The turner's companion /

by Anonymous

THE SCREW.

We now come to the most difficult operation in turning, that of cutting a screw; to perform it well and easily is a proof of the workman’s skill and proficiency in the art. There are many ways of doing it; we shall therefore give the best and least expensive. The screw tools, figures 14 and 15, [plate 1], must fit exactly one into the other. Fig. 15 is an outside, Fig. 14 an inside tool. As the threads may be required to be cut coarse or fine, according to the work you are engaged upon, the small grooves in the tools are made to suit. Having turned your box quite round, and hollowed it out, cut the groove upon which the lid is to fit; place the rest at a convenient distance, turn the wheel, not too fast, and move the outside screw-tool along the rest with a regular horizontal motion, and it will cut a screw, the threads of which will fill up the space between the teeth of the tool. But care must be taken to jerk the tool off when at the end of the space intended for the screw; or if it be allowed to remain stationary, cutting the wood, the threads will be destroyed, and become useless. When this is well done, turn out the lid of the box till it nearly fits the bottom, and in the same manner press the inside screw tool against the side of the cavity, draw it out horizontally as the work moves round, and if carefully managed, it will soon be made to fit upon the outside screw. As, however, to accomplish this well, and with precision, great practice is requisite, an invention, called a traversing mandrel, is frequently used, particularly by beginners: we will endeavour to give a description of its form and use.

At the end of the mandrel A, [pl. 4], is a brass cylinder, I, which fits upon the end, and is kept in its place by a nut, 2, which screws firmly into it. Below this, fixed to a brass plate that rises and lowers at pleasure by turning the screw-key, B, is attached the screw-guide; (a brass plate cut into grooves of various sizes to suit the thread you wish to cut, fig. 3;) this guide moves round on a pin. To use this machine, unscrew the nut B, pull off the brass cylinder, and in its place put on the guide, C, and screw the nut in again; turn the other guide, 3, to the groove which corresponds with it, and which is usually numbered, to avoid mistakes; turn the key B till the lower guide meets the one you have just put on the mandrel, and slips easily into it. You will now find that by only allowing the fly-wheel to move half round and back again, the mandrel will run backwards and forwards, and thus have the exact motion requisite for cutting a screw. Fix your rest, and hold your tool (which must have the same sized thread as the guide then on the mandrel) quite steady upon the rest, against the revolving wood, and in a few minutes the screw will be produced. The inside screw is made in the same manner, with the inside tool, by turning the rest in front of the work. Do not press the tool too hard to the wood at first, till the threads are slightly cut, so that the teeth may enter always in the same place. About six different-sized screw guides and tools to fit will be quite sufficient for an amateur turner. There is also another way of cutting screws, by means of a traversing chuck. On the mandrel, R, [pl. 4], is screwed the chuck B, to which are screwed the chucks of the lathe, R. On the outside of B is turned a screw, fitted to an inside screw worked in the block C, from which extends an arm, D, sufficiently long to allow the arm E to slide up and down it; a piece of iron should be screwed to the circular block, C, of such a length as to be capable of moving in a groove that may be cut in the collar; it is intended to prevent the block C from turning quite round. The rest, G, must not stand, as usual, parallel to the work in cutting the outside screw, but at right angles, as when an inside screw is to be cut, in order that the further arm of the rest, F, may be joined to the end of the second arm, G. It is necessary that the second arm, E, shall be capable of fastening firmly the first arm, D, to any part of the rest, G, F, as also to have a joint at each end, to admit in a horizontal plane its free action. Thus, as the lathe turns to or from us, the arms must traverse forwards or backwards, which gives a similar motion to the tool, H, that is screwed firm to the further arm, F, of the rest, and thus you can cut a screw with a single point tool. Of course any unsteadiness would spoil the screw. If you draw the centre of the rest nearer to you, and thus bring the tool nearer to the arm, E, a screw of a much larger-sized thread will be cut; for as the rest, turning in its socket, moves on a centre, the further the tool is from the centre, the greater will be the radius of the circle described, and vice versâ.

It may, perhaps, be feared that a piece of wood so far from the collar, K, may be apt to spring; but this is easily avoided, by not making use of the chuck, B, till the screw is to be turned. Another disadvantage would seem to arise from the impossibility of cutting screws when the puppet head is made use of. But this may also be obviated by lengthening the arm, E, to the part where the screw is to be cut, and thus we have the same screw as the traversing one. The socket, S, slides on the rest, and may be fastened to it by a screw, the upper part that turns on a pivot admits the arm, E, to slide through it, which arm is held firm with a screw.

At the commencement of the work, the rest stands at right angles with the wood on which the screw must be cut; then, by bringing it back to its original angle, and sliding forwards the tool to the last thread of the screw that was just cut, we proceed to any length required. When two or three threads are cut, the most unskillful turner will be able to continue the screw with a common screw tool.

BORING COLLAR.

Fig. D, [plate 4], is a boring collar, used to support any long slender body which is required to be turned hollow. Without a support of this kind it would be impossible to keep the wood in its place; and it would either incline from the centre, thus causing the hollow to be drilled out quite crooked, or it would spring from the chuck. To obviate these two inconveniences, the two collars, figs. C and D, [plate 4], are employed. In the former one, which is made of iron or brass, the holes are conical, and their centres are all precisely at the same distance from the axis of the collar. In using it, remove the right hand puppet, and provide a much lower one. Through it drill a hole, the same size as that in the centre of the boring collar. The centre of this hole must be in the same line with the centre of the mandrel. The collar, when attached to it, faces the mandrel, and is held firm by a screw. When fixed, the centre hole is opposite the axis of the mandrel; and when the largest hole is used, it clears the top of the headstock to which it is affixed. The end of the work to be bored being placed in the hole which fits it, the tool is held upon the rest against its centre, and the boring is easily and accurately performed.

Plate 3.

The collar, D, is perhaps, a simpler apparatus for supporting long pieces of slender wood or ivory, and has this advantage, that the workman can easily make it for himself. It should be constructed of very hard, well-seasoned wood. The foot, E, must be in breadth exactly the size of the aperture in the bed of the lathe, and is kept quite steady by a bit of wood thrust through it underneath the lathe. Into this collar, fit many pieces of wood with different sized holes bored through them, (all exactly in a line with the axis of the mandrel,) so as to admit large or small pieces of work, the sides being grooved, and the supports sawn to correspond: they all slide in with great ease, and are kept quite steady by an iron pin which runs through the top. The fig. G, shows the collar, with one of the supports slipped in, the other sliding upon it; H is the collar, showing the groove, and L L are two supports that fit into it. The middle of the apertures of these supports, whether large or small, must always be exactly on a line with the axis of the mandrel, therefore, after they are bored quite true on the lathe, they are sawn exactly across the hole. This is a very useful addition to the lathe, not only as a support when boring holes, but also to be used with the right hand puppet, to give strength to any long slender piece of work, as a screen-handle or a pen-holder; for, being of great length, the stress necessary to the proper management of the tools would be apt to break the wood or ivory, and it is easy to make one of the ornamental mouldings of a proper size, to enable it to run smoothly in one of the supports; if too tight, the wheel will not turn, and if too loose, the work will jerk up and down.