US3170453A

US3170453A - Wheel trimmer

Info

Publication number: US3170453A
Application number: US240909A
Authority: US
Inventors: Pernack Frank
Original assignee: National Broach and Machine Co
Current assignee: Nachi Machining Technology Co
Priority date: 1962-11-29
Filing date: 1962-11-29
Publication date: 1965-02-23
Anticipated expiration: 1982-02-23

Description

Feb. 23, 1965 F. PERNACK 3,170,453

WHEEL TRIMMER Filed Nov. 29, 1962 5 Sheets-Sheet 1 INVENTOR. FRANK PER/Vi CK W ,W w I TORNEYS Feb. 23, 1965 F- PERNACK WHEEL TRIMMER Filed Nov. 29, 1962 3 Sheets-Sheet 2 INVENTOR.

Fiend K PA-R/VA CK ATTORNEYS United States Patent 3,179,453 WIEEL TRIMMER Frank Pernaclr, llirrningham, Mich, assignor to National Breach & Machine Company, Detroit, Mich, a corporation of Michigan Filed Nov. 29, I962, Ser. No. 2%,969 36 (Claims. (Cl. 12511) The present invention relates to an improved wheel trimmer and is a continuation-in-part of application U.S. 15,371, filed March 16, 1960, now abandoned. More particularly this invention relates to an improvement in a trimmer adapted to form modified involutes on one or both sides of a grinding wheel.

It is an object of the present invention to provide a trimmer including an involute template, and means on said template for trimming the edge portion or portions of a grinding wheel to a form which is a modified involute.

More specifically, it is an object of the present invention to provide a wheel trimmer comprising a plurality of diamonds, and means for controlling movement of the diamonds relative to the edge portion of a grinding wheel so as to form a single modified involute by the action of the plurality of diamonds.

Still more specifically, it is an object of the present invention to provide a wheel trimmer comprising a single involute template and a pair of diamonds both actuated in synchronism with a follower engageable with said template, said diamonds being positioned to operate simultaneously against circumferentially spaced portions of a grinding wheel.

It is a further object of the present invention to provide wheel trimming mechanism comprising a pair of generally involute templates, a pair of wheel trimming diamonds, and follower mechanism connecting each of said diamonds to one of said templates to provide for simultaneous movement of said diamonds during a trimming stroke to trim predetermined portions of a grinding wheel.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, illustrating preferred embodiments of the invention, wherein:.

FIGURE 1 is a perspective view of a wheel trimmer constructed in accordance with the present invention.

FIGURE 2 is a front elevation of a grinding wheel illustrating various pairs of parallel planes which may be occupied by the diamond trimmers.

FIGURE 3 is a side elevation of the grinding wheel illustrated in FIGURE 2 and shown mounted on a rotary support.

FIGURE 4 is a fragmentary plane view of a somewhat different and simplified embodiment of the present invention.

FIGURE 5 is a sectional view taken on line 5-5 of FIGURE 4.

FIGURE 6 is a right hand side elevation of the embodiment shown in FIGURE 4.

FIGURE 7 is a sectional View taken on line 7-7 of FIGURE 8 and illustrating another embodiment of the present invention.

FIGURE 8 is a sectional view illustrating ball bearings between the trimming elements and the housing.

FIGURE 9 is a sectional view taken on line 99' of FIGURE 7.

Referring first to FIGURE 1, there is shown a trimmer adapted to trim the edge portion of a grinding wheel W at one side thereof to a substantially involute profile which however is modified somewhat from a true involute. The trimmer mechanism comprises a mounting plate 10 adapted to be clamped to an appropriate stationary angle BJWASB Patented Feb. 23, I965 plate on a grinder. Adjustably carried by the mounting plate 10 are a pair of involute template plates 12 and 14. The template plates 12 and 14 are respectively carried by

blocks

16 and 18 mounted foradjustment in the direction of the arrow 20 by suitable means such for example as a screw 22 co-operating with a nut, not shown, fixedly carried by the

block

16 or 18. The screw carries a dial 24 to provide for accurately controlled adjustment of the template.

In addition, the templates are adjustable about axes extending perpendicular to their plane by angular adjustment of support block 25 by means including a worm 23 carried by a shaft having a non-circular actuating head 26 and also provided with an indicator 28 to permit micrometer adjustment of the template about its axis of rotation. The inclination of the templates is indicated generally by graduations 30 on a plate 32 rigidly connected by means including a screw 34 to a worm gear 31 which is in mesh with the worm 23. The templates l2 and 14 may thus be independently adjusted and this independent adjustment is important for reasons which will subsequently appear.

Associated with the templates is a movable carrier which includes a pair of elongated longitudinally movable elements 4-2, which are provided adjacent the lower ends thereof with template followers 44 and 45. One of the followers 44 is connected directly to a diamond trimming element 46. The other template follower 45 includes a laterally extending bracket 48 adapted to carry a second diamond trimming element as in close proximity to the trimming element at. Spring means indicated at 53 are provided urging the template followers and diamond trimmers downwardly as seen in FIGURE 1.

.The movable carrier 86 is mounted by suitable guide means (not shown) for bodily movement in a direction generally transverse to the lines joining the template followers 44 and 4S and the diamond trimmer elements. This means may comprise a rectilinear guideway, guide post, linkage or the like. So long as the orientation of the carrier ll in space is preserved, the exact path of movement of carrier 40 is not important, since the template followers and diamonds are independently slidably supported therein for longitudinal movement. Accordingly, the involute formed on the appropriate surface of the templates l2 and '14 is reproduced generally on an edge portion of a grinding wheel indicated at W. The grinding wheel W is mounted on a rotary shaft or support 47 as best illustrated in FIGURE 3. Obviously, a convex involute form on the template will produce a concave involute form on the grinding wheel.

The purpose of the present invention is to permit the use of involute templates, together with a pair of template followers and diamond trimmers in such a way as to permit formation of modified involute form on the grinding wheel.

A modified involute for example, may be one in which the tip portion of the surface is removed below the true involute so as to produce a condition referred to as minus involute. Conversely, a similar or corresponding modification may be made to the portion of the generally involute surface adjacent its base circle.

Prior to the present invention, a single template and diamond trimmer was employed and if it Was desired to produce a modified involute on the wheel, a corresponding modification was required to be produced on the template. In accordance with the present invention, a plurality of templates and corresponding number of diamond trimmers are employed and each diamond trimmer and its associated template may be so adjusted as to produce a desired portion of the generally involute surface on the grinding wheel.

Prior to the present invention, the single diamond trimmer was caused to move in a path which occupied a plane containing the rotary axis of the wheel. In such a case the plane may be described as extending radially of the grinding wheel. Thus for example, with the arrangement illustrated in FIGURE 1, if the diamond trimmer 46 were the single trimmer of a prior trimming mechanism, it would be located directly beneath the rotary axis of the grinding wheel and would be movable in an involute path which occupied a radial plane containing the rotary axis of the grinding wheel.

In accordance with the present invention, one of the diamond trimmers such as the trimmer 46, when trimming the involute 52 as seen in FIGURES 2 and 3, may occupy and move in the radial plane 54 which contains the rotary axis 55 of the Wheel W. In such a case the associated diamond trimmer 50 will move in a parallel plane 56 displaced laterally from the radial plane 54. By appropriate adjustment of the template t4, the trimmer 59 may be caused to act upon either the root or the tip portion of the involute as required to produce a required modification thereof while the trimmer 46 may trim the remainder of the surface to a true unmodified involute.

In practice it is of course possible to so adjust the mechanism that the trimmers 46 and 50 are displaced equally at opposite sides of the radial plane 54 with reference to the grinding wheel, thus occupying planes 58 and 60 as seen in FIGURE 2. Thus the planes S and 60 are parallel to the radial plane 54-. All of the

planes

54, 56, 58 and 60 are illustrated in FIGURE 2 as perpendicular to and extending into the drawing andas a result thereof only edges of the planes are illustrated. Thus, the

parallel planes

56, 58 and 60 are parallel to the axis 55 of the wheel W.

Since the templates 12 and 14 are independently adjustable, the present invention provides for the utmost flexibility in setting. The trimmer 50 may be adjusted to produce any required modification of the true 1nvolute. If desired, the trimmer 50 may be adjusted into an inoperative position so that the trimmer 46 produces a true unmodified involute on the wheel.

Actuation of the trimmer is by a handle 62 which rotates a rock shaft 64. The rock shaft 64 as suggested above, may produce rectilinear movement of the carrier 40 or swinging movement thereof by appropriate linkage. It will be appreciated that for true reproduction of the involute provided on the templates 12 and 14, the essential requirement is that the longitudinal axis of the longitudinally movable mechanism connecting the template followers 44 and 45 and the diamond trimmers shall maintain its orientation, or in other words, remain always parallel to its original direction in space. With this arrangement, true reproduction of the form on the template is obtained.

Referring now to FIGURES 4-6, there is illustrated a much simpler arrangement which is nevertheless useful in obtaining a predetermined involute modification. In this form of the invention carrier means (not shown) is provided for moving the support 65 in the direction of the arrow 66. Longitudinally movable within the support 65 is an element or shaft 67 including at one end a template follower 68 and at the other end a diamond trimmer 69. 'It will be appreciated that within the support 65 suitable spring means 70 is provided to maintain.

the follower 68 at all times in contact with the surface of a template 71. Upon vertical movement of the support 65 as seen in FIGURE 5, it will of course be'observed that the diamond trimmer 69 will move in the same involute path as is provided on the template 71. Accordingly, if an involute surface is provided on the template 68 the identical involute may be producedon the surface of the grinding wheel.

In accordance with the present invention, the carrier 65 is provided with an adjustable bracket 72 on which is mounted an adjustable slide 74 which in turn carries an elongated diamond support element '76. The bracket 72 may be rotated with respect to the axis of the element 67 by merely unloosening screw 77, rotating bracket 72, and then securing bracket 72 in the new position. Longitudinally adjustable in the diamond support element 76 is a diamond trimmer '78, adjustment of which longitudinally of the support 76 may be effected by rota tion of a screw 89 carried by a single bracket 32 bolted to the slide 74. Vertical adjustment of the slide 74 is accomplished by a screw 84 carried. by a bracket 86 bolted to the adjustable bracket 72. Thus three independently operable adjustment are provided.

As illustrated, it may be assumed that the diamond trimmer 69 operates on center, or in other words, moves in an involute path which occupies the plane 54 containing the axis of the grinding wheel. On the other hand, the diamond trimmer 73 is laterally displaced from the trimmer 69 and accordingly operates in the plane 56 laterally oifset from a radial plane of the grinding wheel. Thus, while the trimmer 73 may move in an involute path which is identical with the path traced by the trimming element 69, it will produce an entirely different form on the grindingwheel due to its offset relationship. The exact. point or zone on the wheel at which the trimmer 73 operates may of course be adjusted by adjustment of the bracket 72 about the axis of the carrier 65, adjustment of the slide 74 relative to the bracket 72, or adjustment of the diamond trimmer 78 forwardly or backwardly by the screw 89.

Referring now to FIGURES 7-9, there is illustrated another arrangement for obtaining a predetermined involute modification. In this form of the invention, the movable carrier means 88, similar to the movable carrier 40 in FIGURE 1, includes a housing 99 which is appropriately secured to the movable carrier 88 by bolts 91.

The housing 90 includes a side 92 which has a pair of spaced

elongated recesses

94 and 96 provided therein. The

recesses

94 and 96 extend the entire length of the housing 90 and are provided with movable elongated elements 93 and 106 respectively which are longer than the housing 90 as best illustrated in FIGURE 7.

Each of the

recesses

94 and 96 is provided with an elongated inner ball bearing race 102 and an outer ball bearing race 104. Both of said races carry a plurality of ball bearings 106. The bottomsurface of each recess is provided with an elongated groove 1% for receiving the ball bearings 196 of the inner race 162. Each of the elements and 160 is provided with an inner elongated groove which receives the balls 106 of the inner race I62 and an outer elongated groove 112 which receives the balls 196 of the outer race 1%.

A closure'plate 113 having an elongated groove 114 therein for receiving the balls 186 of the outer race 104 is located opposite from side 92 of the housing 90 and is appropriately secured thereto by a plurality of adjustable fasteners 116. The fasteners may be adjusted to preload the ball bearings 106. It has been found that in certain applications a relativelysmall load gap, of a few ten thousandths of an inch, may be provided between the side 92 of housing 90 and the inner side of the closure plate 113 so as to permit the mechanic in the field to properly load the ball bearings 166. This is accomplished by adjusting the fasteners 116 and to thereby vary the load on the bearings 106. 7

With such a construction the elements 93 and 106 are slidable within the housing 94). The

elements

98 and 100 are each provided with a recess 120 at one end thereof to receive the inner end of a stylus or template follower 122 an intermediate portion of which is threaded as indicated at 124. A pin 126 is threaded in a recess of each element and has a flat inner end engageable with a flattened sideof the follower 122 to prevent rotation thereof.

Adjustment of the follower 122 longitudinally of the element or shaft is accomplished by a nut 128 retained merits to bias the elements toward their corresponding adjustable means for Varying the load on the bearings While the description of the specific embodiments of the invention illustrated in the accompanying drawings is concerned with a trimmer designed to form the edge portion at one side of the wheel to conform to the spaces between involute teeth on an external gear, it will of course be understood that the invention is also useful in making a straight sides angle trimmer, an internal involute trimmer, as well as other desired forms.

The drawings and the foregoing specification constitute a description of the improved wheel trimmer in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is:

l. A trimmer for a grinding wheel having a rotatable axis, said axis being located in a plane extending radially of the grinding wheel, said trimmer comprising a pair of closely adjacent trimming elements, means mounting said elements for simultaneous movement in trimming relation to the peripheral edge portion at one side of the grinding wheel, each of said elements occupying and being movable in a plane which is parallel to the aforesaid radial plane of the wheel, the plane of one of said elements being laterally spaced from the plane of the other of said elements, and means for moving said elements in the planes which they occupy so as to trim different radially spaced annular zones on the aforesaid edge portion at said one side of the wheel.

2. A trimmer defined in claim 1 wherein the planes of I said elements are spaced on opposite sides of the aforesaid radial plane of the wheel.

3. A trimmer defined in claim 1 wherein the planes of said elements are equally spaced on opposite sides of the aforesaid radial plane of the wheel.

4. A trimmer defined in claim 1 wherein one of said elements occupies and is movable in the aforesaid radial plane of the wheel.

5. A trimmer defined in claim 1 wherein said last mentioned means comprises template means.

6. A trimmer defined in claim 1 wherein said last mentioned means comprises a template for each element, and a template follower connected to each element.

7. A trimmer defined in claim 1 wherein said last mentioned means comprises a single template for both elements, and a single template follower operatively connected to said elements.

8. A trimmer defined in claim 1 wherein manually operable means are provided for actuating both of said elements.

9. A trimmer defined in claim 1 wherein said last mentioned means comprises a template for each. element, and a separately adjustable template follower connected to each element.

1() A trimmer defined in claim 9 wherein manually operable means are provided for actuating both of said elements and associated template followers.

11. A trimmer for a grinding wheel having a rotatable axis, said axis being located in a plane extending radially of the grinding wheel, said trimmer comprising a housing, a pair of closely adjacent trimming elements carried by said housing, each element having a diamondon one end, template follower means operatively connected to said elements, said elements being mounted in said housing for simultaneous movement in trimming relation to the peripheral edge portion at one side of the grin-ding Wheel,

each of said elements occupying and being movable in a plane which is parallel to the aforesaid radial plane of the grinding wheel, the plane of one of said elements being laterally spaced from the plane of the other of said elements, template means for said elements engageable by said template follower means, and means for moving said elements in the planes which they occupy in accordance with said template means so as to trim radially spaced annular zones on the peripheral edge portion at said one side of the wheel with the diamonds.

12. A trimmer defined in claim 11 wherein said template follower means comprises a single template follower, and said template means comprises a single template having a curved surface which is engaged by said template follower.

13. A trimmer defined in claim 11 wherein said template follower means comprises a follower on the other end of each of said elements, and said template means comprises a template for each of said elements having a curved surface which is engaged by the corresponding template follower.

14. A trimmer defined in claim 13 wherein said housing includes ball bearing means for mounting said elements, and adjustable means carried by said housing for loading said ball bearing means.

15. A trimmer defined in claim 13 wherein resilient means are provided for each of said elements for urging the template follower against the template.

16. A trimmer defined in claim 13 wherein manually operable means are provided for actuating both of said elements and associated template followers.

17. A trimmer defined in claim 13 wherein each of said templates are separately adjustable about an axis perpendicular to the aforesaid radial plane.

18. A trimmer defined in claim 13 wherein each of said templates are also adjustable in a plane parallel to the other mentioned planes. 19. A trimmer defined in claim 11 wherein means are carried by said housing for adjusting one of said diamonds with respect to the other of said diamonds.

20. A trimmer for a grinding wheel having a rotatable axis, said axis being located in a plane extending radially of the grinding wheel, said trimmer comprising a pair of closely adjacent trimming elements, means mounting said elements for simultaneous movement in trimming relation to the peripheral edge portion at one side of the grinding wheel, one of said elements occupying and being movable in the aforesaid radial plane containing the rotatable axis of the wheel and the other of said elements occupying and being movable in a plane parallel to and displaced laterally from said radial plane, and template mechanism including a curved surface for moving said elements in the planes which they occupy so as to trim different radially spaced annular zones on the aforesaid edge portion at said one side of the Wheel in accordance with the curved surface on said template mechanism.

21. A trimmer for a grinding wheel having a rotatable axis, said axis being located in a plane extending radially of the grinding wheel, said trimmer comprising a pair of closely adjacent trimming elements, means mounting said elements for simultaneous movement in trimming relation to the peripheral edge portion at one side of the grinding wheel, one of said elements occupying and being movable in'the aforesaid radial plane containing the rotatable axis of the wheel and the other of said elements occupying and being movable in a plane parallel to and displaced laterally from said radial plane, and means for moving said elements in the planes which they occupy so as to trim different radially spaced annular zones on the aforesaid edge portion at said one side of the wheel, said last mentioned means comprising a template for each element, and a template follower connected to each element.

22. A trimmer for a grinding Wheel having a rotatable axis, said axis being located in a plane extending radially of the grinding wheel, said trimmer comprising a pair of closely adjacent trimming elements, means mounting said elements for simultaneous movement in trimming relation to the peripheral edge portion at one side of the grinding wheel, one of said elements occupying and being movable in the aforesaid radial plane containing the rotatable axis of the wheel and the other of said elements occupying and being movable in a plane parallel to and displaced laterally from said radial plane, and means for moving said elements in the planes which they occupy so as to trim different radially spaced annular zones on the aforesaid edge portion at said one side of said wheel, said last mentioned means comprising a template for each element, and a separately adjustable template follower connected to each element.

23. A trimmer for a grinding wheel which comprises a pair of closely adjacent trimming elements, means mounting said elements for simultaneous movement in trimming relation to the peripheral edge portion at one side of the grinding wheel, means for moving said elements so as to trim different radially spaced annular zones on said wheel, said last mentioned means comprising a template for each element, a template follower connected to each element, and manually operable means for actuating both of said elements and associated template followers.

24. A trimmer for a grinding wheel having a rotatable axis which comprises a pair of closely adjacent trimming elements, means mounting said elements for simultaneous movement in parallel planes, one of which planes contains the rotatable axis of the grinding wheel, said one plane extending radially of the grinding Wheel, in trimming relation to the peripheral edge portion at one side of the grinding wheel, means for moving said elements so as to trim different radially spaced annular zones on the aforesaid edge portion at said one side of the wheel, said last mentioned means comprising a template for each element, and a separately adjustable template follower connected to each element, and manually operable means for actuating both of said elements and associated template followers.

25. A trimmer for a grinding wheel having a rotatable axis, said axis being located in a plane extending radially of the grinding wheel, said trimmer comprising a pair of closely adjacent trimming elements, means mounting said elements for simultaneous movement in trimming relation to the peripheral edge portion at one side of a grinding wheel, one of the elements occupying and being movable in the aforesaid radial plane containing the rotatable axis of the wheel and the other element occupying and being movable in a plane parallel to and displaced laterally from said radial plane, and means for moving said elements in the planes which they occupy so as to trim different radially spaced annular zones on the aforesaid edge portion at said one side of the wheel, said last mentioned means comprising a single template having a curved surface, a single template follower, and means connecting said single template follower to both of said trimming elements.

26. A trimmer for a grinding wheel having a rotatable axis, said axis being located in a plane extending radially of the grinding wheel, said trimmer comprising a pair of closely adjacent trimming elements, means mounting said elements for simultaneous movement in trimming relation to the peripheral edge portion at one side of the grinding wheel, each of said elements occupying and being movable in a plane which is parallel to the afore-. said radial plane of the wheel, the plane of one of said elements being laterally spaced from the plane of the other of said elements, and template mechanism including a curved surface for moving said elements in the planes which they occupy so as to trim different radially spaced annular zones on the aforesaid edge portion at said one side of the wheel in accordance with the curved surface on said template mechanism.

27. A trimmer defined in claim 26 wherein the planes of said elements are equally spaced on opposite sides of the aforesaid radial plane of the wheel.

28. The combination of a support, a grinding wheel mounted on said support for rotation, said grinding wheel having a rotatable axis, said axis being located in a plane extending radially of said grinding wheel, and a trimmer for said grinding wheel comprising a pair of closely adjacent trimming elements, means mounting said elements for simultaneous movement in trimming relation to the peripheral edge portion at one side of said grinding wheel, each of said elements occupying and being movable in a plane which is parallel to the aforesaid radial plane of said wheel, the plane of one of said elements being laterally spaced from the plane of the other of said elements, and means for moving said elements in the planes which they occupy so as to trim different radially spaced annular zones on the aforesaid edge portion at said one side of said wheel.

29. The combination defined in claim 28 wherein the planes of said elements are spaced on opposite sides of the aforesaid radial plane of said wheel.

30. The combination defined in claim 29 wherein the planes of said elements are equally spaced on opposite sides of the aforesaid radial plane of said wheel.

31. The combination defined in claim 28 wherein one of said elements occupies and is movable in said radial plane.

32. A trimmer for a grinding wheel having a rotatable axis, said axis being located in a plane extending radially of the grinding wheel, said trimmer comprising an element having a trimming diamond on one end and a template follower on the other end, a bracket carried by said element, a second element carried by said bracket and having a trimming diamond on one end thereof, means mounting said elements for simultaneous movement in trimming relation to the peripheral edge portion at one side of the grinding wheel, each of said elements occupying and being movable in a plane which is parallel to the aforesaid radial plane of the grinding wheel, the plane of said second element being laterally spaced from the plane of said first mentioned element, a template having a curved surface, said follower being in engagement with said curved surface, and means for moving said elements in the planes which they occupy in accordance with said curved surface so as to trim radially spaced annular zones on the peripheral edge portion at said one side of the wheel with said diamonds.

33. A trimmer defined in claim 32 Wherein'adjustment means are interposed between said bracket and said first mentioned element to permit said bracket to be rotated with respect to the axis of said first mentioned element.

34. A trimmer, defined in claim 32 wherein adjustment means are carried by said bracket to adjust said second element in the plane in which it moves.

35. A trimmer defined in claim 32 wherein adjustment means are carried by'said bracket to adjust said second element in a direction perpendicular to the plane in which it moves.

36. A trimmer for a grinding wheel having 'a rotatable axis, said axis being located in a plane'extending radially of the grinding wheel, said trimmercomprising a housing having a pair of elongated spaced recesses in one side thereof, a pair of closely adjacent trimming elements mounted in said recesses, a closure plate on said one side of said housing, adjustable fastening means securing said plate to said housing, ball bearing means for said elements interposed between the bottom of said recesses and said plate, each element having a diamond on one end, template follower means operatively connected to said elements, said elements being mounted in said housing for simultaneous movement in trimming relation to the peripheral edge portion at one side of the grinding wheel, each of said elements occupying and being movable in a planewhich is parallel to the aforesaid radial plane of the grinding wheel, the plane of one of said elements being laterally spaced from the plane of the other of said elements, template means for said elements engageable by said template follower means, and means for moving said elements in the planes which they occupy in accordance with said template means 1% so as to trim radially spacedv annular zones on the peripheral edge portion at said one side of the Wheel with the diamonds, said adjustable fastening means being effective to vary the loading forces on said ball bearing means.

References Cited in the file of this patent UNITED STATES PATENTS Germany Nov. 18, 1929

Claims

1. A TRIMMER FOR GRINDING WHEEL HAVING A ROTATABLE AXIS, SAID AXIS BEING LOCATED IN A PLANE EXTENDING RADIALLY OF THE GRINDING WHEEL, SAID TRIMMER COMPRISING A PAIR OF CLOSELY ADJACENT TRIMMING ELEMENTS, MEANS MOUNTING SAID ELEMENTS FOR SIMULTANEOUS MOVEMENT IN TRIMMING RELATION TO THE PERIPHERAL EDGE PORTION AT ONE SIDE OF THE GRINDING WHEEL, EACH OF SAID ELEMENTS OCCUPYING AND BEING MOVABLE IN A PLANE WHICH IS PARALLEL TO THE AFORESAID RADIAL PLANE OF THE WHEEL, THE PLANE OF ONE OF SAID ELEMENTS BEING LATERALLY SPACED FROM THE PLANE OF THE OTHER OF SAID ELEMENTS, AND MEANS FOR MOVING SAID ELEMENTS IN THE PLANES WHICH THEY OCCUPY SO AS TO TRIM DIFFERENT RADIALLY SPACED ANNULAR ZONES ON THE AFORESAID EDGE PORTION AT SAID ONE SIDE OF THE WHEEL.