The overhead apparatus is applicable not only to revolving cutters in the slide rest, but to other contrivances available where the latter is not possessed. There are many cases in which the back poppet may be brought into use to hold revolving drills, or stationary tools, if the resistance to their action is not too great. The only damage that can well happen in this method is to the pin working in the slot on the outside of the spindle. If this is of steel and tolerably stout and strong (being very short it cannot be subject to any very injurious strain), no harm is likely to result. With this it is possible to drill very neatly, and also to do a little eccentric cutter work, under certain conditions to be described. Screwing, or rather chasing, may likewise be done very passably. We do not, of course, advise this course when the more perfect slide rest is at hand, but there are many who are obliged to put up with all sorts of homemade contrivances, and to press into service for divers operations apparatus and tools not precisely meant to be thus used, and it is as well to learn how to act under an emergency, even if the practice is not intended to be carried out generally. The drill stock is shown in [Fig. 148], in which the screw A fits into the spindle of the back poppet. If the hole in the latter is conical instead of cut with a screw thread, the drill must be made accordingly.
The pulley of brass has a hole drilled through it, and the screw is also drilled, the hole in the latter being rather larger than that in the pulley (which is tapped). The steel pin H, shown white in the sectional drawing, passes truly through the centre of the screw in which it revolves, and is screwed into the pulley. The socket of steel to hold the drill is then screwed or soldered into the opposite face of the pulley. The black part shows a flange on the screw which abuts against the cylinder of the poppet into which it is screwed. Thus the pulley, being attached to the cord from the overhead apparatus, is free to revolve upon the steel pin with great rapidity, and will carry round any drills or cutters placed in the socket B. The simple straight drill being thus worked and advanced by the leading screw of the poppet, will suffice for holes in any work held on the mandrel. On page 335, vol. ii., of the English Mechanic, this method is mentioned, and also a similar pattern of slide tool to be used for boring, being, in fact, the head and spindle of the back poppet, but instead of the standard and sole, a pin, like that of a T, to fit the socket of the rest. This has the advantage of the back poppet, but must be made on purpose, and if any special slide tool is added, a proper slide rest is by far the best. Our present purpose is to describe the use of the back poppet as a substitute for a better tool.
With the following modification of the eccentric cutter, a fair amount of good ornamental work may be done. [Fig. 149] represents the back poppet with the apparatus in position. The various parts are shown separately in A, B, C, D. A is a small frame, two or three inches long, and ¾ to 1 inch wide, cast in iron, with a circular piece at the back, 1½ or 2 inches diameter. This circular piece is to be accurately divided on the edge with any even number, which is divisible as above explained. This is turned and drilled through the centre. B is a flange-shaped piece to screw to the poppet as before, and this is also accurately drilled, and the two are attached by a central steel pin, so that the two flanges can turn face to face, the outer one with frame revolving against the other. The pin must be put in its place in B, and turned at the same time as the face of B, that it may be truly central. The divisions on the edge of the outer flange are to be drilled like the division plate of the lathe, or cut into cogs, and in either case can be held at any point by a spring detent or index attached. C shows the front of the frame, with a screw down its centre and traversing slide f. The head of this screw is divided, and a small brass index marks its position; one side of the frame may likewise be divided. The small brass pulley and drill socket are fixed to revolve in the traversing nut or slide f, as shown in a side view at D. Drills of all shapes, as E 1, 2, 3, 4, may be fixed in the socket at pleasure.
Fig. 149.
Fig. 149E.
