1. Universal Cutter and Tool Grinder
Unit 84

2. Objectives
Identify and state the purposes of the main parts of a cutter and tool grinder
Grind clearance angles on helical and staggered tooth cutters
Grind a form-relieved cutter
Set up the grinder for cylindrical and internal grinding

3. Universal Cutter and Tool Grinder
Designed primarily for grinding of cutting tools such as milling cutters, reamers, and taps
Permits variety of other grinding operation with addition of various attachments
Internal, cylindrical, taper, and surface grinding
Single-point grinding
Cutting-off operations

4. Parts of the Universal Cutter and Tool Grinder
Base
Heavy, cast-iron, boxlike construction
Top of base machined to provide ways for saddle
Saddle
Mounted on ways of base
Moved in and out by crossfeed handwheels
Upper part has machined and hardened ways at right angles to ways on top of base

5. Wheelhead Mounted on column at back of base
Raised or lowered by wheelhead handwheels
May be swiveled through 360º
Spindle mounted in antifriction bearings
Tapered and threaded at both ends to receive grinding wheel collets
Speed varied by stepped pulleys to suit size of wheel

6. Table Stop dogs Two units: upper and lower table
Lower table mounted on upper ways of saddle
Rests and moves on antifriction bearings
Upper table fastened to lower table and may be swiveled for grinding tapers
Unit may be moved longitudinally by three table traverse knobs
Also traversed slowly by means of slow table traverse crank
Locked in place laterally and longitudinally
Stop dogs
Mounted in T-slot on front of table
Control length of table traverse

7. Accessories and Attachments
Right- and left-hand tailstocks
Mounted in T-slot of upper table and support work for certain grinding operations
May be placed at any point along table
Centering gage
Used to align quickly tailstock center with center of wheelhead spindle
Used to align cutter tooth on center
AA Accessories and Attachments

8. Universal workhead Adjustable tooth rest Mounted on left side of table
Used for supporting end mills and face mills for grinding; cylindrical grinding when equipped with pulley and motor;
May have chuck mounted to hold work for internal grinding and cutting-off operations
Adjustable tooth rest
Supports cutter tooth; fastened to wheelhead or table
Another form: universal micrometer flicker type has micrometer adjustment for small vertical movements

9. Plain tooth rest blades
Used for grinding straight-tooth milling cutters
Rounded tooth rest blades
Used for sharpening shell end mills, small end mills, taps, and reamers
Inverted V-tooth rest blades
Used for grinding periphery of staggered-tooth cutters

10. Hook, or L-shaped, tooth rest blades
Used for sharpening slitting saws, straight-tooth plain milling cutters with closely spaced teeth, and end mills
Offset tooth rest blades
Universal type suitable for most applications
Coarse-pitch helical milling cutters and large face mills with inserted blades

11. Cutter grinding mandrels and arbors
Used when grinding milling cutters to they are held in same manner as they are held for milling
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

12. Plain milling and side facing cutters
Held on standard milling machine arbor, should be held on grinding mandrel or cutter grinding arbor
Grinding mandrel
Should be used to hold cutter
Straight length is a sliding fit into cutter and slightly tapered end will hold cutter securely for grinding

13. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

14. Milling Cutter Nomenclature
Primary clearance
Clearance ground on land adjacent to tooth face
Angle formed between slope of land and line tangent to periphery
Prevents land behind cutting edge from rubbing on work
Secondary clearance
Ground behind primary clearance
Gives additional clearance to cutter behind face

15. Cutting edge Formed by intersection of face of tooth with land
Angle formed by face of tooth and primary clearance called angle of keenness
Cutting edges may be on one or both sides as well as periphery
Straight teeth;cutting edge engages along full width of tooth at same moment
Helical teeth; length of cutting edge contacting work varies with helix angle
Produce shearing action reducing vibration and chatter

16. Helix angle (shear angle)
Angle formed by angle of teeth and center line of cutter
Measured with protractor or by bluing edge of cutter teeth and rolling cutter against straightedge over sheet of paper
Marks left by teeth easily measured in relation to axis of cutter
Land
Narrow surface behind cutting edge on primary clearance produced when secondary clearance ground on cutter
On face mills, land called face edge

17. Tooth angle
Included angle between face of tooth and land caused by grinding primary clearance
Angle should be large as possible to provide maximum strength at cutting edge and better dissipation of heat generated during cutting
Tooth face
Surface on which metal being cut forms chip
Flat as in straight-tooth plain milling cutters and inserted face-tooth mills
Curved as in helical milling cutters

18. Cutter Clearance Angles
General rule followed by large machine tool manufacturer for grinding cutter clearance angles:
High-speed steel cutters
5º primary clearance plus additional 5º for secondary clearance
Carbide cutters used on machine steel ground
4º primary clearance plus additional 4º for secondary clearance

19. Table 84.1 from text: Clearance angles for high-speed steel cutters
Material to Primary Secondary Be Machined Clearance Angle Clearance Angle
High-carbon and alloy steels 3° to 5° 6° to 10°
Machine steel 3° to 5° 6° to 10°
Cast iron 4° to 7° 7° to 12°
Medium and hard bronze 4° to 7° 7° to 12°
Brass and soft bronze 10° to 12° 13° to 17°
Aluminum, magnesium, and plastics 10° to 12° 13° to 17°
Guide Only

20. Small portion of complete table
Table 84.2 from Text:  Primary clearance angles for cemented-carbide cutters
Periphery
Type of Cutter Steel Cast Iron Aluminum
Face or side 4° to 5° 7° 10°
Slotting 5° to 6° 7° 10°
Sawing 5° to 6° 7° 10°
Small portion of complete table

21. Methods of Grinding Clearance on Cutters
Three methods of grinding
Clearance
Hollow
Circle
Type of cutter being ground will determine method used

22. Clearance Grinding Produces flat surface on the land
Four in. flaring-cup wheel used and is offset slightly to permit long cutters to clear opposite side of wheel
Tooth rest set between center and top of wheel (never below center)
Higher tooth rest placed, less clearance
Tooth rest may be attached to table or wheelhead (depends on type of cutter)

23. Hollow Grinding Land produced is concave
Six inch diameter dish or cutoff wheel
Cutoff wheel produces better finish
Better to grind diagonally opposite teeth in rotation and take light cuts
Wheel and cutter centers must be aligned
Clearance obtained by raising or lowering wheel

24. Circle Grinding
Provides only minute amount of clearance and used mainly for reamers
Reamer mounted between centers and rotated backward so heel of tooth contacts wheel first
As tooth rotates against wheel, pressure of wheel causes cutter to spring back slightly
Set on center
Secondary clearance must be by clearance or hollow grinding
Also used to obtain concentricity of milling cutters prior to clearance or hollow grinding

25. Methods of Checking Cutter Clearance Angles
Three methods of determining tooth clearance on milling cutter
Dial indicator
Brown & Sharpe cutter clearance gage
Starrett cutter clearance gage

26. To Check Cutter Clearance with a Dial Indicator
Clearance determined by movement of indicator needle from front to back of cutter land
Basic rule used to determine clearance:
Land of 1/16-in width, 1º clearance equivalent to .001 in. on dial indicator
Cutter diameter does not affect measurement

27. To Check Cutter Clearance with a Brown & Sharpe Clearance Gage
Inside surfaces of hardened arms (90º) placed on top of two teeth of cutter
Cutter revolved to bring face of tooth into contact with angle ground on end of hardened center blade
Clearance angle of tooth should correspond with angle marked on end of blade
Two gage blades furnished
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

28. Checking Cutter Clearance with a Starrett Cutter Clearance Gage
Used to check clearance on all types of inch cutters from 2 to 30 in. in diameter providing teeth are evenly spaced
Also small cutters and end mills from ½ to 2 in
Gage consists of frame graduated from 0º to 30º, fixed foot, and beam
Blade used to check angle of land on tooth
Indicated on protractor on top of frame

29. Cutter Grinding Operations and Setups
Important milling cutters ground properly and to correct clearance angles
Will not cut efficiently and life shortened
Important to sharpen cutters when show wear
Cutters should be sharpened when wear land .006 in. for cutters up to ½ in. diameter, and .020 in. for cutters over ½ in. diameter

30. Common Signs of Cutter Wear
Surface finish on workpiece gets poorer
Unusual noise and smoking while cutting
Large burr appears on edge of workpiece
Accuracy of cut changes
Chips being produced turn blue
Wear land on teeth is visible

31. Procedure to Grind a Plain Helical Milling Cutter
Primary Clearance
Mount parallel-ground test bar between tailstock centers and check alignment with indicator
Remove test bar
Mount 4-in. flaring-cup wheel (A60-L 5-V BE) on grinding head spindle so wheel rotates in counterclockwise direction

32. Adjust machine so wheel revolves at proper speed
True face of wheel and dress cutting edge so it is no more than 1/16in wide
Swivel wheelhead to 89º so wheel will touch cutter on left side of wheel only
Using centering gage, adjust wheelhead spindle to height of tailstock centers; Lock wheelhead spindle

33. Move table until cutter near tooth rest
Mount cutter on mandrel and place temporarily between footstock centers on machine table
Set up tooth rest, on which offset tooth rest blade has been mounted, on wheelhead housing
Adjust top of tooth rest to approximately center height
Move table until cutter near tooth rest
Adjust tooth rest between two teeth at approximate helix angle of cutter teeth

34. Chalk or blue top of tooth rest blade
Move cutter over tooth rest blade and rotate it until tooth rests on top of blade
While holding tooth face against rest, traverse table back and forth to mark point where tooth bears on tooth rest blade
Remove mandrel and cutter from between centers

35. Using centering gage, adjust tooth rest so center of marked bearing point on tooth rest is at center height and in center of grinding surface of wheel
Place dog on end of grinding mandrel and mount work between tailstock centers
Adjust cutter tooth onto top of tooth rest blade
Set cutter clearance setting dial to zero and lock and adjust dog into pin of cutter clearance gage

36. Set wheelhead graduated collar to zero
Loosen wheelhead lock and the cutter clearance setting dial lock
Holding cutter tooth on tooth rest blade, carefully lower wheelhead until required clearance is shown on cutter clearance dial
Flaring-cup wheel: distance calculated either
Distance = x clearance angle x cutter dia
Distance = sine of clearance angle x cutter dia /2
If hollow-ground
Distance = x clearance angle x wheel dia

37. Small portion of complete table
Table 84.3 from Text:  Vertical wheelhead adjustment for cutter clearance angles
Cutter Clearance Angle and Distance Diameter ° ° °
(in.) in. mm in. mm in. mm 1/ 3/
1 1/
1 1/
1 3/
Small portion of complete table

38. Remove dog from end of mandrel and unlock table
Adjust table stops so wheel clears cutter sufficiently at each end to permit indexing for next tooth
Start grinding wheel
Carefully feed cutter in until just touches wheel
At rear of machine, turn table traverse knob with left hand; right hand holds arbor firmly to keep cutter tooth on tooth rest

39. Grind one tooth for full length and return to starting position
Traverse table until cutter clear of tooth rest and rotate cutter until diagonally opposite tooth comes in line with tooth rest blade
Grind this tooth without changing infeed setting
Check for taper by measuring both ends of cutter with micrometer

40. Remove any taper, if necessary, by loosening holding nuts on upper table and adjusting table
Grind remaining teeth
Finish-grind all teeth by using a in. depth of cut
If land over 1/16 in. for larger cutters, grind secondary clearance

41. Procedure to Grind the Secondary Clearance of a Plain Helical Milling Cutter
Reset dog on mandrel as for grinding primary clearance
Loosen clearance dial setscrew
Hold cutter tooth against tooth rest and lower wheelhead until secondary clearance shown on setting dial
Lock dial, remove dog, and proceed to grind in same manner as for primary clearance
Grind secondary clearance until land is required width

42. Procedure to Grind a Staggered Tooth Cutter
Carry out steps 1-7 for grinding primary clearance on plain helical milling center
Mount staggered-tooth cutter tooth rest blade in holder and mount unit on wheelhead
Place high point of inverted V exactly in center of width of grinding wheel cutting face and at center height

43. Place centering gage on table and adjust wheelhead eight until highest point of tooth rest blade is at center height
Mount cutter between centers with dog loosely on mandrel and adjust table until one cutter tooth rests on blade and lock table in position
Set cutter clearance dial to zero and tighten dog on mandrel
Loosen cutter clearance dial lock and wheelhead lock

44. Lightly holding cutter tooth onto tooth rest blade, lower wheelhead until required clearance shows on clearance setting dial
Remove clearance setting dog and unlock table
Set stop dogs so wheel clears both sides of cutter enough to allow indexing for next tooth
Start grinding wheel

45. Adjust saddle until cutter just touches grinding wheel
Grind one tooth and move cutter clear of tooth rest
Rotate next tooth, which is offset in opposite direction, onto tooth rest and grind it on the return stroke
After grinding two teeth, check them to see if same height. If not, adjust. Repeat process until teeth are within in.

46. Secondary Clearance
Need to provide adequate chip clearance when milling deep slots
Secondary clearance of 20º to 25º recommended on staggered-tooth cutters
Suggested enough be ground to reduce width of land to approximately 1/32 in.
Permit regrinding of primary clearance at least once without need for grinding secondary clearance

47. Procedure to Grind the Secondary Clearance on a Staggered-Tooth Cutter
Remove tooth rest from wheelhead and mount it on table between tailstocks
Universal micrometer flicker-type tooth rest and straight blade should be used to permit cutter to be rotated
Place centering gage on table and bring center of one tooth to center height
Mark tooth with layout dye or chalk

48. Locate dog on clearance setting dial pin and tighten it on mandrel
Rotate cutter to desired amount of clearance using clearance setting dial
Adjust tooth rest under, or on side of marked tooth
Swivel table to right or left to grind straight land
Grind secondary clearance on this tooth until land is 1/32 in. wide

49. Grind all remaining teeth having the same slope or helix
Swivel table in opposite direction and follow steps 6, 7, and 8 to set up and grind remaining teeth

50. Procedure to Grind Side Clearance
Side of teeth of any milling cutter should not be ground unless absolutely necessary
Mount cutter on stub arbor in workhead
Mount flaring-cup wheel
Tilt workhead to desired primary clearance angle
Generally 2º to 4º
Secondary clearance is about 12º

51. Mount tooth rest on workhead using flicker-type rest and plain blade
Place centering gage on wheelhead and adjust one tooth of cutter until it is on center and level
Clamp workhead spindle
Mount tooth rest on workhead using flicker-type rest and plain blade
Raise or lower wheelhead so grinding wheel contacts only tooth resting on blade
Grind primary clearance on all teeth
Tilt workhead to required angle for secondary clearance and grind all teeth

52. Grinding a Form-Relieved Cutter
Ground on face of teeth rather than on periphery
Form of cutter will be changed when it is sharpened
On the first time, grind backs of teeth before grinding cutting face
Ensures all teeth same thickness
Necessary since locating pawl on grinding fixture bears against back of tooth when ground

53. Procedure to Grind a Form-Relieved Cutter
Swing wheelhead so spindle is 90º to table travel
Mount dish wheel and proper wheel guard
Mount gear cutter sharpening attachment on table to left of grinding wheel
Place gear cutter on stud of attachment so back of each tooth may be ground

54. Move table in until back edge of tooth is near grinding wheel
Place centering gage on wheelhead and adjust wheelhead until center of tooth face is on center
Move table in until back edge of tooth is near grinding wheel
Rotate cutter until back of tooth is parallel with face of wheel
Engage edge of pawl on face of tooth and clamp pawl in place
Grind back of this tooth

55. Move table to left so that cutter is clear of grinding wheel
Index cutter so that pawl will bear against next tooth
Grind backs of all teeth
Reverse cutter on stud and adjust pawl against back of tooth, after face of tooth has been brought to bear against centering gage fastened to attachment
Swing centering gage out of way

56. Adjust saddle to bring face of one tooth in line with grinding wheel.
Thereafter, adjust saddle only to compensate for wheel wear
Loosen one setscrew and tighten other to rotate cutter against grinding wheel
Grind one tooth, traverse table, and index for next tooth
Grind all tooth faces

57. Procedure to Grind Work Parallel Between Centers
With motorized workhead, cutter and tool grinder may be used for cylindrical and plunge grinding
Work ground between centers or held in chuck
Mount motorized workhead on left end of table

58. Examine centers of machine and work to see that they are in good condition
Using centering gage on wheelhead, adjust wheelhead to tailstock center height
Mount a 6 in. straight grinding wheel on wheelhead spindle so that wheel rotates downward at front of wheel
Mount a parallel hardened and ground test bar between centers

59. Mount work between centers
Using dial indicator, align centers for height and then align side of bar parallel with table travel
Remove bar and indicator
Mount work between centers
Set stop dogs so that wheel overlaps work by one-third width of wheelface at each end
Start grinding wheel and workhead
Workpiece should revolve in opposite direction to that of grinding wheel

60. Bring revolving work up until it touches grinding wheel
Traverse table slowly and clean up workpiece
Work travels approximately one-quarter width of wheel for each revolution of work
Measure each end of workpiece for size and taper
After work parallel, set crossfeed graduated collar to zero

61. Feed in work until graduated collar indicates it is proper size
Feed work into grinding wheel approximately .001 in. per pass until work within .001 in. of finished size
Use in. cuts for finishing
Feed in work until graduated collar indicates it is proper size
Traverse table several time to permit wheel to spark out
Same procedure followed for taper grinding, except table must be swung to half angle of taper

62. Procedure for Internal Grinding
Mount test bar in workhead spindle and align it both vertically and horizontally
When grinding tapered hole, workhead spindle must be aligned vertically and then swung to half included angle of taper
Mount internal grinding attachment on workhead
Center grinding wheel spindle using centering gage

63. Mount proper grinding wheel on spindle
Mount chuck on motorized workhead
Mount work in chuck
Set rotation of workhead in opposite direction to that of grinding spindle
Start grinding wheel and workpiece
Carefully bring wheel into hole of workpiece
Set table travel so that only one-third of wheel overlaps hole at each end

64. Clean up inside of hole and check for size, parallelism, and bell-mouthing
Set crossfeed graduated collar to zero and determine amount of material to be removed
Feed grinding wheel in about in. per pass
When work is close to finished size, let wheel spark out to improve finish and remove spring from spindle
Finish-grind hole to size