sharp edges

Figure1.12DDrawingforPost

Thepostdrawingaboveshowsthedatumposition(zero)asthebaseoftheleftboss.

This isdonebecause the criticaldimension for thispart is3.500andnot theoverall

lengthof4.0.

Note: Ifalignment isverycritical(eg.topandbottomplatesneedtobealignedwithin

0.003ofeachother) then theouterdiameterof thepostmustbemachined first to

maintainconcentricitythroughoutthemachiningprocess.Thisisbecausestockmaterial


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40

isoftennotperfectlyround.Machiningthefullouterdiameterlengthisrarelyrequired

inmostapplications.

Latheprocessformachiningmultiplepostswithbosses

Step1FacefirstendofpostandsetZaxisto

zeroonlathedigitalreadout

Step2Turnbosstorequireddiameterand

approximatedepth.

Step3Centredrill Step4Drillendtotapdepth


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Step5Tap.Repeatsteps15forallposts Step6Zerotoolagainstchuckusingshim(make

suretoaccountforshimthickness)

Step7Faceoppositeendofpostto

approximatelythetotallength

Step8Centredrill.Repeatsteps7and8forall

identicalposts

Step9Turnsecondbosswithlivecentre

(Z=criticallengthofpost)

Step10Drillbossofoppositeendtotapdepth

Z


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Step11Tapsecondend Step12Chamferallsharpedges


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2 CNC MILLING

2. 1 SETUPMETHODS

2.1.1

FLATPARTS

FlatpartsareoftenmachinedonaCNCmillusingafixtureplate(Shownbelow).Thishas

manyadvantagesoverconventionallymachinedpart.

o If the part does not have any features in its ends or sides only one setup is

required(Topdownmachining).Thisbeingtherationalefornotplacingholesin

thesidesofflatpartswhenitcanbeavoided.

o Theoutsideofthepartcanbemachinedinonestep.

o Precisecopiesofthesamepartcanberapidlymachined(i.e.leftandrightsides,

topandbottom).

Figure2.1Flatpartwithfixturingplate

Fixtureplate

Part


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Figure2.2Fixturingplatesetupinvise

2.1.2 CIRCULARPARTS

When themilling forceswillbe in the Zaxisonly (eg.Drilling) a circularpart canbe

bolteddowntoaplate(ShowninFigure2.3).

Figure2.3CircularPartbolteddownthroughcenter.


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Inothercaseswherelateralandradialcuttingforceswillbeappliedtothepartajigcan

be used. Figure 2.4 shows an example of a very simple, effective circularholdingjig

which iscommonlyused in theshop.Thescratchmarkson thepartandjigallow the

parttobereplacedintothemillinthecorrectorientationforpostmachiningoperations

ormodifications.

Figure2.4Circularpartwithjig


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Figure2.5Circularpartandjigsetup


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48

3 ORINGS

3. 1 AXIAL ORINGS

ReduceRPM

speeds

when

grooving

Figure3.1showsanexampleaxialoringgroove.

.100.005 2.50 NOM

1.580.003

1.750.003

Figure3.1AxialOringGroove

1. Determinethewidthofthetoolbeingused.Inthiscasethetoolwidthis0.0525.

.0525

2. Usingthefollowingformula,determinetheXpositionfortheO.D.oftheOringgroove

Oring O.D. 2Tool Width

1.750 20.0525 1.645


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WorkpieceMUSTberotatingforsteps3and4.

3. Usingtherightsideofthetool,establishthetoolpositionontheO.D.oftheworkpiece

andentertheO.D.oftheworkpieceintoXonthedigitalreadout(eg.2.500).

4. Usingthetipofthetool,establishthetoolpositiononthefrontfaceoftheworkpiece

bytouchingofflightly.Enter0.000intoZonthedigitalreadout.

TouchoffthetoolwheretheOringgroovewillbelocated.Thescoremarkcreated

fromthetoolwilldisappearwhentheOringgrooveiscut.

Steps5to7willberoughcuts.Roughcutsareusually0.010smallerthanthefinal

tolerance.Thisisperformedtoimprovesurfacefinishandtolerances.

5. MovetoolinXaxisto1.590andthenmovetoolinZaxisto0.090.

.090


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50

6. MovetoolinXaxisoutto1.635.Thisis0.010smallerthanthecalculatedvaluefrom

step2.

7. Performthefinishingcut.MoveXto1.580,nextmoveZinto0.100andthenmove

Xoutto1.625.

This shouldbedone inone fluidmotion.The tool shouldneverbecome stationaryon the

workpiecewhenperforminganycuts.Thiscancausechatterandexcessiveheatgeneration

andwhenmachiningplasticitwillcreateapoorsurfacefinishandthesealmayleak.


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51

3. 2 RADIAL ORINGS

ReduceRPMspeedswhengrooving

Figure3.2showsanexampleradialoringgroove.

.145.005

.250

1.50 NOM

1.320.003

Figure3.2RadialOringGroove

1. Determinethewidthofthetoolbeingused.Inthiscasethetoolwidthis0.0525.

.0525

2. UsethefollowingformulatodeterminethefinalZpositionforthewidthoftheOring

groove.

Groove width Tool Width 'Z' distance from datum surface

0.145 0.0525 0.25 0.343


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WorkpieceMUSTberotatingforsteps3and4.

3. Usingtheleftsideofthetool,establishthetoolpositionontheendoftheworkpiece

and enter the width of the tool into Z on the digital readout (eg. 0.0525). This

establishedtherightsideofthetoolaszerointheZaxis.

4. Usingthetipofthetool,establishthetoolpositionontheO.D.oftheworkpieceand

entertheO.D.oftheworkpieceintoXonthedigitalreadout.(eg.1.500)

TouchoffthetoolwheretheOringgroovewillbelocated.Thescoremarkcreated

fromthetoolwilldisappearwhentheOringgrooveiscut.


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Steps5to7willberoughcuts.Roughcutsareusually0.010smallerthanthefinal

tolerance.Thisisperformedtoimprovesurfacefinishandtolerances.

5. MovetoolinZaxisto0.260andthenmovetoolinXaxisto1.320.

6.

Move tool in Zaxis to 0.333.This is0.010 smaller than thecalculatedvalue fromstep2.

7. Performthefinishingcut.MoveZto0.250,nextmoveXinto1.300andthenmove

Zto0.343.

Thisshouldbedoneinonefluidmotion.Thetoolshouldneverbecomestationaryonthe

workpiecewhenperforminganycuts.Thiscancausechatterandexcessiveheatgeneration

andwhen

machining

plastic

it

will

create

apoor

surface

finish

and

the

seal

may

leak.


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54

4 DRILLINGAN DTAPPING

CentreDrill:

o Useanytimethereisachancethedrillbitmayglanceoffthematerialorwhen

holesneedtobepreciselypositioned(ie.holesonaradius,drilling intoahard

material,etc.).Centredrillsareusedveryoftenwhendrillinginthelathe.

DrillingPlexiglas:

o Plexiglaswilloftentocrackwhenthedrillbitexitsthroughtheothersideofthe

part.Topreventthis,slowdownthedrillfeedforthe last 1mmor1/16while

drillbitexitsthematerial.ThisheatsthePlexiglastomakethe last1/16more

pliabletopreventcracking.Useextracarewhendrillingholesgreaterthan5/16

diameter.

4. 1 TAPPING

Taps:Usedtocutinternalthreads.Thevarioustypesoftapsare:

Spiralpointtapsarethemostcommonlyused.Thefirst3to4threadsonthesetaps

arepartialthereforetheydonotcutfullthreads forthecompletelengthof

engagement. IfthisisrequiredseeBottomingtapsbelow.

o BottomingTap:Usedtocutthreadstothebottomofablindhole.Abottoming

tapdoesnothaveataperedcuttingedgethereforeaplugtapmustbeusedfirst.

Donotuseabottomingtaptocutthreadsinanunthreadedhole.

Tapdrillbit:Specificsizeddrillbitforacertaintap(eg.#6drillfora1/420tap).

PercentageofThread:Thepercentageofthreadreferstotheamountofthreadinterms

ofthetotal threaddepth (crestto root).Usea largertapdrillbit to lower the thread

percentandviceversa.Decreasingthethreadpercentminimizesthetorqueonthetap

anddramaticallyhelpstoavoidbreakingthetap.Italsospeedsupthethreadingpro

Note: Use a bottoming tap only when thread depth is critical (ie. 1/2 plate

requiring 3/8 thread depth). Regular taps will not cut full threads to the

bottomofahole.


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55

Figure4.1Threadpercentageexample

TPI:ThreadsPerInch

Metricthreadsarespecifiedbythedistancebetweenthethreads

Die(externalthreads):Usedtocutexternalthreads.

NPTThreads:(NationalPipeThread)Thesearetaperedthreadsforsealingfluids

Maximumdepthoftappedholesshouldnotexceed3XDiameterofTap.Usaullytwice

thetapdiameterisallthatisrequiredtoprovidemaximumholdingforce.

100%Thread 70%Thread 50 %Thread

CrestRoot


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APPENDICES

MachiningTolerances II

TapDrillSizes III

DrillingandMillingSpeeds IV

ORingGlandSizes(Axial) V

ORingGlandSizes(Radial) VI


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Tapdrillandbodydrillsizes(fromshop)


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Drilling,millingspeeds(fromshop)


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VI


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REFERENCES

Osborn,Joe.2006.TipsonDesigningCostEffectiveMachinedParts.[Online]OMWCorporation.

Availableat:http://www.omwcorp.com/partdesign.html.[Accessed19June2009].

McMasterCarr.2009.[Online]McMasterCarrSupplyCompany.Availableat:

http://www.mcmaster.com.[Accessed07August2009].

ParkerORingHandbookORD5700,Parker,2007.

http://www.parker.com

rodney katz - prototype design and manufacturing manual

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