The Young Mechanic / Containing directions for the use of all kinds of tools, and for the construction of steam engines and mechanical models, including the art of turning in wood and metal

by James Lukin

TURNING BRASS AND OTHER METALS.

I shall now teach you how to turn iron and brass, which, though harder than wood, are not very difficult to cut, if you go to work in a proper manner and understand how to use your tools. What these are like I have already told you, and also how to mount a bar in the lathe by using the driver or point-chuck with a carrier. If the piece to be turned is not a bar, you will have to drive it into a chuck of wood, or clamp it upon a face-plate, or in a self-centring chuck if you have one.

I shall suppose, first of all, a mere straight bar of iron, centred at the ends, as I have shown you. Take off the lathe-cord that you use for wood, and fit one to go upon the largest part of the mandrel pulley, and the smallest upon the fly-wheel. When you now put your foot upon the treadle to work at your usual speed, you will find the mandrel turn quite slowly; but I may at once tell you, that what you lose in speed you gain in power. Set your rest for iron (which is not that used for wood, but one with a broad, flat top) so that it stands a little below the central line of the lathe mandrel and work, which will bring the edge of the tool exactly upon that line. This is always the position of the tool for metal-turning, at any rate for iron.

Begin by trimming the end of the bar next to the back centre. Use a graver, held as I directed you; that is, with the bevel flat upon the face of the iron, which is in this case the end of it. Only let the point cut, and a very little of the edge beyond it, and do not expect to take a deep cut so as to bring off a thick shaving. In metal work you will always have to proceed slowly, but nothing is more pleasant when once you can do it well.

You will at first have to experimentalise a little as to the exact angle at which to hold the tool, but you will soon find out this; and the advantage of hand-tools is, that you can always feel as well as see how they are working, and can ease them here and there to suit the material. It is rather difficult at first to hold the tool still in metal-working, but, like all else, it becomes easy by practice; so much so, that to hold the tool steadily in one hand is not only possible, but is the mode always followed by watchmakers. While you are about it, you should turn the graver over and try it in other positions; for although the two sides of the bevel nearest to the point are the only ones to be used, these may be applied in either direction, because they are both sharpened to angles of 60°, and so long as you present them at the correct angle (the smallest possible in respect of the work), it matters not which face of the tool lies uppermost. After squaring off one end, the approved plan is to remove the carrier, reverse the bar, and do the same to the other end. Then begin to turn from the right hand. Place the graver as before, with the point overlapping the end very slightly (so as only to use the extremity of the cutting edge close to the point), and take off a light shaving along the bar for a distance of about half an inch, or even a quarter, keeping the edge of the graver which is on the rest in one position, and moving the tool, not by sliding it along the rest, but by using the point upon which it lies as a pivot. It is very difficult to describe this exactly, but Fig. 52, O, will help to explain it. The tool is to rest upon one spot, and the point to move in short curves like the dotted lines, being shifted to a new position as you feel it get out of cut. The left hand should grasp the blade and hold it tightly down upon the rest, while the right moves the handle to and fro as required. The curved dotted lines are necessarily exaggerated, but the principle of the work is this, whether you use a graver or a heel-tool. You should turn about half an inch quite round, and then go on to the next, by which you will always have a little shoulder upon the work for the tool to start upon, and this will be nice, clean, bright metal, and will not blunt the tool. But if you go to work differently, so that the edge of the tool comes continually in contact with the rough outside of the iron caused by the heat of the fire, and which is exceedingly hard, the point of the tool will be quickly ground down, while the iron will not be cut into at all.

I need tell you no more about turning a bar of iron in the lathe, because the above directions apply in all cases; but if you have to turn the face of a piece of metal that is carried in a chuck of some kind, you should always work from the middle towards the edge, and if the graver is used, its bevelled face will lie towards you during the process. Take care to chuck the metal very firmly, for it is most annoying to have it suddenly leave the chuck or shift its position after you have been at the trouble of turning part of it truly. In such case it is very difficult to replace it exactly as it was before, and all your work has in consequence to be gone over again. When taking the final cut, or before, if you like, dip the end of the tool into water, or soap and water, and see the effect. The surface turned in this way will be highly polished at once, and the tool will cut with much greater ease, so that a large, clean shaving will come off. When using a slide-rest, you will find it always better to keep water just dripping upon the work and point of the tool; but there is a drawback, nevertheless, to this plan, for, as might be expected, it makes a mess and rusts the lathe, and sometimes the work as well, so the water must be constantly wiped off it.