There is no operation in which the young mechanic is so much at fault as in that of grinding and setting in order the various tools he has to use. Nevertheless he will never become either an independent workman or a good one, if he has to depend upon others for this necessary labour.

No doubt, to sharpen a tool which is in very bad order is a tedious and tiresome job; but it is not so wearisome an affair to keep tools in condition for work, after they have been once thoroughly sharpened by one who understands how to do it. Never, therefore, use a blunt tool, but at once go to the hone or grindstone with it, and put it in first-rate order. Time thus employed is never wasted, but rather saved; and the result will appear invariably in the work which you are engaged upon. You must, in the first place, understand precisely what it is you have to do; and although the following details may be by some considered more adapted for advanced students than for young mechanics, a little attention to the explanations will render the matter clear to any boy of age and intelligence to take in hand, with reasonable prospect of success, the tools of the carpenter, turner, and fitter. I can only say, that boys of this generation are wonderfully well off in having these things explained to them. Twenty years ago young mechanics had to grope along in the dark, ignorant to a great extent of the principles of work, and almost equally uninstructed in the practical part of it.

In Fig. 45 are represented similar angles to those already explained to you, and you will quickly understand how useful is a little knowledge of the elements of mathematics. Suppose A to be a tool, the angle of the point is a right angle, or 90°. B is another of 60° at the point, and I have drawn a line across to show you that the three sides of this figure (called a triangle) are equal. So remember that if you want an angle of 60°, you have only to draw a triangle of three equal sides, and each of these angles will be 60°. Again, I may as well remind you that three times 60° equals 180°, which is equal to two right angles, so we find here that the three angles of an equal-sided triangle equal two right angles, and even if the sides are not equal, the same thing is true. For instance, look at the first tool, across which I have also drawn a line to make a triangle. The point we know is 90°, and if the sides, a b, are equal (although the third line is not equal to either), the two small angles are each 45°, i.e., 90° between them, so the three angles again equal 180°.

The third tool (which we may suppose a turner’s chisel held edgewise) is shown to have an angle of 30°, and I have added one more which has an angle of 45°. Now all tools, if well ground, are ground to a certain known angle, according to the material which they are intended to cut. Tools intended to cut soft woods, like deal, are ground to an angle of 20° to 30°, like the chisel seen edgewise. I shall have a word to say presently as to the direction in which such tools are to be held, in order to make them cut as well as possible. A tool for hard wood is given next at E. The angle is now at least 40°, and it ranges up to 80°, giving a stronger, thicker edge, but not so keen a one. We have, therefore, more of a scraping tool than a cutting one,—at least, in the way it is usually held. Then we come to the tools with which iron is turned and steel also. Fig. F is one of these, and the usual angle is 60°, and thence it ranges to 90°. Thus you see, advancing from soft wood tools to those for hard wood, and thence to a substance still harder, we have increased the angle of the edge, beginning at 30° and ending with 80° or 90°. But now we come to a material which is harder than wood and not so hard as iron, yet we use tools with an angle of 90°, which is still greater, and 70° is the least angle ever used for this metal.

Experience only has taught the proper angle for tools, and it is found, that if brass and gun-metal are turned with tools of a less angle than 70°, they only catch into the material, and do not work at all satisfactorily. You can, however, scrape brass, as a finish, with the thin edge of a common chisel; but then the tool is held so as to scrape very lightly and polish; and its edge will not remain many minutes, unless the maker (intending it to be so used) has made it much harder than he would make it for soft wood cutting.

If you buy your tools at any good shop, you will find that they are already ground to nearly the angles named, and when you re-grind them, you must endeavour to keep them to the same. The bevel, as it is called, of many tools need not be ground at all, as they may be sharpened solely by rubbing the upper face on a hone, or grinding it, holding it so that the stone shall act equally on all parts of it. If, however, the tool should become notched, you must grind the bevel of it, and then you must try and keep the intended angle. One tool, however, or rather one pair of tools, viz., turning-gouges and chisels, are very seldom ground with a sufficiently long bevel when they first come from the maker. The usual shape of the edge is like G, whereas the angle should be much less, as seen at H. This you must correct when you first grind the tools for use, and keep the same long bevel and small angle of edge continually afterwards, for you will never make good work on soft wood if your chisels and gouges are ground with too short a bevel.

I must also guard you against another common error, which, however, is very difficult to avoid at first, and only long practice will enable you entirely to overcome it. I, is the chisel (held edgewise as before) ground as it ought to be; K is the same tool ground as it generally is by young hands, or, even if it is correctly formed at the grindstone, one or two applications to the oilstone almost invariably round it off as shown. The bevel of all tools must be kept quite flat and even, and when the tool is afterwards rubbed on the oilstone to give a finish to the edge, another flat, even bevel should be made. In the same figure at L is an exaggerated view of the chisel, with its first long bevel formed at the grindstone, and the second very small bright bevel seen at the extreme edge of all such tools when they have been set upon the oilstone. This second bevel, slight as it is, you will at once understand makes the angle of the edge a little larger, therefore you must allow for it, and grind a little keener edge than you really require.

Now, all this is very simple and easy to understand, and when you have mastered this much, you will be in a fair way to understand more. The second part of the subject, nevertheless, requires very close attention, and very likely may not become quite clear to you when explained. I shall therefore draw a line here, and make this lesson a special paragraph, which you can look back to some other day, when you are grown from a boy-mechanic to a man, and have had more experience in cutting and turning wood and metal.

The tools above described have their cutting edges formed by the meeting of two planes at a given angle,—these planes being the flat bevels (or the flat top and one bevel) formed by the grindstone. But in some tools three planes meet to form an edge instead of two, and the angle of the cutting edge is not the same as that of either of these, although it depends upon them, and can be nicely calculated. This calculation, however, requires a knowledge of some higher branches of mathematics than the young mechanic is supposed to be acquainted with, and therefore a table is added instead, by which, when the angles of two of these planes are known, the third may be at once seen, which last determines, of course, the angle of the edge.

As an example, take the graver, of which you will find a drawing among the other tools, but which I give again in this place. M, Fig. 45, is the tool, looking at the face or bevel which has been ground upon it, making a lozenge-shape or diamond. But this face is a third plane, and the cutting edges, a and b, depend for their angles upon all three of these. Now, for iron we want an angle of 60°. How are we to make the edges, a b, of that exact size? The bar is first of all square in section, like N, which would be its shape before the third face or bevel is ground, and all the angles are now right angles of 90° each. But instead of this, we want two of them 60°, the other two being of no importance. We simply proceed thus:—Determine which angle is to become the point of the tool (it is no matter in the present case, as all are alike), then grind away underneath till the new bevel forms an angle of 45° with the back (by which I mean the edge which runs along from the sharp point towards the handle—the edge x in fig. O). Trigonometry enables us to find out that an angle of 45° is the one required, but you will find it in the table annexed to this chapter, and an explanation of this table is also given to enable you to use it easily. Thus ground, the edges a b of fig. O will be each formed of two planes meeting at an angle of 60°. You can make a gauge of card or tin, P, to work by, of the required angle.

In order to understand the use of this table, it is necessary to give names to the several angles of a tool. That upon the front or face of the tool, as A of the point-tool, is called the plan-angle; that made by the upper surface and the front edge, as B (a, being the angle in question), is called the section angle, because, if you were to saw right through the central line lengthwise, this is the angle that would appear at the point, viewing it sideways. Now, if we look at C, Fig. 47, we shall be able to understand how the front line, b c, is obtained, which constitutes one side of the section angle of a tool. It results from the meeting of the two diamond-shaped planes at the sides formed by the grindstone, but is dependent also on the plan-angle. These two side-planes are to be generally ground at an angle of about 3° from the vertical, which is to give the clearance of the tool if held in a fixed position, as in the tool-holder of a slide-rest, the tool being supposed horizontal. This is in accordance with what I have before told you, viz., that the cutting edge should be presented to the work at the smallest possible angle, 3° being very small indeed. This angle is generally measured by placing the side ground in contact with a cone of wood or metal, turned to an angle of 3°, such as D,—k being a tool the front of which is evidently 3°; or a piece of tin, l, cut to the same angle, and stood on its edge, will answer the same purpose. By 3°, I mean an angle of 3° measured on the circumference of a circle, as I have already explained in a former page, such angle being of course at the centre of the circle where the lines drawn from the several degrees on the circumference meet.

Now, when you have ground these two surfaces, the line b c of B (or C) will have a certain slope or inclination depending on the plan-angle of the point. The exact inclination of it may be therefore said to be accidental; but, whatever it is, it becomes of great importance in the final result, being one side of the angle which will give any particular angle of cutting edge. And here the table comes into use:—Suppose I wish to have an edge of 60°, for cutting iron. Measure the plan-angle,—say it is 90°, which is that of the graver; then, on the table, under the words “plan angle,” you will see 90°, and opposite, above 60° of “cutting edges,” you will see 45°. You have only to grind back the upper face of the tool, until it makes an angle of 45° (section angle) with the front edge or line, b c, and the edges x x will be angles of 60°. Or take the tool E, of which the plan angle is 120°, and suppose you want cutting edges of 80°, for brass, opposite 120°, and above 80°, is 78° 5. Grind back the top face to an angle of 78° 5 (or 78½) with the point line, and it is done.

Until you have practically proved it, you can have no idea of the vast importance of having correctly-formed cutting edges, and of placing them within a hair’s-breadth of the proper position. But it is in slide-rest work especially, and in cutting metal with tools held rigidly in one position, that this is of such paramount importance. It makes all the difference between cutting off a clean shaving, and tearing from the material by main force a quantity of disjointed particles, the latter process leaving a rough unfinished surface, the former producing one as smooth and polished as a sheet of glass; and the advantage of this short table is, that you can at any time shape your own tools for the particular work in hand.

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.

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.

Such a tool as the last named, which is intended only to cut with the front edge, and which is represented in E, is called a single-edged one, because it only cuts in one direction, but many others are double-edged, cutting the shaving at once on the flat and edge—that is, paring it off from the material below and also from the side. For instance, F is a cylinder of iron, from which a shaving is supposed to be in process of being cut. It has to be removed from the shoulder to which it is represented as still adhering, and also from the flat surface, e b, around which it was, as it were, once coiled. But this requires two cutting edges, both acting at the same time, but in different directions; and good mechanics therefore so form the tools, and so use them, as to cut in both directions, which leaves the work beautifully smooth and even.

These tools are mostly used in the slide-rest, where their true position, once determined, can be accurately maintained; and it is, perhaps, only with the slide-rest that perfect work can be done. There is, however, no reason why you should not use tools of all kinds intelligently, and understand exactly how they should be formed, and how held. Suppose you have a tool correctly made by the aid of the table of tool angles already explained, still looking at fig. F, you can see that the smaller part of the roller is that which is to be left finished, and that it ought to be quite smooth, but the shoulder at a is not of the same degree of importance. A tool fit for such work would evidently be shaped on its plan-angle or face, like H in fig. C or I; and, if held as seen, both edges would be brought into action at the same time, as will be at once evident on inspection. In practice, however, the two edges would not be allowed to touch for their whole length, or the angle on the right would leave a scratch upon the finished work; therefore it would be eased off a little, as at K, L. But this is evidently as nearly as possible the shape and position to be given to such a tool, and the edge which has to leave the finished surface should, as it were, follow the other; the right-hand angle being just and only just kept out of cut.

The hand-tools you will generally use are the heel-tool, M, held on the rest as shown, which, you see, brings the edge into cut at the least possible angle to the work, and the nail-head, which is in fact a heel-tool of four faces, or, if round, a heel-tool all edge, and which can be rolled over as it gets blunted. To these add the graver, of which I have already spoken. I have tried to show its position at O, with the bevel of the face pointed in the direction of the shoulder, and downwards; but it can be held face upwards also, and in one or two other positions. Always remember that the cutting edge is to be presented at a small angle with the work, and you cannot go wrong if the tool is well formed. The nail-head and heel-tools are single edged, and easily ground without the table of angles, but the graver is a double-edged tool, properly speaking, although only one edge may perhaps be used.

Having explained the principles upon which you have to work as regards grinding your tools and holding them when in use, I shall merely add a few remarks as to the action of the grindstone and oilstone, and the proper way of using them.

Always let the stone revolve towards you, as if you had to turn it smooth with the tool you have to sharpen, except when you cannot possibly do so without cutting grooves in it. Chisels, knives, axes, planes, and all similar tools with flat edges, are to be ground with the stone running in that direction, by which means you will avoid giving them a wire edge, as it is called (i.e., a ragged-looking edge), and it will instead be even and sharp; the filament of metal being, as it were, driven back into the substance of the tool, instead of drawn away from it. Gouges may be ground in the same way, but must be rolled about to keep up the form of edge. It is indeed the easiest way with these to hold them across the stone, in the same direction as its axis, and then, by rolling them over backwards and forwards, you can give a very good shape to the edge, which should run slightly to a point, or rather tend to one. They are never to be ground square across, like that of the carpenter.

It is generally necessary to have some sort of rest upon which to lay the tools during the operation of grinding, but do not trust to special contrivances for holding them at the precise angle needed; rather trust to your own skill, which will increase more and more by being severely exercised. Always remember to grind your tools to a sharper angle than will be ultimately required, that the final angle may be given by the oilstone. Of the latter there are many kinds. Nothing probably can surpass a Turkey stone, if good, but this varies considerably in hardness and other qualities. There is a very quick-cutting, slightly coarse stone from Nova Scotia, which is very serviceable, as it does this tedious work with great rapidity, not, however, putting on the tools a very fine edge, but one that admirably suits for such as are to be used on metal. With the rest, a rub or two on Turkey, or Arkansas, or Chorley Forest stone, will impart a finish. Arkansas stone, however, may be had coarse as well as fine; it is much liked by some, but I prefer the Nova Scotia, as it cuts more keenly, and even with the sharpest stone, setting tools is a most laborious process.

The young mechanic will find it very difficult at first to hold the tool steady, and to move it to and fro upon the oilstone so as not to give it any rolling movement, by which the edge and bevel would be rounded, as I before explained, which would in effect enlarge the angle of the cutting edge, besides preventing it from being held at a sufficiently small angle to the work to cut effectively. Nothing but practice will overcome this difficulty; I shall not therefore attempt to describe exactly how the tool should be held and the sharpening effected, such description being not only difficult, but, as experience has proved to me, impossible.