Your cylinder ought now to have a finished appearance when the cover and bottom are placed in position, but the latter have to be permanently attached by small screws, and these I strongly advise you to buy. They cost about 50 cents a dozen, including a tap with which to make a thread in the holes made to receive them; or, if you prefer it, you can buy miniature bolts and nuts at almost as cheap a rate, which would cost you much time and trouble to make for yourself, if, indeed, you succeeded at all. You will want four of these for the top, and the same for the bottom, the holes for which you will make with a small archimedean or other drill.

The mention I have made of this reminds me that I am gradually adding considerably to your list of tools, and it is necessary to do so if you take up model-making. Set down, at any rate, the following:—

And for use in the lathe, either two or three sizes of rose-bits, or engineer’s half-round boring bits, of which I shall have to speak presently; and, unless you buy all screws and nuts, you will want screw-plate and taps, or small stock and dies. Files of square, round, and oblong section are matters of course. Remember, too, that after a file has been used on iron and steel, it is useless for brass; so use new ones on the latter metal first, and after such use they will answer for cast iron and then for wrought iron. You will find the cost of files rather heavy unless you attend to this. Have neat handles to all your smaller files, with ferules to prevent splitting.

When you purchase the castings of the engine, you will find a valve-box to enclose the slide and become a steam-chest, as explained. It is like a box with neither top nor bottom, but with a flange, or turned-out edge all round, for the screws by which it is to be attached to the valve-facings of the cylinder. This box must have its flanges filed up bright on their flat sides and edges—the rest may be painted. It will exercise your skill to get the two faces flat and true, to fit upon the cylinder; and at last you will find it expedient to put a brown paper rim or washer between the surfaces, or a bit of very thin sheet lead, to make a steam-tight joint. Do not solder it, if it is possible to use screws, because this is nearly certain to get melted off; and, if not, it is not nearly so neat and workmanlike a way of uniting the parts. You should, indeed, in all models, put them together in such a way as to be able at any time to separate the different pieces again, either for the purpose of cleaning or repair; and, if you solder, you cannot easily do this.

The valve-casing and its back are generally put on together; four screws at the corners passing through the back and both flanges into the flat side of the cylinder. This depends, however, upon the exact shape of these different pieces; and I can give you no special directions for a particular case unless I could see the castings which you have to fit together. The stuffing-box you will make quite separate, both its outer and inner part, and screw or solder the former into place. It is seldom cast upon the valve-casing, because of the difficulty of chucking a cubical object safely so as to turn any part of it.

You are not to screw or solder the valve-box to the cylinder until you have carefully filed up the valve itself to slide upon the port face, without the possibility of any escape of steam taking place. This needs the greatest possible care; and probably, after doing what you can with a flat file, you will have to put a little emery and oil between the surfaces, and grind them to a perfect fit, by rubbing them together. This grinding with emery is an operation frequently required in mechanical engineering. Lathe-mandrels are fitted in this way into the collars; the cylinder is also ground into the back poppit-head. It is not a very long or difficult operation, but whenever you have had to use it, take care to wipe off the emery, or it will keep on grinding. It is indeed very difficult to do this perfectly; and for very fine work, such as fitting the mandrel of a screw-cutting lathe (i.e., a traversing mandrel), oilstone powder and crocus are used, in place of emery. These, however, cut very slowly, making the operation of grinding exceedingly tedious; and in the present instance, emery will answer quite well enough. In very small engines, a stroke or two of a file is all that is needed to fit the valve, which is so small as hardly to be worthy of the name; but in an engine with cylinder of 1 or 2-inch bore, it will be impossible to do with file alone, as well as you can with grinding.

The piston and piston-rod should be turned at the same time, as already suggested in treating of the atmospheric engine of Newcomen. By this, you will avoid getting the piston “out of square” with its rod, as if you had bored the hole for the latter askew—a not unusual occurrence.

I do not mean to say that it is absolutely necessary for you to turn the piston-rod at all, for, in models, it is generally of round iron or steel-wire, which is as cylindrical as you can possibly make it. Knitting-needles are in general use for this, as being well finished and equalised from end to end. But these are rather hard, being tempered only to about the degree of steel-springs; therefore you must never attempt to cut a screw on them until you have first heated the end to be screwed red-hot, and allowed it to cool again very slowly. If you do this, a screw-plate will put a sufficiently good thread to allow you to attach either the piston, or the small piece of brass necessary to form the hinge, upon the other end of the rod—that is to say, the piece marked H in Fig. 64. Leave this for the present, however, not attempting at present to cut either the piston-rod or valve-rod to its intended length. You cannot do this until you have laid down the exact plan of the engine, and marked on the bed-plate the position of all the parts.