GB2061158A - Work holding device for the tool turret of a turret lathe - Google Patents

Abstract

The tool turret 2 of a lathe has a work holding device 9 capable of supporting a work piece W and driving it in rotation in the same direction and at the same speed as the work piece is driven by the chuck 1 of the lathe in order to prevent a deformity being formed on the workpiece when a parting-off tool 10 is operated to sever the workpiece from the remaining length of stock S. The work holding device 9 may be an attachment for the turret and may include a collet 38 which is closed by a sleeve 37 moved by a pneumatic piston 34. The collet, sleeve and a collet spindle 39 are rotated via gears 45,46 by a pneumatic motor 47. <IMAGE>

Description

SPECIFICATION An improved lathe and an attachment for a lathe This invention relates to lathes, particularly turret lathes.

A turret lathe may be used to perform a series of machining operations on a workpiece which constitutes the leading end portion of a length of metal stock. Following completion of these operations, a cut-off or parting-off tool carried by a slide is used to separate the workpiece from the remaining length of stock and thereby form the rear surface of the workpiece. As the cutting edge of the parting-off tool approaches the axis of the stock, the narrow neck which is in the process of being formed between the workpiece and the remaining length of stock may break through so that a deformity or pip is formed on the rear workpiece face. Each workpiece machined on the lathe must therefore be finished individually to remove the pip before use or further processing.

As a result, the overall time taken to machine each workpiece is unduly long.

The present invention seeks to overcome this problem by equipping the turret of the lathe with a device to support and rotate the workpiece so that there is no tendency for the stock to break and form a pip as the parting-off tool approaches its axis. Not only is the subsequent finishing operation eliminated, but it is made possible for a parting-off tool to be used which machines the rear workpiece face to a desired profile. Furthermore, by virtue of the invention, the turret may be used to transfer the workpiece to other machining stations while machining of a further workpiece is commenced.Various aspects of the invention are set out in general terms in the appended claims and will be described by way of example with reference to the drawings in which: Figure 1 is a diagrammatic plan view of a turret lathe depicting one stage of a machining operation, Figure 2 is a view similar to Figure 1 but depicting the parting-off operation, Figure 3 is a view similar to Figure 1 but depicting the further machining of the parted-off workpiece and the simultaneous machining of a further workpiece, and Figure 4 is a longitudinal section through a turret attachment.

Referring to Figures 1 and 2, a length of circularsectioned bar stock is held in the chuck 1 of a lathe, the bed, headstock and plugboard control of which are depicted in chain lines. With the chuck 1 rotating or stationary depending upon the tool in use at any one time, a sequence of machining operations is performed on a workpiece W constituted by the end portion of the stock which projects from the chuck.

These operations may be carried out by tools on the turret 2 and possibly by other tools on cross slides indicated at 3. The operation depicted in Figure 1 is the turning of the workpiece by a tool 4 on the turret.

By indexing the turret in the direction of the arrow, the workpiece may be successively drilled, reamed and tapped by the tools indicated at 5, 6 and 7. These operations are given purely by way of example and are carried out under the control of a conventional plug board control system. The turret also has a revolving stop 8 and a work holding device 9, the function of which will now be described.

With the operations described above complete, the turret is indexed into the position shown in Figure 2 in which the work holding device 9 is presented to the workpiece W and the turret traversed to introduce the end of the workpiece W into the work holding device which is now operated to grip the work piece. The chuck and work holding device are then driven in the same direction to rotate the workpiece from both ends. A parting-off tool 10 is now fed towards the stock to separate the workpiece W from it. Because the workpiece is held and rotated at both ends, the workpiece is separated cleanly. If desired, the tool 10 may be shaped so that the rear surface of the workpiece is given a desired profile while the leading end of the remainder of the stock is formed with a surface normal to the chuck axis.

At the completion of this stage, the turret may be retracted and the work holding device 9 opened to release the finished workpiece. The turret is then indexed to its next position, and the length of stock fed through the chuck to present a further workpiece ready for the machining cycle to be repeated.

In a modification, as shown in Figure 3, the lathe is provided with one or more tools 11 on slides 12 carried on the bed of the lathe and generally in line with the axis of the turret. With the lathe so adapted, the work holding device 9 may retain the work piece W fol lowing parting-off. The workpiece W is brought into alignment with each of the tools 11 in turn as the turret is indexed during the primary machining cycle performed on anotherworkpieceW'. Each of the secondary machining operations performed by the tools 11 may be carried out before or after the primary machining operation performed by the tool on the turret which is in alignment with the workpiece W'; that is, before or after traverse of the turret.Advantageously, however, the arrangement is such that both primary and secondary machining operations are carried out simultaneously by associating each secondary operation with a suitable primary operation. The workpiece may be ejected when the work holding device reaches the position shown at 13. The length of time needed to perform the primary machining operations on each workpiece held in the chuck 1 may be increased as a result of employing the arrangement shown in Figure 3, but the overall time which each workpiece spends in the machine shop may nevertheless be reduced. When all of the secondary operations have been performed the work holding device 9 is operated to release the finished workpiece.The work holding device may be incorporated in the turret as a permanent fixture, or it may be manufactured for sale and attachment to the turret in the same manner as the standard equipment already available on the market. The work holding device 9 preferably incorporates a pneumatically closable collet arranged to be driven in rotation by a pneumatic motor, since it is conventional to provide a supply of air to the turret. Alternatively, the work holding device may be closed and driven electrically. It is also possible for the work holding device to have no powered rotational drive system of its own but to incorporate a flywheel in which energy is stored during the initial stage of the parting-off operation, in other words before the neck being formed by the parting-off tool becomes too narrow to transmit rotation to the workpiece from the remainder of the stock.At this stage, the flywheel is able to turn the workpiece at the same speed as the remainder of the stock, or at a speed sufficiently close to this speed to ensure that the parting-off operation is completed smoothly without the formation of a pip.

Figure 4 is a part section view of a work holding device 9 in the form of an attachment suitable for fitting to a standard turret 22 having fixing studs 21 and a locating recess 22. The device 9 comprises a body 30 having at its rearward end a spigot 31 for insertion in the locating recess 22 and a peripheral flange 32 formed with bores to receive the studs 21.

Defined within the body is a cylindrical bore 33 which opens to the forward end of the body. A non-rotating operating piston 34 is slidable within the rearward end of the bore under the action of air admitted to a piston chamber 44 through port 35.

The piston has a peripheral seal and an axial extension 36 bearing by way of a thrust bearing on a collet sleeve 37 surrounding a collet 38. The sleeve is surrounded by a collet spindle 39 journal led for rotation within the cylindrical bore. The spindle 39 has a screw-threaded, reduced diameter projection 40 at its forward end onto which is screwed a nose-piece 41. The spindle, sleeve and collet are keyed to one another so as to rotate together, and the sleeve is displaced axially relative to the spindle and collet. A compression spring 43 biases the piston towards the turret. A stop and ejector rod 48 extends through the collet and is guided at its end in an axial bore in the piston extension 36. The rod 48 is biased into the position shown by a compression spring 49.

The reduced diameter end of the collet spindle carries an externally toothed gear ring 45 which is in mesh with a pinion 46 onthe output shaft of a pneumatic motor 47 secured to the body 30. The supply of air to port 35 and to the motor is controlled by valves operated by the plug board control system of the lathe.

Operation of the work holding device takes place as follows: With the device 9 in alignment with the chuck, the turret is traversed towards the position shown in Figure 2. The workpiece presses back the stop and ejector rod 48 against the force of spring 49 and enters the collet. Air is admitted to the chamber 44 through port 25 to shift the piston in the direction away from the turret to cause the collet to close and grip the free end portion of the workpiece. Air is now supplied to the motor 47 to drive the collet and workpiece in rotation, the chuck 1 also being set in rotation in the same direction, and parting-off carried out.

The supply of air to the motor may now be terminated and the turret retracted. Finally, the chamber 44 is vented and the workpiece ejected by the stop and ejector rod 48.

In the event that the lathe is modified to operate as shown in Figure 3, the gearing 45,46 is preferably associated with a ratchet or other mechanism to prevent the workpiece being turned when it is machined by a rotary tool on a slide 12.

An advantage of using a pneumatic motorto drive the collet is that it is unnecessary for the chuck and colletto run exactly in synchronism. Operation may therefore take place at mismatched speeds without damage being caused to the device.

Changes may, of course, be made to the embodiments described herein. Thus, for example, instead of using a spring to bring about opening of the collet a double-acting piston may be used. It is to be noted that by "turret lathe" is meant any lathe in which the work may be machined by different tools carried on a turret or other tool support capable of being indexed to change the tool presented to the work.

Claims (12)

1. A method of machining using a turret lathe, wherein, during the use of a parting-off tool, a workpiece is supported and driven in rotation both by a work holding device of the head stock of the lathe and by a work holding device of the turret.

2. A method of machining using a turret lathe, wherein the turret is intermittently indexed to enable tools on the turret to carry out in a predetermined cycle a sequence of machining operations upon a workpiece carried and when necessary rotated by a work holding device of the head stock, and wherein at the conclusion of the cycle the workpiece is additionally supported by a work holding device of the turret and rotated thereby in the same direction as the workpiece is rotated by the work holding device of the head stock.

3. The method claimed in claim 1 or claim 2, wherein following parting-off, the turret is indexed to present the workpiece supported by the work holding device of the turret to at least one working station.

4. The method claimed in claim 3, wherein a machining operation is performed by such a working station on a workpiece presented to it while a tool on the turret is aligned with a further workpiece carried by the work holding device of the headstock, whereby a machining operation may be performed on the further workpiece while the turret is in the said indexed position.

5. In or for a lathe, a turret which incorporates or has attached to it a work holding device adapted to support and drive in rotation a workpiece.

6. A lathe having a turret as claimed in claim 5, including means on the lathe for machining a workpiece supported by the work holding device of the turret when said turret is in an indexed position out of alignment with a work holding device of the lathe headstock.

7. An attachment for the turret of a lathe comprising a body, means supported by the body for gripping a work piece, mechanism for operating said gripping means, and drive means for driving the gripping means in rotation.

8. An attachment as claimed in claim 7, wherein said mechanism includes a piston slideable within a cylinder under the effect of air admitted to the cylinder.

9. An attachment as claimed in claim 7 or claim 8, wherein the driving means includes a pneumatic motor.

10. A method of operating a turret lathe substantially as described herein with reference to Figures 1 and 2, or with reference to Figures 1,2 and 3 of the drawings.

11. A turret lathe substantially in accordance with any embodiment thereof described and/or illustrated herein.

12. An attachment for the turret of a turret lathe substantially in accordance with any embodiment thereof described and/or illustrated herein.