Fig. 64.
The drawing here described is a plan, i.e., a drawing viewed directly from above; therefore I cannot show you the perspective view of the parts, which are, indeed, in many cases only suggested by the shading. I have, therefore, added a second drawing of the several details. This engine is, in construction, the simplest that can be devised with a slide-valve, there being no additions beyond what are absolutely necessary to make it work; the exhaust-port is below, opposite to the letter B on the valve-box. A, Fig. 64, is the forked connecting-rod, marked H in the previous drawing. This is cast with forked ends, x, and x Y (the latter being F F of Fig. 63). These ends receive brasses in the following way, the end x being represented on a larger scale at B, with such brasses in place; of these there are two shaped like D. One of these lies in the fork of the connecting-rod end. A second similar one lies in the strap of iron C, which reaches beyond the first. A cotter or key, which is, in fact, a wedge of iron, is then passed through a slot in the strap, and a similar one in the rod; and being driven home, draws the two brasses tightly together, causing them to embrace the crank-pin, L, Fig. 63, or any similar bearing. All shafts that revolve in bearings are made to pass through brasses, and whenever these occur at the end of a rod, they are fitted as here described. E is another bearing of cast-iron, also fitted with brasses; but in a case like this, a plate lies on the upper one, and is screwed down by bolts and nuts as required. This bearing would do very well at E, Fig. 63, as a guide for the piston-rod; but in models such guide is commonly made without brasses, like F or G of the present drawing.
At H, I have shown the part F O F of the drawing 63. The middle is of brass or iron; if of the former, g g must be separate, as these gudgeons would not be substantial enough, unless of iron or steel. It is essential that K L, the piston-rod, should be in one right line; but, if this is attended to, they need not necessarily be one piece; and frequently the piston-rod, L, is fixed into one end of the central casting, and another rod, K, is screwed into the other. In a model, the piston-rod should pass quite through, and g g should be two separate gudgeons screwed in, and then turned together in the lathe, to insure their being exactly in one line. These go into the brasses in the forked ends of the connecting-rod, to form a hinge at that part, as will be understood by a reference to Fig. 63.
At M, I have shown another simple eccentric and rod, which is less trouble to make in a model than the other. In this the ring is made in one piece, with a round rod screwing into it. The disc has a slight groove turned in its edge, and a small screw, P, passes through the ring and falls into this groove. This suffices to prevent the ring from falling off sideways, and of course is not screwed down so tight as to prevent the disc from revolving. This is a very easy way to fit the eccentric, and is generally followed in small engines. The lattice eccentric rod is nearly always used in large beam engines.
I do not think the reader will now have any difficulty in understanding the precise arrangement of the various parts in the simple horizontal engine of which I have given a sketch. It is a neat and convenient form, easily arranged as a model, and I shall proceed at once to the practical work of constructing this, and engines in general, presupposing a knowledge of the use of the lathe, and of the few tools required.
