I promised in a previous page to describe a little stove for heating soldering-irons, and doing other light work. It is made as follows, and will be found very useful.

Fig. 71, A, is a tube of sheet-iron, which forms the body of the little stove. Four light iron rods stand out from it, which form handles, but these are forked at the ends, and thus become rests for the handles of soldering-irons, or any light bars that are to be heated at the ends. Below is a tray, also of sheet-iron, upon short legs to keep it off the table—for this is a little table-stove. C is the cast-iron grate. You can buy this for a few pence first of all, and then you fit your sheet-metal to it. It will rest on three or four little studs or projections riveted to the stove inside; or you can cut three or four little places like D, not cutting them at the bottom line, a b, but only on three sides, and then bend in the little piece so as to make a shelf. If the stove is about 4 inches high above the grate, and 2 or 3 inches below it, and 6 inches diameter, it will be sufficiently large for many small operations; but that the fuel may keep falling downwards as it burns, the lower part should be larger than the upper, and, to admit plenty of air, should be cut into legs as shown. Round the top are cut semicircular hollows, in which the irons rest. To increase the heat, a chimney or blower, B, is fitted, which has also openings cut out to match those of the lower part, so that the soldering-irons can be inserted when this chimney is put on. If, however, this is not required, but only a strong draught, by turning the chimney a little, all the openings will be closed. A still longer chimney can be added at pleasure. A hole should be made at the level of the grate to admit the nozzle of an ordinary pair of bellows. This stove you would find of great service, and it may be fed with coke and charcoal in small lumps. Now you may make the above far more useful. It will make a regular little furnace, and not burn through, if you can line it with fireclay. In London and large towns you can obtain this; and it only needs to be mixed up with water, like mortar, when you can plaster your stove inside an inch thick or more, making it so much larger on purpose. There is no need to do this below the level of the grate; but if you cannot get fireclay, you may do almost as well by getting a blacklead-meltingpot from any ironfoundry, and boring a few holes round the bottom for air, and fitting it inside your little iron stove. In this you can obtain heat enough to melt brass, and it will last a great deal longer than the iron alone, which will burn through if you blow the fire much; but for general soldering, tempering small tools, and so forth, you need not blow the fire, as the hood and chimney will sufficiently increase the heat. There is no danger in the use of this little fireplace, but of course you would not stand it near a heap of shavings, unless you are yourself a very careless young “shaver.”

HOW TO TEMPER TOOLS.

There is no reason why the young mechanic should not be told how to make his own tools, and how to harden and temper them, because he ought to be a sort of jack-of-all-trades; and perhaps he may break a drill or other small tool just in the middle of some special bit of work, or his drill may be just a little too small or too large, and there he will be stuck fast as a pig in a gate, and unable to set himself right again any more than the noisy squeaker aforesaid. But to a workman a broken drill means just five minutes’ delay, and all goes on again as merrily as before; and as we wish to make our young readers workmen and not bunglers, we will teach them this useful art at once.

Drills are made of steel wire or rods of various sizes. In old times they were made square at one end, to fit lathe-chucks or braces, but now, for lathe-work, they are generally made of round steel, and fastened into the chuck with a set screw on one side. In this way they can be more easily made to run true. But there are so many kinds of drills that I suppose I had better go into the matter a little—only I have not room to say much more.

Look at Fig. 72, and you will see some of the more usual forms of drills used, but these are by no means all. You will not indeed require such a collection; and yet, if you should grow from a young mechanic into an old one, I daresay you will find yourself in possession of several of them. The first, labelled 1, is the little watchmaker’s drill, of which, nevertheless, this would be considered a very large size. It is merely a bit of steel wire, with a brass pulley upon it, formed into a point at the largest end, and into a drill at the other. The way it is worked is this: At the side of the table-vice—that is, at the end of its jaws or chops or chaps—are drilled a few little shallow holes, in which the watchmaker places the point at the thickest end; the drill-point rests against the work, which he holds in his left hand. A bow of whalebone, a, has a string of fine gut such as is used for fishing, or, if the drill is very small, a horse-hair; and this is given one turn round the brass pulley before the drill is placed in position. The bow is then moved to and fro, causing the drill to revolve first in one direction and then in the other. The general work is in thin brass, and therefore these little tools are sufficiently strong for the purpose. Some of the drills and broaches (four or five, or even six sided wires of steel) are so fine that they will bend about like a hair, and yet are so beautifully made and tempered as to cut steel.

No. 2 is a larger drill, even now much used. In principle it is exactly similar to the last, but the pulley is replaced by a bobbin or reel of wood, made to revolve by a steel bow with a gut string, or a strong wooden bow. The drills, too, are separate, and fit into a socket at the bottom of the drill-stock. The large end is pointed, as in the last, and is made to rest in one of the holes in a steel breast-plate, b, which is tied to the chest of the operator, who, by leaning against it, keeps the drill to its work, while both hands are free to hold the latter steady. There is a modification of this tool, invented by a Mr Freeman, intended to do away with the bow. The bobbin or reel is turned without raised ends, and is worked by a flat strip of wood covered with india-rubber, and turned at one end to form a convenient handle. The having to twist the bow-string round the drill, which is always a bother, is thus done away with.

No. 4 is a drill-stock similar to the last, but in place of the breast-plate a revolving head or handle is put to the top, in which the point works. This is held in one hand, while the drill-bow is worked by the other. This is also generally held against the chest, as the hand alone does not give sufficient pressure. Heavy work, however, cannot well be done by these breast-drills, and they are liable to cause spitting of blood from the constant pressure in the region of the heart and lungs.

No. 3 is the Archimedean drill-stock, now very common, but originally invented by a workman of Messrs Holtzappffel’s, the eminent lathemakers of London. It now comes to us as an American drill-stock. It is a long screw of two or more threads, with a ferule or nut working upon it. The upper end revolves within the head, which is of wood; the lower end is formed into a socket to receive the drills, which revolve by sliding the ferule up and down. Some are 14 inches long, and others not more than 5. The first are used with the pressure of the chest, the latter with that of the left hand. For light work these are very useful, and you will seldom need any other in the models of small engines, &c.

No. 5 is another watchmaker’s drill, but serves also as a pin-vice to hold small pieces of wire while being turned or filed in the little lathes which are used in that trade, and which are worked by a bow with one hand, while the tool is held in the other. This is by no means a useless tool, even without the pulley. It is made by taking a round (or better, an octagon, or five or six sided) piece of steel, drilling the end a little distance, and then sawing the whole up the middle. The slit thus made is then filed away to widen it, and leave two jaws at the end, which grasp the pin or drill; a ring slips over, and keeps the jaws together.

We now come to fig. 6, which represents the best of all drills for metal. It is really American this time, and does our Transatlantic cousins great credit, as does the machinery generally invented or made by them (the Wheeler and Wilson sewing-machines for instance). The steel of which this drill is made is accurately turned in a lathe, and the spiral groove is cut by machinery. This groove acts in two ways—first, as allowing the shavings (not powdery chips) to escape as the tool penetrates, but as forming the cutting edges where they (for there are two) meet at the point. These, however, require a lathe with a self-centring chuck made on purpose. They are sold in sets upon a stand, chuck and all complete, and each is one-thirty-second of an inch larger than the other. Some are as small as a darning-needle, or less, and they run up to an inch or so in diameter. There are large and small sets.

We now pass to the old-fashioned smith’s brace, fig. 7, shown in position, drilling the piece e. Pressure is kept up either by a weighted lever, or by a screw, as shown here. The brace is moved round by the hand of the workman. Very often this tool is arranged on the vice-bench, so that the work can be retained in the jaws of the vice while being drilled. Sometimes it is mounted on a separate stand, having a stool below, and a special kind of vice or clamp is added. Well made, this is not so bad a tool as it looks, but those used ordinarily in smiths’ shops are very clumsy, and do not even run true, and the drills are badly made, although by sheer force they are driven through the work.

Whatever form of drill-stock is used, the main thing is to have the drills properly formed. You will recognise k and n as common forms, than which m is considerably better. For cast-iron n would not be a bad point, because the angle is great, much greater, you see, than k; and the bevels which form the cutting edges of a drill should also not be too sharp, as they are generally made, for, as they only scrape away the metal, their edges go directly.

The common way to make a drill is this: A piece of steel wire of the required size is heated until red hot (never to a white heat, or it would be spoiled). The end is then flattened out with a hammer, and the point trimmed with a file. It is then again heated red hot, and dipped into cold water for a second. Then held where the changes of colour, which ensue as it cools, can be seen plainly; and as soon as a deep yellow or first tinge of purple becomes visible, it is entirely cooled in water. It is then finished, except as regards fitting it to the drill-stock, which may be done before or after it is hardened, because care is taken only to dip the extreme point. To get proper cutting edges the drill is taken to the grindstone, and each side of the point is slightly bevelled, but in opposite directions, so as to make it cut both ways. It is not, however, left of equal width, like o, but the flattened sides are ground away, so as to make more of a point, like p and n.

Now, this is all right enough as regards forging and hardening, and tempering, and for the smallest drills this is the only way to make them. (Only watchmakers heat them in the candle till red, and then cool and temper by running them into the tallow.) But if you want a good drill that will cut well and truly, you should file away the sides of a round bar like m, only spreading the point very slightly indeed, just to prevent the drill sticking fast in the work. Another drill, indeed, is spoken of very highly, which is also carefully made like m, but the places which are here flat are hollowed out or grooved lengthwise, the section of the point—i.e., the appearance of the end of the drill—becomes rather curious, like r. I am assured by those who have used them, that these cut quite as well as the twist drills which I have described already. These which I am now speaking of are also American; and I don’t know how it is, that somehow America is a far better place for improvements in tools and machines than our own Old England. And if I had a wonderful invention—a new birch-rod-making and flogging-machine for very troublesome boys, for instance—I am afraid I should go to America to patent it; but I daresay English boys would not object to that.

If not, they had better not let me patent my flogging-machine. Luckily it is not invented yet.

The cutting edges of drills come under the same rules as other cutting edges. You might, for instance, hold a large drill flat on the rest, and use either edge as a turning-tool. You will see at once that these edges will not cut if made in the usual way, but only scrape. The bevel wants to be ground only to 3°, as before explained, to give the proper clearance, and the cutting edge requires to be then made by grinding back the upper surface, which is just the same in effect as is produced by twisting the metal or cutting a spiral groove, which hollows out this upper surface and gives it cutting power. It is no use grinding a sharper-looking bevel, or making more of a point—you only weaken the edge; m or n is quite pointed enough, though the first is a right angle and the second greater; and, for cast-iron, a rounded point, showing no angle at all, will do just as well, or better, when once it has begun to penetrate. Do not be deceived, therefore, by making drills look pointed and keen, for, I repeat, they are scraping tools only, unless you file an edge by bevelling back the upper face of each side of the point. If you were to make a very thick, strong drill, you might begin by grinding back the two sides to 3°, to form the accidental front line of the point or section angle, and then grind back, at 45° from this line, the upper face, by which you would do just what you did to give the graver cutting edges of 60°—only a drill thus formed must have a point of 90°. It would cut in two directions, like one for a drill stock and bow.

I hope my bigger boys will not pass over the remarks on cutting edges interspersed in this book, for, once understood, they will be found to be most valuable. Indeed, they cannot work intelligently until they understand exactly the nature and principles of the tools which they have to use. In drilling iron, use water or oil, or soap and water, or soda-water—either will do; but the holes are drilled in the ships’ armour-plating with soap and water to cool the drill; and very well it answers, for these plates are several inches thick, but the holes are soon made. When working in brass and gun-metal, use no water, but work the drill quite dry. The same rules, in short, apply to drilling as to turning or planing metal; and if you could see the action of a well-made American twist-drill, you would recognise this similarity, for you would see the metal come forth in long, bright curls, as pretty and shining as those of your favourite young lady or loving sister—one of which you have, I daresay.

To give you some idea of what a straight course a drill will take, if rightly made and skilfully used, I may tell you that a twist-drill has been run through a lucifer-match from end to end without splitting it; and as to the fineness possible, I have seen a human hair with an eye drilled through it, by which, needle-like, it was threaded with the other end of itself.

I told you how to bore a cylinder, which is but drilling on a larger scale, and in Fig. 65 I sketched the method of doing this in the lathe with a rosebit. But I did not explain another tool used just in the same way, but which will bore holes in solid iron wonderfully. Fig. 65, L, H, K, is one of these. This is an engineer’s boring-bit, and is made of all sizes, from that required to bore the stem of a tobacco-pipe—(don’t smoke, boys, it will dry up your brains)—to that which would bore a cannon. A rod of steel is forged with a boss or larger part at one end. This is centred in the lathe, and the centre-marks are well drilled, and not merely punched, especially that at the small end. The boss is then turned quite cylindrical, after which it is filed[4] away exactly to the diametrical line, as you will see by inspection of L. The end is then ground off a little slanting, to give, as before, about 3° of clearance. The cutting edge thus obtained, and the end in which the centre hole still remains, are carefully hardened. You thus have a tool which will bore splendidly, but you must give it entrance by turning a recess first of all in the work, or drilling, with a drill of equal size, a little way into the material. Used like the rosebit, this tool will run beautifully straight, so that you can bore very deep, long holes with it, and cylinders can be most beautifully bored with it. I think you would be able to make these tools with a little care; but, when you harden them, only heat and dip the extremities, or it is ten to one your steel rod will bend and warp in cooling, and you will not be able to rectify it. If the ends are quite hard, it is as well that the rest should be soft, as the tool will not then be so liable to get broken.

There are many other tools used for boring iron and steel, but you need not trouble yourself at present to learn anything of them—they are no use to you now.

I have headed this chapter “Hardening and Tempering” tools, but as yet I have only partially explained the process, which is a very curious one; and though the result is highly necessary in many cases, it is by no means well understood what really takes place in the process, or why this effect should occur in steel, but not in iron, or brass, or other metals.

If you heat a piece of bright steel over a clear gas jet or fire which will not smoke it, you will see several colours arise as the metal gets hotter and hotter, until finally it becomes red. These are due to oxidation, which is so long a word that I am not sure I can stop to explain it thoroughly. Let us see, however, what we can make of it. The air we breathe contains two gases, oxygen and nitrogen, with a small proportion of a third called carbonic acid. Neither of these alone will support life, or keep the fire burning, or enable vegetables to live and grow, but it is the first which is in this the chief support. The second is only used by Nature as we use water to brandy, viz., to dilute it and render it less strong. If we breathed oxygen alone, we should live too fast, and wear out our bodies in a few hours. If we breathed nitrogen only, we should die, and so of carbonic acid. Now this oxygen seizes upon everything in a wonderful and sometimes provoking manner. If you leave a bright tool out of doors to get damp, down comes our friend oxygen and rusts it. It combines with the iron and makes oxide of iron, which is what we call rust. I suppose, however, this oxygen comes more from the water than the air, because water is made also of two gases, hydrogen and this same oxygen. It is certain that oxygen in this case always finds any bright tools that we leave about in the wet, and coats them with a red jacket very speedily. Then if you look at a blacksmith at work, you will see scales fall from the hot iron as he hammers it. These are black, but our old friend has been at work, and united with the red-hot metal and formed another oxide of iron, called black oxide. We can understand this. If a man eats a good deal, or drinks a good deal, he gets red in the face; if he eats till he chokes himself, he gets black in the face, and I suppose it is much the same when oxygen eats too much iron. Well, when we begin to heat the steel, down comes oxygen and begins his work; and first he looks very pale; then he gets more bilious and yellower; then he gets hotter and shows a tinge of red with the yellow forming orange; then he begins to get purple, then blue, then deeper blue; and finally black before he gets absolutely red and white hot.

Now to temper steel, we first heat it red-hot, not minding these colours, and then we cool it suddenly in cold water. This renders it very hard indeed. No file will cut it, or drill penetrate it; but if we strike it, behold it breaks like glass! This is too hard for general work, for the edge will break and chip if it meets with any hard spot in the metal, or chances to bite in too deep. Its teeth are too brittle, and so get broken off. For this reason we have to “let down,” or temper, the tool, and we proceed as follows: The part to be tempered is ground quite bright. It is then laid upon a bar of iron heated red-hot, or if small, it is held over a gas jet or in a candle; heated, in short, in any way most suitable and convenient. And now, first, our friend oxygen puts on a pale yellow face as before. This will do for turning steel and iron, but is still too hard for general work. Then comes the orange, and this presently tends slightly to blue; at which point, if the tool is instantly cooled in water, it will be found to bear a good edge, hard, but sufficiently tough for work. Most tools for metal and drills are let down to something between the yellow and blue, and we know that the more they approach blue, the softer they will be. Thus we can easily manage our tools;—some to bear hard blows, like axes, which are tempered to a blue colour; some like files, which a blow will break, but which are famous for their own special work—these are let down only to a pale yellow; others, like springs and saws, are let down to a more thorough blue, because they are required to be elastic and tough, but are not needed to be so particularly hard. Then tools like turnscrews, and bradawls, and gimblets are left even softer, sometimes not tempered or hardened at all, but just forged and ground to the required shape.

Now, I fancy some of my sharp boys will say that the first description I gave of the mode of hardening and tempering was not exactly like this; nor was it, yet in principle it is the same. For instance, if you give a drill to a smith to make, he will do as I then said. He will heat the extreme point red-hot, then dip the point in water, give a rub on the stone or bricks of the forge, and watch the colours. This can be done when the tool is of sufficient substance to retain heat enough after the edge has been dipped to re-heat that edge sufficiently. In this case there is no need to chill the whole tool and then heat it again. But in the case of small drills and tools, pen-knife-blades, and other articles of this nature, there will not be sufficient heat retained, after dipping, to bring up to the surface the desired colours; for oxygen likes a hot dinner as well as you do, and if the iron is not hot enough he will have nothing to do with it.

One great difficulty you would find if you had much tempering to do, viz., that the articles bend under the operation, some more than others. Try this: Take a thin knitting-needle when the owner is not looking, and run off with it;—it is all in the cause of science! Heat it red-hot, and with a pair of pliers take it up and drop it sidewise in a basin of water. It will bend like a bow. Heat again, straighten it, re-heat, and this time pop it in lengthwise—endwise, point first—I mean (don’t you see that a round needle has no sides, and puts me into a perfect quagmire of difficulty). However, you will understand this, and will find the needle not bent nearly so much as before, but still it is not straight. As I explain most things as I go on, I may as well explain why this bending occurs before I tell you how to straighten your work again. All metals expand with heat, and contract with cold. I am sure I contract terribly in the winter until I have had plenty of hot soup, and hot roast-beef, and plum-pudding; and I know my temper improves, too, when I get expanded and warm. Well now, when you dropped your sister’s knitting-needle all hot on its side into the water, that side contracted before the other, and consequently the needle bent; but when you put it in the water, end on, it was cooled all round at once, and if you could but cool a piece of metal equally all over, inside and out, at once, all parts would shrink equally fast, and the article would remain straight.

But there is, unfortunately, another cause of this bending, which is, that all articles are not of such form that the same quantity of metal is on all sides of the axial line. Take a half-round file, for instance; one side is flat, the other curved, so that taking these two surfaces into consideration, one contains a great deal more metal than the other, and will not cool at the same rate. These articles are far more liable to bend than those whose sides are parallel. Another result of the hot mass being cooled most quickly on the outside is, that cracks are produced in the latter, because, so to speak, the skin is contracted, and can no longer contain all the expanded metal within it. Hence, to make a mandrel for a lathe, it is common to bore it out first, before hardening, to remove this mass of metal, and to allow the water to touch it inside as well as out. Such mandrels seldom crack or bend.

The only way to straighten articles which have warped by hardening, is by what is called hacking or hack-hammering, which is nothing more than hammering the concave or hollow side with the edge of the steel pane of a hammer. This spreads the metal upon the hammered side, and, by expanding it, straightens the tool, for the hollow side, remember, is that which was too much shrunk or contracted. This is not an operation you will have to do, especially if you only harden the extreme points of the drills and little tools you make.

There is another way of hardening, not steel, but iron, called “case hardening,” because it puts a case of steel over the surface of the metal. Obtain a salt called prussiate of potash. It is yellow, like barley-sugar, but is poison. Heat the iron red-hot, and well rub it upon this salt, and then cool it in water. You will find that now a file will not touch it, its surface being as hard as glass. It is carbonised on its exterior, and made into hard steel. This can be done in another way, as gun-locks, snuffers, and many other things are case hardened. They are enclosed in an iron box, with cuttings of leather and bone-dust, and the box is luted about with clay and put in the fire. All the pieces get red-hot, and the leather chars and blackens, and some of it combines as before with the hot iron, and makes it into steel. And our friend oxygen is considerably at a loss in this case to find his way in, or he would make black scales again and spoil the work; or combine with the carbon (or charcoal) and make it into gas. Probably, however, as we shut up a little oxygen with the contents of the box, this change DOES take place, but just as the gas rises the iron seizes it, and holds it fast.

And now, boys, I find it necessary to lay down the pen, which I see has almost run away with me, and written a good many more pages than I at first intended. Since I began to write I have visited the workshops at King’s College, and seen a sight to gladden my eyes. Boys carpentering, boys turning, boys filing; engines of real use, with single and double cylinders, finished, and in course of construction, and all these the work of schoolboys, whose hands and brains are alike engaged in this delightful branch of industry. Let no one, therefore, pretend that boys are not capable of executing good work of this kind in a masterly manner, or that what they do is always child’s-play, or I shall take up the cudgels in their behalf. I have also seen, in the Working-Men’s Exhibition, a very neat little engine, made by a boy only twelve years of age, which makes me hope and believe that the few hints upon wood and metal work which I have here thrown together will neither be unacceptable nor useless to those whom I address in these pages. In this hope I take my leave, and sign myself, with gratification and pride—

The boy mechanic’s faithful friend,

THE AUTHOR.