US2649667A - Abrading device - Google Patents

Description

Aug. 25, 1953 CQOKE 2,649,667

ABRADING DEVICE Filed Aug. 25, 1952 3 Sheets-Sheet l INVENTOR FRANK COOKE.

ATTORNEY Aug. 25, 1953 F. CIOOKE 2,649,667

ABRADING DEVICE Filed Aug. 25, 1952 a Sheets-Sheet 2 l l /l/// mvau'roa.

COOKE.

AT TORNEI F. COOKE Aug. 25, 1953 ABRADING DEVICE 3 Sheets-Sheet 5 Filed Aug. 25, 1952 INVENTOK FRANK Cooxa Patented Aug. 25, 195? ABRADING DEVICE Frank Cooke, North Brookfield, Mass., assignor to American Optical Company, Southbridge, Mass., a voluntary association of Massachusetts Application August 25, 1952, Serial No. 306,161

7 Claims.

This invention relates to improvements in abrading devices and has particular reference to an improved ring-type abrading tool for use in generating curved surfaces on articles such as lens blanks.

One of the principal objects of this invention is to provide an abrading device embodying an annular abrading tool adapted to be mounted for rotatable engagement with an article such as a lens blank to be surfaced and adapted to abrade the article along a predetermined path of generation, said tool comprising a pair of concentric annular abrading members respectively carrying abrasive particles thereon of different abrading characteristics and disposed one within the other, with one of the members being adjustable with respect to the other member in a direction longitudinally of the tool, and with the adjoining sides of the members being provided throughout with interfitting irregularities of a controlled size and shape extending alternately across said path of generation.

Another object i to provide an abrading tool comprising a pair of concentric annular abrading members respectively carrying abrasive particles thereon of different abrading characteristics and disposed one within the other, with one of the members being adjustable with respect to the other member in a direction longitudinally of the tool, and with the adjoining sides of the members being provided throughout with interfitting scalloped shaped surfaces whereby portions of said respective surfaces will extend alternately across said path of generation at acute angles with respect to the tangent of said path of generation and thereby greatly improve the texture of the resulting abraded surface.

Another object is to provide an abrading tool of the above character wherein one of said annular abrading members will be provided with abrasive particle of relatively coarse mesh and the second annular abrading member will be provided with abrasive particles of relatively fine mesh whereby the abrading members may be used respectively for rough and fine grinding operations and wherein the sizes of the scallops and/or the thickness of the fine grinding member is increased relative to the size of the scallops and/or the thickness of the rough grinding member by an amount to substantially balance the wear and durability of said respective members.

Still another object is to provide an abrading tool of the above character embodyin annular abrading members one disposed within the other and provided with interfitting portions so arranged as to provide restricted opening between said annular members at spaced intervals throughout the path of generation to permit the fiow of a lubricant therethrough.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a front elevational view of abradin apparatus embodying the present invention;

Fig. 2 is a side elevational view of the apparatus shown in Fig. 1, part of which is taken in section along line 2-2 of Fig. 1;

Fig. 3 i an enlarged vertical sectional view taken substantially on line 3-3 of Fig. 2;

Fig. 4 is a horizontal sectional View substantially on line 44 of Fig. 3;

Fig. 5 is a fragmentary front elevational view partly in section illustrating the method of fine grinding a convex surface on a lens blank;

Fig. 6 is a view generally similar to Fig. 5 illustrating particularly the method of fine grinding a concave surface on a lens blank;

Fig. '7 is a perspective view of an abrading tool of the preferred type;

Fig. 8 is an enlarged face view of the abrading surface of the tool shown in Fig. '7

Figs. 9, l0, and 11 are enlarged face views similar to Fig. 8 illustrating modifications of the abrading tool;

Fig. 12 is a fragmentary side elevational view partly in section of the mechanism for adjusting the tool-carrying head; and

Fig. 13 is a diagrammatic illustration of the manner in which a scallop approaches an area of the article to be abraded.

Prior to the present invention, it has been the usual practice in the ophthalmic industry to form the desired curved surfaces on articles such as lens blanks by abrading methods requiring the use of at least two separate machines. One of the machines was provided with a rough abrading tool and an article such as a lens blank was previously secured to a suitable holder and then placed in this machine and the surface thereof was initially abraded to substantially the shape desired. The second machine was provided with a fine abrading tool. The article being surfaced was transferred from the first machine to the second machine and then abraded to substantially the final shape and surface texture desired by the fine abrading tool. Subsequent polishing operations provided the exact optical surface desired of the article.

It is apparent that with the foregoing method, two separate abrading machines were necessary for performing the individual rough and fine grinding operations, thus requiring considerable floor space, and possibly requiring different operators, with consequent added operational expense. Considerable time was involved in transferring the articles from one machine to another with the added existent possibility that the articles might be chipped or otherwise damaged or broken during transfer. In addition to the above undesirable features was the fact that resultant surfaces produced on the articles might be inaccurate due to human error in making the separate adjustments of the two machines. 'Also the possibilities for errors were increased due to the factthat the articles might be accidentally dislocated with respect to the holder when being transferred.

Therefore, it is one of the prime factors of the present invention to provide a single machine which will perform both the rough and fine grinding operations successively without necessity of transferring the articles 5 between operations, which machine requires but one setting and embodies a dual abrading tool which is comprised of individual portions for performing the respective rough and fine grinding operations as a substantially single continuous operation, thereby resulting in a decrease in the amount of floor space and operational expense required and also decreasing the possibilities of error.

Referring more particularly to the drawings wherein like characters of reference designate like parts throughout the several views, apparatus embodying the invention comprises a housing I5 having a head I8, pivotally attached thereto by a relatively large bearing 51. A. complete description of the machine is given in the specification forming a part of United States Patent No. 2,286,361 issued on June 16, 1942 to Lloyd W. Goddu. For details of the construction and operation of this machine which are not included in the following description, reference is made to the above-mentioned patent.

The housing I5 has a"work-supporting spindle I8 therein (Fig. 2), the spindle is being rotatably supported in a sleeve I9 longitudinally movable in a bearing ZIlcarried by a web. 2I internally of the housing I5. The spindle is supported adjacent its opposed ends by ball. bearings 22 and 23 mounted internally of shouldered recesses 2 3 and 25 in the sleeve I9. against longitudinal movement in the sleeve 59 by a plate 26 attached to the upper end of the sleeve I9. The plate 26 overlies the bearing 22 which, in turn, engages an annular shoulder 27-? formed on the spindle H8. The spindle I8 is provided with a reduced end portion'ZB fitted within a sleeve-like bearing member 29 supported internally of spaced ball bearings 30 and 3|. The end portion 28 is keyed to the sleeve-like bearing29 so as to rotate as an integral unit and to permit longitudinal movement of said end portion 28 internally of the sleeve-like bearing 29. The sleeve-like bearing 29 is held in desired relation with the ball bearings 36 and 3| by means of a lock nut 32 adjacent the upper end thereof and a plate 33 adjacent the lower end thereof, the plate. 33 being secured to the end of the bearing 20 by suitable. means such as screws 3%. The sleeve-like, bearing 29 has a drive pulley 35 secured thereto which is connected by a belt 35 and similar pulley 37 to a motor 38 supported internally of the hous'ing'l5. Operation of motor 38 will, through pulley 3 7-, belt 36, pulley r35 and sleeve-like bearing 29, cause rotation of the spindle I8.

The upper end of the spindle I8 is provided witha threaded portion 33- on which a shield M is mounted. The spindle, directly above the threaded portion 39, isjprovided with a tapered end 4| which is adapted to support a block adapter l2v which is retained thereon as by set screw 43 and which carries thereon a block 44.

A lens blank 85 or similar article to be abraded is secured to the block 43 by pitch 44a orother suitable adhesive and is thus adapted to be rotated The spindle i8 is held d I 4} with the block 44 and adapter 42 when the spindle I8 is rotated.

The'spindle, I8 and consequently theilens blank G5 are vertically adjustableby means of a rack 46 which is provided on the sleeve I9. The rack 46 has a portion extending into an elongated groove 4] formed in the bearing 20 and, through its engagement with the side walls of the groove 41, prevents rotation of'the sleeve I9. The rack is in'constah mesnwith a pinion 42 located within an enlarged portion 49 of the bearing 20. The pinion 4 8, is carried by a shaft 50 (Figs. 1 and 2) which extends through a side wall of the housing I5 and which has a hand lever 5i attached to its outer end. Manual rotation of the hand lever 5| will cause rotation ofthe pinion s8 and will consequently cause upward or downward; move ment of the'rack 46, sleeve Ia and spindle I 8-; and thus of the lens blank 45.* The upper end of the sleeve I9 is provided with a flange 52 which" is adapted to engage the upper endof the bearing ZIlfor limiting the extent of downward movement of the sleeve I9.

The motor 38 is so constructed as to also rotate a pulley 53 (Fig. 2) by means of a flexible shaft 5 connected thereto, the pulley 53 being rotatably secured internally of the upper end of the head It and being connected with a second spaced similarly mounted with pulley 53 and is keyed to a tool-supporting spindle 5? as illustrated at 53 whereby the spin-- dle 57 Will also rotate. The spindle 5'; is mounted in ball bearings 59- and Iijl which are supported,

in shouldered annular recesses 6i and @Zinternally ofa sleeve or quill 63 which is carried with: in a vertical bore (54 (Fig. 2) formed in a support 65 provided in the head IS; A collar 66 (FigQ3) is fixed to the spindle 57- adjacent the ball bearing as and thus prevents undesired raisingof the spindle 51 in the sleeve 63. A nut Si is, attached to one end of the spindletl adjacent the pulley 55 and prevents dislocation of the pulley, 55 which, in turn, rests againstball bearing 59. The nut 56. is threaded onto the threaded end 68 of the spindle. El-and thus isadapted to take up any looseness or end'thrust play is adjustable to compensate for wear of a dual abrading tool 69 carried by the opposed tapered,

end is of the spindle 51.

An annular hub H is provided witha tapered opening '32 therein which is adapted to, fit upon and frictionallybind with the tapered end lilzof the spindle 57. peripheral flange 73 to wise secured an aim forming a part of the dualtool ,ss.

flange 13 is positioned adiSe-like supporting member '35; having a hub fi'i} slidably positioned fill of the opening 12 within an enlarged portion in the annular hub 11. A second annular abrading member 18- is soldered'or otherwise attached to the disc-like member '15 and,closely interiits,

With the inner surface of theouter abrading member 14- (Figs. 3, 5, e and 7),

The inner abrading member 13 is adapted to,

move longitudinallyofthe tool. with respectto the outer abrading'member it. A stud 19 is threaded into the disc like member 75;and slidably extendsupwardly; into a bore 86' formed in the annular hub TH, (Figs. 3 and 5).- spring 8 I is positionedover. thestud iflbetween a head 82 on the endof the stud Wanda shoulderbore 80,

83 formed by a reducedlpor-tion of .the the spring 8! servingtacqntinuallymrgethe disc- I pulley 55; by a belt st. The second pulley 554s thus adapted to rotate,

in the spindle 51 and The, hub n .is.,provid d with a' which is soldered or other-- ulari abrading member 74' Vithin the A coiled like member I5 and inner abrading member I8 upwardly to a position where the abrading surface of the inner member will be retracted with respect to the abrading surface of the outer member l4.

To locate the inner abrading member in extended position beyond the plane of the abrading surface of the outer member 14, a shaft 84 is extended longitudinally through the spindle 51 and has its lower end positioned against the hub of the disc-like member I5. The upper end of the shaft 84 is located in a recess 05 provided therefor in the inner end of a knob 86 which is threadedly inserted in the adjacent portion of the housing 87 of the head I6 (Figs. 1, 2 and 3). Downward threading of the knob 86 will cause downward movement of the shaft 85 which, in

turn, will cause the disc-like member 75 and in-' ner abrading member If? to move downwardly against the inherent tension of spring 8!. Upon turning the knob 86 in the opposite direction, the spring BI will cause retraction of the inner abrading member l8 as described and will also simultaneously raise the shaft 84.

The knob 85 is provided thereon with a cylinder 88 having graduations 89 thereon (Fig. l) which are adapted to register with an indicator 95 secured to the housing 8! whereby the extent of movement of the inner abrading member l3 with respect to outer member is is visually indicated.

In accordance with this invention, the abrading surfaces of each of the annular abrading members I l and 78 are provided with particles of abrading material such as diamonds or other suitable material, the inner member 18 preferably being of relatively coarse mesh for the rough grinding of the lens blank and the outer member M preferably being of relatively fine mesh for the fine grinding.

To position the tool 69 and lens blank in abrading relation, the hand lever 5I is manually operated to raise the work-supporting spindle I8 and, consequently, the lens blank 45 into position against the tool 69. Means such as a weight 9| (Fig. 1) suspended by a cord 92 which is wound on a pulley 93 carried by the shaft is provided for continually urging the spindle I8 and lens blank upwardly as the surface of the lens blank 45 is being abraded by the tool 09. However, in order to limit the extent of the upward movement of the spindle I8 and consequently to control the depth of the cut and amount of material being removed from the surface of the lens blank 55, an elongated threaded stop member 54 is carried by a support 95 carried by the head I6 and is adapted to be engaged at one end by the flange 52 on the sleeve I9 as the spindle I8 moves upwardly. Adjustment is accomplished by threading the stop member 94 upwardly or downwardly by means of the knob 96 provided therefor on the opposite end of the member 94.

In order to provide the desired surface curvature on the lens blank 45, the head I6 is adapted to be adjusted about the axis of the bearing I! and locked in adjusted angular position by means of a screw device 91 as described in the aforementioned Goddu patent. The head I0 is thus adapted to be tilted to a desired position determined by a suitable degree scale 98 and Vernier 99 (Fig. l).

It is to be understood that the head I6, whe pivoting on the bearing I I, pivots about an effective center I00 which is preferably located in axial alignment with the center of curvature of the abrading surfaces of the abrading members I4 and F8. The center I00is also located on the axis of rotation AA of the lens blank (Figs. 3, 5 and 6). The pitch diameter ofthe tool 69 is slightly larger than the radius of the lens blank 45. Thus, with the head I6 tilted as described and the tool 69 in engagement with the lens blank 45, the motor 38 may be operated torotate both the tool and lens blank and cause the tool 69 to abrade the surface of the lens blank 45.

The lens blank'45 will be abraded by the tool 59 along a predetermined substantially annular path or line of generation. This path is indicated in Figs. 8, 9, 10, 11 and 13 as line IOI, which line may be a continuation of any point in the path forming a circle having a center I03 on the axis of the tool.

In accordance with this invention, however, the meeting or adjoining sides of the annular abrading members 14 and 18 are provided with a plurality of closely interfitting irregularities preferably in the form of scallops 14a and 18a respectively (Figs. 7 and 8). The scallops 14a, on the outer abrading member I4 extend inwardly to overlie the line of generation IOI and the scallops 1811 on the inner abrading member 18 extend outwardly to overlie the line of generation IIII, the recesses between the scallops on the respective members, however, being disposed on the same side of the line of generation IOI as the major portion of the members. Thus, in face elevation the line of juncture between the abrading members 14 and 18 appears, as shown in Figs. 8 through 11, as an endless serpentine line weaving continuously alternately back and forth across the line of generation I0 I.

In setting up the device for rough grinding of the lens blank 45, the inner abrading member I8 is extended slightly beyond the abrading surface of the outer member 14. The inner member 18 carries the coarse particles of abrading material and is illustrated in Fig. '7 in greatly exaggerated extended relation to the outer fine grinding member I4. Thus, with the inner rough grinding member I8 extended, this will cause the center of curvature of the abrading surface thereof to move slightly in a direction toward the lens blank 45 to the position indicated by numeral I02 in Fig. 3. This center I02 will also be displaced slightly with respect to the axis line AA. Such displacement of the center I02 of the abrading surface of the rough grinding member will, however, cause no resultant error since after the rough grinding operation has been completed, the inner member 18 will be retracted and the outer fine grinding member I4 will provide the lens blank 45 with the exact surface curvature required. The center I00 of the fixed abrading member It will remain on the axis line A-A and will still'be concentric with the axis about which the head I6 is adjusted. Thi operation will compensate for any error introduced by displacement of the center I02 of the inner tool 13.

One feature of the tool construction which is especially desirable is the fact that the fine grinding member 14 is mounted on relatively fixed supporting means while the rough grinding member I8 is mounted on the movable parts which would be most likely to become loose or slack. However, since the fine grinding member 14 is relatively fixed, any error caused by looseness of the parts supporting the inner rough grinding member 18 will be compensated for. This, of course, would not be true if the rough and fine grinding members were reversed.

apogee? Another-desirable-result of providing the composite toolwith-abrading members'l land 18 constructed as described is that 'allof the abrading of the individualinner=and-outer members will be performed along-a single path of generation without requiring any adjustment other than the slight longitudinal adjustment of the rough grinding memberto extend or retract its abrading surface as described with respect to the-surface of the fine grinding-member.

An additional and particularly desirable accomplishment of an abrading tool constructed and arranged in accordance with this invention is that the resultantsurfacesformed on the lens blanks are of improved texture. This is believed to beaccomplished by the provision of the seallops Ma. and 18a which are preferably shaped as curved segments. It--wi11:beapparent that as the tool is rotated, while in engagement with the lens blank, the 'le'adingedge of theact'ual effective abrading :area preach scallop T4a'and18a will approach a particular surface area, to be abraded at an acute angle to :theitangentp'fthe line or .path .of generation at the :point at which the leadingedge of :theabrading area crosses the line or pathof generation. "This is illustrated in Fig. 13 wherein theileadingedge 1240mm abrading portionofaiscalloprlliais shown as being at an acute angleXto the tangent "I25 of the path or line'of generation llll at the'pointat which said leadingedge 1240f the scallop 78a crosses saidpath-orline'of generation I'D-I.

.This wilLcauseiasshearing action to take place inremoving. materialsfro'm :the len blank rather than therchiselingaction-whichwould occur if the advancing edge of thecuttingarea was-disposed :in 5113131119 normal :to -tthe tangent of the line :of generation. Thu-s, vvh'en the abrading areas of :the 'tool .iapproach the material to be removed :in .the above manner and continue to slither across-"the surface, the resultant surface textureisof h'igh quality.

Although the :foregoing description refers particularly topthe formation of a convex surfaceon alens blankAi-thisinvntion readily adapted b to iforming concave surfaces. Referring to Fig.

6, a lens blankifl lisattached to a concave block l'flfi byaglayeriofpitchzflw. The head! 6 is't'il'ted about the 'center 100 in the opposite direction which will-angle thertool B9 soz-that the abrading surface f :thefi-ne grinding member 14 at the "point whichdstontheiaxisiline AA about which the work rotates; will be lower thanthe diametrically :opposed abrading surface thereof by an amountrinaccordance with'the curvature to be 7 generated. and theangle of tilt ofthe'head as in- -dicated on sca1e:98,

The present invention is adapted to the use of tools 69 of various diameters and, therefore, meansis provided for adjusting the tool-support- ,ing devicesoas to position the center I 00 about which the head is tilted on axisline A-A. To accomplish this,:th'e top of the housing 5 isprovided with "slid'eways ill! on which a table I08 carrying the head IS-is adapted to move in a "horizontalgdirection (Figs. 2 and 12). The table .108 carries :on its underside a drive shaft "F09 which isjournalediin depending portions 1 Ill-of the table m8 .andis; threaded through :an upwardly *extend-ingportion H .o'r" .the housing 15. A I

hand-crank -H Z ;is,-mounted onthe outer end-of the shaft 4-0.9. :manual rotation of the crank "l I 2 will cause rotation of the shaft- 4 09 and v will consequently'moverthe table MB and head 116 along the slidewayszifl l. 'Ihe aadjustment is visuallyindicated by a pointer 'I I 3 on the side of the table I08 which registers with a scale on the side of the housing [5.

It is known that a fine grinding tool of the presently described type will wear somewhat faster than a rough grinding tool. Therefore, it is sometimes advisable to form the tool as shown in Fig. 10 wherein the outer fine grinding member I M with scallops H5 which have a longer contact area along the line of generation it]! than the scallops H6 on the inner rough grinding member Ill.

Another modification is shown in Fig. 11 wherein the outer fine grinding member I I8 is thicker than the inner rough grinding member i 19 which will also compensate for additional wear of the fine grinding member H8.

In instances wherein it is desired to supply an oil or coolant as a lubricant through the abrading tool, supply means such as described in the aforementioned Goddu patent may be connected with a longitudinal bore H9 (Fig. 5) in the tool adjusting shaft 8 whereby the lubricant may flow downwardly therethrough and through bores :20 and i2! in the hub extension '16 into the space 522 between the upper surface of the disc-like member and annular hub it. Then the lubricant can flow through one or more spaces 523 (Fig. 9) formed adjacent the ends of the scallops 74a and 78a to the surfaces of the abrading members 76 and 78 and surface of the lens blank 45.

It is particularly pointed out that a machine constructed and arranged according to the foregoing description will perform both rough and fine grinding operations successively in one substantially single continuous operation without necessity of moving the articles between the rough and fine grinding operations and with only one adjustment or setting up operation being required.

From the foregoing description, it will be apparent that all of the objects and advantages of the invention have been accomplished. However, it will also be apparent that many changes may be made in the arrangement of parts shown and described without departing from the spirit of the invention. Therefore, it is to be understood that all matter shown or described should be interpreted as illustrative and not in a limitmg sense.

I claim:

I. An abrading tool of the character described comprising a pair of annular abrading elements having different abrading characteristics and disposed one within the other, said abrading elements being coaxial with one thereof being retractable and extendible with respect to the other, and said abrading elements being provided on their adjoining sides with interfitting scallops extending alternately across .a given path .of

generation whereby said respective elements at a given angular position of adjustment of the tool are capable of generating curved surfaces of substantially equal radii.

2.. An abrading tool for abrading the surface "of an article along a predetermined path of gensaid abrading members being disposed in coaxial intimate relationone within the other and being provided on their adjoining sides with interfitting "scallops extending alternately across said path of generation, and means for moving one of said supporting members longitudinally of its axis to extend or retract the abrading surface of the annular abrading member thereon axially relative to the abrading surface of the other annular abrading member whereby said abrading members may be selectively extended into abrading position.

3. An abrading tool for generating a curved surface on an article comprising a pair of coaxial supporting member disposed telescopically one within the other and each having thereon an annular abrading member, said abrading members being disposed in intimate relation one within the other, said supporting members adapted to be rotated simultaneously about their common axis to cause said abrading members to individually abrade an article when selectively located in engagement therewith, the adjoining sides of said abrading members being provided with interfitting scallops extending alternately across a given path of generation whereby as the tool is rotated the abrading portions of the scallops of the selected annular abrading member will abrade the surface of said article when positioned thereupon.

4. An abrading tool for generating a curved surface on an article comprising a pair of annular abrading elements having different abrading characteristics and disposed one within the other, i

said abrading elements being coaxial and simultaneously rotatable with one thereof being retractable and extendible with respect to the other, and said abrading elements being provided on their adjoining sides with interfitting scallops extending alternately across a given path of generation whereby said respective elements at a given angular position of adjustment of the tool are capable of generating curved surfaces of substantially equal radii, said scallops being of controlled curved contour shapes whereby as the tool is rotated the leading edges of the abrading portions of the scallops will approach the surface area to be abraded at an acute angle to the tangent of said path of generation at the point at which said leading edges cross said path of generation.

5. An abrading tool for generating a curved surface on an article comprising a pair of coaxial supporting members disposed telescopically one within the other and each having thereon an annular abrading member, said abrading members being disposed in intimate relation one within the other, said supporting members adapted to be rotated simultaneously about their common axis to cause said abrading members to individually abrade an article when selectively located in engagement therewith, the adjoining sides of said abrading members being provided with interfitting scallops extending alternately across a given path of generation whereby as the tool is rotated the abrading portions of the scallops of the selected annular abrading member will abrade the surface of said article when positioned thereupon, said scallops being of controlled curved contour shapes whereby as the tool is rotated the leading edges of the abrading portions of the scallops will approach the surface area to be abraded at an arcuate angle to the tangent of said path of generation at the point at which said leading edges cross said path of generation.

6. An abrading tool for generating a curved surface on an article comprising a sleeve having a first annular abrading member on one end thereof, a support within said sleeve having a second annular abrading member thereon disposed in intimate relation with the inner side of said first annular abrading member, said support being coaxial with said sleeve and adapted to be rotated simultaneously therewith about their common axis to cause said abrading members thereon to abrade an article when in engagement therewith, means for moving said support longitudinally of said axis to retract or extend the abrading surface of said second annular abrading member axially relative to the abrading surface of said first annular abrading member whereby said abrading surfaces may be selectively extended into abrading position, the adjoining sides of said abrading members being provided with irregular contours in the form of interfitting scallops extending alternately across a given path of generation, said scallops being of curved contour shape whereby as the tool is rotated the leading edges of the abrading portions of the scallops will approach the surface area to be abraded at an acute angle to the tangent of said path of generation at the point at which said leading edges cross said path of generation.

7. In; abrading apparatus of the character described embodying a base having a work supporting device thereon for rotatably supporting an article to be abraded and a tool supporting head for rotatably carrying a tool for abrading said article, an abrading tool carried by said head comprising a sleeve having a first annular abrading member on one end thereof, a support within said sleeve having a second annular abrading member thereon disposed in intimate relation with the inner side of said first annular abrading member, said support being coaxial with said sleeve and adapted to be rotated simultaneously therewith about their common axis to cause said abrading members thereon to abrade an article when in engagement therewith, means for moving said support longitudinally of said axis to retract or extend the abrading surface of said second annular abrading member axially relative to the abrading surface of said first annular abrading member whereby said abrading surfaces may be selectively extended into abrading position, the adjoining sides of said abrading members being provided with irregular contours in the form of interfitting scallops extending alternately across a given line of generation, said scallops being of curved contour shape whereby as the tool is rotated the leading edges of the abrading portions of the scallops will approach the surface area to be abraded at an acute angle to the tangent of said line of generation at the point at which said leading edges cross said line of generation.

FRANK COO-KE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 108,822 Pitkin et a1. Nov. 1, 1870 1,828,663 Jopp Oct. 20, 1931 2,600,815 Turner June 1'7, 1952 FOREIGN PATENTS Number Country Date 199,312 Germany Nov. 10, 1907 562,128 Germany Nov. 3, 1931 247,293 Switzerland Nov. 17, 1947 804,762 Germany Apr. 30, 1951

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