Surface Grinders

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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 Tools6th Edition

Surface Grinders and

Accessories

Unit 81


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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


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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


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81-4

Grinding Process

Workpiece brought into contact withrevolving grinding wheel

Each smallabrasive grain onperiphery of

wheel acts asindividual cutting tooland removes chipof metal

Copyright The McGraw-Hill Companies, Inc.

Permission required for reproduction or display.


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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


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4. If wheel appears too soft or wears rapidly,

decrease speed of work or increase speedof 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


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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


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Surface Grinding

Refers to production of flat, contoured, andirregular 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


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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


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81-10

Parts of a Hydraulic

Surface Grinder Base

Generally heavy cast-iron construction

Usually contains hydraulic reservoir and pump tooperate 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


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Column

Mounted on back of frame

Contains ways for spindle housing and

wheelhead

Wheelfeed handwheel provides means ofmoving wheelhead vertically to set depth of cut

Table traverse handwheel or hydraulic

control valve lever Means to control manually the reciprocating

action of table


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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


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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


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Procedure for Mounting a

Grinding Wheel1. 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 wheel diameter

4. Tighten adapter flanges so holds firmly


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Two Methods of

Balancing a Wheel

1. Static balancing

Wheel balance off machine with use ofbalancing stand and arbor

Counterweights in wheel flange must becorrectly positioned in order to balance

2. Dynamic balancing Automatically balanced wheel while revolving

using ball-bearing balancing devices onmachine


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Procedure To Balance a

Grinding Wheel

1. Mount wheel and adapter on surfacegrinder and true wheel with diamonddresser

2. Remove wheel assembly and mountspecial tapered balancing arbor in hole of

adapter3. Place wheel and arbor on balancing stand

that has been leveled


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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 mark7. Check wheel in four positions (Steps 4, 5)


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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


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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


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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


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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


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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

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Procedure To True and Dress a

Grinding Wheel1. 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

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5. Raise wheel above height of diamond

6. Move table longitudinally so diamondis offset approximately in. to left ofcenterline of wheel

7. Adjust table laterally so diamond ispositioned under high point on face ofwheel

8. Start wheel revolving and carefullylower wheel until high point touchesdiamond

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9. Move table laterally, using crossfeed

handwheel to feed diamond across faceof 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

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Helpful Ideas When Truing or

Dressing Grinding Wheels1. To minimize wear on diamond, rough-

dress with abrasive stick

2. If coolant to be used during grinding, usecoolant 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

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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

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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

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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 forlubrication

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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 180 to off position

Moves bars and inserts out of line so work not held

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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 in.)

Magnetic chuck blocks provide means ofextending flux paths to hold workpieces that

cannot be held securely on chuck face

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How to Make Magnetic Chuck

Blocks Last Longer

1. Clean thoroughly before and after use

2. Store in covered wooden box3. Check frequently for accuracy and burrs

4. If regrinding necessary to restore

accuracy, take light cuts with dressed

wheel

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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

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More Work-Holding Devices

Magna-vise clamps

Used when workpiece does not have large bearingarea on chuck or work nonmagnetic

Consist of comblike bars attached to solid bar bypiece of spring steel

Work placed on chuck surface between toothed

edges Special fixtures

Used to hold nonmagnetic and odd-shaped work

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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

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Types of Grinding Fluids

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

2. Soluble chemical grinding fluids andwater 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

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Methods of Applying Coolants

Flood system

Coolant directed onto work by nozzle and recirculatedthrough system

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

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

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

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

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Factors Affecting Surface Finish

Material being ground

Amount of material being removed

Grinding wheel selection

Grinding wheel dressing

Condition of machine Feed

Surface Grinders

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