Fig. 248.

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Fig. 250.

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Fig. 252.

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Numerous self centering wire and die chucks with three slides, appear to have been derived from Mordan's, or from Hick's expanding mandrel, fig. 278, or are combinations of the two. Perhaps the best construction is that known as the Beach chuck, figs. 253 to 255 ; formed of three main pieces and three dies, and carried upon a conical plug which screws upon the mandrel.

The conical plug screwing upon the mandrel, fig. 253, carries the entire chuck upon a plain fitting turned in the first piece A., shown in section fig. 254. The central portion of the chuck B., is bored out behind to fit upon A., and is cut with a screw, while in front it is hollowed and turned externally to a cone. The shell of the cone upon B., is completely severed along its entire length by three equi-distant parallel slits, for the insertion of the hardened steel dies, drawn also separately in two views, fig. 255. The three dies are precisely alike in all respects, their outer edges are filed to the angle of the cone B., and are formed with narrow fillets or enlargements, that are received in corresponding recesses at the sides of the slits, to prevent them dropping through the cone. The straight inner faces which grasp the work, are filed to a central angle of 120°, and at the base they have a transverse notch, fig. 255, loosely fitting the flat, button shaped front end of the piece A. The third piece of the chuck C, is a hollow cone permanently screwing to the front of B., to cover and retain the dies in position.

Fig. 253.

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Fig. 254.

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Fig. 255.

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The dies being attached by their notches to the flat extremity of the piece A., traversing the front portions of the chuck further on to the screw of the latter, causes them to slide down the cone and to approach each other until they meet, when they also project beyond the front of the chuck; screwing the chuck in the reverse direction, causes them to retire up the cone, separating them to enlarge the grasp. Fig. 253 has but a limited range in diameter, while its many parts and the distance from the mandrel at which it supports the work, confines its use to wires, drills and small objects of round section, from a quarter of an inch in diameter downwards; a second chuck is required for objects ranging from one quarter, to five eighths of an inch in diameter. The grasp of the hand in turning either chuck, suffices to fix the work.

Self centering chucks with three slides, are confined to round work, and are obviously inapplicable to square and other regular or irregular sections. The round work also can no longer be made to assume any eccentricity, necessary to counteract its own irregularities, to prevent undue waste of material or for other purposes, all easily accomplished in chucks that have two slides, self acting or otherwise; the round object therefore, also requires to be prepared more nearly true or straight, and usually takes the form of drawn wire, to which fig. 253 is particularly suitable.

The Wire chuck with split dies figs. 250. 251, has a limited power of adjustment and is convenient and simple in construction. A cylindrical recess in the front, is filled by several dies or plugs, bored with holes of definite sizes, varying not more than about one sixteenth of an inch in diameter; the plugs are sawn through for almost their entire length, and are closed upon the work by a binding screw, pressing upon a flat filed upon their sides. This chuck is employed for turning screws, pins and small objects, made from pieces of metal or wire which nearly fit the holes in the dies, and the gradations of size being small, very little material need be turned to waste. Similar chucks are employed to carry pieces of wood or metal of peculiar form, parts of which may require turning, as in fig. 252, in which the pivot to be turned or drilled, is also supposed to be inclined to the general axis of a piece of rectangular section. A plug or socket is made to the chuck, with the ordinary cylindrical hole replaced by an aperture, corresponding in form and angle with the particular piece to be turned, of which any number can then be exactly repeated.