US3562960A

US3562960A - Apparatus for the grinding,honing and abrasive finishing of annular workpieces,especially bearing rings

Info

Publication number: US3562960A
Application number: US830264A
Authority: US
Inventors: Ernst Thielenhaus
Original assignee: Ernst Thielenhaus GmbH and Co KG
Current assignee: Ernst Thielenhaus GmbH and Co KG
Priority date: 1968-03-28
Filing date: 1969-06-04
Publication date: 1971-02-16
Anticipated expiration: 1988-02-16
Also published as: FR2010416A1

Abstract

AN APPARATUS FOR THE GRINDING, HONING OR ABRASIVE FINISHING OF BEARING RINGS IN WHICH A TURRET OR MAGAZINE IS PROVIDED WITH A PLURALITY OF ANGULARLY EQUISPACED OUTWARDLY OPEN POCKETS. THE WORKPIECE ARE FED TO THE POCKETS IN SUCCESSION AND ARE SWUNG BY THE TURRET DISK INTO AT LEAST TWO WORKING POSITIONS BEFORE BEING RELEASED AT A DISCHARGE STATION. EACH OF THE WORKING STATIONS INCLUDES A DRIVE SPINDLE ADAPTED TO BEAR AGAINST ONE FACE OF THE WORKPIECE WHILE THE OTHER FACE THEREOF IS ENGAGED BY A FREELY ROTATING SLEEVE COMBINED WITH A FLUID-CENTERING ARRANGEMENT WHICH IS AXIALLY THRUST INTO THE INTERIOR OF THE RING-SHAPED BODY. A SHAPING TOOL ENGAGES THE OUTER PERIPHERY OF THE RING.

Description

Feb. 16, 1971 THIELENHAUS 3,562,960

APPARATUS FOR THE GRINDING, HONING AND ABRASIVE FINISHING 0F ANNULAR WORKPIECES, ESPECIALLY BEARING RINGS Filed June 4. 1969 4 Sheets-Sheet l INVENTOR:

ERNST THIELENHAUS m jams ATTORNEY 15, 1971 THIELENHAUS 3,562,969

APPARATUS FOR THE- GRINDING. HONING AND ABRASIVE FINISHING OF ANNULAR WORKPIECES ESYECIALLY BEARING RINGS Filed Juno 4. 1969 4 Sheets-Sheet 2 LL II 1 F I G 3 m :5 2a\ 2 1 i 24d Q 7 Y INVENTOR.

ERNST THlELENHAUS ATTORNEY Feb. 16, 1971 lE N AUs 3,562,966

APPARATUS FOR THE GRINDING, HONING AND ABRASIVE FINISHING OF ANNULAR WORKPIECES, ESPECIALLY BEARING RINGS. Filed June 4. 1969 4 Sheets-Sheet 3 FIG.4

INVENTOR: ERNST THIELENHAUS BY ATTORNEY Feb. 16, 1971 THELENHAUS 3,562,960

APPARATUS FOR THE GRINDING. HONING AND ABRASIVE FINISHING OF ANNULAR WORKPIECES, ESPECIALLY BEARING RINGS Filed June 4. 1969 4 Sheets-Sheet 4 INVENTOR; ERNST THIELENHAUS ATTORNEY United States Patent No. 830,264 Claims priority, application Germany, June 8, 1968, P 17 52 064.1 Int. Cl. B24b 7/00 US. Cl. 51-58 Claims ABSTRACT OF THE DISCLOSURE An apparatus for the grinding, honing or abrasive finishing of bearing rings in which a turret or magazine is provided with a plurality of angularly equispaced outwardly open pockets. The workpieces are fed to the pockets in succession and are swung by the turret disk into at least two working positions before being released at a discharge station. Each of the working stations includes a drive spindle adapted to bear against one face of the workpiece while the other face thereof is engaged by a freely rotating sleeve combined with a fluid-centering arrangement which is axially thrust into the interior of the ring-shaped body. A shaping tool engages the outer periphery of the ring.

This application is a continuation-in-part of my application Ser. No. 810,529 filed Mar. 26, 1969.

My present invention relates to an apparatus for the finishing of annular bodies and, more particularly, to a machine for accurately grinding, honing, polishing, microfinishing or treating with abrasive, ring-shaped bodies such as ball-bearing races along the external periphery of the ring.

In abrasive-tool machines for the grinding, honing, and microfinishing of annular bodies known heretofore, considerable problems have been encountered because of the nature of the finishing process and the characteristics of the workpieces to be finished. For example, in certain earlier devices or proposals, the ring is clamped in the jaws of a chuck and is rotated on the spindle carrying the chuck while a tool engages the periphery of the workpiece. This system has the disadvantage that, when a three-jaw or self-centering chuck is provided, the workpiece is often deformed into a triangular configuration as a result of the grip of the jaws. Such deformation destroys the circularity of the workpiece. Furthermore, such systems are often characterized by inexactitude of the rotation of the spindle, i.e. the spindle does not always rotate with perfect circularity about a fixed axis. More often, the axis of rotation of the spindle migrates or oscillates to a certain extent. In conventional ring-machining systems, this inexactitude of the concentricity of the spindle is transformed into an inexact machining, shaping or finishing of the workpiece. The problem is multiplied when the machines for the finishing of bearing faces, for example, are required to have relatively high capacities. In some cases, it has been proposed to provide hydraulic or hydrostatic bearing systems for the spindle to eliminate the lack of concentricity thereof. Indeed, such hydraulic journal arrangements reduce the deviation, but are ineffective when high-machining rates and capacities, in terms of workpiece output, are necessary.

It is possible to reduce the inaccuracies of such finishing processes when the workpiece is retained in a socalled magnetic chuck in which magnetic devices retain the ring against a surface of the chuck. The lastmentioned system has the significant disadvantage that a residual magnetism is found in the workpiece at the conclusion of the machining operation and such magnetic remanence is undesirable in many applications in which the bearing races may be desirable.

It is the principal object of the present invention to provide an apparatus for the machining and high rates of circular workpieces such that additional inaccuracies are not reproduced in the workpiece as a result in the way the workpiece is held.

Another object of my invention is to provide an improved apparatus for the fine polishing, grinding, honing and microfinishing of circular workpieces, especially ballbearing races, which is capable of permitting external peripheral finishing of the roller-engaging surface of an inner bearing race.

Yet another object of the instant invention is the provision of a machine for the purposes described which will obviate the aforementioned disadvantages and enable finishing, especially microfinishing, of ring-shaped workpieces with a high degree of accuracy and with improved surface characteristics.

It is still another object of my invention to extend the principles set forth in my application Ser. No. 810,529, filed Mar. 26, 1969, to the external peripheral machining of bearing races and the like.

In the aforementioned application, I have described an apparatus for the finshing of annular bodies, e.g. bearing rings or races and like workpieces, wherein a plurality of drive spindles is angularly spaced about an axis to define respective machining stations, each spindle being associated with a respective tool, preferably in the form of a grinding, polishing or honing stone.

The invention described in application Ser. No. 810,529 provides a magazine or turret in the form of a disk-shaped plate rotatable about its horizontal axis and lying perpendicularly thereto in a vertical plane and at right angles to the axes of the spindles, while being formed with a plurality of angularly spaced workpiece-retaining seats respectively alignable with the spindles upon rotation of the magazine or turret plate by a turret shaft to which the plate is aflixed, the tools being engageable with inner surfaces of the workpieces at the respective finishing stations.

The workpieces are held against the respective spindles and rotatably entrained thereby when the turret carrying the workpieces register with the spindles axially. The centering of the workpieces with respect to the tools and the spindles is of the fluid type, the principles of which are described in my US. Pat. No. 3,082,013. The centering system is a narrow annular gap between the outer periphery of the workpiece and the respective seat to which fluid is forced under pressure, the fluid preferably being a liquid. Thus all portions of the workpiece are held away from the confronting walls the seat by a constant fluid pressure and at a constant distance, any deviation being limited automatically by the pressurized fluid.

At least two such driven spindles are provided at the finishing stations in succession along the path of the angularly displaceable turret and are associated with respective abrasive stones of progressively increasing fineness so that each workpiece remains in its assigned seat during the multistage processing by the successive stones, thereby preventing nonuniformity or distortion from developing as a result of the change in position of the workpiece from one operation to the next.

According to a feature of the invention described in my prior application, the axes of the spindles and the turret shaft are generally horizontal, while the turret plate lies in a vertical plane and the machining head is formed with a workpiece-inserting station having means for successively inserting the workpiece rings into the successive seats prior to rotation of the turret to position each workpiece at the initial machining station. An ejection station is also provided to dislodge, via suitable means the finished ring-shaped workpiece from each seat before the turret is stepped to align the empty seat with the input station.

The fluid-centering means of that system includes a fluid-distribution duct network or manifold at the junction between the turret shaft and the turret plate to which fluid is delivered by a pump or the like through a passage in the shaft. Each seat is formed with one or more annular inwardly open grooves communicating with the fluid-distributing network and generating the centering pressure between the exterior of the workpiece and the inwardly facing wall of the respective circular seat. The seat was, therefore, formed with grooves and had an annular configuration so as to be received in a suitably dimensioned socket at each of the angularly spaced locations about the turret plate. The seating annuluses were fixed to the turret plate, e.g. via retaining means such as screws threaded therein, or were rotatable in the turret plate with the workpiece. In the latter case, the high-pressure fluid formed a lubricant between the turret plate and the seating annuluses which was freely rotatable with the workpiece.

In order to insure effective centering of the annular workpieces in the seating annuluses of that system and to maintain the position of the workpiece during machining, I provided that the pressure in the gap between the workpiece and the inner annular surface of the seating ring was in a relation to the pressure and viscosity of the fluid, such that the maximum machining force in the radial direction was balanced and the workpiece body was retained at a distance from the surrounding surface at all points. The hydraulic medium used as a fluid, especially oil, permitted the difference between the internal diameter of the seating annuluses and the external diameter of the workpiece to range between 0.05 and 0.02 mm. The hydraulic pressure in this case was determined by the relationship described in the aforementioned patent. The spindles for driving the workpiece bodies at the machining locations have surfaces or thrust disks substantially flush with the reverse sides of the turret or magazine while the apparatus was provided along the front side of the plate at least at the machining stations, with a pressing mechanism designed to retain the workpieces against the spindles. The pressing arrangement included a yoke pivoted at its bight for rotation about an axis perpendicular to the axis of the workpiece body and the spindle but intersecting the latter. The shanks or arms of the U carried diametrically opposed rollers with a common axis parallel to the face of the turret place and perpendicular to the axis of rotation of the workpiece body and to the pivoting axis of the yoke. These rollers bear upon the front face of the workpiece.

The machining tool of that system was a generally radial machining stone carried by an arm or holder extending into the race and having a rounded machining and engaging the raceway generally radially. The apparatus also included means for swinging the tool and the holder about an axis corresponding to the center of curvature of the raceway.

In systems in which pressurizable-fluid centering of an annular workpiece takes place upon a stud extending through the center of the workpiece, thereby permitting the machining or surfacing of the outer periphery, it has heretofore been customary to rotate this stud, thereby driving the spindle, the workpiece being retained against a shoulder of the stud from frictional entrainment about the axis thereof. The journaling deficiencies or eccentricities of the spindle are here also transferred to the workpiece. The problem is multiplied when the workpiece must be placed upon several centering studs for successive machining operations. Thus, simply carrying out a kinematic reversal of the system described in my above identified application to permit machining of the external periphery, using a centering stud that frictionally engages the workpiece to drive the latter, has not proved satisfactory.

According to the present invention, a grinding machine for the honing, polishing, microfinishing or other abrasive treatment of outer peripheral portions of annular workpieces, especially ball-bearing races, comprises a pair of workpiece-drive spindles engageable with one face of the workpieces and coaxially aligned with centering studs adapted to effect a pressurized-fluid centering of the workpieces at least at two angularly spaced locations about a common axis, the stud being receivable within the interior of the workpiece rings for sustaining the introduction of fluid under pressure to the gap between the stud and the workpiece; thus I maintain a uniform clearance to properly center the workpiece.

Along the outer periphery of the workpiece, a machining stone is provided, e.g. as described in the aforementioned application, to form the bearing race.

The machine according to the present invention is characterized by the provision of at least two such driven spindles and machining locations, each having a respective centering stud axially aligned with the respecti e drive spindle and confronting the latter across a gap.

A magazine disk or turrent plate is rotatable through this gap about the aforementioned axis and is provided along its periphery with a plurality of angularly equispaced pockets, open outwardly, i.e. radially, to permit machining of the workpieces through the opening in the plate at each pocket. The pockets are successively alignable with the spindles and centering studs of each station for coarse and fine finishing, respectively, and the centering studs are preferably axially shiftable to enter and withdraw from the workpieces when the latter are positioned at the machining station and swung in the plane of the plate, i.e. in a vertical plane, between the stations.

An important feature of this invention is the provision at each of the centering studs of a thrust sleeve which surrounds the stud with play and is freely rotatable about the axis thereof while bearing upon the workpiece along an annular zone to retain the workpiece against the opposite drive spindle. In other words, the centering stud and pressing sleeve are no longer part of the drive spindle and the centering stud is non-rotatable. Preferably, the system is so constructed and arranged that the centering stud is connected with an axially reciprocable threadedspindle drive arrangement.

According to another feature of this invention, the spindle sleeve of the axial-reciprocation drive also is coupled with the pressing sleeve to advance the latter and release this sleeve to permit rotation of the turret plate when the centering stud is withdrawn. The pressurized-fluid medium serving as the centering force, is preferably hydraulic, i.e. oil, and the centering stud is therefore provided with an axially extending manifold passage which, in turn, communicates with radial passages opening between the workpiece ring and the outer periphery of this centering stud.

In addition, I prefer to provide further passages in the centering stud which open between the outer surface thereof and the inner surface of the surrounding pressing sleeve so that the latter defines with the centering stud a hydrostatic bearing.

To take up the axial forces between the shoulder of the spindle sleeve and the pressing sleeve, while permitting free rotation of the latter, I also make use of a thrust hearing at the end of the pressing sleeve remote from the workpiece.

In addition to the working stations described above, the apparatus of the present invention comprises an in sertion station in which a succession of coarse-finished bearing rings are inserted into the empty pockets of the turret plate as they are swung into position alongside a supply chute, the insertion means including a plunger shiftable generally radially with respect to the axis of rotation of the turret plate. The turret plate also is provided with a discharge station at which the pockets, after leaving the final work station, open downwardly and thereby discharge the finished workpieces into a collection chute which in turn may lead to a receptacle. In this construction, as in the system described in the aforementioned copending application, the machining stone may have a rounded end conforming to the curvature of the bearing race and may be swung about an axis perpendicular to the axis of the bearing ring, the axis of the tool lying generally at the center of curvature of the bearing race.

The machine of the present invention, as outlined above, has the significant advantage that inexactitudes of the drive-spindle bearings and eccentricities thereof cannot be transmitted to the workpiece since the workpiece is no longer fixed to rotate about the center of the spindle. It is, however, free to rotate concentrically with respect to the centering stud which, according to the instant invention, is fixed and permits a highly exact positioning of the workpiece, especially when the latter rests against the hydrostatically journaled pressing sleeve. In addition, the workpiece can be brought from one machining stage to another without withdrawal and without difiiculty since both centering studs may be positioned with great precision, since they are nonrotating.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a front view of a machine according to the present invention, the drive-spindle assemblies having been removed;

FIG. 2 is a side view of the machine with the drivespindle assembly in place;

FIG. 3 is a plan view of the machine;

FIG. 4 is an enlarged view of the turret plate as seen in FIG. 1;

FIG. 5 is a section generally along the line V-V of FIG. 4; and

FIG. 6 is a section along the line VI-VI of FIG. 5.

In FIGS. 1-6 of the drawing, I have shown a system for the finishing of the external peripheral raceways of a bearing ring or workpiece W. The raceway to be polished is represented at R (FIGS. 5 and 6).

The machine comprises a pair of rotatably driven spindles 1, 2 (FIGS. 2 and 3), driven about mutually parallel axes 1a, 2a by a common motor 50 mounted upon a support table 18, the base of which is shown at 18a in FIG. 2. The spindle drive assembly 50 is horizontally shiftable with its base 50a along the table 18 as indicated by the arrow A in FIG. 2, disposed on one side of a magazine or turret disk 3 best seen in FIGS. 4 and 5. The magazine disk 3 is secured to a turret shaft 14 by bolts shown in section at 14a in FIG. 4. A shoulder 14b of this shaft forms an abutment against which the turret 3 is held by the bolts 14a while a centering stud 140 of shaft 14 is received in a centering opening 3a of the turret disk.

The apparatus, illustrated by way of example in the drawing, includes a plurality of stations (four in number) angularly equispaced about the axis B of the plate 3 which lies in a vertical plane and extends perpendicularly to this axis. In the lower right-hand quadrant of the path of the disk 3, there is provided an insertion station represented at I while the upper right-hand quadrant defined the first or relatively coarse finishing stage II. The upper left-hand quadrant forms the final polishing of fine finishing stage III. The lower left-hand quadrant is a discharge station represented at IV. The disk 3 rotates counterclockwise as viewed in FIG. 4 and as indicated by the arrow C.

The disk '3 is provided with a plurality of outwardly open, circular or semicircular pockets 7 whose centers 7a lie along radii of the disk and which can receive a rough workpiece W as it is thrust in the direction of arrow 4 into the pocket 7 at the insertion station I. At the discharge station IV, the finished workpiece W is permitted to drop from the disk as represented by the arrow 5 in this figure. The pockets of the disk are designated by the

individual reference numerals

8, 9, 10 and 11.

At each of the working stations, there is provided, as shown in FIG. 5, a pair of axially shiftable centering studs '12, 13, adapted to extend into the internal cavity of a workpiece W aligned with the stud in the pocket 7 at stations II and III. The centering

studs

12, 13 are shiftable as represented by arrow D into and out of the workpiece and are tubular with internal bore 27 being connected to a high-pressure source 27a, a reservoir 27b, etc. for the pressurized-fluid centering of the workpiece W. Bore 27 communicates with a plurality of angularly equispaced radial bores 27c (FIGS. 5 and 6) opening into the slight clearance 27d between the outer cylindrical periphery of stud 12, 1 3 and the inner cylindrical periphery of the workpiece W.

Upon the centering

studs

12, 13, there are provided (with circumferential play P), respective pressing sleeves 15 whose front faces 15a are adapted to support the workpiece W against the rotating spindles 1, 2. The centering

studs

12, 13 are provided with outwardly extending annular flanges 24 against which thrust bearings 23 are seated, the thrust bearings receiving axial pressure from the rear end of sleeve 15. A cap 26a, bolted to the housing 26b, has an inwardly turned flange 26c co-operating with the outwardly extending ridge 15d of sleeve 15 to prevent axial movement of the sleeve 15 to the left relative to the centering

stud

12, 13.

The centering

stud

12, 13 is also formed with a tapered shank 24a which is retained in a complementary frustoconical seat 24b of a spindle sleeve 12a or 13a, forming a collet from which the centering stud may be withdrawn upon release of a threaded rod 24c extending through the spindle sleeve 12a and terminating in a handwheel 24d adapted to lock the centering

studs

12, 13 into the spindle sleeve. The spindle sleeves 12a, 13a are axially shiftable in sliding bearings 26d of the fixed housing 26 under the control of a piston-and cylinder arrangement 26a to insert the centering stud into and remove it from the workpiece W as they are positioned at the stations II and III.

The turret shaft 14 is rotated by a motor 20 (FIGS. 3 and 5) which, in turn, is controlled by a timer or other programmer 20a, the latter also triggering the cylinder 26c when the turret has halted and, via output 20b operates the insertion mechanism as well.

Reverting to FIG. 1, it can be seen that the table 18 also is provided with a

chute

52, 53 along which the workpieces W roll downwardly (arrow B) to the insertion station located at the lower right-hand quadrant of the machine. Radially aligned with each pocket 7 as the empty pockets are stepped to the insertion station I, is a plunger 4a operated by a fluid pressure cylinder 4b under the control of the output 20b of the programmer, to shove successive workpieces W into the properly aligned empty pocket 7.

To prevent the workpieces from falling from the newly filled pocket, an arcuate guide 54 closely flanks the turret disk *3 between a position in which the pocket 7 opens downwardly and the first working position in which the pocket opens upwardly.

On the other side of the disk 3, an arcuate sheetmetal guide 55 prevents dislodgment of the workpiece W which has completed finishing operations, until the pocket 7 is positioned at the lower left-hand quadrant to dump the bearing ring onto the chute 53 from which the ring passes into a collecting receptacle 56.

As can be seen from FIG. 5, the machine is designed to form a raceway R with a double curvature along the outer periphery of the workpiece W. The raceway R has a first center of curvature corresponding to the axis A of the shaping station to form the circumferential surface as the workpiece is rotated at high speed. In addition, the transverse curvature about the center F is required when a ball-bearing race is to be produced. To this end, the finishing stone 6 at each working station is mounted so as to swing about the center F as described in my application Ser. No. 810,529. To this end, each stone 6 is driven by a

mechanism

21, 22, the function of which will be set forth below.

Polishing stones 6 are each carried at the end of a respective tool holder or rod 6a and are swingable via their respective holders about the oscillation point represented at

F. Leadscrews

6b and 6c permit positioning of the tools in the direction of arrows G and H, respectively. Motor 21 is mounted on the slide 21a and connected by a belt transmission 21b with a speed-reducing transmission 22 adapted to transform the rotary movement of the motor into an oscillation of the tools.

At each work station, the spindles 1, 2 are provided with flanges 1b, for example, to which thrust members are bonded at 1a, the thrust members 10 have annular surfaces 1e engageable with the front faces of the workpieces W to frictionally drive the latter.

The free rotation of the workpieces, in spite of the axial thrust applied to them, is promoted by mounting the sleeve as a hydrostatic or fluid-pressure bearing. To this end, the passage 27 is provided with additional radial bores 27f which communicate with the clearance P between the pressing sleeve 15 and the centering

studs

12, 13.

In operation, assuming three previous cycles of machining, the completely finished workpiece W.,, in the pocket 9 of the turret plate 3 will drop from the turret in the direction of arrow 5, roll down the ramp 53 into the receptacle 56 when rotation of the disk 3 in the direction of arrow C ceases to conclude the previous cycle.

At the insertion station, the previously empty pocket 8 is radially aligned with the feed plunger 4a which thrusts an unfinished workpiece W into this pocket and holds the workpiece there until rotation of the turret disk 3 begins again.

During the insertion and discharge operations, the workpiece W inserted in the previous cycle, is carried to the station 11 and aligned along the common axis A of the centering stud 12 and the drive spindle 1 so that the annular face 1e of the drive spindle is juxtaposed with the left-hand annular face of the workpiece (FIG. 5). While held in registry by pocket 11 of the disk with the centering stud 12, sleeve 12a is shifted to the left (arrow D) to insert the stud into the bearing ring and bring sleeve 15 against the workpiece to hold the latter on the spindle 1. During this movement, programmer a, via output 20c, opens a valve 27a to permit fluid centering of the bearing ring and the sleeve 15. Once the workpiece W is clamped in place, output 20d of programmer 20 energizes motor 50 to rotate the rings W at high speed. The stones 6 finish the raceways as described above and in the aforementioned application. The centering operation is effected as described in the patent identified earlier. At station III, finishing-polishing is carried out on a workpiece W in pocket 10 with the centering stud 13 and the drive spindle 2.

Upon conclusion of the finishing operation, programmer 28 energizes motor 20 to rotate the disk 3 through an additional angle of 90 to repeat the cycle.

The cap 26a locks an abutment ring against the remainder of the fixed housing 26 such that the inwardly extending flange 26c and member 25 receive the thrustbearing ring 23a and the rib 1.5a with axial play and form a lost-motion connection therewith. Consequently, when the

stud

12 or 13 is axialy withdrawn (to the right in 8 FIG. 5), the thrust-bearing ring 2311 engages abutment 25 and further axial movement of the stud to the right strips the workpiece W from the centering stud or dislodges it fixedly to enable its release. As can be seen from FIG. 5, member 12 can be fully withdrawn into the pressing sleeve 15.

The improvement described and illustrated is believed to admit of many modifications within the ability of persons skilled in the art, all such modifications being considered within the spirit and scope of the invention except as limited by the appended claims.

I claim:

1. An apparatus for the external machining of annular workpieces, comprising:

a support;

a turret plate mounted on said support and rotatable about an axis perpendicular thereto, said turret plate being formed with a plurality of outwardly open pockets angularly spaced about said axis;

at least two spindles mounted on said support and rotatable about the axis parallel to one another but perpendicular to said turret plate and alignable with respective pockets therein for engagement with workpieces positioned in said pockets;

a respective centering stud axially aligned with each of said spindles and axially shiftable relatively to said turret plate for insertion into a workpiece positioned in a corresponding pocket of said plate, said stud being provided with means for introducing a fluid under pressure between the periphery of said stud and the workpiece, thereby fluid-centering the workpiece; and

tool means reaching into the pockets aligned with said spindles and said centering stud for machining the peripheries of the workpieces through the mouth of said pockets.

2. The apparatus defined in claim 1 wherein said spindles and the respective centering studs are angularly spaced about the axis of said turret plate, said turret plate being rotatable along a closed path for sweeping said pockets in succession past an insertion station angularly spaced from a first work station formed by one of the spindles and the respective centering stud, said first work station, a second work station formed by the other spindle and the respective centering stud, and a discharge station, said apparatus further comprising insertion means at said insertion station for positioning annular workpieces to be machined in said packet, each of said centering studs being provided with a pressing sleeve mounted with play thereon and bearing against the workpiece to hold the same against the respective spindles.

3. The apparatus defined in claim 2 wherein each of said studs is provided with means for introducing a fluid under pressure between the stud and the respective sleeve for fluid centering the sleeve on the stud.

4. The apparatus defined in claim 3 wherein each of said studs is received in a respective spindle sleeve nonrotatably mounted on said support, said spindle sleeves being axially shiftable relative to said turret plate.

5. The apparatus defined in claim 4, further comprising a thrust bearing between said pressing sleeve and the respective centering stud.

6. The apparatus defined in claim 4 wherein said stud is retractable from the respective workpiece, said support having an abutment engageable with the respective pressing sleeve upon withdrawal of the stud from the workpiece to dislodge the workpiece therefrom.

7. The apparatus defined in claim 4 wherein the means for introducing a fluid under pressure between said stud and said workpiece and between said stud and said pressing sleeve includes a source of fluid under pressure and passages formed in said stud and opening along the periphery thereof.

8. The apparatus defined in claim 7 wherein said turret plate is rotatable in a vertical plane and its axis of rotation is horizontal, said insertion station and discharge stations being located at opposite lower quadrants of the rotation of said turret plate, said insertion station being formed with a chute extending downwardly toward said plate for positioning successive workpieces in radial alignment with the pockets of said plate and means for radially introducing said workpieces into the successive pockets, said discharge station including a chute leading downwardly and away from said plate for conducting discharged workpieces from the latter, said apparatus further comprising guide members flanking said plate for preventing release of said workpieces during movement of said plate to carry the pockets between said insertion station and said first work station and between said second work station and said discharge station.

9. The apparatus defined in claim 8 wherein said tool means includes respective abrasive stones engaging the peripheries of the workpieces positioned at said work stations, said stones being oscillatable about centers of curvature close to the workpieces machined thereby.

10. The apparatus defined in claim 9 wherein each of said studs has a frustoconical portion remote from the respective workpiece and said spindle sleeves from collets releasable receiving said studs, said apparatus including threaded rods retaining said studs in said spindle sleeve, said centering studs being further provided with outwardly extending annular flanges, thrust-bearing means between said pressing sleeves and said thrust-bearing means with limited axial play to form a lost-motion connection between said support and said pressing sleeves.

References Cited UNITED STATES PATENTS 1,881,244 10/1932 Raule 5l3 3,040,486 6/1962 Balsiger 51-236 3,209,494 10/ 1965 Seidel 51-236 WILLIAM R. ARMSTRONG, Primary Examiner US. Cl. X.R.