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

After you have had some practice in turning, you should certainly learn to shape your tools from square bars of steel, worn files, and broken steel tools of various kinds; and before you have arrived at sufficient dexterity to do this entirely by yourself, you will get them roughly shaped for you by the blacksmith, and then with grindstone and file you will further perfect the angles for use. Steel does not require, and must on no account be subjected to, a white heat, or you will spoil it hopelessly; and you can always heat it in a common fire, or in the little stove that I shall describe in a subsequent chapter, to a temperature that will allow you to bend it into any required form with the hammer and anvil—a bright red being the utmost heat it must be brought to.

POSITION OF CUTTING TOOLS.

We must now consider the mode of applying the edge of a tool to the work, so as to produce the best effect. First, we will consider the case of a gouge and chisel acting upon soft wood.

Fig. 48.

In Fig. 48, A represents a piece of wood in the lathe, as you would see it if you stood at one end of it, and a chisel is being held against it. The arrow shows the direction in which the wood is supposed to be revolving. Held thus, the chisel would scrape, and its edge would be carried off at once; it could not possibly cut. But, held as at B, it would cut off a clean and continuous shaving as the wood revolved against it, and this shaving would slide off along the upper face, b, of the tool, so that you can see that this face ought to offer the least possible resistance to it. The tool acts, in fact, like a very thin, sharp wedge, which divides the material by pressure, which has to be great or slight according as the edge is sharp and thin or the contrary. Now, if you again look at A, you will see that this wedge-like action cannot take place, so that the tool is in its worst possible position.

Between the two positions, however, here shown, are several others at a greater or less angle to the surface of the wood; but the smallest possible angle it can make is the best, so long as the thickness of shaving removed will suffice for your purpose. This rule holds good with all tools, whether carpenters’ or turners’, which are made with sharp-cutting edges. Care must be taken, however, that the lower face of the tool does not rub against the work, which, again, it is evident, limits to a given degree the angle at which the cutting edge is to be applied to the work.

We now pass on to C, which represents the ordinary tool for turning iron, held flat upon the rest, the position it usually occupies. We see at once that in this case also we have a scraping tool only, and that, although the angle of the edge is far greater than that of the chisel, it must soon be ground off by the action of the metal to which it is applied, or of the hard wood, which is also cut in this way. But with this form of tool we shall find it impossible to apply it so as to cut in the best way; because if we lower the handle, as we did that of the chisel, the part below the edge will rub against the work, while the edge itself will be moved out of contact with it. Thus we are obliged to hold the tool in the position first shown; but we may therefore conclude that the tool itself is a badly formed one for the intended purpose; and so it is, although you will see it in almost every workshop in the kingdom. Let us see what can be done to improve it. At D, I have represented the same tool, but the blackened part shows what has been filed away from the upper face, and the dotted lines show that, when this has been done, a tool is made very similar to the chisel for wood, and that it is also now in a good position for cutting (not scraping), although it is still held horizontally upon the rest. Shavings of iron curl off the upper face of this, as wood shavings curl off upon a chisel.

If the angle, however, is too small, the edge will soon be broken off, and the tool will dig into the work; hence the necessity of knowing at what angle a tool ought to be ground to cut any particular metal successfully.