NutsandBolts

Description

This Activity Planwillenable students toidentify thedifferences betweenmetric andimperialbolts (capscrews).Theywill learnhow to measurea bolt and determine thethread typeby usingathread gauge. Studentswillalso be taught how todrill a hole and tapa thread into apieceofsoft metal. After makingthethreads,they willbe shownthe causes of stripped threads andhowtostripthosethreads. After thedestructionofthethreads the studentswillbeshowna threadrepair method by installing a product calledaHeliCoilinsert.

LessonOutcomes

The student willbeableto:

• Make threadsin apieceofaluminumandthen strip the threads to allow for a new threadinsert tobeinstalled.

• Identify metricandimperial bolts bytheirdesignationmarks

• Usea threadgaugetoidentify thedifferent types ofthreadpitches

Assumptions

Students havelittleor no previousknowledgeor skill inthe materialbeing covered.

Terminology

Any terminologyusedwill be explained as required duringthe activity.

EstimatedTime

2 hours

RecommendedNumberofStudents

20, basedontheBCTechnology Educators’Best PracticeGuide

Facilities

Shopspace with bench space anda metal work viseforeach group pair(12 stations)

Tools

•Metalwork vises

•Sufficient hammersandcentrepunches

•A drillpress,if studentshave previouslybeentaughthowto safely operate it

•Handdrillstodrill aluminum strips,with drillbitssizedto match thethreadsbeingtapped

•Threadingoilor lubricant

•Tapanddiesets sufficient fortheclasssizebeingtaught

•Torquewrench

•Threadgauge

Materials

•A 1" x 1" x ¼" piece ofaluminumflatbarforeachstudent

•Selectionof boltsof various types, threadsandsizesfor demonstration examples

•Sufficientboltsforstudentstomatchtothethreadsbeingtappedinthe aluminum strip

Introduction:CommonTypesofNutsandBolts

Vehiclescontainmany differentstylesandtypesofnutsandbolts.Belowisalistofcommontypesofnutsandboltsthatstudentsshouldbecomefamiliarwith.

Hexorflatnut:generalusage

Locknut(Nylocknut):usedforsafetyreasonswhenanutshouldnotcomelooseduetovibrations.Locknutsareoftenfoundonfrontwheeldriveaxlesor exerciseequipment.

Taper nut:usedtohelpcentreobjects,forexample onthewheelofacar

Slottedorcastlenut:usedinconjunctionwithacotterpinonobjectsthatturnortwist,forexampleonatierodorballjoint

Caporacornnut:usedtogive afinishedappearanceby coveringtheendofthethread

Wingnut:usedwhenonlyhandtighteningisneeded

Capscrew:oftenreferredtoasabolt

Thumbscrew:usedwhenonlyhandtighteningisneeded

Setscrew:usedtosecureobjectswithouttheheadprotruding,forexampleonapulley sothebeltdoesnotrip

Ubolt:usedtosecureobjectstoashaft,forexamplespringstothedifferential

Note:Students may benefitfromasafetydiscussionpertainingtotheuseoftaperedlugnutsandtorquepatterns.SeeActivityPlan4:RoadsideSurvivalformoredetailedinformation.

Activity1:IdentifyingBolts

1.Lay out aselection ofbolts on the workbenchin randomorder.Have each student select abolt and describewhatmarkings theysee.

2.Have students work together in pairsusinga steel rule(not “ruler”—that’s aking)tomeasure the lengthand diameter of the bolt theyhaveselected.Each steelrule should begraduated in both scales, asboth imperialand metric canbe found inCanada.

3.Workingfrom their handout,students should be abletodocument each bolt theyidentify fortype, length,threadpitchandstrengthclassification.

4.Additionalhandouts can then be modified andhandedouttostudentsas a testpageat alaterdate.

MetricandStandardSizing

Allimport vehicles—includingboth EuropeanandAsianmodels—have metric nuts andbolts.Theonly exception isolder Britishvehicles(pre-1985), whichcouldhaveWhitworth, standardormetricsizes.

Alldomestic vehiclesfabricatedbefore 1975—includingCanadianand Americanmodels—havestandardnuts and bolts. In 1975, Canada adopted themetricsystem. During thetransitionperiodbetween 1975 and 1985,Canadian-made vehicleshada mixture of metricand standardnuts andbolts.Chassis partsandheavy-duty truckswere the lastitems to completely change.Virtually all new Canadian-madevehiclesarenow madewith metric nuts and bolts. Exceptionsincludesomeparts such astransmissions, which may bemade inthe USA and shipped toCanadato beinstalled inCanadian vehicles.These mayhavestandard or metric nutsandbolts,as the USA is slowlyswitchingto metric. Makesure you are aware of whattypeofnutor boltyouareworkingon.Checkthe fit ofthesocket or wrenchtomakesureitistight(nowiggle)beforeattemptingto tighten or loosenit.

An easyway to determine ifacap screw(bolt)isstandardor metricis to look at the markings onthe head. A standard capscrew will haveradial linemarkings on the head.Themore lines, thehigher the quality and strengthofthecapscrew.A minimum grade 5bolt(standard) or

8.8(metric) isrequiredfor all automotive applications.


Grade2Grade5Grade7Grade8 /
Figure1—Standardcapscrewmarkings / Figure2—Metric capscrewmarkings

Figure3—Metric and standardcapscrews

Activity2:TapaHole

1.Cut a 1" piece ofaluminumand file theendssmoothtoremoveanysharpedges.

2.Mark outthecentre of the pieceofmetaland centre punchamark forthedrill bit to locate.

3.Drillthe appropriate size hole forthe size of tapbeing usedto tapthe threads. Referto aTapandDrillChart.

Note: Theappropriate hole sizeto be drilledmust be smallerthan theintendedfinishedsize.This is because thetapmusthavesomething tocut threadsinto. Remember: the outsidediameter of a bolt includes the crest of the threads. Forexample, a¼" bolthas anoutsidediameter of¼". Ifyouwere to drill thehole¼", the threadsof the bolt(andthe tap) would havenothingto grab onto.Youmustdrillthe hole slightly smaller sothe tapcanmake threads to thecorrect¼" size.

4.Installtheappropriatetapinto ataphandle.

5.Make sure thetap is straightandperpendiculartothe metal.

6.Turnthe taphandleoneturn clockwise tobegin threadingthe hole.

7.Rotate thetap handle½ turn counter-clockwisetobreakthechipbeing created.

8.Repeatsteps 6and 7 until the hole iscompletely tapped (orthreaded).

Activity3:TestThreads

1.Find a boltthatwill fit yournewly formed hole.

2.Insmallincrements,usea torquewrench to tighten theboltinto the newly formedhole.

3.Continueto tighten thebolt until thethreads strip.This is where thethreads fail andtheboltwillcontinue to move but will nevertighten.Recordthe torque reading.

4.A regularnut and boltof the same sizecan nowbe demonstratedusing the sameprocess,toshow how muchmore strain canbe applied to steel compared with aluminum threads.

Activity4:TeacherDemonstration—InstallaHeliCoilInsert

Nowdemonstrate drillingoutthedamaged threads and installing aHeliCoil insert. Itmay becost-prohibitivefor all students to installa threadinsert, but itwouldbe best iftheywere abletodo so.

GeneralInstructionsforInstallingaHeliCoilInsert

HeliCoils are precision-formedscrew threadcoils of18–8stainlesssteel wire.Theyaredesignedto replacedamaged threads and toreinforce tappedthreadsin lightmaterials, metalsandplastics. Each coilpossesses a tangthatis usedto drivethe insertinto a tapped hole. Afterinsertion, thetangis snappedoff.

Figure4

Theseinstructions should beconsideredguidelinesonly.Alwaysfollow manufacturer’sinstructions wheninstalling aHeliCoilinsert.

Figure5

1.Drill

Identify thedamagedthreadsbypitchandsize. Drill themoutusingthe specified drillsize.

2.Tap

Usingthescrewthread insert tap, tap theholetotheminimumdepth specified tofullyinstallthe HeliCoilinsert—and thebolt or screw that will bescrewed inafterwards.

3.Install

InstalltheHeliCoil assembly using theappropriate installationtool. The coilshould beinstalledtobetween one-quarter and half a turnbelow thetop surfaceofthetapped hole.

4.RemoveTang

Removethe tangto allowthe bolt or screw topassallthe way through theinsert. Breakoffthetangwith a flat-bottomedpunch or thetangbreakofftoolprovided.Placethetoolsquarely overthe tangand then strike itsharplywithahammer.Tangs onsparkplug

inserts and HeliCoil inserts with adiametergreater than ½"(12mm),canberemoved usingneedle-nosepliers.

Figure6—InvertedHeliCoilinsert

Note the notchat the tang’sbase,designed sothetang will breakoffmoreeasily uponimpact when struck with thetangbreakofftool

Resources

ThreadRepairUsingaHeliCoilInsert—RepairEngineering.com

EvaluationGuidelines

•Each studentwillbe gradedon the quality ofthethread madein the supplied aluminumbar.(Note:Thisshould be markedbefore thethread is stripped.)

Handouts

Thehandouts canbereused as atest at a laterdate bydeleting relevantinformationofthethreadtypeandsizeidentification.

Measurement Test

Individualskill tests canbe arranged byhavingstudentsphysically measureacollectionofdifferent bolts, andthen sort them bytypeand size.

ComprehensionTest

Haveeach studentexplain in writing,in his or herown words:

1.Theprocess andprocedure of how to tapa thread

2.Theprimary reasonshowand why a threadisstripped

3.Howa thread insertcanbe used toreplace the damagedthreads

4.Whena threadinsert wouldbe usedin place of undamaged threads (stateseveralexamples)

5.Howa torque wrench isused and whyit is necessary

Howto UseaTapandDrillChart

1.Determinethe size (diameter)andpitch of thread to beused.This is calledthetap size.

2.Find thehorizontal rowonthe chart thathas thedetermined tap size.

3.Find theappropriate drill sizeonthe samerow.Note: An alternatedrill size is oftengiven,duetothe fact thatdrillsizing canbedenoted in anumberof different ways—mm,fractions(inches), letters andnumbers.

Example1—Metric(Figure6)

M3.50.6requiresa2.9mmor#32drillbit.

If achart isnot available,the usualrule of thumb is to use thenextsize smallerdrill bit.

TapandDrill—MetricChart
TapSize / DrillSize(mm) / DrillSize(inch)
M1.6x 0.35 / 1.25 / #55
M2x 0.4 / 1.60 / #52
M2.5x0.45 / 2.05 / #46
M3x.05 / 2.50 / #39
M3.5x 0.6 / 2.90 / #32
M4x 0.7 / 3.30 / #30
M5x 0.8 / 4.20 / #19
M6x 1 / 5.0 / #8
M8x 1.25 / 6.8 / H
M8x 1 / 7.0 / J
M10x 1.5 / 8.5 / R
M10x 1.25 / 8.8 / 11/32
M12x 1.75 / 10.2 / 13/32
M12x 1.25 / 10.8 / 27/64
M14x 2 / 12.0 / 15/32

Figure7—Exampleofdrill bit sizechartformetrictaps

Example2—Imperial;alsoknownas“standard,”orinches(Figure7)

A�⁄��–18tapsizerequiresa.2570"or“F“drillbit(inthiscase,a.2500"or¼"wouldsuffice).

Figure8—Exampleofdrill bit sizechartforimperial taps