US2305115A - Wheel dresser and method of dressing grinding wheels - Google Patents

Description

J. SNEED Dec. 15, 1942. 2,305,115

} WHEEL DRESSER AND METHOD OF DRESSING GRINDING WHEELS Filed March, 9, 1959 2 Sheets-Sheet 1 I! w W miwun I JQ/f/V sun-p BY z 7 ATTORN Dec. 15, 1942. J. SNEED 2,305,115

WHEEL DRESSER AND METHOD OF DRESSING GRINDING WHEELS 2 Sheets-Sheet. 2

Filed March 9, i959 INVENTO. JOHN s/vp v %V6r% ATTORNEYS Patented Dec. 15, 1942 WHEEL DRESSER- AND METI IOD 0F DRESS- ING GRINDING WHEELS John Sneed, Grosse Pointe Shores, Mich. Application March 9, 1939, Serial No. 289,797

-13 Claims. (Cl. 125- 11) This invention relates to a method and means of dressing grinding wheels and the tools and other instrumentalities to be shaped, dressed, or formed thereby or therewith. More especially this invention is concerned with obtaining great accuracy in dressing grinding wheels (and the corresponding work) in which theface of the wheel and/or work is to be given an irregular or non-lineal contour, along with a method and apparatus that is simple, economical, foolproof and inherently free from tendency to err or fall out of adjustment.

Prior to my invention, the art of dressin grinding wheels has been attended with elaborate mechanisms and costly methods of forming the working contour of the wheel to correspond to the desired or intended shape. Moreover, the

prior art left much to be desired in speed of operation, ease of re-dressing, accuracy of dressing and re-dressing, and general simplicity of means and economy of operation.

in the position and general relationship of parts in which the follower is given the contour cor responding to and aligned with the contour of the dressingtool.

In Figure 3 the parts illustrated in Figure 1 are shown in operative position with relation to a grinding wheel to be dressed along with appropriate supporting means for the wheel and illustrative clamping means and other support for the base block.

Figure 4 is an illustrative plan view showing on the left side the base block, carrier block with attendant devices and mechanisms in relation to a dressed grinding wheel, and showing on the right side an illustrative piece of. work to be dressed in its relation to the grinding wheel,

Within the objects of my invention I have sought to cure the defects existing in the art as mentioned in part above, and to provide a meth- 0d and means of dressing grinding wheels having low initial cost and unkeep, great and continuing accuracy inherent in its design and operation, ruggedness and simplicity in its construction and operation, all to the ultimate end of faithfully and consistently reproducing in and through the dressing of a grinding wheel the shape, contour or form sought to be transferred or reproduced in the tool or other instrumentality to be dressed or formed.

Other objects and advantages of my invention will become evident from the following description of a preferred form of an embodiment of my invention along with exemplary structures,

I.am aware of the disclosure and claims of U.- S. Patent No. 2,137,690 issued November 22; 1938,

and believe myself to be the first and original inventor of so much of the subject matter there- .of as I have disclosed and claimed in this application. I

In the drawings Figure 1 is a perspective view of the base block, template, carrier black, dressing tool and feeler or follower associated together in substantially the relation and position for the wheel dressing operation.

Figure 2 illustrates the carrier block with its dressing tool and feeler or follower beinz supported in relation to a second grinding wheel although out of contact therewith.

Figure 5 is a plan view of an illustrative form of' template.

Figure 6 is a partly diagrammatic elevation of the mechanism and parts illustrated in Figure 4 showing the relation thereof in a vertical plane.

To illustrate a manner in which my invention may be put into practice there is shown in. Figure 5 a template T, having formed on one face thereof between about the points ll-the irregular tion. In Figure 4, for example, it will be seen that I have shown the contour of the face of the grinding wheel precisely corresponding to the contour of the template T as a result of the operations to be described.

Preferably the template T comprises a thin hardened steel plate with its rearward edge a preferably ground straight and true to facilitate its support during the time its contour l-i is .being formed. The template also preferably has holes 3 by virtue of which it may be fixedly and rigidly secured to the base block B, see Figure 1,

by appropriate clamping means 5 which may conveniently comprise shouldered studs with clamping nuts arranged to hold the body of the template-preferably in a true'horizontal plane in fixed parallel relation to the block B. Preferably theholes 3 are equally spaced from the true back edge of-the template, and are pro!- erably aligned to be parallel with the adjacent verticalface of the ,base block B, whereby the template T or any other template having similar characteristics with the same or different contours l-l, will always take the same position with respect to the base block B, and the wheel to be dressed, for various or succeeding operations. Preferably the true back edge of the template will lie parallel to the axis of the wheel to be dressed.

The base block B is preferably formed of hardened steel or other substantial material, preferably having considerable mass and general ruggedness, whereby to be substantially unyielding and inflexible in its intended use and to present and maintain the bearing points or areas in its upper surface 6 in a true geometric plane surface throughout its operation in carrying out the objects of my invention. The upper surface 8 of the block B may preferably be grooved with relatively small longitudinally extending grooves 1,

, which are provided for the purpose-of preventing the collection or accumulation of dust. grit or any extraneous material on the supporting surface whereof, or more particularly on the portions of the surface lying in the plane which in the aggregate comprises the true planular supporting surface 6 of the top face of the block B.

Preferably the side faces of the block B lie at right angles to the top surface 6 and at the right angles to each other, and are grooved as at 8 for the reception of clamping blocks 9, see Figure 3, whereby the block B may be fixedly secured to any convenient support 10, which I have shown for illustration in Figure 3. By way of example of a useful size of the block B the same may conveniently be about 8" to 10" square and 2" or 3" deep where grinding wheels up to about 10" diameter are to be dressed. In the dressing of larger or smaller wheels, the block B and associated parts may, of course, be similarly enlarged or reduced in size, while retaining the characteristics essential to the practice of my inven tion.

Resting upon the block B as'shown in Figure 1 is a carrier block C, the size of which in relation to the block B and the wheel W may preferably be about that shown in the drawings. This block may be conveniently made of material similar to that of the block B, and preferably comprises a solid block of hardened steel of substantial mass and stability so as to be substantially unyielding and inflexible in carrying out its part in the practice of my invention. The weight of the block C is preferably sufficiently great to tend to cause the block C to lie firmly though slidably upon the block B and be inherently free from tendency to tip without manual support during dressing operations.

As shown in Figure 1 the block C receives and firmly embraces near its upper end a dressing tool D carrying a diamond or other hardened wheel cutter II. .The dressing tool D preferably has its body embraced within the body of the carrier block C in a relatively snugly fitting hole, wherein it may be fixedly though removably secured by such means as set screws l2. Embraced in a similar mannerwithin the carrier block C is a follower or feeler F similarly, securely and removably held in the lower portion of the carrier block C with the aid of set screws I3. The dressing tool D and the feeler F, as shown, are in vertical alignment, preferably both having their bodies lying parallel and in about the same vertical plane and extending at substantial right angles to the rear face H of the carrier block C, see also Figure 4. As shown in Figure 1' the carrier block C has its lower end supporting face l5, see also Figure 2, grooved with its grooves arranged to lie generally transverse to the grooves of the block B, so that the block C will rest upon the block B on a plurality of small surfaces defined by the respective grooves in the'respective blocks, which surfaces all lie in a true geometric plane. The supporting face l5 of the block C,

geometric plane disposed at right angles to the back face I of the carrier block C and thereby substantially parallel with the axis of the tools D 1 and F when the latter are securely embraced in the block C as shown. The other external configuration of the carrier block C'may preferably follow the shape disclosed in Figure 1 of the drawings, and is preferably of a size such that the carrier block C may be securely grasped by human hands, such as with the bases of the palms, and perhaps also the thumbs gripping the back face l4 thereof and-with the fingers extending around to engage the inclined faces 16 of the block C.

From the arrangement of parts shown in Figure 1 those skilled in the art will understand that if the horizontal contour of the follower F, or at least the portions thereof which contact the working contour I-l of the template T, comprise a true vertical projection of the contour of the cutting face of the dressing tool D, and if the plane of the top surface of the block B and the bottom surface l5 of the block C is truly horizontal as shown in Figure 3, and the cutting edge of the dressing tool D is addressed to the grinding wheel W in the horizontal plane of the axis thereof, that the contour Il' of the template I may be transferred to the face of the grinding wheel W by sliding the block C around on the upper face of the block B with the dressing tool 40. cutting thewheel W to the depth limited by contact between the feeler F with the template T. Since the block C rests freely upon the block B and the same may be moved around within a wide angle whereby to accommodate the follower 5 F to contact with the irregular contour l-I of the template T, and at the same time to present the'dressin tool D to the wheel in precisely the same relation that the feeler addresses the tem plate, that the wheel can be dressed to the same operative contour as that possessed by the template.

The first step, therefore, in the practice of my invention is to form the working end of the follower F to such a shape that when the parts are the follower F which contacts the contour ll of the template T will represent a true vertical projection of the outline of the cutting surface of the dressing tool D, i. e., in the form shown, the cutting surface of the diamond I i mounted therein. To this end I provide that the side wall I! of the block C lie at right angles to both the walls or surfaces H and I5 thereof and in the position shown in Figure 1 truly vertical and normal to the bottom surface l5 and the top surface 6 of the block B. I provide of course that the dressing tool D with its diamond or other cutter l I be such that it will cut or dress a grinding wheel, suchas a carborundum wheel, but that the follower F, preferably being of hardened steel, be of such material that it will be cut or abraded by the wheel or wheels which are capable of being cut or dressed by the dressing tool D.

. For the purpose of giving the desired contour 1 except for the grooves thereupon, comprises a assembled as shown in Figure 1, that portion of example,1ie horizontally, and which has a true rearward supporting edge 20 against which the face ll 'of the block C may rest, whereby to align the block C on the chuck I8 with corresponding points of the tool D and feeler F in a' plane normal to the axis of a grinding wheel 2| with respect to which the block C may be moved in parallel relationship. That is, the block C supported on the chuck l8 or otherwise, as may be more convenient, is so supported as to be moved back and. forth in true parallelism to a plane normal to the axis of the grinding wheel 2|, and is also so supported in the relationship shown in Figure- 2 that the .block as a whole maybe moved upwardly toward the axis of this grinding wheel in successive passes as the dressing tool D cuts into the-grinding wheel 2| to. give to the grinding wheel H a cutting'face or contour 22 which is a true complement of the cutting edge of the dressing -tool D. The follower F in the first instance is formed with its Working end of such shape 7 as to be greater in cross sectional area than the is brought into contact with the samepoint or.

zone of the wheel 2 I in the same horizontal motion. The result is that the dressing tool first takes a cut from the face of the grinding wheel, giving it the operative shape and contour of so much of the dressing tool as has contacted therewith, and then the wheel in turn imparts the same shape and contour to the working end of the follower F as it is passed under the wheel 2| in the same relation thereto as the dressing tool D. A plurality of such passes of the block C with relation to the wheel 2! and the gradual raising of the block C, while maintaining it in the same geometric relationship to the plane of the wheel 2|, ultimately imparts to the face of the wheel 2! the whole contour of the cutting edge of the dressing tool and the wheel in turn imparts to the follower F the same contour, i. e.

relation to the body of the work, and that the template may preferably be positioned on the base block B and both secured with the true back edge of the template parallel to the axis of the wheel W. Thus when the work is dressed by the dressed wheel it may be conveniently secured and moved with relation thereto in 8. corresponding manner to receive the contour from the dressed wheel in the same or other predetermined relation to its body or any trued surface thereof.

The wheel W may, of course, be rotatably supported and driven in a suitable frame 25 with appropriate bearings and otherwise, as iswell known in the art, whereby to cause it to revolve about a true axis, and the baseblock B, being secured to a support It, may be raised and low- I and partly by the grip of the hands which guide it, being held in firm; even sliding engagement between its lower face I5 and the top face 8, the latter being kept clean for obvious reasons, and being largely self-cleaning through the grooves in the surfaces thereof, whereby to maintain the cutting edge of the dressing tool in direct vertical alignmentwith the corresponding contour of the follower F. As viewed in Figure 4 the carrier block C may be slid directly toward the grinding 'wheel and template, and may be swung trans versely with respect to the plane of the grinding wheel more or less and as much as may be desired, consistent with presenting the cutting edge of the dressing tool to the working face of the wheel and at the same time presentingthe working end of the follower tool to the contour 5-8 of the template T. In this manner, as the carried blockC is slid over the face of the base block I B, and swung more or less transverselyof the a precise lineal projection of the cutting edge of the dressing tool at right angles to the plane of the bottom face l5 of the carrier block 0.

Thereafter the carrier block is ready, when positioned upon the base block B, asshown in Figures 1, 3, 4 and 6, to be used for dressing-the grinding wheel W. As shown particularly in Figures 3, 4 and 6 (having in mind that in Figure 3 the dressing tool is shown to the right of the wheel whereas in Figures 4 and 6 the dressing tool is shown to the left of the wheel) the base block the dressing tool D'has its cutting edge in and movable in the horizontal plane of the axis of I the undressed contour of the. face of the wheel.-

It will be understood as shown in Figure 4 that the contour l --l of the template should preferably be related to the body thereof in the same way that the contour is desired to be created in B is secured in such relation to the wheelW that.

plane of the grinding wheel, the whole cutting.

edge of the dressing tool may be advantageously employed to attack various faces of the grinding wheel in a manner which the operator may find most convenient. So long as the carrier block C'is caused to rest in firm engagement with the top face of the base block B, the cutting edge ot the dressing tool D cannot come nearer to the axis of the grinding wheel than a true vertical projection ofthe contour ll of the template T or any part thereof; and solong as the operv ator urges the carrier block toward the grinding wheel and urges the follower tool into contact with the template throughout the whole of the contour thereof, the wheel will be dressed until it corresponds precisely with the contour of the template. During this operation the cutting edge of the dressing tool always is constrained to I move in the plane of the axis of the wheel (pref erably a horizontal plane asshown) parallel to the plane of the contour l--l of the template and normal to the lines of projection of corresponding points in the cutting .edge of the tool D and feeler F. The finlshedsurfacebf the feeler F also moves in the plane of the contour I--l and parallel to the plane of motion of the cutting-edge of the dressing tool. v

At this-point it is well to mention that it is preferable that the cutting edge of the tool D and the corresponding face of the feeler F project not substantially farther from the face of the block C than is necessary for convenient address of the feeler to the contour of the template and the tool to the face of the wheel W. Thus the tendency of the tool to chatter or of the block C to tip or chatter relative to the block B is held to a minimum.

As shown by way of illustration in Figures 4 and 6, the work K may, when convenient, be secured in position on the same table ID as that which supports the block B, so that after the wheel W is fully or partly dressed the work may be passed under the wheel to be given the contour of the dressed face of the Wheel by various or repeated passes thereunder, and particularly in those instances where new work is being formed from fresh stock or a new wheel is being given its initial form, it may be desirable to do a rough job of wheel dressing and then a rough job of forming the work in the first instance. In such a case the'convenience of the arrangement shown in Figures 4 and 6 will be'apparent since after the rough dressing and grinding has been done, the dressing equipment, comprising the blocks B and C with attendant parts above described, may again be brought to operative relationship with the wheel W, and the wheel re-dressed or given a finished dressing before completing the grinding of the work K.

It will, of course, be appreciated that the wheel may be dressed and re-dressed any number of times by positioning the dressing equipment in the relationship indicated, and pro eding within the precepts described above. It will, of course, be understood that'whenever the contour of the dressing tool has become worn to an extent reater than the accuracy required in any particular job, that the carrier block C with its tools F and D may be returned to the operation described with reference to Figure 2, and the follower tool re-formed to the altered'contour of the dressing tool, whereupon the parts will be ready again for dressing the wheel W. It will be further understood that the template T and the contour thereof is only illustrative of any one of an infinite number of contours or templates that may be used, and that the fineness or narrowness sake of convenience of description as well as for ordinary convenience of operation and use, referred to the vertical alignment of the points of the dressing tool with corresponding points on the feeler, and have indicated that the cutting edge of the dressing tool should lie in the horizontal plane of the axis of the wheel to be dressed, as shown in Figs. 2 and 4, that the essential geometric relationship is not necessarily limited to the vertical or horizontal as such, but on the contrary those skilled in the art will understand that the essential angular relationships may be retained if the departure from strict verticalness and horizontalness is made without altering the essential geometrical relationship of the parts to each other. For example, in the arrangement shown in Figure 3 the top surface of the base block B might conceivably be inclined from the horizontal plane without departing from the precepts of my invention, so long as the plane of the surface 6 of the base block was parallel to the" axis of the wheel W and normal to the lines oftangency from the face of the grinding wheel, which met the grinding wheel at the point of contact with the dressing tool in the plane of the axis of the wheel W. As a result the point of contact between the dressing tool and the face of the grinding wheel would lie in a line tangent to the dressing wheel, which line would also include the corresponding point in the follower or feeler so that when the wheel was finally dressed such a line of tangency would also embrace the point of contact between the follower or feeler and the contour of the template; the contour of the template lying in a plane parallel to the top surface 6 of the block B, and also normal to the aforesaid line or lines of tangency to the face of the dressed wheel.

Similarly in the operation described with reference to Figure 2 the horizontal disposition and motion of the block C might be altered so long as the dressing tool and the feeler contacted the wheel 2| with corresponding points lying in the same plane normal to the axis of the wheel, and in the same line or lines tangent to the face of the wheel in said planes.

I have indicateda preference for using hardened steel in the blocks B and C because, among of the cutting edge of the diamond or other" dressing tool with the corresponding fineness or narrowness of the working end of the follower F should bear a reasonable relationship to the nature of the contour l-l or the like in the template, i. e. where simple curved contours are to be developed in the dressing wheel, and are pro vided in'the template, then, of course, coarser and more rounded dressing tools and followers or feelers will be adequate and desirable, but that where sharper angles are formed in the contour .of the template, the shape of the dressing tool and follower must be such as to facilitate the following of allof'the details of the contour of the template. In all events, the cutting point or cutting points of the dressing tool, being in direct lineal alignment, i. e. vertical alignment as shown herein, with corresponding points on the working end of the'follower, the contour of the template will be accurately translated into the dressed face of the wheel to be dressed, care being taken that the shape of the dressing tool and follower is such as to traverse and contact all essential points of the contour of the template.

Those skilled in the art will understand that while in the foregoing description I have, for the other reasons, I find that such material aids in maintaining the mutual bearing surfaces thereof true and free from scratches or abrasions for a longer life. Other materials may 'of course be used or found to have equal or better properties in respect to the practice of my invention. The magnetic properties of hardened steel permit the use of magnetic chucks, but of course the'practice of my invention would not be enhanced by binding the block C'to the block B by magnetism or otherwise to substantially interferewith the intended freedom of movement of one block relative to the other.

While I'have illustrated and described a preferred embodiment of the method and means to which my invention pertains, numerous modifications and changes therein will occur to those skilled in the art, all within the major precepts of my invention, and I do not care to be limited in the scope of my patent to the particular or preferred form herein disclosed, or in any manner other than by the claims appended hereto with their full range of equivalents to which they are entitled in view of the state of the A a desired contour comprising, a base member, a template mounted thereon having a predetermined contour at one edge to be reproduced in the peripheral face of a grinding wheel, a memher having a base adapted to be moved horizontally over the upper side of the first mentioned base in any direction, a holder for a wheel dressing implement connected with and located above said second base, aldressing implement carried by said holder, said wheel dressing implement being adapted to be pointed toward and located in the same horizontal plane with the axis about which the grinding wheel to be dressed rotates, and a feeler mounted on said second base adapted to be brought against the contour edge of said template, said feeler having a feeler contact point in direct vertical alignment with the point ofsaid dressing implement, and having sides corresponding to the sides of said dressing implement, as and'for the purposes specified.

2. Apparatus for shaping the peripheral face of a grinding wheel to a desired contourco'mprising, a base member having a'flat upper side, a template secured at the forward end and above said base member, said template being positioned 5: a carrier block slidably supported upon said base member and rigidly carrying a wheel dressing tool disposed to contact the wheel in the plane of theaxis thereof parallel to said first named plane and in any angular relation to the plane of the wheel, a template having a contour to be reproduced in said wheel fixedly secured to said base block with the contour lying in a plane parallel to the said first named plane and intersecting lines tangent to the finally dressed face of the wheel where said cutting tool has' contact therewith, and a feeler rigidly carried by said carrier block positioned to have contact with the contour of said template, all points in said feeler having contact with said contour lying in the projection of corresponding points in the cutting edge of said dressing tool at right angles to said plane. g

5. Grinding wheel dressing mechanism comprising in combination a base member adapted to be held in fixed relation to the axis of the wheel to be dressed and having a supporting surface adapted to cause a body moved thereover substantially horizontal and having its rear edge shaped in accordance with a desired contour to be given to a grinding wheel, a member including a base structure having a fiat under side adapted to be moved slidably over the upper side of the first base member in any direction, a post extending upwardly from said second base, a horizontally located dressing tool holder carried by said post and extending in a forward direction, a dressing tool carried by said holder, having a head with a dressing point at the front end thereof, a feeler adjustably mounted at the upper side of said. second base member having a pointed front end portion, the end of which is in direct vertical alignment with the front end of the dressing tool and having sides corresponding to the sides of said dressing tool, said feeler at its forward end being adapted to follow the contouor at the rear edge, of said template, as specified.

3. Apparatus for shaping grinding wheelsto a desired contour comprising, a base member having a flat horizontal upper side, a horizon-' tally'disposed template mounted on and above said base at one end thereof having an edge a fiatunder side adapted to rest upon and move over the upper side of the first mentioned base in any direction, a holder for a wheel dressing implement connected with and locatedabove said second base, a wheel dressing implement secured in said holder adapted to be pointed toward and have its dressing end lie in the same horizontal plane with the axis about which the grinding wheel to be dressed rotates, and a feeler-mounthorizontal plane'with said template, said feeler having a free end to bear against the template and follow the contour thereof, the point of ento be, held in fixed relation to the axis of the ed on-said second baseln substantially the same in sliding contact to move upon a plane disposed parallel of the axis of the wheel to be dressed, a carrier block of substantial mass slidably supported upon said base member and rigidly carrying a wheel dressing tool disposed in the plane of the axis of the wheel parallel to said first plane, a template having a contour to be reproduced in said wheel fixedly secured to said base block with the contour substantially parallel to the said plane and intersecting lines tangent to the finally dressed face of the wheel where said cutting tool has contact therewith, and a feelerrigidly carried by said carrier block positioned to have contact with the contour of said template along points in its working facewhich lie in lines embracing corresponding points on the cutting edge of said dressing tool and parallel to said tangents said carrier'block with its tool and feeler being free to assume any angle relative to the plane of the wheel to .be dressed and to swing about the point of contact of the tool with the wheel as a center.

6. Mechanism for the dressing of grinding which lie in corresponding points in the cutting edge ofvsaid dressing tool and the working face of said follower tool, said block also having a supporting face at right angles to said first named face and parallel to said lines, said dressing tool being hard enough to cut or abrade a grinding wheel, and said follower tool being of hardness such that it in turn .can be abraded by the same grinding wheel when supported on said second named surface and moved in said lines.

'7. A wheel dresser comprising a dressing tool having a cutting edge, means for supporting said tool in dressing relation to the face of said wheel in the plane of the axis thereof and permitting said' tool to swing about its cutting edge as a wheel to be dressed and having 'a supporting surface adapted to cause a body moved thereover in sliding contact to moveupon a plane parallel of the axis of the wheel to be dressed,

center, a template having the contour to which said wheel is to be dressed, and means havin a surface the replica of the cutting edge of said tool engageable with said contour mil-312E 25 with said first named means for restraining the cutting edge of. said dressing tool from movementbeyond said contour but in any angular relation thereto, said contour being disposed in the tangential projection of the face of said wheel from the point of contact of said dressing tool therewith.

'8. Apparatus according to claim 1 in which said bases have limited spaced areas of contact separated by grooves in the bearing surface of at least one of said members. I

9. Mechanism for dressing grinding wheels, comprising a carrier block rigidly supporting a wheel dressing tool and a follower or feeler and adapted to be moved so that the dressing tool will bear upon the face of the grinding wheel and the follower tool will bear upon a template having the contour to be developed'in said wheel, said carrier block having one substantially planar surface with its bearing points defining a plane normal to lines which lie in corresponding points in the cutting edge of said dressing tool and the working face of said follower toolfisaid block being movable on said plane to swing said tool about its cutting edge as a center and means for supporting said block for free movement in any direction on said plane.

10. The mechanism of claim 5 in which the contacting surfaces of said base member and carrier block are each grooved to-provide a plurality of narrow lands, those in the base member lying transversely to those in the carrier block when the carrier block is at a substantially neutral angular position relative to the plane of the wheel whereby the block is supported on the member at a plurality of points of limited area which have self cleaning sliding contact upon sliding movement of said block relative to said member.

11. The combination of claim 7 in which said. v first named means includes a fixed member having bearing surface exposed to grit and dust from said wheel and a moveable member slideably sup ported thereupon, and means for excluding such grit and dust from said surface.

12. The mechanism of claim 9 in which said carrier block has parts defining a plane disposed at right angles to said substantially planar surface and disposed oppositely of said dressing tool and follower.

13. The mechanism defined in claim 9 in combination with means for cleaning said last named means of extraneous matter coming in contact therewith.

JOHN SNEED.

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