1. Surface Grinders and Accessories
Unit 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

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

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.

5. General Rules for Grinding
Use silicon carbide wheel for low-tensile-strength material and aluminum oxide wheel for high-tensile-strength materials
Use hard wheel on soft materials and soft wheel on hard materials
If wheel too hard, increase speed of work or decrease speed of wheel to make it act as softer wheel

6. Glazed wheel will affect finish, accuracy, and metal-removal rate.
If wheel appears too soft or wears rapidly, decrease speed of work or increase speed of wheel
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

7. If wheel wears too quickly, cause may be any of the following:
Wheel too soft
Wheel speed too slow
Work speed too fast
Feedrate too great
Face of wheel too narrow
Surface of work interrupted by holes or grooves

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

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

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

11. Table traverse handwheel or hydraulic control valve lever
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

12. Power crossfeed control
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

13. Guidelines for Grinding Wheel Care
When not in use, store properly
Should be tested for cracks prior to use
Select proper type wheel for job
Should be properly mounted and operated at recommended speed

14. Procedure for Mounting a Grinding Wheel
Test wheel to see that it is not cracked by ring testing with handle of screwdriver
Clean grinding wheel adapter
Mount adapter through wheel and tighten threaded flange
Place blotter on each side prior to mounting
Should be good fit on adapter or spindle
Diameter of flanges not less ½ wheel diameter
Tighten adapter flanges so holds firmly

15. Two Methods of Balancing a Wheel
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
Dynamic balancing
Automatically balanced wheel while revolving using ball-bearing balancing devices on machine

16. Procedure To Balance a Grinding Wheel
Mount wheel and adapter on surface grinder and true wheel with diamond dresser
Remove wheel assembly and mount special tapered balancing arbor in hole of adapter
Place wheel and arbor on balancing stand that has been leveled

17. Allow wheel to rotate until it stops
Rotate wheel and stop it at three positions: one-quarter, one-half, and three-quarters of a turn to check balance
Loosen setscrews in wheel counterbalances, in grooved recess of flange, and move counterbalances opposite chalk mark
Check wheel in four positions (Steps 4, 5)

18. Move counterbalances around groove equal amount on each side of centerline and check for balance again
Continue to move balances away from heavy side until wheel remains stationary at any position
Tighten counterbalances in place

19. Grinder Safety Use the right wheel Ring test the wheel before mounting
Always use mounting blotters
Tighten clamping nuts only enough to prevent wheel from slipping
Be sure flanges are flat and free from burrs and gouges

20. Check arbor holes – wheel should slip freely, not loosely, onto spindle arbor
Do not exceed maximum speed
Always use wheel guard supplied
Stand to one side whenever wheel started
Always wear safety glasses when grinding

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

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

23. Procedure To True and Dress a Grinding Wheel
Check diamond for wear and if necessary, turn it in holder to expose sharp cutting edge
Clean magnetic chuck thoroughly with cloth
Place piece of paper on left-hand end of magnetic chuck
Place diamond holder on paper and energize chuck

24. Raise wheel above height of diamond
Move table longitudinally so diamond is offset approximately ½ in. to left of centerline of wheel
Adjust table laterally so diamond is positioned under high point on face of wheel
Start wheel revolving and carefully lower wheel until high point touches diamond

25. Lower grinding wheel about .001 to .002 in. per pass
Move table laterally, using crossfeed handwheel to feed diamond across face of wheel
Lower grinding wheel about .001 to .002 in. per pass
Rough-dress face of wheel until flat and dressed all around circumference
Lower wheel in. and take several passes across face of wheel

26. Helpful Ideas When Truing or Dressing Grinding Wheels
To minimize wear on diamond, rough-dress with abrasive stick
If coolant to be used during grinding, use coolant when dressing wheel
Loaded wheel indicated by discoloration of periphery or face – remove completely
If rapid removal of metal more important than surface finish, do NOT finish-dress

27. 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

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

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

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

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

32. How to Make Magnetic Chuck Blocks Last Longer
Clean thoroughly before and after use
Store in covered wooden box
Check frequently for accuracy and burrs
If regrinding necessary to restore accuracy, take light cuts with dressed wheel

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

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

35. Four Purposes of Grinding Fluids
Reduction of grinding heat
Lubrication
Removal of swarf from cutting area
Small metal chips and abrasive grains
Control of grinding dust

36. Types of Grinding Fluids
Soluble oil and water
Milky solution applied by flooding surface
Soluble chemical grinding fluids and water
Used with "through-the-wheel" systems
Contains rust inhibitors and bactericides
Straight oil grinding fluids
Applied by flood system and used for high finish, accuracy and long wheel life

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

38. Factors Affecting Surface Finish
Material being ground
Amount of material being removed
Grinding wheel selection
Grinding wheel dressing
Condition of machine
Feed