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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.

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Presentation on theme: "Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar Gill Smid Technology of Machine."— Presentation transcript:

1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar Gill Smid Technology of Machine Tools 6 th Edition Universal Cutter and Tool Grinder Unit 84

2 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 84-3 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 84-4 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 84-5 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 84-6 Table –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 84-7 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

8 84-8 Universal workhead –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 84-9 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 84-10 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 84-11 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 84-12 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 84-13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

14 84-14 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 84-15 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 84-16 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 84-17 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 84-18 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 84-19 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 steels3° to 5°6° to 10° Machine steel3° to 5°6° to 10° Cast iron4° to 7°7° to 12° Medium and hard bronze4° to 7°7° to 12° Brass and soft bronze10° to 12°13° to 17° Aluminum, magnesium, and plastics10° to 12°13° to 17° Guide Only

20 84-20 Table 84.2 from Text: Primary clearance angles for cemented-carbide cutters Periphery Type of CutterSteel Cast Iron Aluminum Face or side4° to 5°7°10° Slotting5° to 6°7°10° Sawing5° to 6°7°10° Small portion of complete table

21 84-21 Methods of Grinding Clearance on Cutters Three methods of grinding –Clearance –Hollow –Circle Type of cutter being ground will determine method used

22 84-22 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 84-23 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 84-24 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 84-25 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 84-26 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 84-27 To Check Cutter Clearance with a Brown & Sharpe Clearance Gage Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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

28 84-28 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 84-29 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 84-30 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 84-31 Procedure to Grind a Plain Helical Milling Cutter Primary Clearance 1.Mount parallel-ground test bar between tailstock centers and check alignment with indicator 2.Remove test bar 3.Mount 4-in. flaring-cup wheel (A60-L 5-V BE) on grinding head spindle so wheel rotates in counterclockwise direction

32 84-32 4.Adjust machine so wheel revolves at proper speed 5.True face of wheel and dress cutting edge so it is no more than 1/16in wide 6.Swivel wheelhead to 89º so wheel will touch cutter on left side of wheel only 7.Using centering gage, adjust wheelhead spindle to height of tailstock centers; Lock wheelhead spindle

33 84-33 8.Mount cutter on mandrel and place temporarily between footstock centers on machine table 9.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 10.Move table until cutter near tooth rest 11.Adjust tooth rest between two teeth at approximate helix angle of cutter teeth

34 84-34 12.Chalk or blue top of tooth rest blade 13.Move cutter over tooth rest blade and rotate it until tooth rests on top of blade 14.While holding tooth face against rest, traverse table back and forth to mark point where tooth bears on tooth rest blade 15.Remove mandrel and cutter from between centers

35 84-35 16.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 17.Place dog on end of grinding mandrel and mount work between tailstock centers 18.Adjust cutter tooth onto top of tooth rest blade 19.Set cutter clearance setting dial to zero and lock and adjust dog into pin of cutter clearance gage

36 84-36 20.Set wheelhead graduated collar to zero 21.Loosen wheelhead lock and the cutter clearance setting dial lock 22.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 1.Distance =.0087 x clearance angle x cutter dia 2.Distance = sine of clearance angle x cutter dia /2 If hollow-ground 1.Distance =.0087 x clearance angle x wheel dia

37 84-37 Table 84.3 from Text: Vertical wheelhead adjustment for cutter clearance angles Cutter Clearance Angle and Distance Diameter 4° 5° 6° (in.)in.mmin.mmin.mm 1/2.0170.45.0220.55.0260.65 3/4.0260.65.0330.85.0401 1.0350.9.0441.1.0531.35 1 1/4.0441.1.0551.4.0661.65 1 1/2.0531.35.0661.65.0792 1 3/4.0611.55.0761.95.0922.35 Small portion of complete table

38 84-38 23.Remove dog from end of mandrel and unlock table 24.Adjust table stops so wheel clears cutter sufficiently at each end to permit indexing for next tooth 25.Start grinding wheel 26.Carefully feed cutter in until just touches wheel 27.At rear of machine, turn table traverse knob with left hand; right hand holds arbor firmly to keep cutter tooth on tooth rest

39 84-39 28.Grind one tooth for full length and return to starting position 29.Traverse table until cutter clear of tooth rest and rotate cutter until diagonally opposite tooth comes in line with tooth rest blade 30.Grind this tooth without changing infeed setting 31.Check for taper by measuring both ends of cutter with micrometer

40 84-40 32.Remove any taper, if necessary, by loosening holding nuts on upper table and adjusting table 33.Grind remaining teeth 34.Finish-grind all teeth by using a.0005 in. depth of cut 35.If land over 1/16 in. for larger cutters, grind secondary clearance

41 84-41 Procedure to Grind the Secondary Clearance of a Plain Helical Milling Cutter 1.Reset dog on mandrel as for grinding primary clearance 2.Loosen clearance dial setscrew 3.Hold cutter tooth against tooth rest and lower wheelhead until secondary clearance shown on setting dial 4.Lock dial, remove dog, and proceed to grind in same manner as for primary clearance 5.Grind secondary clearance until land is required width

42 84-42 Procedure to Grind a Staggered Tooth Cutter 1.Carry out steps 1-7 for grinding primary clearance on plain helical milling center 2.Mount staggered-tooth cutter tooth rest blade in holder and mount unit on wheelhead 3.Place high point of inverted V exactly in center of width of grinding wheel cutting face and at center height

43 84-43 4.Place centering gage on table and adjust wheelhead eight until highest point of tooth rest blade is at center height 5.Mount cutter between centers with dog loosely on mandrel and adjust table until one cutter tooth rests on blade and lock table in position 6.Set cutter clearance dial to zero and tighten dog on mandrel 7.Loosen cutter clearance dial lock and wheelhead lock

44 84-44 8.Lightly holding cutter tooth onto tooth rest blade, lower wheelhead until required clearance shows on clearance setting dial 9.Remove clearance setting dog and unlock table 10.Set stop dogs so wheel clears both sides of cutter enough to allow indexing for next tooth 11.Start grinding wheel

45 84-45 12.Adjust saddle until cutter just touches grinding wheel 13.Grind one tooth and move cutter clear of tooth rest 14.Rotate next tooth, which is offset in opposite direction, onto tooth rest and grind it on the return stroke 15.After grinding two teeth, check them to see if same height. If not, adjust. Repeat process until teeth are within.0003 in.

46 84-46 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 84-47 Procedure to Grind the Secondary Clearance on a Staggered-Tooth Cutter 1.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 2.Place centering gage on table and bring center of one tooth to center height Mark tooth with layout dye or chalk

48 84-48 3.Locate dog on clearance setting dial pin and tighten it on mandrel 4.Rotate cutter to desired amount of clearance using clearance setting dial 5.Adjust tooth rest under, or on side of marked tooth 6.Swivel table to right or left to grind straight land 7.Grind secondary clearance on this tooth until land is 1/32 in. wide

49 84-49 8.Grind all remaining teeth having the same slope or helix 9.Swivel table in opposite direction and follow steps 6, 7, and 8 to set up and grind remaining teeth

50 84-50 Procedure to Grind Side Clearance Side of teeth of any milling cutter should not be ground unless absolutely necessary 1.Mount cutter on stub arbor in workhead 2.Mount flaring-cup wheel 3.Tilt workhead to desired primary clearance angle Generally 2º to 4º Secondary clearance is about 12º

51 84-51 4.Place centering gage on wheelhead and adjust one tooth of cutter until it is on center and level Clamp workhead spindle 5.Mount tooth rest on workhead using flicker-type rest and plain blade 6.Raise or lower wheelhead so grinding wheel contacts only tooth resting on blade 7.Grind primary clearance on all teeth 8.Tilt workhead to required angle for secondary clearance and grind all teeth

52 84-52 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 84-53 Procedure to Grind a Form- Relieved Cutter 1.Swing wheelhead so spindle is 90º to table travel 2.Mount dish wheel and proper wheel guard 3.Mount gear cutter sharpening attachment on table to left of grinding wheel 4.Place gear cutter on stud of attachment so back of each tooth may be ground

54 84-54 5.Place centering gage on wheelhead and adjust wheelhead until center of tooth face is on center 6.Move table in until back edge of tooth is near grinding wheel Rotate cutter until back of tooth is parallel with face of wheel 7.Engage edge of pawl on face of tooth and clamp pawl in place 8.Grind back of this tooth

55 84-55 9.Move table to left so that cutter is clear of grinding wheel 10.Index cutter so that pawl will bear against next tooth 11.Grind backs of all teeth 12.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 84-56 13.Adjust saddle to bring face of one tooth in line with grinding wheel. Thereafter, adjust saddle only to compensate for wheel wear 14.Loosen one setscrew and tighten other to rotate cutter against grinding wheel 15.Grind one tooth, traverse table, and index for next tooth 16.Grind all tooth faces

57 84-57 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 1.Mount motorized workhead on left end of table

58 84-58 2.Examine centers of machine and work to see that they are in good condition 3.Using centering gage on wheelhead, adjust wheelhead to tailstock center height 4.Mount a 6 in. straight grinding wheel on wheelhead spindle so that wheel rotates downward at front of wheel 5.Mount a parallel hardened and ground test bar between centers

59 84-59 6.Using dial indicator, align centers for height and then align side of bar parallel with table travel Remove bar and indicator 7.Mount work between centers 8.Set stop dogs so that wheel overlaps work by one-third width of wheelface at each end 9.Start grinding wheel and workhead Workpiece should revolve in opposite direction to that of grinding wheel

60 84-60 10.Bring revolving work up until it touches grinding wheel 11.Traverse table slowly and clean up workpiece Work travels approximately one-quarter width of wheel for each revolution of work 12.Measure each end of workpiece for size and taper 13.After work parallel, set crossfeed graduated collar to zero

61 84-61 14.Feed work into grinding wheel approximately.001 in. per pass until work within.001 in. of finished size Use.0002 in. cuts for finishing 15.Feed in work until graduated collar indicates it is proper size 16.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 84-62 Procedure for Internal Grinding 1.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 2.Mount internal grinding attachment on workhead 3.Center grinding wheel spindle using centering gage

63 84-63 4.Mount proper grinding wheel on spindle 5.Mount chuck on motorized workhead 6.Mount work in chuck 7.Set rotation of workhead in opposite direction to that of grinding spindle 8.Start grinding wheel and workpiece 9.Carefully bring wheel into hole of workpiece 10.Set table travel so that only one-third of wheel overlaps hole at each end

64 84-64 11.Clean up inside of hole and check for size, parallelism, and bell-mouthing 12.Set crossfeed graduated collar to zero and determine amount of material to be removed 13.Feed grinding wheel in about.0005 in. per pass 14.When work is close to finished size, let wheel spark out to improve finish and remove spring from spindle 15.Finish-grind hole to size


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