fitting and machinig 7.6

8/3/2019 Fitting and Machinig 7.6

1/48


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Lathe operations--turning 267

Figure 89 Centering using a short drillFigure 86 Setting a circular form tool to the work

Drilling in the latheWhen drilling in a lathe it is usual to hold the workpiecein the chuck and the drill in the tailstock, either in a drillchuck or directly in the tailstock quill, depending on theshank (see Fig. 87).

Figure 87 Drilling in the latheFor accurate, true and smooth holes, the following conditions are essential:

an accurate ground drill; thr: headstock and tailstock in alignment; the drill be given a t rue start by 'centre drilling'.MethodsTrue start of drillThis can be done as illustrated in Figure 88 or by 'centering' using a short or flat drill, as in Fignres 89 and 90.

rFigure 88 Centre drilling using a centre drill

o

work-piece

Figure 90 Centering using a short flat drilltool bitI

- L L . . L - . L L - " - - " ~ workpieceFigure 91 centering using a lathe toolI f a true start for the drill is required, the centre spot couldbe machined with a single-point cutting tool (Fig. 91).Large drills used in tailstockBy attaching a lathe carrier to the drill and allowing itto rest against a metal bar held in the tool-post, large drillsare prevented from rotat ing and thus damaging thetapered bore in the tailstock spindle (see Fig. 92).

Figure 92 Lathe carrier attached to large drill


3/48

16Drills and reamers

Drm TypesTaper Shank DrillsTaper shank drills (Fig. I) are general purpose drills suitable for a wide variety of materials and applications. Theyhave morse taper shanks for holding and driving. Thetang at the end of the shank is used for ejecting the drillfrom the socket or sleeve.

Fractional drills are manufactured to ANSIB94.11-l967 Standard. Metric drills are made to theAmerican Metal Cutting Tool Institute Standard.Extra length drills-taper shankExtra length taper shank drills (Fig. 2) are used for deepholes and for locations that cannot be reached with standard length drills. Various combinations of diameter,overall length and flute length are available.Core drills-taper shankTaper shank four-flute core drills (Fig. 3) are used toenlarge drilled, punched or pre-cored holes in a widerange of materials. A core drill cannot produce a holefrom the solid. The advantages of core drills are: increased productivity, superior surface finish, and greateraccuracy in the hole size and location.Straight Shank DrillsJobber drills-straight shankJobber drills (Fig. 4) are the most popular drills, usedby engineers, tradespeople and at home. These drills aredesigned to give optimum performance in a wide range

Figure 1 Taper shank drill

Figure 3 Taper shank core drill

of materials. They are manufactured to ANSI B94.111967 Standard.Stub drills-straight shankStub drills (Fig. 5) are shorter overa.l1 and have a shorterflute length than jobber drills. Therefore they have greaterrigidity. They are widely used by engineers and tradespeople. Major applications are: drilling of sheet metal; drilling of shallow holes in a wide range of materials; drilling of hard metal, for example stainless steel; drilling out broken studs; more accurate hole location.Long series drills-straight shankLong series drills (Fig. 6) have the same flute length andoverall length as standard taper shank drills. They areused for drilling deep holes or in locations that cannotbe reached with standard length jobber drills.Deep hole drills-straight shankDeep hole drills (Fig. 7) have been specially designed fordeep hole drilling applications. The parabolic flute designenables the swarf to be cleared from the drill withoutfrequent withdrawal of the drill and provides a heavierweb, which makes the drill far stronger than conventionaldrills. The improved rigidity of the drill improves production rates and the drilled holes are more accurate andstraighter. Deep hole drills are available in various fluteand overall lengths and can be used in locations that cannot be reached with standard long series drills.

Figure 2 Taper shank drill extra length

Figure 4 Jobber or straight shank dril l

Figure 5 Stub drill or straight shank drill Figure 6 Long series straight shank drill

.Figure 7 Deep hoie straight shank drill142


4/48

Drills and reamers 143Centre Drills (combined drill and countersink)Plain TypeCentre drills (Fig. 8) are used to drill female 60 centreholes in the ends of shafts and components that will laterrevolve between centres. Centre drills are also used toensure accurate startingand centering. They are manufactured to ANSI B94.1I-1967 Standard.Masonry Drills-Tungsten Carbide TippedMasonry drills (Fig. 9) are used for drilling holes inmasonry materials. These drills are available in threedifferent lengths: type SF for short fixing devices; typeSB for drilling through 4 t in. (29 em) brick plus renderand tile; and type DB for drilling through a double cavitybrick wan plus render and tile. All drills are suitable foruse in portable electric drills, hand drills and drill presses. A specially designed IMP drill is available for usein rotary-impact portable drilling machines.

Figure 8 Centre drill (combined drill and countersink)

Panel DrillsPanel drills (Fig. 10) have been developed to drill holesfor rivets in flat and curved panels and are used by sheetmetal workers, and other tradespeople. 'l;hese drills arerecommended only for shanow holes no deeperthan Ittimes the drill diameter. They can also be usedfor drilling hard materials such as stainless steel. Theymay be either single ended ('Buns-eye') or double ended('Twin-point'). When using twin-point drills, ensure thatthe chuck jaws are fully tightened.Reduced Shank DrillsReduced shank drills (Fig. 11) are designed to increasethe drilling capacity o f t in., -!-in. and+n. diameterdrill chucks. These drills must be used with extreme careand run at recommended speeds to avoid overheating ofthe drill point.

Figure 9 Masonry drill

Figure 10 Panel drills

Figure 11 Reduced shank drillD BitThe D bit (Fig. 12) is a round tool bit of hardened steelground to the required size and shape (Fig. 12). I t is usedas a quick means of making a hole-sizing tool or forflattening the bottom of a drilled hole.

cuttingedge",( ('-----'---91'u-Q ------I.--li1

Figure 12 D bit

Drm Accessoru@sDrill ChuckParanel shank drills and tools are held in a drill chuck

Figure 13 Drill chuck and key

(Fig. 13). Fig. 13 shows the keyed type commonly canedJacobs (who has been the largest manufacturer). Keylesschucks are also used, but lack gripping power.Drill SleevesDrill sleeve. (Fig. 14) are used to increase the taper sizeof a tool to suit the machine being used.

Figure 14 Drill sleeve, No. 1-5 inside 2-6 outsideDrill DriftThe drill drift (Fig. 15) is used to remove taper shank drills

Figure 15 Taper shank and socket


5/48

144 Drills and reamersfrom the machine or sleeve. Never use a file tang orsimilar tool. Always place a piece of wood or similarmaterial on the machine table or work for the tool to landon as it is drifted out. It must not fall free.Nomenclature (Fig. 16)Body The portion of the drill extending from theextreme cutting end to the start of the shank.Body clearance The portion of the body reduced indiameter to provide diametral clearance.Chiseledge angle The obtuse angle between the tangentto the projection of the chisel edge at the axis, and theprojection of the line through either outer corner and thecorresponding chisel edge corner on a plane normal tothe (drill) axis. This angle lies in a plane normal to thedrill axis.Drill diameter The measurement across the cylindricallands at the outer corners of the drill.Flute length The axial length from the outer corners ofthe cutting lips to the extreme back end of the flutes.Helix angle The acute angle between the tangent to thehelical leading edge of the flute at a point in this edgeand a plane containing the (drill and helix) axis and thepoint in question. This angle lies in a plane normal tothe radius at the point on the edge. The helix angle isusually measured at a point close to or coincident withthe outer corner.Lip clearance angle The acute angle between a planenormal to the (drill) axis and the tangent, at a point onthe lip, to the drill flank in a plane normal to the radiusat the point in question. This angle is usually specifiedand measured at the outer corner.

Lip length The minimum distance between the outercorner and the chisel edge corner or inner corner. (Fora straight lip it is the true length of the lip.)Overall length The distance between two planes normalto the drill axis at the extreme endsof the cutting diameterand shank respectively.Point angle The included angle between the projectionsof the lines joining the outer corners and the corresponding chisel edge corners on a plane parallel to one (or both)of these lines and the drill axis.Web.{core) thickness The diameter of the circle normalto the axis through the roots of the flutes at the point endof the drill.Flutes The grooves in the body of the drill to providelips and to permit the removal of chips and allow cuttingfluid to reach the lips.Operation of drillsFor efficient drilling operations, adherence to the following guiding principles is recommended. Selection of thecorrect drill for the application is most important. Mostdrills have a point angle of 118 0 , which is suitable formost materials. However, performance can be improvedwhen drilling somematerials by repointing the drill. Nextit is important to select the correct speed and feed. Thechoice of speed and feed are restricted by the degree ofhardness of the work material. Initially, use moderatespeed and feed, increasing one or both to achieve maximum production for a reasonable drill life beforeresharpening.The workpiece must be securely held and supported asclose as possible to the drill. Always clamp the work,never hold it by hand. When using a straight shank drill

TAPER SHANK - IN ACCORDANCEWITH BRITISH STANDARD 65.10-MACHINE TAPERS

webchisel edge

body land width

flutesIf------ flute length1-- - - - - - body ------. .Joverall length

S h ~ l - a - X - i s - _ - _ - _ ~ ~ : t r : : a : i g : ; : h t ; - - _ - r - t : ~ ; : : - - ....diameter shank~ shank-JI - - l eng th

neck

e taper shanktang tang

6 ~ C I J

--f reduced shank E----Figure 16 The important features of a drill


6/48

146 Drills and reamersTable 3 (cont)

Material and hole condition

R Monel, nickelMagnesium andalloys

Die castings(zinc base)Gunmetal leaded& brass casflngs

None

Sulphur basedoil

Soluble oil

Soluble oilSoluble oiland kerosene

Soapy waterSoluble oil

SUlphur baseoil

Cutting fluidIncludedpoint Speedangle (ftlmin) (m/min)118 0 300-400 91-1221180 150-300 46- 91118 0 200-500 61-153118 40-100 12- 30135 0 20- 60 6- 18135-140 30- 50 9- 1590 100-300 30- 91118 120-150 37- 46118 120-140 37- 431180 100-115 30- 35118 0 65- 90 20- 27140 0 25- 65 7.6-20118 0 50- 70 15- 21118-140 40- 55 12- 17130-150 30- 40 9- 12118 0 50- 90 15- 27125-135 35- 50 11- 15118 20- 30 6- 9125-135 40- 55 12- 171180 25- 40 7.6-1260_90 0 300-500 92-153

170

190-240

45- 5540- 70

155

70- 90

110-200160-275

210

110-130130

200-400250300340150-200250170250

Hardnessrange(B.H.N.)

Tool and- spring55 tonne65 tonne75 tonneFerriticMartensiticAustenitic,Mart. freemachiningAust. freemach.ining

3 ~ O / o nickelsteelFree CuttingMild 30 tonMedium carbon35 tonMedium carbon45 ton

Thermo-plasticsNickel alloys

Steel, stainless

Wood

K Monei

Plastics

SteelSteel. alloy

Sleel

Table 4 Recommended feeds for various diameter drillsDiameter of drill(inches)

Undert]-to+ttott to 11 inch and over

Feed(inches per revolution).001 to .003.002 to .006.004 to .010.007 to .015.015 to .025

is 118. The angle must be equal on both sides ofthe axis(59) and the cutting edge lip must be the same lengthon both sides of the drill axis (Fig. 17). If the two cuttingedges are not equal in length and/or the angles are notequal, the drill will cut an oversized hole and breakagemay occur. The drill must be sharpened with a lip clearance of 12 to 15 (Fig. 18). I f the lip clearance isexcessive, the strength of the cutting edge is reduced andmay result in fracture of the cutting edge.Note: It is best to start with a moderate speed and feed, increasing either one,or both, after observing the action and condltion of the drill. Use conversion tables for metric equivalents.Drill SharpeningMost drilling problems are due to improper sharpeningof the drill. For general purpose drilling the point angle

Hand-grinding drillsWhenever possible drills should be sharpened on a drillpointing machine, but when this is not possible thefollowing guidelines will help when sharpening drills byhand. The thumb and forefinger of the left hand are usedas a pivot, as illustrated and the back of the drill is heldwith thumb and forefinger of the right hand, as shownin Figure 19. The drill is rotated in a clockwise direction,advancing into the wheel.The intense local heat that can be generated in grinding operations frequently results in surface crackingbecause of uneven thermal expansion and contraction.Grinding pressures should therefore be moderate whenpointing drills and the use of a free-cutting wheel and acopious supply of water is desirable. When water is notavailable grinding can be done dry by taking very lightcuts. If excessive heat is generated the drill should notbe cooled in water but left to cool in air. Grinding cracksthat seem invisible can enlarge under working conditions

Lip clearancechisel angle125" . 135'

Point angle~ ' : >


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Dril ls and reamers 147

Table 5 Trouble-shooting chart for high-speed steel drills

Split pointingSplit pointing is recommended to reduce the point pressure and greatly improve the cutting action of the chiseledge. (Fig. 22.)Trouble ShootingA useful chart , which can be used to identify and thenremedy a variety of possible drilling problems, is shownin Tabie 5.

Figure 19 Sharpening by handWeb thinningMost drills have a web that is thin near the point of thedrill. As a drill is resharpened it becomes shorter, the webthickness becomes greater, and the drill point developsa much longer chisel edge. This longer chisel edge willresult in more pressure being required for penetration,resulting in greater heat generation and a reduction in thelife of the drill. The chisel edge can be reduced by webthinning.

For correct web thinning it is important that equalamounts of material be ground from either side of thechisel edge until the total length of the edge returns tothe same value as that found on a new drill. (Excessiveweb thinning weakens the point of the drill and splittingof the web may occur.)The ground surface produced by web thinning mustblend evenly into the flutes without ending abruptly. Theweb thinning should extend 50"70 to 100% of the drill diameter along the flute. (See Fig. 20.)~ - - - - - - - - - - ~ - - -The web is the metal column which separates~ - ~ . eb thickness near shank showing web A drill with webpOint Increase properly thinnedFigure 20 The web and th inned webPOint geometryDrills are given points on precision automatic grindingmachines. The standard point geometry on drills has anincluded angle of 118' with a lip relief angle of 12' to15'. Such a drill is suitable for most materials. However,a user will sOmetimes find it necessary to give the drilla point that is better suited to the material beingmachined. (Fig. 21.)

ProblemShort paint-life

Blue cutting lipsouter cornersburnt offChipped cutting

lips or outercorners

Drill breaks

Hole oversize

Rough hole finish

Drill splits up

Tang twisted

Metal welds todiameter landor flute face

Possible cause Suggested remedySpeed too fast. Reduce speedblues cutting lips Apply cutting fluidMetal is hard, Reduce speedwears cutting lips Apply cutting flUidInsufficient ijp Repaintrelief, drilling dry Apply cutting fluidSpeed too fast Reduce speedNo coolant Apply cutting fluidExcessive lip Regrind

reliefExcessive feed Reduce feedGrinding cracks Regrind withoutfrom plunge overheatingcoolingFeed too high Reduce feedFlutes packed with Wtthdraw frequentlychips to clearMisaligned or Realign and clampunclamped fixture firmlyBlunt drill Resharpen soonerSpring in work Pack and clampmore rigidlyMachine spindle AdjusVrepiaceend-play machine bearingsWorn front-taperon diameter lands,jams drill in hole Shorten drill, repaintCutting lip length Repointnot equalAngle, axis tocutting lips differ RepaintPoint thinningnot central Repoint then thinWorn machineconditions Recondition machineDrill guide bush worn Replace guide bushBiunt drill ResharpenPoint poorlysharpened ResharpenFeed too highIncorrect or nocutting fluid Apply cutling fluidFeed too high Reduce feedInsufficient lip relief RegrindWork deflectionupwards at break Support and clampthrough work firmlyThick web increasespressure Thin webMatching tapers Clean up shanks, reamor shank and sleeves or spindlessleeve dirty,burred or wornHeat from high Use floW of correctrevolutions, coolant if trouble

incorrect or no persists, reducecutting fluid speedContinued on next page


8/48

148 Drills and reamersTable 5 (cant)ProblemExcessive feedpressureUnequal chipsfrom cutting lipsDrill squeaks

Multi-sided holethrough thinmaterial

Burrs on holeundersideReduced shankbroken from drill

Possible causeWeb too thickDrill bluntInsufficient l ip reliefPoint has unequallip lengths and/orpoint anglesInsufficient lip fsUefFront-taper worn ondiameter lands

Excessive lip relief

Blunt drillFeed too highFeed too high,flutes ciogged,pistol drill leanedsideways jammingdril l in hole

Suggested remedyThin webRepaintRegrind

RepaintRegrindShorten drill, repaintReduce lip relief toabout one degree;drill through thinmetal into supportingmetal or hardwoodbase; clamp the workRepaintReduce feedReduced feed, clearflutes ,frequently,keep drill aligned

Using Centre DrillsThe centre drill must be held firmly. Misalignmentbetween drill and workpiece will allow the drill to cut onone lip only and will impose an uneven cutting load onthe drill point. Forcing or pumping the centre into theworkpiece will split the drill web. Dulling or cutting onthe outer corners or cutting lips indicates an excessivecutting speed is being used or that the drill requiresresharpening. A plentiful supply of the recommendedcutting fluid must be applied to the centre drill andworkpiece.CountersinkingMaking a cone-shaped enlargement at the entrance of adrilled hole for the purpose of providing a seat for thehead of a countersunk screw, a bearing surface in thework for a centre lathe, or a recess in which the end ofa rivet may be spread, is called countersinking.Figure 23 shows the common countersinking drill usedfor this purpose. For large holes a countersink having apilot to fit the previously drilled hole is necessary to keepthe drill true and to prevent chatter (see Fig. 24).

CHISEL ANGLE90 . 100'

.. HARD and TOUGH MATERIALSMANGANESE STEEL RAILS, etc,CHISEL ANGLE1150 .125

.. CRANKSHAFT or SPLIT POINT forDEEP HOLESOvef'comea excessive thrust (due to heavy web)HARD and TOUGH MATERIALS

~ 1 1 8 .HISEL ANGLE125 135.. BRASS and SOFT BRONZE

CHISEL ANGLE CHISEL ANGLE1250 1350 125 135 0

.. HARDWOOD, BAKELITE, HARD RUBBER and .. WOOD, RUBSER, BAKELITE, FIBER,FIBERS, SOFT and MEDIUM CAST IRON MOULDED PLASTICS

IMPORTANT: lip lengths and angles must b8equal.

.. REGULAR POINT ... GENERAL PURPOSE,MILD STEELS, LAMINATED PLASTICS, elc. .. SOFT ALUMINIUM, MAGNESIUM, COPPER .. HEAT TREATED STEELS. DROP FORGINGSand MEDIUM HARD BRASS and CONNECTING RODSCHiSEL ANGLE115125CHISEL ANGLE125 1:35CHISEL ANGLE1 2 5 ~ - 1:35"


9/48

Dril ls and reamers 149leave .00511 to.015/1 chisel edge

axis -

grind to followchisel edgeFigure 22 Geometry of the split point

Tabie 6 Recommended speeds fo r centre drilling

Speed Number size of centre drill(feeY (metresl CuttingMaterial min) min) 2 3 4 5 6 7 fluidAluminium and Kerosene andits alloys 250 76 20537 15278 10213 7640 5093 3820 3055 soluble oilBrass & bronze,ordinary 225 69 18382 13750 9191 6876 4582 3438 2749 DryBronze, hig htensile 110 34 8986 6722 4493 3361 2246 1660 1344 DryIron cast:Soft 100 30 8170 6111 4085 3056 2037 1528 1222 Dry, air blastMedium 75 23 6112 4584 3056 2292 1528 1146 917 orHard (chilled) 15 4.6 1224 918 612 459 306 229 183 Soluble oilMalleable 85 26 6944 5194 3472 3598 1732 1208 1039 Soluble oil

metal orhigh nickel steel 40 23 3268 2445 1634 1222 815 611 489 Mineral lardoilPlastics 200 61 16340 12222 8170 6112 4074 3056 2444 Dry

Mild .2-.3C 95 29 7761 5806 3880 2902 1938 1451 1161 Soluble orMild .4-.5C 75 23 6112 4584 3056 2292 1528 1146 917 SUlphUrized oilTool 55 17 4493 3361 2246 1680 1123 840 672 Sulphurized oilForgings 45 14 3676 2750 1838 1375 917 687 550 Sulphurized oilAlloy 25 7.6 2042 1527 1021 762 509 382 305 SulphUrized oilHigh tensile:35-40 Re. 35 10.7 2860 2138 1430 1070 713 534 428 Sulphurized oil40-45 Re. 30 9.1 ' 2452 1833 1226 917 611 458 367 Sulphurized oil40-45 Re. 20 6.1 1634 1222 817 611 407 306 244 Sulphurized on

steel:Free machining 55 17 4493 3361 2246 1680 1123 840 672 Sulphurized oilWork hardening 35 10.7 2860 2138 1430 1970 713 534 428 Sulphurized oilTable 7 Recommended feed rates for centre drilling

Drill number Feed (inches per revolution) Feed (millimetres per revolution)No.1t04 .001 to .003 .025 to .076No.4 to No. 6 .002 to .006 .051 to .152No.6 to No. 7 .004 to .010 .102 to .254

Figure 23 Countersink Figure 24 Countersink withpiiot


10/48

Drills and reamers 145hold it firmly in the chuck as slippage will inevitably causedrill breakage.

Taper shank drills are driven by tbe taper and not thetang. The tang is designed for ejection not driving. I t isessential that the drill shank and socket are a good fit andfree of burrs and grit, otherwise slippage will twist thetang. When removing a taper shank drill ensure that thecorrect sized drift is used and take precautions againstdamaging the drill point when it falls from the sleeve.When drilling by hand apply a constant pressure. Donot allow the drill to 'dwell' as this will cause dulling ofthe cutting edge. Some materials harden by being workedand immediately destroy the cutting lips. The flutes ofthe drill must be kept clear. Clogging of the drill flutesprevents sufficient lubricant from reaching the drill point.The drill flutes may be cleared occasionally by withdrawing the drill after penetrating about two or three diametersin depth.Excessive heat damages the drill cutting lips. Use aplentiful, well directed flow of cutting fluid to absorb theheat generated during cutting.Deep-hole DrillingDeep holes are usually defined as holes having greaterdepth than four times the diameter of the drill. Speciallydesigned deep-hole drills are available, which are morerigid than standard drills and clear the swarf moreefficiently. The advantage of deep-hole drills is that fasterfeed can be used and deeper holes can be drilled beforeswarf has to be cleared from the drill flutes. Oil-hole drillsare also recommended for drilling deep holes.Deep holes can be drilled using standard drills but itis necessary to use slower speeds and feeds and to frequently withdraw the drill to clear the flute of swarf.When using standard drills select the speed and feed, andreduce by the percentage reduction listed in Table I.Some Criteria for Drill UsageLimits of tolerance on the diameter of twist drills arelisted in Table 2.

A guide for selection and use of drills is given inTable 3.Recommended feeds for various diameter drills areshown in Table 4.

Table 1 Recommended speed and feed reduction when deepdrilling with standard drillsDepth of hole Feed Speedin drill reduction reductiondiameters ('!o) (%)

5 10 12.56 12 157 14 17.58 16 209 18 22.510 20 2511 22 27.512 24 3013 26 32.514 28 3515 30 37.516 32 4017 34 42.518 36 4519 38 47.520 40 50

Table 2 Umits of tolerance on the diameter of twist drillsDrill diameter at point Back taper on diameterUp to andOver including Tolerance Tolerance

0.32 mm t + .0000 - .0005 .0000 to .0008 per inch.L t + .0000 - .0007 .0002 to .0008 per inch8.L 1- + .0000 - .0010 .0002 to .0009 per inch4.L 1 + .0000 - .0012 .0003 to .0011 per inch21 2 + .0000 - .0015 .0004 to .0015 per inch2 3 + .0000 - .0020 .0004 to .0015 Inch

ANSI 894.11 1967Table 3 Guide for seiection and use of drills

Hardness Includedrange point SpeedMaterial and hole condition (B.H.N.) angle (ft/min) (mlmin) Cutting fluidAluminium alloys Deep hole 50-140 118 200-300 61- 91Alum alloys cast High silicon 45-120 118 80-120 24- 37 Soluble oil

Low silicon 35-110 118 0 140-200 43 - 61Aluminium forged Shallow hole 50-140 1180 200-500 61-153Alum alloys Keroseneforged Deep hole 50-140 118 0 200-500 61-153Brass .Leaded freemachining 100-150 118 0 200-300 61- 91Bronze Castings 80-120 118 0 60- 90 18- 27Wrought 120-220 1180 35- 80 11- 24 Soluble oilCast iron Chilled or white 400 150 0 15- 25 4.6-7.6Hard grey i ron Over 200 118 0 45- 50 14- 15Cast iron Medium grey iron 150-200 90 0 _110 0 60-110 24- 34 Dry orSoft grey iron Below 150 90 0 140-150 43- 46 compressedair

Malleable 140 118 0 80-100 24- 34Cast Iron 8,G, As cast 220 118 0 40- 50 12- 15Annealed-ferritic 190 1180 45- 65 14- 20 Soluble oilCopper 45-110 1000 70-100 21- 30"---Continued on next psg,


11/48

270 Lathe operations-turning

radial line

normal rake

cutting edge

positive inclination

direction of cut


12/48

Lathe operations-turning 271

Figure 104 Boring tool for counterbore

Boring a Tapered HoleThe set-up for boring a tapered hole is essentially the sameas for parallel boring except for tool setting, compoundslide setting and measuring.

Speeds and FeedsRevolutions per minute (r.p.m.) The r.p.m. figure is set inrelation to the hole size, material to be cut, cutting toolmaterial and the rigidity of the set-up. The r.p.m. valuedetermined from a cutting nomogram or chart makes agood starting point. Variation in r.p.m. is often requiredas a remedy for chatter when the set-up unavoidably lacksrigidity. In such cases, r.p.in. may be reduced for oneor two cuts until the chatter marks are removed.Feed The rate of feed is set to suit the conditions asfollows: Tools with an approach angle can use faster feeds thantools with a relief angle on the cutting edge (see Figs103 and 104). Cast iron, bronze and brass are machined better withfeeds faster than those used for cutting mild steel. Good finishes require finer feeds.Note: Tradespeople can generally overcome mostmachining problems by variation of speeds and feeds.Boring Technique and MeasurementI Take a short cut (2 mm approx.) to establish a trialhole 0.5 mm undersize, measuring with a steel rule. Thetrial hole can be used to indicate this size.2 Using a light cut true the bore.3 Check for parallelism using inside calipers and amicrometer, or telescopic gauge and a micrometer, oran inside micrometer if the hole is large enough.If the hole is not parallel, check the machine slidesand adjust the gib strips. Interference by the boringbar or misalignment of the headstock will also causeerrors.4 Measure the diameter of the bore and calculate thedepth of cut required to reach the finished size.5 Use cross-slide dial settings for successive cuts (usingautomatic feeds) until the correct bore diameter isreached.6 Measure the size of the hole in the first 2 mm beforetaking the final cut.

face relief1J--_r--J~ : ; : ; : : : ; : : ; : . : - \ owork / / Tnose radius end relief

cutting edge

Boring I i Parallel HoleDifficulty in obtaining good finish and accurate size isoften the most important factor in accurate boringoperations.Selection of Boring Bar or Boring ToolI t is difficult to provide a rigid set-up because: the tool must fit into a hole smaller than the finishedsize and also allow chip space; the bar must be long enough to pass through the holewithout interference.For maximum rigidity select the shortest boring tool (orset the shortest extension of the boring bar) for the lengthof the hole.

Boring tools for through holes produce the best resultsif an approach angle of approximately 15 and a reliefangle of 5 are provided (see Fig. 103).Boring tools for stepped holes must have approximately5relief behind the tool point for both the face and thediameter (see Fig. 104).Nose radius should be kept to a minimum to avoidchatter, but must be large enough to maintain toolstrength and provide the desired finish.

Tool SettingHeight of the tool When boring parallel holes, it is usualto set the tool a little above centre height (I mm approximately). This has no effect on parallelism of the bore butgives the following two advantages:. Downward pressures decrease the depth of cut andtherefore prevent damage to the bore should the tooldig in.. Morechip space is provided under the bar so there isless likelihood of the tool digging in because of chipsjamming underneath the bar.Alignment of the bar The bar is set parallel to the directiou of travel (feed), otherwise interference might occur,which could deflect the bar, causing tapering or bellmouthing of the hole.

Tool SettingThe tool point must be on centre height (see Fig. 105)otherwise the tapered sides cannot bemachined straight.tool point oncentre height

Figure 105 Tool point on centre height


13/48

150 Drills and reamersCounterboringThe operation of enlarging the end of a hole to providea recess for the cylindrically shaped heads of certainscrews, bolts and pins is called counterboring.It is essential for a counterbore to be provided witha pilot to guide it into position and keep it steady duringthe cutting. Figures 25 and 26 illustrate two different typesof counterbore.

Figure 25 Counterboring Figure 26 Inserted cuttertype of counterboreSpot facingThe operation of facing the surface around the end ofa hole to provide a flat seat for a bolt head, the shoulderon a shaft, or similar fitting, is called spot facing (Fig. 27).Spot facing may be performed using some counterboring tools.

Figure 27 Spot facing

Reamillg produces holes having a high degree ofaccuracy, roundness, parallelism, and finish.The operation may be carried out at the bench, usinga hand reamer, or it may be done in the lathe or drillingmachine using machine reamers (hand reamers may beused in the lathe if no machine reamers are available).Types ()f ReamerHand ReamersHand reamers (Fig. 28) are right-hand cutting tools withleft-hand helical flutes. The cutting end of the handreamer is ground with a starting taper to provide easyentry of the reamer into the hole. The reamer is operated by using a tap wrench on the square-ended shank.Adjustable Hand ReamersAs the name implies, adjustable hand reamers areadjustable for diameter (Fig. 29). They are invaluable inthe jobbing shop where a part is required to have a boreof non-standard size, for example a +in. reamer can beadjusted from Hin. to H in. (12 to 13.5 mm).Machine ReamersMachine reamers (Fig. 30) also are right-hand cuttingtools with left-hand helical flutes; they have a 45 bevellead, and a morse taper shank.Chucking ReamersChucking reamers (Fig. 31) also are right-hand cuttingtools with left-hand helical flutes and a 45 bevel lead.They are designed for use in drill presses, turret lathesand automatic machines.Taper Pin ReamersTaper pin reamers (Fig. 32) have a taper of t inch perfoot and are designed to ream holes for standard taperpins. Thebest results are obtained if the hole to be reamedis drilled a few thousandths of an inch smaller than thesmall diameter of the finished ream hole. The point ofeach reamer will enter the hole reamed by the nextsmallest size.

Figure 28 Hand reamer

Figure 29 Adjustable hand reamer

Figure 30 Machine reamer taper shank

Figure 31 Chucking reamer straight shank; ; , , = ~ -Figure 32 Taper pin hand. reamer


14/48

Drills and reamers

;1.. LFigure 33 Bridge reamer taper shank

151

Figure 35 Morse taper socket reamers-finishingBridge ReamersBridge reamers (Fig. 33) have been specifically designedfor reaming rivet and bolt holes in structural iron andsteel work. The cutting end of the flutes is tapered to permit the reamer to enter holes that are out of alignment,thus facilitating the reaming operation.Morse Taper Socket ReamersMorse taper socket reamers (Figs 34 and 35) are righthand cutting tools with left-hand helical flutes. Bothroughing and finishing types are available.Shell ReamersThe shell reamer (Fig. 36) is a short reamer, approximately twice as long as its diameter, and made in sizesof 1 in. to 2j-in., with a tapered bore and driving slotenabling it to be mounted onto a suitable shank formachine reaming. The cutting lead is the same as thatof a machine reamer and the flutes are backed off or cylindrically ground. Cylindrical grinding is also referred toas rose grinding.

Figure 34 Morse taper socket reamers-roughing

Figure 36 Shell reamer

Adjustable Machine ReamerMany types of single-blade, two-cutting-edge reamers areavailable for machine reaming, mainly in mass production applications. Three of the many designs are illustrated in Figures 37, 38 and 39.

~ F - - ~ . p - -L ~ - - - - - - -~ ~ ~ . adjusting screwt ---u: : l r==--_)=3+---+-

Figure 37 Double-endedcutter

Figure 38 Adjustabledouble-ended cutter

steel ball r / adiusting screw

-tt:3 E--! VJ retaining plate Figure 39 Floating doubleended cutter


15/48

Lathe operations-turning 273Tool setting and measuring are done by the samemethods previously described. Advantages are:

Automatic feeds can be used; The taper length can be considerably longer than is possible when using a compound slide.Accurate Setting Angle of the Compound SlideFirstly clamp a good parallel strip on the cross-slide surface ahead of the tool-post and set it true with the bedways by using a clock indicator. Place a sine bar againstthe parallel with gauge blocks for the required angle.Using a clock indicator from the tool-post operatingagainst the sine bar, the compound slide can be set tothe precise angle. Remember the cutting tool must be onthe centre line to produce the correct angle. (See Fig. 110.)

Figure 110 Accurate setting of angle of compound slide

Reaming produces holes with a high degree of accuracy,roundness, parallelism and finish more easily and consistently than other methods.F'reparatkm of the WorkThe diameter of the hole must be smaller than that ofthe reamer. This diameter depends on: the type of reamer; the diameter of the reamer; the kind of material to be cut.Note: Reaming does not correct any errors in positionor alignment of the hole, therefore it is necessary to borethe hOle to the required size, thus correcting errors of thistype.Before reaming, it is necessary to drill to remove excessmetal. Then the hole is rounded by boring to leave thereaming allowance as specified in Chapter 16, 'Drills andReamers'.ReamiU1J9 UsiU1Jg a Machine Reamer1 Prepare the hole by drilling and/or boring.2 Check the alignment of the tailstock; misalignment cancause a tapered or oversize hole.3 Clean the tapered surfaces of the reamer and the tail

stock quill. Fit the reamer into the tailstock and lockthe tailstock in position.

4 Set the revolutions per minute to give a cutting speedas specified in Chapter 16, 'Drills and Reamers'.5 Apply a cutting fluid as required for the type ofmaterial to be reamed. This will help the cutting action,give a better finish, and reduce wear on the reamer.6 Enter the reamer into the hole, using a steady even feed(see Fig. 111).7 Withdraw the reamer, for which the lathe can bestopped.8 Never turn the reamer backwards; this tends to dulland damage the cutting edge.

Figure 111 Reaming using a taper shank maohinereamer

Reaming Using a Hand ~ e a m e r1 Fit a suitable tap wrench to the reamer.2 Enter the reamer into the prepared hole, then bring thetailstock centre into position to support the reamer;then arrange that the tap wrench rests on the top slide(see Fig. 112).3 Apply a cutting fluid (as recommended in Chapter 16,'Drills and Reamers').4 Turn the workpiece by hand and turn the tailstockhand-wheel to push the reamer through tbe hole.5 Withdraw the reamer without turning the work.

Figure 112 Reami ng using a hand reamer


16/48

Drills and reamersamer Nomenclature (Figs 40 and 41)

diameterno circularlandbevel leadlength

bevel leadtaper lead

taper lead ===:3::::::::::::qangle .=t ~ bevel lead circularangle land taperlead length

d reamer

40 The important features of a hand reamer

hine reamer bevel lead

; ; ; ;;;;;;~ ; ; ; ~ ~ - ' ~ e v e l l e a d;;;;;;; ::i angle. I .1circular l a n ~ l-- bevel leadlength

diameter

41 The important features of a machine reamer

iand The cylindrical ground surface adjacent toe cutting edge, on the leading edge of the body land.rimary clearance That portion of the land removed toovide clearance immediately behind the cutting edge.econdary clearance That portion of the land removedprovide clearance behind the primary clearance.aper lead The tapered cutting portion at the enteringnd to facilitate the entry of the reamer into the hole.t is not provided with a circular land.) It is 2 included

lead The angular cutting portion at the enteringd to facilitate the entry of the reamer into the hole.It is not provided with a circular land.)taper The reduction in diameter of the reamer .rom the entering end towards the shank.

iameter The maximum cutting diameter of the reamr at the entering end. It is measured directly behind thepered lead on hand reamers and behind the bevel leadmachine and chucking reamers.

aper lead length The length, measured axially, of theer lead, usually It times the dial1!-eter.lead length The length measured axially of the bev

Reamer TolerancesLimits of Tolerance on Cutting DiameterThe tolerance on the cutting diameter is measured immediately behind the bevel or taper lead for parallel reamers. The diameter tolerance is that of an m6 shaft to British Standard 1916, as stated in B.S. 122: Part 2: 1964,also Australian Standard B43, Part 2-1967. Reamershaving m6 diameter limits are intended to produce H8limit holes for high-tolerance reamers and smaller H7limit holes from low-tolerance reamers.Table 8 Reamer tolerances

Nominal diameter Cutting-edgerange diameter(inches) (mm) (inches) (mm)Up to Up toOver and Over and High Low High Lowincluding including + + + +

0.0394 0.1181 1 3 0.0004 0.0001 0.009 0.0020.1181 0.2382 3 6 0.0005 0.0002 0.012 0.0040.2362 0.3937 6 10 0.0006 0.0002 0.015 0.0060.3937 0.7067 10 16 0.0007 0.0003 0.018 0.0070.7087 1.1811 18 30 0.0008 0.0003 0.021 0.0081.1811 1.9685 30 50 0.0010 0.0004 0.025 0.009


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Drills and reamers 1530PWSJt!OI'l elf ReamersThe conditions under which reamers are used vary considerably and the figures given in the following paragraphsare intended as a guide only.Correct Hole SizeThe correct amount of stock must be left for removal bythe reamer if true holes with good surface finish are tobe produced. For machine reaming, 0.15 to 0.25 mm(0.006 to 0.010 inch) for reamers up to 10 mm (finch)diameter and 0.25 to 0.4 mm (0.010 to 0.015 inch) forreamers IO to 25 mm (f inch to 1 inch) is generally satisfactory. For these sizes, and particularly those larger, theamount of stock required is determined by such factorsas type of material, feed, finish required, depth of holeand chip capacity of the reamer.For hand-reaming stock, allowances are much smallerand a nominal allowance would be 0.075 to 0.15 mm(0.003 to 0.006 inch).Avoid ChatterReamer chatter must be eliminated to obtain the bestresults in finish and size. While the geometry of a reamerincludes features to reduce the probability of chatter, lackof rigidity in the machine jig or holder, or an excessivedistance between the holder and the work, will promotechatter (the material being cut will also affect chatter).Someways to reduce chatter include: reducing the speed,increasing the rigidity of the tool holder, chamfering theTable 9 Recommended speeds and cutting fluids for reaming

entering end of the hole, using a piloted reamer, reducing the angle of clearance.Selecting Speeds and FeedsSpeeds and feeds for reaming are governed by the finishrequired, the material, rigidity of set-up and the cuttingfluid used.Generally, the feed is two to three times, and the speedtwo-thirds to three-quarters that of a drill of the samediameter.When close tolerances and fine finish are required, itmay be necessary to finish reaming at considerably slowerspeeds than normal.The amount of feed required will varywith the materialbeing cut. A good starting point is between 0.025 and0.10 mm (0.001 and 0.004 inches) per tooth perrevolution.Too Iowa feed may result in glazing, excessive wear,and occasionally chatter. Too high a feed tends to reducethe accuracy of the hole and may lower the quality ofthe surface finish.

It is recommended that the highest feed to produce therequired finish and accuracy be used. Table 9 lists recommended speeds and cutting fluids.Avoid ReversingReamers are intended to be passed through the work:never reverse the rotation of the reamer, even whenwithdrawing from the work.

Material Speed Cutting fiuid(ltlmin) (m/min)Aluminium 150-200 46-61Aluminium alloys 135-160 41-49Brass, free cutting leaded 140-200 43-61 Kerosene, kerosene and oil, or soluble oilBrass 120-160 37-49Bronze, ordinary 130-200 40-61Bronze, high-tensile 45-65 14-20 Soluble oll or lard oilCast iron, soft 70-110 21-34Cast iron, medium 55-75 17-23Cast iron, hard 50-70 15-21 Dry or compressed airCast iron, chilled 15-25 5-8Copper, soft 80-130 24-40Copper, medium 45-65 14-20 Kerosene, soluble or sulphurized oilCopper, hard 30-45 9-14Magnesium and magnesium alloys 150-250 45-76 Dry or compressed airMalleable iron 50-60 15-18 Mineral oil or soluble oilMaganese copper 10-15 3-5 Soluble oil or sulphurized oilManganese steel 8-12 2-4 SUlphurized oilMonel metal 25-40 8-12 Soluble, lard, or sulphurized oilPhosphor bronze, soft 140-170 43-52 Soluble lard or lard oilPhosphor bronze, medium hard 100-130 30-40Plastic 65-80 20-24 Soluble oilSteel, free cutting 80-100 24-30Steel, 100-200 Brineil 65-85 20-26Steel. 200-300 Brineli 30-45 9-14 Soluble oil or sulphurized oilSteei. 300-400 brinell 20-30 6-9Steel, over 400 Brine11 8-15 2-5Steel, stainless, free cutting 40-50 12-15 Sulphurized oilSteel, stainless


18/48

154 Drills and reamersSharpening of ReamersWhen resharpening reamers, grind only the lead at theleading end, ensuring that the original angle of clearanceis maintained. Care should be taken so that each toothis ground exactly even, as any lack of concentricity orunevenness in the position of the chamfer will promoterapid tool, wear, poor finish and oversize cutting.

Storage of ReamersStorage and handling of reamers when not in use shouldbe given particular attention. Since they are delicate tools,easily damaged, they should be transported and storedin containers with separate compartments for eachreamer. They should be covered with a good rust pre-ventive compound when not in use,


19/48

Useful facts and figuresX Machine tapers

Manufacturers over the years have used a variety of tapersin machine tools; some of these are rarely used today,although they are nominally still in use. It is advisablealways to be on the alert as some appear to be almostinterchangeable.

e Tapermorse taper is universally used for taper shank toolslathe centres.

Morse taper shanks

xxvii

pTR

S

Shank Tongue KeywayDiam. of Oiam. at Standard End of


20/48

Lathe operations-turning 26128 mm Taper turning

Figure 64 Stepped spindle

Taper Turning Using a Form ToolThis method of taper turning is often employed whensmall par ts are to be produced in large numbers. Thelength of surface is limited by the ability of the lathe tocut a broad surface without chattering. About a 12 mmlength of face is often possible. A very short taper is oftenknown as a chamfer and the method for producing it isthe same as described here.Shape of the Form ToolThe cutting edge of the form tool must be straight andhorizontal because the surface of the taper is straight. (SeeFig. 65.) A small clearance angle 30 to 50 is used and thenormal rake angle is ground to suit the material to be cut.

When the turned surface of a workpiece is to be conicalinstead of cylindrical, the production of such a surfaceis known as taper turning.Taper fits are often preferred between the mating partsof assemblies used in machines, tools and equipment,motor cars etc.Because the taper ensures accurate location with a tightfit, the parts are readily assembled or separated.There are four methods by which tapers may bemachined in a lathe, namely by:

use of a form tool; use of the cross-slide and the top-slide; use of the taper-turning attachment; offsetting the tailstock.Whichever method of turning tapers is adopted, the toolmust be set at centre height, otherwise the angle of thetaper produced will not be accurate.

Position of the Form ToolI t is important that the complete cutting edge of the formtool is on centre height, otherwise a different taper willbe turned.

The cutt ing edge must be set to the angle shown onthe drawing. Figure 66 shows a taper with a 900 included angle; the cutting edge must be set to 45 0 measuredfrom the axis. To do this. the stock of the pmlractor islocated along the diameter (which must be parallel) andthe position of the cutting edge is adjusted to align withthe blade. (See Fig. 67.)

Figure 65 Plan view of form tooi

straight~ - cutting edge

= 6.85 mm=_6.45 mm __

0.40 mmtop slideNumber of graduations ": m ( ) ' : ~ p - , , ! , l . - .

(0.02 mm/grad.) 0.02= 20 graduations

Use of a Graduated Dial for Cutting LengthsTho top slide is fitted with a graduated dial having divisions representing decimal parts of a millimetre. Formachhling short accurate lengths:I Set the top slide on zero.2 Locate the tool approximately and lock the saddle

damp.3 Cut a trial length, locating the tool by using the top~ i U d e .4 Set the graduated dial to zero.5 Me"stlre the trial length (a depth micrometer may beIlsed).6 Move the graduated dial the difference between thetrial length and the required length.

For example:Required lengthTrial length

19mmdatumface

L - 8 ~ProcedureI Locate the position of the datum face and machine itby facing.2 Rough turn the largest diameter approximately 0.6 mmoversize.3 Mark the length of the next largest diameter and roughturn it about 0.6 mm short. A quick method of marking the length is to position the cutting tool, rotate theworkpiece by hand (to see that everything is clear) andfeed the tool to cu t a small mark around the diameter.Check the position of the mark before proceeding withthe cut.4 This rough turning is continued with all diameters andlengths, starting with the largest and proceeding to thesmallest.5 Then, use the same cutting method for finish turning: The cutting tool must be sharp.,. The revolutions per minute are increased. The feed is decreased. The finished size may be measured using a micrometer when the size is important, that is, when thesize is to fit a mating part, or when the size is expressed with a tolerance.


21/48


Figure 66 Included angleof taper

4 Use the cross-slide to feed the tool into the workpiece.This process is known as plunge cutting.Note: An alternative method is to use the saddle toplunge cut the taper.5 Check the included angle and make any necessaryadjustments to the position of the tool before cuttingto finished size.

work-piece 1"-+--_. --- . ,-II, '

Figure 67 Setting theform tool using aprotractor

MethodI Locate the saddle to align the cutting tool with the areato be cut.2 Lock the saddle to prevent it moving away under thecutting force.3 Set the cutting speed to suit the material and the largestdiameter. It is sometimes necessary to use a slowerspeed to produce a good finish.

Figure 68 Turning a taper on a workpiece held in achuck

Taper Turning Using the Top-slideThis method is suitable for turning or boring tapers, butthe maximum length of taper that can be machined islimited to the amount of travel of the top-slide, and thefeed must be by hand.Holding the WorkpieceThe work may be held in a chuck as shown in Figures68 and 69, or between centres as in Figures 70 and 71.

Figure 70 Turning a taper on a workpiece held betweencentres

Figure 71 Turning a taper on a workpiece held on amandrel

1I1/2 includedangle

I--. IFigure 69 Compound s!ide settirlg


22/48


cross-slidemovement

Taper Turning Using a Taper TurningAttachmentThe taper t.urning attachment shown in Figure 73 provieles a simple method of turning tapers and eliminatesthe disadvantages of other methods.

".- frame_/ L sliding blockL swivel slide

DescriptionIt is essential in this taper turning operation that the cutting tool is made to travel along an angular path by thecombination of two movements, the saddle movementand the cross-slide movement (see Fig. 72).These movements are controlled by a slide (swivelslide), which may be set to the required angle. The swivelslide is supported in a frame at the back of the saddleand. is fixed in position by a clamp on the lathe bed.

A sliding block fits over the swivel slide and is attachedto the cross-slide. As the saddle moves along the bed, thesliding block follows the angular setting of the swivel slideand causes the cross-slide to move accordingly.Types of Taper Turning AttachmentThe foregoing principle is applied to two types of taperturning attachment. The main difference between themis the method of attaching the cross-slide to the slidingblock and of overcoming the restriction to movementcaused by the cross-slide serew and nut.Attachment with telescopic feed screwThe telescopic feed screw passes through the sliding blockand therefore as the block moves it pushes the feed screw,nut and cross-slide.As the cross-feed screw moves towards the handwhee1it enters a tube provided for it. A key between the twoenables a drive from the handwheel to the crossfeedscrew, hence depth of cut settings may be made in thenormal way.To operate:I Set the swivel slide to the desired angle, which is alwayshalf the included angle.2 Clamp the swivel slide to the bed so that the tool is

about 12 mm from the work and the sliding block hassufficient movement to eomplete the taper.3 Make certain that all slides are clean and lubricated andthat the action is smooth when the saddle is moved byhand.4 Proceed with turning the taper.f ~ resulta'1t lOOI--=.J.movement ~ ' saddle movement

FigUt'8 72 Path of travel

FigUi'e '73 Taper turningattachment with telHscoplcscrew

MethodI Set the top-slide to the angle.2 Set the tool at centre height. In taper turning this isimportant otherwise the taper will be incorrect.3 Ensure that the tool position allows for an end-reliefangle.Locate the carriage so that the top-slide movementcovers the length of the taper. Lock the saddle inposition.S Mark the length of the taper on the work and take alight cut within the length to check the top-slide setting. Make necessary adjustments.6 Set the cutting speed and, using a two-handed control'

of the top-slide, feed the tool with successive cuts untilthe eorrect diameter and length are reached.

Setting the Top-siidehe base a f the top-slide is graduated in degrees to allowthe setting of the slide at any required angle. The graduations arc usually numbered from zero at the front to 90at the sides.

The angle to set the top-slide is the angle that one sideof the work makes with the axial centre line, that is, onehalf of the included angle.


23/48

264 Lathe operations-turningtaperattachment

raper turning with fixed screw attachmentI The cross-slide nut is disengaged to allow the cross-slideto move freely.2 An extension piece is fitted to the cross-slide. This piececovers the sliding block and is clamped to it, hence asthe sliding block moves so does the cross-slide.

3 The compound rest is set at 90' to enable the top slideto be used for setting the cutting tool to depth.Nole: When using these attachments, set each cut withthe tool about 12 mm beyond the end of the work so thatany backlash or 'play' in the attachment will not producea short parallel section on the work.Advantages of Taper Turning Attachments They can be used for internal or external work. Automatic feed can be used. Any work holding method can be used. The length of stock does not affect the taper. Time is sa ved realigning centres because it is unnecessary to alter the correct setting. Tapers can be set in degrees or units of taper to length.

Taper Turning by Offsetting theTailstockWhen turning, the tool moves parallel to the axis of thelathe spindle and the ways of the lathe bed; therefore,if the tailstock is offset, as shown in Figure75, the workpiece will be turned smaller at one end than the other,thus forming a taper. The amount to offset the tailstockis onehalf of the amount oftaper reckoned on the totallength of the work. This may be calculated by directproportion.

axi'3 of work being turned,\

lathe axis 14---\ --- -'--- \ olfsel -'---'-1r ~ J = ~ ~ / c f ~ ~ BI . / b.':-t:=s=J ( . : ' n : ' 0 ~ : ~ _travel of too! paral lel to ways 01 jatlleFigure 75 The effect of offsetting the taiislock centre

Measuring the OffsetTwo common methods of measuring the olfset are asfollows: By means of the scale on the end of the tailstock (seeFig. 76). By holding a bar in the tool post and using the graduations on the cross-slide dial to measure the amountto set the bar back from the tailstock quill. The tailstock is then adjusted until the tailstock quill contactsthe bar in the tool-post (see Fig. 77).

Care should be taken when using this method toavoid errors through backlash in the cross-slide Screwand nut.

Nole: The above methods must be followed by the 'cutand check' procedure.Disadvantages of the Offset Method It is suitable only for turning external tapers when theworkpiece is held between centres. The work centres do not bear uniformly on the lathecentres. This causes them to wear out of shape andspoils them for parallel turning (see Fig. 78). The range of tapers that can be cut is limited to theamount of cross adjustment of the tailstock. For shortwork it is inadvisable to use the full range of the tailstock adjustment. When turning duplicate workpieces, a variation in thelength of the material or in the depth of the workcentres will affect the angle of the taper (see Fig. 79). Each time the tails tock is offset for taper turning, itmust be realigned for parallel turning.

Form turningIn the previous section, the use of various lathe slides weredescribed: the saddle for parallel turning the cross-slide for face turning the top-slide for taper turningAs with the controlled combinations of saddle and crossslide movements in the taper turning attachment, eachof these processes produces straight surfaces.When form turning, a curved surface is produced andthis often requires the use of two or more slides, which

may be manipulated as follows: hand-controlled for simple, approximately accurate,pieces produced in small numbers; or automatically and mechanically controlled for accuratepieces or when pieces are to pe produced in largenumbers; using a specially prepared form tool to plunge cut theform, (as previously described) - this method is limited to a comparatively short length of cut.Free-hand Form TurningFigure 80a represents a handle to be fitted to a controllever. It requires a smooth outline rather than veryaccurate machining. The work can be turned by the freehand method using a round nose-cutting tool controlledby the combined movement.s of the top-slide andcross-slide.


24/48

256 Lathe operations-turningMethods of Aligning CentresApproximate methods By carefully bringing the centres together (Fig. 46) andadjusting the tailstock for a visual alignment. By checking the zero lines on the end of the tailstock(see Fig. 47).

F;gure 41 Checking the alignment 01 the zero lines

Figure 46 Checking the alignment of the points of thelathe centres. Note the use of white paper to give aclearer viewFigure 42 Hole too deep

Figure 43 Hole not inalignment

Figure 'Ill Centring in a drilling machine

Figure 41 Hole tooshallow

F;gure 44 Centres in line, work turned in parallel

Figure 45 Centres out of line, work turned tapered

The method is carried out on the piece of metal to beturned.Mount the workpiece between centres and set the toolfor a short light cut.2 Take a short light cut at the tailstock end of the workpiece and note the reading on the cross-feed dial (seeFig. 48).3 With the machine running, re-set the tool to take a cut

2nd cut 1st cut

cross-feed dial readingto be the same for both cutsF;gure 48 Checking the alignment by the cut and checkmethod

These two approximate methods should be followed byone of the more accurate methods described below.Cut and check method

Aligning lathe CentresFor parallel turning between centres, the axis or centreline of the work must be parallel with the ways of thelathe bed and therefore with the line of travel of the carriage and the tool. To accomplish this, the headstock andthe tailstock centres must be in alignment (see Fig. 44).

I f the tailstock centre is out of line with the headstockcentre then the work will be turned tapered (see Fig, 45).

oo


25/48


4 Clamp the tailstock to the bed so that the tailstockquill has the miuimum overhang for the requiredmovement of the carriage.5, Place the workpiece on the headstock centre with theleg of the carrier in front of the driving pin, and windthe tai/stock centre into position.6 Tighten the tai/stock hand-Wheel firmly to ensure thatthe lathe centres are properly seated in the work.7 Readjust the tai/stock hand-wheel so that the workmayrotate freely but without end play. Lock the quill toretain this adjustment. 'Ibis is important.

I f the work is adjusted too tightly, the centres will quicklyheat during cutting and the expansion will cause the centreto overheat and possibly to weld itself to the workpiece.

I f the workpiece is too loose it will rattle and may bethrown out as it rotates at high speed. This is extremelydangerous.The tailstock centre should be carefully watched andif overheating is noticed or a rattling noise is heard,readjustment is immediately necessary.

Figure 51 Packingprojection

Figure 52 Carrier contactinglathe centre

incompletecontact

no clearance

Figure 50 Carrier tail notclearing bottom of drivingplate slot

o

Using a parallel test mandrelThis method is very accurate, provided that the mandrelis approximately the same length as the workpiece, so thatthe tailstock will not have to be moved after the setting.The test mandrel is parallel in diameter having beenaccurately ground between centres.Clean and fit the headstock centre and check for running true.2 Clean and fit the tailstock centre.3 Lock the tailstock to suit the length of work andmandrel.4 Clean centres and centre hold and mount the testmandrel.5 Clamp a dial indicator in the tool-post, setting thestylus horizontal at about centre height and square tothe mandrel axis (Fig. 49).6 Adjust the cross-slide to depress the indicator stylus.7 Rotate the mandrel to check for running true at eachend.8 Set the dial to zero at one end and move the saddletowards the other end. Note the dial reading and adjustthe tailstock to remove any variation.

at the headstock end of the workpiece. The same crossfeed dial reading must be used.4 Using a micrometer, measure the diameter at bothpositions.5 I f the diameter differs, adjust the tailstock towards thetool if the tailstock end is larger, but away 'from thetool if the tailstock end is smaller.6 The amount of adjustment should be one-half of theamount of taper reckoned on the total length of theworkpiece.7 Repeat the procedure until both diameters are the same.

Figu,e 49 Checking the alignment using a test mandreland indicatorSeUnng the Workpiece Between CentresFitting the Carrier1 Select a lathe carrier that will fit the workpiece but notproject beyond the driving pin or the driving plate.2 Fit the carrier to the workpiece so that it will not prevent the proper fitting of the work on the centres. Some

of the faults that may occur if the carrier is not properlyfitted are shown in Figures 50, 51 and 52.3 Use a copper packing to protect the finished workpiecefrom damage by the carrier screw.Setting the Workpiece1 See that the bed and slides are clean and lUbricated.2 Clean the lathe and work centres.3 Lubricate the work centre at the tailstock end, ensuring that the lubricant fills the reservoir.

The two types of cutting tool in general use are referredto as 'solid tools' and ' tool bits'.A solid tool is a large section of tool steel that can beclamped directly in the tool-post. A tool bit is a smallsection of tool steel that must be held in a tool holder.The tool holder is clamped in the tool-post.To obtain satisfactory results from either of these tools,the points discussed below should be Observed.Note: Solid tools include clamped carbide tip tools.Overhang and RigodityI f the cutting edge is extended too far beyond the clamping position, the tool is likely to deflect under cutting pressure, causing a poor surface finish (chattering) andinaccuracy.


26/48

276 Lathe operations-turning-ff3t - ~ - _ e q U a lclearance

Figure 124 Equal side clearance in the groove

Parting-off ProcedureI Set the r.p.m. for a cutting speed about two-thirdsof that required for turning.2 Move the tool into position for'the cut, using movemellts of both the top-slide and cross-slide.3 Apply a constant supply of cutting compound onmaterials needing ii. This is particularly important forsteel.4 Feed the tool into the workpiece at a steady, constant rate and observe the chip. Steel should be cut witha continuous clock-spring type of chip; if this is notthe case a heavier feed should be tried.Problems When Parting OffParting off is a skilled operation but if the methoddescribed is strictly followed the difficulties will be greatlyreduced.Causes of failure to cut a blunt tool; a tool set above centre; insufficient front clearance on the tool.Causes of 'chatter' looseness in the lathe spindle bearings and slides; nearings in need of lubrication;~ . too l too wide;IY excessive front clearance on the tool; excessiw overhang of the tool; excessive overhang of the workpiece; excessive cuttilng speed. I f the speed is normal it shouldnot be reduceduntii other possible causes of chatter

h a v ~ been elimin,ated.Causes of a tool 'digging in', jamming or breaking tool incorrectly ground;'. tool blade not vertical, or not set square to the work; tool above centre or below centre;t looseness in the lathe bearings and slides; too much top rake on the tooL

Work requiring steady restsA steady rest is used as an additional bearing to suppowork that, because of its length, its slender nature Or ia rea to be machined, presenls par ticular machinindifficulties. There are two types of steady rest: The fixed steady rest, which is boited to the lathe be The travelling steady rest, which is bolted to the carrage and therefore travels with the cutting tool.Fixed Steady RestThe fixed steady rest (Fig. 125), has a hinged top halwhich may be opened to permit the work to enter. -n,readjustable pads act as bearings to support the work,

3 pads

' L r - c q - ~r J lathe bedC _ -_-:::J clampFigure -125 Fixed steady rest

Setting Up the Fixed Steady RestI Clamp the steady rest to the lathe bed in the p o ~ i t i o to support the work.2 Set the work in place, with the pads clear of the S13face. (The work may be held between the "wtre;; oin a chuck.)3 Adjust the portion of the work to be supported so thait is running truly.4 Adjust each pad so that it lightly touches the workI f operations 3 and 4 are correctly carried out, the slcadrest will then be in linc with the headstock spindle beariogs. This is an essential part of the process.5 Lubricate the pads.Examples of Work Requiring a Fixed Steaay RestWork held In a chuck Figure 126 shows a headstocspindie where it is required that the taper in the ,;pindl

A " = = - ; - ~ m _ a _ i n _ b , e a _ r _ i r ; _ g _ j O ~ n a I S - - - _ ~ - - - - ? - - : : ' 7 7 - r , 1 v /r taper to be---- = ~ _ ---t--El"-_:_:-: ~ " f - t - - machined Figure 126 Headstock spindle


27/48

Lathe operations--turning 277

Figure 127 Supporting work held in a chucknose is in line with the two main bearings. The work isheld by the small journal in a four-jaw chuck. A dial indicator is used to check the running truth of both journals.A pipe centre is a useful aid for supporting the outer endof the work. The fixed steady rest supports the large journal, which would otherwise move during the taper boringoperation becauseof the extension from the chuck jaws.The set-up referred to above is shown in Figure 127.It applies also to long pieces of work held in a chuck fordrilling, boring, reaming and other internal or externaloperations.

I f the work has not been machined on the outside, itmay be supported by the tailstock centre while a shortlength is turned. The fixed steady rest is then set to thisportion, thus ensuring exact alignment.Work held between centres Figure 128 illustrates a tiebolt, which has to be turned and threaded for a considerable length from the tailstock support, and because ofits length and small diameter it tends to deflect and chatterduring the cutting process..The problem may be solved using the setting shownin Figure 129.A short length (a littlewider than the steady rest pads)is turned on the shaft. .The steady rest is set to the turned portion.Note: Turning the short length may be very difficult,even if light cuts are used. I f the shaft is square, hexagonalor irregular in shape, it may be undesirable to machineit round. In such cases a 'cathead' is used to fit looselyover the work and is adjusted by set-screws until thebearing surface runs true. The steady rest is then adjusted tothe .cathead (see Figs. 130 and 131).

Figure 129 Supporting work held between centres

Figure 130 The cathead

Figure 131 Using the cathead

Figure 128 Tie bolt

__~ = _ = [ = e = 2 0 = = : : = . : : . = = = ~ __~ ~ _ O -4-__ 900600 . _ - _ . ~ ~


28/48

278 Lathe operations-turningThe Travelling Steady RestThe travel ling steady rest (Fig. 132) is used to supportwork that is to be turned or otherwise externallymachinedfor most of its length. Two pads act as bearings to support the work and are normally positioned behind the cutt ing tooL

Figure 132 Travelling steady restTo Set the Travelling Steady Rest (Plain Turning)

Figure 133 Supporting work with a travelling steady restClamp the steady rest to the carriage with the pads clearof the work.2 Set the work in place (see Fig. 133).

3 Set the cutting tool in advance of the pads (about 2to 4 mm)

bearing pad

Figure 134 Bearing pad behind the tool4 Take a cut at the tailstock end of the work to aboutthe width of the pads. This establishes a true surfaceon which the pads operate (Fig. 134).5 Adjust the pads to lightly touch the true surface.6 Lubricate the pads continually as the cut is being taken.

Note: Any further reduction in diameter will requireresetting of the pads.Examples of Work Requir ing a TravellingSteady RestFigure 135 shows a cross-slide screw for a lathe. Thespindle is to be turned all over and then a 20 x 3.0 mmpitch Acme thread is to be cut.Turning the blank (plain turning) The work should be heldbetween centres and turned in progressive steps. Thetravelling steady rest should be used to support the workand should be set as described above.Cutting the thread This is performed as follows:I Grind and set the screwing tooL2 Posit ion the screwing tool (by moving the top-slide)behind the pads (see Fig. 136). This will support thework throughout the screw-cutting process and shouldnot require readjustment although the screwing toolposition will alter.3 Cut the thread, keeping the pads lubricated.

Problems with Unstable WorkMany turning problems can be solved by using either fixedor travelling 'steadies'. There are occasions when the useof both types is needed to provide enough support to thework. The skilful machinist may also consider the alteration of tool angles as a means of reducing the distorting pressures on slender shafts.Consider the forces acting towards the axis of the workin the two examples shown in Figures 137 and 138.In Figure 137, the forces are inclined to the axis and

therefore contribute to deflection even though the chipis thinner for the same feed rate. In Figure 138 the direction of the force is changed and the length of the chipis reduced by setting the cutting edge square to the axis.This, together with changes of speed and feed, shouldbe t ried when steady rests fail to solve the problem.

Work requiring the use of mandrelsUse of MandrelsMuch work, such as gear blanks, pulleys, bushes andsleeves, has to be gripped in a chuck while the bore is


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28lathe operations-Turning

and removing ChllCk, faceplate,driving piate and centree back or the back plate of the chuck is machined tot the design of the lathe spindle nose. Back plates areewed, (see Figure I). Other chucks are bolted directlythe spindle nose (see Fig. 2). A number of designsclude a driving key and keyway. The camlock (Fig. 3)now widely used and accepted for its simplicity in useits rigidity.The design of the mating parts includes a flat locatingface and a cylindrical or tapered recess to ensure thate face and the axis of the chuck run true. When mount-g the chuck these locating surfaces must be clean and

Threaded parts, and shoulders and recesses, must beean and free from burrs to ensure proper engagement;ey must not be forced together by extra leverage or

igure 1 Screwed spindle nose and chuck

Figure 3 Cam lock spindle nose and chuckFitting the Chuck, Faceplate and DrivingPlateThe sequence should be as follows:I Place a board on the lathe bed to protect the bed frompossible damage.2 Check all mating surfaces for cleanliness and freedomfrom damage.3 Lubricate mating parts with a light application of oil.4 Carefully lift the chuck into place and lock it securelyby hand. Do not force the two together by using extraleverage or impact.5 Check that the diameter and the face are running trueby starting the machine and observing the surfaces.

2 Two types of less common spindle noses and chuck backplates


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251

Fitting the Chuck JawsThe jaws and their corresponding slots are numbered.They must be engaged in the correct sequence, beginningwith No. I jaw, then as the scroll is turned, No.2 jaw,and finally No.3 jaw. Before assembly, the jaws and thescroll should be cleaned, then lubricated lightly with oil.Setting Up Workpieces in a Self-centering ChuckWorkpieces suitable for this chuck are, within limits,automatically centered. The limits of accuracy will dependon the care previously taken with the chuck.

I f the work must protrude far from the chuck jaws orif it is in the form of a disc, it will require either the outerend or the face to be tapped true. (See Figs 8 and 9.) Asoft hammer must be used on finished Or soft metals.

Methods of Holding WorkThe three methods of holdingworkpieces (seeFig. 6) maybe employed on self-centering chucks; however, a secondset of reverse jaws (see Fig. 6b) must be used becausethe curvature of the scroll thread in each jaw cannot bereversed.

Figure 17 Self-centering chuckUses of Self-centering ChucksA self-centering chuck will remain accurate only if usedin the propermanner. The three-jaw chuck should be usedfor holding accurately machined, rolled or extruded,round or hexagonal sections.

bination scroll plate and bevel gear, which is rotated bysmall bevel pinions with square holes for the chuck key(see Fig. 17).

Lathe operations-turning

counterbalanceweight16 Counterbalancing work in the chuck

f aids are not available, or if they are too small toure accuracy, then some preliminary marking outill be necessary.f the machining is external it is usually good practiceset up to an internal surface that will ensure evenl thickness and balance of revolving parts (see Fig.f the machining is internal, use an external surface for

up (see Fig. 15).terbalancing Using an Independent Chuckis the technique of applying weights

the chuck of the face plate to bring the work into corct static balance. When irregular work is held in a chuck, as will be explained later, on a faceplate, its shapethe method of holding it may cause a portion of theto be off centre. Operating the lathe under theseditions will cause:

vibration;uneven cutting speed;work to be machined ou t of round;excessive wear on the bearing of the lathe;a dangerous situation, particularly if the spindle isrotated at high speed.w to counterbalanceSet the lathe so that the spindle is free to rotate.Spin the work by hand and allow it to come to rest.Chalk mark the light por tion at the top.Select the weights (to approximately match the amountof balance) and attach them at the top. Slots or T-slotsare provided for purposes of attachment (seeFig. 16).

work

Spin the work and allow it to come to rest. The heavyarea will swing either side of the centre at the bottom.Mark the light portion at the top.Move the balance weight towards the second chalkmark.Continue this process until it is found that the workwill stop in any position without a tendency to reversedirection.e Three-jaw Self-centering Chucklf-centering chucks usually have three jaws (seeFig. 17),t some have two or four jaws. This type of chuck isconstructed that the jaws move in unison and therere are always the same distance from the centre.The movement of the jaws is obtained with a com-

Faceplates are required for holding workthat cannot beconveniently held in a chuck. The shape or size of thework and, in some cases pre-machining, may indicate theselection of a faceplate as a more suitable holding devicethan a chuck (see examples illustrated in'Figs 18 to 23.)Methods of Holding WorkWork Clamped Directly to FaceplateWork that has been previously faced or machined is thetype most suited to being directly clamped to thefaceplate. This method ensures that any operation donewhile the work is on the faceplate will be either parallelto or square with the original face. Figure 18 shows a casting clamped directly to the faceplate before being boredand faced.


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19 Clutch member on faceplate

counterbalance" " ' ~ " weight

stop

the casting and the face adjacent to the faceplate havebeen previously machined and the position of the borehas been marked out. The bosses on the casting makeit necessary to rest the casting on parallel strips.

?-_- - : " , gauge rod

The following method of setting up this eccentric istypical of most work that is clamped against the faceplate:1 Place the faceplate upwards on the bench, clean themating surfaces and remove any burrs.2 Place the work on parallel strips, which are laid inapproximate position on the faceplate.3 Locate the bore of the work in the approximate centreof the faceplate using the surface gauge or other suitable equipment, measured from the outer diameter ofthe faceplate.4 Clamp the work lightly, Avoid using bolts longer thanthe required length and set the clamps so that the pressure is on the parallel strips.5 Mount the faceplate on the spindle nose and check fortrueness, rotating by hand.6 Set up the work to the marking out by tapping witha soft-faced hammer to obtain adjustment. (It shouldbe noted that heavy work must be supported by a hoist;this will allow clamps to be released enough to permitadjustment.)7 Tighten all clamps and re-check the setting.S Counterbalance.9 Proceed with the machining.

parallel stripsFigure 21 Eccentric set up for boring

setting stripsFigure 20 Work set on setting strips

Work Clamped to an Angle PlateAn angle plate is used in conjunction with a faceplatewhen the work face to be machined is at right angles tothe locating face. A cast iron elbow is set up (see Fig.22) with the elbow clamped to the outer face of the angleplate.

parallel strips

clamp

set screw

machined face

face/ plate

Parallel strips are used to pack work out fromhe faceplate so that boring tools do not foul thefaceplate. The clamps must be placed directly over theparallel strips. Parallel strips may be necessary to packork out from the faceplate when the work has bossesr projections preventing direct clamping.Another example of work clamped directly to thefaceplate is shown in Figure 19. In this case the work,hich is the sliding member of a cone clutch, has to beurned and has been bored accurately true to the conicalface, which was turned at a previous setting.

Set screws have been substituted for the packingf the clamp plates. The advantages are that they do notlip, they are adjustable, and they are part of the clamptself. The clamps are also placed where they will not dis-ort the work. If there is danger of the clamp distortinge work, the latter may often be gripped in special jaws.See Fig. 24.)One of the advantages of the faceplate is that, wheneveral parts are to be machined, stops can be used toet the work quickly. Holes can be spaced or bored iniIle on the faceplate by using stops, gauge blocks andetting strips (see Fig. 20).The eccentric illustrated in Figure 21 is typical of thelass of work clamped to the faceplate. The outside of

~ C l a m p18 Work clamped to a faceplate


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Lathe operations-turning 253counter balance

angle - - -" ' ? 'plate -===?/Figure 22 Cast iron elbow set on angle plate

fuming betweelll centresGeneral DescriptiOlI1CentresThe headstock and the tailstock of a lathe have morsetapers into which centres may be fitted.These centres are used to support a workpiece at eachend. The headstock centre rotates with the workpiece andis therefore only a support. The tailstock centre usuallyremains fixed and therefore not only supports thework-piece but also acts as a bearing (see Fig. 26).

Figure 23 Bearing set on angle plate

pin for straightcarriers

Figure 26 Work supported between centres

Driving PlateA driving plate is fitted to the headstock spindle usingthe samemethod as for fitting a chuck. The driving platerotates the workpiece through a lathe carrier attached toit. The driving plate may have a driving pin or a slot toengage with the lathe carrier (see Fig. 27).

Figure 27 The driving plate

Lathe CarriersThe lathe carrier is a simple clamp attached to the work-piece (see Figs 26 and 28).A straight carrier is used with driving plates having adriving pin.A bent leg carrier is used with slotted driving plate.Note: For safety reasons, the selected carrier should nothave any portion extending beyond the driving pin or thedriving plate.

angleplate

==-::1 workace plate

The use of face and angle plates (Fig. 23) ensures thatall bearings bored at that setting will be identical in heightfrom the base to the centreof the bore, and the bore willbe machined parallel to the base. The special design ofthe angle plate allows the split bearing to be machinedwithout extending the angle plate beyond the peripheryof the faceplate. Such an extension could be very dan-gerous and would be likely to foul the lathe bed.Special adjustable jaws may be clamped in any con-venient position on the faceplate (see Fig. 24). Holdingand adjusting the work is simplified and subsequent work-pieces are easily set up. Figure 25 shows a simple bracketfor holding a large pulley on the faceplate. These bracketscan also be used if adjustable jaws are not available.

" chuck "'=;m-!jawsFigure 24 Special adjustable jaws

Figure 25 Bracket holding device Figure 28 Some types of carriers


33/48

186b e a r i n g ~ " x : : : ; : : ; ; ; : l I : ; z ~ ' ; ; P i n i o n s

\ gearrack /'

Marking and measuring toolsConstruction of Dial IndicatorsA study of a dial indicator will show that great caremube exercised when using the instrument to prevent damagto the bearings and gears. Figure 98 shows a view insida dial indicator that is face down and has had the bacremoved. Movement of the contact point moves the rackwhich turns a small pinion. A large gear is fixed to thsame shaft as the small pinion and meshes with anothesmall pinion (shown dotted) in the centre front of thindicator. The pointer is attached to the central pinioshaft. A very light return spring keeps the contact poinagainst the work.The gears act as a compound lever arrangement, ana small movement of the contact point is magnified tan observable movement of the pointer.

contact point...---FI\lure 98 Construction of a dial indicator

continuousreading dialtype

Types of Dial IndicatorA variety of indicators are used in the workshop. Figur99 shows two plunger-type dial indicators. Thplus or minusdial type

Figure 99 Plunger-type dialindicators

" " f " ' ~ " '~ " 7 . _ - , : ' : _

; ~ i : : ' ,

I-I..


34/48

Marking and measuring tools 187

orillspindle

Figure 104 Testing size of work Dial indicator set up asa comparatorWhen a dial indicator is set up as shown in Figure 104,it may be used for comparing the sizes of parts. Theoriginal setting is obtained by using a gauge or workpiece

of known size. The gauge is rested on the surface plate,and the indicator set to it with its pointer on zero. Variations of size will be measured when the work pieces arepassed between the surface plate and the dial indicator.When a finger-type indicator is set up as shown inFigure 105, the angle of taper of a workpiece can bechecked using a sine bar. Figure 106 shows the same typeof indicator being used to check straightness of aworkpiece.

pivot

Figure 101 Testing chuck work

continuous-dial type can be used for measuring movement, and the plus-or-minus dial type can be used as acomparator. Figure 100 shows a range of finger-type dialindicators.Uses of Dial IndicatorsDial indicators have many applications in the workshop,some being: to set work accurately in a machine; to test the accuracy ofmachine slides, and play adjustments, etc. to use, in conjunction with other equipment, such asgauges and surface plates, as a simple comparator. machine tableFigure 101 shows a dial indicator used for testing workthat is held in a lathe chuck. The indicator is supported Figure 103 Testing running truth of a machine spindlefrom either the lathe bed or the toolpost and carefullybrought into contact with the work until the pointer hasmoved about 0.5 mm on the scale. The dial is set to zeroand the work turned by hand so that the error of settingcan be noted. The setting is tested as close to and as farfrom the chuck jaws as possible.

Figure 102 Using an internal attachment

Figure 102 shows a dial indicator fitted with an attachment that penmits internal or otherwise inaccessible placesto be Checked. This attachment is a 1:1 ratio lever, thebend of which will enter small spaces such as a cylinderore .. A typical set-up for testing the bearings of a machineIS shown in Figure 103 which depicts a dial indicator beingUsed to test a drilling machine spindle for true running.

work-piece

Figure 105 Checking the angle 6f taper of a workpiece


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After the workpiece has been fastened securelyto a face plate, It will be necessary to align thecentre punch mark, hole or diameter with theaxis of the lathe. Punch marks can be alignedwith a centre tester, or a wiggler and indicator,if greater accuracy is required. An indicatorshould be used when truing holes or diameters.The centre tester, which is mounted on the toolpost, consists of an adjustable needle, held in auniversal joint. The poin t of the short arm isplaced in the centre punch mark. When thelathe sp in dl e is rotated by hand, anymisalignment of the work is magnified andindicated by rotation of the long arm aroundthe tailstock centre.The centre finder consists of a needle (wiggler)held at one end by a universal joint. The shankof the centre fi nd er is g rippe d by a drill chuCkmounted in the tails tock spindle. The point ofthe wiggler is placed in the centre punch mark.A dial indicator Is mounted on the tool post withits point in contact witt) the wiggler. When thelathe spindle is rotated by hand, anymisalignment of the work is shown by adeflect ion of the dial indicator needle.

14.4.1 Truing a Centre Punch MarkWith a Centre Tester

CENTRE TESTER

C):::':::!~ ~ = : OG=! 0

Shank- r

~ = = = -

Tighten all bolts securely and recheck theaccuracy of the centre punch markalignment.

Mount a centre tester on the tool post.Place the left hand point of the centretester, i.e. short arm, in the centre punchmark.Adjust the cross slide and the centretester until the right hand point of thecentre tester, i.e. long arm, is close to thepoint of the tai lstock centre.Rotate the lathe spindle by hand andobserve how much the point of the centretester revolves around the tailstockcentre.Tap the workpiece with a hardwood blockor brass rod until the point of the centretester does not revolve around thetai lstock centre when the lathe spindle isrotated.

61

WigglerDrill chuck mountedin tailstock spindle

CENTRE FINDER-.:s\late

Centre testerTailstock cen: l

- - - - - - -_ ._- - - - - - - - -_ /


36/48


37/48

41 Clean the face plate thoroughly andmount it securely on the spindle.

14.5 TURNING WORK ON A FACEPLATE

Balance the work on the face plateaccurately to reduce vibration duringmachining.

Work

CounterweightI\ Angle plate

BALANCING WORK ON A FACE PLATEAlways turn the lathe spindle one full turnby hand to ensure that the work on theface plate clears the bed and c

fitting and machinig 7.6

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