wsfiling and grinding textbook

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Krar • Gill • Smid

Technology of Machine Tools6th Edition

Hand-Type Cutting Tools

Unit 23

23-2

Objectives

• Select and use the proper hacksaw blade for sawing a variety of materials

• Select and use a variety of files to perform various filing operations

• Identify and know the purpose of rotary files, ground burrs, and scrapers

23-3

Sawing, Filing and Scraping

• Often necessary to perform certain metal-cutting operations at bench or on job

• Common tools– Hacksaws– Files– Scrapers

• Usually need practice to become proficient

23-4

Pistol-Grip Hand Hacksaw

• Composed of three main parts– Frame, handle, and blade

• Solid frame more rigid and will accommodate blades of one specific length

• Adjustable frame more common and will take blades from 10 to 12 in. long– Wing nut provides adjustment

23-5

Hacksaw Blades

• Made of high-speed molybdenum or tungsten-alloy steel (hardened and tempered)

• Two types– Solid blade (all-hard)

• Hardened throughout and very brittle

– Flexible blade • Teeth hardened, while back of blade soft and flexible• Stand more abuse than all-hard blade, but will not last

long in general use• Used on channel iron, tubing, copper and aluminum

23-6

Blade Pitch

• Number of teeth per inch• Manufactured in various pitches

– 14, 18, 24, and 32• General use choice – 18 in. tooth blade• Choose as coarse blade as possible

– Provides plenty of chip clearance and to cut through work as quickly as possible

• Should have at least two teeth in contact with work at all times– Prevent work from jamming and stripping teeth

23-7

Guide for Proper Blade Selection


23-8



23-9



23-10



23-11

Files

• Hand cutting tool made of high-carbon steel• Series of teeth cut on body by parallel

chisel cuts• Used to remove surplus metal and to

produce finished surfaces• Manufactured in variety of types and shapes

– Each has specific purpose

• Two classes: single-cut and double-cut

23-12

Single-cut Files


• Single row of parallel teethrunning diagonally across face

• Used when smooth finish desired

• Include mill, long-angle lathe, and saw files

23-13

Double-cut Files

• Two intersecting rows of teeth– First row coarser and called overcut– Second row called upcut

• Hundreds of cutting teeth– Provide for fast removal of metals and easy

clearing of chips


23-14

Degrees of Coarseness

• Both single- and double-cut files come in various degrees of coarseness– Rough– Coarse– Bastard– Second-cut– Smooth– Dead smooth

Most CommonCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

23-15

Machinist Files

• Types most commonly used by machinists

– Flat– Hand– Round– Half-round– Square

– Pillar – Three-quarter– Warding– Knife

23-16

Cross-sectional Views of Machinists' Files


23-17

Care of Files

1. Do not store files where they rub together2. Never use file as pry of hammer3. Do not knock file on vise or other metallic

object to clean it (use brush or file card)4. Apply pressure only on forward stroke5. Do not press too hard on new file6. Too much pressure also results in

"pinning" which scratches work surface• Small particles wedged between teeth

23-18

Points to be Observed When Cross-filing

1. Never use file without handle

2. Fasten work to be filed in vise, at about elbow height

3. To produce flat surface, hold right hand, right forearm and left hand in horizontal plane

• Push file across work face in straight line• Do not rock file

23-19

4. Apply pressure only on forward stroke

5. Never rub fingers or hand across surface being filed

– Oil will clog file– Oil causes file to slide over instead of cutting

6. Keep file clean by using file card frequently

For rough filing, use double-cut file and cross stroke at regular intervals to keep surface flat and straight. When finishing, use single-cut file and take shorter strokes tokeep file flat.

23-20

Draw Filing and Polishing

• Draw filing– Used to produce smooth, flat surface on

workpiece– Removes file marks and scratches left by cross-

filing

• Polishing– After surface filed, finished with abrasive cloth

to remove small scratches left by file• Moved back and forth along work

23-21


23-22

Rotary Files

• Teeth cut and form broken lines

• Dissipate heat of friction

• Useful for work on tough die steels, forgings, and scalysurfaces


23-23

Ground Burrs

• Teeth uniform in tooth shape and size – Unbroken flutes– Flutes machine ground to master burr to

ensure uniformity of tooth shape and size– May be made of high-speed steel or

carbide– Carbide last up to 100 times

longer• Used on nonferrous metals• Better chip clearance






Grinding Section 15

80-25

Grinding

• Characteristics of an abrasive must be:– Harder than material being ground– Strong enough to withstand grinding pressures– Heat-resistant so that it does not become dull at

grinding temperatures– Friable (capable of fracturing) so when cutting

edges become dull, they will break off and present new sharp surfaces to material being ground





Types of Abrasives

Unit 80

80-27

Objectives

• Describe the manufacture of aluminum oxide and silicon carbide abrasives

• Select the proper grinding wheel for each type of work material

• Discuss the applications of grinding wheels and abrasive products

80-28

Abrasive Classes

• Natural abrasives– Sandstone, garnet, flint, emery, quartz, corundum– Used prior to early part of 20th century– Almost totally replaced by manufactured abrasives– Best natural abrasives is diamond (high cost)

• Manufactured abrasives– Used because grain size, shape and purity can be

closely controlled– Aluminum oxide, silicon, carbide, boron carbide,

cubic boron nitride and manufactured diamond

80-29

Aluminum Oxide

• Most important abrasive

• Make up 75% of grinding wheels

• Used for high-tensile-strength materials

• Manufactured with various degrees of purity– Hardness and brittleness increase as purity

increases

80-30

Aluminum Oxide Purities

• Regular aluminum oxide (Al2O3) at 94.5%– Tough abrasive capable of withstanding abuse– Grayish in color– Used for grinding steel, tough bronzes, etc.

• Aluminum oxide at 97.5%– Not as tough as regular but still gray in color– Used in manufacture of grinding wheels for centerless,

cylindrical, and internal grinding of steel and cast iron• Purest form of aluminum oxide

– White material that produces sharp cutting edge– Used for grinding hardest steels and stellite

80-31

Silicon Carbide

• Suited for grinding materials that have low tensile strength and high density

• Harder and tougher than aluminum oxide• Color varies from green to black• Green used mainly for grinding cemented

carbides and other hard materials• Black used for grinding cast iron and soft

nonferrous metals (also ceramics)

80-32

Manufactured Diamonds• 1954, General Electric Company produced Man-

Madey diamonds in laboratory• 1957, General Electric Company began

commercial production of diamonds• First success involved carbon and iron sulfide in

granite tube closed with tantalum disks were subjected to pressure of 66,536,750 psi and temperatures between 2550ºF– Temperatures must be high enough to melt metal

saturated with carbon and start diamond growth

• Industrial diamonds referred to as bort

80-33

Diamond Types

• Type RVG Diamond– Elongated, friable crystal with rough edges– Letters indicate it can be used with resinoid or

vitrified bond and used for grinding ultrahard materials

• Tungsten carbide

• Silicon carbide

• Space-age alloys

– Used for wet or dry grinding

80-34

• Type MBG-II Diamond– Tough and block-shaped crystal– Not as friable as RVG type– Used in metal-bonded grinding wheels– Used for grinding cemented carbides, sapphires,

and ceramics as well as electrolytic grinding

• Type MBS Diamond– Blocky, extremely tough crystal with smooth,

regular surface and not friable– Used in metal-bonded saws to cut concrete,

marble, tile, granite, stone, and masonry

80-35

Ceramic Aluminum Oxide

• Known as SG abrasive, introduced by Norton Company in 1988

• Outperforms conventional aluminum oxide• Made by nonfused process

– Thousands of submicron-sized particles are sintered to provide single abrasive grain of uniform shape and size with more cutting edges that remain sharp

• SG abrasive well suited to CNC grinding– Fewer wheel changes, less wheel dressing, higher

productivity and therefore lower labor costs

80-36

Advantages of SG Abrasives Over Conventional Abrasives

• Last 5 to 10 times longer than conventional wheels

• Metal-removal rates are doubled

• Heat damage to surface of very thin workpieces reduced

• Grinding cycle time reduced

• Dressing time reduced as much as 80%

80-37

Abrasive Grain

• Aluminum oxide or silicon carbide abrasive used in most grinding wheels

• Each grain on working surface of grinding wheel acts as separate cutting tool– Removes small metal chip as passes over

surface of work– As grain becomes dull, fractures and presents

new sharp cutting edge to material• Fracturing action reduces heat of friction, producing

relatively cool cutting action

80-38

Grain Size

• Abrasive ingot (pig) removed from electric furnace, crushed, grains cleaned and then sized by passing them through screens– Contain certain number of meshes or openings

per inch

8-grain 24-grain 60-grain


80-39

Grain Sizes

• General applications for various grain sizes– 8 to 54 for rough grinding operations

– 54 to 400 for precision grinding processes

– 320 to 2000 for ultra precision processes to produce 2 to 4 µ (micron) finish or fine

80-40

Factors Affecting Selection of Grain Sizes

1. Type of finish desire

2. Type of material being ground

3. Amount of material to be removed

4. Area of contact between wheel and workpiece

80-41

Bond Types

• Function of bond is to hold abrasive grains together in form of wheel

• Six common bond types used in grinding wheel manufacture:– Vitrified– Resinoid– Rubber– Shellac– Silicate– Metal

80-42

Vitrified Bond

• Used on most grinding wheels• Made of clay or feldspar• Fuses at high temperature and when cooled

forms glassy bond around each grain• Strong but break down readily on wheel

surface to expose new grains during grinding• Bond suited for rapid removal of metal• Not affected by water, oil, or acid

80-43

Resinoid Bond

• Synthetic resins used as bonding agents

• Generally operate at 9500 sf/min

• Wheels are cool-cutting and remove stock rapidly

• Used for cutting-off operations, snagging, and rough grinding, as well as for roll grinding

80-44

Precautions to Observe When Handling and Storing Grinding Wheels

1. Never handle wheels carelessly• Treat them as precision instruments

2. Dry at a reasonable temperature3. Store wheels properly

• Straight or tapered wheels best stored on edge in individual racks to prevent rolling

• Thin, organic bonded wheels laid on flat horizontal surface to prevent warping

• Small cup and internal wheels put separately into boxes, bins, or drawers

• Large cup and cylindrical wheels should be stored on flat sides with packing between wheels

80-45

Characteristics That Indicate Wheel Too Soft

1. Breaks down too fast

2. Poor surface finish

3. Cuts freely

4. Sparks out quickly

5. Difficult to maintain size

6. Scratches (fishtails)

80-46

Characteristics That Indicate Wheel Too Hard

1. Wheel glazes quickly2. Loading (material ground fills voids)3. Burned work surface4. Squealing noise5. Doesn't cut freely6. Inaccurate work dimensions7. Surface finish get progressively better8. Won't spark out9. Heat checks

80-47

Inspection of Wheels

• Inspect wheels after they have been received– Damage might occur during transit

• Suspend and tap lightly with screwdriver handle for small wheels or with wooden mallet for larger wheels– Vitrified or silicate wheels give clear, metallic

ring when sound– Organic-bonded wheels give duller ring– Cracked wheels do not produce ring





Surface Grinders and Accessories

Unit 81

81-49

Objectives

• Name four methods of surface grinding and state the advantage of each

• True and dress a grinding wheel

• Select the proper grinding wheel to be used for each type of work material

81-50

Grinding Process

• Workpiece brought into contact with revolving grinding wheel

• Each small abrasive grain on periphery of wheel acts as individual cutting tool and removes chip of metal


81-51

General Rules for Grinding

1. Use silicon carbide wheel for low-tensile-strength material and aluminum oxide wheel for high-tensile-strength materials

2. Use hard wheel on soft materials and soft wheel on hard materials

3. If wheel too hard, increase speed of work or decrease speed of wheel to make it act as softer wheel

81-52

4. If wheel appears too soft or wears rapidly, decrease speed of work or increase speed of wheel

5. Glazed wheel will affect finish, accuracy, and metal-removal rate.

• Main causes of wheel glazing are:• Wheel speed too fast

• Work speed too slow

• Wheel too hard

• Grain too small

• Structure too dense

81-53

Surface Grinding

• Refers to production of flat, contoured, and irregular surfaces on piece of work– Passed against revolving grinding wheel

• Four distinct types of surface grinding machines– Horizontal spindle grinder, reciprocating table– Horizontal spindle grinder, rotary table– Vertical spindle grinder, reciprocating table– Vertical spindle grinder, rotary table

81-54

Guidelines for Grinding Wheel Care

1. When not in use, store properly

2. Should be tested for cracks prior to use

3. Select proper type wheel for job

4. Should be properly mounted and operated at recommended speed

81-55

Grinder Safety

1. Use the right wheel

2. Ring test the wheel before mounting

3. Always use mounting blotters

4. Tighten clamping nuts only enough to prevent wheel from slipping

5. Be sure flanges are flat and free from burrs and gouges

81-56

6. Check arbor holes – wheel should slip

freely, not loosely, onto spindle arbor

7. Do not exceed maximum speed

8. Always use wheel guard supplied

9. Stand to one side whenever wheel started

10. Always wear safety glasses when grinding

81-57

Truing a Grinding Wheel

• Process of making grinding wheel round

and concentric with its spindle axis and

producing required form of shape on wheel

– Involves grinding of a portion of the abrasive

section of grinding wheel

81-58

Dressing a Grinding Wheel

• Operation of removing dull grains and metal particles

• Exposes sharp cutting edges so cuts better

• Reasons for dressing wheel– Reduce heat generated between work and wheel– Reduce strain on grinding wheel and machine– Improve surface finish and accuracy of work– Increase rate of metal removal

81-59

Procedure To True and Dress a Grinding Wheel

1. Check diamond for wear and if necessary, turn it in holder to expose sharp cutting edge

2. Clean magnetic chuck thoroughly with cloth

3. Place piece of paper on left-hand end of magnetic chuck

4. Place diamond holder on paper and energize chuck

81-60

5. Raise wheel above height of diamond6. Move table longitudinally so diamond

is offset approximately ½ in. to left of centerline of wheel

7. Adjust table laterally so diamond is positioned under high point on face of wheel

8. Start wheel revolving and carefully lower wheel until high point touches diamond

81-61

9. Move table laterally, using crossfeed handwheel to feed diamond across face of wheel

10.Lower grinding wheel about .001 to .002 in. per pass

• Rough-dress face of wheel until flat and dressed all around circumference

11.Lower wheel .0005 in. and take several passes across face of wheel

81-62

Helpful Ideas When Truing or Dressing Grinding Wheels

1. To minimize wear on diamond, rough-dress with abrasive stick

2. If coolant to be used during grinding, use coolant when dressing wheel

3. Loaded wheel indicated by discoloration of periphery or face – remove completely

4. If rapid removal of metal more important than surface finish, do NOT finish-dress

81-63

Work-Holding Devices

• Work must be held in vise, held on V-blocks or bolted directly to table for some surface-grinding operations

• Most of ferrous work ground on surface grinder held on magnetic chuck– Clamped to table of grinder

81-64

Two Types Magnetic Chucks

• Electromagnetic chuck– Uses electromagnets to provide holding power– Advantages

• Holding power may be varied to suit area of contact

• Special switch neutralizes residual magnetism in chuck

• Permanent magnetic chuck– Holding power provide by means of permanent

magnets

81-65

Four Purposes of Grinding Fluids

1. Reduction of grinding heat

2. Lubrication

3. Removal of swarf from cutting area

• Small metal chips and abrasive grains

4. Control of grinding dust

81-66

Types of Grinding Fluids

1. Soluble oil and water• Milky solution applied by flooding surface

2. Soluble chemical grinding fluids and water

• Used with "through-the-wheel" systems• Contains rust inhibitors and bactericides

3. Straight oil grinding fluids• Applied by flood system and used for high

finish, accuracy and long wheel life

81-67

Methods of Applying Coolants

• Flood system– Coolant directed onto work by nozzle and recirculated

through system

• Through-the-wheel cooling– Fluid pumped and discharged into dovetailed groove in

wheel flange (with holes), fluid forced through wheel by centrifugal force

• Mist cooling system– Atomizer principle: air passes through line, as passes

reservoir draws coolant and discharges it in vapor form directed at point of contact

81-68

Factors Affecting Surface Finish

• Material being ground

• Amount of material being removed

• Grinding wheel selection

• Grinding wheel dressing

• Condition of machine

• Feed





Surface Grinding Operations

Unit 82

82-70

Objectives

• Set up various workpieces for grinding

• Observe the safety rules to operate the grinder

• Grind flat, vertical, and angular surfaces

82-71

Surface Grinding

• Primarily for grinding flat surfaces on hardened or unhardened workpiece

• Perform operations such as form, angular, and vertical grinding

• Good results depend on several factors:– Proper mounting– Proper wheel selection for job

82-72

Mounting Workpiece for Grinding Flat Work or Plates

1. Remove all burrs from surface of work2. Clean chuck surface with clean cloth3. Place piece of paper slightly larger than

workpiece in center of magnetic chuck face4. Place work on top of paper, and be sure to

straddle as many magnetic inserts as possible5. If workpiece warped, shim work to prevent rocking6. Turn handle to on position7. Check work to see it is held securely

82-73

Short Workpieces

• Work that does not straddle three magnetic poles generally not held firmly enough for grinding

• Advisable to straddle as many poles as possible– Set parallels or steel pieces around work to

prevent it from moving• Parallels should be slightly thinner than workpiece

82-74

Grinder Safety

1. Before mounting a grinding wheel, ring test wheel to check for defects

2. Be sure grinding wheel properly mounted on spindle

3. See wheel guard covers at least one-half wheel

4. Make sure magnetic chuck has been turned on by trying to remove work

82-75

5. See that grinding wheel clears work before starting grinder

6. Be sure grinder operating at correct speed for wheel being used

7. When starting grinder, always stand to one side of wheel

8. Never attempt to clean magnetic chuck or mount and remove work until wheel has stopped completely

9. Always wear safety glasses when grinding

82-76

Procedure to Grind a Flat (Horizontal) Surface

1. Remove all burrs and dirt from workpiece and face of magnetic chuck

2. Mount work on chuck, placing piece of paper between chuck and workpiece

3. Check to see that work held firmly

4. Set table reverse dogs so center of grinding wheel clears each end of work by 1 in.

82-77

5. Set crossfeed for type of grinding operation – roughing cuts, .030 to .050 in.; finishing cuts, .005 to .020 in.

6. Bring work under grinding wheel by hand, having about 18 in. of wheel edge over work

7. Start grinder and lower wheelhead until wheel just sparks work

8. Wheel may have been set on low spot of work.

82-78

• Cutting fluid should be used whenever possible to aid grinding action keep cool

9. Start table traveling automatically and feed entire width of work under wheel to check for high spots

10. Lower wheel for every cut until surface is completed – roughing cuts, .001 to .003 in.; finishing cuts, .0005 to .001 in.

11. Release magnet and remove workpiece by raising one edge to break attraction

82-79

To Grind the Edges of a Workpiece

• Edges ground square and parallel so edges may be used for further layout or operations

• Flat surfaces ground first, permits them to be used as reference surfaces for setups

• Clamp work to angle plate so two adjacent sides ground square without moving workpiece

82-80

3. Place ground edge of workpiece on paper• If work 1 in. thick and long enough to span

three magnetic poles on chuck, and no more than 2 in. high, no angle plate required

• If work less than 1 in. thick and does not span three magnetic poles, fastened to angle plate

• Place ground edge on paper and place angle plate no higher than workpiece against workpiece

• Turn on chuck and clamp work to angle plate

4. Grind third edge to required size

5. Repeat operations 1 to 3 and grind 4th edge

82-81

Mounting the Workpiece

4. Remove burrs from magnetic chuck and workpiece and thoroughly clean chuck

5. Place piece of smooth paper between work and magnetic chuck; energize chuck

Setting Speeds and Feeds

6. Adjust table reverse dogs so center of grinding wheel clears each end of work to be ground by 1 in.

82-82

7. Set table crossfeed:• Rough grinding – ¼ to ½ wheel width• Finish grinding – smaller crossfeed increments

8. Set table speed rate from 50 to 100 ft/min

9. Set spindle speed for size and type of CBN wheel used

Setting wheel to work surface

10. Set wheel to top of work surface

11. Traverse workpiece under revolving wheel to locate high spot of work surface

82-83

12. Move table so wheel clears edge of work surface to be ground

Coolant

13. Use proper grinding fluids to suit wheel and workpiece

14. Stop grinder spindle and adjust coolant nozzle so it is about ¼ in. above work surface and as close to wheel face as possible

82-84

15. Place dummy block, slightly lower than work surface, at right-hand end so entire surface receives coolant at all times


82-85

Grinding the Surface16. Start grinder spindle and lower wheelhead

.001 in. for first cut17. Start coolant flow18. Start table reciprocating and engage

crossfeed to take roughing pass19. Be sure edge of grinding wheel clears side

of work after each pass20. Take as many passes (.001 in.) as needed21. Set wheelhead for .0005 in. depth for final

pass to improve surface finish

wsfiling and grinding textbook

Documents

coarse blade

proper hacksaw blade

blade soft

hard blade

blade pitchnumber of

brittleflexible blade

temperedtwo typessolid

single row of parallel