Rectilineal Chuck
Fig. 311 represents a modification of the eccentric chuck, when the latter is used as a fixture, to present to revolving cutters and drills the different parts of the work which is to be operated on. The eccentric chuck is commonly made to slide in one direction only, and the traverse is limited. In the present case there is ample traverse in both directions, the slide being arranged to descend to the lathe bed, and upwards to an equal degree. A is a cross section of this chuck, the length of which is 7½ inches. It is very strongly made in brass, and is altogether much more substantial than the eccentric chuck. B and C are the guide bars, between which works the sliding part. The nut of the leading screw is below this as usual. The tangent wheel has 120 teeth, and is thus divided: 0—12—24, &c. The tangent screw head is divided thus: 0—1—2—3—4—5, with half divisions, marked but not numbered. This rectilineal chuck is most commonly used in a vertical position, but may be otherwise placed. In using it for any work likely to bring a strain upon it, the ordinary spring index attached to the lathe for use with the face plate, should not be entirely relied on to keep it in position. It is safer to make use in addition of the segment engine stops or other available contrivance. The special function of the chuck is the production of straight lines on the face of work forming stars or radial flutes, which can be worked with a drill. Fluting is also readily done by its aid, with the addition of the vertical eccentric, or dome chuck, already described. Its use is, however, by no means confined to ornamental work—small tenons, mortises, and even dovetails are producible by it; and in fitting together the various parts of temples, shrines, and similar complicated specimens, its uses will be innumerable; and here may be noted the extension of the lathe and its apparatus to work apparently in no way suited to it. It has now become more of a universal shaping machine than it used to be, owing to the great accuracy of the work done by it, and the variety of fittings that can be added to it. In a later page will be found a drawing and description of a new device of the kind—a planing machine, devised by an ingenious and first-class maker, Munro, of Lambeth, and patented by him. Mention is made of it in this place, because the rectilineal chuck is in some degree capable of similar work. The slide moved up and down by a screw the handle of which is of extra length to allow the vertical traverse, is also capable of being moved by a cam-eccentric chain or rack and cogged wheel, so that by pulling down a handle the slide may be made to slide up and down more rapidly than by the screw motion; any piece of wood of rectangular or other figure may thus be planed on the face, by being fixed on the rectilineal chuck, and acted upon by a fixed tool in the slide rest, the latter affording the horizontal traverse of the tool across the face of the work, the former the perpendicular movement of the material. If a slide rest is thus arranged in combination with the chuck in question, and the lathe bed is imagined to be set up on end with the chuck downwards and horizontal, the whole will become, in fact, a precise counterpart of those planing machines, the bed of which traverses to and fro, with the work under a fixed tool. Munro’s arrangement is, of course, of far more extended application, and more suited for metal work; but for lighter and more delicate operations of a similar kind the rectilinear chuck and slide rest will be found very serviceable. It is with such an adaptation of this chuck as has been alluded to, namely, a quick speed movement of the slide by a lever handle, that the rays are drawn so exquisitely fine and close upon the faces of many gold dial plates of watches, the handle being arrested by a stop at any given point, so that these rays shall not transgress their appointed limits. It will be hardly necessary to allude to those other applications of this apparatus, or other particulars in which it is identical with the eccentric chuck, as the description already given of the latter applies to both alike, the extra traverse of the present in both directions being its chief distinguishing feature.