1. Cylindrical Grinders
Unit 83

2. Objectives Set up and grind work on a cylindrical grinder
Internal-grind on a universal cylindrical grinder
Identify and state the principles of three methods of centerless grinding

3. Cylindrical Grinder
Grinds accurately to size and high surface finish the diameter of a workpiece
Two types of machines
Center type
Plain – Generally manufacturing type of machine
Universal – More versatile since wheelhead and headstock may swivel
Centerless type

4. Universal Cylindrical Grinder
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5. Parts of the Universal Cylindrical Grinder
Base
Heavy cast-iron construction for rigidity
Top of base machined to form ways for table
Wheelhead
Mounted on cross-slide at back of machine
Mounted on ways right angle to table way
May be swiveled to permit grinding of steep tapers by plunge grinding

6. Parts of the Universal Cylindrical Grinder
Table
Mounted on ways, driven back and forth by hydraulic or mechanical means
Lower table rest on the ways
Upper table may be swiveled
Headstock and footstock used to support work held between centers
Trip dogs
Control reversal of table

7. Parts of the Universal Cylindrical Grinder
Headstock
Mounted on left end of table
Contains motor for rotating work
Dead center mounted in headstock spindle and used to overcome any spindle inaccuracies
Two dead centers rotate work mounted between centers by means of dog and driveplate
Footstock
Supports right end of work (adjustable)

8. Parts of the Universal Cylindrical Grinder
Backrest (steadyrest)
Provides support for long, slender work and prevents it from springing
May be positioned anywhere along table length
Center rest
Resembles lathe steadyrest
Mounted at any point on table
Used to support right end of work when grinding confined to end of workpiece

9. Parts of the Universal Cylindrical Grinder
Internal grinding attachment
Mounted on wheelhead for internal grinding
Usually driven by separate motor
Diamond wheel dresser
Clamped to table to dress grinding wheel
Coolant system
Provide dust control, temperature control and better surface finish on workpiece

10. Procedure To True and Dress the Wheel
Start grinding wheel to allow spindle bearings to warm up
Mount proper diamond in holder and clamp it to table
Diamond should be mounted at angle of 10º to 15º to wheelface and held on centerline of wheel
Adjust wheel until diamond almost touches high point of wheel

11. Turn on coolant if it is to be used for grinding operation
Feed wheel into diamond about .001 in. per pass
Move it back and forth across wheelface at medium rate until wheelface has been completely dressed
Finish-dress wheel by using infeed of in. and slow traverse feed

12. Procedure to Parallel-Grind an Outside Diameter
Lubricate machine as required
Start the grinding wheel to warm up spindle bearings
True and dress grinding wheel, if required, and then shut off spindle
Clean machine centers and center holes of workpiece

13. Align headstock and footstock centers with test bar and indicator
Lubricate center holes with suitable lubricant
Set headstock and footstock for proper length of work so center of work will be over center of table
Mount work between centers with dog mounted loosely on left end of work
Tighten dog on end of work and engage driveplate pin in fork of dog

14. Adjust table dogs so wheel will overrun each end of work by about one-third of the width of the wheelface
Set grinder to proper speed for wheel being used
Set work speed for diameter and type of material being ground
Set headstock spindle to revolve work in opposite direction to that of grinding wheel

15. If machine equipped, set automatic infeed for each table reversal
Set dwell time which permits wheel to clear itself at each end of stroke
Select and set desired table traverse or speed
Table move one-half or two-thirds of wheel width per revolution of work
Start table and move wheel up to workpiece until it just sparks

16. Engage wheelfeed clutch lever and grind until work cleaned up
Check work for taper and adjust if necessary
Determine amount of material to be removed and set feed index for this amount
Infeed of wheel will stop automatically when work at proper diameter
Stop machine with wheel clear of work and measure size of workpiece

17. To Grind a Tapered Workpiece
Work held between centers
Ground in same manner as parallel work
Exception: table swiveled to half the included angle of the taper
Taper should be checked for accuracy after workpiece cleaned up
Short, steep tapers ground by swiveling wheelhead to desired angle and plunge-grinding tapered surface with face of wheel

18. Plunge Grinding
Feeding wheel into revolving work with table remaining stationary
Grinding wheel fed automatically to setting on feed index
Dwells for suitable time to permit "spark out" and retracts automatically
Length of surface to be ground must be no longer than width of grinding wheel face

19. Internal Grinders
Designed for accurate finishing of holes in workpiece by grinding wheel
Originally designed for hardened workpieces
Now used for finishing holes in soft material
Wheel fed into work automatically until hole reaches required diameter
Wheel withdrawn and automatically dressed

20. Internal Grinding on a Universal Cylindrical Grinder
Used in toolrooms for this purpose
Attachment mounted on wheelhead column
Swung into place when required
Outside and inside diameters of workpiece may be finished in one setup
Grade of wheel will depend on type of work and rigidity of machine

21. Wheels Used for Internal Grinding
Generally softer than those for external grinding
Larger area of contact between wheel and workpiece
Requires less pressure to cut than hard wheel
Reduced spindle pressure and spring

22. Procedure To Grind Parallel Internal Diameter on Universal Cylindrical Grinder
Mount workpiece in universal chuck, collet chuck, or on faceplate
Swing internal grinding attachment into place and mount proper spindle in quill
Mount proper grinding wheel for job
Adjust spindle height until center is in line with center axis of hole in workpiece

23. True and dress grinding wheel Set wheel speed to 5000 to 6500 sf/min
Set work speed to 150 to 200 sf/min
Adjust table dogs so only one-third of wheel width overlaps ends of work at each end of stroke
Blind holes – dog set to reverse table just as wheel clears undercut at bottom of hole
Start work and grinding wheel

24. Touch grinding wheel to diameter of hole
Turn on coolant
Grind until hole just cleans up, feeding wheel in no more than .002 in. per table reversal
Check hole size and set automatic feed to disengage when work roughed to within .001 in. of size
Reset automatic infeed to in. per table reversal

25. Finish-grind work and let wheel spark out
Move table longitudinally and withdraw wheel and spindle from workpiece
Check hole diameter and finish-grind if necessary

26. Procedure To Grind a Tapered Hole
Same procedures and precautions should be followed as for grinding parallel holes
Exception:
Workhead must be set to one-half included angle of taper
Very important that centerlines of grinding wheel and hole be set at same height

27. Centerless Grinders
Work not supported on centers but by work rest blade, a regulating wheel, and a grinding wheel
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28. How Centerless Grinders Work
Work supported on work rest blade equipped with suitable guides
Rotation of grinding wheel forces work onto rest blade against regulating wheel
Regulating wheel controls speed of work and longitudinal feed movement
Set at slight angle (angle controls rate of feed)
Centers fixed – diameter of work controlled by distance between wheels and height of work rest blade

29. Methods of Centerless Grinding
Three methods
Thru-feed
Infeed
Endfeed

30. Thru-Feed Centerless Grinding
Consists of feeding work between grinding and regulating wheels
Work fed by regulating wheel past grinding wheel
Speed of feeding work controlled by speed and angle of regulating wheel
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31. Infeed Centerless Grinding
Form of plunge grinding
Used when work being ground has shoulder or head
Several diameters of workpiece may be finished simultaneously
Work rest blade and regulating wheel clamped in fixed relation to each other
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32. Endfeed Centerless Grinding
Used for grinding tapered work
Grinding wheel, regulating wheel, and work rest remain in fixed position
Work fed in from front up to fixed stop
Grinding wheel and regulating wheel often dressed to required taper
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33. Advantages of Centerless Grinding
No limit to length of work being ground
No axial thrust on workpiece
Permits grinding of long workpieces that would be distorted by other methods
Less stock required on workpiece for truing purposes
Less wheel wear and less grinding time required because there is less stock to be removed

34. Check textbook for full tables that list the faults that might occur with the probable causes and a suggested remedy.
Table 83.1   Cylindrical grinding faults, causes, and remedies
Table 83.2   Internal grinding problems, causes, and remedies