Fig. 143.
[Fig. 143] shows the chuck complete. Suppose we have to face up a round disc in its central part, or to perform any surface work in which the jaws will not be in the way of the tool, the centre of the plate is marked at the back of it, and this mark laid on the central pin. The work can be clamped down by the three jaws, and the necessary work may be done. Now so far the chuck is but a simple affair, and the receding pin does not show itself to such great advantage; we will therefore suppose a plate is to be drilled at several spots; let these be marked at the back by a centre punch. It is now only necessary to bring these marks in turn upon the central point, and clamp the plate in position. Bring the point of the drill against the work and keep it up to cut by the back poppet screw. In the same way eccentric work or any operation may be done to such a plate, with the certainty that the point to be thus worked upon is precisely central with the axis of the pulley, or mandrel. Many similar applications of this chuck will present themselves to the reader upon due consideration. We present the chuck in this place because we have had occasion to speak of drilling as connected with the slide rest, and there are many pieces of work that could not otherwise be conveniently held in the desired position.[10]
[10] The MS. book containing the above was kindly lent to the author of the present work by Mr. Hoblyn, of Bishop's Stortford, who is the inventor of a new form of slide rest, which will be introduced in a later page. The chuck in question is, however, commonly attached to the watchmakers' lathes of the present day, and therefore may not, as the writer supposed, be actually the invention of the late Mr. Wilcox.
[Overhead Apparatus.]
It now becomes necessary to speak of another addition to the lathe, by means of which the use of the slide rest is considerably extended. We mean the overhead motion. Of this there are several patterns, and we have sketched three of these. As to their respective merits we can hardly venture to speak. They all answer equally well the purpose for which they have been designed, and the turner must select according to his fancy, or, if he please, design a better for himself. A, [Fig. 144], represents the lathe bed. From the left-hand standard rises a round iron rod, not less than one inch in diameter. This is not generally fixed, but is attached to the standard by two staples, a, b, which hold it securely in an upright position, but allow it to turn with its projecting bar F, F, after the manner of a crane. It may thus be turned back, out of the way, or brought into any desired position. The part F, F is made to slide up and down on the part B, and is fixed by a clamping screw D. Thus, if the cord should break and require to be shortened, the arm can be brought nearer to the bed of the lathe. Upon F, F slide two rings, or rather short pieces of tube, from which depend two India rubber springs (door springs), E, E, now procurable at any ironmonger's at one shilling each. From these hang double pulleys, or better still two single ones. These pulleys, with their attachments, are adjustable at any position on the arm F, F, which may be round or square. If considered desirable, a second standard can be added, so as to uphold both ends of this bar; but it is hardly necessary, as the latter is seldom required of greater length than half that of this lathe-bed. It is evident that the above addition to the lathe can be made complete for a few shillings. The following are more expensive, but more general, the writer having devised the above to suit his own fancy, and for his own use. In [Fig. 145] A represents the standard as before, the top of which is forked, as shown at E, and sustains the ring, free to revolve in its arms, as seen in the sketch. Through this passes a bar, B B, with a heavy ball C cast on its end to act as a counterbalance to the longer arm and its connections, and to keep the cord stretched. By sliding this bar either way through the ring which supports it, the tension of the cord can be increased or lessened.[11] When in position it must be very securely fixed by the screw T, which should not simply press against it, but enter one of a row of depressions made for the purpose. The pulleys C, D are double, as in the previous plan of overhead, and are likewise adjustable at any position on the bar B, B. The only drawback to this pattern is the danger of the heavy ball slipping out and falling. We prefer to hang a weight from the end of the lever, as shown by the dotted line. This may be within a few inches of the floor, and if it should fall no harm can ensue. The third pattern, [Fig. 146], is the most expensive, but although it is of a more finished appearance, and wears an aspect more stiff and stable, it is not practically any better than the last. From a standard A, with overhanging bar F, F, is suspended a frame H, by means of two coiled springs in brass boxes B, B, which keeps up the necessary tension on the cord, or rather cords, for in this case two are needed—one from the flywheel to the small pulley, and a second from the roller to the slide rest.
[11] Sometimes the bar is merely hung on pivots, and the weight is made to slide upon it.
Fig. 144.