US3393478A

US3393478A - Method of grinding shaper cutters and the like

Info

Publication number: US3393478A
Application number: US360798A
Authority: US
Inventors: Edward F Fabish; James R Tookey
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 1964-04-07
Filing date: 1964-04-07
Publication date: 1968-07-23
Anticipated expiration: 1985-07-23

Description

METHOD oF GRINDING SHAPEF. CUTTERS AND THE LIKE Filed April '7, 1964 July 23, 1968 E, F, FAB|5H ET AL l0 Sheets-Sheet. l

ATTORNEY INVENTORS EDWARD F. FABISH BJAMES ROBERT TOOKEY 22241092 XwDZ- m IT mzojou :qu 25 E397..

July 23, 196s E. F. FABISH ET AL METHOD OF GRINDING SHAPER CUTTERS AND THE LIKE Filed April 7, 1964 FIGA GRINDING WHEEL INCREMENT SLI DE DRESSER PAD f;

GRIN DIN G SPINDLE HOUSING 10 Sheets-Shee 2 DREssER F IG .3

INVENTORS EDWARD F. FABISH JYMES ROBERT TOOKEY ATTORNEY July 23, 1968 E, F. FABlsH ET AL 3,393,478

METHOD OF GRINDTNG SHAPED. CUTTERS AND THE LIKE Filed April 7, 1964 lO Sheets-Sheet 5 ATTORNEY July 23, 1968 E. F. FABISH ET AL 3,393,478

METHOD OF @BINDING SHAPER CUTTERS AND THE LIKE Filed April 7, 1964 10 Sheets-Sheet 4 TILTING CYLINDER CRANK ARM ,1/ BASE 32/ CRANK WHEEL AND MOTOR CAM INVENTORS EDWARD F- FABISH BYlAMfs Ro ER rooKEv "im @1 ATTORNEY FlC lla

METHOD op GRlNDING SHAPE-R cuTTERs AND THE LIKE Filed April 7. 1964 July 23, 1968 E. F. FABlsH ET Al.

10 Sheets-Sheet 5 ZOE. mOa muzmmmumm U m m n INVIENTORS EDWARD F. FAB|SH BYAM/EBERT TOOKEY ATTORNEY July 23, 1968 Filed April v, 1964 METHOD OF GRINDING SHAPEF. CUTTERS AND THE LIKE l0 Sheets-Sheet C ,INDEX PAwL INDEX TRIP DOG FOLLOW E R CAM CRANK ARM GRlNDlNG WHEEL INVENTORS EDWARD F'. FABISH ymmg Ron TooKEv ATTORNEY CRANK WHEEL July 23, 1968 E. F. FABlsH ET Al. 3,393,478

METHOD OF GRINDING SHAPER CUTTERS AND THE LIKE Filed April 7, 1964 10 Sheets-Sheet '7 FIG IO o m lNvEN'roRs EDWARD E FABISH BMES ROBE T TKEY ATTORNEY July 23, 1968 E, F, FABlsH ET AL 3,393,478

SHAPER CUTTERS AND THE LIKE l0 Sheets-Sheet 8 METHOD OF GRINDING Filed April 7, 1964 INVENTORS EDWARD F. F'ABISHv www ATTORNEY July 23, 1968 E. F. FAB|sH ET AL 3,393,478

F GRINDING SHAPEP. CUTTERS AND THE LIKE l0 Sheets-Sheet 9 FIGIS Jv )linx /86 METHOD O Filed April 7, 1964 FIG.I4

PRIOR ART ARC HEIGHT /80 /74-/80 INVENToRs F |G.|8 EDWARD F. FABlsH BAMEs ROBERT TooKEv fj @M ATTORNEYM A July 23, 1968 E, F, FABISH ET AL 3,393,478

METHOD OF GRINDING SHAPER CUTTERS AND THE LIKE Filed April 7, 1964 10 Sheets-Shay lO FIOZOA FIGROB /66 /65 DE LI-IELIXANOLE w SIDE RELIELANOLE ON DOwNI-IIII. sIDe OUI S UPHILLSID 7( DONNHILLSIDE ANEE '2 SECTION OF TGD SHAPER ON FITCH CYLINDER/70 CUTTER sI-:CTION a-Ia SECTION A-A (CUTTER AT I-:ND (CUTTER New) CUT OF LIFE) /72 74 RAMP CUTTER BASE CCIRCLE d /74 180 5x MODIFICATION "x /78 FOLLOwER TRlFJgFIw/OLUTE TIPRED FIG24 INVENTORS MODIFICATION EDWARD F. FABIsI-I BYJAMES ROBERT TOOKT-:v

ATTORNEY n United States Patent O 3,393,478 METHOD F GRINDING SHAPER CUTTERS AND THE LIKE Edward F. Fabish, Glenview, and James R. Tookey, Rolling Meadows, Ill., assignors to Illinois Tool Works Inc., Chicago, Ill., a corporation of Delaware Filed Apr. 7, 1964, Ser. No. 360,798 7 Claims. (Cl. 51-287) ABSTRACT OF THE DISCLOSURE Method of grinding Shaper cutters and the like wherein grinding takes place in an incremental or slow continuous `fashion in a single direction with a discrete portion of each of the teeth less than their total length being ground prior to grinding a succeeding portion along the length of the teeth.

This invention relates in general to a method of grinding toothed forms and the like on the periphery of a Workpiece and more particularly relates to a method of the manufacture of Shaper cutters, master gears, gauges, and the like.

The production of Shaper cutters, master gears, etc., involve the most complex and sophisticated arts of the machine tool builder not readily apparent to the casual observer. The Shaper cutter resembles a gear or Spline having a pl-urality of teeth on the periphery thereof which is reciprocated relative to a workpiece to remove metal therefrom in only one direction of the stroke. Thus the profile of the teeth on the gear Shaper cutter provides the cutting action in formation of gears, splines, ratchets, and other generated shapes. Further, while the following discussion Shall be directed toward the method and apparatus for grinding toothed forms on Shaper cutters for gears and is mainly related to the formation of involute forms of teeth and modifications thereof, it is to be remembered that this is illustrative rather than limiting.

The Shaper cutter may be rused to cut teeth for an external gear, for a rack, and for an internal gear. The Shaper cutter is a full generating tool generally used to cut involute teeth of a finite base circle radius, as well as other forms and shapes as is quite well understood in the art.

In order that a Shaper cutter may remove metal, the profile cutting edges must be relieved as the entire profile for-ms an active cutting surface in the generation of a gear tooth or the like. In order for the Shaper cutter to have a useful life, the Shaper cutter must be designed so it may be sharpened. Further, the sharpening of a Shaper cutter must be' done in such a manner that the working profile which is presented to the workpiece is of such a nature that substantially identical gears may be manufactured from the same Shaper cutter throughout the effective life of the cutter.

Thus, the desirable qualities of a Shaper cutter are:

(1) Long usable life determined by the number of times it may be sharpened (assuming that a finite number of gears may be cut with a Shaper cutter with each sharpening thereof).

(2) Maintaining the same effective profile of the cutter teeth throughout its useful life.

(3) Having a profile that is extremely accurate to desired form.

(4) Having a form of tooth profile which -may be selectively varied during manufacture to present modifications frorn true involute shape to impart desired characteristics to the part to be cut.

(5) All of the above with a cutter which will impart "ice a desired surface finish to the part to be made, and provide a strong tool, are with good hardness, durability and eXtreme accuracy.

(6) May be made in an economical manner so that it can compete with other methods of producing the Same shape.

Prior art practices in forming Shaper cutters suffer in that Shaper cutters made by the prior art methods and apparatus do not provide cutters having all of the above characteristics. More particularly, -major prior art methods of making Shaper cutters may be characterized as falling within one of the three following groups, i.e.,

(a) The Standard plunge cut approach to manufacturing the Shaper cutter;

(b) The so-called stroking approach to manufacturing a Shaper cutter; and

(c) The hollow ground approach to forming a Shaper cutter.

In the manufacture of Shaper cutters, and in order to get the extreme accuracies required to provide high quality gears, it is desirable to finish the Shaper cutters by a grinding process. To this end the final finish form of the Shaper cutter is produced by a grinding Wheel. Briefly, some of the disabilities encountered by the standard plunge cut grinding process a above, are:

(1) Inability to maintain extreme accuracy (in some measure due to the deflection problems encountered with the grinding Wheel, particularly as it is leaving the tip of the Shaper cutter tooth);

(2) A non-uniform ramp surface adjacent the base of the Shaper cutter tooth which is determined by the radius of the grinding wheel (which presents problems in maintaining a uniform profile throughout the life of the cutter); and

(3) In at least certain instances, the increased time in manufacture (due to geometries involved So that generally speaking only one side of a tooth may be ground at each path of the workpiece past the grinding station).

Some of the disabilities that accrue to the so-called stroking approach of grinding type b above, are:

(l) Inability to get a true involute shape coextensive the height of the teeth of the cutter (since the stroking action must impart a series of very tiny flats, the number of flats being dependent upon the number of relative strokes of the grinding wheel to the motion of the workpiece past the grinding area);

(2) Errors incurred (due to tolerances in the head and slide for the grinding wheel);

(3) Deflections from desired shape (incurred from the grinding wheel as it enters and leaves the tooth spaces of the workpiece);

(4) Finish problems on the teeth of the Shaper cutter (since grinding wheels are not perfect and a piece of grit will make a mark completely traversing the length of a Shaper cutter tooth);

(5) Further, inflexible form of ramp surface (the stroking method as presently practiced must leave a ra-mp surface at the base of the Shaper cutter tooth which is a Straight line which is a disability for certain Shaper cutters); and

(6) Wear problems and vibration problems d-ue to the extreme accelerations and decelerations involved in each stroke.

The disabilities encountered with the hollow ground type of method c above, are:

(1) There is a change in profile across the effective length of the teeth;

(2) The shape varies with the pressure angle being imparted to the teeth; and

(3) The ramp portion of the teeth is necessarily a compromise (it is very difficult by this method to deviate from one shape of profile to impart desired modifications into the tooth form so as to provide desired modifications in the gear).

It is an object of this invention to provide a method and apparatus for overcoming the disabilities of the prior ar-t methods and apparatus for forming Shaper cutters and other articles having generated tooth forms.

An important object of this invention is to provide a grinding method and apparatus which has great flexibility in that it is adapted for single fiank and two flank grinding, where the feed of the grinding Wheel relative to the workpiece may be an intermittent or a slow continuous feed, and where the relative path of motion of the feed of the grinding wheel means to the workpiece may be on a straight line or in certain forms may be convex or concave each of which feed paths being desirable in different design parameters.

It is an object of this invention to provide a method which is versatile and flexible in imparting to Shaper cutters and other articles, desired modifications of tooth forms so as to provide a Shaper cutter with a high degree of accuracy and a long useful life.

A still further object of this invention is to provide a method for forming Shaper cutters wherein the tooth may be varied to suit to thereby impart modifications to the profile of the teeth in an accurate manner without an expensive inventory of cams and cam followers.

Another object of this invention is to provide a method as aforestated which may use an incremental feed of a grinding wheel in a manner to provide a true involute curve tooth form to a major portion of the profile of a Shaper cutter tooth and which will accommodate itself to easy desired selected modifications thereof.

Another object of this invention is to provide a method of grinding a Shaper cutter wherein the grinding wheel moves on a curvilinear feed path in the grinding area to impart desired ramp configurations to the anks of the teeth is desired geometric relationship to other fea-tures of the teeth of the shaper cutter.

The novel features that are characteristic of the invention are set forth with particularity in the appended claims. The invention itself, both as to its organiza-tion and its method of operation, together with additional objects and advantages thereof will best be understood by the following description of specific embodiments when read in connection with the accompanying drawings in which:

FIG. 1 is a side elevational view of the grinding machine embodying my inventive concepts;

FIG. 2 is a side elevational view along line 2-2 of FIG. 1;

FIG. 3 is a top plan view along line 3 3 of FIG. 2;

FIG. 4 is an enlarged fragmentary sectional view of a portion of FIG. 2;

FIG. 5 is a sectional view through the sp-indle mechanism and generating slide along line 5 5 of FIG. 3;

FIG. 6 is a semidiagrammatic view, in larger scale, of a portion of the crank, work spindle, cam and cam follower mechanism shown in dotted line in FIG. 1;

FIG. 7 is a semidiagrammatic View showing the relative positionsof the grinding wheel to a workpiece during the grinding operation;

FIG. 8 is a graph indicating the tooth form modi-fications which may be imparted to the Shaper cutter teeth with the mechanism shown in FIGS. 1 through 7;

FIGS. 8A through 8D are semidiagrammatic views showing the mathematical correlations and relationships involved in the graph shown in FIG. 8;

FIG. 9 is a semidiagrammatic perspective view of the mechanism shown in FIGS. 5 and 6;

FIG. 10 is a semidiagrammatic side elevational view of an alternate embodiment of grinding mechanism;

FIG. 11 is a front elevational view of the apparatus shown in FIG. 10;

FIG. l2 is a side elevational View of another embodiment of grinding mechanism;

FIG. 13 is a front elevational view of the apparatus shown in FIG. 12;

FIG. 14 is a semidiagrammatic view of the side of a Shaper c-utter tooth formed by one of the prior art methods of manufacture conventionally known as the plunge cut approach;

FIG. -15 is a semidiagrammatic view similar to FIG. 14 illustrating a tooth formed by the apparatus shown in FIGS. 1 9,-

FIG. 16 is a semidiagrammatic view similar to FIGS. 14 and 15 made by the apparatus shown in FIGS. l0 and 11;

FIG. 17 lis a semidiagrammatic view similar to FIGS. 14-16 illustrating a second prior art approach -known as stroking;

FIG. 18 is a View similar to FIGS. 14 through v17 illustrating in full line a tooth formed by the apparatus of FIGS. 12 and 13 and in dotted line the use of the same apparatus as modified;

FIG. 19 is a view similar to FIGS. 14 through 18 illustrating a tooth form as provided by apparatus such as shown in FIGS. 10 and l1 as modified;

FIG. 20A is a semidiagrammatic Side elevational View of a Shaper cutter presented for illustration purposes;

FIG. 20B is a semidiagrammatic view illustrating the use of a Shaper cutter to form the teeth `of an external gear or an internal gear;

FIG. 21 is a view, greatly distorted for purposes of illustration, of a section of a Shaper Cutter to show the complete side 0f the tooth;

FIG. 22 iS a semidiagrammatic view illustrating the change in shape of a Shaper cutter at two different stages of the life thereof;

FIG. 23 is a semidiagrammatic view Showing the cooperation of the cutter with the gear tooth being formed and the imparting of modifications to the gear tooth;

FIG. 24 is a view, greatly enlarged, illustrating modifications of a gear tooth obtainable with the apparatus discussed in the foregoing figures;

FIG. 25 is a semidiagramrnatic view of a gear tooth illustrating certain relationships to facilitate understanding of the invention.

Returning now to FIGS. 1 through 3 of the drawings, a machine is shown for grinding Shaper cutters and the like. The machine 30 essentially comprises a base 32 mounting a generating slide means 34 on suitable bearings 36. The generating slide 34 reciprocates back and forth on the bearings 36 as shall be explained.

A work arbor spindle 38 is mounted on the generating slide and in turn mounts a work arbor 40 which mounts the workpiece 42. The spindle arbor and workpiece move with the generating slide 34 and additionally rotates on the slide in a manner to be explained. Means 44 for reciprocating the slide is shown diagrammatically in FIG. 1 by the double arrow, said slide being biased to the right by a counter-weight means 45 or other suitable means.

Means 46 is associated with means 44 and is provided on the generating slide for causing partial rota-tion of the spindle, arbor and workpiece during reciprocation of the generating slide. Also means 48 is provided for automatically deviating the composite rotary and reciprocatory movement of the workpiece from `a theoretical norm as shall be set forth hereinafter.

It will be realized that while the instant apparatus is discussed as having the generating slide means 34 reciprocate in a path so that the axis of the work spindle moves relative to the base 32, it is perfectly permissible to have the axis of the work spindle remain Stationary and provide the translational movement in the grinding wheel, the important thing being the relative motion therebetweenstated another way, the vertical slide means 50 could be mounted relative to the base 32 to impart the motion shown by the arrow 44 so that the grinding wheel means has the reciprocating motion indicated by the arrow 44. This, however, does not mean that the work spindle 40 would be Stationary since it is neecssary that this spindle have a counterclockwise and clockwise rotative movement in timed relationship to the reciprocatory motion illustrated diagrammatically by the arrow 44. However, for simplicitys sake, only the one form, ie., the movement of the generating slide will be shown and discussed and is to be considered illustrative rather than limiting.

The vertical slide means 50 in the apparatus 30 is shown mounted to the front of the base 32 and terminates in a horizontal surface mounting a swivel means 52 which is pivotally mounted and adjustably clamped in the desi-red position as shall be apparent. A sub-base portion 54 is mounted on the swivel means 52, the upper surface thereof being curvilinear to provide an angular setting for the in-feed slide base means 56 which is adjustably mounted thereon. The grinding wheel slide means 58 is mounted on the in-feed base means 56 for movement toward and from the workipiece. Means 60 is associated with the in-feed base means 56 in the slide means 58 to provide incremental or slow continuous feed of the slide means S8 for purposes hereinafter appearing. A grinding wheel 62 is mounted for rotation on the slide means 58 and for movement therewith and into intersecting relationship to the workpiece in the 4grinding area, said wheel being ydriven by suitable motor means `64. A pair of dresser means 66 are mounted rearwardly (to the left as viewed in FIG. 2) of the wheel 62 for dressing the grinding wheel in a conventional manner.

While a two flank grinding wheel is diagrammatically shown in FIG. 7 and a pair of dresser means 66 are shown in FIG. 3, lthis is to be taken as being illustrative rather than limiting. Two flank grinding has many advantages, one or more of which may be so important as to dictate the choice of this method. In conjunction with a straight, convex or concave grinding wheel path (to be discussed in more detail later), the two flank grinding method always produces the same relationship of tooth thickness to a modification, such as a ramp, on the shaper cutter throughout the sharpening life of the cutter. Thus, while the two flank grinding with a straight or curvilinear wheel path produces a modified cutter more favorable (than is produced, for example, by the plunge cut method) for Icutting external type gears, the shaper cutter so produced is less favorable for cutting internal type gears. The key relationship of ramps on a shaper cutter tooth is in terms of the tooth thickness relationship on the gear being cut, throughout the life of the cutter, which is not only a function of the relief angles on the shaper cutter teeth, but also in a function of the changing rolling diameter occasioned by sharpening which reduces the overall O.'D. size of the cutter. This will be more apparent through later discussion.

Therefore, in spite of manifest advantages in grinding with both grinding wheel flanks so as to grind opposed flanks of adjacent teeth of a workpiece during each pass of the `grinding wheel relative to the workpiece, the specifications and geometrical considerations with respect to the shaper cutter teeth and the gear to be formed thereby will sometimes ydictate that single iiank grinding be used in connection with either a straight or curvilinear wheel path. With -diverse and complex parameters involved in the grinding of shaper cutters and the like, the use of a single flank grinding wheel sometimes allows a greater freedom of choice in determining the best cornbination of grinding conditions inherent with single Hank grinding in combination with .a straight or curvilinear grinding path and in combination with a feed which may be of the incremental or slow continuous type as shall be discussed.

Index means 68 is associated with the generating slide and the spindle, said index means cooperating with th'e means -for revolving the spindle 38 and the means for modifying the relative movement of the workpiece 42 as shall be more particularly discussed. The index means may be operable on each one-half cycle or full cycle ofthe reciprocating movement of the generating slides.

A grinding station or :area 70 (see IFIGS. 2-3) is provided by relatively locating the grinding wheel 62 in a predetermined position and relatively passing the workpiece 42 past the grinding wheel (while the latter is revolving), the workpiece moving through th'e grinding area with a combination reciprocating and revolving motion. This motion is akin to a rolling movement of the workpiece. After a predetermined number of passes of the workpiece past the grinding area 70, as determined by the indexing mechanism, the grinding wheel 62 is incrementally fed to another position slightly spaced from the first position whereupon the workpiece is again passed through the grinding area. The means for incrementally feeding the in-feed slide means 58 comprises a master hydraulic metering cylinder 60 which controls a rod 74. The cylinder 60 is commercially available and is of the high precision type sold under the registered trademark Airmatic by Airmatic Valve Inc. of Cleveland, Ohio.

The cylinder 60 may also be programmed to provide a slow continuous yfeed as distinct from an incremental feed. My slow continuous feed it is meant that every time the workpiece is indexed, the grinding wheel has been feed another few thousandths or ten thousandths of an inch inwardly it having a continuous slow feeding motion. The eX-act amount of `the slow continuous feed relative to the tooth length of the workpiece being ground may be a variable depending upon the size of the workpiece, the geometry thereof, the amount of metal being removed as a grinding cut, and the surface finish desired. However, a characteristic of the continuous feed and the' incremental feed is that a discrete portion, substantially less than the entire portion of the tooth form of each individual tooth on the periphery of the workpiece, is engaged by the grinding wheel successively prior to the grinding wheels traversing the length of the tooth form. Stated another way, there are several revolutions, by indexing, of the workpiece before the grinding wheel has engaged the entire length of the tooth face of the individual teeth.

The cylinder 60 is mounted in a cut-out portion of the in-feed slide base 56 (see FIG. 4), the rod 74 controlled thereby being attached to a lug 76 by suitable attachment means such as nuts 78. Actuation of this cylinder 60 causes movement of the rod 74 to in turn cause movement of the lug 76 which is attached to the in-feed slide mechanism 58 causing the latter to move.

Turning now to FIG. 5 of the drawing showing a sectional View of the generating slide mechanism, the spindle 38 may be in the form of a rod having a chuck means 80 of suitable form for mounting the work arbor 40 at one end thereof. The spindle means 38 mounts an index plate 82 at the end opposite the chuck means 80 and is held in place by a suitable bolt means 84. The spindle means 38 is mounted in bearings 86, said bearing-s separating the spindle 38 from an outer spindle 88 which is concentric and surroudingly mounted to the inner spindle means 38. The outer spindle means 88 is in turn mounted for rotation on

lsuitable bearings

90 and 92 attache-d to the generating slide means housing. A plate 94 at the end of the -spindle means 88 adjacent to the index 82 is xed by suitably fastening means for revolution therewith. The plate 94 has `a lug portion 96 mounting an index pawl means 98 which cooperates with the index plate 82. The pawl 98 is actuated by a pin 102 and dog 104, the latter being attached to generating slide housing 106. The pawl 98 and index plate 82 cause the

spindles

38 and 88 to rotate together except 'when the pawl 98 is released from engagement with the index plate as shall become apparent.

Cam means 108 may be mounted intermediate the ends of the outer spindle 88 to control the reciprocatory portion of the movement of the generating slide. Cam surface 110 on the cam 108 cooperates with the follower means as shall be more particularly explained. A crank arm 112 is also mounted to the spindle 88 for causing 7 partial revolution thereof, said crank arm 112 being connected to a link 114 by a suitable pivot pin 116. The link 114 is in turn attached to a crank wheel at the other end thereof which is `driven by a suitable motor 120. This is perhaps best illustrated in FIGS. 6 and 9.

As the motor 120 causes crank wheel 118 to revolve, the link 114 in turn causes the crank arm 112 to irnpart partial rotation to the outer spindle 88. This in turn causes cam 108 to rotate. The inner spindle 38 rotates with the outer spindle under the influence of the index pawl 98 which in turn causes the workpiece 42 to rotate. The re-ciprocatory movement of the slide is controlled by the cam 108, operating against a biasing means such as the counterweight 45, the surface 110 of the cam engaging the -follower means. 122.

The follower means 122 is a part of a control means 48 for modifying the involute producing movement of the generating slide. These modifications are of two major types, i.e., producing different fixed involute forms of teeth or varying the form of a single involute form from true involute shape. As may be best perceived in FIG. 6 the means 4S for modifying the movement from both true involute producing movement or to provide various involute forms is fixedly mounted to the base 32, the follower 122 having a surface 126 which engages the cam 108. The follower 122 is pivotally mounted at'124 on a lug portion upstanding from the base, there being a precision metering cylinder 128, similar to cylinder 60, which controls the movement of the follower 122 through a rod 130 which is pinned to the rear end of the follower at 132. The follower 122 is tilted by the cylinder 128. This may be in timed relationship to the movement of the generating slide to impart modification to the tooth form being ground on the workpiece as shall be set forth hereinafter. Also, the follower may maintain a predetermined fixed altitude to produce a desired involute.

As is apparent from the geometry of the mechanism heretofore explained, a single cam 108 if operated against a fixed follower 122, could produce only a single involute. IIn the manufacture of Shaper cutters, it is most unusual that a single machine can be used in production to produce only a single Shaper cutter involute form, thus, every time a different size shaper cutter or master gear involute or other desired generated form is desired, a new cam has heretofore been necessary. If it is considered that all Shaper cutters, master gears, etc. are specially engineered for specific applications and they may range in pitch from approximately 120 d.p. to l d.p., they may range in diameter from 3/16" p.d. to 12" p.d., they may be made in manufacturing lot sizes of from one piece to upwards of one hundred pieces, and they may be of simple involute form or involve modifications for producing undercut, tip relief, chamfer, etc., alone or in combination and they may be of a commercial accuracy, or of highest accuracy for the more precise types of gears, splines, clutches, and the like, etc., the necessity for versatility in a production machine for manufacturing of Shaper cutters, etc. is apparent. Thus, the need for versatility in ability to produce different involute forms and modifications thereof, various other generated shapes as well as for grinding versatility is of importance.

From FIG. 8, it will be seen that the movement of the follower 122 from a first position perpendicular to the travel of the slide to a new relatively fixed position will effectively change the particular involute produced by the cam. This has the advantage of utilizing a single cam 108 for a range of involutes greatly reducing the number of involute cams and set-up time required for production of Shaper cutters, etc. FIGS. 8 and 8A through 8D show the relative relationships in semidiagrammatic and graphic form. More particularly, FIG. 8A shows slide travel s as a straight line controlled by the cam, the dimension c being the amount of travel of the slide permitted by the cam. The dimension c is in essence the rise of the cam, or stated another way, is the amount of travel of the slide afforded by the cam as a function of the base circle of the cam which is the difference between the dimensions c1 and c2 shown in FIG. 6. R equals the angular rotation of the cam from a reference point such as c1 or c2 and this rotation, due to the common rotation of the workpiece and the rotation of the cam, applies to the movement of the workpiece. In FIG. 8A, the circle B.C. is the base circle of any particular cam which, of course, is a space figure from which the involute surface of the cam is derived. (It might be noted at this juncture that while all of the discussion of the graphs and the movement of the slide mechanism and workpiece will be discussed in terms of an involute spiral on the cam 108, this is a matter of choice rather than of necessity. An Archimedian spiral may be used, or other spiral, the involute spiral being picked for ease of handling since most gear teeth are formed in an involute form and hence the shaper cutters and master gears, etc. are formed in an involute form (modifications aside) and further the use of an involute cam makes for easy handling for mathematical computations.

In FIG. 8A the dimension A is a diagrammatic showing of the change in the slide travel s due to the tipping of the follower in a clockwise direction from a reference position x, i.e., the full line position shown for the follower 122. While the follower 122 does not move to position a, the tilting of the follower will affect the slide travel s by the dimension A when the follower is moved so that it is tilted clockwise through angle f to a position indicated by dotted line y. The dimension B shown in FIG. 8A is the change in the slide travel afforded by the movement of the follower 122 to a new angular position about its pivot through angle g in a counterclockwise tilting from the reference position x. When the follower surface of the follower 122 is disposed perpendicular to the direction of the slide, the involute cam 108 will produce the smallest involute possible to be produced for that particular cam. This is shown in FIG. 8B and illustrated as a line s=c in the graph in FIG. 8, the graph being a graph of cam rotation r and work rotation relative to the slide travel s and the travel of the work. For convenience sake, as shown in FIG. 8B the perpendicular position of the follower 122 is shown in a vertical position which produces 0 cam angle relative to the cam and thus the slide travel s is equal to c which is the rise afforded by the involute cam 108.

FIG. 8C is a graphic presentation showing the tilting of the follower 122 through angle d to produce a larger base circle and hence larger involute. The angle d is merely one 0 reference position, the latter being perpendicular to the slide travel. This changes the slide travel s an amount which is equal to c times the secant of d which has been denominated as the d cam angle. The maximum cam angle e is in the neighborhood of 25 as determined by the geometry of the machine and the friction engendered between the tilted cam follower and the cam. If more than 25 of tilt is obtained, it is found that the slide travel is not uniform and does not reproduce Well. e is merely a larger tilt than angle d and the same observations apply.

The immediate past discussion of tilting the follower 122 has been relative to changing the base circle of the involute to provide different size involute teeth on the Shaper cutter utilizing a single cam. This mainly affects set-up. We have heretofore mentioned the desirability of this in the sense that a lesser number of cams are needed for a production machine to produce a whole range of involutes. Thus, a single cam 108 can produce an infinite number of involutes within a predetermined range depending upon the angular setting of the follower 122. Let us assume that an involute x which we will call the reference involute has been picked for the manufacture of a particular Shaper cutter, master gear, etc. This will provide a predetermined involute shape on the Shaper cutter teeth and reference x has been picked as a position other than where the cam follower 122 is at perpendicular, i.e., it is in a tilted position affording movement thereof both in a clockwise and a counterclockwise direction. If the requirements of the particular shaper cutter, master gear, etc., to be ground, are such that modifications of the involute form are desired on the individual teeth, such modifications usually occurring at the tip or at the base of the tooth as shall be explained more thoroughly hereinafter, it will be seen that tilting the follower in synchronized movement to the angular position of the slide, will cause a change of the involute from the reference involute x. Referring to FIGS. 8A and 8, the reference position x of the follower will produce an involute denominated as a straight line in the graph of FIG. 8. Tilting of the follower to position y causes a modification of the involute form. By tilting the follower through angle f, a new smaller involute y will be formed once the follower attains its new position. During movement of the follower while there is movement of the slide, i.e., those portions of the graph indicated as tip and return, the travel of the slide s relative to the rotation will not produce a true involute surface on the workpiece, As will be seen in FIG. 8A, f is the angular change of the cam in degrees from the reference position x toward position to produce a smaller base circle involute when the reference position x is at some plus degree position.

Angle g is the same as angle f except that it is an angular change of the cam in degrees from the reference position away from 0 to produce a larger base circle involute when the reference position is in an original position ranging from 0 to 25. It will be observed that movement of the cam follower 122 from the 0 position of 8B in a direction clockwise will increase the base circle exactly the same as counterclockwise motion from the 0 position. Thus, the movement of the cam follower through angle g from the reference position x will cause a new larger base circle z to be attained for that period it is held steady at its new position, however, again the portion of the cycle during which the cam follower is actually moving produces a curve other than that of true involute.

In essence, FIG. 8 shows the two distinctive functions that are attainable with the movable follower 122, i.e., it is possible to have one cam serve for a great plurality of base circles and further by having a movable follower and by moving same during the travel of the slide, modifications may be imparted to vary the surface produced on the workpiece as suitable and desired. It will be further realized that FIG. 8 applies to only a single side of a grinding wheel rather than utilizing both sides of a wheel as shown in FIG. 7, except in certain geometries.

Before discussing the utilization of the means 48 for automatically deviating the composite rotary and reciprocatory movement of the workpiece from a theoretical norm as applied to a specific workpiece, two alternate embodiments of machines 30a and 30h will -be discussed. The machine 30a is substantially similar, in many respects, to the machine 30 aforediscussed and only deviations will be examined in detail. Similar parts have been identified with similar reference numerals with the addition of the suixes a and b respectively.

The machine shown in FIGS. 10 and ll has a generating slide 34a which has a movement under the inuence of means 44a which is substantially identical to that aforediscussed relative to machine 30. The essential difference of the machine 30a resides in the means for moving the grinding wheel 62a relative to the workpiece 42a. Upright member 140 mounts a vertical slide means 50a which in turn pivotally mounts swinging arm housing means 142 which is mounted on an upright slide as shown in FIG. l0 at pivot 144. The lower end of housing means 142 mounts a grinding Wheel 62a. Actuator means 146 is pivotally attached to vertical slide 50a at 14S into the arm housing means 142 at 150 as shown. The actuator means 146 may Abe of one or two types, both being basically hydraulic feed mechanisms of a type similar to the actuator 60, different only in its actuation, the first type may be set for a small incremental feed or slow continuous feed similar to the hydraulic feed mechanism `60, or the second type may be set for a rapid stroking movement, i.e., it may be set to traverse the workpiece 42a very rapidly relative to the rocking movement of the workpiece. From the geometry of the above parts it Will be seen that the edge of the grinding wheel 62a will follow a path 152 during movement thereof upon movement of the actuator 146 as indicated by the double arrow 154. It will be appreciated the path 152 is arcuate labout pivot point 144 which has the effect of greatly increasing the apparent radius of the wheel 62a. Stated another way, a relatively small wheel `62a will follow a grinding path that `would be normally provided by a much larger grinding wheel having a center rotation about pivot point 144.

I'he embodiment 30h shown in FIGS. l2 and 13 is of the pivotal type also and machine 30b is in a sense a reversal of parts of the embodiment shown in machine 30a. In this instance the grinding wheel 62b is mounted on slide 50b with elongated arm 156 being pivoted about pivot 158 under the influence of actuator 146b. The path of motion of the wheel 62b is shown diagrammatically by the arrow 152b when the actuator is moved as indicated by the double arrow 15417. The path 152b is curvilinear and opposite in direction to path 152 for purposes hereinafter appearing. The path 152b will put a convex surface on the ramp surface of a tooth 134 whereas the tooth 152 will put a concave surface on the ramp. If a stroking motion is used as the grinding wheel traverses the workpieces, the ramp will be smooth and if an incremental feed is used, then a series of small curvilinear surfaces convex or concave, as will be apparent, are provided and shall be discussed in more detail relative to FIGS. 14-19. If a slow constant feed movement is used, then the series of small curvilinear surfaces, convex or concave, as will be apparent are provided but each of them shall traverse the tooth face from the tip to the base so as to give a skewed appearance on the side of the face. The spacing of the curvilinear scallops on the ramp will be determined by the amount of feed relative to the indexing action of the machine, and the ramp scallops will be similar in appearance to those produced in an incremental feed.

Before discussing the modifications of the tooth form of the Shaper cutter provided by the machines 30, 30a and 30'b, perhaps a discussion of specific surfaces and requirements of the shaper cutter 42 would be in order. Referring to FIGURES 20A and 20B a standard shaper cutter 42 is shown. The Shaper cutter 42 has teeth 136 on the periphery thereof which may be used to shape an internal gear such as 166, a rack such as 168, or an external gear 167 by reciprocation of the Shaper cutter past the workpiece blank. The shaper cutter is a full generating tool having an involute of finite base circle radius. The number of teeth on-the Shaper cutter 42 may be varied (within limits) from t-he number of teeth on the gears being cut provided that the pitch, helix angle and pressure angles are the same. The nature of the shaping process (the reciprocating motion of the cutter past the workpiece blank) presents two conliicting requirements namely the individual cutter teeth 136 must be designed so that the cutting edges (profile of the teeth) must have relief in all directions while on the other hand, the Shaper cutter must be designed in such a manner that it may be sharpened so that it will have a long and useful tool life. These 'two requirements conflict, in a sense, since the geometry of relief to all of the active cutting or generating surfaces necessarily requires change in t-he profile upon the sharpening back of the cutter and reduction of the O.D. of the cutter. In spite of the variation in dimensions and appearances of a shaper cutter tooth as the cutter is sharpened back, it is important to remember that the base circle must remain constant throughout the life of the cutter.

1 1 Since the base circle is constant throughout the cutter life, the base pitch also remains constant. FIGURES 21 and 22 show a cutter tooth 136 at the beginning and at the end of its life (relative to the base circle).

It will be noted that the sharpening back process, as can be observed from FIGS. 2l and 22, necessarily requires that the outer diameter of the cutter is reduced by every sharpening of the cutter. Thus, the rolling diameter changes with every sharpening. Because of this changing rolling diameter with every sharpening, the relationship and geometry of the ramp surface to the tooth thickness relationship on the gear being cut is also of major importance.

On most gear shaper cutters, the same diameter of base circle is used to generate both sides of the cutter tooth and the same is true with herring bone cutters. However, the actual size of the base circle for the cutter is not the same as the vbase circle of a gear of equivalent size. There must be an adjustment in base circle diameter for the cutter to correct for face shapening angle and Side relief angles.

On helical gear shaper cutters with normal sharpening (or some lesser `or greater angle than normal) different base diameters are used to generate the involutes on the two sides of the cutter tooth. They also are adjusted for diameter because of the compound angle on the tooth face and the side relief angles.

When new, the Shaper cutter is frequently made with an oversized operating diameter; when sharpened back, the operating diameter gradually becomes basic, then undersized in regard to the nominal value. The limitation imposed by this action is one element in determining the usable length of tooth and is a design consideration on the part of the manufacturer of cutters which is in turn limited by the method and apparatus available for manufacturing the cutter.

The further the operating (rolling) diameter of the cutter 42 is away from the root diameter of the gear being cut, the greater the fillet at the root of the teeth of the gear. Then, as the shaper cutter is sharpened back, it will produce smaller and smaller fillets in the roots of the teeth in the gear. Occasionally, at the end of the usable life of the shaper cutter, this action may result in undercutting of the gear tooth profile near the root on external gears. The size of the permissible fillet must be evaluated in reference to the mating gear and not the gear being cut. The larger the mating gear the greater the danger of interference.

In order to build as much usable life as possible into each shaper cutter for external gears, they should be made oversize with respect to the nominal pitch diameter when new. In addition to the limitations on the amount of oversize based on the maximum permissible gear fillet there is a strength limitationas the amount of oversize is increased, the width of the flat 172 at the outside diameter is decreased. The amount of oversize must not be so great as to result in a weak tooth tip on the shaper cutter 42. In some cases, particularly for internal gears, no cutter oversize is permissible, and for some applications Shaper cutters must be undersized when new.

The usable life of the cutter is determined by the maximum permissibe amount of oversize, by the maximum permissible amount of undersize and by the side relief angles on the cutter teeth. In the case of cutters designed to produce modifications in the gear tooth profile or designed to produce such features as chamfers on the gear teeth, further limitations on the amount of usable life on any one cutter may be imposed.

Since the effect of oversize and undersize is relative to the size of both the shaped gear and the mating gear and is complicated by the size of the Shaper cutter, the pitch, the pressure angle and tooth modification individual Shaper cutters must be tailored for a specific job to secure maximum product quality and maximum life. Therefore, as

aforementioned, extreme versatility in the manufacturing process is desired.

As can be seen from the difference in profiles on the tooth 136 in FIG. 22, i.e. section A-A of the cutter when new and section B-B, the cutter at the end of life, there is a radical difference therebetween. The angle (see FIGS. 20A and 21) denominated the Outside angle on the outside diameter of the shaper cutter, depends upon the pressure angle and the side relief angles of the teeth 136. It will normally be in the range of 31/2 to 8, but in special cases may be as low as 2 or as high as 16. The higher the pressure angle on the cutter, the smaller the outside angle 170; on the other hand, higher values of side relief result in a greater outside angle. Heretofore the Ioutside angle has generally been a straight line, i.e., surface 172 (the top of the tooth) recedes from line 174 (a construction line parallel with the axis of the cutter) at a linear constant angle. In many shaper cutters a constant outside angle 170 provides a practical and satisfactory cutter, but in certain instances it is found that a straight line is a compromise from theoretical and in point of fact the outside angle 170 prefereably should be a convex curve on cutters for external gears and a concave curve on cutters for internal gears to preserve exact depth relationships when sharpening back. As will be appreciated, machine 30a will impart a concave surface and 30h will provide a convex surface on surface 172.

When a shaper cutter is to be semitopping, that is, to cut a chamfer 176 on the tips of the gear tooth 178 (see FIGS. 23 and 24), a ramp surface 174 is formed at the base of the shaper cutter tooth 136. Since the tooth form on the Shaper cutter is produced by a generating action, any changes in the profile thereof to produce undercut for `shaving or grinding, tip relief on the gear tooth, chamfering, or topping requires special operations in manufacture. Thus movement of the follower 122 while manufacturing the gear shaper tooth profile will have a consequent effect upon the shape of the gear tooth produced.

The intentional provision of a ramp surface 174 on a cutter provides the tip chamfer 176 on the individual gear tooth 178, and the provision of a tip relief surface on the gear is called adding an approach to the cutter. Two types of approach are generally used, one called the tangent approach, and the other, the so-called constant approach with which We are concerned here. This first type or tangent approach produces a tip relief that varies during the life of the cutter, which is not particularly desirable. The constant approach is an attempt to provide a constant tip relief on the gears produced throughout all stages of sharpening of the cutter. To properly understand this, consideration must be given to the three dimensional view of the surface 174 as imparted by the necessity for side relief on the cutter tooth. This is illustrated in FIG. 22 by the curvilinear line 180. It must be remembered that the surface 174 is an approach and is usually an involute surface which intersects the involute surface of the side of the shaper cutter tooth and preferably this line 180 remains constant relative to the point on the involute where it intersects the side of the tooth as the cutter is sharpened back relative to the tooth thickness of the cutter tooth. Thus the junction line 180r on the cutter tooth between the involute and the approach surfaces is a curve in the horizontal plane as viewed in FIG. 22 and preferably closely approximates the taper in the vertical plane on the outside diameter of the cutter. If it exactly corresponds with the tooth thickness of the cutter then a constant tip relief will be provided. It will be seen that when surface 172 is convex then 180 should be convex in the vertical plane the same relationship occurring with concave surface 172. In the art of gear teeth, the term tip relief and chamfer are generally similar types of modifications on the gear tooth profiles and sometimes the following differentiation has been used between the two (confer FIG. 25), for example when the ratio of the distances B over A is greater than the modification is called a tip relief, and when the ratio of B to A is less than 10 it is called a chamfer, where B equals the radial distance of the modification on the gear tooth (as measured from the axis) of the deviation from the trueinvolute curve and where A represents the circumferential offset of the modification from the true involute curve as considered from the central axis of the gear. For reasons not important here, gear teeth 178 sometimes need tip relief and the other gear teeth 178 may need a chamfer 176 and thus a methodology which can produce shaper cutters with ramp surfaces 174 to provide both types of modifications in a simple and expedient manner with high accuracy is important (see FIG. 23).

Another type of modification of true involute form that is required for shaper cutter teeth is the form operable to provide an undercut at the base of the gear tooth. This is accomplished by providing a so-called protuberance 179 on the shaper cutter tooth at the radial extremity of the tooth and circumferentially offset outwardly from the involute of the anks. In FIG. 24 a protuberance 179 is shown by that portion of the figure which lies to the right of the true involute form adjacent the top of the tooth 136. Also gear teeth occasionally require an enlarged root area which would be imparted by modification 177.

Returning now to FIG. 14, a semidiagrammatic showing of a prior art plunge cut tooth of a Shaper cutter is shown in this figure. This prior art tooth shape is formed by -bringing the workpiece cutter into engagement with a fixed grinding wheel and of necessity lines `174-180 (which is a semidiagrammatic showing of the ramp surfaces on the tooth) must be formed in an arc that is directly related to the diameter of the grinding wheel. Since it is impractical and often impossible to use grinding wheels which have an extremely large diameter, this arc is too large and the plunge cut prior art method of forming a shaper cutter tooth does not provide desirable ramp surfaces and tooth thickness requirements for all forms of desired teeth.

The prior art method of forming a shaper cutter tooth by the so-called stroking method, i.e., rapidly reciprocating the grinding wheel across the length of the tooth from front to back produces a form of indicated semidiagrammatically in FIG. 17. When this approach will produce some desired relationships between the top surface 172 and the lines 174-180 lof the ramp surface as well as tooth thickness requirements, the side surfaces of the tooth are characterized as being a plurality of small flats 182. The flats 182 have been considerably exaggerated in FIG. 17, but not withstanding these ats are a deviation from a true involute surface on the sides of the shaper cutter teeth. A further disability that occurs to the stroking method is that when there is a piece of grit on the grinding wheel which is malf-Ormed outwardly on the side of the grinding wheel, it will impart a defect to a corresponding portion on the side of the tooth. Further, the stroking method shown in FIG. 17 produces a straight line ramp surface 174-180 which is always a compromise approximation in certain forms of cutters.

FIG. l5. illustrates the grinding technique of the apparatus shown in FIGS. 1-9. The grinding wheel as it is incrementally fed will produce a series of slight scallops 184 in the ramp area 174-180 and a series of scallops 186 in the side surface of the tooth. However, a key difference between these very slight scallops as versus the flats 182 of the prior art tooth of FIG. 17 caused by stroking, is that the scallops are each in and of themselves perfect involute surfaces. Further, any defects -in the grinding wheel 62 are not imparted to the tooth of the Shaper cutter because this protuberance type of defect will uniformly hit all surfaces on the tooth due to the nature of the grinding process as aforedescribed. It will be realized that the locations of the positions of the grinding wheel indicated by the arrows in FIG. is completely semidiagrammatic and that the arcs 184 are considerably exaggerated for purposes of pictorial representation. A slow continuous feed will cant the scallops an amount depending lon the feed rate.

FIG. 16 is a semidiagrammatic representation of the -grinding wheel relative to a shaper cutter tooth indicating the relative positions of the grinding wheel to the shaper cutter teeth when the apparatus is of the type 30a shown in FIGS. 10 and l1. When the device 30a is operated by an incremental feed, the arc height on the ramp 174aa is independent of the size of the wheel 62. Again a series of lshallow scallops 184a will be placed on the ramp surfaces 174a-180a as indicated -by reference numeral 184 and similar slight scallops 186 will be placed on the side surface of the tooth by the incremental and slow continuous feed.

When the grinding wheel 62 is rapidly reciprocated past the workpiece in machine embodiment 30a the scallop 184 and in the side surface of the tooth are eliminated as shown in FIG. 19 but the line 174a-180a of the ramp surface is curvilinear which is desired for certain types of Shaper cutters as aforediscussed. `Further the amount of curvature of ramp surfaces 174-180 is independent of the size ofthe grinding wheel 62a.

FIG. 18 indicates the type of tooth form that may be imparted by the apparatus 30b of FIGS. 12 and 13. The dotted lines indicate the incremental feed approach and the full line indicates the stroking approach with the apparatus 30b. It will be observed that line 174b-180b is convex with respect to the axis of the gear cutter which is desirable for other cutters as aforediscussed.

From the foregoing it will be observed that shaper

cutter grinding machines

30, 30a, and 30b are well adapted for the sophisticated high accuracy, high quality grinding required by the geometries of a shaper cutter. Due to the controlling means 48 associated with 4each of these machines, modifications lof the gear shaper cutter tooth such as shown in FIG. 24 may be imparted to the side of the tooth in any desired amount and the deviations may be either inwardly or outwardly from the true involute form. Further it will be realized that the arcs of the ramp surface 174 shown in the various figures is a considerable distortion of the actual curve's of the ramp surface. Further, the scallops discussed, in point of fact, would be virtually indetectable with current measuring devices and are shown in this form for illustrating the nature of the incrementa feed and slow continuous feed generatprocess of the operation of the machine 30, 30a and From the foregoing, it will be seen that a method and apparatus have been disclosed which is exceedingly versatile involving both single flank and dou-ble flank grinding, straight and curvilinear feed paths lbetween the workpiece and the grinding wheel, and the selective introduction of modifications of tooth form both from a setup consideration which saves in terms of provision of a large number of cams and in addition setup time as well as the utilization of the adjustment means during the reciprocatory relative motion of the workpiece and grinding wheel so as to introduce modifications of the involute form during the grinding operation.

Although the various embodiments of the invention have been shown and described, it is with full awareness that many other modifications are possible, The invention, therefore, is to be construed in the light of the prior art and the spirit of the appended claims.

We claim:

1. The method of grinding a shaper cutter having partally formed teeth thereon comprising the steps of mounting aworkpiece on an arbor revolving on an arc about its own axis, the arbor having limited reciprocal movement in a plane transverse to the axis thereof, incrementally feeding a grinding wheel toward said workpiece in the longitudinal direction of the teeth to engage the partially formed teeth thereon, said grinding wheel being moved in a plane generally intersecting with the path of reciprocatory movement of said workpiece arbor, and rotating said workpiece tooth `by tooth by indexing on its axis until every tooth has been engaged by said grinding wheel to finish to form a discrete longitudinal portion of the teeth and then incrementally feeding the grinding Wheel in the same direction along the flank of the teeth to a new position and continuing the formation of the teeth.

2. The method of grinding a workpiece having teeth on the periphery of generally involute shape comprising the steps of:

(a) Placing a tooth of a workpiece in a grinding station while revolving the workpiece on its axis through an arc in a clockwise and counterclockwise direction, and providing relative translational movement between the workpiece and a grinding wheel to be engaged with its,

(b) Moving a grinding wheel toward said workpiece in the longitudinal direction of the teeth to engage a discrete portion, less than the total length, of a first tooth between the tip and base thereof,

(c) Indexing said workpiece to present a different p0rtion of the workpiece periphery to the grinding station,

(d) Then, after indexing, engaging a discrete portion of the adjacent tooth less than the total length thereof with the grinding wheel, and

(e) Continuing t0 index and engage discrete portions of successive teeth while providing a feeding movement of the grinding wheel in the same direction along the workpiece until the entire tooth length of each tooth has been covered by successive positions of the grinding wheel to thereby grind a predetermined generally involute tooth form on the periphery of the workpiece.

3. The method set forth in claim 2 wherein the feed movement of the grinding wheel is in discrete increments 16 and the same portions of successive teeth on the periphery of the workpiece are engaged by the grinding wheel between successive incremental feeding movements of the grinding wheel.

4. The method set forth in claim 2 wherein the feed of the grinding wheel is characterized as being slow continuous.

5. The method of claim 2 wherein said feeding movement takes place in increments following every 360 degree indexing revolution of said workpiece.

6. The method set forth in claim 5 wherein the path of movement of the grinding wheel between its successive positions is a straight line.

7. The method set forth in claim 5 wherein the path of movement of said grinding wheel between its successive positions is curvilinear.

References Cited UNITED STATES PATENTS 1,351,580 8/1920 Maag et al. 51-52 X 1,492,611 5/ 1924 Stevenson et al 51-52 X 1,580,442 4/1926 Schurr 51-123 1,666,737 4/ 1928 DeLeeuw 51-,287 X 1,858,468 5/1932 Simmons 51-123 1,964,233 6/1934 Uhlich 51-52 X 2,176,924 10/1939 Olson 51--123 X 2,850,851 9/1958 Graf 51-123 1,183,020 5/1916 Maag 51-123 1,870,764 8/1932 Aeppli 51-287 X 2,136,266 11/1938 Reinecker 51-52 2,257,850y 10/1941 Miller 51-123 2,258,510 10/ 1941 Laessker 51-287 X 2,364,542 12/1944 Miller 51-123 X 2,404,573 7/1946` Graf 51-123 2,958,984 11/1960 Hopkins 51-52 LESTER M. SWINGLE, Primary Examiner.