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Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display.
PowerPoint to accompany
Krar Gill Smid
Technology of Machine Tools6thEdition
Surface Grinding
Operations
Unit 82
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Objectives
Set up various workpieces for grinding
Observe the safety rules to operate thegrinder
Grind flat, vertical, and angular surfaces
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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
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Mounting Workpiece for Grinding
Flat Work or Plates1. Remove all burrs from surface of work
2. Clean chuck surface with clean cloth
3. Place piece of paper slightly larger thanworkpiece in center of magnetic chuck face
4. Place work on top of paper, and be sure tostraddle as many magnetic inserts as possible
5. If workpiece warped, shim work to prevent rocking6. Turn handle to on position
7. Check work to see it is held securely
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Thin Workpieces
Tend to warp because of heat created
during grinding
Minimize by mounting workpiece at angle of
15 to 30 from side of chuck
Reduces length of time wheel in contact with work
Use adapter if available and mount work atan angle
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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
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Grinder Safety
1. Before mounting a grinding wheel, ring
test wheel to check for defects
2. Be sure grinding wheel properly mountedon spindle
3. See wheel guard covers at least one-half
wheel4. Make sure magnetic chuck has been
turned on by trying to remove work
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5. See that grinding wheel clears work
before starting grinder6. Be sure grinder operating at correct speed
for wheel being used
7. When starting grinder, always stand toone side of wheel
8. Never attempt to clean magnetic chuck ormount and remove work until wheel hasstopped completely
9. Always wear safety glasses whengrinding
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Procedure to Grind a Flat
(Horizontal) Surface1. 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.
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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 overwork
7. Start grinder and lower wheelhead until
wheel just sparks work8. Wheel may have been set on low spot of
work.
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Cutting fluid should be used whenever
possible to aid grinding action keep cool9. Start table traveling automatically and feed
entire width of work under wheel to check
for high spots10. 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
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Table 82.1: Surface grinding problems,causes, and remedies
Grinding
Problem Cause Possible Rem
Burning or Wheel is too hard. Use a softer, free-cutting whe
discoloration Decrease wheel speed.
Increase work speed.Coarse-dress the wheel.
Take lighter cuts and dress
the wheel frequently.
Use coolant directed point ofcontact between wheel, wor
Burnished Wheel is glazed. Dress the wheel.
work surface Use a coarser-grit wheel
Use a softer wheel.
Portion of table
taken from text
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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
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Setting Up the Workpiece
1. Clean and remove all burrs fromworkpiece, angle plate, and magnetic chuck
2. Place piece of paper slightly larger thanangle plate on magnetic chuck
3. Place one end of angle plate on paper
4. Place flat-ground surface of workpieceagainst angle plate so top and one edge ofwork project 12 in. beyond edges of angleplate
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5. Hold work firmly against angle plate and
turn on magnetic chuck
6. Clamp work to angle plate and set clamps
so they will not interfere with grinding
operation
7. Turn off magnetic chuck and carefully
place base of angle plate on magnetic
chuck8. Carefully fasten two more clamps on end
of workpiece to hold work securely
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Grinding Edges of Workpiece
Square and Parallel1. Raise wheelhead so it is about 12 in. above
top of work
2. Set table reverse dogs so each end of work
clears grinding wheel by about 1 in.
3. With work under center of wheel, turn
crossfeed handle until about 18 in. of
wheel edge overlaps edge of work
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4. Start grinding wheel and lower wheelhead
until wheel just sparks work5. Move work clear of wheel with crossfeed
handle
6. Raise wheel about .005 to .010 in. in casewheel has been set to low spot on work
7. Check for high spots by feeding table by
hand so entire length and width of workpasses under wheel
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8. Engage table reverse lever and grind
surface until all marks removed Depth of cut for roughing cuts .001 to .003 in.
Depth of cut for finishing cuts .0005 to .001 in.
9. Stop machine and remove clamps from
right-hand end of work
10. Turn off magnetic chuck and remove angle
plate and workpiece as one unit
11. Clean chuck and angle plate
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12. Place angle plate (with attached
workpiece) on end, with surface to beground at top
13. Fasten two clamps to right-hand side of
workpiece and angle plate14. Remove original clamps from top of setup
15. Repeat steps 1 to 8 and grind second edge
16. Remove assembly from chuck and removeworkpiece from angle plate
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Grinding the
Third and Fourth Edges
First two edges used as reference surfaces
to grind other two sides1. Clean workpiece, angle plate, and
magnetic chuck thoroughly and remove
any burrs2. Place clean piece of paper on magnetic
chuck
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3. Place ground edge of workpiece on paper
If work 1 in. thick and long enough to spanthree 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 4thedge
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Grinding a Flat Surface with a
CBN Wheel
Grind hardened tool and die steels more
efficiently than aluminum oxide wheels
Increase productivity, improve work
quality, and reduce grinding costs
Wear slow, uniform and life long
Not necessary to dress wheel frequently
Grind cool so stay sharp longer
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Conditioning CBN Wheels
For best performance, important they areconditioned (trued and dressed ) properly
Truing Operation of making grinding wheel round and
concentric with spindle axis
Usually leaves grinding surface smooth
Dressing Operation of removing some of bond material
from surface of trued wheel to expose abrasivecrystals and allow wheel to cut
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Properties of a Trued and
Dressed Wheel Produce accurate workpieces and good
surface finish
Use minimum of grinding power
Produce work without burn, surface
damage, or chatter marks
Increase material-removal rates and lower
grinding costs
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Procedure for Truing
a CBN Wheel Example assumes use of an impregnated
diamond wheel to true SBN resin-bond
(100% concentration) wheel
1. Mount CBN wheel on grinder, snug up
flange nut, and indicate wheel
circumference to within .001 in. or lessrunout
2. Tighten flange nut securely
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3. Clean magnetic chuck and place diamond
holder on left-hand side of chuck Cover as many magnetic inserts as possible
Energize chuck
4. Adjust grinder table to locate diamond nibabout 12 in. to left of wheel centerline
Lock table in position
5. Lower wheelhead by hand until justtouches piece of paper held between
wheel and diamond
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6. Turn grinder crossfeed handle so diamond
clears edge of wheel7. Lightly coat wheel surface to be trued with
wax marking crayon
8. Start grinder spindle and feed wheelheaddown in .0004 in. increments until contactmade with diamond
9. Direct coolant to wheel-diamond interface
10. Feed diamond across wheel face at3 to 12 in./min
11. Continue truing until crayon removed
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Dressing a CBN Wheel
After truing, surface smooth, no abrasive
grains sticking out
Wheel cannot cut
Wheel bond must be partially removed or
lowered to expose abrasive crystals
Simplest, least expensive and most popularmethod of dressing is with aluminum oxide
dressing stick or block
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Procedure For Dressing
a CBN Wheel1. Select 200 grit, C-grade aluminum oxide
dressing stick
2. Hold dressing stick in vise so half of
thickness above vise jaws
3. Mount vise on magnetic chuck so dressing
block parallel to table travel
4. Lower stationary wheel until just touches
top of dressing stick
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5. Use crossfeed handle to bring edge of
dressing stick even with edge of wheel
6. Move table so wheel just clears right-hand
end of dressing stick
7. Start grinder spindle and coolant
Feed wheel down about .020 in.
8. Using slow but steady feedrate ( 5 to 10ft./min) take one pass lengthwise along
dressing stick
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9. At end of pass, index table slightly less
than width of grinding wheel
10. Repeat procedure until width of dressing
stick ground
11. Downfeed wheel after full surface ofdressing stick has been ground
12. When grinding wheel appears to be
cutting dressing stick freely, stop andinspect wheel face
Surface feels rough dressing complete
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Grinding a Flat Surface
Job used to show procedures is a piece of
die steel (AISI M-4) Rc-62 that must be
reground1. Select 100-concentration CBN resin-bond
wheel to grind M-4 steel
2. Mount CBN wheel securely on grinderspindle
3. True and dress wheel
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Mounting the Workpiece
4. Remove burrs from magnetic chuck andworkpiece and thoroughly clean chuck
5. Place piece of smooth paper between work
and magnetic chuck; energize chuckSetting Speeds and Feeds
6. Adjust table reverse dogs so center of
grinding wheel clears each end of work tobe ground by 1 in.
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7. Set table crossfeed:
Rough grinding to 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 CBNwheel 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
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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 in. above work
surface and as close to wheel face aspossible
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15. Place dummy block, slightly lower than
work surface, at right-hand end so entiresurface receives coolant at all times
Copyright The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
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Grinding the Surface
16. Start grinder spindle and lower wheelhead.001 in. for first cut
17. Start coolant flow
18. Start table reciprocating and engagecrossfeed to take roughing pass
19. Be sure edge of grinding wheel clears sideof work after each pass
20. Take as many passes (.001 in.) as needed
21. Set wheelhead for .0005 in. depth for finalpass to improve surface finish
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Procedure to Grind
a Vertical Surface1. Mount proper grinding wheel; true, dress
and balance
2. Dress side of wheel to give it slight
clearance
3. Clean surface of magnetic chuck and
mount work
4. With indicator, align edge of work parallel
to table travel
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5. Turn on magnetic chuck and test to see if
work held securely6. Set reversing dogs
7. Bring side of wheel close to vertical
surface to be ground8. Lower wheel to within .002 to .005 in. of
flat or horizontal surface finish ground
9. Start table slowly and feed wheel acrossuntil just sparks vertical surface
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10. Rough-grind vertical surface to within
.002 in. of size by feeding table in .001 in.maximum per pass
11. Redress side of wheel if necessary
12. Finish-grind vertical surface by feedingtable approximately .0005 in. maximum
per pass
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To Grind an Angular Surface
Work may be held at angle by sine bar andangle plate, sine chuck , or adjustable angle
vise Ground with flat-dressed wheel
Hold work flat and dress grinding wheel torequired angle with sine dresser
Sine dresser not available, parallel set to desiredangle by means of sine bar may be clamped toangle plate setup placed on magnetic chuck
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Form Grinding
Production of curved and angular surfacesproduced by means of specially dressed
wheel Reverse form or contour
required on workpiece isdressed on grinding wheel
Contours and radii may beproduced by means of radiuswheel dresser
Copyright The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
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Procedure to Dress a Convex
Radius On a Grinding Wheel1. Mount radius dresser squarely on clean
magnetic chuck
2. Set both stops on radius dresser so it canbe rotated only of turn Two stops 90 apart
3. Fasten diamond height-setting bar inradius dresser
Bottom surface of height-setting bar is centerof radius dresser
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4. Place gage block buildup using wear
blocks on each side, equal to radiusrequired on grinding wheel
Between height-setting bar and diamond point
5. Raise diamond until just touches gageblocks then lock in position
6. Move table longitudinally until diamond is
under center of grinding wheel7. Lock table to prevent longitudinal
movement
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8. Rotate arm of radius dresser of turn so
diamond is in horizontal position
9. Start machine spindle and bring diamond
in until just touches side of grinding wheel Using crossfeed handle
10. Lock table cross-slide in position
11. Stop grinder and raise wheel until clearsdiamond
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12. Start grinder and lower wheel until it just
touches diamond Slowly rotate diamond back and forth through
90 arc
13. Feed wheel down approximately .002 to.003 in. for every rotation of dresser
14. Continue to dress radius until periphery of
wheel just touches diamond when it is in
vertical position
15. Stop grinder, raise wheel, remove dresser
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Crush-Formed Wheels
Copyright The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
Tool-steel or carbide roll having desired form or
contour of finished workpiece
Forced into
grinding wheel
Grinding wheel assumes reverse form
of crushing roll
Wheel then used to grind
form or contour on
workpiece
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Crush-Formed Grinding Wheels
Tolerances as close as .002 in. and radii assmall as .005 in. depending on grit size andstructure of wheel
Gradually wear out of tolerance and formmust be redressed
Not advisable to perform on machine
equipped with ball-bearing spindle Machines equipped with roller bearings proved
satisfactory for crush-dressing operations
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Cutting-Off Operations
Using thin cutoff wheels to cut off hardened
materials using the surface grinder
Work clamped in fixture or vise andpositioned below wheel
Thin, short pieces, wheelhead fed straight
down; longer pieces, work mounted andtable is reciprocated while wheel fed down
Diamond wheels used on carbide
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