BACKGROUND ART Many types of chuck are known, however, most suffer from several disadvantages in that they are limited as to the diameter of the work piece able to be held, and also the shapes of acceptable workpieces. A further problem is that the chuck normally bears on the workpiece in a small number of locations (typically 3) and the area of contact between the workpiece and the chuck is normally relatively small. Thus some materials such as wood and other easily bruised substances, cannot be turned, or can only be turned with great difficulty, without damaging the material. This particularly applies where the article to be turned is a bowl or some other article having a thin wall section.

It is the object of the present invention to overcome the abovementioned disadvantages by the provision of a chuck attachment which permits the article to be turned to be gripped over a large area of contact.

DISCLOSURE OF THE INVENTION According to one aspect of the present invention there is disclosed a chuck attachment for use in turning workpieces, said attachment comprising a plurality of segmental chuck plates having a rear surface shaped to permit said plates to be mounted on a conventional chuck and be radially reciprocatable thereby, and a like plurality of segmental carrier plates formed from turnable material and respectively connected to the front surface of the corresponding one of said chuck plates. Preferably the carrier plates are releasably connected to the chuck plates by means of fasteners such as wood screws or countersunk metal screw.

BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the present invention will now be described with reference to the drawings in which;

Fig. 1 is a plan view of one of the three segmental chuck plates of the chuck attachment of the preferred embodiment,

Fig. 2 is cross section along the line II-II of the chuck plate of Fig. 1,

Fig. 3 is a cross sectional view along the line III-III of the chuck plate of Fig. 1,

Fig. 4 is a view similar to Fig. 2 but showing, in cross section, the corresponding segmental carrier plate mounted on the chuck plate, and

Fig. 5 is a view similar to Fig. 4 but showing a carrier plate adapted to mount a different workpiece.

Fig. 6 is an exploded perspective view from the rear showing the carrier plate and chuck plate, and

Fig. 7 is a perspective frontal view of the apparatus of Fig. 6. BEST MODE OF CARRYING OUT THE INVENTION

The chuck plate attachment of the preferred embodiment comprises three segmental chuck plates 1 (of which only one is illustrated in Figs. 1 to 5), and three segmental carrier plates 2 (of which only one is again illustratedin Figs 1 to 5). As seen in Figs. 1 to 3, each chuck plate 1 is formed from a 120° segment and has a rear surface 3 and a front surface 4. A part annular ridge 5 is provided on the front surface and two recesses 6, 7 extend forwardly into the chuck plate from the rear surface 3. The recesses 6, 7 are shaped to mate with the bottom half of a conventional two piece jaw of a conventional scroll or self centering engineer's chuck 20.

Although the abovementioned jaws are not illustrated, the mounting of the chuck plates 1 on the scroll chuck 20 will be apparent to those skilled in the art and the position of. the scroll body relative to the chuck plates 1 is indicated by means of broken lines in Figs. 2 to 5.

In addition, the chuck plates 1 are provided with a

plurality of apertures 8 which are preferably counter sunk on the rear surface 3 in order to permit attachment of a segmental carrier plate 2 by means of a conventional counter sunk wood screw 9 as illustrated in Figs. 4, 5 and 6. The surface of the carrier plate 2 which mates with the front surface 4 of the chuck plates 1, is provided with a part annular groove 10 which corresponds with, and mates with, the ridge 5. The interengagement of the ridge 5 and groove 10 together with the fasteners 9 ensures a secure interconnection between each of the chuck plates 1 and the corresponding carrier plate 2 which is able to withstand centrifugal forces.

As seen in Figs. 4 and 7, the outwardly facing surface of the carrier plate 2 is turned in order to provide one or more recesses 11 which have a diameter corresponding to the diameter of the bowl 12 or other similarly shaped workpiece to be held. Preferably the recesses 11 are provided with a rounded arris 13 so as not to dent the bowl 12 and the recesses 11 are also preferably slightly undercut. The recesses 11 are turned with the chuck jaws located approximately at the middle of their radial range of movement. After turning of the recesses 11, the chuck jaws are slightly expanded (as seen in Fig. 7), the lip of the bowl 12 (Fig. 4) is placed interior of the recess 11 to which it corresponds and the chuck jaws, chuck plates 1 and carrier plates 2 are then moved radially inwardly in order to grip the rim of the bowl 12. In this way the base of the bowl, for example, can be turned and the large area of contact between the rim of the bowl 12 and. the carrier plates 2 ensures that the bowl 12 is not bruised or otherwise damaged.

Fig. 5 schematically illustrates an arrangement where it is desired to internally grip a workpiece such as a bangle, wooden curtain ring, or other similar annular article. Again, with the chuck jaws set towards the middle of their radial range, the carrier plate 2 is turned so as to provide a central stub 14. A radially outwardly facing recess 15 is then turned in the central stub 14, the chuck

jaws moved radially inwardly, the workpiece 16 located over the recess 15 and the chuck jaws, chuck plates 1 and carrier plates 2 then move radially outwardly in order to grip the workpiece 16. The central stub 14 enables the radially outward surface of the workpiece 16 to be turned as desired. A central stub 14 is also illustrated in Fig. 7.

The foregoing describes only one embodiment of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention.

INDUSTRIAL APPLICABILITY For example, although the chuck attachment of the preferred embodiment has been described in relation to a three jaw scroll chuck, the invention is also clearly applicable to four jaw scroll chucks. Similarly, the recesses 6, 7 in the chuck plates 1 are required to be shaped to be engageable with the two piece jaws of particular brands of chuck for which the attachment is intended to be used. The most suitable material for the chuck plates 1 is metal, although plastic, resin impregnated materials, and other such rigid turnable materials are also possible. The preferred material for the carrier plates 2 is wood, particle board material, or the like which is relatively easily turned and also relatively low cost since in time such carrier plates are discarded and a new set of carrier plates used.

Alternatively, the carrier plates can be of metal (or some other turnable material) and turned so that they can securely grip-either the outside of a rim or spigot, or the inside of a recess. Each set of these alternative carrier plates is particula-r to a specific gripping situation and is exchanged for a different set of carrier plates rather than being re-machined or re-turned for each different gripping situation.

A further modification is illustrated in Fig. 2 by means of dashed lines. In this modified arrangement the annular ridge 5 is formed so as to have a generally dovetail

cross-section. The modified ridge 25 can then be used to clamp directly onto, say, the base of a bowl as a modified chuck jaw.

It will be apparent that one of the advantages of the above described arrangement is that the chuck plates 1 can be formed to have a substantially larger diameter than the scroll chuck itself and that, if desired, the radial extent of the carrier plates 2 can be even greater thereby enabling large diameter work pieces to be turned on relatively smaller chucks. For example, a wooden bowl having a diameter of 8,10, or 12 inches could not be turned directly on a 4, 5 or 6 inch diameter chuck respectively. However, with the carrier plates 2 of the preferred embodiment, such size diameter bowls can be easily turned on chucks of that size.