PowerPoint to accompany
Technology of Machine Tools
6th Edition
Krar • Gill • Smid
Surface Grinders and
Accessories
Unit 81
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
81-2
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
81-3
Grinding
• Important part of machine tool trade
• Applied extensively to production of
unhardened parts where high accuracy and
surface finish required
• Has eliminated need for conventional
machining
• Modern grinding machines permits faster
manufacture of intricate parts
81-4
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
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
81-5
General Rules for Grinding
1. Use silicon carbide wheel for low-tensilestrength 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
81-6
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
81-7
6. If wheel wears too quickly, cause may be
any of the following:
1. Wheel too soft
2. Wheel speed too slow
3. Work speed too fast
4. Feedrate too great
5. Face of wheel too narrow
6. Surface of work interrupted by holes or
grooves
81-8
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
81-9
Horizontal Spindle Reciprocating
Table Surface Grinder
• Most commonly used
• Either hand or hydraulically operated
• EZ-SURF® Grinder
– TEACH mode: operator can teach and program
up to 100 points for X and Z coordinates
– "Intelligent DRO": helps increase productivity,
improve accuracy and simplify grinding
operations
81-10
Parts of a Hydraulic
Surface Grinder
• Base
– Generally heavy cast-iron construction
– Usually contains hydraulic reservoir and pump to
operate table and power feeds
• Saddle
– Moved in or out across ways, manually or auto
• Table
– Mounted on top of saddle
– Ways for table at right angles to those on base
81-11
• Column
– Mounted on back of frame
– Contains ways for spindle housing and
wheelhead
– Wheelfeed handwheel provides means of
moving wheelhead vertically to set depth of cut
• Table traverse handwheel or hydraulic
control valve lever
– Means to control manually the reciprocating
action of table
81-12
• Stop dogs
– Mounted on side of table
– When strike table traverse reverse lever the
direction of table reversed
• Crossfeed handwheel
– Manual means for table to be fed toward or
away from column
• Power crossfeed control
– Automatic means for table to be fed toward or
away from column
81-13
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
81-14
Procedure for Mounting a
Grinding Wheel
1. Test wheel to see that it is not cracked by ring
testing with handle of screwdriver
2. Clean grinding wheel adapter
3. Mount adapter through wheel and tighten
threaded flange
1. Place blotter on each side prior to mounting
2. Should be good fit on adapter or spindle
3. Diameter of flanges not less ½ wheel diameter
4. Tighten adapter flanges so holds firmly
81-15
Two Methods of
Balancing a Wheel
1. Static balancing
•
•
Wheel balance off machine with use of
balancing stand and arbor
Counterweights in wheel flange must be
correctly positioned in order to balance
2. Dynamic balancing
•
Automatically balanced wheel while revolving
using ball-bearing balancing devices on
machine
81-16
Procedure To Balance a
Grinding Wheel
1. Mount wheel and adapter on surface
grinder and true wheel with diamond
dresser
2. Remove wheel assembly and mount
special tapered balancing arbor in hole of
adapter
3. Place wheel and arbor on balancing stand
that has been leveled
81-17
4. Allow wheel to rotate until it stops
5. Rotate wheel and stop it at three positions:
one-quarter, one-half, and three-quarters
of a turn to check balance
6. Loosen setscrews in wheel
counterbalances, in grooved recess of
flange, and move counterbalances
opposite chalk mark
7. Check wheel in four positions (Steps 4, 5)
81-18
8. Move counterbalances around groove
equal amount on each side of centerline
and check for balance again
9. Continue to move balances away from
heavy side until wheel remains stationary
at any position
10. Tighten counterbalances in place
81-19
Grinder Safety
1.
2.
3.
4.
Use the right wheel
Ring test the wheel before mounting
Always use mounting blotters
Tighten clamping nuts only enough to
prevent wheel from slipping
5. Be sure flanges are flat and free from
burrs and gouges
81-20
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
81-21
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
81-22
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
81-23
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
81-24
5. Raise wheel above height of diamond
6. 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
81-25
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
81-26
Helpful Ideas When Truing or
Dressing Grinding Wheels
1. To minimize wear on diamond, roughdress 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
81-27
Work-Holding Devices
• Work must be held in vise, held on V-blocks
or bolted directly to table for some surfacegrinding operations
• Most of ferrous work ground on surface
grinder held on magnetic chuck
– Clamped to table of grinder
81-28
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
81-29
Permanent Magnetic Chuck
Construction
• Base plate
– Provides base for chuck and means of
clamping it to table of grinder
• Grid (magnetic pack)
– Houses magnets and grid conductor bars
– Moved longitudinally by handle
• Case
– Houses grid assembly, permits longitudinal
movement, and provides oil reservoir for
lubrication
81-30
• Top plate
– Contains inserts or pole pieces separated
magnetically from surrounding plate by means
of white metal
• Necessary to conduct magnetic lines of flux
– Work place on face of chuck (top plate) and
handle moved to on position, grid conductors
bars and inserts in line
• Permits magnetic flux to pass through work
– Handle rotated 180º to off position
• Moves bars and inserts out of line so work not held
81-31
Magnetic Chuck Accessories
• Holding power of magnetic chuck
dependent of size of workpiece, area of
contact, and thickness of workpiece
• Adapter plate used to securely hold thin
work (less than ¼ in.)
• Magnetic chuck blocks provide means of
extending flux paths to hold workpieces that
cannot be held securely on chuck face
81-32
How to Make Magnetic Chuck
Blocks Last Longer
1. Clean thoroughly before and after use
2. Store in covered wooden box
3. Check frequently for accuracy and burrs
4. If regrinding necessary to restore
accuracy, take light cuts with dressed
wheel
81-33
More Work-Holding Devices
• Sine Chuck
– Use when required to grind angle on work
– Form of magnetic sine plate
• Double-faced tape
– Used for holding thin, nonmagnetic pieces on
chuck for grinding
– Two adhesive sides: places between chuck and
work
81-34
More Work-Holding Devices
• Magna-vise clamps
– Used when workpiece does not have large bearing
area on chuck or work nonmagnetic
– Consist of comblike bars attached to solid bar by
piece of spring steel
– Work placed on chuck surface between toothed
edges
• Special fixtures
– Used to hold nonmagnetic and odd-shaped work
81-35
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
81-36
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
81-37
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
81-38
Factors Affecting Surface Finish
• Material being ground
• Amount of material being removed
• Grinding wheel selection
• Grinding wheel dressing
• Condition of machine
• Feed