GB2200305A

GB2200305A - A collet assembly

Info

Publication number: GB2200305A
Application number: GB08702365A
Authority: GB
Inventors: Clive Stuart Levan
Original assignee: Bristol Tool and Gauge Co Ltd
Current assignee: Bristol Tool and Gauge Co Ltd
Priority date: 1987-02-03
Filing date: 1987-02-03
Publication date: 1988-08-03
Also published as: GB8702365D0

Abstract

The assembly (16) comprises a drive element (18) and a collet (20) which are initially separate but are assembled together by screwing a spigot of the drive ring (18) into a recess of the collet (20) by means of screwthreads (48, 50). Thereafter, one of the screwthreads (48, 50) may be treated, for example by deforming it, so that the drive ring and the collet cannot be easily separated. After assembly, the drive ring (18) and the collet (20) are relatively moveable to a limited extent axially and radially to allow correct alignment of a tool (30) in a chuck provided with the collet assembly (16). The drive ring (18) has screwthreads to be engaged by a tool (30) and is prevented from station in the assembiy body (2) by lugs (22) in sockets in a ring (12) or the body. <IMAGE>

Description

A COLLET ASSEMBLY This invention relate# ta a collet assembly for receiving the shank of a tool such as a milling cutter.

According to the present invention there is provided a collet assembly for receiving the shank of a tool, the assembly comprising a collet and a drive element which are connected together in a manner which permits limi ted relative movement between the collet and the drive element, The relative movement between the collet and the drive element may be radial and/or axial movement with respect to the axis of a cutter received in the collet assembly.

The connection between the collet and the drive element may be established by retaining means which prevents separation of the components in the axial direction of the tool. The retaining means may comprise cooperating formations on the collet and the drive element, and these cooperating formations may comprise screwthreads. Thus, the drive element may comprise a spigot which extends into the collet and which has an external screwthread on its free end. The collet may have an internal screwthread at one end.

When the collet and the drive element are connected together, the screwthread on the spigot of the drive element is disposed further into the collet than the internal screwthread on the collet, so that the two screwthreads are no longer in mesh with each other.

Thus, axial movement #f the drive claimant within the collet is permitted, but the drive element and the collet can be separated only by unscrewing one from the other.

In order to prevent separation of the components, even by unscrewing, one or both of the screwthreads may be treated td prevent the screwthreads from cooperating properly with each other. For example, one or both of the screwthreads may be mechanically deformed after the drive element has been screwed fully into the collet.

Alternatively, material such as adhesive or molten metal (for example, solder) may be applied to one or both of the screwthreads. This makes the two components inseparable except by the application of substantial force.

For a better understanding of the present invention, and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a sectional view of a machine tool chuck carrying a milling cutter; Figure 2 is a sectional view of: a component of the chuck of Figure 1; Figure 3 is an end view of the component shown in Figure 2; and Figure 4 is a view corresponding to Figure 3, but showing an alternative embodiment.

The chuck shown in Figure 1 comprises a chuck body 2 having a tapered shank 4 which, in use, is inserted into a correspondingly tapered recess in a drive spindle of a machine tool, where it is secured by a screwthreaded shaft engaging an internal screwthread 6 in the chuck body 2.

At the end opposite the screwthread 6, the chuck body 2 is provided with a recess 8 having an internal screwthread 10. A locking bush 12 is received in the recess 8. The locking bush 12 llas an external screwthread 14 which engages the internal screwthread 10.

The locking bush 12 retains in the recess 8 a collet assembly 16, which comprises a drive ring 18 and a split collet 20.

The drive ring 18 tidt radially extending lugs 22 which extend into slots 24 in the locking bush 12.

Consequently, the lugs 22 and the slots 24 prevent rotation of the drive ring 18 relatively to the locking bush 12.

A centre 26 is mounted in the chuck body 2. This centre has a conical tip 28 which is accurately aligned with the rotary axis of the chuck body 2.

As shown in Figure 1, a milling cutter 30 is received in the chuck. The milling cutter 30 has a cutting portion 32 provided on a shank 34. At its end away from the cutting portion 32, the shank 34 has a screwthreaded portion 36, which, as shown in Figure 1, cooperates with an internal screwthread 38 provided on the drive ring 18.

In order to fit the cutter 30 into the chuck, it is introduced through an internal bore 40 of the collet 20 and screwed into the drive ring 18. A conical recess in the end face of the cutter 30 engages the centre 28, and eventually the centre 28 will prevent further movement of the cutter 30 to the left, as seen in Figure 1. When this happens, further turning of the cutter 30 will cause the drive ring 18 to move towards the right. It will be appreciated that the engagement between the lugs 22 and the recesses 24 prevents rotation of the drive-ring 1~8 relatively to the chuck body 2.

As the drive ring 18 moves to the right, it engages the collet 20 so that the collet 20 is also driven towards the right. As will be appreciated from Figure 1, the collet 20 has a tapered external surface which engages a correspondingly tapered internal surface of the locking bush 12, and consequently this axial movement of the collet 20 causes the bore 40 to contract about~ the shank 34. As a result, the cutter 30 is securely held within the collet assembly 16.

The collet assembly 16 is shown in Figures 2 and 3. The drive ring 18 comprises et a flange 42 on which the proJ#c;tions 22 are provided. a spigot 44 extends from the flarlqe 42, and enters a recess 46 provided in the collet 20. The bore 40 in the collet 20 opens at one end into the recess 46. At the open end of the recess 46, a short 46, screwlhread 40 is provided on the collet 20. A corresponding screwthread 50 is provided on the .e,ne tree ena or cue spigot 44.

The screwthreads 48 and 50 have a left-hand thread, and it will be appreciated that, from the position shown in Figure 2, the drive ring 18 can be separated from the collet 20 only by rotating the components relatively to each other to engage the screwthreads 48 and 50 in the proper manner. While the drive ring 18 and the collet 20 are in the position shown in Figure 2, they are free to move relatively to each other into a limited extent, both axially and radially, and consegJently the components are able to shift to some extent as the cutter 30 is inserted in order to ensure that correct alignment of the cutter 30 with the centre 28 is achieved.

Xn order to prevent separation of the drive ring 18 and the collet 20, at least one of the screwthreads 48 and 50 may be treated in a manner which will prevent normal cooperation between the screwthreads. For example, the screwthread 50 may be distorted by means of a tool inserted through the slots in the collet 20.

As a result of this distortion, the screwthreads will not engage properly, and it will then not be possible to turn the components relatively to each other with ease. Alternatively, the same effect may be achieved by filling the spaces between adjacent threads of at least one of the screwthreads, for example with adhesive or a molten material such as solder.

By ensuring that the drive ring 18 cannot easily be separated from the collet 20, while permitting limited displacement between these two components, it is possible to ensure that the cutter 30 can be properly aligned with the rotary axis of the chuck, while avoiding the possibility that one or other of the drive ring 18 and the collet 20 may be mislaid. The drive ring 18 shown in Figure 4 is similar to that of Figures 1 to 3 except that the lugs 22 are replaced by projections 52 which have a shorter circumferential extent, The drive ring of Figure 4 is intended for use in chucks where the locklng bllsh 12 has no slots 24, and thus does not engage the drive ring 18. Instead, the chuck body 2 has internal recesses which engage the projections 52 to drive the ring 18.

This possibility arises because the collet assembly 16 would normally be one of a range of assemblies, having bores 40 of different diameter to receive tool shanks 34 of different size. Thus, for every collet assembly 16 fitted to the chuck, there would be several assemblies which would not be in use.

If each assembly comprised a collet and a drive ring which were separate from each other, and were only brought together when f@@ted to the chuck, the machine 7 operator would need to select and marry together the collet and drive ring of the correct size in each case.

Apart from being inconvenient, there is the danger that ono or othsr of the coll@t snd drive ring could becorn# mislaid.

Claims

1. A collet assembly for receiving the shank of a tool, the assembly comprising a collet and a drive element which are connected together in a manner which permits limited relative movement between the collet and the drive element.

2. A collet assembly as claimed in claim 1 or 2, in which the relative movement between the collet and the drive element is radial movement.

3. A collect assembly as claimed in claim 1 or 2, in which the relative movement between the collet and the drive element is axial movement.

4. A collet assembly as claimed in any one of the preceding claims, in which the connection between the collet and the drive element prevents their separation.

5. A collet assembly as claimed in claim 4, in which the collet has a recess in which a spigot of the drive element is received, the spigot and the internal wall of the recess having formations for preventing separation of the collet and the drive element.

6. A collet assembly as claimed in claim 5, in which the formations comprise an external screwthread on the spigot and an internal screwthread on the portion of the wall of the recess, the screwthread on the spigot being situated inwardly of the recess with respect to the screwthread on the wall of the recess.

7. A collet assembly as claimed in claim 6, in which the screwthreads on the spigot and the wall of the recess are of a form such as to permit cooperation of the screwthreads, at least one of the screwthreads being treated to prevent such cooperation.

8. A collet assembly as claimed in claim 7, in which the treatment of the or each screwthread comprises deformation of that screwthread.

9. A collet assembly as claimed in any one of the preceding claims, in which the drive element comprises a ring with projecting lugs for entrainment of the drive ring with a rotating tool holder, the drive ring also having an internal screwthread for engagement with a tool.

10. A collet assembly substantially as described herein with reference to, and as shown in, the accompanying drawings.

11. A machine tool chuck provided with a collet assembly in accordance with any one of the preceding claims.