Disc grinder with floating grinding wheel

A grinding and polishing tool includes a pair of opposed grinding wheels for grinding or polishing simultaneously each of a plurality of discs located therebetween. Outer pulley wheels on a collar in cooperation with an inner pulley wheel support the discs peripherally and permit both rotation about and translation along the respective rotational axis of each disc in response to forces imposed by the grinding wheels. A uniform thickness of the discs is achieved by employing the discs themselves randomly distributed about the collar as spacers between the non-resilient grinding wheels to initially contact and grind the thicker discs until all discs are of equal thickness. Gimbal mounting one grinding wheel permits self-alignment thereof in a parallel relationship with the other grinding wheel to obtain parallel ground or polished surfaces on each disc.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to machine tools and, more particularly, to 
grinding and polishing tools for discs. 
2. Description of the Prior Art 
The computer industry employs rigid discs of various diameters for storage 
and retrieval of information encoded therein. The surfaces of these discs 
are scanned by close tolerance accurately positionable heads. The accuracy 
and density of the information storage and retrieval capability is a 
function of the degree of parallelism between opposed surfaces and the 
degree of finish on each surface. It is therefore very desirable to grind 
the discs to a high degree of parallelism between opposed sides, with each 
side being highly polished. 
Various devices have been developed for truing the opposed sides of discs 
and grinding and polishing the respective surfaces. U.S. Pat. No. 
3,845,587 is directed to a tool for spindle supporting each of a plurality 
of discs positioned intermediate extremely large sized and rigid grinding 
wheels. The opposed grinding wheels are dressed in situ and the 
grinding/polishing surfaces are maintained parallel to one another through 
employment of massive shafts, bearings and interconnecting framework. U.S. 
Pat. No. 1,656,820 is directed to a pair of grinding wheels having a 
vertically oriented axis of rotation. The upper grinding wheel rests upon 
the work piece being ground and the grinding force imparted thereto is a 
function of the weight of the grinding wheel and its spindle. U.S. Pat. 
No. 2,225,193 is directed to a grinding wheel having imbedded in the face 
thereof segmented abrasive elements. U.S. Pat. No. 2,371,021 is directed 
to a rotatable sanding or buffing tool which is preloaded. U.S. Pat. No. 
2,826,877 is directed to a grinding and polishing element having a 
flexible intermediate member for preloading the grinding wheel. U.S. Pat. 
No. 3,676,957 is directed to apparatus for grinding helicoid springs. U.S. 
Pat. No. 3,668,812 is directed to a device for dressing the abrasive 
elements on a grinding wheel. 
SUMMARY OF THE INVENTION 
The grinding and polishing apparatus described herein includes a readily 
replaceable collar for supporting a plurality of uniform sized discs to be 
ground or polished. An axially repositionable grinding wheel cooperates 
with a gimballed grinding wheel rotating at a different rate of rotation 
to reduce the thickness of all of the discs to a uniform size and obtain 
parallelism between opposed sides of each disc. The disc supporting collar 
may be rotatably mounted to permit rotation of a set of discs at a rate 
which is a function of the rotational speed difference between the 
grinding wheels; the collar rotation speed may be reduced by a selectively 
actuatable drag brake. The use of a rotatable collar also aids in 
repositioning the discs for manual or mechanical disc mounting and 
demounting. And, the collar may be skewed off center to provide a 
continuously varying width swath being ground. 
It is therefore a primary object of the present invention to provide a 
grinding tool for grinding to uniform thickness a set of discs. 
Another object of the present invention is to provide a grinding tool for 
grinding parallel opposed surfaces on each disc of a set of discs. 
Still another object of the present invention is to provide a collar for 
supporting a plurality of discs of uniform size intermediate a pair of 
opposed grinding wheels. 
Yet another object of the present invention is to provide a disc mounting 
mechanism for rotatably supporting each of a plurality of discs at the 
respective perimeters thereof to permit both independent rotation and 
axial displacement of the discs commensurate with wear of grinding wheels 
acting thereupon. 
A further object of the present invention is to provide a disc mounting 
collar axially offset of the axis of rotation of opposed grinding wheels 
to obtain more uniform grinding of each of the collar supported discs. 
A yet further object of the present invention is to provide a selectively 
actuatable drag brake for restraining rotation of a disc supporting 
rotatable collar. 
A still further object of the present invention is to provide a grinding 
tool for grinding a plurality of differently sized sets of discs by 
interchanging disc supporting collars. 
These and other objects of the present invention will become apparent to 
those skilled in the art as the description thereof proceeds.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown a robustly constructed frame 10 for 
supporting a two station disc grinding machine tool 12. First station 14, 
illustrated on the left side of the figure, may be used for grinding each 
of a plurality of discs. Second station 16, illustrated on the right side 
of the figure, may be used for polishing each of a plurality of discs. 
Various embodiments of the machine tool may be configured whereby both 
stations can operate concurrently but independently of one another or in 
concert with one another. In the following description, the details of the 
invention will be primarily directed to station 14; it being understood 
that station 16 is essentially a duplicate or mirror image thereof. 
Discs used in the computer field for data storage and retrieval purposes 
operate most accurately if the opposed surfaces are truely parallel to one 
another and of a smoothness exceeding that of three microns and highly 
polished. Grinding and polishing discs for such tolerances requires highly 
specialized equipment to be able to do it on a commercial basis. 
Frame 10 is purposely built extremely robust and rigid to provide a firm 
foundation for the plurality of axially aligned grinding wheel supporting 
and rotating shafts. Any misalignment of such shafts, and more so any 
movement of the shafts lateral to the axis of rotation, will produce 
deviant grinding/polishing results which are intolerable. Vats 18, 20 are 
located within frame 10 to collect the oil discharged upon the discs 
during grinding at stations 14, 16, respectively. 
Station 14 of machine tool 12 includes an outer grinding wheel 22 supported 
upon a shaft 24 rotatably mounted within pillow blocks 26, 28. Hydraulic 
means 30, or other regulatable repositioning means, is employed to axially 
reposition shaft 24 and grinding wheel 22, on command. Inner grinding 
wheel 32 is supported upon a shaft 34 (see FIG. 2) rotatably mounted 
within pillow blocks, of which one pillow block is illustrated. Station 16 
includes an outer grinding wheel 38 supported upon axially displaceable 
shaft 40, the latter being mounted within pillow blocks 42, 44. Hydraulic 
means 46, or the like, is employed to axially reposition shaft 40 on 
command. An inner grinding wheel 48 is also mounted upon shaft 34 (see 
FIG. 2). 
The rotational drive mechanism for the grinding wheels will be described 
with joint reference to FIGS. 1 and 2. Shaft 34 is rotatably driven 
through a chain 50 and sprocket 52 mounted on shaft 34. Shaft 24 is driven 
by a belt 54 engaging a pulley 56 mounted on the shaft. A belt 58 is 
attached to a pulley mounted on shaft 40. Chain 50 and belts 54, 58 are 
driven through appropriate sprocket and pulleys nonrotatably mounted upon 
a common rotary shaft 60. Shaft 60 is rotated through a chain and sprocket 
mechanism 62 by a drive motor. For safety purposes, chain 50 and its 
engaged sprockets are housed within a cover 64. Covers 66, 68 envelope 
belts 54, 58 and their pulleys, respectively. 
It is preferable that the rotational speed of the grind wheels of any 
opposed pair of grinding wheels be different; otherwise, waves in the 
element to be ground are likely to develop. To assure nonsynchronous 
rotation, the drive mechanism or shaft 34 supporting the inner grinding 
wheels is of a nonslipping chain and sprocket type. The drive mechanisms 
for each of the outer grinding wheels are of the belt and pulley type 
which inherently cause some slippage and with loading cause further 
slippage. Thus, even if the gear ratios of the chain and sprocket and belt 
and pulley mechanisms are identical, the rotational speed of the 
respective driven shafts will be out of synchronization due to the 
slippage inherent in belt drives. 
To aid the grinding/polishing process, oil is continually ejected upon 
discs through a tube 67. The oil flowing therefrom may be directed upon 
the adjacent discs, wherefrom it is transferred to the grinding wheels and 
remaining discs by gravity and certrifugal force. A stop cock 69 or other 
means can be incorporated to control the flow rates, etc. 
Referring jointly to FIGS. 1, 2 and 3, the means for supporting a set of 
discs at each station will be described. A collar 70 is rigidly attached 
to a pair of studs, of which stud 72 is illustrated. These studs may be 
located diametrically opposed and lateral of inner grinding wheel 32. A 
means for mounting the studs may be by clamping each stud within a pillow 
block such as pillow block 74 illustrated. A central aperture 76 is formed 
within the collar. A plurality of pairs of pulley wheels 78, 80 are 
rotatably mounted adjacent the perimeter of collar 70. Each of these 
pulley wheels includes annular rails 82, 84, each of which rails has a 
slightly inwardly sloping inner radial surface. Rail 82 of each of pulleys 
78 includes an arched or straight line indentation 86, the purpose of 
which will be described below. As particularly illustrated in FIG. 3, each 
of discs 88 are supported at two points by one of pairs of wheels 78, 80 
and another of the adjacent pairs of pulley wheels. The third point of 
support for each of discs 88 is provided by a central pulley wheel 90, 
which is affixed to grinding wheel 32 in axial alignment therewith. The 
pulley wheel includes an annular flange 92 having an inner surface 94 of a 
slight inward slope. By having the inside surfaces of the rails of all 
pulley wheels slightly tapered, only the peripheral edge of the disc will 
come in contact therewith and no wear band attendant the sides of the 
discs can or will be formed. 
The spacing intermediate rails 82, 84 of pulley wheels 78, 80 and flange 92 
of pulley wheel 90 permit travel of discs 88 in a direction along the axis 
of rotation of the discs. Removal of the discs laterally is precluded by 
the three point support for the discs. To mount and demount each disc, the 
respective pulley wheel 78 is rotated to position indentation 86 in 
alignment with the perimeter of the respective disc. As the arc of 
indentation 86 is equivalent to the curvature of the disc perimeter, 
displacement of the edge of the disc past rail 82 may be effected. Upon 
each displacement, the disc may be demounted as the remaining contact is 
then limited to that of pulley wheel 80 and pulley wheel 90. In normal 
operation, the forces imposed upon disc 88 will not cause the disc to be 
relocated laterally at any instant during which it may be in coincidence 
with indentation 86. 
The mounting of pulley wheel 90 upon grinding wheel 32 will be described 
with specific reference to FIG. 4. Grinding wheel 32 includes a massively 
constructed head 98 of aluminum or similar material. The massive 
construction of the head essentially precludes any measurable deformation 
or resilience thereof during normal operation. A grinding or polishing 
medium 98 is attached in a ring-like configuration on face 100 of head 96 
and extends inwardly from the perimeter a given distance. 
A pair of bolts 102, 104 are recessed within and extend through pulley 
wheel 90 for threaded engagement with threaded cavities 106, 108 within 
head 96. The pulley wheel is spaced from face 100 by use of a plurality of 
spacers 110, 112 penetrably engaged by bolts 102, 104, respectively. The 
width of perimeter surface 114 of pulley wheel 90 may be configured to be 
somewhat greater than the width between rails 82, 84 of pulley wheels 78, 
80; the width of which is, in turn, controlled by the amount of wear of 
the grinding medium tolerable before readjustment of the position of the 
collar in the axial direction is necessitated. In practice, the width of 
perimeter surface 114 is substantially less than the width of grinding 
medium 98. Accordingly, repositioning of pulley wheel 90 and collar 70 is 
necessitated periodically as grinding medium 98 wears away. Such 
repositioning is effected by periodic removal of spacers 110, 112 and 
repositioning of the collar supporting studs. 
The preferred horizontal spacing maintained between inner surface 94 of 
pulley wheel 90 and the working surface of grinding medium 98 is somewhat 
greater than the width of the discs being ground to preclude forced 
contact of the discs with inner surface 94 and to provide limited play for 
mounting and demounting of the discs in contact with perimeter surface 
114. To maintain such relatively small spacing during wear of grinding 
medium 98, it becomes necessary to periodically relocate pulley wheel 90 
toward head 32. Such relocation is effected by periodic removal of spacers 
110, 112. The axial excursion of the discs resulting from wear of grinding 
medium 98 is accommodated by pulley wheels 78, 80 through appropriate 
spacing between rails 82, 84. Accordingly, pulley wheels 78, 80 need not 
be relocated despite wear within a relatively large range of the grinding 
medium. 
Referring momentarily to FIG. 2, grinding wheel 22 includes a massive head 
115 of turned aluminum or the like. A ring of grinding medium 116 is 
attached to surface 117 of the head. The grinding wheel is rigidly 
attached to shaft 24 by conventional means well known to those skilled in 
the art. 
Referring to FIG. 5, there is shown a mounting means for grinding wheel 32 
which mounting means is in the nature of a gimbal mounting. An axial 
recess 118 is formed in rear face 120 of the grinding wheel. A support 
plate 122 is placed partially within recess 118 and is rigidly attached to 
rear face 120 by bolts 124. The support plate includes a circular cavity 
126 configured slightly larger in diameter than the diameter of shaft 34. 
The cavity includes an annularly enlarged section 128 to preclude contact 
of shaft 34 with most of the length of the wall of cavity 126. Each of 
pins 130 nest within a portion of support plate 122 and the end of shaft 
34 and serve as translation members to effect rotational movement of 
grinding wheel 32 commensurate with rotation of shaft 34. Because shaft 34 
does not fit snugly within cavity 126, some angular movement of grinding 
wheel 32 off the axis of rotation of shaft 34 is possible; the extent of 
such angular movement is a function of the degree of tolerance between 
cavity 126 and the diameter of shaft 34. 
Support plate 126, and hence grinding wheel 32, is maintained mounted upon 
shaft 34 by means of a keeper plate 132. The keeper plate includes a 
central aperture 134 for loosely penetrably receiving shaft 34. A snap 
ring 136, or the like engages a groove 138 about shaft 34. The resulting 
interference between the keeper plate and the snap ring precludes further 
movement of the keeper plate toward the end of the shaft. Four bolts 140 
equiangularly spaced about the keeper plate threadedly engage respective 
apertured cavities 142 in the support plate. Accordingly, movement of 
grinding wheel 32 along the axis of rotation of shaft 34 is precluded by 
the mechanical engagement between the keeper plate and the snap ring. 
In practice, grinding wheel 32 is mounted upon shaft 34 by drawing support 
plate 122 toward keeper plate 134 through equal turns of each of bolts 
140. Thereby, parallelism between the keeper plate, support plate and disc 
grinding wheel 34 is achieved. However, as the keeper plate is not fixedly 
attached to the shaft, it has sufficient freedom of movement to 
accommodate some "rocking" commensurate with the angular movement of head 
96 afforded by the end of the shaft disposed within cavity 126. In this 
manner, grinding wheel 32 is gimbal mounted upon shaft 34. 
Referring jointly to FIGS. 6 and 7, a means employed for rigidly mounting 
the belt driven pulleys upon their respective shafts will be described. It 
is to be understood that while the structure attendant shaft 24 will be 
described specifically, similar structure is employed attendant shaft 40. 
Shaft 24 is formed with an axially aligned groove 142 adapted to slidably 
receive a pair of oppositely oriented dogs 144, which dogs are L-shaped 
and include a base 146 and a leg 148. Hub 150 of pulley 56 includes an 
internal radially oriented groove 152 configured to snuggly receive bases 
146 of opposed dogs 144. Additionally, the outward edges of hub 150 are 
indented by radially aligned indentations 154 to snuggly receive legs 148 
of the respective dogs. Collars 156, 158 positionally retain the hub on 
shaft 24 and maintain legs 148 of the dogs within respective indentations 
154. It is to be understood that hub 150 slidably receives shaft 24 
whereby movement of pulley 56 along the shaft may be effected with 
relative ease. 
To lock pulley 56 upon shaft 24, the shaft is penetrably engaged with hub 
150. Dogs 144 are placed within groove 142 and slid into the hub within 
groove 152 and respective indentations 154. Thereafter, rotation of pulley 
56 independent of shaft 24 is precluded. Pulley 56 is driven by belt 54 
which belt is an engagement with a pulley mounted on shaft 60 (see FIG. 
1). Accordingly, pulley 56 must be maintained in general alignment with 
the belt and the respective pulley mounted upon shaft 60. To maintain such 
alignment of pulley 56 despite movement of shaft 24 along its axis of 
rotation, a pair of spacers position hub 150 intermediate pillow blocks 
26, 28. Thereby, axial repositioning of shaft 24 will not cause relocation 
of pulley 56 yet a rotational force imparted by the pulley to the shaft 
will be continuously maintained during any axial movement of the shaft. 
By rotating, rather than rigidly mounting, collar 70, certain benefits are 
achieved. First, an operator will have axis to each of the disc positions 
by simply turning the collar until each disc position comes within easy 
reach. At such position the operator may readily mount or demount the 
respective disc. Secondly, limited rotation of the collar will have at 
least a tendency to produce a more fine grind or polish upon the discs. 
The collar may not be freely rotating or else it will rotate commensurate 
with rotation of the grinding wheels, except as modified by the slight 
rotational speed difference therebetween, and grinding of the discs will 
not be effected. Therefore, a drag brake or retardation means acting upon 
the collar is preferable. It is to be understood that such drag brake or 
retardation means is preferably configured not to be an impediment to an 
operator manually rotating the collar. 
Referring primarily to FIGS. 8, 9, 10 and 11, the means for rotatably 
mounting the collar and applying a drag brake or retardation force thereto 
will be described. A mounting ring 160 is attached to the studs previously 
described with respect to collar 70 and of which stud 72 is illustrated. A 
groove 162 is developed in the perimeter of mounting ring 160 to receive a 
commensurately configured perimeter 164 of a wheel 166. The wheel is 
rotatably mounted upon a stud 168 through a bearing 170 and secured in 
place by a bolt 172. A collar 174, similar in function and configuration 
with collar 70 described above, supports each of a plurality of discs 88 
by pulleys 78, 80 and pulley wheel 90, as described above. It is to be 
understood that collar 174 is centrally apertured by aperture 76 to 
accommodate grinding wheel 32 and pulley wheel 90. A mounting plate 176 is 
adjustably attached to collar 174 by nut and bolt means 178 extending 
through each of slots 180, 182. The mounting plate also includes a 
threaded cavity 184 for threadedly engaging bolt 172 whereby the bolt 
secures stud 168 to the mounting plate. Slots 180, 182 in the mounting 
plate provide an adjustment capability for centrally mounting collar 174 
with respect to ring 160 and for providing adequate and requisite 
clearance for rotational engagement of wheels 168 with groove 162. From 
the above description, it becomes apparent that collar 174 is free to 
rotate about fixed mounting ring 160. 
Rotational restraint upon collar 174 is provided by means of a chain and 
sprocket arrangement. An annular sprocket 186 is attached to the perimeter 
of collar 174 by a plurality of plates 188 extending between the collar 
and annular sprocket and attached thereto by attachment means 190, such as 
nut and bolt combinations, rivets, etc. A chain 192 interconnects annular 
sprocket 186 with a sprocket wheel 194 mounted upon a shaft 196. To retard 
or place a drag upon rotation of collar 174, any number of mechanisms 198 
may be employed. One such mechanism might be a brake acting upon sprocket 
194 to retard rotational movement thereof. Alternatively, a mechanical 
brake, eddy current generator, etc., may be attached to shaft 196 
directly, or flange extending therefrom, etc., the selection of which is 
well known to those skilled in the art. 
The utility of grinding tool 12 may be greatly enhanced by adaptations of 
variants thereof which permit grinding and polishing of several 
differently sized discs. In example, the computer industry presently 
employs discs of 51/4" diameter, 8" diameter and 14" diameter. The 
grinding tool described herein can accommodate grinding and polishing of 
each of these sizes of discs. In the preceding description, the structure 
illustrated is particularly adapted for grinding a set of 51/4" discs. To 
grind 8" discs, collar 70 (or collar 174) need be enlarged by only a few 
inches to accommodate a number of 8" discs. To grind 14" discs, collar 200 
illustrated in FIG. 12 is particularly well adapted. 
Collar 200 is essentially a triangular plate fixedly attachable to the 
mounting studs, of which stud 72 is shown in FIG. 1. To grind 14" discs, 
support for the three discs 202 illustrated is provided by six pulley 
wheels. Pulley wheels 204 rotatably mounted at each of the apexes of 
collar 200 include indentations 206 in rails 208 in the manner of pulley 
wheels 78 described above. Thereby, removal of each disc 202 may be 
effected by rotating the respective pulley 204 until indentation 206 is 
coincident with the perimeter of the disc and thereafter relocating the 
disc laterally to disengage it from the pulley. Each of rotatably mounted 
pulleys 210 support two adjacent discs. Thereby, a three point support is 
provided for each of the three 14" discs illustrated. Necessarily, pulley 
wheel 90, mountable upon grinding wheel 32, is removed in order to provide 
the requisite clearance for the discs. Collar 200 is centrally apertured 
by aperture 212 to permit penetration therethrough of grinding wheel 32. 
In the previously described collar 70 for 51/4" discs, the width of the 
swath ground or polished by the grinding wheels remained constant since 
the distance between the center of rotation of the grinding wheels and the 
center of rotation of each disc was maintained constant, irrespective of 
whether the collar revolved about the axis of the grinding wheels. By 
varying the width of the swath ground by the grinding wheels, it is 
possible to obtain a slightly finer and more smooth finish. 
Referring to FIG. 13, there is illustrated a collar 220 for mounting a 
plurality of discs, which mounting means is duplicative of that shown in 
FIG. 3 with respect to collar 70. Collar 220 is attached to machine tool 
12 by mounting it upon studs 72, in the manner described above. Perimeter 
222 of collar 220 has a center 224, which center is not coincident with 
the axis of rotation of the grinding wheels. Center 225 of interior 
aperture 226 is coincident with the axis of rotation of grinding wheel 32 
in the manner of aperture 76 of collar 70. The size of aperture 226 is 
greater than that of grinding wheel 32 in the manner of aperture 76 of 
collar 70. However, center 225 of aperture 226 is offset from center 224 
of the collar by a distance defined by the letter "X", as shown in the 
drawing. The displacement or offset "X" is a function of the maximum width 
swath upon the discs to be ground provided that a certain minimum width 
swath is also maintained. 
The mounting of pulley wheel 228 upon inner grinding wheel 32 in order to 
accommodate the off center mounting of the set of discs will be described 
with primary reference to FIG. 14. Grinding/polishing medium 98 is 
attached to head 96, as described above. A mounting plate 230 is centrally 
attached to head 96 by means of countersunk bolts 232, or the like. The 
mounting plate includes a threaded aperture 234 for receiving the threaded 
shaft of a retaining bolt 236. A retaining plate 238 is penetrably mounted 
upon bolt 236 and bears against a sleeve 240, which sleeve bears against 
one or more spacers 242. The resulting structure defines a space of fixed 
width intermediate retainer plate 238 and outermost spacer 242, which 
width is defined by the length of sleeve 240. Pulley wheel 228 includes an 
enlarged central aperture 244 for penetrably receiving sleeve 240. The 
thickness of the pulley wheel interior of annular flange 246 is made 
somewhat less than the length of sleeve 240. Thereby, retaining plate 238, 
assuming it has a radius greater than the diameter of aperture 244, will 
retain pulley wheel 228 juxtaposed with the outermost one of spacers 242 
in a loose fit. The loose fit, in combination with enlarged aperture 244, 
accommodate radial repositioning of pulley wheel 228 due to any forces 
imposed upon its perimeter. As described above, discs 88 bear upon and are 
supported by peripheral band 248 of the pulley wheel. 
Collar 220 will be skewed in one direction from the axis of rotation of the 
grinding wheels by the set of discs mounted thereon by an amount 
equivalent to "X". That is, the offset in axis of rotation between the 
grinding wheels and the collar, distance "X", is accommodated by the 
radial translation available to pulley wheel 228 whereby the previously 
discussed three point support for the discs is continuously maintained. 
Accordingly, collar 220, which is rotatable by mounting it on apparatus 
described primarily with reference to FIGS. 9, 10, 11 and 12, will cause 
the discs mounted thereon to travel on a circular path eccentric to the 
axis of rotation of the grinding wheels. Such travel results in cyclical 
radial travel of the discs with respect to the grinding wheels and varies 
the width of the swath being ground or polished. 
From the above description, it may be evident that machine tool 12 may be 
readily adapted to grind differently sized discs simply by mounting an 
appropriately sized or configured collar. And, the swath being ground or 
polished may be continuously varied. The resulting versatility of the 
machine tool is immeasurably enhanced. 
As will be evident by inspection, grinding wheel 22 is essentially and 
practically totally nonresilient and nondeforming during the grinding 
operation. Accordingly, the face of the grinding wheel is and will be 
maintained in a nonchanging, nonaltering planar relationship. In prior art 
grinding tools it was usually necessary to rigidly mount both opposed 
grinding wheels with massive structure such that the face of each grinding 
wheel was always maintained parallel to the opposing face to maintain them 
parallel with one another. By gimbal mounting grinding wheel 32, it is 
capable of continuing angular adjustment to maintain the face thereof 
continuously parallel with the face of grinding wheel 22. Thus, the rigid 
mounting structures attendant prior art devices are obviated. 
The parallel relationship between the opposing faces of the grinding wheels 
is established by the discs being ground themselves. That is, by random 
mounting of discs of somewhat different thicknesses, a concentration of 
the more thick discs on one side of the collar will not occur. 
Accordingly, the discs themselves will act as spacers between the grinding 
wheels and the more thick discs will be ground down until all discs are of 
the same thickness. The nongrinding of the less thick discs initially is 
precluded by the robust nature of the head of each of grinding wheel which 
precludes any localized deformation or bending of the heads. The end 
result in that of obtaining not only discs of uniform thickness but discs 
having opposed sides essentially absolutely parallel with one another. 
The operation of grinding tool 12 is controlled by automated controls which 
periodically reverse the rotation of direction, axially reposition the 
outer grinding wheel pertinent to mounting and demounting and insure that 
rotation of the grinding wheels continues through the make and break 
contact with the discs to avoid localized overgrinding. Moreover, the 
extent and application of load, axially directed, can be closely regulated 
commensurate with rotational acceleration/decceleration and reversal of 
rotation. By periodically reversing rotation, the grinding media tend to 
be self-dressing and thereby avoid down time of machine tool 12 due to 
dressing. 
While the principles of the invention have now been made clear in an 
illustrative embodiment, there will be immediately obvious to those 
skilled in the art many modifications of structure, arrangement, 
proportions, elements, materials, and components, used in the practice of 
the invention which are particularly adapted for specific environments and 
operating requirements without departing from those principles.