US3905156A

US3905156A - Thread grinding machine with a device for the relief grinding of the threads on tap drills and internal thread formers

Info

Publication number: US3905156A
Application number: US505057A
Authority: US
Inventors: Emil Vogelsanger
Original assignee: Reishauer AG
Current assignee: Reishauer AG
Priority date: 1973-09-17
Filing date: 1974-09-11
Publication date: 1975-09-16
Anticipated expiration: 1992-09-16
Also published as: DE2442384B2; GB1485433A; CH570239A5; JPS5056692A; DD113464A5; DE2442384C3; HU171509B; JPS5835830B2; DE2442384A1

Abstract

A thread grinding machine with a device for the relief grinding of the thread on tap drills and internal thread formers having straight or helically-shaped grooves or rolling edges, in which the rotating work-piece which is disposed coaxially with the axis of the work-piece spindle on the work-piece carriage, is guided past the grinding disk along the axial direction of the workpiece to produce the desired thread pitch, and said grinding disk being radially adjustable with respect to the work-piece carriage.

Description

United States Patent 1 1 1111 3,905,156

Vogelsanger Sept. 16, 1975 THREAD GRINDING MACHINE WITH A [56] References Cited DEVICE FOR THE RELIEF GRINDING OF UNITED STATES PATENTS THE THREADS 0N TAP DRILLS AND 1,798,832 3 1931 Buckingham 51/50 PC x INTERNAL THREAD FORMERS 2,469,077 5/1949 Rickenmann.... Inventor: Em g g Dictlikon, 2,929,172 3/1960 Pasell 51/95 R 1 1 Switzerland Primary Examiner-Donald G. Kelly [73] 'Assignee: Reishauer AG, Zurich, Switzerland Attorney, Agent, or FirmHill, Gross, Simpson, Van 'Filed p 11 1974 Santen, Steadman, Chiara & Simpson [211 App]. No.: 505,057 [57] ABSTRACT A thread grinding machine with a device for the relief [30] Foreign Application Priority Data grinding of the thread on tap drills and internal thread Se t 17 197,; Switzerland 13301 /73 formers having straight or helically-shaped grooves or p rolling edges, in which the rotating work-piece which U S 5l/46 51/48 HE 51/50 PC, is disposed coaxially with the axis of the work-piece 51/9; C. 51/95 3 51/288 spindle on the work-piece carriage, is guided past the In Cl 2 B24B 3/22 B24B 3/24 grinding disk along the axial direction of the work- [58] Fie'ld 48 HE R 50 PC piece to produce the desired thread pitch, and said grinding disk being radially adjustable with respect to the work-piece carriage.

13 Claims, 11 Drawing Figures 21 2 1o A l 2s 9 I I l 15 1o 18 1s PATENTEE: 6 m5 SHEET 3 [IF 4 This invention relates to improvements on thread grinding machines.

Different devices are known for the relief grinding of l I the thread on tap drills and internal thread formers, in connection with which the relief grinding movements are carried out as follows:

a. Some devices use oscillating movements of the grinding-disk orof the grinding carriage, respectively, which is guided in the sliding guideways or roller guideways, in radial direction with reference to the rotating work-piece which is shifted in its axial direction.

b. Other devices use oscillating swivel movements of the grinding disk or grinding spindle support in radial direction about an axis positioned in the grinding carriage with reference to the rotating work-piece which is shifted in its axial direction.

0. Use is also made of oscillating swivel movements of the work-piece or of the work-piece support in radial direction about an axis located in the work-piece carriage with reference to the rotating grinding disk, while the work-piece rotates and is shifted with the workpiece carriage in its axial direction.

d. Means are also provided for using the forward and backward rotary movements of the eccentric bearing bushings of the grinding spindle arranged in the grinding carriage, whereby oscillating movements are imparted to the grinding disk in radial direction with reference to the rotating work-piece which is shifted in its axial direction.

e. Other devices use forward and backward rotary movements of the eccentric bearing bushings for the LII reception of the centering tips in the work-piece spin- I dle and in the tailstock, by means of which oscillating movements are impartedto the work-piece in a radial direction with reference to the rotating grinding disk, while the work-piece rotates and is shifted in its axial direction.

f. Still other devices use swivel movements only of the tip of the tailstock about a point of rotation which lies in the general axial plane of grinding disk and workpiece, whereby during the grinding, the work-piece carries out oscillating swivel movements with reference to the rotating grinding disk, while the work-piece rotates and is shifted in its axial direction. Relief grinding according to this method, however, results in a geometrical flaw, as the relief grinding movements are carried out by means of oscillating swivel movements of the tool, which leads to flaws in the included angle of thread on the thread profile.

In order to beable to make use of the advantages resulting from high speed grinding, that is, grinding with higher circumferential speeds of the grinding disk, for example 60 meters per second, the circumferential speed of the work-piece must be brought into a suitable relationship with the circumferential speed of the grinding disk. In order to be able to fulfill this requirement the rate of rotation of the work-piece would have to be increased substantially as compared with conditions previously'in' use. This, however, demands necessarily also a correspondingly. greater frequency of the number of relief grinding movements determined by the rate of rotation of the work-piece and number of grooves (in the case of the internal thread former it is the number of rolling edges). The means and methods mentioned above in paragraphs a to f, however, do not allow relief grinding strokes of high frequencies because large masses must be moved back and forth in very short periods of time over very short distances.

SUMMARY OF THE INVENTION It becomes'appropriate, therefore, to develop an apparatus which is capable of substantially increasing the frequency of the relief grinding stroke as compared with machines previously available.

By way of summary the purpose of the invention herein is to provide in a thread grinding machine means for efficiently increasing the frequency of the relief grinding strokes. This is done by providing a work carriage constructed in two parts (a base portion and upper portion) which are interconnected to each other by yieldable guide elements which allow an essentially friction free oscillation of the two parts with respect to each other. In addition the guide elements are subject to only a minimum of wear. Furthermore, control means interconnecting the two parts are provided and this control means includes means for varying the amount of the relief grinding stroke between zero and a predetermined maximum value.

Other features and advantages of the invention will become more readily apparent when the description is considered in connection with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a view in elevation of a thread grinding machine for thread borers and internal thread formers;

FIG. 2 shows a section through line II--II of FIG. 1 through the upper portion, the base portion and the guide of the base portion in the frame;

FIG. 2a shows a modified version in section of a leaf spring similar to that shown in FIG. 2;

F IG. 3 shows a view in elevation of the upper portion and of the base portion partially in section;

FIG. 4 is a plan view of the upper portion (partially in section) showing the mechanism for the adjustment of the relief grinding stroke;

FIG. 5 is a plan view of the mechanism for the adjustment of the relief grinding stroke with a relief grinding stroke of the size zero;

FIG. 6 is a plan view showing a gearing arrangement for a relief grinding device embodying the invention;

FIG. 7 is an enlarged detail of a portion of the gearing arrangement shown in FIG. 6;

FIG. 8 is a diagrammatic illustration of the leaf spring connection of the base portion with the upper portion showing the pretensioning;

FIG. 9 is a thread boring device withtrelief thread profile in cross-section; and

FIG. 10 is an internal thread former in cross-section.

DESCRIPTION OF A PREFERRED EMBODIMENT The thread grinding machine shown diagrammatically in FIG. 1 has a frame 1 which serves as base for the slidable reception of the work-piece carriage consisting of the base portion 2, upper portion 3 and grinding carriage 4. The feed and return device for the grinding carriage 4 with the grinding disk 5 and the grinding disk driving motor 6 as well as other elements of the thread grinding machine not influencing the relief grinding device according to the invention are not specifically shown and described as they are well known.

At the one end of the base portion 2 of the workpiece carriage is arranged the work-piece gearbox 7 which is rigidly connected to' the base portion 2. The upper portion 3 with the center rest 8 (FIG. 4) affixed thereto and the longitudinally slidable tailstock 9 is connected with the base portion 2 through leaf springs 10 or leaf spring stacks 11 (FIG. 2a) so that a type of flexible rectangular joint is formed (FIGS. 2 and 8) whereby the upper portion 3, by means to be hereinafter described, may be set in oscillating motion, that is, to produce relief grinding movements extending transversely to the work-piece axis A (FIGS. 2 and 4). The transfer of the rotary movement from the nonoscillating work-piece gearbox 7 to the workpiece spindle 12 in the center rest 8 which oscillates together with the upper portion 3, takes place through a coupling 13 generally known in the trade (FIG. 6) which permits of a transverse displacement (parallel shifting) of the axes to the extent of the relief grinding stroke.

The production of the oscillating movements of the upper portion 3 is accomplished with the aid of a changeable cam disk 14 (FIG. 4) which is fixed on the shaft 43 rotatably positioned in the base portion 2 and is driven through the work-piece gearbox 7 (FIG. 6). For the transfer of the deflections caused by the cam disk 14 to the upper part 3, a rocking lever 15 is used (FIGS. 4 and 6). The rocking lever 15 is pivotally mounted in the base portion 2 on a shaft 16. A template profile or cam C (FIGS. 4, 5) comprising a radially inwardly projecting portion formed in the bore of bushing 17 rotatable in the rocking lever functions to adjust the desired size of the relief grinding or of the stroke B respectively, of the upper portion 3 between zero and a ccrtain maximum value (FIGS. 6, 810). The rocking lever 15 arranged pivotally in the base portion 2 is in continuous frictional engagement with the cam disk 14 on the one hand and with the slide roll 19 positioned on shaft 18 in the upper portion 3 on the other hand. The slide roll 19 is freely rotatable on the shaft 18. The change in the relief grinding stroke B is brought about by means of a change in the position of the lever arm on the rocking lever 15. It is carried out by means of a change in position of the cam C with reference to the center of rotation D of the rocking lever 15, in that the bushing 17 which is positioned on the rocking lever 15 is rotated with the cam C. When a relief grinding stroke for the upper portion 3 of the value zero is desired (FIG. 5) the locus of the radius of the cam Cs circular arcuate surface, point E (FIG. 4) must be brought into coincidence with the pivot point D of the rocking lever 15 by means of rotation of the bushing 17 (FIG. 5). The rotation of the bushing 17 which is provided with a set of teeth F on the outer periphery thereof takes place by means of rotation of the pinion 20 which is in engagement therewith. Adjusting to the desired relief grinding stroke B is undertaken with the aid of a zero mark which is positioned on the rotary button 21 of the pinion 20 and a scale ring 22 connected therewith. To avoid wear, there is provided on the rocking lever 15 a roller follower 23 which continuously rides on the cam disk 14 under the influence of compression Spring 24.

The control members l4, 15, 16, l7, l8, l9 and 23 used for the production of the oscillating movements of the upper portion 3 are arranged and installed in such manner that the leaf springs 10 or stacks of leaf springs 11 are always deflected in the same direction, for example, to the left as shown in FIG. 8, and therefore, they are subjected to an initial pretensioning force G always acting in the same direction. For this reason, within the entire relief grinding stroke range, the upper portion 3 is biased continuously with respect to the baseportion 2 via the mentioned control members by a similarly directed spring force H, that is, by means of the reaction force to the initial stressing force G. With this arrangement under constant tension a connection free from play is insured between the upper portion 3, the mentioned control members disposed therebe' tween and the base portion 2 (FIGS. 4 and 5). The force components are divided in the rocking lever 15 and depending on the size of the lever arm at the moment are imparted in corresponding portions through the axis of rotation 16 and the cam disk 14 to the base portion 2. Upon adjusting to a relief grinding stroke B of the value zero, at which position the lever arm likewise amounts to zero, the mentioned spring force H acts directly on the point of rotation D of the rocking lever 15. The rocking lever 15 could be lifted in this zero position from the cam disk 14. In order to prevent this, or in order with very small relief grinding strokes B, to insure the required safety of operation, there is arranged between the base portion 2 and the rocking lever 15 a compression spring 24. During the relief grinding, the return movements of the upper portion 3 leading away from the grinding disk 5 are brought about solely by means of the spring force H (FIG. 8) of the deflected leaf springs 10 or stacks of leaf springs l 1, while the feed movements of the cam disk 14 are necessarily imparted through the rocking lever 15 to the upper portion 3. The length of the leaf springs or leaf spring stacks, respectively, arranged between the upper and base portion parallel to the axis of the work-piece is coextensive with the length of the upper and base portions. This prevents debris from being deposited on the mentioned control members consisting of a cam disk, roller, rocking lever, bushing, slide roll and two rotary axles.

The motor 25 (FIG. 1) which is fixed on the workpiece gearbox 7, serves for the production of the rotary movement of the work-piece 26, the longitudinal shifting of the work-piece carriage which consists of the base portion 2 and the upper portion 3 and it serves also for the production of the rotary movement of the cam disk 14 or the oscillating movements of the upper portion 3, respectively.

The gear 28, the gear 29, the shaft 30, the change gear 31, the change gear 32 and the shaft 33 are driven by the motor 25 (see FIG. 6) through the shaft 27. When grinding a right hand thread on the work-piece 26, its drive is effected by the shaft 33 through the axially shiftable or sliding gear 34 which is frictionally connected with said shaft and via the gear wheel which is in engagement with said shiftable gear 34 and the gear wheel 35 on the shaft 36 which is in engagement with the gear 34 and from there through the transversely slidable coupling 13, the work-piece spindle 12 in the center rest 8, the driving disk 37 and the lathe dog 38 (FIG. 4). In the case of grinding a left hand thread, the sliding gear 34 is shifted to the right and is brought into engagement with the ring gear I of the double gear wheel 39 which is connected to the shaft 40. Under these conditions the drive of the shaft 36 takes place from the shaft 33 through the sliding gear 34, the ring gear I of the double gear wheel 39 and its ring gear to the gear wheel 35,:which is connected to the shaft The latter andthe workpiece 26 (FIG. 6) supported between the centering

tips

4 and 42,rotate in the opposite direction as comparedwith the previous action. it

The shaft 30 also drives the shaft 43 positioned in the base portion 2. The cam disk l4 isfixed to the shaft 43 for the production of the relief grinding stroke. For grinding straight grooved work-pieces, the"stcm 48 of the differential drive'arranged between the

shafts

30 and 43 is lockedby means, not shown. From' the shaft 30, the rotary movement is transferred through the

gear wheels

44, 45, 46and 47 to the shaft 43. Under of rotation as the shaft 30. V I

The changeable gear, drive, comprising 'the

gear wheels

31 and 32, se es'for the determination of the various rates of rotat between work-piece 26 and cam disk 14, whereby an the workpiece 26to be ground a relief grinding movementmust be applied to each groove or roller' l When the grinding of thread borers with helically shaped grooves or internal thr ead formers withhelically shaped roller edges, depending on the direction of these conditions, th'e' shaft' 43 rotatesat the same rate, I

the helically extendinglgrooves or roller edges'respec tively, positive 'or .negativ' e additional rotary movement must be imparted'to the cam disk '14 corresponding to the longitudinal displacementfof the work-piece carriage, the amount of thegro tary moyer ne ntjbeing dependent onthe angle of ltwist of'the-grooves or roller edges, respectively. In order to produce'the necessary additional ,rotary movemennan adjustable arm 4? is used nos. 1 and 7), whiehisadjustably secured on the frame 1 Its angulanp os ition is selected according tothe groove or rolleredge angleof-twist,respectively, presennon. the work-piece gmu'm I A pin S O arranged, axially slidablyinthe work-piece gearbox .7. rides on. the arm ,49 when the work-piece carriage consisting of thebase portion 2 and upperjportion 3 slides longitudinally in the guideway sl of the frame 1 FlG. 2). The axial,displacernent-of the pin 50 caused by the arm 49 which is-positioned at anangle parted by meansof its gear rack L totthe pinion gear M of the gear wheel cluster 5210 rotate -theilatter. The latter is rotatably positioned onthe shaft 53 and has a second ring gear N. Each rotary movement of the gear wheel cluster 52 is transferred through the gear N to the gear 0 of the gear wheel cluster 54 loosely rotatably disposed on the shaft 27 and from the latter through the ring gear P to the gear wheel 55. The latter is fixed on the stem 48 of the differential gear. As a result the stem 48 carries out a rotary movement which, through the

gear wheels

44, 45, 46 and 47 of the differential drive already mentioned, is transferred to the shaft 43 or the cam disk 14 fixed thereupon.

Furthermore, the drive of the guide spindle or lead screw 56 or the longitudinal displacement of the workpiece carriage, which consists of base portion 2 and upper portion 3, takes place by the mentioned shaft 33. The number of revolutions of the lead screw 56 is determined by means of the change gears 57, 58, 59 and 60 in a mathematical ratio determined by the rate of rotation of the workpiece 26, so that the desired thread pitch is produced on the workpiece 26 to be ground.

The sliding gear cluster 61 comprising the gears Q and R which is slidably arranged on the shaft 33, is

shifted into itsleft hand position-(FIG. 6) for the grind- I ing" of threads measuredlin the metric system whereby its gear Q comes into engagement with the gear S of the gear cluster 62 which is loosely rotatably disposed on the shaft 30. For the grinding of threads measured in the English system, the mentioned sliding gear cluster 61 is pushed to the right, whereby its gear R comes into engagement with the ring gear T of the gear cluster 62. The rotary movement of gear cluster 62 is transferred from the gear U to the gear wheel 64 which is rigidly connected to the shaft 63. From the shaft 63, rotary movement is imparted to the lead screw 56 via the change gears 57, 58, 59 and 60. The lead screw 56 itself is rotatably positioned in the base portion 2 of the 'work-piece carriage or in the work-piece gearbox 7 connected with it, but is held against axial movement. The guide spindle56 provided with a left hand thread is screwed into the spindle nut 65 which is secured on theframe l by screws or other suitable means and is further secured against rotation. During the operating cycle, that is, the displacement of the work-piece carriage from left to right, the guide spindle 56 is secured in the spindle nut 65. For the return movement-of the work-piece carriage, the direction of rotation of the motor 25 is changed. The guide spindle or lead screw 56.as a result is screwed out of the spindle nut 65 and as a'result of this the work-piece carriage is displaced from right to left.

relief grinding of the thread on threaded, tools, asfor :example on thread boring devices andinternal thread formers. ,By utilizing yieldable guide elements which have reduced friction, it is possible due to the utilization of .spring force tomaintain continuously a biased connection or a connection under tension, that is, free from play, of the upper portion 3 with the control members for the relief grinding movements in both shifting directions, in that a pre-tensioning force is imparted by the mentioned guide elements.

While a preferred embodiment of the invention has been disclosed it will be appreciated that this has been shown by way of example only, and the invention is not to be limited thereto as other variations will be apparent to those skilled in the art and the invention is to be given its fullest possible interpretation within the terms of the following claims.

What is claimed is:

l. A thread grinding machine with a device for the relief grinding of the thread on thread boring devices and internal thread formers in which the rotating workpiece is positioned coaxially with the axis of the workpiece spindle on a work-piece carriage comprising:

a grinding disk assembly mounted on the machine movable radially with reference to the work-piece and parallel to the axis of the work-piece;

a work-piece carriage including an upper portion and a base portion, which are relatively movable to each other;

means for rotatably supporting a work-piece on said upper portion;

means interconnecting said upper and base portions said interconnecting means comprising yieldable guide means which extend between said upper and base portions in 'a manner to position said upper and base portions in spaced relation to each other and to guide said upper portion in its movement with respect to said base portion and thereby reduce friction and wear on said base portion; and

control means for displacing said upper portion with respect to said base portion including a rocking lever interconnecting said upper and base portions for controlling said displacement in accordance with the desired relief grinding movement.

2. The grinding machine of claim I wherein said guide means comprise leaf springs interconnecting said base portion and said upper portion.

3. The grinding machine of claim 2 wherein said leaf springs or leaf spring stacks are connected in the assembly under the influence of a prestressing force.

4. The grinding machine of claim 2 wherein said guide means comprise leaf springs interconnecting said base portion and said upper portion, and

said control means for displacing said upper portion includes v an interchangeable cam disk,

a rocking lever pivotally mounted in said base portion and operatively associated with said cam disk to be actuated by the rotation of said cam disk, and

a sliding roller rotatably positioned in said upper portion and operatively associated with said rocking lever whereby oscillating movement of said rocking lever is transmitted through said sliding roller to said upper portion.

5. The grinding machine of claim 4 including a circumfcrentially adjustable cam associated with said control means for the displacement of said upper portion include an interchangeable cam disk, a rocking lever pivotally mounted in said base portion and operatively associated with said cam disk to be actuated by the rotation of said cam disk, and a sliding roller rotatably positioned in said upper portion and operatively associated with said rocking lever whereby oscillating movement of said rocking lever is transmitted through said sliding roller to said upperportion. 8. The grinding machine of claim 7 wherein the rocking lever includes a follower roller rotatably positioned thereon and which is in continuous engagement with said cam disk. 9. The grinding machine of claim 1 including a circumferentially adjustable cam associated with said rocking lever through which cam said rocking v lever acts on said sliding roller rotatably positioned on a shaft fixed in said upper portion, whereby the amount of the relief grinding stroke may be adjusted between zero and a predetermined maximum value. 10. The grinding machine of claim 1 including an adjustable cam disposed in the bore of a bushing rotatably disposed in said rocking lever. 11. The grinding machine of claim 10 wherein said adjustable cam comprises a radially inwardly projecting portion formed on the internal surface of said bushing. 12. The grinding machine of claim 10 wherein said adjustable cam comprises a radially inwardly projecting portion formed on the internal surface of said bushing, said projecting portion comprising an arcuate portion whose circumscribing radius coincides with the pivotal pointof said rocking lever. 13. The grinding machine of claim 10 including first gear means operatively associated with said bushing; and i second rotatable gearmeans in mesh with said first gear means for rotating said first gear means and said bushing and said adjustable cam associated therewith for makaing a setting of the desired relief grinding stroke.

Claims

1. A thread grinding machine with a device for the relief grinding of the thread on thread boring devices and internal thread formers in which the rotating work-piece is positioned coaxially with the axis of the work-piece spindle on a work-piece carriage comprising: a grinding disk assembly mounted on the machine movable radially with reference to the work-piece and parallel to the axis of the work-piece; a work-piece carriage including an upper portion and a base portion, which are relatively movable to each other; means for rotatably supporting a work-piece on said upper portion; means interconnecting said upper and base portions, said interconnecting means comprising yieldable guide means which extend between said upper and base portions in a manner to position said upper and base portions in spaced relation to each other and to guide said upper portion in its movement with respect to said base portion and thereby reduce friction and wear on said base portion; and control means for displacing said upper portion with respect to said base portion including a rocking lever interconnecting said upper and base portions for controlling said displacement in accordance with the desired relief grinding movement.

2. The grinding machine of claim 1 wherein said guide means comprise leaf springs interconnecting said base portion and said upper portion.

4. The grinding machine of claim 2 wherein said guide means comprise leaf springs interconnecting said base portion and said upper portion, and said control means for displacing said upper portion includes an interchangeable cam disk, a rocking lever pivotally mounted in said base portion and operatively associated with said cam disk to be actuated by the rotation of said cam disk, and a sliding roller rotatably positioned in said upper portion and operatively associated with said rocking lever whereby oscillating movement of said rocking lever is transmitted through said sliding roller to said upper portion.

5. The grinding machine of claim 4 including a circumferentially adjustable cam associated with said rocking lever through which cam said rocking lever acts on said sliding roller rotatably positioned on a shaft fixed in said upper portion, whereby the relief grinding stroke may be adjusted between zero and a predetermined maximum value.

6. The grinding machine of claim 2 wherein the length of said leaf springs or leaf spring stacks are arranged parallel to the axis of the work-piece between said base portion and said upper portion of the work-piece carriage and said length is coextensive wiTh the length of said base and upper portions.

7. The grinding machine of claim 1 wherein said control means for the displacement of said upper portion include an interchangeable cam disk, a rocking lever pivotally mounted in said base portion and operatively associated with said cam disk to be actuated by the rotation of said cam disk, and a sliding roller rotatably positioned in said upper portion and operatively associated with said rocking lever whereby oscillating movement of said rocking lever is transmitted through said sliding roller to said upper portion.

8. The grinding machine of claim 7 wherein the rocking lever includes a follower roller rotatably positioned thereon and which is in continuous engagement with said cam disk.

9. The grinding machine of claim 1 including a circumferentially adjustable cam associated with said rocking lever through which cam said rocking lever acts on said sliding roller rotatably positioned on a shaft fixed in said upper portion, whereby the amount of the relief grinding stroke may be adjusted between zero and a predetermined maximum value.

10. The grinding machine of claim 1 including an adjustable cam disposed in the bore of a bushing rotatably disposed in said rocking lever.

11. The grinding machine of claim 10 wherein said adjustable cam comprises a radially inwardly projecting portion formed on the internal surface of said bushing.

12. The grinding machine of claim 10 wherein said adjustable cam comprises a radially inwardly projecting portion formed on the internal surface of said bushing, said projecting portion comprising an arcuate portion whose circumscribing radius coincides with the pivotal point of said rocking lever.

13. The grinding machine of claim 10 including first gear means operatively associated with said bushing; and second rotatable gear means in mesh with said first gear means for rotating said first gear means and said bushing and said adjustable cam associated therewith for makaing a setting of the desired relief grinding stroke.