HOW TO MAKE AN ENGINE.
The very first mechanical work of difficulty, but of pre-eminent importance, in making an engine, is boring the cylinder, that is, if the same is a casting, and not a piece of tube ready made and smooth on the inside. This is, properly speaking, lathe work, yet may be done in a different way. Suppose you have bought your entire set of castings, which is the best way, and that the cylinder is half an inch diameter inside, which is a manageable size to work upon. Get a half-inch rosebit, which is very like the countersinks sold with the carpenter’s brace and bits. Mount it in the lathe in a chuck, A, Fig. 65. Unscrew the point of the back poppit, and slip over the spindle a boring-flange, B, which is merely a flat plate like a surface chuck, only the socket is not screwed but bored out, generally large enough to slip over the spindle. Sometimes there is, however, a screw at the back, to screw into the spindle, the same as the points or centres. On the face of this lay a piece of board of equal thickness, but it is as well if not planed, as its object is partly to prevent the cylinder from slipping about during the operation, as it is sometimes inclined to do upon the smooth metal flange, and partly to prevent the borer or rosebit from coming in contact with the flange when it has passed through the cylinder. Grasp the latter in the left hand, and you can easily prevent it from revolving with the drill, which will go through rapidly, and leave the hole beautifully finished and quite true from end to end,—indeed, I have bored iron also, rapidly and with great ease, with this tool.
Fig. 65.
It is absolutely necessary, remember, that this hole bored in the cylinder should be at right angles to the ends of the same, and to secure this you must now make use of it to mount the cylinder in the lathe to turn these ends or flanges. I will show you a simple and easy way to do this. C is a bar of iron or steel, preferably of the latter, about 6 inches long, and three-eighths diameter, filed into six sides. It is a good plan to have three or four sizes of such bars, with centre holes drilled carefully into each end, so that you can mount them with a carrier-chuck, as you would if you were going to turn them. Taking one of about the size named, mount upon it a piece of wood, and turn this down until your cylinder will just go tightly upon it. Being a six-sided bar, it is easy to mount the wood upon it by boring the latter with a gimlet and then driving the bar into it. It will hold tightly, and not turn round upon the metal. The cylinder being fixed in this way, you must turn the two flanges with a graver if the cylinder is of iron, but with a flat tool or the four-sided brass tool if of the latter metal; and also turn the edges of the flanges. The rest of the cylinder will be left in the rough, and may be painted green or black. I should advise you always to bore the cylinder first when possible, and then to mount it as described and turn it on the ends, which are thus sure to be correctly at right angles to the bore. Some cylinders, however, especially short ones, may be squared up first, and then mounted on a face-plate and bored. Unless, however, you have either a grip-chuck, which is self-centring, or some clamps properly constructed for this particular work, you will find the first method the easiest, especially for small light work.
You should now make the ports for steam and exhaust. Mark them upon the flat part of the casting, after you have filed this as level as you can, and do not mark them so long as not to leave you room beyond the ends of the ports for the steam-box or case which has to be placed here. The upper and lower ports are to be the same size, but the middle one may be a trifle larger with advantage. In larger engines these are cast in the metal, and have only to be trimmed and faced; but in the small models you have to drill them out in the boss cast on the cylinder. Drill down from the top, as shown at D by the dotted lines, but take great care not to go farther than the outer ports, which are to be therefore first made, so that you can tell when the drill has gone far enough. If you pierce the middle port from either end, the cylinder is spoiled. To cut the middle one, you merely drill a hole straight in towards the cylinder, and meet it by another drilled from the side, into which the pipe for the exhaust is to be screwed. You also drill straight through into the cylinder at a b, and you then plug the end of f, and that at the other end of the cylinder. Your port faces, however, are generally oblong, and not round. Make a row of holes with the drill, and then, with a little narrow steel chisel and light hammer, chip out the superfluous metal, and finish with a small file. You can always make narrow channels with squared sides by thus drilling two or more holes, and throwing them into one with a file; but in reality, for these small engines, it is very little matter whether the ports are round in section or square.
The bottom and top of the cylinder demand our next attention. E and F show these. They are easily and instantly mounted in a self-centring chuck, but can be held very well in one of wood carefully bored with a recess of the right size and depth. You must here, nevertheless, be very particular, else you will get your work untrue at this point, and then your piston-rod will stand awry, and all your subsequent fitting will be badly done. I therefore give you at G a section of the chuck bored to take the cover truly. Recess the part down to the line a b, to fit the cover exactly, taking care to level very carefully the bottom of the recess. Below this cut a deeper hole, to allow the flange in which the stuffing-box will be to go into it. It need not, however, fit the flange. The rough casting will hold very well in a chuck like this, even if it is of iron. You now carefully face the bottom of the cover, and turn the slight flange exactly to fit into the cylinder; then reverse it in the chuck, so as to get the stuffing-box outside; and in doing so, take the greatest care that it beds flat upon the bottom of the chuck. Turn off level the top of the flange first at x of fig. E, and then place a drill with its point against the middle of this, and its other end (with a little hole punched in it to keep it steady) against the back poppit centre, and carefully drill a hole down to the level of c, large enough to admit the gland of the stuffing-box or nearly so; but remember that you must not go too far, because the rest of the hole must only just allow the piston-rod to go through it. Therefore, after you have drilled about three-fourths of the distance, replace this drill by a smaller one, and with it bore quite through. The advantage of beginning in this way is, that you can now bring up the back centre of your lathe to steady the cylinder cover while you finish turning it; and as you will have to make a chuck only to take hold of the flange b, while you turn the edge, you will need probably some extra support of this kind. I have, nevertheless, turned an iron cylinder cover 2½ inches diameter without any such support; the actual strain not being very severe, provided you understand how a tool should be made and held.
The above directions apply equally to the cylinder bottom, the great secret in this and all similar work being to take care to bed the work well and truly against the bottom of the recess, turned in the chuck; this being neglected, will result in the two faces not being parallel, which will terribly throw out of truth the rest of your work. Indeed, in all fitting of this kind, it is absolutely necessary to be exact in the squaring and truing of each several piece that has to be turned or filed; otherwise no planning or clumsy arrangement will make your mechanism work as it ought to do. Take a week, if necessary, over any part, and don’t be content until it is well done.