A is the boiler lifted out of B, the outer case or stand, which you can make out of tin, and paint to imitate bricks. It is almost a pity to waste sheet-brass upon it, because it is not very important, its object being only to carry the boiler. It is like D before being folded round and fastened (not with solder, which would soon melt, but) by a double fold of the joint, similar to that which you made round the boiler itself, but turned over once more and hammered down. The holes are punched with any round or square punch with a flat end, and are intended to give more air to the lamp C, which should have three wicks, or two at the least, to keep up a good supply of steam. I have shown the flat piece of tin with three legs only, which is as well as if it were made with four; but you can please yourself in this matter.
The lamp I need hardly tell you how to make, for it is easier than the boiler, being merely a round tin box, in the top of which are soldered three little bits of brass tube for the wicks, and a fourth for the oil to be poured in—the latter being stopped with a cork.
You should remember that no soldered work, like the inside of the boiler, must come in contact with the heat of the lamp, unless it has water about it, because if the water should at any time entirely boil away, the boiler will leak and be spoiled. A little care in this respect will insure the preservation of a model engine for a long time; but boys generally destroy them quickly by careless treatment.
Let us now turn our attention to the cylinder. Cut off a piece of three-quarter-inch brass tube, 2½ inches in length—you can do this with a three-square file—mount it in the lathe by making a chuck like Fig. 59, E, of wood, the flange of which is just able to go tightly into one end of the tube. The other end will probably centre upon the conical point of the back poppit, over which it will go for only a certain distance. If your back centre will not answer on account of its small size, you must make a similar flange to go into the other end; but take care that when the back centre is placed against it, it runs truly. If the chuck is well made, it will do so. You can now with any pointed tool turn off the ends of the tube quite squarely to the side; but you should only waste one-quarter of an inch altogether, leaving it 2¼ inches long. When this is done, take it out of the lathe, and in place of it, mount a disc of brass rather more than one-eighth of an inch thick, or if you have none at hand, take an old half-penny or penny piece, which is of copper, and lay it upon the flat face of a wooden chuck, driving four nails round its edge to hold it, and with a point-tool cut out neatly the centre, of a size to fit inside your tube. You will scarcely, however, effect this perfectly without further turning; so take care to cut it too large; but before you cut it completely through, make the hole for the tube which you soldered into the top of the boiler, which is three-eighths diameter. This you can do beautifully in the lathe with a pointed tool, or with a drill, centred against the point of the back poppit, as I showed you before.
Cut the disc quite out (too large, mind) and then turn a spindle like G, mount the disc upon it as shown, by its central hole, and turn the edge with a graver or flat tool, such as is used for brass, until it will exactly fit the brass tube. You can cut out round discs of one-eighth or one-fourth sheet-brass by mounting any square piece on a wooden face chuck, keeping it down by four nails or screws, and then with a point-tool cutting a circle in it until the disc falls out. You will often save time by so doing. You now have a disc of brass or copper with a hole three-eighths of an inch wide in it; and as the disc is three-fourths of an inch in diameter (i.e., six-eighths), you will have three-eighths remaining, or three-sixteenths, each way on the diameter between the edge of the hole and that of the disc. This will just give room for the two small holes required, one on each side of the central one, for the pipes from the cold-water cistern and to the well below the pump. These must both be of brass; and the first should be turned up and end in a jet, like a blowpipe, so as to make the water rise in a spray under the piston; the other should be as long as can be conveniently arranged.
The bottom of the cold-water cistern is drawn a little above the top of the cylinder, which is 2¼ inches high. A jet would theoretically rise in the cylinder to nearly the height of the level of water in the cistern; but with a small pipe, and other drawbacks inseparable from a model, you must not reckon on more than about half that height, which should be sufficient to condense the steam. The piston had better be nicely fitted, but not packed. You cut a disc of brass as before, drill the hole for the piston, make a spindle, or put in the piston-rod, and centre this as a spindle, which is the best plan, and then with a flat brass tool turn the piston accurately to fit the tube. Or, if you think it easier, or wish to fasten the piston with a nut, as drawn, you can, if you like, turn it on a separate spindle; and thirdly, you may tap the hole in the piston, and screw the end of the piston-rod. The great thing to attend to is, to turn the edge of the piston square to the sides.
For the piston-rod, a steel knitting needle or piece of straight iron wire will do very well; but it will have to be flattened at the upper end, or screwed into a little piece of brass, which must be sawn across to make a fork by which the chain can be attached which goes over the beam. Do not solder the cistern pipes in just yet, but go on to other parts.
The cistern itself can be made out of any tin box. A seidlitz-powder box will answer well, or you can make one about that size, say 4 inches long, 2½ wide, and 2 deep. The cistern for the pump will, of course, require to be the same size or a little larger; it may stand on legs or be fastened to the bed-plate direct.
This bed-plate is shown below the picture of the engine. It is merely an oblong plate of iron one-sixteenth inch thick, or in this particular engine may be of tin neatly fastened to a half-inch mahogany board, which will keep all firm. The white places show the position of the boiler and of the pump cistern, the inner rounds indicating the lamp, and pump, and cylinder. The square is merely made to show a boiler of that shape, which some prefer;—it is not so good as a cylindrical one.