US2861400A - Machine for grinding parallel surfaces - Google Patents

Description

Nov. 25, 1958 7 Sheets-Sheet 1 Filed Nov. 28, 1955 a H @w m .M\ 0 \x mfi w L Nov. 25, 1958 Filed Nov. 28, 1955 R. G. ELLIS 2,861,400

MACHINE FOR GRINDING PARALLEL SURFACES 7 Sheets-Sheet 2 INVENTOR. F0 770 &= 1/27 s.

Nov. 25, 1958 R. G. ELLIS,

MACHINE FOR GRINDING PARALLEL SURFACES 7 Sheets-Sheet 3 Filed Nov. 28, 1955 INVENTOR.

F0770 IZ/zlsc M J1 TOWNEV-$ NOV. 25, 1958 ELLIS 2,861,400

MACHINE FOR GRINDING PARALLEL SURFACES Filed Nov. 28, 1955 7 Sheets-Sheet 4 INVENTOR. E .4=. F0770 d Z'Z'Zzls'.

Nov. 25,- 1958 R. G. ELLIS MACHINE FOR GRINDING PARALLEL SURFACES 7 Sheets-Sheet 5 Filed Nov. 28, 1955 INVENTOR. 5 [7778.

*Bha fay/2504s? Nov. 25, 1958 R. G. ELLIS 2,861,400

MACHINE FOR GRINDING PARALLEL SURFACES Filed Nov. 28, 1955 '7 Sheets-Sheet 6 INVENTOR. 307% & ZIZZzLs.

Nov. 25, 1958 R. G. ELLIS 2,851,400

MACHINE FOR GRINDING PARALLEL SURFACES Filed Nov. 28, 1955 7 Sheets-Sheet 7 INVENT R. I] z i Em: v.

FNZ/ST United States '7 Rollo G. Ellis, Royal Oak, MiClL, assignor to Micromatic Hone Corporation, Detroit, Mich, a corporation of Michigan Application November 28, 1955, Serial No. 549,427

18 Claims. (Cl. 51-118) This invention relates to improved flat surface lappers and more particularly to flat surface lappers of the opposed wheel type for grinding opposed faces on workpieces.

In contemporary abrading and lapping machines, as the condition of the wheels or laps deteriorate due to wear, they do so irregularly, resulting in poor quality of output. Uniformity of workpiece size and maintenance of parallelism between the opposed faces of the workpiece have heretofore been exceedingly difficult to achieve in a single operation. It is typical of present-day lappers to have a high percentage of rejects since it is not uncommon for workpieces to be permanently ruined due to their being machined undersize or with their opposed faces nonparallel.

This nonuniform wear, which has been characteristic of conventional lapping machines, lowers production efficiency in that frequent interruption is required for supplemental dressing of the abrading wheels. Frequent shut-downs for supplemental dressing of the abrading wheels are costly as they greatly reduce the production throughput of the machine. Moreover, with each supplemental dressing, the rather expensive abrading wheels are deeply cut by the diamond dressers, thus sacrificing a good deal of the working surfaces of the abrading wheels.

With the foregoing in view, it is an important object of the present invention to provide a fiat surface lapper which is economical in operation and wherein the production efliciency of the same is greatly enhanced.

It is another object of the present invention to provide a flat surface lapper wherein uniformity of work size and parallelism between opposed faces of workpieces are consistently maintained.

It is another object of the present invention to provide a flat surface lapper which automatically compensates itself for the condition of its abrading wheels to maintain a predetermined gap therebetween.

It is another object of the present invention to provide a fiat surface lapper which is responsive to the precision quality of its output and which exercisesa control over the condition affecting said quality.

It is another object of the present invention to provide a fiat surface lapper wherein workpieces are fed between the abrading disks in a novel manner so as to produce a characteristic wheel wear which maintains parallelism between the abrading disks throughout the life of the same.

It is another object of the present invention to provide a fiat surface lapper wherein workpieces are fed between the abrading disks in a novel manner so as to establish annular zones of abrasion between the working surfaces of the abrading wheels.

It is another object of the present invention to provide 7 *atent abrading wheels which alternate in the type of work burden said annular zones assume.

It is another object of the present invention to provide a flat surface lapper wherein workpieces are fed between the abrading disks in a novel manner so as to uniformly distribute the abrading effort over the entire working surfaces of the abrading wheels, virtually eliminating the need for supplemental dressing. 7

Other objects and advantages of the present invention will be apparent during the course of the following description, taken in conjunction with the accompanying drawings, forming a part of the specification, and in which like numerals are employed to designate like parts throughout the same:

Figure 1 is a plan view of the machine of the present invention;

Fig. 2 is a right side elevation of the machine shown in Fig. 1;

Fig. 3 is a front elevation of the machine of Fig. 1;

Fig. 4 is a vertical section taken along the line 4-4 of j Fig. 1 with the feed disk swung out of. position;

Fig. 5 is a fragmentary left side elevation of the machine shown in Fig. 3 with certain parts removed for the purposes of clarity; v V

Fig. 6 is a sectional view taken along the line 6 -6 of Fig. 5; a

Fig. 7 is a view taken along the line 7-7 of Fig. 1,

partly in section;

Fig. 8 is an enlarged plan view showing in detail certain portions of the machine shown in Fig. 1;

Fig. 9 is an elevation partly in section of certain parts of Fig. 8 viewed as shown by the line 99 of Fig.- 8; Fig. 10 is a vertical section taken along the line 10-10 of Fig. 8; and 7 Fig. 11 is an elevation of certain parts of Fig. 8 viewe as shown by the lines 1111 of Fig. 8.

Referring now to the drawings, wherein for the purpose manner for reasons which will appear more fully herein-' after. Disposed above feed disk 17 is a feed chute, designated generally at 21, which conveys workpieces 23 into the workpiece-receiving apertures 19 on feed disk 17.

After the workpieces 23 are placed in the workpiece receiving apertures 19 on the feed disk 17, they are conveyed in the direction of the arrow into the working gap 25 (Fig. 4) between an upper abrading disk 27 and a lower abrading disk 29. In passing between the upper abrading disk 27 and the lower abrading disk 29, the workpieces 23 have their opposed faces ground to a predetermined size between their time of entry into and exit from the working gap 25. Upon their exit from the working gap .they pass between a sensing means, for example, a thickness gauge 31, whose function will be hereinafter more particularly described. Those workpieces which meet the standards predeterminedly set for the machine are dropped to a con-v veyor belt 33 disposed beneath the feed disk 17 whereby they are conveyed to a handling or take-.offstation. Those a which are too thick to meet the predetermined standards are required'to repeat their passage through the Working gap for additional stock removal;

Patented Nov. 25, 1958 Rotary motion of abrading disks The abrading disks 27 and are driven in the same direction of rotary movement as thatof feed disk 17. Their motion is continuous, but their relative speeds difier slightly so as to permit a, gradual and continual change of orientation between the upper and lower work surfaces of the abrading disks. The drive for the abrading disks is a motor 35. The motr'35, through V-belts and pulleys, drives-a shaft 37 which is the common drive shaft for rotating the upper and lower abrading disks. The lowerabrading disk 29 is rotated from the shaft 37 by thematingofa worm screw 39 secured to the shaft 37 with a worm gear'41, The worm gear 41 is secured to a base member 3 upon which, is affixed a backing plate 55 for the lowerabrading disk 29.. vThehase member 53 is rotatably carried on a thrust ring;57z and a stationary thrust -s eat;59 The assembly. Of the lower abrading disk 29 and the base member 53 are adapted to rotate about a stationary cente post 651 bymeans of bearing sleeves 61 and 63.

Also driven from the shaft 37 by a belt 43 and a pulley 45 (Fig. 3 is a shaft 47 which rotates the upper abrading wheel 27 through a worm screw 49, and a worm gear 51 (Fig 4). The upper abrading disk 27 is carried by ashaft 67 through a flange assembly 69 at its upper end, which, in turn, is secured to a backing-plate 71. The

shaft 67'issplined at its lower endso that it may assume different vertical positions and still be rotated by the worm-gear 51.

Vertical motion of the abradinig wheels Relatively speedy adjustment in a vertical direction of the upper abrading-disk 27 'i sprovided by a piniongear 73 which mates with a toothed segment 75 of an outer cylindrical spindle 77 disposed aboututhe shaft 67 for moving the same in a vertical direction. Motion is-imparted to the'pinion gear 7,3, through :arack 79 which moves backward and forwardjinahorizontal direction. Therack 79 is connected to a piston rod 81 of'a fluidactuated cylinder 83 aflixed onanyupfight side of the machinebaselia. Backwardandforward motion of the rack 79 causes the pinion 73 to rotate onits axis and raise or lower the cylindrical spindle 77 a and its upper abrading disk 27 in response to the movement of the PiStQnrod 81 of the fluid-actuated cylinder 83. This provides relatively fast movement of the upper abrading disk 27 toward'or away from thelower abrading disk 29, for various-purposes, for example, for replacing the abrading disks, for setup to accommodate workpieces of differentsize for a new operationand for initial dressing. Provision is also made for line adjustment of the gap between the abrading wheels. This maybe done manually if; desired, although it is a special feature of the present invention to provide for automatic adjustment of the gap between the abrading wheels to compensate for continual wear of the same during use. To accomplish this fine adjustmentof the gap between the abrading wheels, there are'arranged rollers 85 at the lower extremity of the cylindrical member 77. The rollers 35 ride on a wedge 87 which constitutes anadjustable dimensional stop for regulating the gap betweentheworking surfaces of the abrading wheels. Figs. 5 and 6 show inmore detail how the actuation of the wedge 87 is accomplished. The wedge 87 is supportedfrom below by the rollers 89 and. may be actuated laterally in increments by a screw 91 which is threadably engaged with thewedge 87. The screw 91 maybe manually rotated by a handwheel 93 so asto either raise or lower the upper abrading disk' de pending upon the direction in which the handwheel 931s rotated. g I

Automatic actuating means are'also provided for lateral adjustment of the wedge 87; This consists'of a gear 7 motor 95 which rotatably drives a pinion 97 which, in turn, meshes with a gear 99 causing the latter to rotate continually so long as the motor 95 is in operation. A gear 101, however, which meshes with a gear 103, the latter ultimately turning the screw 91, does not rotate together with the gear 99 except when a magnetic clutch 165 is energized. The operation of the magnetic clutch is controlled by an electrical switch 107 (Fig. 5). The switch 107, in turn, is opened and closed by a cam 109 mounted on the shaft of the gear motor 95. The cam 109 is provided with an adjustable lobe 111 which periodically releases a follower roll 113' to close the switch 167. While the follower roll 113 of the switch 107 is released by the lobe 111 of the cam 109 during each revolution of the cam, the magnetic clutch is momentarily engaged by conduction of electrical current through collector rings 115, providing that the gap between the abrading wheels requires adjustment for correction of wheel wear. The sensing means to determine whether the abrading wheels need vertical adjustment for wheel wear will be hereinafter more particularly described, along with its relation to the above-described means for fine adjustment vertically of the gap between the abrading wheels. If no correction is needed, as determined by the sensing means to be hereinafter described, no current will flow through the collector rings 115 even though the switch 107 is closed by the lobe 111 on the cam 109. Hence, the magnetic clutch will not be engaged unless a correction for wheel wear is required.

Intermittent feed motion The feed diskfor introducing the workpieces between the working surfaces of the abrading wheels may be driven continuously, although it is preferred that an intermittent feed motion be employed. Intermittent indexingof the workpieces substantially eliminates the need for supplemental dressing of the abrading wheels. It has been found that by rapidly moving the workpieces through successive positions of rest, the abrading wheels initially wear to a state of stability and thereafter the wear on the abrading wheels becomes uniform. Because the bulk of work by the abrading effort is performed during stages of rest, wear of the abrading wheels correlates to the dimensional change in the workpieces as they proceed through the operaing cycle. The abrading wheels will inherently acclimate themselves to a. steady state in each annular zone of abrasion where a workpiece is being ground. With a controlled time of dwell of each workpiece in each zone of contact, and \vitha rapid transference of the workpieces through successive zones, the

working surfaces of the abrading wheels adjust to a steady state in each zone of abrasion which produces a characteristic wheel wear so as to maintain the working surfaces parallel throughout the life of the abrading disks as will be developed in detail hereinafter. It is the above type of motion which the term intermittently index, as used in the appended claims, is intended to mean, viz., a progressive advance of the workpieces wherein they are hesitated in a position of rest and thereafter rapidly transferred to a new position of rest.

Before description of the intermittent feed employed with the device of the present invention, a special feature will be noted concerning the novel means of feeding the workpieces between the working surfaces of the abrading wheels. Reference is made to Fig. 1, wherein a number of annular zones of abrasion established during the machining operation are represented by mean radii y, y, y", x, x and x. Although all stations of the feed disk lying between the abrading wheels contain a workpiece, no two of them occupy the same annular zone of abrasion in the smi ing surf es of the bradin wheels. Mean radius y; for example, passes through the center of workpiece 23a at the exit side of the feed disk and yet passes through the mid-point of the space between the workpieces 23b land 23c on the entrance side of the feed disk. Similarly,

mean radius y passes through the center of a workpiece at the exit side and passes through the mid-point of. the

space between two workpieces on the entrance side, and- By disposing the workpieces in such array, there are established annular zones of abrasion in the working surfaces of the abrading wheels, each of which does work on a different workpiece at one time and each of the workpieces in succession. The annular zones of abrasion in the working surfaces of the abrading wheels will acclimate themselves to a steady state of wear so that the abrading disks are maintained parallel because of the amount of work performed in each zone and the disposition of the several zones. The centers of the annular zones through the peculiar disposition of the workreceiving apertures in the feed disk will be alternately disposed through the cross-section of the abrading wheels. That is to say, the centers of the annular zones, which contain workpieces on the entrance side of the feed disk, will alternate with the centers of the annular zones which contain workpieces on the exit side of the feed disk. Since the workpieces on the exit side of the feed disk are in a slightly greater state of completion than those on the entrance side of the feed disk, the amount of wear in the annular zones on the exit side of the feed disk will be successively slightly less than the amount of wear in the annular zones on the entrance side of the feed disk. This will result in annular zones of alternately greater and less wear throughout the cross-section of the abrading wheels, though the variations in the amount of wear in each annular zone, of course, will be very small, depending upon how much work is done upon the workpieces from the time of their entry until the time of their exit. Nonetheless, the disposition of these annular zones of abrasion h ing lternately slightly greater and slightly less wear throughout the cross-section of the abrading wheels results in maintenance of superior parallelism be tween the abrading wheels. This superior parallelism imparted to the abrading wheels by the characteristic wear thereof is thought to account for the unexpected result that the need for supplemental dressing of the abrading wheels is eliminated. Furthermore, this superior parallelism maintained in the abrading wheels effects a precision type of grinding whereby workpieces are produced having consistently parallel opposed faces and which are of uniform size.

As has been previously pointed out, the use of an intermittent feed mechanism for the rapid transference of the workpieces through successive positions of rest causes the abrading wheels initially to wear toward a state of stability and uniformly thereafter. Intermittent indexing of the workpieces through the working gap is a substantial factor among others contributing toward elimination of the need for supplemental dressing of the abrading disks.

The intermittent feed mechanism will now be described. The first workpiece, having been rapidly indexed to position by feed disk 17, is operated upon by the abrading wheels While the workpiece is static therebetween. After a sufficient time interval, the workpiece is rapidly in- 6 dexed to its succeeding position. During each such index, a preceding workpiece is moved into the zone which has been vacated by the succeeding one. Eventually all of the zones contain a workpiece, each in a slightly more advanced state toward completion than the preceding one. The mechanism for intermittently indexing the feed disk, i. e., causing intermittent movements with relatively long periods of rest between such movements is accomplished by well-known means, such as the Geneva movement shown in Fig. 7. A Geneva cam wheel 117 is keyed to a shaft 119 on the lower portion of which is secured a pinion gear 121 which meshes with a gear 123 on the lower end of a feed disk spindle 125. The feed disk spindle 125 is adapted to rotate about its vertical axis in accordance with actuation from the Geneva cam wheel 117. The Geneva wheel 127, secured to a shaft 128, has a plurality of pin rollers 129 secured thereto and as they rotate in succession, they engage with the Geneva cam wheel 117 causing intermittent rotary movement to occur in the feed disk 17 throughits spindle 125. The Geneva wheel 127 is rotated through a worm gear 131 keyed to the shaft 128 of the Geneva wheel 127 meshing with a worm screw 133. The worm screw 133 is secured to a shaft 135 and driven through a series of V-belts and pulleys by a motor 137. The Geneva wheel 127 is driven from a variable speed drive so as to control the rate at which the workpieces are indexed through the working gap. The shaft 128 of the Geneva wheel 127 also drives the conveyor 33 to carry away workpieces after ejection from the feed disk to an unloading station. The preferred conveyor shown is a link chain'conveyor and it will be apparent that other elongated conveying means may be employed.

Vertical adjustment of the indexing mechanism It has been previously shown that the upper abrading wheel is automatically adjusted in height relative to the lower abrading wheel to compensate for wear of the wheels as the grinding operation proceeds in order to control the thickness of workpieces produced. As the wheels wear, it is expedient that the indexing disk 17 also be periodically adjusted so as to continually maintain approximate midposition between the upper and lower abrading wheel faces. Vertical adjustment of the indexing mechanism can be accomplished both manually and automatically. Manual adjustment is accomplished by turning a handwheel M51 (rigs-2 and 3), although during operation, adjustment takes place automatically. Auto matic adjustment of the indexing mechanism is accomplished through a sensing means responsive to a follower riding on the lower abrasive wheel, as will be presently described. Before this, however, the mechanism for vertical movement of the indexing assembly will be described. The source of power for vertical movement of the indexing assembly comprises a gear motor 139 carrying a helical-toothed pinion 141 which, in turn, meshes with a gear 143 mounted on an adjusting screw 145. The adjusting screw 145 is disposed within a vertical post 147 and threadably engages the upper portion of a supporting block 149 for the feed mechanism to vertically move the same. Depending upon the'direction of rotation of the gear motor 139, the' feed mechanism will be caused to move upward or downward on the post 147. Inorder to eliminate undue bending moments on the post 147 by the weight of the supporting block 149, additional support is provided under the center of the shaft 125 for the feed disk, as shown by the support block screw 153. The screw 153 is actuated by a helicaltoothed shaft 155 meshing with gears 157 and 143. Thus, the adjusting screws 145 in timed relation so as to maintain the feed disk horizontal regardless of its position of adjustment.

As mentioned, thereis present invention means for automatically adjusting the height of the feed disk in order that it will be at all 151 carried by a and 153 may be caused to move 2 provided in the device of the times. be substantially midway between the abrading wheels. During the grinding .operation the abrading wheels. gradually .wear and compensation for this wear automatically occurs through the lowering of the ,upper abrading wheel relative to the lower abrading wheel in response to workpiece oversize. As the gap between the abrading wheels is adjusted for wheel wear, so also is the height of the feed disk adjusted- Automatic regulation of this adjustment of the feed disk is made responsive to wheel wear, and the means (as best shown in Figs. ,8, 9, 10 and 11) foraccomplishing this regulation will now be described. The means for. automatically adjusting the height of the indexing mechanism as the abrading wheels wear isresponsive to..a.follower roll 15.9 riding .on the upper face of thelcwerabrading wheel 29. The followe roll 159. isrotatably disposed in a follower housing 162 mounted on a follower. base 161. Thefollower base 161.

is floatably carried and partially counterbalanced on guide pins 163' and 165through. leg portions 164 and 166 in such a manner as to besupported in its vertical position by the contact of. the follower roll 159 on the upper surface of lower abrading wheel 29. .The axis .of rotation of the follower roll 159 is so disposed (asshownin Figs. 9 and 10) as to contact only the lower abrading wheel. As the lower abrading wheel 29 wears, the Weight of the follower base161 causes thefollower roll 159 to follow the wheel wear downward. A depending foot 167 is secured to the follower base .161and moves downward with the follower roll 159 and the follower base 161.

The depending foot 1671s that part of the circular track 176 which runs beneath the'workpieces from the exit end to the entrance end of the working gap. The depending foot 167 represents a break in the track 176 just before the entrance end of the working gap and serves to retain the workpieces in the work-receiving apertures 19 in their final path of travel toward the working gap. 7 The depending foot 167 which moves downward in response to wheel wearhas a sensitive switch 169 mounted thereon. The sensitive switch 169 in its downward travel with the follower roll 159 is actuated by a trip arm 171 mounted on the'track 176 for the indexing assembly carrying the feed disk 17. The. track 176.is mounted on the support 149 for the indexing mechanism which is adjustable vertically, as previously described, by the gear motor 139 (Fig. 7). 169 and the triparm 171 determines whether or not the gear motor 139 is energized. When it is energized, the entire indexing'assembly ismoved ina vertical direction, the arrangement of 'theadjustable supports being such that the feed disk is always maintained horizontal regardlcss of .the' vertical position to which the indexing mechanism is adjusted. The sensitive switch 169 is caused to approachthe'triparm.171.in response to a change in vertical positionof: the follower roll 159 resulting from wear on the lowertabradinglwheel 29. In due course, when suflicient accumulated change of position between the sensitive switch 169 and the trip arm 171 has occurred, thelcontacts of the sensitive switch 169 will close,

thereby energizing the gear motor 139 which moves the indexing assembly together with the feed disk downward. This movementcauses thetrip arm 171 to gradually'recede from the sensitive switch 169. When sufficient downwardmovernent has occurred to open the contacts of the sensitive switch 169 by relaxation of its pressure against the trip arm 171, the gear motor 139 is de-energized and the indexing mechanismretains this newly adjusted position. This new position of the trip arm 171 is shown in dotted lines in Fig. 11 by the reference numeral 171'. As the abrading wheels continue to wear, in due timethe follower roll 159 will again move vertically downward together with the follower base 161 and the depending foot 167.: The depending foot 167 will carry The relative positions of the sensitive switch L This'new position of .the sensitive. switch 169 is shown in Fig. 11 by the. reference numeral169, The continued downward movement of the follower roll 159 will gradually increase the pressure between the trip arm 171' in its new position and the sensitive switch 169' in its new position. When the pressure between the two has increased sufficiently, the contacts of the sensitive switch 169 will close, thereby again energizing the gear motor 139 which moves the indexing assembly downward'on ce again. This movement causes the trip arm 171 in its new position to again recede gradually from the sensitive switch 169 in its new position. When sufficient downward movement has occurred to open the contacts of the sensitive switch 169, the gear motor 139 is de-energized and the indexing mechanism retains this second newly adjusted position until the contacts of the sensitive switch 169 are again closed. This operation repeats. itself as many times as is required to keep the feed disk in a position midway between the working surfaces of the abrading wheels.

Control of the quality of output There is provided in the device of the present invention.

means to control the thickness of the workpieces produced so that a uniform dimension of workpieces is consistently maintained. The dimensional standards which the workpieces must meet before they are ejected from the device as a finished product are predeterminedly set before the grinding operation. Workpieces that do not meet. the

standards so set are made to pass through the abrading wheels again by suitable meansso that a uniform product is regularly obtained. At the time that suitableimeans are actuated to make each oversize workpiece passionce again through the abrading wheels, an adjustment of the working gap between the abrading wheels is simultaneously made to compensate for wear of the abrading wheels. The mechanism for accomplishing these functions will now be described.

The sensing means 31, previously mentioned, is shown 1 in Fig. 7 and is responsive to variations from a predetermined thickness of workpieces and operates on the workpieces following their exit from between the working surfaces of the abrading wheels. By way of example, the sensing means may be a thickness gauge as shown in the drawings. The sensing means may be of any suitable type adapted to close a-pair' of electrical contacts when the gauge senses that the workpieces are'oversize and to open the contacts when theworkpieces are within 7 the required tolerances. So long as these contacts remain open, that is, when a workpiece coming off the 9 176 (Figs. 3, 7), previously mentioned, which runs beneath the workpieces in a substantially continuous circular path from the exit end of the working 'gap to the entrance end of the working gap, being again broken by the gate 175below the sensing means 31. The eir cular track 176 beneath the workmeceiving apertures retains theoversize workpieces within the work-r'eceiving apertures on the feed disk 17 as they travel from the sensing means 31 back tothe entrance side of the working gap. The track 176 is supported by Z -shaped members 178 afiixed to the supporting block 149 for the feed mechanism. Gate 175 remains open for workpieces of correct size. If, however, any workpiece is oversize, the electrical contacts of the sensing means are closed. The closing of the electrical contacts of the sensing means 31 completes an electrical circuit which actuates a fluid-actuated cylinder 177, a pistonrod 179 of which is in operative relation with the gate 175. Actuation of the fluid-actuated cylinder 177 closes the gate 175 with the result that the oversized workpiece and succeeding ones to reach this gate are retained in the feed disk by track 176 to repeat their passage between the abrading wheels for additional stock removal. It will be apparent that the fluid-actuated cylinder 177 may be replaced by a solenoid or other suitable means.

As has been previously mentioned, the sensing means 31 determines whether the abrading wheels need vertical adjustment for wheel wear. The operation of the sensing means, along with its relation to the previously described means for fine adjustment vertically of the gap between the abrading wheels will now be described.

Automatic adjustment of the gap between the grinding wheels to compensate for continual wear of the same during use is brought about by the sensing means 31 which forms a series circuit with the contacts of the previously described switch 107 providing the latter are also closed, which is the case during an adiustably short interval of each revolution of the cam 109. For the period of time that this series circuit persists, the magnetic clutch 105 is engaged, causing rotation of the screw 91 and thus minutely retracting the wedge 87. When correction is needed, the magnetic clutch 105 is energized to retract the wedge 87, and each such movement of the wedge 87 permits the upper abrading wheel 27 to make a corresponding downward movement toward the lower disk 29, thus reducing the gap between the abrading wheels. The reduction of the gap between the abrading wheels reduces the thickness of the workpieces which may pass therebetween and corrects for the oversize which previously the abrading wheels had produced on the workpieces. Each such movement of size compensation can occur only during those intervals of simultaneous closing of each of the contacts in the sensing means 31 and the switch 107. The angular speed of rotation of the cam 109 limits the possible frequency of these com ensating movements, whereas the width of the adjustable lobe 111 on the cam 109 determines their duration.- The closing of the contacts of the sensing means 31 determines whether a compensating movement should take place, and controls how many successive cycles are required to establish the desired workpiece thickness.

Setup To facilitate replacing of the abrading wheels and to mount them on their respective shafts, provision is made to unclamp and swing the entire indexing mechanism around the post 147 (Fig. 7) so that the feed disk 17 occupies the position 17, as shown by the dotted lines in Fig. 1. This withdraws the feed disk 17 from the. gap between the abrading wheels. The abrading wheels are rapidly separated a sufiicient distance by the means previously described to facilitate changeover. After new abrading wheels are installed, the indexing mechanism is raised to a height to pass the feed disk 17 over the top surface of the lower abrading disk 29. This may be accomplished by energizing the gear motor 139, but preferably is done manually by the hand wheel 181 (Fig. 3). The indexing mechanism is then swung back to its normal working position, as shown in full lines in Fig. 1, and reclamped. The hand wheel 93 is cranked to return the wedge 87 to its starting position with the thicker portions of the wedge between the. rollers 89 and 85, as shown in Fig. 3, as this is the position for new unworn abrading wheels. As the wheels wear, the wedge is automatically retracted laterally until it occupies the position 87' (Fig. 3) for abrading wheels which have worn considerably. The sensing means .31 is calibrated for a new setup to close its contacts at the upper tolerance of thickness predetermined for the workpieces.

. movement 'to' the succeeding position of rest.

Provision for dressing As hereinbefore mentioned, the need for supplemental dressing of the abrading wheels is virtually eliminated by the special features of the present invention. It has been found that it is unnecessary to redress the abrasive disks throughout their wear-life, except in instances of accident or when resetting the machine to accommodate workpieces of substantially changed physical dimensions. Also, it is preferable to initially dress the working faces of the new abrading wheels to make them fiat and parallel to each other before using them on a new machining operation. However the need may arise, there is provided means for dressing the abrading wheels. To accomplish this, a dressing unit 183 (Fig. 1), powered by a motor 184, is swung counter-clockwise from the position shown so as to position its guide bars 185 and 186 parallel to the line passing through the centers of the abrading wheels and a mounting post 187 of dressing unit 183. The parallel guide bars are connected at one end by a slide block 189 upon which are mounted diamond dressing tips 191 above and below the slide block'189. The diamond dressing tips 191 are adjusted to produce a depth of cut in the upper and lower abrading wheels sufficient to remove any nonuniformity or waviness therein, and then power fed radially across,

the wheel faces. Thereupon, the dressing unit 183 is swung back into its position as shown in Fig. 1, which is the inoperative position thereof.

Operation Workpieces are loaded by suitable means (not shown) into the loading chute 21 and the machine is started. When the machine is started, fluid pressure enters the cylinder 83 and actuates the piston rod 81 which moves the rack 79, thereby causing the upper abrading disk to move downward. The rollers 85 prevent further downward travel of the upper abrading wheel when they contact the wedge 87. The fluid cylinder 83 is thereupon de-actuated. The gap between the abrading disks is predicated upon the horizontal position of the wedge 87, the latter being disposed with its thicker portion between the rollers 85 and 89 for new unworn abrading wheels.

The motor 35 is the source of power for rotary mo tion of the abrading disks, and the energization of the motor 35 causes the common drive shaft 37 to rotate by means of suitable V-belts and pulleys which also provide for speed adjustability. The upper and lower abrading disks 27 and 29 are continuously rotated about a'vertical axis from the power transmitted to the common drive shaft 37. To provide for a gradual change of orientation between the working surfaces of the two disks, their relative speeds are made to differ slightly although their direction of rotation is the same. The peripheral speeds of the abrading disks are low as compared to conventional disk grinding and, becausea moderate speed of abrading movement is employed, a depth of cut is obtained which is sufficient to produce enough grain breakdown on the surface of the abrading disks to keep the grains sharp without supplemental dressing. The feature of the variable speed drive employed for rotating the abrading wheels provides for accelerating or retarding the dressing effect upon the wheels depending upon the physical properties of the stock material and the results desired in the final product.

The feed disk 17 has been actuated and is intermittently indexed by the Geneva-type drive previously described. The movement of the feed disk provides for a controlled time of dwell in one position of rest followed by rapid 7 As each work-receiving aperture 23 of the feed disk 17 registers with the loading chute 21, a workpiece is deposited therein. When work-receiving apertures in all of the positions between the abrading disks contain workpieces, the

manual operation of the hand wheel 93 is etfected to withdraw the wedge 87 until the upper disk 27 contacts the upper surface of the workpieces.

Preliminary to starting the machine, the thickness gauge 31 is adjustedto respond to the desired thickness of workpiece. Initially each workpiece leaving the abrading wheels is oversize and the contacts of the gauge 31 are closed. The gate 175 thereby remains closed and the workpieces will return to the gap between the abrading disks so long as they remain oversize, being held in their apertures by the track 176. During some portion of each revolution of the cam 199 as determined by the adjustable lobe 111 thereon, the contacts of the switch 107' close. The simultaneous closure of the contacts of the thickness gauge'31 and the contacts of the switch 137 forms a series circuit which energizes the magnetic ciutch 105 causing rotation of the screw 91, thus automatically retracting the wedge 87. The upper abrading wheel 27 is moved downward corresponding to each such retraction of the wedge 87 and the reduction of the working gap thereby elfected begins to compensate by additional stock removal for the oversize of workpieces previously pro-- duced. This intermittent adjustment of the gap between the abrading disks continues automatically until the desired workpiece thickness is obtained, as indicated by a workpiece passing under the thickness gauge 31 which is within the predetermined tolerance. When this occurs the contacts of the gauge 31 are opened and the fluid cylinder 177 is actuated opening the gate 175. The work piece of the desired size is allowed to drop out of the feed disk 17 onto the conveyor 33 after being indexed to position over the gate 175. Each succeeding workpiece checked and passed by the gauge 31 is conveyed away to a handling station in a similar manner. It is normal that wheel wear should occur but since it is substantially equal throughout the annular zones, a series of workpieces will eventually exit from the working gap which are oversize from lack of suflicient stock removal. Should this occur, the contacts of the gauge 31 will close,

closing the gate 175, thereby preventing the dropping out of the oversize workpieces from the work-receiving apertures 19 and at the same time intermittently withdrawing the wedge 87 to close the working gap for additional stock removal. It should be pointed out that not only is there provided by the means described a sensing means to determine variation from a predeter-' mined size so that control may be exercised over the condition causing the variation, but the amount of. control exercised over the condition is adjustable for work pieces having different characteristics as by setting the length of the lobe on the cam and the speed of rotation thereof. Furthermore, the total number of size com: pensations which occur will be a function of the amount of variation of the workpiece from the predetermined size. There is thus provided an automatic compensation for the working gap which is completely reliable in its operation and at the same time is fully sensitive to' all phases of the machining operation sistently uniform output.

As the upper abrading disk is automatically adjusted in height relative to the lower abrading disk to crntrol the quality of output and to compensate'for wheel wear,

to maintaina con so also is the feed disk automatically adjusted to main recedes from the sensitive switch 169 and the gear motor 139 'is de-energized. The feed disk 17 is lowered in proportion to the wear experienced on the lower abrading disk and the position of the feed disk is always maintained horizontal and midway between the working surfaces of the abrading disks. The control over the adjustment of the indexing assembly, it will be observed, is a function of the amount of wear experienced by the lower abrading disk.

The novel structure described produces workpieces of a consistently uniform size and with a precision parallelism between opposed faces long sought for but heretofore never realized in a flat surface lapper, and manifestly this is due to the unique operation of the combination of elements, particular attention being directed. to the manner of feed of the workpieces between the abrading disks, the cooperative motion of the abrading wheels and the nature of the wheel wear attendant thereupon. The establishment of annular zones of abrasion by the array of workpieces wherein the centerline of those on one side, e. g. the exit side, are disposed at the midpoint of the spaces between those on the other side produces a characteristic wheel wear discovered to occur whereby the working gap inherently wears so as to maintain itself parallel as the machining operation proceeds. The annular zones of abrasion thus established by the novel manner of feed alternate in the type of work burden assumed and this alternation is thought to account for the beneficial self-dressing which continually takes place.

It will be observed that the first annular zone of abrasion is established by work done, for example, on a workpiece that is in the initial position of travel through the working gap while the adjacent zone is established by work done on a workpiece that is in the furthermost position of travel through the working gap. Similarly, the third annular zone of abrasion is established by work done, for example, on a workpiece that is in the second position of travel through the working gap while the adjacent zone is established by work done on a workpiece that is in the second last position of travel through the working gap; This alternation in the type of work bur-' den assumed in the annular zones of abrasion continues in like manner throughout the cross section of the working gap, the effect of which is to self-dress the working surfaces so that they always tend to remain parallel. That this is true can be demonstrated if it is borne in mind that wear caused by the workpieces on the entrance side of the feed is slightly greater than the wear caused by the workpieces on the exit side since the latter are in a more advanced state of completion. Since this is true, the annular zones of abrasion on the entrance side will be slightly greater in depth due to greater wear than the annular zones on the exit side but, since the annular zones on the entrance side alternate with the annular zones on the exit side, the depth of the working gap will remain substantially parallel throughout its cross section. A zone having slightly greater depth due to wear will be adjacent a zone having slightly lesser depth and the next succeeding adjacent zone will be one of slightly greater depth followed by one of slightly lesser depth and so on throughout the working gap. The abrading wheels thus tend to wear substantially parallel and the need for supplemental dressing has been found to be non-existent as a result of this characteristic wheel wear. In actual practice it has been found that, initially, the annular zones of abrasion on the exit side assume more of the work burden as the zones on the entrance side wear, until wear on all the zones becomes stabilized and thereafter further wear in each annular zone becomes substantially equal so that the difference in depth of each alternate zone smooths out to a negligible difference to produce a uniformly parallel wear between the working surfaces of the abrading disks.

Prominently contributing to this superior type of wheel wear characteristic of the machine of the present inven- :asemootion is the feature of the feed cycle wherein a workpiece is maintained in an annular zone of abrasion for a controlled time of dwell followed by a rapid transference to the next succeeding zone for a like period of dwell. Manifestly, the pronounced effect of these annular zones of abrasion, established as heretofore described by the amount of work done on the stock, can be attributed in great measure to this manner of progressively indexing them across the working gap.

It will thus be seen from the foregoing description that there has been provided a flat surface lapper which produces a consistently uniform product throughout its operation, which automatically compensates itself for the condition of its abrading disks in response to the quality of its output and which is characterized by uniform wheel wear such that opposed faces of workpieces exiting from the machine are maintained parallel throughout the wear life of the abrading disks.

What is claimed is:

1. In a flat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, telescoped drive means to rotate said disks, means for axially moving one of said telescoped drive means relative to the other, means to index a plurality of workpieces through said working gap, sensing means responsive to variations from a predetermined thickness of workpieces leaving said working gap, means responsive to said sensing means to axially move one of said drive means relative to the other to change the spacing of said disks to adjust the size of said working gap to compensate for thickness-variations of said workpieces from a predetermined thickness, and means to adjust said index means to retain it within the space between the abrading disks out of contact therewith.

2. In a flat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, telescoped drive means to rotate said disks, means for axially moving one of said telescoped drive means relative to the other, means to index a plurality of workpieces through said working gap, sensing means responsive to variations from a predetermined thickness of workpieces leaving said working gap, means responsive to said sensing means to axially move one of said drive means relative to the other to change the spacing of said disks to adjust the size of said working gap, said last-mentioned means including means to control the frequency and duration of said compensating movements of said one disk, and means to adjust said index means to retain it within the space between the abrading disks out of contact therewith.

3. In a flat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in sub stantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a feed disk having a plurality of spaced apertures to receive workpieces therein, means to intermittently index said feed disk through said working gap to move said Workpieces toward and away from the center of said working gap, sensing means responsive to variations from a predetermined thickness of workpieces leaving said working gap, 3. first means responsive to said sensing means to move one of said abrading disks relative to the other of said abrading disks to adjust the size of said working gap, ejecting means associated with said workpieces leaving said working gap to eject said workpieces from said feed disk, and a second means responsive to said sensing means to actuate said ejecting means.

4. In a flat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a feed disk having a plurality of spaced apertures to receive workpieces therein, means to intermittently index said feed disk through said working gap to move said work pieces toward and away from the center of said working gap, sensing means responsive to variations from a predetermined thickness of workpieces leaving said'working gap, a first means responsive to said sensing means to move one of said abrading disks relative to the other of said abrading disks to adjust the size of said working gap, said first meansincluding means to control the frequency and duration of said compensating movements of said one abrading disk, ejecting means associated with said workpieces leaving said working gap to eject said workpieces from said feed disk, and a second means responsive to said sensing means to actuate said ejecting means.

5. In a flat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a feed disk having a plurality of spaced apertures to receive workpieces therein, means to intermittently index said feed disk through said working gap to move said workpieces toward and away from the center of said working gap, sensing means responsive to a change of dimension of one of said abrading disks occasioned by wear on the working face of said one abrading disk, and means responsive to said'sensing means to move said feed disk relative to said one abrading disk to maintain constant the relative position between said feed disk and the working face of said one abrading disk.

6. In a fiat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a feed disk having a plurality of spaced apertures to receive workpieces therein, means to feed said feed disk through said working gap to move said workpieces toward and away from the center of said working gap, sensing means responsive to a change of dimension of one of said abrading disks occasioned by wear on the Working face of said one abrading disk, and means responsive to said sensing means to move said feed disk -relative to said one abrading disk to maintain conhaving oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a feed disk having a plurality of spaced apertures to receive workpieces therein, means to intermittently index said feed disk through said working gap to move said workpieces toward and away from the center of said working gap, 21 first sensing means responsive to variations from a predetermined thickness of workpieces leaving said working gap, means responsive to said sensing means to move one of said disks relative to-the other of said disks to adjust the size of said working gap, a second sensing means responsive to a change of dimension of one of said abrading disks occasioned by wear on the working face of said one abrading disk, and meansresponsive to said second sensing means to move said feed disk relative to said one abrading disk to maintain constant the relative position between said feed disk and the working face of said one abrading disk.

, 8. In a flat surface lapper, a pair of abrading disks ing means to move one of said abrading disks relative to the other of said abrading disks to adjust the size of said working gap, ejecting means associated with said workpieces leaving said working gap to eject said workpieces from said feed disk, a second means responsive to said first sensing means to actuate said ejecting means, a second sensing means responsive to a change of dimension of one of said abrading disks occasioned by wear on the working face of said one abrading disk, and means responsive to said second sensing means to move said feed disk relative to said one abrading disk to maintain constant the relative position between said feed disk and the working face of said one abrading disk.

9 In a flat surface lapper, a pair of abrading disks havlng oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therehetween, means to rotate said abrading disks, a feed disk, means to feed said feed disk through said Working gap to move a plurality of workpieces toward and away from the center of said working gap, said feed disk having a plurality of apertures to receive said workpieces, said apertures being so spaced on said feed disk that the centers of workpieces leaving said working gap occupy the midpoint of the spaces between workpieces entering said working gap, sensing means responsive to variations from a predetermined thickness of workpieces leaving said working gap, a first means responsive to said sensing means to move one of said abrading disks relative to the other of said abrading disks to adjustthe size of said working gap, ejecting means associated with said workpieces leaving said working gap to eject said workpieces from said feed disk, and a second means responsive to said sensing means to actuate said ejecting means.

10. In a flat surface lapper, a pair of abrading disks having oppositely disposed'working faces'lying in substantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a

16 abrading disk, ejecting means associated with said workpieces leaving said working gap to eject said workpieces from said feed disk, and a second means responsive to said sensing means to actuate said ejecting means.

12. In a flat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a feed disk, means to feed said feed disk through said working gap to move a plurality of workpieces toward and away from the center of said working gap, said feed disk having a plurality of apertures to receive said workpieces, said apertures being so spaced on said feed disk that the centers of workpieces leaving said working gap occupy the midpoint of the spaces between workpieces entering said working gap, sensing means responsive to a change of dimension of one of said abrading disks occasioned by wear on the working face of said one abrading disk, and means responsive to said sensing means to move said feed disk relative to said one abrading disk to maintain constant the relative position between said feed disk and the working face of said one abrading disk.

13. in a flat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a feed disk, means to intermittently index said feed disk through said working gap to move a plurality of workpieces toward and away from the center of said working gap, said feed disk having a plurality of apertures to receive said workpieces, said apertures being so spaced on said feed disk that the centers of workpieces leaving said working gap occupy the midpoint of the spaces between feed disk, means to feed said feed disk through said working gap to move a plurality of workpieces toward and away from the center of said working gap, said feed disk having a plurality of apertures to receive said workpieces, said apertures being so spaced on said feed disk that the centers of workpieces leaving said working gap occupy the midpoint of the spaces between workpiecesentering said working gap, sensing means responsive to variations from a predetermined thickness of workpieces leaving said working gap, a first means responsive to said sensing means to move one of said abrading disks relative to the other of said abrading disks to adjust the size of said working gap, said first means including means to control the frequency and duration of said compensating movements of said one abrading disk, ejecting means associated with said workpieces leaving said working gap to eject said workpieces from said feed disk, and a second means responsive to said sensing means to actuate said ejecting means.

11. in a flat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a feed disk, means to intermittently index said feed disk through said working gap to move a plurality of workpieces toward and away from the center of said working gap, said feed disk having a plurality of apertures to receive said workpieces, said apertures being so spaced on said feed disk that the centers of workpieces leaving said working gap occupy the midpoint of the spaces between workpieces entering said working gap, sensing means responsive to variations from a predetermined thickness of workpieces leaving said working gap, a first means responsive to said sensing means to move one of said abrading disks relative to the other of said abrading disks to adjust the size of said working gap, said first means including means to control the frequency and duration of said compensating movements of said one workpieces entering said working gap, sensing means responsive to a change of dimension of one of said abrading disks occasioned by wear on the working face of said one abrading disk, and means responsive to said sensing means to move said feed disk relative to said one abrading disk to maintain constant the relative position between said feed disk and the working face of said one abrading disk. 7

14. In a fiat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a feed disk, means to intermittently index said feed disk through 1 said working gap to move a plurality of workpieces'toward and away from the center of said working gap, said feed disk having a plurality of apertures to receive said workpieces, said apertures being so spaced on said feed disk that the centers of workpieces leaving said working gap occupy the midpoint of the spaces between workpieces entering said working gap, a first sensing means responsive to variations from a predetermined thickness of work pieces leaving said working gap, means responsive to sald first sensing means to move one of said abrading dISkS relative to the other of said abrading disks to adjust the size of said working gap, a second sensing means responsive to a change of dimension of one of said abrading disks occasioned by wear on the working face of said one abrading disk, and means responsive to said second sensing means to move said feed disk relative to saidone abrading disk to maintain constant the relative position between said feed disk and the working face of said one abrading disk,

15. In a fiat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a feed disk, means to feed said feed disk through said working gap'to move a plurality of workpieces toward and away from the center of said working gap, said feed disk having a plurality'of apertures to receive said workpieces, said apertures being so spaced on said feed disk that the centers, of workpieces leaving said working gap occupy the midpoint of the spaces between workpieces entering said working gap, a first sensing means responsive to variations from a predetermined thickness of workpieces leaving said working gap, means responsive to said first sensing means to move one of said abrading disks relative to the other of said abrading disks to adjust the size of said working gap, a second sensing means responsive to a change of dimension of one of said abrading disks occasioned by wear on the working face of said one abrading disk, and means responsive to said second sensing means to move said feed disk relative to said one abrading disk to maintain constant the relative position between said feed disk and the working face of said one abrading disk.

16. In a flat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a feed disk, means to intermittently index said feed disk through said working gap to move a plurality of workpieces toward and away from the center of said working gap, said feed disk having a plurality of apertures to receive said workpieces, said apertures being so spaced on said feed disk that the centers of workpieces leaving said working gap occupy the midpoint of the spaces between workpieces entering said working gap, a first sensing means responsive to variations from a predetermined thickness of workpieces leaving said working gap, a first means responsive to said first sensing means to move one of said abrading disks relative to the other of said abrading disks to adjust the size of said working gap, ejecting means associated with said workpieces leaving said working gap to eject said workpieces from said feed disk, a second means responsive to said first sensing means to actuate said ejecting means, a second sensing means responsive to a change of dimension of one of said abrading disks occasioned by wear on the working face of said one abrading disk, and means responsive to said second sensing means to move said feed disk relative to said one abrading disk to maintain constant the relative position between said feed disk and the working face of said one abrading disk.

17. In a flat surface lapper, a pair of abrading disks having oppositely disposed working faces lying in substantially parallel planes so as to define a working gap therebetween, means to rotate said abrading disks, a feed disk, means to feed said feed disk through said working gap to move a plurality of workpieces toward and away from the center of said working gap, said feed disk having a plurality of apertures to receive said workpieces, said apertures being so spaced on said feed disk that the centers of workpieces leaving said working gap occupy the midpoint of the spaces between workpieces entering said working gap, a first sensing means responsive to variations from a predetermined thickness of workpieces leaving said working gap, a first means responsive to said first sensing means to move one of said abrading disks relative to the other of said abrading disks to adjust the size of said working gap, ejecting means associated with said workpieces leaving said working gap to eject said workpieces from said feed disk, a second means responsive to said first sensing means to actuate said ejecting means, a second sensing means responsive to a change of dimension of one of said abrading disks occasioned by wear on the working face of said one abrading disk, and means responsive to said second sensing means to move said feed disk relative to said one abrading disk to maintain constant the relative position between said feed disk and the working face of said one abrading disk.

18. In a flat surface lapping device, a pair of abrading disks having oppositely disposed abrading faces lying in substantially parallel planes and spaced apart to provide a workpiece receiving gap therebetween, drive means for said disks, a third disk having apertures therethrough near the peripheral edge for carrying workpieces through said gap to have the opposite ends thereof machined by said abrading faces, sensing means responsive to an increase in thickness of the space between the dressed ends of the workpiece, means responsive to said sensing means for adjusting one of said disks for decreasing the gap between the abrasive disks, and means for adjusting another of said disks to have the said third disk disposed substantially midway in said gap out of contact with said working faces.

References Cited in the file of this patent UNITED STATES PATENTS 1,198,772 Roach Sept. 19, 1916 1,371,854 Buck Mar. 15, 1921 1,926,974 Einstein Sept. 12, 1933 2,122,942 Hutchinson July 5, 1938 2,148,744 Hall Feb. 28, 1939 2,580,542 Heath Jan. 1, 1952 FOREIGN PATENTS 417,400 Great Britain Oct. 4, 1934 661,214 Great Britain Nov. 21, 1951 718,087 Great Britain Nov. 10, 1954

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