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Training ManualDrilling Operation and Tools

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Drilling

Drillingisacommonlyemployedholemakingprocessthatusesadrillasacuttingtoolforproducing

roundholesofvarioussizesanddepths.Drilledholesmaybesubjectedtoadditionaloperationsfor

bettersurfacefinishanddimensionalaccuracy,suchasreamingandhoning.

ProcessDrillinginvolverelativerotationalandaxialmotionbetweendrillandtheworkpiece.usuallythedrill

rotatesrelativetoworkpieceandadvanceintotheworkpiecebutsometime oppositeistrue.Chips

areremovedbyflowingalongthegroovesorflutesofthedrill

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Dril

l Tool Par s

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Description

AXISThe

longitudinal

centre

line

of

the

drill.

BACKTAPERTheslightdecreaseindiameterfromthefronttothebackinthedrillbody.BODYTheportionofthedrillextendingfromthecuttinglipstotheshank.BODYCLEARANCETheportionofthelandthathasbeencutawaytoprovidediametricalclearance.CHISELEDGE Theedgeformedbytheintersectionofthecuttinglips.CHISELEDGE ANGLETheincludedanglebetweenthechiseledgeandthecuttinglipwhenviewedfromthepointendofthedrill.CYLINDRICALLAND(MARGIN)Thecylindricalportionofthelandthatisnotcutawaytoprovideclearance.CYLINDRICALLANDWIDTHThedistancebetweentheleadingedgeandtheheeloftheland,measuredatarightangle(MarginWidth)totheleadingedge.DIAMETERThemeasurementacrossthecylindricallands(margin)attheoutercornersofthedrill.FLANKThesurfaceofthedrillpointextendingbehindtheliptofollowtheflute.FLUTELENGTHTheaxiallengthfromtheextremeendofthepointtotheterminationoftheflutesattheshankendofthedrill.Asthisincludesthefluterunout,flutelengthdoesnotindicatetheusablelengthofthedrill.FLUTERUNOUTTheendoftheflutesneartheshankwheretheyjointhedrillbody.FLUTESThegroovesinthebodyofadrillwhichprovidethecuttinglips,allowswarfandchipejection,andpermitcuttingfluidtoreachthecuttinglips.HEELTheedgeformedbytheintersectionofthbodyclearanceandtheflutesurface.HELIXANGLETheangleformedbytheleadingedgeofthelandandtheplanecontainingtheaxisofthedrill.LANDTheperipheralportionofthebodybetweenadjacentflutes.LEADOFHELIXThedistancemeasuredparalleltotheaxisbetweencorrespondingpointsontheleadingedgeofthelandinoneturnofthedrill.LIPCLEARANCEANGLETheangleformedbetweentheoutercornerofthelipandaplaneatrightanglestotheaxisofthedrill,andusuallymeasuredattheperipheryofthedrill.LIPSThecuttingedgesofatwoflutedrillextendingfromthechiseledgetotheperipheryofthedrill.OVERALLLENGTHThetotallengthmeasuredfromtheextremepointtotheendoftheshank.POINTThesharpenedendofthedrillcomprisingthecuttinglips,chiseledge,landsandtheweb.POINT ANGLE The included angle between the cutting lips. (brittle material 900118) and(118

0

135

0ductile

and

hard

material)

RELATIVELIPHEIGHTTherelativepositionofthelipsmeasuredattheoutercornersinadirectionparalleltothedrillaxis.RECESSThesectionofreduceddiameterbetweentheshankandthebodyofadrill.SHANKThepartofthedrillbywhichitisheldanddrivenTANGTheflattenedendofatapershankintendedtofitintoadrivingslotinasocket.WEB(CORE)Thecentralportionofthedrillthatjoinstheland.Theendofthewebformsthechiseledge

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Key System Components

Drillsareclassifiedby Materialfromwhichtheyaremade Methodofmanufacturing Length Shape Numberandtypeofhelixorflute shank Pointcharacteristics Sizeseries

Selectionofdrilldependsonseveralfactors Hardnessandcompositionoftheworkpiece,withhardnessbeingmoreimportant Rigidityofthetooling Holedimensions Typeofdrillingmachine Drillapplicationoriginatingorenlargingholes Tolerances Cost

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Types

Amongthecommontypesofdrillsare

Combineddrillandcountersinkorcenterdrill Shortdrillusedtocentershaftsbeforesquaringandturning Thestepdrill,withtwoormorediameters Thespadedrillwhichhasaremovabletiporbitclampedinaholderonthedrillshank,usedfor

largeanddeepholes

Thetrepanningtoolusedtocutacorefromapieceofmetalinsteadofreducingallthemetalremovedtochips

Thegundrill,runatahighspeedunderalightfeed,andusedtodrillsmalllongholes Thecoredrillusedtoboreoutcoredholes Theoilholedrill,havingholesortubesinitsbodythroughwhichoilisforcedtothecuttinglips Three andfourfluteddrills,usedtoenlargeholesafteraleaderholehasbeencored,punched,

ordrilledwithaDrillingtwofluteddrill

Twisteddrillsmadefromflathighspeedsteelordropforgedtodesireshapeandthentwisted.Drillsarealsomadeofsolidcarbideorofhighspeedsteelwithaninsertofcarbidetoformthe

chiseledgeandbothcuttingedges.Theyareusedprimarilyfordrillingabrasiveorveryhard

materials.

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Varieties of Classification for Drills

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Effects and Consequences of Drill

features

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Sel

Sel

SpeedrefshouldroforsatisfPeripher

(SFPM).

ctio

ctin

erstotheretateatasetctorydrillinlspeedisthhisspeedis

of D

Drill

olutionsperpeedthatis.Thespeedspeedofaelatedtoth

ill

Spe

minute(RPselectedfortwhichadririllatitscirdistancea

d

)ofthedrillihematerialllturnsandcumferencerillwouldtr

ngmachineeingdrilled.

utsiscalledtxpressedinavelifrolled

pindle.FordCorrectspeheperipheraurfacefeetonitsside.F

rilling,thespdsareessenlspeed.erminuteorexample,

indletial

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peripheralspeedof30feetperminutemeansthedrillwouldroll30feetin1minuteifrolledonitsside.Ithasbeendeterminedthroughexperienceandexperimentthatvariousmetalsmachinebestatcertain

speeds;thisbestspeedforanygivenmetaliswhatisknownasitscuttingspeed(CS)

Starting a Hole

Thebestmethodtoalignandstartaholeistousethecombinationcountersinkanddrill,knownasthe

centerdrill.Setthedrillingmachinespeedforthediameterofthetipofthecenterdrill,startthe

machine,andgentlylowerthecenterdrillintocontactwiththework,usinghandandeyecoordination.

Therevolvingcenterdrillwillfindthecenterpunchedmarkontheworkpieceandproperlyalignthe

holefordrilling.Thedepthofthecenterdrilledholeshouldbenodeeperthantwothirdthelengthof

thetaperedportionofthecenterdrill.

Afterthedrillhasbeenalignedandtheholestarted,theninsertthepropersizedrillandcontinue

drillingintotheworkpiece,whileapplyingcuttingfluid.Thecuttingfluidtousewilldependonwhat

materialisbeingmachined.Usethecuttingfluidsfreelyasthedrillsizeincreases,boththesizeofthe

webandthewidthofthechiseledgeincrease.

LargeHolesThechiseledgeofdrilldoesnothaveasharpcuttingaction,scrapingratherthancuttingoccurs.In

largerdrills,thiscreatesaconsiderablestrainonthemachine.Toeliminatethisstrainwhendrillinga

largehole,apilotholeisdrilledfirstandthenfollowedwiththelargerdrill.Adrillwhosediameteris

widerthanthewebthicknessofthelargedrillisusedforthepilothole.Thisholeshouldbedrilled

accuratelyasthelargerdrillwillfollowthesmallhole.

Apilotdrillcanalsobeusedwhenaveragesized.Holesaretobedrilledonsmalldrillingmachines.The

smallmachinemaynothaveenoughpowertodrivethelargerdrillthroughthemetal.Avoidmakingthe

pilotdrilledholemuchwiderthanthewebofthelargerdrill.Toowideofapilotdrilledholemaycause

thelargerdrillcuttinglipstograbandsnagwhichmaycauseexcessivechatteroranoutofroundhole.

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AnglesThehelixanglesoftheflutesvaryfrom10to45.Thestandardpointangleis118.Thereareanumber

ofdrillgrindersonthemarketdesignedtogivetheproperangles.Thepointmaybegroundeitherinthe

standardorthecrankshaftgeometry.

MaterialThemostcommontoolmaterialfordrillsishighspeedsteelM1,M7,andM10.Highspeedsteelismost

commonlyuseditprovidesstrength,toughnessandhightemperaturestrengthatcomparativelylow

cost.Carbidetrippeddrillsareusedforspecialapplicationssuchasabrasivematerialoflowtensile

strengthorheatresistancealloys.Solidcarbidedrillsareusedwhereextremerigidity,accuracyandlong

toollifeisrequired

MachineabilityRatingSoftmaterialssuchasaluminumandplasticsareratedwelltoexcellentwhilecastironandmildsteel

haveafairtogoodmachineabilityrating.Stainlesssteelhasapoortofairratingbecauseofits

roughnessanditstendencytoworkharderwhenmachined

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SpeedsandfeedsTheoptimalspeedandfeedfordrillingdependonworkpiecematerial,toolmaterial,depthofhole,

designofdrill,rigidityofsetup,tolerance,andcuttingfluid.

RecommendationsforspeedsandfeedsindrillingavarietyofmaterialsaregiveninTable

CoolantUse

DeflectionAccuracy(Workrotating)

DeflectionAccuracy(Toolrotating)

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UnevenWorkSurfaces

WORKCLAMPINGANDSUPPORT

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Drilling Problems and Causes

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Common Reasons for Drill Failure

(pictorial form)

OVERSIZE HOLELipsofunequallengthOnelipdoingalltheworkSuggest:Regrindingthedrill

ChiseledgenotcentralSuggest:regrindingthedrill

MachinespindleoutoftrueCheckfordamagetochuck orspindle

UNEQUAL CHIPS

Lipsofunequallengthasin1alongchipfromonesideindicatethatitisdoing

all

the

work.

Suggest:

Re

grinding

the

drill

Drillpointangleisoff;lowononesideandhighontheotherconsequentlythe

chiseledgewillbeoffcentre

Relativelipheight;toogreatadifference

SPLITTING UP THE WEB

InsufficientlipclearanceSuggestregrindingdrill

Toohighafeedrate.Checkrecommendedconditions

Strikingdrillpointwithhardobject

EjectingdrillontomachinebaseBothc.&d.causebruisingtothechiseledge,

whichwill

show

up

under

use

as

afracture

Surfacecracksontheflankscanbecausedbyoverheatingwhengrindingand

thenquenching

BROKEN TANGThetangisforejectionpurposesonly.Allowingthetorquetobetakenbythe

tangwillresultinbreakage'sAlwaysensurethatthetapersocketisfreefrom

foreignmatteranddamage,SothatfrictionalonedrivesthroughthetaperThe

positivehelixangleofthedrill,will,whenopeningoutanexistingholepullthe

Morsetaperoutofcontact,whichwillresultinabrokentang.Pilotholes

shouldonlybe1.5timesthechiseledgelength

Breaking Down Of Outer Corners

Peripheralspeedtoohighburningoutthecorners

Inadequatelubrication/coolantandWorknotsupportedadequately

Interruptedfeedonworkhardeningmaterials

Openingoutexistingholes

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Contd. (pictorial form)CHIPPING OF LIPSLipclearancetoogreat

Feedratetoohigh

Drillsurgingonbreakthrough

Quenchingdrillonregrinding

BREAKING OF DRILLSDrillwornorimproperlypointground

DrillslippingindriveandWorknotrigid

DrillfluteschokinginswarfandInsufficientlipclearance

Feedratetoohighordrillpullingthroughonbreakthrough

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DRILLING MACHINE SAFETY

Drillingmachinesareoneofthemostdangeroushandoperatedpiecesofequipmentintheshoparea.

Followingsafetyproceduresduringdrillingoperationswillhelpeliminateaccidents,lossoftime,and

materials.Listed

below

are

safety

procedures

common

to

most

types

of

drilling

machines

found

in

the

machineshop.

(MakeSureYouHaveReadAnyKindOfInstructionsPlacedonMachineorShopFloore.g.Safety

Instruction,NoticeBoard,AnySortofSignsBoardThesethingsareforussopayattention)

PersonalSafetyintheWorkshop Wearproperprotectiveclothingandbuttonitup. Iflongsleeves,rollthemuporbuttonthecuffs. Wearpropersafetyshoesorboots. Putonsafetygoggleswheneverthemachineprocessinvolvessparksorchipsflyingout. Donotwearrings,wristwatches,glovesoranythingthatmightbecaughtintheMachine. Donotrun. Donotoperatethemachineunlessallguardsandsafetydevicesareinpositionandworking.

DuringMachineryOperation Donotsupporttheworkpiecesbyhand.Useaholdingdevicetopreventtheworkpiecefrom

beingtornfromtheoperator'shand.

Nevermakeanyadjustmentswhilethemachineisoperating. Nevercleanawaychipswithyourhand.Useabrush. Makesurethatthecuttingtoolsarerunningstraightbeforestartingtheoperation. Neverplacetoolsorequipmentonthedrillingtables. Easeuponthefeedasthedrillbreaksthroughtheworktoavoiddamagedtoolsorworkpieces. Removeallchuckkeysandwrenchesbeforeoperating. Remembertostopthemachinefirstbeforewalkingawayforanyreason. Donotleanonamachine,especiallyifitisrunning. Learnhowtostopyourmachineinanemergency

UseofCompressedAir Neverdirectcompressedairtowardsyourself,oranyoneelseforcleaning. Neverusecompressedairforcleaningawaychipsanddust.Flyingparticlescanbedangerous.