US3056238A - Grinding machine - Google Patents

Description

Oct. 2, 1962 R. s. HAHN 3,056,238

GRINDING MACHINE Filed June 24, 1960 3 Sheets-Sheet l F/G. l.

Rosmr s. HAH/v g I INVENTOR Oct. 2, 1962 R. s. HAHN GRINDING MACHINE 3 Sheets-Sheet 2 Filed June 24, 1960 k ROBERT 5. HAH/V INVENT OR ATTORNEYv Oct. 2, 1962 Filed June 24, 1960 R. S. HAHN GRINDING MACHINE 3 Sheets-Sheet El ROBERT S. HAH/V INV ENTOR United rates This invention relates to a grinding machine and more particularly to apparatus arranged to finish a surface of revolution by abrasion.

In the finishing of cylindrical surfaces and the like by grinding, it is common practice, particularly in the socalled centerless grinding technique, to clamp the workpiece at its ends between two members while its periphery is held in a supporting apparatus such as a set of shoes. Usually, one of the clamping members is driven to rotate the workpiece while the abrasive wheel is held against the surface to be finished. For extremely accurate grinding, particularly when the workpiece is of a thin-walled variety, the stresses set up in the workpiece by the clamping members and the supporting apparatus can bring about irregularities in the form of the surface generated by the grinding operation. Analyses of the forces which exist between the backing plate, the workpiece, the abrasive wheel, and the supporting shoes have been made; the backing plate forces have been studied particularly for two commonly-encountered special cases: first, where the work contacts the backing plate at three equally spaced points and, secondly, where contact is made at only two diametrically opposite points. This type of twoor three-point contact between the end of the workpiece and the backing plate takes place because of irregularities in manufacture of the end surfaces. ln most Workpieces, such as a race of a ball bearing, the end surfaces need not be finished with extreme accuracy, so that such irregularity of contact with the clamping plates is quite possible. Theoretical studies of the twoand three-point situation indicate that large speed fluctuations occur under this type of Contact condition. Also, excessive variations in the skewing force which urges the work into the supporting shoes may also occur under certain conditions. This would appear to be the cause for a twolobed and a three-lobed bore. Furthermore, in the previously-known centerless internal grinding machines, it has been necessary to have considerable friction between the supporting shoes and the periphery of the workpiece; otherwise, the abrasive wheel would speed up the workpiece well beyond the speed of the driving plate. This action would, of course, reduce the difference in speeds between the abrasive wheel and the workpiece, leading to ineicient grinding. At very high speeds, even the friction of the supporting shoes has not been suiiicient to prevent such action and this has been a limiting factor preventing grinding at the more efficient high speeds. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a grinding machine in which irregularities in the finished surface are eliminated.

Another object of this invention is the provision of a centerless grinding machine in which variations in driving friction force on the workpiece are reduced to a minimun1.

tent @di 3,056,233 Patented Get. 2, H962 A further object of the present invention is the provision of an internal grinding machine in which the ends of the workpiece are clamped between plates and driven and the periphery is `supported on shoes in -which irregularities in contact between the end of the workpiece and the backing plate do not bring about irregularities in the formation of the finished bore.

lt is another object of the instant invention to provide an internal centerless grinding machine having an outboard clamping plate of novel construction.

It is a further object of the invention to provide an internal centerless grinding machine having shoes for supporting the periphery of the workpiece, which shoes present relatively little friction force on the workpiece, which will not score the external surface of the workpiece, and which may be used at high work speed.

A still further object of this invention is the provision of a centerless grinding machine having an integrated hydraulic system for supporting and clamping the workpiece.

it is a still further object of the present invention to provide an internal centerless grinding machine having a novel means for aligning the axis of the workpiece with the axes of rotation of the clamping members.

A further object of this invention is the provision of an internal grinding machine of the centerless type in which the shoes, instead of presenting appreciable friction to the periphery of the workpiece, as in prior art machines, acts as a frictionless bearing for the workpiece, so that high speeds may be used without scoring of the workpiece, wearing of the shoes, and uncontrollable spinning of the workpiece at high grinding forces and high `work speeds.

With these and other objects in View, as will be appar ent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms as illustrated by the accompanying drawings in which:

FIG. 1 is a vertical sectional view through the center of a grinding machine embodying the principles of the present invention;

FIG. 2 is a view of the invention taken on the line Il-II of FIG. l;

FIG. 3 is a view of the invention taken on the line lli-Ill of FIG. 1, and

HG. 4 is a somewhat schematic view of the hydraulic system provided in the machine.

Referring to FIG. l, it can be seen that the grinding machine, indicated generally by the reference numeral It), is shown in use in iinishing an internal bore of a workpiece l1, which is shown as a short, tubular member, such as a bearing race. The machine is provided with a base l2 on which is mounted a work head 13, a support ld, an outboard clamping plate l5, and a pressure roll 16. The machine also includes the usual abrasive wheel 17.

The outboard clamping plate 15 consists of an annular frame 18 having a large bore 19 extending therethrough. A diaphragm 21, which may be formed of a thin metallic sheet, is fastened at its periphery to the frame. The diaphragm is provided with a central circular aperture ZZ to the edge of which is fastened a contact member 23 which is provided on one side with an annular lip 24 3 adapted to contact one end of the workpiece 11. Generally speaking, the width of this lip is less than the thickness of the workpiece. Opening on the face of the lip are a series of pockets 25 which are connected by passages 26 to tubes 27 leading to a source of pressure lubricant.

The support 14 is provided with a shoe 28 having two contact surfaces 29 Iand 311 adapted to engage the outer cylindrical surface of the workpiece 1l. The surfaces 29 and 311 are curved to fit the outer periphery of the workpiece 11 but are provided with a radius of curvature slightly greater than the radius of curvature of the workpiece, in accordance with the teachings of the patent to Blood `Reissue No. 24,202. The surface 29 is provided with a shallow pocket 32 leading through a passage 33 to a tube 34 leading to a source of pressure lubricant. In the same way, the surface 31 is provided with a pocket 35 connected by a passage 36 to a tube 37, which tube is also connected to a source of lubricant under pressure.

The pressure roll 16 is provided at its outer periphery with a rubber tire 38 and is provided centrally with a hub 319 by which it is mounted on a shaft 41 by means of set screws extending through the hub `and contacting the shaft. It will be understood that the shaft and Wheel are associated Iwith a well-known mechanism serving to remove the wheel from the workpiece for unloading and loading operations, but normally it is spring-biased toward the surfaces 29 and 31 of the shoe 28.

The workhead 13 is provided with a drive shaft 42 which extends therethrough and is provided on the end of the ywork head closest to the workpiece with a backing plate 43 adapted to engage that end of the workpiece which is opposite the end contacted by the outboard clamping plate 15. The other end of the drive shaft 42 extends from the workhead and has keyed thereto a pulley 44 which is connected to a motor (not shown). The work head is provided with a horizontal bore 45 through which the drive shaft extends. At the end adjacent the backing plate 44 a counterbore 46 is provided. In this counterbore is located a ball bearing 47 having an inner race 48, an outer race 49, and spherical balls l. Located between the ball bearing and the bottom of the counterbore 46 is a pressure plate 52 having an annular ilange 53 `which engages the inner side of the outer race 49. The pressure plate is biased toward the workpiece area by a series of coil springs 54 located in small bores 55 drilled horizontally into the bottom of the counterbore 46. At the other end of the workhead is a counterbore 56 and in this counterbore is located a ball bearing 57 having an outer race 58, an inner race 59 and spherical balls 6l. A retainer plate 66 holds the bearing 57 in the counterbore 56. Within the bore 45 and extending between the inner races 48 and 59 of the bearings is a sleeve 67. Centrally of the bore 45 the work head is provided with a groove 68 from which a passage 69 extends to the exterior of the Iworkhead for the purpose of providing the groove 68 with a supply of lubricant for the bearings. The outer end of the passage 69 is normally provided ywith a plug 71. The upper part of the workhead 13 is provided with a bore 72 which opens on the side adjacent the pulley 44 and which is normally closed by a plug 73. In this bore is located a piston 74 having a groove 75 extending around its central portion in which resides an O-ring 76; the O-ring is large enough to be slightly compressed against the sides of the bore to act as a piston ring. The piston is provided with a piston rod 77 which extends through a bore 78 opening on the face of the workhead adjacent the workpiece. The outer end of the piston rod 77 is provided with an arm 79 which extends downwardly and in line for contact with the outer face of the outer race 49 of the bearing 47. At one end of the bore 72 (which it will be understood constitutes the cylinder of a hydraulic linear actuator) a passage 81 is provided leading to a tube 82 connected to a source of uid under pressure; in the same Way the other end of the bore 72 is provided with a passage 83 leading to a tube 84, which in turn is connected to a source of iluid under pressure. It 4will be understood that there are three such hydraulic linear actuators :spaced 120 apart in the work head, all having arms which can contact the outer race of the ball bearing 47; for the purposes of simplifying the drawings and description, however, only one of these actuators is shown, it being understood that the pistons and their controls are connected in parallel for simultaneous operation.

Referring to FIG. 3, it can be seen that the hydraulic portions of the clamping plate 15, the supporting shoe 28, and the piston '74 are all supplied with grinding iluid from a pump 85 which is supplied with iluid through a conduit 86 from a sump tank 87. The pump is connected to a conduit 88 from which the various circuits are supplied with tiuid. For instance, the pump l85 is connected throught a pressure regulating valve 89 and through fluid resistances `91 and 92 (which are preferably in the form of orilices) to the tubes 34 and 37, respectively, which provide the passages 33 and 36 and the pockets 32 a-nd 35 with fluid. In a similar manner, the conduit 88 is connected through a pressure regulating valve 93 to a manifold tube `94 which is connected to the outer ends of uid resistances 95 leading to the tubes 27 which, through the passages 26, supply the pockets 25 with fluid. The conduit 88 is connected through a pressure-regulating valve 96 which is connected to the input port of a four-way valve 97. The output ports of the valve are connected through a conduit 98 to the sump tank 87 for discharge. One output port 99 is conected by the tube 84 to one side of the bore 72. Another output port 101 is connected through the tube 82 to the other end of the bore 72. The valve is provided with a spool l102 which selectively connects the various ports to one another. In the condition shown in the drawing, the spool connects the fluid originating in the regulating valve 96 to the output port 101 so that pressure lluid is provided at the right hand side of the piston 74. The other side of the bore 72, which is connected through the tube 84 to the port 99, is connected through the tube 84 to the port 99, is connected to a discharge port for the passage of fluid through the conduit 98 to the sump tank 87. One end of the spool 102 is provided with a solenoid 103 having an actuating coll which is in the control circuit of a control element of the machine so that, after the pressure wheel 16 has been returned after loading to hold the workpiece 11 in its shoes, fluid is permitted to pass through the tube 82 to the right hand side of the cylinder to move the piston 74 to the left. 'Ihe nature of this electrical control is not part of this invention, but would be part of the conventional cycling controls of an internal grinding machine.

The operation of the invention will now be readily understood in View of the above description. The drive shaft 42 is operated continuously, is driven `through the pulley 44, and does not have its rotation interrupted during the normal machine cycle. In the same way, fluid would -be `supplied to the pockets 25 of the outboard clamping plate 18 at all times during the cycle. Similarly, the pockets 32 and 35 of the shoe 28 would be provided with pressure fluid at all times. When a workpiece is not in the machine, the resistances in series with these iiuid pockets are sufficient to keep the ilow at a reasonable value. At the beginning of a machine cycle, a new workpiece 11 is inserted in the machine and the pressure roll 16 presses on the outer periphery of the workpiece opposite the shoe 28. As is evident in FIG. 2, the surfaces 29 and 31 form a V, that is to say, the surfaces are symmetrical about a vertical plane passing through the center line of the workpiece in a longitudinal direction. This V-shaped shoe serves to compensate automatically for variations in the outside diameter of the workpiece in a manner well known in the art. The pressure roll 16 serves to keep the workpiece in the shoe despite the tendency of the abrasive wheel 17 to force the workpiece out of the shoe because of the horizontal force that it exerts on the inner bore of the workpiece. During the loading operation, the plunger 102 of the four-way valve 47 is located by the solenoid 103 in such a position -that pressure fluid originating in the pump `85 goes to the left hand side of the piston 74, thus moving the piston rod 77 and the arm 79 to the right. Because of the symmetrical location of the various pistons around the bearing 47, this causes an axial force to be exerted on the outer race i9 of the bearing 47 by the springs; that is to say, `the biasing pressure of the springs 54 cause `the stressing of the bearing in the horizontal direction. This means that the balls S1 will be tightly squeezed between the inner and outer races Of-the bearing and the shaft d2 will be rigidly held about the same axis at both ends. As soon as a new workpiece 11 has been loaded into the machine and the pressure roll 16 is in place, the driving action of the backing plate 43 against the end of the workpiece will cause the workpiece to rotate. At the same time, the solenoid w3 is actuated to reverse the valve 97 and to cause the pressure to go yto the right side of the piston 74 and so that the left side of the piston is connected to discharge. This causes the arm 79 associated with the piston rod 77 to move toward the outer race of the bearing 47 so that the springs 54 are relieved of biasing operation. This relieves the internal stress in the ball bearing and causes the balls 51 to be loosely held between the inner and outer races. The result of this action is that the end of the shaft 42 on which the backing plate 44 is attached is free `to move in any direction transversely of the axis of the shaft. Since `the shaft is free to wobble, the skewing action, which takes place when the workpiece 11 and the backing plate 43 are eccentric and rotated on their own independent axes, will cause the backing plate to rotate on the axis of the workpiece, the workpiece itself being fixed by the surfaces 29 and 31 of the shoes and by the pressure roll 16. The workpiece and the drive shaft then rotate as a single shaft and they act Ias though they are supported in only two bearings, one bearing being the ball bearing 57 at the left side of the workhead and the other being the bearing provided by the surfaces 29 and 31 of the shoe 28.

It should be pointed out that, although the bearing 57 is relieved of its preloading stress by the same action that relieves the preloading stress in the front bearing 47, it is not as subject to wobbling action, since it is so far from the workpiece and since it is pressed to one side by the tension in the drive belt acting on the pulley 44. Then the machine proceeds with the usual grinding operation; once the wheel 17 is removed, the pre-loading pressure is applied to the ball bearing t7 and the workpiece is removed. The loading of the workpiece between the backing plate 43 and the clamping plate 18 takes place because of the natura] resilience inherent in the plate 23 because of the diaphragm 21. The workpiece is thus squeezed very readily between the two clamping members. There is no scratching of the workpiece s-ince the lubrication supplied from the pockets 25 prevents `such action. Furthermore, if, because of differences in outside diameter of successive workpieces, the clamping plate 18 is slightly eccentric with regard to the workpiece, there is no skewing action which would tend to defeat the purpose of the invention because of the lubrication. The film between the clamping plate and the workpiece is provided in a hydrostatic manner by the fluid in the pockets 25. It will be understood that, as the workpiece begins to rotate at operating speed, an additional hydrodynamic lm may be formed, thus clearly separating the workpiece vfrom the thrust plate 23. The type of `lubrication described above is also to be found in connection with the surfaces 29 and 31 of the shoe 28. Pressure iiuid from the pockets 32 and 35 operate bydrostatically when the workpiece is coming up to speed, but, when it reaches its operating speed, there may be a degree of hydrodynamic lni developed, so that scratching of the workpiece will be eliminated and also `resistance to rotation of the workpiece will be avoided. Furthermore, as has been described above, the clamping plate y15 produces little in the way of friction force on the workpiece surface. Therefore, most of the torque supplied to the workpiece will be that required to rotate the workpiece despite the peripheral forces on the interior of the bore provided by the abrasive wheel 17. It Will be understood that, because there is no necessity for slippage between the backing plate 43 and the workpiece, the workpiece is clamped tightly against the backing plate. The backing plate, therefore, not only drives the workpiece, but also prevents it from speeding up under the action of the abrasive wheel. This permits operation at high wheel speeds and loads.

It will be understood that while the energy of rotation has been supplied in the preferred embodiment through the drive shaft 42, the machine could be built with an idling shaft and with the force supplied to the workpiece by the pressure wheel 16.

In the preferred embodiment, it will be noted that the inner races of the two ball bearings are held in place by a shoulder at the right end of the drive shaft 42 which contacts the outboard side of the inner race 48 of the ball bearing 47 and a boss on the pulley 44 which engages the outer side of the inner race 55' of the ball bearing 57. Furthermore, the outer race 58 of the ball bearing 57 is locked in place by the plate 66 so that the bearing is under an initial pre-loading stress Vand the balls 61 are tightly held between the inner and outer race so that that end of the shaft 42 is iixedly located, although, of course, rotation can take place. So far as the bearing 47 is concerned, the inner race is locked in place tightly, because of the shoulders and bosses which combine with the sleeve 67 to hold the inner races in place; the outer race, however, is permitted to move, on occasion, to remove the pre-loading so that the shaft i2 is capable of wobbling at the backing plate end.

It is obvious that minor changes may be made in the Aform and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent,

1. A grinding machine for finishing a workpiece cornprising a grinding wheel, a driving spindle adapted to contact one end of the workpiece, a clamping plate adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, the spindle being mounted for rotation in a work head, a sub st antial length of the spindle at the end thereof which contacts the said one end of the workpiece being capable of movement in any direction transversely of its axis.

2. A grinding machine for finishing a workpiece, com prising a grinding wheel, a spindle adapted to contact one end of the workpiece, a plate adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, the spindle being mounted for rotation in a work head, a substantial length of the spindle at the end thereof which contacts the said one end of the workpiece being capable of movement in any direction transversely of its axis, and a pressure wheel to press the workpiece into contact with the support means.

3. A grinding machine for finishing a workpiece, comprising a grinding wheel, a driving spindle adapted to contact one end of the workpiece, a clamping plate adapted to contact the other end of the workpiece, a support adapted to contact the periphery of the workpiece, the said clamping plate having a flexible diaphragm whose outer periphery is securely held in a frame and having a contact member mounted in the central portion of the diaphragm.

4. A grinding machine for finishing a workpiece, comprising a grinding wheel, a driving spindle adapted to Contact one end of the workpiece for the. rotation thereof, a non-rotating clamping plate adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, and means supplying the lubricant to the clamping plate to cause a iilm to exist between the plate and the said other end of the workpiece.

5. A grinding machine as recited in claim 4 wherein means is provided for supplying lubricant to the supporting means to cause a ilm to exist between the means and the said periphery of the workpiece.

6. A grinding machine for finishing a workpiece, comprising a grinding wheel, a driving spindle adapted to contact one end of the workpiece, a clamping plate adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, the spindle being mounted for rotation in a work head, a substantial length of the spindle at the end thereof which contacts the said one end of the workpiece being capable of movement in any direction transversely of its axis, the said clamping plate having a flexible diaphragm whose outer periphery is securely held in a frame and having a contact member mounted in the central portion of the diaphragm.

7. A grinding machine for finishing a workpiece, comprising a grinding wheel, a driving spindle adapted to contact one end of the workpiece for the rotation thereof, a non-rotating clamping plate adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, the said clamping plate having a flexible diaphragm whose outer periphery is securely held in a frame and having a contact member mounted in the central portion of the diaphragm, and means for supplying the lubricant to the clamping plate to cause a film to exist between the plate and the said other end of the workpiece.

8. A grinding machine for finishing a workpiece, cornprising a grinding wheel, a driving spindle adapted to contact one end of the workpiece for the rotation thereof, a non-rotating clamping plate adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, means supplying lubricant to the clamping plate to cause a iilm to exist between the plate and the said other end of the workpiece, the spindle being mounted for rotation in a workhead, a substantial length of the spindle at the end thereof which contacts the said one end of the workpiece being capable of movement in any direction transversely of its axis.

9. A grinding machine for finishing a workpiece, comprising a grinding wheel, a driving spindle adapted to contact one end of the workpiece for the rotation thereof, a non-rotating clamping plate adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, the spindle being mounted for rotation in a workhead, a substantial length of the spindle at the end thereof which contacts the said one end of the workpiece being capable of movement in any direction transversely of its axis, the said clamping plate having a flexible diaphragm whose outer periphery is securely held in a frame and having a contact member mounted in the central portiorrof the diaphragm, and means supplying lubricant to the'giclamping plate to cause a film to exist between the plateand the said other end of the workpiece.

10. A grinding machine for finishing a workpiece, comprising a grinding wheel, a Vspindle adapted to contact one end of the workpiece, a plate adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, a substantial length of the spindle at the end thereof which contacts the said one end of the workpiece being capable of movement in any direction transversely of its axis, and a pressure wheel to press the workpiece into contact with the support means, the said plate having Va flexible diaphragm whose outer periphery is securely held in the frame and having a contact member mounted in the central portion of the diaphragm.

11. A grinding machine for nishing a workpiece, comprising a grinding wheel, a driving spindle adapted to contact one end of the workpiece for the rotation there- 0f, a non-rotating clamping plate adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, the said clamping plate having a exible diaphragm whose outer periphery is securely held in a frame and having a contact member mounted in the central portion of the diaphragm, means supplying lubricant to the clamping plate to cause a film to exist between the plate and the said other end of the workpiece, and means supplying the lubricant to the supporting means to cause a iilm to exist between the means and the said periphery of the workpiece.

12. A grinding machine for finishing a workpiece comprising a grinding wheel, a spindle adapted to contact one end of the workpiece, a non-rotating plate adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, the spindle being mounted for rotation in a work head, a substantial length of the spindle at the end thereof which contacts the said one end of the workpiece being capable of movement in any direction transversely of its axis, a pressure wheel to press the workpiece into contact with the support means, means supplying lubricant to the plate to cause a film to exist between the plate and the said other end of the workpiece, and means supplying lubricant to the supporting means to cause a iilm to exist between the means and the said periphery of the workpiece.

13. A grinding machine for finishing a workpiece, comprising a grinding wheel, a spindle adapted to contact one end of the workpiece, a non-rotating plane adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, the spindle being mounted for rotation in a work head, a substantial length of the spindle at the end thereof which contacts the said one end of the workpiece being capable of movement in any direction transversely of its axis, a pressure wheel to press the workpiece into contact with the support means, the said plate having a flexible diaphragm whose outer periphery is securely held in a frame and having a Contact member mounted in the central portion of the diaphragm, means supplying lubricant to the plate to cause a film to exist between the plate and the said other end of the workpiece, and means supplying the lubricant to the supporting means to cause a film to exist between the means and the said periphery of the workpiece.

14. A grinding machine for iinishing a workpiece, comprising a grinding wheel, a driving spindle adapted to contact one end of the workpiece, a clamping plate adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, the spindle being mounted for rotation in two longitudinally-spaced ball bearings in a work head, each bearing having inner and outer races and ballsheld therebetween, means for axially pre-loading the bearings, and means for selectively relieving the said pre-loading in the bearings to render a substantial length of the spindle at the end of which contacts the said one end of the workpiece capable of movement in any direction transversely of its axis.

15. An internal grinding machine for vfinishing a workpiece, comprising a grinding wheel, a driving spindle adapted to contact one end of the workpiece, a clamping plate adapted to contact the other end of the workpiece, a V-type supporting shoe adapted to contact the periphery of the workpiece, the said clamping plate having a iiexible diaphragm whose outer periphery is securely held in a frame, the clamping plate having a circular aperture centrally thereof, and an annular contact member fastened to the edge of the aperture.

16. A grinding machine for finishing a workpiece, comprising a grinding wheel, a backing plate adapted to contact one end of the workpiece, a clamping plate adapted to contact the other end of the workpiece, a support means adapted to contact the periphery of the workpiece, the backing plate being mounted for rotation in a work head, the backing plate being capable of movement in any direction transversely of its axis, and means supplying lubricant to the supporting means to cause a lilm to exist between the means and the said periphery of the workpiece.

References Cited in the lile of this patent UNITED STATES PATENTS Dix Apr. 19, 1955 Dix Nov. 15, 1955 Bidwell July 17, 1956 Boyd Dec. 4, 1956 Arms May 28, 1957 Thompson Dec. 8, 1959 Manard Sept. 6, 1960

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