1. Field of the Invention
The present invention relates to a chuck used to hold a work on a machine tool.
2. Description of the Related Art
A chuck is usually used in order to hold a work on a spindle of a machine tool such as a lathe.
Referring to FIGS. 27 and 28 of the accompanying drawings, a chuck 100 of the related art comprises: a chuck body 1 attached to a spindle of a machine tool; master jaws 2 fixedly positioned in the chuck body 1 along the normal of the chuck body 1 and having T-shaped grooves 2a extending along the length thereof; T nuts 3 having heads 3a and trunks 3b, the heads 3a being slidable in the T-shaped grooves 2a along the normal of the chuck body 1; gripping claws 4 having work holding surfaces 4a and grooves 4b engageable with the trunks 3b of the T nuts 3; and claw attaching members 5 inserted into holes 3c and 4c extending across the T nuts 3 and the gripping claws 4 which are engaged with one another. In this case, the claw attaching members 5 are bolts.
In this chuck 100, the gripping claws 4 usually have their work holding surfaces 4a shaped in order to reliably grip the work.
Therefore, the work holding surfaces 4a of the gripping claws 4 are re-shaped each time they are applied to works having different shapes. Further, even if works of the same shape are to be held, the work holding surfaces 4a have to be reshaped in order to reliably grip the works each time a machining process is changed. The work holding surfaces 4a gradually wear out, so that they should have large reshaping margins as possible.
With the chuck 100 of the related art, the holes 3c and 4c vertically extend through the T nuts 3 and the gripping claws 4 where the claw attaching members 5 are inserted are in parallel with the spindle 0 of the chuck 100, as shown in FIGS. 27 and 28.
With the related art, the holes 3c and 4c occupy a large portion of each gripping claw 4, which means that reshaping margins of the work holding surfaces 4a of the gripping claws 4 are reduced. This would lead to shorter life of the gripping claws 4, which is uneconomical.
Bolts are used as the claw attaching members in the related art, so that it is troublesome to attach the gripping claws to the T nuts. Further, since the bolts are inserted into threaded holes in the T nuts, it is time consuming to make such threaded holes. Sometimes, chips may remain in the threaded holes, which would lead to damages on the threaded holes and threads on the bolts.
The present invention has been contemplated in order to overcome the foregoing problems of the related art, and is intended to provide a chuck in which gripping claws have a little space for holes into which claw attaching members are inserted, and have sufficient reshaping margins of work holding surfaces. The invention further provides gripping claws for such a chuck.
Another object of the invention is to provide a chuck in which gripping claws can be easily attached to T nuts, and to provide gripping claws for such a chuck.
According to a first feature of the invention, there is provided a chuck comprising: a chuck body attached to a spindle of a machine tool; master jaws attached to the chuck body along the normal of the chuck body and formed with T-shaped grooves extending along the length thereof; T nuts having tops and trunks, the tops being slidably fitted in the T-shaped grooves of the master jaws; gripping claws having work holding surfaces and grooves for engagement with the trunks of the T nuts; and claw attaching members inserted into holes in the T nuts and the gripping claws and used for attaching the gripping claws to the T nuts. In the chuck, the holes are formed across the T nuts and the gripping claws which are engaged with one another. This structure is effective in increasing reshaping margins of the wok holding surfaces of the gripping claws, improving the life of the gripping claws, and reducing the running cost of the chuck.
The claw attaching members are constituted by eccentric shafts which have eccentric cams, are rotated and relatively move the T nuts and the gripping claws. The holes in the T nuts and the gripping claws are provided with cam parts with which the cams of the eccentric shafts come into contact.
The gripping claws can be easily attached to the T nuts by slightly turning the eccentric shafts. The holes into which the eccentric shafts are inserted can be formed with ease. Chips remaining in these holes would not extensively damage them.
The holes in the T nuts have cam parts with which cam parts of the eccentric shafts come into contact.
The eccentric shafts have cylindrical stems which are inserted into the holes of the gripping claws. The cams of the eccentric shafts inserted into the holes of the T nuts are thinner than the cylindrical stems, which is effective in preventing chips from getting to the cams of the eccentric shafts, and improving the life of the chuck.
In accordance with a second feature of the invention, there is provided a gripping claw for the foregoing chuck. The gripping claw has a groove for engagement with the trunk of the T nut, and has holes into which the claw attaching members are inserted for attachment of the gripping claw to the T nut, and the holes extend across the T nut and the gripping claw which are engaged.