[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.
Fig. 311.
Fig. 312.
[Epicycloidal Chuck.]
This chuck has been in use for many years, and has in consequence been of late rather neglected. It is, nevertheless, the parent of those more elaborate contrivances included under the general title of Geometric Chucks, of which Ibbetson's stands first in order of date, and possibly of merit, though this last qualification may admit of question. The epicycloid, defined mathematically, is a curve described by the revolution of a point in the circumference of a circle, when the latter is made to roll upon the concave or convex side of another circle. A pin in the rim of a wheel revolving round and in contact with another wheel, therefore, describes this curve, which constitutes two or more loops, as will be seen by the annexed illustrations. The number of these loops is variable, and the chuck will produce almost any number by changing the pinions, and thus altering the relative velocities of the revolving parts. The following description will make the action of this chuck clear, and enable any good mechanic to construct one for himself. In the first place, the above remarks show a necessity for a fixed wheel, round which another may revolve. [Fig. 313] represents this attached to a plate of brass, which can be fixed to the lathe head, the mandrel passing through its centre. This is the original pattern of plate, and need not, of course, be adhered to, as the form can be modified to suit the lathe to which it is to be applied. It is merely necessary to affix such a wheel to the face of the poppet, so as to be concentric with the mandrel [Fig. 314], behind which is mounted the cogwheel, B. The axis of this wheel passes through the plate, and is carried by another plate, e, which is curved and adjustable upon the former. The axis of this wheel carries a small pinion, D, so that the whole turn together. This pinion being one of a set of change wheels, necessitates the possibility of adjusting the plate which carries its axis, as all the several change wheels must gear with E, which always retains its position on the chuck. The sliding plate in question being put in place, is clamped by the screw F. A plate of iron, G, of the form shown, and of sufficient thickness for the secure attachment of the wheel and of the screw which carries the ordinary chucks, is fitted to turn on the axis of the wheel E. Its larger end traverses within the arc H, which is graduated. The arc is bevelled underneath, serving to hold down securely to the foundation plate the piece of iron which is chamfered to fit it. At the left side of the back plate is seen a stop, L, which is placed in such a position, that when the iron plate rests against it, the screw M is concentric with the mandrel, and work may be turned as upon an ordinary chuck. To throw the iron plate, and consequently the nose of the chuck, on one side, or in other words to place the work eccentrically, the screws which retain the arc are loosened and the adjustment made by hand. The eccentricity is marked by an index on the iron plate, which points to the graduations seen upon the face of the arc. The eccentricity being determined, the arc is again screwed down to retain the movable plate in its new position. [Although this is Bergeron's method, it appears vastly inferior to the plan of racking the edge of the iron plate, and moving it to any required degree of eccentricity by the aid of a tangent screw.] When made as above, the chuck will produce loops varying in number according to the relative dimensions of the pinion (or change wheels gearing with E) and the central wheel, M. If the latter has 120 teeth, and the change wheel 60, two loops will result. If the pinion has ten teeth, the number of loops will be 12, and so forth. The practical limit to the number depends on the possibility of diminishing the pinion in size and number of cogs, and still keeping the latter of such size and pitch as to gear with E. If, therefore, a larger number of loops is required than can be obtained thus, it becomes necessary so to modify the form of chuck as to permit of intermediate change wheels, and when the modification is carried out, we have the geometric chuck, the most perfect, but the most complicated and expensive of all. To understand the nature of the work, the following is given in clear language by Bergeron, and will sufficiently explain and simplify matters.
