GB2362345A

GB2362345A - Collet chuck

Info

Publication number: GB2362345A
Application number: GB0009473A
Authority: GB
Inventors: Anthony Paul Wyatt
Original assignee: 600 UK Ltd
Current assignee: 600 UK Ltd
Priority date: 2000-04-17
Filing date: 2000-04-17
Publication date: 2001-11-21
Anticipated expiration: 2020-04-17
Also published as: GB2362345B; GB0009473D0

Abstract

A chuck arrangement comprises a chuck body (10) rotatable by a hollow spindle (not shown) though the intermediary of a rear element (12). The chuck body (10) includes a tapered part (16) having an inwardly tapered surface which is in contact with the externally tapered surface of a multi-segment collet (44). A cap (34) makes contact with a peripheral part of the larger-diameter end of the collet (44) and is connected via studs (20) and a retracting ring (24) to a tubular draw bar (not shown) by means of which the cap (34) can be pulled rearwardly into the chuck body so as to slide the collet (44) against the tapered part (16) of the chuck body (10). The arrangement is particularly suited for use in a machine tool where a programmable ram situated rearwardly of the chuck body pushes the work piece to successive predetermined longitudinal positions for machining operations. When the collet (44) is pulled rearwardly by the draw bar into the tapered part (16), it ensures that the work piece abuts against the ram, to avoid any inertially induced separation therebetween.

Description

1 1 2362345 1 MACHINE TOOL ARRANGEMENTS The invention relates to machine

tool arrangements. More specifically, it relates to chuck arrangements for holding work pieces or bar stock in machine tools.

According to the invention, there is provided a chuck arrangement for securing a work piece to a rotatable machine spindle, comprising a chuck body connectable to and for rotation by the spindle and having an internal and axially tapered surface portion extending between axially spaced small and large diameter ends for receiving a generally matching external axially tapered surface portion of a collet, collet control means engaging the collet at a large diameter end thereof, and draw means connected to the collet control means and operative when actuated to move the collet control means relative to the chuck body so as to move the collet axially towards the small diameter end of the internal surface portion of the chuck body, whereby the collet grips a work piece therein.

According to the invention, there is also provided a machine tool arrangement, comprising a chuck body mounted for rotation by a machine spindle, the chuck body presenting an internal axially tapered surface expanding towards a first, forward, axial direction, a multi-segmented collet having an external axially tapered surface and mounted within the chuck body with its external tapered surface generally matching and for contact by the internal tapered surface of the chuck body and with a larger-diameter 2 end facing in the forward direction, collet control means slidably mounted on the chuck body and making contact with at least a peripheral portion of the larger-diameter end of the collet, connecting means for connecting the collet control means with draw means for causing the collet control means to slide in a second, rearward, direction thereby pushing the collet against the internal tapered surface of the chuck body to cause the segments of the collet to move from a released condition into a gripping condition in which they firmly grip a work piece when mounted in the collet and extending outwardly from the larger-diameter end thereof to a machining position, and ram means mounted rearwardly of the chuck body for receiving a rearward end of the work piece, the ram means being actuatable to push the work piece forwardly through the released collet segments towards a predetermined position, whereby the collet segments when gripping the work piece tend to maintain contact between the rearward end of the work piece and the ram means.

Chuck and machine tool arrangements embodying the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which:

Figure 1 is a cross-section through one of the chuck arrangements, taken on the line PI of Figure 2; Figure 2 is an end view of the arrangement of Figure 1; and 3 Figure 3 is a crosssection through a machine tool arrangement incorporating the chuck arrangement of Figures 1 and 2.

Referring to Figure 1, the chuck arrangement has a generally hollow and cylindrical chuck body 10 which is secured to the machine spindle (not shown) through the intermediary of a ring-shaped rear element 12 having an aperture 27. The rear element 12 is fixed to the chuck body 10 by means of bolts 14 of which there are three (only one shown in Figure 1). The chuck body 10 has a tapered part 16 defining an inwardly facing axial tapering surface 17. The chuck body 10 has six through bores 18 (only one visible in Figure 1) in each of which is freely slidable a respective stud 20. Each stud 20 has an externally threaded end 22 of reduced diameter which is screwed into a respective threaded bore in a ring- shaped retracting plate 24 having an aperture 29. The plate 24 carries a flange 26 locating in a shoulder 28 of the internally tapered part 16 of the chuck body 10. The opposite end of each stud 20 has an internally threaded bore 30 in which is received the threaded end of a respective bolt 32. The six bolts 32 have enlarged heads by means of which they secure a ring-shaped cap 34 to the studs 20 and thus to the retracting plate 24.

The cap 34 is a close but sliding fit within a circular flange 36 at the open end of the chuck body 10. An 0-ring 3 8 provides a seal between the cap 34 and the flange 3 6 to prevent ingress of moisture, swarf etc.

4 The cap 34 has a circular flange 40 which engages in recesses 42 of a multi-segment collet 44 to be described in more detail below. The individual segments of the collet 44 have externally tapered outer surfaces in contact with the inwardly tapered surface 17 of the tapered part 16 of the chuck body 10.

The chuck body 10 also has six clearance bores 46 (only one shown in Figure 1) which are aligned with respective bores 48 in the rear element 12. Bolts 50 engage the clearance bores 46 and 48 and have protruding threaded ends 52 for connecting to the machine spindle (not shown).

A circular elastomeric ring-shaped seal 54 is secured over the outer face of the collet 44 by means of a retaining ring 56 which is secured to the cap 40 by means of four screws 58 (only one shown). The seal 54 has an aperture 60 sized to suit the size of the work piece to be fixed in the collet 44. The retaining ring 56 has an aperture 61.

The draw bar (not shown) for the chuck and collet arrangement extends through the hollow spindle (also not shown) and is externally threaded to engage an internal thread 62 of the retracting plate.

The collet 44 is of known construction comprising several (e.g. eight) separate metal elements which have externally curved and tapered surfaces and internal part-cylindrical surfaces, such as sold by the Applicants under the trade mark MULTIBORE. The elements are spaced slightly apart around the axis of the collet and are linked together by flexible links advantageously made of rubber and also by external circlips (not shown in the Figures). The external curvatures and tapers of the individual elements together match the tapered surface 17 of the tapered part 16 of the chuck body 10. The internal surfaces of the separate elements of the collet form respective parts of a generally cylindrical inner work piece receiving surface 64.

In use, the work piece or bar stock to be machined by the machine tool is fed from the rear; that is, the work piece is fed through the aperture 27 in the rear element 12, through the aperture 29 in the ring-shaped plate 24 into the hollow cylindrical interior 66 of the collet 44, then through the opening 60 in the seal 54 and then through the aperture 61 in the retaining seal 56 into a region A where a machining operation may be performed thereon. The machine tool is then activated to retract the draw bar (not shown) - which thus moves the retracting plate 24 to the left (as viewed in Figure 1). Through the intermediary of the studs 20, the retracting plate 24 retracts the cap 34 so that the latter's flange 40 draws the collet 44 inwardly of the tapered part 16 of the chuck body 10. The spaced-apart segments of the collet 44 are thus moved forcibly towards each other and firmly grip the work piece.

Figure 3 explains the advantages of the arrangement of Figures 1 and 2. Figure 3 shows the chuck arrangement of Figures 1 and 2 at 68 and also shows the hollow machine spindle 70 connected to the rear element 12 for rotating the chuck body 10, and the 6 hollow draw bar 72 connected to the retracting plate 24.

In addition, Figure 3 shows the work piece or bar stock 74 extending forwardly through the collet 44 to the region A and rearwardly to an end 75 in abutting engagement with a ram 76. The ram 76 is part of a programmable bar feeding unit shown diagrammatically at 78.

In operation, and under numerical control, the draw bar 72 releases the collet 44 - that is, the draw bar 72 is advanced forwardly to the right (as viewed in Figure 3) so that the cap 34 (Figure 1) exerts no pushing force on the segments of the collet 44 which thus release the bar stock 74. The bar feeding unit 78 then advances the ram 76 to the right (as viewed in Figure 3) by a predetermined amount so as correspondingly to advance the bar stock 74 into the region A. The draw bar 72 is then retracted to cause the cap 34 (Figure 1) to be correspondingly retracted, thus forcing the segments of the collet 44 inwardly of the tapered part 16 of the chuck body 10, so that the collet now firmly grips the bar stock. The machine spindle 70 is now rotated and a machining operation is carried out on the bar stock in the region A (by tool means not shown).

Thereafter, the draw bar 72 once more releases the collet 44 so as to free the bar stock 74. The ram 76 is then advanced again by a predetermined amount so as correspondingly to advance the bar stock 74 to a new longitudinal position. The draw bar 72 is then retracted so that the collet 44 once more grips the bar stock 74, for a new machining operation to 7 be carried out on a new predetermined part of the bar stock. The process then repeats as necessary, with the bar stock 74 being advanced each time to a new predetermined position by the ram 76 under numerical control.

During each such operation of the ram 76 to advance the temporarily freed bar stock 74 to a new longitudinal position, the end 75 of the bar stock may, by inertial effect, move away by a minute dimensional amount, from the face of the ram 76. However, because the collet 44 is retracted into the chuck body to grip the bar stock 74 in its new position, the bar stock is automatically pulled back into contact with the face of the ram 76. Errors in the longitudinal position of the finished components produced by the machining operations are thus avoided.

The chuck arrangement thus differs from arrangements in which the collet is held stationery within the chuck body and closure of the collet onto the bar stock is achieved by pushing forward a tapered sleeve which surrounds the outside of the stationery collet and is attached to the draw bar for sliding within the interior of the chuck body. With such arrangements, the bar stock 74 will not be pulled back into abutment with the face of the ram 76, and the dimensional machining errors mentioned above may thus occur.

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Claims

1. A chuck arrangement for securing a work piece to a rotatable machine spindle, comprising a chuck body connectable to and for rotation by the spindle and having an internal and axially tapered surface portion extending between axially spaced small and large diameter ends for receiving a generally matching external axially tapered surface portion of a collet, collet control means engaging the collet at a large diameter end thereof, and draw mcans connected to the collet control means and operative when actuated to move the collet control means relative to the chuck body so as to move the collet axially towards the small diameter end of the internal surface portion of the chuck body, whereby the collet grips a work piece therein.

2. An arrangement according to claim 1, in which the collet comprises a plurality of separate externally tapered segment portions flexibly linked together.

3. An arrangement according to claim 1 or 2, in which the collet control means comprises ring-shaped means contacting a peripheral part of the large diameter end of the collet and apertured to allow passage of the work piece out of the collet.

4. An arrangement according to claim 3, including connecting means extending slidably through the chuck body and mechanically interconnecting the ring-shaped means to the draw means.

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5. An arrangement according to claim 4, in which the connecting means comprises a plurality of studs extending slidably through the chuck body and connecting the ringshaped means to a hollow circular member which is connectable to the draw means in the form of a hollow tubular draw bar.

6. An arrangement according to any one of claims 3 to 5, in which the ring-shaped means is a sliding fit within a part of the chuck body.

7. An arrangement according to claim 6, in which the ring-shaped means carries an external sealing ring for sealing the sliding fit.

8. An arrangement according to any one of claims 3 to 7, including a ringshaped seal mounted on the ring-shaped means around the aperture thereof.

9. An arrangement according to any preceding claim, including means for connecting the chuck body to the machine spindle for rotation thereby.

10. A machine tool arrangement, comprising a chuck body mounted for rotation by a machine spindle, the chuck body presenting an internal axially tapered surface expanding towards a first, forward, axial direction, a multi-segmented collet having an external axially tapered surface and mounted within the chuck body with its external tapered surface generally matching and for contact by the internal tapered surface of the chuck body and with a larger-diameter end facing in the forward direction, collet control means slidably mounted on the chuck body and making contact with at least a peripheral portion of the larger-diameter end of the collet, connecting means for connecting the collet control means with draw means for causing the collet control means to slide in a second, rearward, direction thereby pushing the collet against the internal tapered surface of the chuck body to cause the segments of the collet to move from a released condition into a gripping condition in which they firmly grip a work piece when mounted in the collet and extending outwardly ftorn the larger-diameter end thereof to a machining position, and ram means mounted rearwardly of the chuck body for receiving a rearward end of the work piece, the ram means being actuatable to push the work piece forwardly through the released collet -,egments towards a predetermined position, whereby the collet segments when gripping the work piece tend to maintain contact between the rearward end of the work piece and the ram means.

11. An arrangement according to claim 10, in which the draw means comprises a hollow tubular draw bar co-axial with the work piece and connected by the connecting means to the collet control means.

12. An arrangement according to claim 11, in which the collet control means comprises a ring-shaped member.

An arrangement according to claim 12, in which the connecting means comprises a plurality of studs extending slidably"through the chuck body and connecting the ringshaped member to a hollow circular member which is connectable to the draw bar.

14. An arrangement according to any one of claims 12 or 13, in which the ring-shaped member is a sliding fit within a part of the chuck body.

15. An arrangement according to claim 14, in which the ring-shaped member carries an external sealing ring for sealing the sliding fit.

16. A chuck arrangement, substantially as described with reference to Figures 1 and 2 of the accompanying drawings.

17. A machine tool arrangement, substantially as described with reference to the accompanying drawings.