milling tutorial
TRANSCRIPT
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TexasTechUniversity
ElectricalEngineeringDepartment
IEEEStudentBranchMillingTutorial
AnEEsGuidetoUsingtheMillingMachine
Writtenby:JuanJoseChong
Photosby:DavidHawronsky
IEEE#:90499216
March24,2011
Rev.A
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ContentsTableofFigures............................................................................................................................................. 3
Introduction.................................................................................................................................................. 4
Whatismilling?............................................................................................................................................. 4
Whylearnhowtomill?................................................................................................................................. 4
Whatwillyouneedinordertomill?............................................................................................................ 4
CopperSubstrate...................................................................................................................................... 5
MillingBits................................................................................................................................................. 5
Tape........................................................................................................................................................... 6
HowtoMill.................................................................................................................................................... 6
DrillinganAlignmentHole........................................................................................................................ 6
TurningonandInitializingtheMachine................................................................................................... 7
PlacingCopperontheTable..................................................................................................................... 8
LoadingFiles,Mirroring,andIsolating...................................................................................................... 8
PlacingtheCircuit................................................................................................................................... 11
RunningLayers........................................................................................................................................ 12
DrillLayer................................................................................................................................................ 12
TopIsolationLayer.................................................................................................................................. 14
FlippingtheBoard................................................................................................................................... 15
CuttingOutYourDesign......................................................................................................................... 16
Cleanup................................................................................................................................................... 16
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TableofFiguresFigure1 OriginalCircuitBoardvs.MilledReplacementBoard................................................................... 4
Figure2 30Degree(Left)vs.60Degree(Right)Endmill............................................................................. 5
Figure3 DrillBit(Left)andRoutingBit(Right)........................................................................................... 6
Figure4 InitializingSelection...................................................................................................................... 7
Figure5 MaterialChangeButton................................................................................................................ 7
Figure6 CopperPlacedontheMachineTable........................................................................................... 8
Figure7 SelectingtoAutoDetectFiles....................................................................................................... 8
Figure8 DecimalSelection.......................................................................................................................... 9
Figure9 IsolateButton................................................................................................................................ 9
Figure10 IsolationWindow........................................................................................................................ 9
Figure11 IsolatedCircuit.......................................................................................................................... 10
Figure12 LayersButton............................................................................................................................ 10
Figure13 IsolationWindowwithMirroringEnabled................................................................................ 10
Figure14 SelectingLayoutforMoving..................................................................................................... 11
Figure15 JumptoCursor.......................................................................................................................... 12
Figure16 RunningaLayer......................................................................................................................... 12
Figure17 ToolChangeWindow................................................................................................................ 13
Figure18 CheckingDepthofaDrillBit..................................................................................................... 13
Figure19 MachineJogWindow................................................................................................................ 14
Figure20 IsolationDepthTesting............................................................................................................. 15
Figure21 CopperBoardFlipped180Degrees.......................................................................................... 15
Figure22 JumpingtoMirrorCursor......................................................................................................... 16
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IntroductionSoyouveprobablyheardpeopleinprojectlabaskingaboutmilling,andmaybehaveseenaboardor
twobefore,butneverknewexactlywhatitwas.Well,thisguideisjustforyou!ItswrittenbyanEE
student,forEEstudents!Ifyouhavedoubtsabouthowsomethingisdoneafterreadingthisguide,ask
upperclassmen.Itwillhelpeveryonetohaveapositivemillingexperience(andalsokeepyoufrombeing
theguywhobrokethemachine!)
Whatismilling?Millingistheprocessbywhichacircuitdesignisetchedintoacoppersubstratebymeansofa2axis
CNCmachine,orforusEEs,itsbasicallyawaytodesignandbuildcircuitsquicklyandeasily.Onceyou
understandhowtheprocedureworks,andwithabitofpractice,youcanhaveafullcircuitboardin
about20minutes!Thismethodmayalsobecomeyourpreferredmethodofprototypinginsteadofusing
protoboardorbreadboardswithbreakoutboards.
Figure1 OriginalCircuitBoardvs.MilledReplacementBoard
Whylearnhowtomill?Whilemillingisnotstrictlynecessaryfortheearlyprojectlabs(1&2),itisagoodideatogetyourfeet
wetandlearnhowitsdonebeforeitbecomesnecessaryinfuturelabs.Millingalsomakesitpossibleto
makemuchmorecomplicatedandcleanercircuitdesigns.
Millingopensthedoortosurfacemountpartswhicharenearlyimpossibletouseonprotoboardand
muchless,breadboards.MoreandmoremanufacturersaremovingfromDIP(throughhole)packagesto
muchsmallerandcheaperSMT(surfacemount)parts.Whilesolderingthesepartsmayrequiresome
morepractice,asstatedearlier,thesooneryoubeginworkingwiththesepartsandtools,theeasier
futureprojectswillbe.
Whatwillyouneedinordertomill?WhileTexasTechandtheEEdepartmentprovidethemachineandsoftwarenecessarytomill,youmust
providesometoolsyourself.
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CopperSubstrateThisoneisprettyessential;ifyoudonthavecoppertomillyourcircuitonto,youcantmill!The
substrateisbasicallytwothinpiecesofcoppergluedontoafiberglasssubstrate.Thissubstrateiscalled
adielectricandcanvaryinwidth,ascanthewidthofthecopper.IfyouredoingsomesortofVHF/UHF
projectwhereimpedancemustbepreciselycontrolled,youmusttakethesemeasurementsinto
account,butformostprojects,anycopperavailableinthestockroomshouldsuffice.
Itshouldalsobenotedthatsincethesubstrateistwoconductorsseparatedbyadielectric,itisbasically
acapacitor.Becauseofthis,youcanexpectslightlymorecapacitancebetweentraces.
MillingBitsAsmentionedearlier,thisprocessusesaspecialbitcalledanendmilltoseparatetracesfromtherestof
theplane.Therearemanytypesofendmillsavailable,buttypicalsizesareanythingfrom10to100mills
(1mill=1/1000inch). Youmayfindsomeendmillsaresoldin45,60,and90degreeincrementsaswell.
Thesemeasurementsspecifytheanglewhichtheendmillspointmakes.90degreeendmillscancut
tracesofabout16mills,45degreescancuttracesofabout12millsand45degreescancutabout6mill
tracesifyourecareful.Mostofthesebitscanbefoundonline.Theretailerwhichistypicallyusedis
http://www.precisebits.com
Thereisalsoanothersetofbitsthatisrequiredtomill.ThesebitsarecalleddrillbitsandareusedtodrillholesforIClegs,headermounts,VIAs,etc.Youmustusedifferentsizesofbitsinordertodrill
differentsizedholes.Ifyourcircuitrequiresacertainsizeofbit,itisimperativethatthepropersizebe
used.Ifthisruleisnotfollowed,theholesdrilledmayeitherbetoolargeortoosmallforyourpart.Too
small,andthepartwillnotfitintotheboard.Toolarge,andtherewillnotbeenoughofapadleftonthe
boardtosolderto.Typicalsizeswillrangefrom28to45mills.Thesebitsmaybepurchasedfromthe
previouslymentionedwebsite,orfromHarborFreightTools(34thandI27).
Figure2 30Degree(Left)vs.60Degree(Right)Endmill
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Thefinalsetofbitsareoptional,butwillmakecuttingoutthecompletedboardmucheasier.Thisbitis
calledaroutingbit(alsoknownasacutoutbit)becauseitwillcleanlycutoutthecompletedcircuitfromtherestofthecopper.SomeprefertouseacopperpressoraDremel,butIhavefoundthesebits
toproducethebestresults.
TapeTapewillberequiredinordertotemporarilyholdyourcopperboardtothemachineandsacrificiallayer
placedonthemachine.Silverducttapeistypicallyused,butmostothertypesoftapewillalsowork.
HowtoMillDrillinganAlignmentHoleFirstthingyouhavetodoisdrillanalignmentholeforyourcopperboard.Besuretomeasureexactly
themiddleoftheboardanddrillasshowninthefigure.Iftheholeyoudrillisoffbyevenatinybit,the
boardwillbeslightlyoffsetlateronintheprocessandwillnotlineupproperly.
Figure3 DrillBit(Left)andRoutingBit(Right)
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TurningonandInitializingtheMachineToturnonthemachine,firstflipthepowerswitchesonthethreemachinesnexttothemillingPC.Also
turnonthemillingPCifitisoff.Oncefinished,opentheprogramnamedIsoProonthedesktop.Thisis
theprogramwewillbeusingtocontrolthemillingmachine.
Thefirstthingtodoisinitializethemachine.Thisprocessresetsthemachineandletsthecomputer
knowwherethemachinesboundariesare.GotoMill>Initializetoinitializethemachine.Itshouldbegin
movingandonceitsfinished,itshouldstopatthefrontcenterofthetable,justabovethealignment
pin.InitializationmustbedoneeverytimeIsoProisstarted.
Figure4 InitializingSelection
Oncethemachineisfinished,anewbuttonlabeledMaterialChangeshouldbecomeactive.Clicking
thiswillcausethemachinetomovethemachinehead,orspindle,outoftheway,allowingyouto
replacematerialonthemachinetable.
Figure5 MaterialChangeButton
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PlacingCopperontheTableWiththespindleoutoftheway,makesurethetableiscleanandplaceyourcopperboardonit.Once
alignedwiththefaceofthemachineasshown,tapedowntheboard.2or3piecesoftapeshould
suffice.
Figure6 CopperPlacedontheMachineTable
LoadingFiles,Mirroring,andIsolatingThenextstepistoloadyourfilesintotheprogramandbeginpreparingthem.Inordertodothat,click
onFile>Import>AutoDetectFiles
Figure7 SelectingtoAutoDetectFiles
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IfyouareusingtheTTUMilling.camfilefromEagleCADorimportingfromOrCADyoumustselectthe
optionsshowninthefollowingfigure.Thissettingtellsthemachinehowmanydecimalplacesitshould
takeintoaccountwheninterpretingyourgerberfiles.Thecorrectsettingisfourintegerdigitsandfour
decimaldigits.
Figure8 DecimalSelection
Oncethemachineisfinishedimportingyourfiles,thenextstepistoisolateyourtraces.Isolationisthe
processofisolatingyourtracesfromtherestofthecopperboard.Todothis,clickontheIsolate
button,selectyourtopandbottomlayers,andtypeinthespacewhichyouwishtoisolate.
Figure9 IsolateButton
Formostapplications15millsisusuallymorethanenough,butifyouareworkingwithsurfacemount
componentsaslittleas6millsmightberequired.
Figure10 IsolationWindow
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Oncethecomputerfinishesisolating,youwillseethattheprogramhasdrawnlinesaroundyourtraces.
Theselinesarethepathsthatthespindlewilltakewhencuttingoutyourtraces.Besuretocheckfor
errorsorpartswhereisolationdidnotworkcorrectlyandadjustasneeded.
Figure11 IsolatedCircuit
Onceyouarehappywiththeresults,clickontheLayersbuttonandselectMirrornexttoyour
bottomandcutoutlayers(ifoneexists).Mirroringtheselayerswillmakethemachineinterpret
everythingproperlywhentheboardisflippedlateronintheprocess.Alsonotethatifyouareusinga
cutoutlayer,youmustalsochangeitstypefromComponenttoIsolationinadditiontomirroringit.
Figure12 LayersButton
Figure13 IsolationWindowwithMirroringEnabled
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PlacingtheCircuitThefinalthingtodobeforemillingistomakesurethatyourcircuitwillproperlyfitonthecopper
substrateyouhaveplacedonthemachine.Todothis,rightclickonanyofthelayerstotheleftand
selectEditAll.Afterdoingso,drawaboxaroundallyourtracesandcutoutlayer.Besuretoselect
everylayer.Youcanzoomoutifneeded.
Figure14 SelectingLayoutforMoving
Abitofguessworkisrequiredtogettheboardtofitproperlysometimes,butitisimportanttomake
surethattheboardisproperlypositionedforagoodcircuittobemilled.Onceplaced,rightclickonone
ofthecornersofyourlayoutandselectJumptoCursor.Themachinewillmovetothelocation
specified.Dothisfortheoppositecornerandmakesureyouhaveenoughspace.Keeprepeatingthis
processuntilyouresureyouhaveenough.
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Figure15 JumptoCursor
RunningLayersNowthateverythinghasbeenprepared,layersmustberun.Irecommendrunningyourdrilllayerfirstin
ordertoensurethatpadsdonotgetdamagedandalsotogiveyoureferencepointswhenmillingthe
restofthecircuit.
DrillLayerInordertorunthedrilllayer,rightclickonthelayertotheleftofthescreenandselectRunLayer.
Figure16 RunningaLayer
Youwillnoticethatthemachinewillmoveoffofthetableandisaskingforabit.Thisdialogwindowwill
askforaspecificbitanditwillalsoshowyouwhatthediameterofthebitshouldbe.Besuretogivethe
machineabitclosetothesizeitrequests!Ifyoudontdothis,youmaynothaveenoughofyourpads
lefttosolderto!Youcansafelyroundupordown1or2millsifyoudonthavetheexactmeasurement.
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Figure17 ToolChangeWindow
Thetoolshouldbesnug,butnotoverlytight.Besuretonotdropthetoolswheninsertingorremoving
them!Ifoneisdropped,itwillshatter!!
Onceyouveinsertedyourtoolintothemachine,youmustensurethatthespeediscorrect.Thespindlespeed(howfastthetoolspins)shouldread60,000RPM.Afeedrate(howfastthetoolcutstraces)of60in/minisokayfordrillingonly.Slowerspeedsshouldbeusedforeveryotherprocess.
Thelaststepbeforestartingischeckingdepth.Inordertodothis,presstheheadofthemachinedown
manuallyandcompareittotheedgeoftheboard.Thetoolshouldjustpenetratetheloweredgeofyour
copperboard.Toadjusttheheightofthebit,turntheknobonthemachineheadmarkedwitha+and .
Donotadjustthefournutstotheleftofthespindle!!Also,dontgotoodeepintothesacrificiallayeras
youmighthitthealuminumtableandshatterabit!
Figure18 CheckingDepthofaDrillBit
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Onceallthesepreparationsarecompleted,clickRunLayertobeginthedrillingprocess.Themachine
willstopandaskfordifferentsizebitsifyouusedtheminyourdesign.
TopIsolationLayerThenextthingwehavetorunistheisolationlayer.Inordertodothis,wemustonceagaincheckfor
depth.Theprocessisnearlyidenticaltothepreviousone,theonlydifferencebeingthatwehaveto
slowthefeedratetoabout14in/minwhilekeepingthespindlespeedat60,000RPM.Theslowerthe
feedratetheslowerthewearonyourtoolsandthemorepreciseyoucanbe,butthelongeritwilltake
tomill.
Thetoolshouldjustbarelycutthecoppersurface;justenoughforittocompletelycutthroughthe
copper,butnotdiveintothefiberglasssubstrate.Onceyouinsertyourtoolintothemachine,clickon
theJogbutton.Thisbuttonwillallowyoutocontrolthemachineheadmanuallyinorderadjustthebit
depth.Youcanmovethespindlewiththearrowkeysonthekeyboard.ClickingtheSpindleOnbutton
will
turn
on
the
spindle
and
Head
Down
will
lower
the
head
using
air,
just
as
if
you
were
running
the
layer.Irecommendturningonthespindlebeforeloweringtheheadbecauseitwillcauselessstresson
thetoolandkeepyoufrombreakingit.
Figure19 MachineJogWindow
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Figure20 IsolationDepthTesting
Oncethoseadjustmentsaremade,click"RunLayer"andsitbackwhileyourboardismade.Youshould
watchtheprocessabittomakesurethatthetooliscuttingenoughcopper.
FlippingtheBoardOncetheisolationlayerisfinishedrunning,clickthe"MaterialChange"buttonandfliptheboard180
degreesasshown.Youshouldflipitsothatthealignmentholeisstilloverthepegatthefrontofthe
machine.Tapetheboarddownjustasyoudidbefore.
Figure21 CopperBoardFlipped180Degrees
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Theprocessforrunningthebottomisolationlayershouldbeidenticaltothetop,withtheexceptionof
onestep.Wemustfirstmakesurethattheholeslineupproperlysothattheisolationdoesn'tcuttraces
incorrectly.Todothat,rightclickonthecenterofanyholeonyourschematicandselect"Jumpto
MirroredCursor".Thiswillforcethemachinetomovethespindletothatspecifichole.Dothiswitha
coupleholesonoppositeendsofyourcircuitandchecktomakesuretheylineup.Makeadjustmentsto
thetapeandcopperboardasneeded.
Figure22 JumpingtoMirrorCursor
Rememberthatdepthmustbecheckedonceagaininordertoensurethatyoudon'tbreakabit!The
processisthesameasbefore.Besuretocheckthesettingsandonceyouarereadytoproceed,click
"RunLayer".
CuttingOutYourDesignIftheTTUMilling.camfilewasusedinEagleCAD,itwillhaveacutoutlayerreadymadeforyou.Thislayer
willbegeneratedusingtheDimensionslayerinEagleCAD.Ifyouwouldliketocutoutyourdesign
usingthislayer,someminorchangeswillneedtobemadeforittowork.Ifyouhavefollowedthis
tutorial,youshouldhavealreadychangedthelayertypefromComponenttoIsolationandmirrored
it.Ifyouarenotsure,gobackintotheLayerswindowanddoublecheck.
Onceyouarefinished,rightclickonthecutoutlayer,select"RunLayer",insertyourcutouttool,and
adjustthedepth.Itshouldbeaboutthesameusedfordrilling.Besurethatthespindlespeedis60,000
RPMandthefeedrateisabout12in/min.
CleanupOncefinished,removeyourtool,clicktheChangeMaterialbuttontogiveyouenoughspaceto
removeyourcopperboardandyourcircuit,sweepoffanyexcessdust,closetheprogram,andturnoff
alldevices.
Congratulations!You'vejustfinishedmillingaboard!