GB2213080A - Collet chuck - Google Patents

Abstract

The chuck, for use on woodturning lathes, comprises three or more petals 2 defining a circular section counter bore and being joined adjacent their lower extremities to a base 4 adapted for affixation directly or indirectly to a driven spindle, e.g. via a sleeve 11, and a shroud 7 adapted to fit about the petals, the internal surface of the shroud and the external surfaces of the petals coacting to move the petals progressively radially inwards by axial shroud movement thus captivating any plug or other such object which may be present in the counter bore. The shroud 7 is retained in a variety of positions about the petals by a ring 10. <IMAGE>

Description

IMPROVED OOLLEr CHUCK The present invention relates to a collet type chuck as may be utilised on a woodturning lathe or other wood turning machine.

Before a piece of wood may be worked on a lathe it must first be affixed in some manner to a drive spindle. It is extremely important that such method of affixation is as secure as possible particularly where it is desired to produce hollow forms which may not be additionally stabilised by an opposing spindle or other work support element.

At present expanding collet chucks are being utilised to secure pieces of woodwork to lathes and such expanding collet chucks are designed to expand within a counter bore provided in the base of the piece being worked. In order that the base of the piece being worked may resist the forces generated by the outwardly expanding collet chuck its base must be relatively thick adjacent the periphery of the counter bore and hence shaping of the base of the piece adjacent the counter bore whilst the piece is still on the lathe is often not possible. The fact that some shaping of the base of a piece is usually necessary furthermore dictates that the counter bore be relatively shallow and consequently the available area for contact between the expanding collet chuck and the piece is relatively small.

Some of the problems associated with expanding collet chucks may be overcome by utilising external chucks which close around a plug of circular section forming part of or inserted into the base of a piece to be worked thus allowing shaping of the base of the piece whilst still on the lathe; the plug later being cut off flush with the base. Existing external dixis however, particularly those of the three jaw variety,have been found inadequate insofar as rings have to be utilised to spread the forces generated by the steel jaws closing around a wooden plug.

In addition to the rings being inconvenient they have still been known to work loose and present a significant danger to the user in such event.

It is accordingly the object of the present invention to alleviate one or more of the disadvantages associated with existing chucks or at least provide the consumer with a choice.

According to the present invention there is provided an external collet chuck with a collet comprising three or more petals defining a circular section counter bore and being joined adjacent their lower extremities to a base adapted for affixation directly or indirectly to a driven spindle; a shroud adapted to fit about the ~ petals, the internal surface of the shroud and the external surfaces of the petals being shaped such that in use urging the shroud upwards from the base around the petals causes the petals to move progressively radially inwards thus captivating any plug or other such object which may be present in the counter bore; means for locking the shroud in a variety of positions about the petals.

One embodiment of the present invention will now be with reference to the accompanying drawings in which: Figure 1 is an end view of a collet in accordance with the present invention; Figure 2 is an exploded side elevation of the components of a chuck in accordance with the present invention, partly in section.

The embodiment of figures 1 and 2 depict a collet 1 comprising eight petals 2 defining a circular cross-section counter bore 3 and being joined at their lower extremity to a base portion 4. It should be noted that the petals comprise a thickened portion 5 displaying an external taper 6 adapted to co-operate with internal taper 7 of shoud 8. The petals additionally comprise a thin flexible portion 9 adjacent the base 4 in order to accommodate the radially inward movement exerted when shroud 8 is urged upwardly such as to engage taper 7 with taper 6.

It has been found that the collet may advantageously be fabricated from 10/40 or 10/45 6-8 ton tensile stronger than mild steel.

The embodiment of figures 1 and 2 further utilises a locking ring 10 and a main body 11.

In operation the components would be assembled as follows.

The internal thread of locking ring 10 would be engaged with the external thread of main body 11 and the ring would be run down to an area adjacent the base and driven spindle engaging end of the main body. The shroud 8 would be placed over the opposite end of the main body and it should be noted that such shroud is not internally threaded. The external threads on the base 4 of the collet may then be engaged with the internal threads 12 of the main body and the assembled chuck engaged with external threads of a drive spindle of a lathe by means of internal threads 12 at the base of main body 11. A piece of wood (not shown) would normally then be engaged in the collet jaws and two "C" spanners inserted in the locking holes 13 of the main body and locking ring.The "C" spanner engaged with the main body may then be moved anti-clockwise and the "C" spanner engaged with the locking ring. move clockwise. This motion will cause the shroud to move along the main body towards the collet thus closing the jaws of the collet upon the piece of wood in counter bore 3. It should be noted that the external thread on the main body and the internal thread of the locking ring are lefthanded such that the rotation of the driven spindle of a conventional lathe will tend to further secure the piece of work in annular void 3 rather than loosen locking ring 10.

The embodiment lastmentioned has been found to provide a particularly stable mount for a piece of wood insofar as counter bore 3 is relatively deep. The fact that shroud 8 does not itself rotate with respect to the collet during closing of the collet jaws is furthermore considered significant insofar as ease of operation is enhanced due to lessened friction between the tapered surfaces. The lastmentioned embodiment utilises a twelve degree taper on the external surface of the collet although those skilled in the art will appreciate that other specifications are possible. A fifty millimetre diameter counter bore has additionally been found to be practical.

It will be appreciated that apparatus in accordance with the present invention is superior in many aspects to other types of chucks presently available. For example a chuck similar to that used in relation to power drills utilises a stationary ring and movable jaws with the jaws mowing towards the work as they close. This type of chuck does not permit quick centering and predictable placement of the work as each time the chuck is open or closed the work may end up in a different position on a lathe.

Claims (6)

The claims defining the invention are as follows:

1. An external collet chuck with a collet comprising three or more petals defining a circular section counter bore and being joined adjacent their lower extremities to a base adapted for affixation directly or indirectly to a driven spindle; a shroud adapted to fit about the petals, the internal surface of the shroud and the external surfaces of the petals being shaped such that in use urging the shroud upwards from the base around the petals causes the petals to move progressively radially inwards thus captivating any plug or other such object which may be present in the counter bore; means for locking the shroud in a variety of positions about the petals.

2. A collet chuck in accordance with claim 1 hereof wherein the means for locking the shroud in a variety of positions about the petals is an internally threaded locking ring.

3. A collet chuck in accordance with claim 1 hereof wherein the base of the collet is externally threaded in order that it may be screwed into an internally threaded circular cross section tubular body portion; the shroud being annular in configuration and adapted to pass over the tubular body portion; the external surface of the tubular body portion being threaded such that an internally threaded locking ring may be run up on the body to lock the shroud in a variety of positions about the petals.

4. A collet chuck in accordance with claim 1 hereof wherein there is a taper on the external faces of the petals such that they increase in diameter towards their free ends; a corresponding taper on the internal surface of the shroud such that urging the shroud upwards from the base around the petals causes the petals to move progressively radially inwards.

5. A collet chuck in accordance with claim 1 hereof wherein the petals are defined by linear longitudinal cuts; the petals being capable of resilient radial deflection in an outward direction due to a thin walled portion adjacent their lower extremities acting as a

6. A collet chuck in accordance with claim 1 hereof wherein there are provided eight petals and wherein the petals are fabricated from steel.