1996_army_tc_9_524 - fundamentals of machine tools - 309 pg

7/29/2019 1996_Army_TC_9_524 - Fundamentals of Machine Tools - 309 Pg

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Preface

The purpose of this training circular is to provide a better understanding of power-driven machine tools. It alsosupp lements technical manu als in the 9-3400-series covering p ower-dr iven machine tools.

One of the main objectives is for this publication is to be clear and understandable. Illustrations throughout thispu blication show the step-by-step process of many machine shop operations. The tables, charts, formu las, weights,and measurements in this publication can be a ready reference for selecting the proper tooling and math formulasfor machining d ifferent ma terials.

The propon ent of this publication is HQ TRADOC. Send comm ents and recommend ations on DA Form 2028directly to the Department of the Army, Training Directorate, ATTN: ATCL-AO, 801 Lee Avenue, Fort Lee,Virgin ia 23801-1713.

Unless this publication states otherwise, masculine nouns and pronouns do not refer exclusively to men.

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Chapter 1

INTRODUCTION TO THE MACHINE SHOP

GENERAL INFORMATION

FORMS, RECORD S, AND REPORTS

Accurat e records ar e valuab le. Unit officers are respon siblefor completion of forms, records, and reports. DA Pam 738-750 lists records, reports, and au thorized form s that arenorm ally used for inspection and repair. Properly executedforms authorize and record repair or replacement of materiel.The forms, records, and reports document th e work r equired,follow the p rogress of the work w ithin the shops, and ind icate

the status of the material upon completion of repairs.

FIELD REPORT OF ACCIDENTS

The reports necessary to comply with the requirements ofthe Army Safety Program are prescribed in detail in AR 385-40. These reports are required for any accidents involvinginjury or damage. For a listing of all forms, refer to DA Pam25-30.

Any deficiencies detected in the equipment covered hereinshould be immediately reported in accordance with DA Pam738-750. These reports w ill be subm itted as an Equipm entImpr ovement Recommend ation on SF 368.

DEFINITIO N OF MACHINE TOOLS

Machine tools are power-driven equipment designed todrill, bore, grind , or cut metal or other m aterial.

LISTING O F MACH INE TOOLS

A complete list of machine tools including specializedmachine tools currently authorized for issue is in Component

List C 3405/ 70-lL.

SPECIALIZED M ACHINE TOO LS

In view of the different design and operating featuresincorporated in specialized m achine tools (cylind er boring

machines, brake reliners, valve seat grind ers. and so forth) bvarious manufacturers, no attempt has been made to includeinformation pertinent to them in this man ual. For completinform ation on these too ls, see per tinen t TM 9-3400-, TM 95100-, and TM 9-9000-series techn ical man ua ls covering thspecific machines.

RISK-MANAGEMENT

To assure a high degree of safety, no machine -tool is to bused unless the risk management process as outlined below iunderstood and applied by the user and the sup ervisor:

1. Identify the poten tial hazard (s) that th e ma chine tool cagenerate.

2. Assess the pr obability and severity ofthe hazard (s) butilizing the Risk Assessment M atrix in figure 1-1. Risacceptance d ecision aut hority for th e risk levels is as follows:

a. Extremely high - CG, TRADO C; DCG, TRADO Cor the Chief of Staff, TRADOC.

b. High - Major subord inate comm and s, installationcommand ing generals, and school comm andan ts of generaofficer rank.

c. Moderate and low - Delegated to the app ropriatelevel in your unit chain of command.

3. Determine the risk control measures that will eliminate thhazard(s) or reduce the risk.

4. Implement the risk control measures before and d uringoperation of the m achine tool to eliminate th e hazard s o

reduce their risks.

5. Sup ervise and evaluate the p rocess. Enforce theestablished standards and risk control measures. Evaluate theeffectiveness of the control measures and adjust/ upd ate themas necessary.

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A.

B.

C.

D .

E.

PROBABILITY

FREQUENT - Individu al soldier/ item - Occurs often inthe career/ equipm ent service life. All soldiers or iteminventory exposed - Continuously experienced duringoperation/ mission.

LIKELY - Individu al soldier/ item - Occurs several timesin career/ equipm ent service life. - All soldiers or item

inventory exposed. - Occur s frequently duringoperator/ mission.

OCCASIONAL - Individual soldier/ item. - Occurssometimes in career/ equip ment service life. All soldiersor item inventory exposed. Occurs sporadically, orseveral times in inventory service or operations/ mission.

REMOTE - Individ ual soldier/ item - Possible to occurin career/ equipm ent service life. All soldiers or iteminventory exposed, Remote chance of occurrence -Expected to occur sometime in inventory service life oroperation/ mission.

UNLIKELY - Individual soldier/ item - Can assume w illnot occur in career/ equipment/ service life. All soldiersor item inventor y exposed. - Possible, but impr obable;occurs only very rarely du ring operation/ mission.

SEVERITY

I. CATASTROPH IC - Death or permanent totaldisability. System loss. Major property damage.

II CRITICAL- Permanen t par tial disability. Temp orarytotal disability in excess of 3 months. Major system damage.Significant property damage.

III. MARGINAL - Minor injury. Lost w orkday accidentwith compensable injury/ illness. Mirror system dam age.Minor property damage.

IV. NEGLIGIBLE - First aid or m inortreatment. Minor system impairment.

RISK LEVELS

supportive medical

EXTREMELY HIGH - Loss of ability to accomplishmission.

HIGH - Significantly degrades mission capabilities in termsof required mission standard s.

MODERATE- Degrades m ission capabilities in term s ofrequired missions standards.

LOW - Little or no impact on accomplishment of mission.

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MACHINE SHOP WORK

SCOPE

Machine shop work is generally understood to include all

cold-metal work by which an operator, using either powerdriven equipm ent or han d tools, removes a p ortion of themetal and shapes it to some sp ecified form or size. It does notinclude sheet metal work and coppersmithing.

LAYING OUT WO RK

Laying out is a shop term wh ich m eans to scribe lines,circles, centers, and so forth, up on th e surface of any m aterialto serve as a guide in shap ing the finished wor kpiece. Thislaying out proced ure is similar to shop dra wing bu t differsfrom it in one important respect. The lines on a shop drawing

in the finished w orkpiece, For tha t reason, all scribed lin

should be exactly located and all scriber, divider, and centpoints should be exact and sharp.

SCRIBING LINES ON METAL

The shiny surface, found on most metals, makes it difficuto see the layou t lines.

Layout d ye (Figure 1-2), when app lied to the m etal surfacmak es it easier for the layout lines to be seen. Layout d yeusually blue and offers an excellent contrast between the metand the layout lines.

are used for reference purp oses only and are not m easured or

transferred. In layout w ork, even a slight error in scribing a Before applying layout dye, ensure that all grease and oline or center may result in a corresponding or greater error has been cleaned from th e work surface. Otherw ise the dy

will not adhere properly.

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COMM ON LAYOUT TOO LS

Scriber

To obtain an accurate layout, fine lines must be scribed inmetal. A scriber (Figure 1-3) is the layout tool that is used

prod uce these lines. The p oint is made of hardened steeld is kept chain by honing on an oilstone.

Divider

When laying out circles, arcs, and radii, it is best to use thevid er (Figur e 1-4). The legs of the d ivider m ust be o f theme length and be kept sharp. The divider cart be used to

lay out an d measure distances (Figure 1-5). To set the d ividerto the correct length, place one point on an inch mark of asteel rule and open the d ivider until the other leg matches thecorrect measure-merit required (Figure 1-6).

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Trammel

When scribing circles, arcs, and ra dii that are too large to beprodu ced with the d ivider, a tramm el should be used (Figure1-7). The tram mel is made of thr ee main p arts: the beam, twosliding heads with scriber points, and an adjusting screw thatis attached to one of the heads. The trammel can be made toscribe larger distances with the u se of extension rods. Thislayout tool is set in the same manner as the divider.

Hermaphrodite Caliper

The herm aphr odite caliper (Figure 1-8) is a tool used to layout lines that are parallel with the edges of the workpiece(Figure 1-9). It can also be used to locate the center ofcylind rical shaped work places (Figure 1-10).

Surface Gage

A surface gage (Figur e 1-11) is used for man y pu rposes,is most often used for layout w ork. The gage can be usescribe layout lines at any given distance parallel to the wsurface (Figure 1-12).


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The spindle may be adjusted to any position with respect tothe base and tightened in place with the spindle nut (Figure 1-11). The rocker adjusting screw provides for finer adjustment

of the spindle by pivoting the spindle rocker bracket. Thescriber can be positioned at any h eight and in an y desireddirection on the sp indle by ad justing the scriber. A surfaceplate and combination square (Figure l-13) are needed to setthe surface gage to the correct dimension.

Surface Plate

A surface plate (Figure l-14) provides a true, smooth, planesurface. It is used in conjunction with surface and height gagesas a level base on w hich the gages and th e work piece areplaced to obtain accurate measurements. These plates are

mad e of semi-steel or granite and should n ever be used forany job that would scratch or nick the surface.

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Vernier H eight Gage

The vernier h eight gage (Figure 1-15) is a caliper with aspecial foot block to adap t it for use on a sur face plate. Heightgages are available in several sizes: the most common are the

10, 18, and 24 inch gages in English measure and the 25 and46 cm gages in m etric measure. Like the vernier caliper, theseheight gages are gra du ated in d ivisions of 0.025 inch an d avernier scale of 25 units for reading measurements tothousandths of an inch. Always be sure the bottom of the footblock (Figure 1-15) is clean an d free from bu rrs.

upright beam.

Figure 1-16 shows the height gage with a tungsten carbidemarker. This marker is used to lay out lines on glass, hardenedsteel. or other hard materials.

Figure 1-17 illustrates the use of an offset scriber with thheight gag e. This scriber reaches below th e gage base. Do nattempt to adjust the sliding jaw while it is clamped to th

Combination Squ are Set

The combination square set (Figure 1-18) is used fornu mb er of layout op erations. The set consists of a blad(graduated rule), square head, protractor, and center head.

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Blade

The blade is designed to allow the different heads to slidelong the blade and be clamped at any desired location. The

groove in the blade is concave to eliminate dirt buildup andperm it a free and easy slide for the head s. By remov ing all the

eads, the blade may be used alone as a rule.

Square Head

The square head is designed w ith a 45 and 90 edge, whichmakes it possible to be used as a try square and miter square.By extending the blade below the square, it can be used as aepth rule. The square head can also be used as a level.

Protractor H ead

The protractor head is equipped w ith a revolving turr etrad uated in degrees from 0 to 180 or to 90 in either direction.

t is used to measure or lay out angles to an accuracy of 1.

Center Head

The center head, when inserted on the blade, is used toocate and lay out the center of cylindrical workplaces.

Bevel Protractor

The bevel p rotractor (Figure 1-19) consists of an adjustablelade w ith a grad uated dial. The blade is usu ally 12 inches

ong and 1/ 16 inch thick. The dial is graduated in degreeshrough a complete circle of 360. The most common use forhis tool is laying ou t p recision a ngles. The vernier scale issed for accurate angle adjustmen ts and is accurate to 5

minutes or 1/ 12.

STEPS IN M AKING A LAYOUT

Planning before beginning any layou t is one of the mostimportant steps. Each job may require different layout toolsdep endin g on the accuracy needed; however, there are certain

procedures which should be followed in any layout. Figure 1-20 shows a typical layout.

Study the shop drawing or blueprint carefully before youcut off the stock. Allow enough material to square theends if required.

Remove all oil and gr ease from the w ork surface andapply layout dye.

Locate and scribe a reference or base line. All the othermeasurements should be made from this. If the workpiecealready h as one tru e edge, it can be used in p lace of the

reference line.

Using the b ase line as a reference line, locate and scribeall center lines for each circle, radius, or arc.

Mark th e points w here the center lines intersect using asharp prick punch.

Scribe all circles, radii, and arcs using the divider ortrammel.

Using the correct type protractor, locate and scribe allstraight and angular lines.

Scribe all lines for internal openings.

All layout lines should be clean, sharp , and fine. Reapplylayout d ye to all messy, wide, or incorrect lines andrescribe.

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JIGS AN D FIXTURES

The primary purpose of jigs and fixtures is to align thThe layout tools mentioned in this section are only the most and hold the workpiece properly during machining. A f

commonly used . For more information on the use and care of is a device which holds the w ork w hile cutting tools these tools and other layout and measuring tools, refer to TM operation . It differs from a jig in that it has n o guid9-243.

special arrangements for guiding tools. A jig is also a fifor locating or holding the work and guiding the cuttinin operations such as d rilling, reaming, coun terboringcountersinking.


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Jigs and fixtur es can gr eatly redu ce the cost ofmanufacturing large quantities of parts. Their use is also anadv antage wh en the interchangeability and a ccuracy of thefinished products are important. They also can be used in lowor limited production jobs if extreme accuracy must bemaintained. One of their greatest advantages is that relativelyun skilled labor can accomp lish th e job u sing these special

tools.

MECHANICAL DRAWINGS ANDBLUEPRINTS

Mechanical Drawin gs

A m echanical drawing, mad e with special instruments an dtools, gives a true rep resentation of an object to be mad e,including its shape, size, description, material to be used, andmethod of manufacture.

BlueprintsA blueprint is an exact duplicate of a mechanical drawing.

These are the m ost econom ical and satisfactory w orkingdrawings in u se. They do not soil easily and arecomparatively easy to read. Blueprint paper is a good grade ofwhite paper coated with a chemical solution. making itgreenish yellow. A blueprint is made by placing a tracing of amechanical draw ing on a sheet of blueprint pap er andexposing it to light. During exposure. the light penetrateswh ere there are no lines or printing on the tracing but doesnot pen etrate where ther e are lines or printing. The print isthen washed in water. which changes the exposed chemical to

a dar k blue and wash es the chemical off where lines andprinting pr evented exposure. In other w ords. the processleaves white lines on d ark blue background.

Working From D rawings

Detail prints usually show only the individual part or piecehat mu st be produced. They show two or more orthographic

(straight-on) views of the object. and in special cases. theymay show an isometric projection. without dimension lines,near the u pp er right corner. An isometric projection showshow the p art will look when m ade. Each draw ing or blueprintcarries a number. located in the upper left-hand corner and in

he title box in the low er right-hand corner of the pr int. Theitle box also shows the part name, the scale used, the patternnumber. the material required. the assembly or subassemblyprint number to which the part belongs. the job order number,he quantity and date of the order. and the names or initials ofhe persons w ho drew. checked. and approved the drawingsFigure 1-20). Accurate and satisfactory fabrication of a partescribed on a drawing depends upon the following:

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Correctly reading the drawing and closely observing alldata on the drawing.

Selecting the correct tools and instruments for laying outthe job.

Use the baseline or reference line method of locating the

dimensional points during layout. thereby avoidingcumulative errors.

Strictly observing tolerances and allowances.

Accurate gaging and measuring of work throughout thefabricating process.

Giving due consideration when measuring for expansionof the workpiece by heat generated by the cuttingoperations. This is especially importan t wh en checkingdimensions during operations, if work is being machinedto close tolerances.

Limits of Accuracy

Work must be performed within the limits of accuracyspecified on the drawing. A clear understanding of toleranceand allowance will help you avoid making small, butpotentially large errors. These terms m ay seem closely relatedbut each has a very precise meaning and application. Theparagraphs below p oint out the m eanings of these terms andthe importance of observing the distinctions between them.

Tolerance

Working to th e absolute or exact basic dimension isimpractical and unnecessary in most instances: therefore, thedesigner calculates. in ad dition to the ba sic dimensions, anallowable variation. The amount of variation. or limit of errorpermissible is indicated on the drawing as plus or minus (+ )a given am ount. such as + 0.005 or + 1/ 64. The differencebetween the allowable minimum and the allowable maximumdimension is tolerance. When tolerances are not actuallyspecified on a d raw ing, fairly concrete assump tions can bemade concerning the accuracy expected. by using thefollowing principles, For dimensions which end in a fractionof an inch. such as 1/ 8, 1/ 16, 1/ 32, 1/ 64. consider the

expected accuracy to be to the nearest 1/ 64 inch. When thedim ension is given in d ecimal form the following ap plies: If adim ension is given a s 2.000 inches, the accura cy expected is+0.005 inch: or if the dimension is given as 2.00 inches, theaccuracy expected is +0,010 inch. The +0.005 is called inshop terms, "plus or minus five thousandths of an inch. The+ 0.010 is called p lus or m inus ten t housan dth s of an inch.


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Allowance

TC 9

Precautions

Allowance is an intentional d ifference in d imensions ofmating p arts to pr ovide the d esired fit. A clearance allowancepermits movement between mating parts when assembled. For

example, when a hole w ith a 0.250-inch d iameter is fitted w itha shaft th at has a 0.245-inch d iameter, the clearance allowanceis 0.005 inch. An in terference allow ance is the op posite of aclearance allowance. The d ifference in dim ensions in th is caseprovides a tight fit. Force is required when assembling partswh ich h ave an interference allowan ce. If a shaft w ith a 0.251-inch diameter is fitted in the hole identified in the precedingexample, the difference between the dimensions will give aninterference allowance of 0.001 inch. As the shaft is larger

Be sure you h ave the correct print for the part to be m arepaired. You w ant the p rint wh ich has not only the cotitle, but also the correct assembly nu mb er. Never ta

measurement with a rule directly from the print becaustracing from which the print was made may not have copied from the original drawing perfectly and may conscaling errors. Also, paper stretches and shrinks with chain atmosp heric cond itions. Dimensions mu st be taken from the figures shown on the dimension lines. Be careful in han dling all blueprints and w orking drawWhen they are not in use, place them on a shelf, in a cabor in a dr awer. Return them to the blueprint file as soon a

than the hole, force is necessary to assemble the parts. job is d on e. Blu ep rin ts and w or kin g d raw in gs are alwvaluable and often irreplaceable. Make it a point nevmutilate, destroy, or lose a blueprint.


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GENERAL SHO P SAFETY

All tools are dan gerous if used imp roperly or carelessly.Working safely is the first thing the user or operator shouldlearn because the safe way is the correct way. A p erson

learning to operate machine tools must first learn the safetyregulations and precau tions for each tool or machine. Mostaccidents are caused by not following prescribed procedures.Develop safe work habits rather than suffer the consequencesof an accident.

Most of the safety practices men tioned in this section aregeneral in natu re. Safety precau tions for specific tools andmachines are described in detail in the chapters along with thedescription of the equipment. Study these carefully and be onthe alert to apply them.

EYE PROTECTION

Using eye protection in the m achine shop is the m ostimportant safety rule of all. Metal chips and shavings can flyat great speeds and distances and cause serious eye injury.Safety glasses must be worn when w orking with hand cuttingtools, since most han dcutt ing tools are made of harden ed steeland can break or shatter when used improperly.

There are man y d ifferent typ es of safety glasses available inthe sup ply system; how ever, the ones that offer the bestprotection are the safety glasses w ith side shields. Safetygoggles should be wor n over p rescription glasses. For specificinformation abou t eye protection, contact the Occupationa lHealth Clinic or refer to TB MED 586.

HAZARDO US NOISE PROTECTION

Noise hazards are very common in the machine shop. Highintensity noise can cause perm anent loss of hearing. Althou ghnoise hazards cannot always be eliminated, hearing loss isavoidable with ear m uffs, ear plugs, or both. These areavailable through the local supply system or from theOccup ational Health Clinic. Ear plugs m ust be p roperly fittedby qu alified p ersonnel. For specific information on h earingprotection, refer to TB MED 501.

FOOT PROTECTION

The floor in a machine shop is often covered w ith razor-sharp m etal chips, and heavy stock may be d ropped on thefeet. Therefore, safety shoes or a solid leather sh oe m ust beworn at all times. Safety shoes are available in the supply

system. These have a steeldesigned to resist impact.instep guard.

plate located over the toe and areSome safety shoes also have an

GRINDING DUST AND H AZARDOUS FUMES

Grinding dust from abrasive wheels is made up of extremelyfine p articles of the m etal and th e wh eel. Some grindingmachines are equipped with a vacuum dust collector. Whenoperating a grinder without a vacuum, wear an approvedrespirator to avoid inhaling the dust. Whenever possible, usecoolant when grinding. This will aid in dust control. Grindingdust can be very dangerous to your health, especiallyberyllium or parts u sed in nu clear systems. These materialsrequire careful control of grinding dust.

Metals such as zinc give off toxic fumes w hen h eated abovetheir boiling point. Inhaling th ese fum es may cause temporarysickness, or death. The fum es produ ced from lead andmercury are very harmful, as their effect is cumulative in thebody and can cause irreversible damage. When unsure of thematerials being machined, it is advisable to wear a respirator.For more sp ecific information on r espirator safety, refer to TBMED 502.

PROPER LIFTIN G PRO CEDURES

Using improper lifting procedures may result in a permanent

back injury. Back injury can be avoided if the correct liftingprocedures are followed. When lifting heavy or large objects,get some assistance or use a hoist or forklift.

Objects within y our ability can be lifted safely as long as th efollowing procedures are followed:

Keep your back straight.

Squat down, bending at the knees.

Use the leg mu scles to do the w ork and lift slowly. Donot bend over the load as this will put excessive strain on

your spine.Carry th e object wh ere it is comfortable, and pay closeattention to where you are walking and objects aroundyou.

When placing the object back on the floor, use the sameprocedures as when it was lifted.

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ELECTRICAL SAFETY

Exposu re to electrical hazard w ill be minim al unless theoperator becomes involved w ith machine repair. The machineoperator is mostly concerned with the on and off switch on themachine tool. However, if adjustments or repairs must be

mad e, the pow er source should be disconnected. If themachine tool is wired perm anently, the circuit breaker shouldbe switched off and tagged w ith an approp riate w arningstatement. Most often the power source will not bedisconnected for routine adjustment such as changing machinespeeds. How ever, if a speed change involves a belt change,make sure that no other person is likely to turn on the machinewhile the operators hands are in contact with belts andpulleys.

SAFETY RULES FOR M ACH INE TOO LS

Since different cutting tools and machining procedures areused on various m achine tools, the safety precautions for eachm ay vary. The follow ing are genera l safety ru les for anymachine tool:

Gears, pulleys, belts, couplings, ends of shafts havingkeyways, and other revolving or reciprocating partsshould be guard ed to a height of 6 feet above the floor.The guards shou ld be rem oved only for repairing oradjusting the m achine and mu st be replaced beforeoperating it.

Safety setscrews shou ld be used in collars and on all

revolving or reciprocating members of the machine toolor its equipment.

Do not op erate any machine tool without p roper lighting.

Never attempt to operate any machine tool until you fullyund erstand h ow it works and know how to stop it quickly.

Never w ear loose or torn clothing and secure long hair,since these items can become caught in revolvingmachine parts. Ties should be removed and shirt sleevesshould be rolled up above the elbow.

Gloves should never be w orn w hen operating machineryexcept when absolutely necessary.

Alw ays stop the m achine before cleaning it or takingmeasurements of the workpiece.

Do not lubr icate a m achine while it is in motion. Injurythe operator and d amage to the machine may result frthis practice.

Never remove metal chips, turnings, or shavings wyour hands; they may cause a serious cut. If the shavinare long, stop the machine and break them with pliers obent rod, and then brush chips off the machine. Remocast-iron chips, wh ich break into sm all pieces, witbrush. Never wipe away chips when the machineoperating.

Always w ear safety glasses or goggles while operatimachine tools. Also, wear respiratory p rotectionoperation creates hazardous dust. All persons in the awh ere power tools are being operated should also wsafety eye protection and respirators as needed.

Know where tire extinguishers are located in the sharea and how to use them.

Never wear jewelry while working around machine tooRings, watches, or bracelets maybe caugh t in a revolvipart which could result in the hand being pulled into tmachine.

Avoid horseplay. Tools are very sharp and machines amad e of hard steel. An accidenta l slip or fall may cau sserious injury.

Never use compressed air without a safety nozzle to clemachines or clothing. It will blow sharp , dangerou s mechips a long distance.

Keep the floor arou nd machines free of tools, stock, ogrease, and m etal chips. Tripping over m etal on the floespecially round bars, can cause dan gerous falls. Wipe all oil, grease, and cutting fluid sp ills on th e floor as soas possible to prevent a fall. Metal chips are v ery shaand can easily become em bedd ed in the soles of shoemaking them very slipp ery, especially when w alking onconcrete floor.

Never p lace tools or other m aterials on the machine tabCluttering up a machine w ith tools or materials creatunsafe working conditions. Use a bench or table near tmachine for this purpose.

Always use a rag w hen hand ling sharp cutters such milling cutters and end mills.

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Do not expose pow er tools to rain or use in d amp or w et Remove adjusting keys and wrenches. Form a habit oflocations. checking to see that keys and wren ches are removed from

tools before turning them on.Always secure the workpiece. Use clamps or a vise. It issafer than u sing your hand s, and it frees both han ds to Do not operate any machine tool while under the

operate the tool influence of drugs, alcohol, or any medication that couldcause drowsiness.Do not abu se electrical cords. Never carry a tool by itscord or ya nk it to d isconnect it from a recepta cle. Keepelectrical cords away from heat, oil, and sharp edges.Have dam aged or worn power cords and strain relieversrepaired or replaced immediately.

SAFETY COLOR COD E MARKIN GS AND SIG NS

USE OF PAINT

All maintenance shops and work areas should be markedwith the correct colors to identify hazards, exits, safewalkways, and first-aid stations. It is acceptable to usematerial other than paint, such as decals and tapes, in theppropriate, similar colors. Listed below are the main colorsuthorized for use in maintenance shops.

Red color markings should be used to identify the followingquipment or locations:

Fire alarm boxes (pu ll boxes).

Fire blanket boxes.

Fire extinguishing containers.

Fire extinguishers, u nless painting is unn ecessary. Forlarge areas and w hen th e extinguisher is not readilyvisible to the area occupants, use red on the housing wallor support above the extinguisher to show its location.

Fire hose locations.

Fire pumps.

Fire sirens.

Sprinkler piping.

Fire buckets.

Fire reporting telephone stations.

Store all idle tools in a safe, dr y p lace.

Provide visitors to the work area requ ired personn elprotection equipment.

An exception may be made to comply with local laws orwhen current facilities provide green exit signs.

Emergency stop buttons for electrical machinery.

Emergency stop bars on hazardous machines.

Yellow color markings should be used to identify thefollowing equipment or locations:

Industrial areas where particular caution is needed, suchas hand rails, guardrails, bottom edge of overhead doors,or top and bottom treads of stairways.

Fire hydrant barrels.

Caution signs.

Piping systems containing flammable material.

Waste containers for highly combustible material.

A hazardous area or a safe aisle within a hazardous area.

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Lower pulley blocks and cranes.

Coverings and guards for guy wires.

Pillars, posts, or columns that are ph ysical or shophazards.

Fixtures suspended from ceilings or walls that extend intonormal operating areas.

Corner markings for storage piles.

Exposed and unguarded edges of platform s, pits, andwells.

Green color markings normally on a white color backgroundshould be used for the following equipment or locations:

First-aid equipment.

First-aid dispensaries.

Stretchers.

Safety starting buttons on machinery.

Safety instruction signs.

Black and white are the basic colors for designatinghousekeeping and interior traffic markings. The following areexamp les of where solid w hite, solid black, single-colorstriping, alternate stripes of black and white, or black andwhite squares will be used.

Locations and width of aisles in nonhazardous areas.

Dead ends of aisles or passageways.

Directional signs.

Locations of refuse cans.

White corners of rooms or passageways.

Clear floor area around first-aid, fire-fighting, and theiremergency equipment.

Blue color ma rkings are u sed on th e outside of switch boxeselectrical controls that are the starting point or power sourcefor hazardous electrical machinery or equipment.

TC 9

Orange markings are used to designate dangerous parmachines or energized equ ipment, including electrconduits, which may cut, crush, shock, or injure.

CATEGORIES OF SIGNS

Signs are placed in categories according to their purpUse the examp les in the following pa ragrap hs as guides wchoosing the correct sign d esign to disp lay a m essageoverseas commands, the use of International Standard SaSigns is encouraged and authorized.

WORDING O F SIGNS

Ensure that the wording of any sign-

Is concise and easy to read.

Contains enough information to be easily understood.Is designed for the m essage to be carried in a p ictwhen app ropriate.

Is a positive rather than a negative statement wappropriate.

Is bilingual with the second language common tolocal personnel when appropriate.

SIGN INSPECTION AND MAINTENANC

Signs should be inspected regularly and m aintained in gcond ition. They should b e kept clean, well illumina ted, legible. Replace or repair d amaged or broken signs. All swill be designed with round ed or blunt corners and withsharp projections. Put the end s or head s of bolts or otfastening devices where they will not cause a hazard.

SELECTION OF SIGN SIZE

When choosing a sign, consider dimensions that will peeconomical use of standar d size material. Base the size ofsign on the following:

Location at which the sign will be placed.

Character of the hazard involved.

Purpose of the sign.

Distance from which the sign should be legible.


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REQUIRED SIGN COLORS

All signs require a predominant color based on the signsrpose. Below are the five types of signs and theirdominant color.

Danger signs: RED.

Caution signs: YELLOW.

Safety instruction signs: GREEN.

Directional signs: BLACK.

Informational signs: A variety of colors may be used,except for red, yellow, or magenta (purple).

DANGER SIGNS

Danger signs should only be used when immediate hazardsts. There will be no variations in the type or design ofns posted to war n of specific danger. All personn el will betructed that danger signs indicate immediate danger and special precautions are necessary.

CAUTION SIGNS

Caution signs should be used only to warn against potentialards or to caution against unsafe practices. All personnell be instructed th at a caution sign indicates a possible

ard against which proper precautions will be taken.

DIRECTIONAL SIGN S

Directional signs should be used in sufficient numbers toicate the w ay to stairwa ys, fire escapes, exits, and other

ations.

Many other safety media are available for use in militaryntenance shops.

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Chapter 2

PROPERTIES, IDENTIFICATION,

AN D

HEAT TREATMENT OF METALS

GENERAL

PURPOSE

This chapter contains basic information pertaining toproperties and identification of metal and heat-treatingprocedures used for metals. For more specific information on

metal an d heat-treating techniques, refer to TM 43-0106.

METAL CLASSIFICATION

All metals may be classified as ferrous or nonferrous. Aferrous metal has iron as its main element. A metal is stillconsidered ferrous even if it contains less than 50 percent iron,as long as it contains more iron than any other one metal. Ametal is nonferrou s if it contains less iron than any oth ermetal.

Ferrous

Ferrous metals include cast iron, steel, and the various steelalloys, The only d ifference between iron an d steel is the carbon

content. Cast iron contains more than 2-percent carbon, wsteel contains less than 2 percent. An alloy is a substcomposed of two or m ore elements. Therefore, all steel

an alloy of iron an d carbon, but the term alloy snormally refers to a steel that also contains one or more elements. For example, if the main alloying elemetungsten, the steel is a tungsten steel or tungsten allothere is no alloying material, it is a carbon steel.

Nonferrous

Nonferrous metals include a great many metals that are mainly for metal plating or as alloying elements, such azinc, silver, and gold . Howev er, this chap ter will focuson the m etals used in th e manu facture of parts, sucaluminum, magnesium, titanium, nickel, copper, analloys.


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GENERAL

PROPERTIES O F METALS

The internal reactions of a metal

known as mechanical properties. The

to external forces are

mechanical propertiesare directly related to each other. A chan ge in one prop ertyusually causes a change in one or more ad ditional properties.For example, if the hardness of a metal is increased, thebrittleness usually increases and the toughness usuallydecreases. Following is a brief explanation of the mechanicalproperties and how they relate to each other.

TENSILE STRENG TH

Tensile strength is the ability of a metal to resist being pulledapart by opposing forces acting in a straight line (Figure 2-1).It is expressed as the number of pounds of force required topull apart a bar of the material 1 inch wide and 1 inch thick.

SHEAR STRENGTH

Shear strength is the ability of a metalfractured by op posing forces not acting in

to resist beinga straight line

Figure 2-2). Shear strength can be controlled by varying thehardness of the metal.

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COM PRESSIVE STRENG TH

Compressive strength is the ability of a metal to withstandpressu res acting on a given p lane (Figure 2-3).

ELASTICITY

Elasticity is the ability of metal to return to its original size

and shape after being stretched or pulled out of shape (Figure2-4).

DUCTILITY

Ductility is the ability of a metal to be drawn or stretchedpermanently without rupture or fracture (Figure 2-5). Metalsthat lack ductility will crack or break before bending.

MALLEABILITY

Malleability is the ability of a metal to be hammered,rolled, or pressed into various shapes without rupture orfracture (Figure 2-6).


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TOUGHNESS

Toughn ess is the ability of a metal to resist fracture p lusthe ability to resist failure after the damage has begun. Atough metal can w ithstand considerable stress, slowly or

suddenly applied, and will deform before failure.

HARDNESS

Hardness is the ability of a metal to resist penetration andwear by another metal or material. It takes a combination ofhardn ess and toughness to withstand h eavy pound ing. Thehard ness of a metal limits the ease with w hich it can bemachined, since toughness decreases as hardness increases.The hardness of a metal can usually be controlled by heattreatment.

MACHINABILITY AND WELDABILITY

Machinability and weldability are the ease or difficultywith which a material can be machined or welded.

CORROSION RESISTANCE

Corrosion resistance is the resistance to eating or wearingaway by air, moisture, or other agents.

HEAT AND ELECTRICAL COND UCTIVITY

Heat an d electrical condu ctivity is the ease with w hich ametal conducts or transfers heat or electricity.

BRITTLENESS

Brittleness is the tend ency of a m aterial to fracture o rbreak w ith little or no d eformation, bend ing, or twisting.Brittleness is usually not a desirable mechanical property.Normally, the harder the metal, the more brittle it is.

IDENTIFICATION OF METALS

GENERAL

Part of the metalworkers skill lies in the ability to identify

various metal produ cts brought to the shop. The metalworkermust be able to identify the metal so the proper work methodscan be applied. For Army equ ipment, draw ings should beavailable. They must be examined in order to determine themetal to be used and its heat treatment (if required). If nodrawing is available, knowledge of what the parts are going todo will serve as a guide to the type of metal to use.

TESTING OF M ETALS

Simple tests can be made in the shop to identify metals.Since the ability to judge metals can be developed onlythrough personal experience, practice these tests with known

metals until familiar with the reactions of each metal to eachtype of test.

App earance Test

This test includes such things as the color and appearanceof machined as well as unmachined surfaces.

2-4

Fractu re Test

Some metals can be quickly identified by looking at thesurface of the broken part or by stu dying the chips prod ucedwith a ham mer and chisel.

Spark Test

This is a simp le iden tification test used to observe th ecolor, spacing, and quantity of sparks produced by grinding. Itis a fast and convenient method of sorting mixed steels withknown spark characteristics. This test is best conducted byholding the steel stationary and touching a high-speed portablegrinder to the steel with sufficient pressure to throw a sparkstream about 12 inches long. The characteristics of sparks

generated by a spark grinding test are shown in Figure 2-7.These spark p atterns provide general information about thetyp e of steel, cast iron , or alloy steel. In all cases, it is best touse standard samples of metal when comparing their sparkswith that of the test sample.


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HE ROCKWELL HARDNESS NUMBER IS

ETERMINED BY THE DEPTH O F THE

MPRESSION WHILE THE BRINELL HARD NESS

UM BER IS DETERMIN ED BY THE AREA OF THE

MPRESSION

File Test

One simple way to check for hardness in a piece of metal isfile a small portion of it. If it is soft enough to be machinedth regular tooling, the file will cut it. If it is too hard to

achine, the file will not cut it. This method will indicatehether the m aterial being tested is softer or harder than thee, but it will not tell exactly how soft or hard it is. The filen also be used to determine the hard er of two p ieces ofetal; the file will cut the softer metal faster and easier. Thee method shou ld only be u sed in situations wh en the exactrdness is not required. This test has the added advantage of

eeding very little in the w ay of time, equipm ent, andperience.

Rockw ell Hardn ess Test

This test determines the hardness of metals by measuring thedepth of impression which can be made by a hard test pointun der a k nown load. The softer the metal, the deep er theimpression. Soft metals will be indicated by low hardness

num bers. Harder m etals permit less of an impression to bemade, resulting in higher hardness numbers. Rockwellhardness testing is accomplished by using the Rockwellhard ness testing m achine (Figure 2-8).

Brinell H ardn ess Fest

Brinell hardness testing operates on almost the sameprinciple as the Rockwell test. The difference between the twois that the Rockwell hardness nu mber is determined by thedepth of the impression w hile the Brinell hardness nu mber isdetermined by the area of the impression. This test forces a

hard ened ball, 10 mm (0.3937 in) in diameter, into the surfaceof the metal being tested, under a load of 3,000 kilograms(approximately 6,600 lb). The area of this impressiondetermines the Brinell hardness number of the metal beingtested. Softer metals result in larger impressions but havelower hardness numbers.

NUM ERICAL CODES

Perhaps the best known numerical code is the Society ofAutom otive Engineers (SAE) code. For the metals ind ustry,this organization p ioneered in developing a un iform codebased on chemical analysis. SAE specification num bers arenow used less widely than in the past; however, the SAEnu merical code is the basic code for ferrous metals Figure 2-9).

The SAE system is based on the use of four-or five digitnumbers.

The first nu mb er indicates the typ e of alloy u sed; forexample, 1 indicates a carbon steel.

Two indicates nickel steel.

The second, and sometimes the third, number gives theamount of the main alloy in whole percentage numbers.

The last two, and sometimes three, num bers give thecarbon content in hundredths of 1 percent (0.01 percent).

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The following examp les will help you und erstand this SAE 1045system:

1- Type of steel (carbon).

0- Percent of alloy (none).

45- Carbon content (0.45-percent carbon).


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SAE 2330

2- Type of steel (nickel).

3- Percent of alloy (3-percent nickel).

30- Carbon content (0.30-percent carbon).

SAE 71650

7- Type of steel (tungsten).

16- Percent of a lloy (16-percent tun gsten).

50- Carbon content (0,50-percent carbon).

SAE 50100

5- Type of steel (chromium).

0- Percent of alloy (less than l-percent chromium).

100- Carbon conten t (1-percent carbon).

AA Code

A system similar to th e SAE classifications for steel andlloys has been developed by the Aluminum Association (AA)or wrought aluminum and aluminum alloys.

This identification system of aluminum, as shown in Figure2-10, consists of a four-digit number which indicates the typeof alloy. control over impu rities, and th e specific alloy. The

first nu mb er ind icates the typ e of alloy. For examp le, 2 iscopper, 3 is manganese, 4 is silicone, and so forth. The secondnum ber indicates the control that has been used. The last twonum bers usually indicate an assigned composition. Thus, AA-2024 means:

2 - Type of alloy (copper ).

O - Control of imp urities.

24 - Exact comp osition (AA nu mber 24).

Aluminum alloys vary greatly in their hardness and

physical condition. These differences are called temper,Letter symbols represent the different tempers, In addition to aletter, one or m ore num bers are sometimes used to ind icatefurther differences. The temper designation is separated fromthe basic four-d igit identification nu mber by a dash ; for ex-amp le, 2024-T6. In this case there is an a luminum alloy, 2024,with a T6 temp er (solution heat treated and then artificiallyaged). Figure 2-11 shows the nu merals 2 through 10 that havebeen assigned in the AA system to indicate specific sequencesof annealing, heat treating, cold working, or aging.

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A stencil

METHODS O F MARKING

Stenciling

and wh ite or black paint, whichever shows up

Stamping

Stamping the specification number into the metal should better on the metal being marked, should be u sed wh en the used when it is impossible to use the stencil method. It size of the metal p iece p ermits. The federal or military usually necessary to cut or eliminate the marked portion of thspecification numbers should be stenciled on the metal in metal prior to using the material for work stock. Therefore, thvertically or hoizontally aligned rows. The distance between marking should be located w here waste will be held tothe vertical rows should not exceed 36 inches, and the distance minimum. Gothic style numerals and letters should be usebetween the horizontal rows should not exceed 10 inches. the height may be 1/ 16 inch, 1/ 8 inch, or 1/ 4 inch, dependin

GENERAL upon the size of the material being marked.

FERRO US M ETALSCAST IRON

Ferrous metals are those that contain iron as the base metal.

The properties of ferrous metals may be changed by adding Cast iron is a metal that is widelv used. It is a hard, brittvarious alloying elements. The chem ical and mechan ical .metal that has good wear resistance. Cast iron contains 2 to properties need to be combined to produce a metal to serve a percent carbon. White cast iron is very hard and is usespecific purp ose. The basic ferrous metal form is pig iron. Pig mostly where abrasion and wear resistance is required. Whitiron is produced in a blast furnace that is charged with an iron cast iron may be made into malleable iron by heating it; theore, coke, and limestone. The four p rincipal iron ores arehematite, limonite, magnetite and faconite.

cooling it very slow ly over a long p eriod of time. Malleabliron is stronger and tougher than white cast iron; however, it imuch more expensive to produce. Gray iron is another form ocast iron. It is used mostly for castings because of its ability tflow easily into complex shapes.

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WROUGHT IRON

Wrought iron is an iron that h as had m ost of its carbonemoved. It is tough; however, it can be bent or twisted veryasily. Wrought iron is used mostly in ornamental ironwork,

uch as fences and handrails, because it is welded or paintedasily and it rusts very slowly.

STEEL

Steel is an alloy of iron and carbon or other alloyinglements. When the alloying element is carbon, the steel iseferred to as carbon steel. Carbon steels are classified by theercentage of carbon in points or hundredths of 1 percent

hey contain.

Low Carbon Steel(Carbon content u p to 0.30 percent or 30 points).

This steel is soft and du ctile and can be rolled, pu nched,heared, and worked when either hot or cold. It is easily

machined and can be readily welded by all methods. It doesot harden to any great amount; however, it can be easilyase- or surface-hardened.

Medium Carbon SteelCarbon content from 0.30 to 0.50 percent or 30 to 50 points).

This steel may be heat-treated after fabrication. It is used foreneral machining and forging of parts that require surfaceardness and strength. It is made in bar form in the cold-rolled

the normalized and annealed condition. During welding, theeld zone w ill become hard ened if cooled rap idly and m ust beress-relieved after welding.

High Carbon Steel(Carbon content from 0.50 to 1.05% or 50 to 105 points)

This steel is used in th e man ufacture of drills, taps, dies,prings, and other machine tools and hand tools that are heat-eated after fabrication to develop the hard structure

necessary to w ithstand high shear stress and wear. It ismanu factured in bar, sheet, and w ire forms, and in theannealed or n ormalized condition in order to be suitable formachining before heat treatmen t. This steel is difficult to weldbecause of the hardening effect of heat at the welding joint.

Tool Steel(carbon content from 0.90 to 1.70 percent or 90 to 170 points)

This steel is used in the manu facture of chisels, shear blad es,cutters, large taps, woodturning tools, blacksmiths tools,razors, and other similar parts where high hardness is requiredto maintain a sharp cutting edge. It is difficult to weld due tothe high carbon content.

High-Speed Steel

High-speed steel is a self-hardening steel alloy that can

withstand high temperatu res without becoming soft. High-speed steel is ideal for cutting tools because of its ability totake deeper cuts at higher speeds than tools made from carbonsteel.

Tungsten Carbide

Tungsten carbide is the hardest man-made metal. It is almostas hard as a d iamond. The metal is molded from tungsten andcarbon pow ders un der heat and pressure. Tools mad e fromthis metal can cut other metals many times faster than high-speed steel tools.

Alloy Steels

Steel is man ufactured to m eet a wid e variety ofspecifications for hardness, toughness, machinability, and soforth. Manufacturers use various alloying elements to obtainthese characteristics. When elements other than carbon, suchas chromium, m anganese, molybdenum, nickel, tungsten, andvanadium are used. The resulting m etals are called alloysteels. Figure 2-12 shows some of the general characteristicsobtained by the use of various alloying elements.

NONFERROUS METALS

ALUMINUM

There are many metals that do not have iron as their base Aluminum and its alloys are produced and used in manyetal. These metals, known as nonferrous metals, offer shapes and forms. The common forms are castings, sheet,

pecific propert ies or combina tions of prop erties that mak e plate, bar, rod, channels, and forgings. Aluminum alloys haveem ideal for tasks where ferrous metals are not suitable.onferrous metals are often used with iron base metals in the

many desirable qualities. They are lighter than most othermetals and do not rust or corrode under most conditions.

nished p rodu ct. Aluminum can be cast-forged, machined, and welded easily.

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MAGNESIUM

Magnesium alloys are produced and used in many shapesand forms, for example, castings, bars, rods, tubing, sheetsand plates, and forgings. Their inherent strength, light weight,

and shock and vibration resistance are factors which maketheir use advan tageous. The w eight for an equ al volume ofmagnesium is app roximately two-thirds of that for aluminumand one-fifth of that for steel. Magnesium has excellentmachining qualities; however, care must be taken whenmachining because the chips are highly flammable.Magnesium fires bum so hot that they cannot be extinguishedby conventional fire extinguishers.

COPPER

Copper is a reddish metal, very ductile and malleable, andhas high electrical and heat conductivity. Copper can beforged, cast, and cold worked. It also can be weld ed, bu t itsmachinability is only fair. The principal use of commerciallypure copper is in the electrical industry where it is made into

wire or other such cond uctors. It is also used in manufacture of nonferrous alloys such as brass, bronze, monel metal. Typical copper products are sheet roofi

cartridge cases, bushings, wire, bearings, and statues.

BRASS AND BRON ZE

Brass, an alloy of copper and zinc (60 to 68 percent copand 32 to 40 percent zinc), has a low melting point and hheat conductivity. There are several types of brass suchnaval, red, adm iralty, yellow, and comm ercial. All diffecopper and zinc content. All may be alloyed with otelements su ch as lead, tin, manganese, or iron, and all hgood machinability and can be welded. Bronze is an alloycopper and tin and may contain lead, zinc, nickel, manganeor ph osph orou s. It has high strength , is rust or corrosresistant, has good machinability, and can be welded.

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LEAD

Lead is used mainly in the manufacture of electricalquipment such as lead-coated pow er and telephone cablesnd storage batteries. Zinc alloys are used in the manufacture

f lead weights, bearings, gaskets, seals, bullets, and shot.any types of chemical compound s are produ ced from lead.mong these are lead carbonate (paint pigment) and tetraethylad (antiknock gasoline). Lead is also used for X-rayotection (radiation shields). Lead has more fields ofplication than any other metal. It can be cast, cold worked,elded, and machined. Lead has low strength w ith heavyeight.

TIN

The ma jor u se of tin is in coating steel. It is the bestntainer for preserving p erishable food. Tin, in the form of

il, is often used in wrap ping food p roducts. A second majore of tin is as an a lloying element. Tin is alloyed w ith copperproduce bronze, with lead to produce solder, and withtimony and lead to form babbitt. Tin can be die cast, coldorked , machined, and soldered; however, it cannot belded.

NICKEL

Nickel is used in making alloys of both ferrous andnferrous metals. Chemical and food processing equipm ent,ctrical resistance heating elements, ornamental trim, and

parts that must withstand elevated temperatures are allprod uced from nickel containing m etal. Alloyed w ithchromium, it is used to make stainless steel. Nickel alloys arereadily welded by either gas or arc methods and can bemachined, forged, cast, and easily formed.

COBALT-CHROMIUM-TUNGSTEN

MOLYBDENUM WEAR-RESISTANTALLOYS

These alloys feature a wear resistance which makes themideal for m etal-cutting op erations. Their ability to reta inhard ness even at red-heat temp eratures also makes themespecially useful for cutting tools. Common cutting tools willlose their edge at high heat, wh ereas this alloy group isactually tougher at red heat than it is when cold; as a result,

higher speeds and feeds may be used when machining withtools made with these alloys.

PRECIOUS M ETALS

These include silver, gold, platinum, palladium, iridium,osmium, rhodium, and ruthenium, and their alloys. Thesealloys are produced under technical and legal requirements.Gold alloys used for jewelry are described in karats. The karatis the content of gold expressed in twenty-fourths. An 18-karatgold alloy would conta in 18/ 24 gold (75 percent by weigh t).Other than jewelry, there are many industrial uses for preciousmetals.

HEAT TREATMENT OF METALS

Heat treatment is any on e of a num ber of controlled h eatingd cooling operations used to bring about a desired change ine physical properties of a metal. Its purpose is to improvee structural and physical properties for some particular usefor future w ork of the m etal. There are five basic heatating processes: hardening, case hardening, annealing,rmalizing, and tempering. Although each of these processesng about different results in metal, all of them involve threesic steps: heating, soaking, and cooling.

HEATING

Heating is the first step in a heat -treating process. Manyoys change structure w hen they are h eated to sp ecific

mperatures. The structure of an alloy at room temperaturen be either a m echanical mixture, a solid solution, or ambination solid solution and mechanical mixture.

2

A mechanical mixture can be compared to concrete. Just asthe.sand and gravel are visible and h eld in place by thecement. The elements and compoun ds in a m echanicalmixture are clearly visible and are held together by a matrix ofbase metal. A solid solution is when two or more metals areabsorbed, one into the other, and form a solution. When analloy is in the form of a solid solution, the elements andcompound s forming the metal are absorbed into each other inmuch the same way that salt is dissolved in a glass of water.The separate elements forming the metal cannot be identified

even under a microscope. A metal in the form of a mechanicalmixture at room temperature often goes into a solid solution ora partial solution when it is heated. Changing the chemicalcomposition in this w ay brings abou t certain pred ictablechanges in grain size and structure. This leads to the secondstep in the heat treating process: soaking.


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ANNEALING

Once a metal part has been heated to the temp erature atwhich d esired changes in its structure w ill take place, it m ustremain at that temperature until the entire part has been evenlyheated throu ghout. This is known as soaking. The more m ass

the part has, the longer it must be soaked.

COOLING

After the p art has been p roperly soaked, the third step is tocool it. Here again, the structure may change from onechemical composition to an other, it may stay the same, or itmay revert to its original form. For example, a metal that is asolid solution after heating may stay the same d uring cooling,change to a mechanical mixture, or change to a combinationof the two, depending on the type of metal and the rate ofcooling. All of these changes are predictable. For that reason,many metals can be m ade to conform to specific structures in

order to increase their hardness, toughness, ductility, tensilestrength, and so forth.

HEAT TREATMENT O F FERROUS M ETALS

All heat-treating operations involve the heating andcooling of metals, The common forms of heat treatment forferrous m etals are hardening, tempering, annealing,normalizing, and case hardening.

HARDENING

A ferrous metal is normally hardened by heating the metalto the required temp erature and then cooling it rapidly byplunging th e hot metal into a quenching mediu m, such as oil,water, or brine. Most steels must be cooled rapid ly to hardenthem. The hard ening process increases the hardn ess andstrength of metal, but also increases its brittleness.

TEMPERING

Steel is usu ally harder th an n ecessary and too brittle forpractical use after being hardened. Severe internal stresses areset up du ring the rap id cooling of the metal. Steel is temperedafter being hardened to relieve the internal stresses and reduce

its brittleness. Tempering consists of heating the metal to aspecified temperature and then permitting the metal to cool.The rate of cooling usually has no effect on the metal structureduring tempering. Therefore, the metal is usually permitted tocool in still air. Temperatures used for tempering are normallymuch lower than the hardening temperatures. The higher thetempering temp erature used , the softer the metal becomes.High-speed steel is one of the few metals that becomes hard erinstead of softer after it is tempered.

Metals are annealed to relieve internal stresses, soften tmake them more d uctile, and refine their grain structuMetal is annealed by heating it to a prescribed temperaholding it at that temperature for the required time, and

cooling it back to room temp erature. The rate at wh ich mis cooled from the annealing temperature varies greatly. Smu st be cooled very slowly to produ ce maximu m softnThis can be done by burying th e hot part in sand, ashesome other substance that does not conduct heat rea(packing), or by shutting off the furnace and allowingfurnace and part to cool together (furnace cooling).

NORMALIZING

Ferrous metals are normalized to relieve the internal streproduced by machining, forging, or welding. Normalisteels are hard er and stronger than annealed steels. Stemuch tougher in the normalized condition than in any ocondition. Parts that w ill be subjected to impact and partsrequire maximum toughness and resistance to external streare usually normalized. Normalizing prior to hardeninbeneficial in obtaining the d esired hard ness, providedharden ing operation is p erformed correctly. Low carbon sdo n ot usu ally require n ormalizing, but no har mful effresult if these steels are normalized. Normalizing is achieby heating the m etal to a specified tem peratu re (whichigher than either the hardening or annealing temperatursoaking the metal until it is uniformly heated, and cooling still air.

CASE HARD ENING

Case hardening is an ideal heat treatment for parts whrequire a wear-resistant surface and a tough core, sucgears, cams, cylinder sleeves, and so forth. The most comcase-hardening processes are carburizing and nitridDuring the case-hardening process, a low-carbon steel (eistraight carbon steel or low-carbon alloy steel) is heated specific temp erature in the p resence of a material (soliquid, or gas) which decomposes and deposits more carinto the su rface of a steel. Then, when the p art is coorapidly, the outer surface or case becomes hard, leaving

inside of the piece soft but very tough.

HEAT TREATMENT OF NONFERROUSMETALS

Two types of heat-treating op erations can be performenonferrous metals. They are annealing and solution htreating.

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ANNEALING

Most nonferrou s metals can be annealed. The annealingprocess consists of heating the metal to a specific temperature,soaking, and cooling to room temperature. The temperatureand m ethod of cooling depend on the type of metal. Annealing

is often accomplished after various cold working operationsbecause many nonferrous metals become hard and brittle aftercold working. Also, annealing is used to remove the effects ofsolution heat treatment so that machining or working qualitiescan be improved.

SOLUTION HEAT TREATMENT

The tensile strength of many nonferrous alloys can beincreased by causing the materials within the alloy to go into asolid solution and then controlling the rate and extent of returnto an altered mechanical mixture. This operation is calledsolution heat treatm ent. After an alloy has been heated to aspecified temperature, it is quenched or cooled rapidly,which traps the materials in the solid solution attained d uringthe heating process. From this point, the process varies greatlydepending on the metal. To be sure the materials in the alloydo not revert to their original configuration after a period oftime, a process of aging or precipitation hardening mustfollow. In this process the materials in the alloy are allowed tochange or to precipitate out of the solid solution.

This process occurs under controlled conditions so that theresultant grain structure will produce a greater tensile strengthin the metal than in its original condition. Depending on thealloy, this precipitation process can also consist of simply

aging the alloy at room temperature for a specified time andthen air-cooling it; this is called artificial aging.

Aluminum alloys can be obtained in various conditions ofheat treatment called temp er d esignations. Figure 2-11, onpage 2-9, shows the various temp er designations and theprocess to which they ap ply. The term strain-hardened refers to aging or hard ening that has been brought about bycoldw orking th e alloy. Stabilizing refers to a par ticularaging pr ocess that freezes or stops the intern al changes thatnormally would take place in the alloy at room temperature.Magnesium alloys can be subjected to all of the nonferrousheat treatm ents, but the d ifferent alloys w ithin the series

require different temp eratures and times for the variousprocesses. Copper alloys are generally hardened by annealing.The nickel alloys can also be ann ealed and certain types canbe hardened by heat treatment. Likewise, titanium may beannealed (mostly relieve machining or cold-working stresses)but is not noticeably affected by heat treatment.

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Chapter 3

PORTABLE MACHINE TOOLS

The portable machine tools identified and described in this Portable machine tools are pow ered by self-containedchapter are intended for use by maintenance personnel in a electric motors or compressed air (pneumat ic) from an outsideshop or field environment. These lightweight, transportable source. They are classified as either cutting took (straight andmachine tools, can qu ickly and easily be moved to the angle hand drills, metal sawing machines, and metal cuttingworkp lace to accomplish machining operat ions. The accuracy shears) or finishing tools (sanders, grinders, and polishers).of work performed by portable machine tools is dependentupon the u sers skill and experience.

SAFETY PRECAUTIONS

GENERAL

Portable machine tools require special safety precautionswh ile being used. These are in add ition to th ose safetyprecautions described in Chapter 1.

PNEUMATIC AND ELECTRIC TOOL

SAFETY

Here are some safety precautions to follow:

Never use electric equipment (such as drills,sanders, and saws) in wet or damp conditions.

Properly grou nd all electric tools prior to use.

Do not use electric tools near flammable liquids orgases.

Inspect all pneumatic hose lines and connectionsprior to use.

Keep constant watch on air pressure to stay withinspecified limits.

Keep all equipment in proper working order, anduse the equipment according to the manufacturersinstructions.

Remove chuck keys from dr ills prior to use.

Hold tools firmly and maintain good balance.

Secure the work in a holding d evice, not in yourhands.

Wear eye protection while operating thesemachines.

Ensure that all lock buttons or switches are offbefore plugging the machine tool into the powersource.

Never leave a portable pneumatic hammer with achisel, star drill, rivet set, or other tool in its nozzle.

ELECTRIC EXTENSIO N CO RD S

Use the right w ire gage for the length of the cord. As thelength of the extension cord increases, heavier gage w ire must

be used. Lengthening extension cords by connecting severalsmall gage cords together causes a serious drop in voltage.This results in the cord overh eating. Extension cords thatoverheat will bum away th e insulation, creating a potentialelectric shock hazard and fire hazard. See Table 3-1,Appendix A, for proper gage and length of extension cords.

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PORTABLE DRILLS

PURPOSE AND TYPES

The portable drill is a hand -sup ported, pow er-drivenachine tool that rotates twist drills, reamers, counterbores,d similar cutting tools. The portable drill may be electricallywered by means of an internal electric motor (Figure 3-1) oray be pneumatically powered (Figure 3-2). Portable d rillse rated by the maximum size hole that can be drilled in steelthout overtaxing the motor or drill.

Therefore, a 1/ 4-inch-capacity drill is capable of dr illing a1/ 4-inch diameter hole or smaller in steel. Portable electricand p neum atic drills rated at 1/ 4 to 1/ 2-inch maximumcapacities are usually equipp ed w ith geared d rill chucks formounting straight, round shank twist drills or other similartools by using a chuck key (Figure 3-3). Heavier p ortabledrills (Figure 3-4) having a 3/ 4- to 1 1/ 4-inch capacity usetaper shank chucks to mount drills and other similar tools.

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Portable drills have many different characteristics (Figure3-5) depending on how the job is to be done. They may be setfor one speed or they maybe variable speed drills. A variablespeed d rill is an excellent tool for use as a power screwdr iver.Portable drills may be equipp ed w ith a reversing switch toallow a screwd river attachment to reverse bolts and screwsout of holes. Special 90 angle portable drills (Figure 3-8) areavailable for drilling in confined spaces where a stand ard sizedrill will not have sufficient clearance. For corners and tightspots, a 360 angle portable p neum atic drill (Figure 3-2) isavailable which can be swiveled to any desired angle andocked into position. Most portable drills have a lock button

near the on-off switch which allows for continuous operationwithout h olding the trigger. Side hand les and rear spad ehandles (Figure 3-5) can be attached to most drills to stabilizedrilling and to allow for better control. Special devices. suchas a vertical stand (Figure 3-6) or feed screw (Figure 3-7), canbe used on some of the portable drills to make a job easier ormore proficient.

The size, type. and power capacity of portable drills selectedepends on the job to be performed. Before attempting a

rilling job, check the capabilities of the portable drill withe manufacturers instruction manual.

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DRILLING O PERATION S

Operation of the p ortable electric and pneumatic drillsdiffers from recomm ended operating procedures for theupright drilling machine. The portable dr ill is hand suppor tedfor most operations, and the cutting speed of the dr ill is fixed

or dependent upon the operator to control. When hand sup-ported, the d rill must be carefully aligned w ith the workp iece(Figure 3-9) and this alignment must be maintainedthroughout the drilling operation. Care must be taken not tolose control of the portable drill and allow it to be wrenchedfrom the operators hands. The larger portable drills (Figure3-10) can be very dangerous if not held firmly by the operator.If the cutting speed is fixed, the operator mu st learn to controlthe feed of the portable drill by applying sufficient pressurefor the drill to cut, but not too much p ressure as to causeoverheating of the twist d rill or stalling of the portable drillmotor.

When metal is to be drilled with the portable drill, tworkpiece must be p repared by locating the center positionthe potential hole and m arking the location w ith a centpunch. When a large drill is to be used, it will be necessa

first to d rill a pilot hole slightly larger in diameter than tthickness of the larger drills web, which will allow for thdrag caused by the larger drills chisel edge (Figure 3- 11).

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Portable pneum atic drills require sp ecial attention tolubricate their internal moving p arts. Each drill may be mad eslightly d ifferent, so refer to the pertinent lubrication order ormanufacturers instruction manual before drilling.

For drilling by hand, the workpiece must be mountedsecurely. Thin w orkplaces should be backed up with a thickerpiece of wood or metal to prevent the drill from snagging inthe workp iece. Do not attempt to hold any workpiece by handor serious injury could result.

Select a twist dr ill of the proper size for the hole to bedrilled. Ensure that the twist drill selected has the right type ofshank for the type of chuck mounted on the portable drill.Taper shank drills cannot be mounted in a d rill with a gearedchuck. Check each tw ist drill for sharp cutting edges prior touse.

After securing th e twist d rill in the prop er chuck, connectthe portable drill to its power source. Position the portabledrill perpendicular to the workpiece and center the chisel pointof the drill in the center-pu nched h ole of the workpiece.Apply firm but not too heavy pressure upon the portable drill,pu ll the trigger or throttle button to start the d rill.

Apply a few drops of cutting oil to the twist drill and hole(Figure 3-12) to improve the cutting action and preventoverheating of the twist drill. For long drilling operations, stopthe d rill and allow it to cool; then apply ad ditional cutting oilto the drilling area. The lock button can be engaged forlengthy cutting op erations.

Continue drilling the hole while applying enough pressureto produce a clean chip, but not so much p ressure as to causethe motor to strain or the drill to bind. The drill must be heldfirmly at all times to prevent the d rill from being w renchedfrom the hand s of the operator if the flutes of the drill shouldsnag on a m etal burr in the hole.

As the tw ist drill nears the back wall of the workp iece,release the lock button so that th e drill can be stopp edimmediately if required. Decrease the feed pressure as the drillbreaks through, and cautiously feed the dr ill through the wallof the workp iece. If the drill should sn ag on a bu rr, stop

drilling immediately and withdraw from the hole. Carefullyfeed th e drill back into the hole while the d rill is turning to cutthrough the burr.

When a portable drill is mounted to a vertical stand, theoperating procedure is identical to that used for the uprightdrilling machine. Use the lock button while drilling and usethe hand lever to drill to the required depth.

Portable drilling operations can be difficult to aninexperienced operator. It is difficult to keep the twist drillperpendicular to the workpiece during drilling, and it is hardto drill to a desired depth accurately. If help is available, use

the buddy system to keep the drill aligned while drilling. Todrill to depth, mark the twist drill with a light colored m arkingpen or a strip of tape and keep a close watch on the drill as itcuts. Another way to drill to depth accurately using theportable drill is to use a jig, such as a p iece of metal pipe ortubing cut to length, to indicate when the drill has reached thedesired depth.

PORTABLE GRINDERS

PURPOSE AND TYPES A small portable chuck type grinder m ay be known as adie grinder and is available with a number of accessories.

The portable grinder is a lightw eight, hand-operatedmachine tool. It can be powered electrically or pneumatically,depending on the model selected. The portable grinder is usedin the field or m aintenance shop to grind excess metal fromwelds, remove rust, and for special finishing operationsaround the work area. Since this tool is hand operated, thequality of the work depends upon the ability and experience ofhe operator.

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These accessories include rotary files, small circular saws,wire brushes, assorted grinding wheels, and small sanding andpolishing disks. These accessories are mounted to straightshank ar bors wh ich fit into the collet chuck of the grinder.Special reduction collets are provided so that smaller diameter

arbors or shanks can be moun ted in the chuck. Operationsperformed with this portable grinder include shaping andsmoothing intricate dies and castings, removing bu rrs fromedges and surfaces, cleaning and repairing threaded p arts,repairing keyways and splines, grinding bevels,countersinking holes. and repairing scored and mutilatedsurfaces.

The portable grinder (wheel type) (Figure 3-14) can beelectric or pneumatic and is designed for heavy-duty portablegrinding operations. It is capable of mounting and rotating 6-inch-diameter grinding abrasive wheels and 6-inch-diameterwire brushes and polishing wheels. This grinder is used as a

hand grinder for removing rust, corrosion, and sharp burrsfrom large workpieces (Figure 3-15).

Most portable grinders come with a grinder stand (Figu3-16). Mounted on this stand , the grinder can be used sharpen twist drills and cutter bits in the machine shop. Mogrinders also come equipped with a wheel guard that shoulremain in p lace at all times to protect the operator from flyin

sparks and waste material. The portable grinder is designed that the face of the grinding wheel is used; never u se the sidof the wheel or serious injury or damage could occur (Figur3-17).

The angle grinder (disk type) (Figure 3-18) can be electrior pneumatic, and is designed for heavy duty grindinoperations. The angle grinder consists of a depressed centeabrasive grinding disk with wheel guard attached to the basiportable motor assembly (Figure 3-19). Care must be taken tcheck the wheel for cracks and to ensure that the w heel guarstays in place while operating.

OPERATIONS WITH PORTABLE GRIND ERS

Before operating any portable grinder, check the grind inwheel for cracks and check that th e arbor hole is the prop esize for the grinder to be used. When operating these grinderskeep a light pressure on the work to avoid damaging the wheeor overheating the workpiece.

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Both the small and the larger portable grinders operate at aigh speed, so avoid letting the wheel rest on one spot for tooong. This could cause the work to burn or the w heel to cracknd explode. Always check the manufacturers instruction.

man ual before operation to ensure the grind ing wh eelsmaximum rated speed is rated h igher than the maximum sp eed

f the grinder.

When grinding, buffing, or polishing with any portablegrinder, always keep a firm grip on th e tool to avoid injury ordamage to equipment

PORTABLE SAND ERS AND POLISHERS

PURPOSE AND TYPES

Portable sanders and polishers are used for surfacenishing of materials such as metal, wood, ceramics, andastics. Both tools are Lightweight and fairly easy cooperate.hey can be p owered electrically or pneumatically and can beght-duty or heavy du ty.

Portable sanders are used to remove paint, ru st, corrosion,d imperfections from the surface of workplaces to produce a

mooth surface for finishing. Field an d machine shopaintenance personnel use the disk-type portable sander

igure 3-20). The disk-type p ortable sander has a high-speedotor that rotates an abrasive disk, wire wheel, or a grindingheel to p repare a surface for finishing. For sand ing, a disk ofrasive paper is mounted with a flexible backing pad on theotor spindle (Figure 3-21). The basic motor unit is similar toe motor unit used for angle grinding, but with sanding thereno need for a wheel guard. On some m odels the motorindle can be locked by depressing a lock button to install or

remove the sanding disks. A side handle on the motor housingis used to supp ort the sander du ring operation. This handle canbe removed and screwed into the opposite side of the motorhousing for left-handed operation. Pneumatic sanders have anadvantage over electric sanders because they are lighter inweight and easier to handle which usually produces a betterfinished p rodu ct.

NOTE: Portable sanders are not intended for use as portableabrasive cutoff saws. The torque for cut off sawing will ruinthe soft gearing in the sander m otor unit.

Various abrasive disks are used in the operation of theportable electric sander. These disks consist of differentabrasive grains that have been bonded or glued onto a cloth orpaper disk (see Table 3-2) in Appendix A..

The backing material that supports the abrasive disk ismade of a tough vulcanized ru bber or fiber that can withstand

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hard use and constant flexing. Norm ally, the abrasive grainused on the disk is aluminum oxide, and the bonding agent isglue or special resin. Abrasive disks come in open-coat orclosed-coat types, depend ing on the w ork to be performed.The closed-coat disk has the abrasive grains bonded close

together, while the open-coat disk has the abrasive grainsspaced further ap art. Open-coat abrasive disks are used forsanding soft materials that could p ossibly load up a closed-coat disk, for example, wood sanding, removing paint an drust, and plastic. Closed-coat abrasive disks are used forsanding metal, finishing ceramics, and for smoothing roughersanded areas.

Most portable sanders come with an instruction man ualand those accessories that the manufacturer recommends forits use. These accessories can include a sanding setup whichincludes a flexible rubber backing plate, several types ofsanding disks, and the hardware to secure the disk to the

motor assembly. Other accessories may include flexiblegrinding disks with wheel guards, wire wheels, and odd-shaped grind ing cups with the appropriate wheel guard. Onlyuse accessories approved by the manufacturer to avoid injuryor damage to equipment.

The portable polisher (Figur e 3-22) is used to produ ce a

super finish or shine to the workpiece surface. Polishing orbuffing a surface is desirable at times to increase smoothnessand make the surface easier to clean. By polishing a surface, aworkp iece can also be mad e more w ear resistant. Portablepolishers are generally more powerful than portable sanders

Since they encounter a greater frictional resistance whenoperation, portable polishers operate at slower speeds than

in

portable sanders so as not to m ar the finished surfaPneumatic portable polishers are lighter in weight than elecmodels and may make fewer buffing marks on the finishorder to improve the surface quality of a workpiece thropolishing, it is necessary to use a soft bonnet or cover over

sander backing p ad.

Lambs wool polishing bonnets are recommended witsoft rubber cushion pad separating the bonnet and the backpad. Polishing compound, wh ich is a mild abrasive, is usedhelp polish the surface. A left- or right-handed side hand lattached to the m otor housing to h elp control the polisduring operations.


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OPERATION S WITH TH E PORTABLESANDER AND POLISHER

Operating the portable sander is difficult due to therotating force of the disk, so the quality of the work depends

mostly on the experience of the machine operator. Hold theportable sander so that the abrasive disk forms an angle ofapproximately 15 to the workpiece surface (Figure 3-23). Apply just enough pressure against the sander to bend thesanding p ad and abrasive disk so that about 2 inches of thedisk contact the surface. Move the sander from sid e to side,overlapping each path with the next. If the sander cutsirregularly or is hard to control, the sander is most likely at anangle less than the required 15 to the workpiece. If the sandergouges or leaves rough edges, the angle formed by the sanderis most likely too great. When the sand er is operating, keep itmoving back and forth across the w orkp iece or lift it free toavoid damaging the surface.

The portable polisher looks like the portable sander but itis built with a slower speed and h igh torque needed forpolishing. Polishing is performed by placing the spinninglambs wool polishing bonnet lightly against the workpieceand moving the polisher lightly back and forth whilemaintaining a light pressure on the workpiece. Avoid pressingdown too hard, or the surface could get damaged. Use separatepolishing bonnets for different

1996_army_tc_9_524 - fundamentals of machine tools - 309 pg

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