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We must next turn our attention to the connecting-rod (Fig. 21). My readers will observe that it is constructed in the shape of a fork, and, for that reason, this style of rod is termed a fork connecting-rod. The proper way of making it will be to get a piece of iron forged down to as near the size as possible, and then finish it by turning and filing. Avoid brass, as it looks too much like the toy

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shop style. The distance between the centre of the piston cross-head-pin and that of the crank-pin should be 6 in. The arms are to be 3 in. long, taking the measurement from the top of the radius of the inside of the fork to the centre of the hole for the cross-head-pin. The object of this kind of connectingrod, in our case, is to allow the rod to work clear of the guide for the piston-rod.

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The next consideration will be the eccentric-sheave (Fig. 22) and strap (Fig. 23). In theory the eccentric is really only a modification of the crank, and.

like the crank, always imparts twice the motion of its own throw. The eccentric is used for working the slide-valve, regulating the admission of steam into the ports on the cylinder face. Now, supposing we wish to give a valve a travel of four inches, we should first find the geometrical or real centre of the sheave, from that we should mark off two inches, which would be the centre for the hole for the shaft. This is a very nice operation and requires a great deal of care, else the eccentric may give the valve either too much or not sufficient travel. The travel of the slide-valve, as a general rule, is twice the width of one of the steam-ports, so that if the width of one of the steam-ports be taken for the throw of the eccentric, the required travel of the slide-valve will be found. If the slide-valve were placed exactly in the centre of the cylinder-face, it would be found to extend slightly beyond the edges of the ports in the forward direction: this is termed the "lap" of the valve, its object being to ensure the perfect covering of the steam-ports when the valve is in a central position. The eccentric is keyed on to the shaft, similar to the fly-wheel. When the right position of the eccentric on the shaft has been found, it is a good plan to make a centre punch-mark on the sheave, as also on the shaft. For the eccentric we shall require a piece of brass or wrought iron 2 in. diameter and in. thick; a groove in. wide and in. deep must be turned in its periphery to hold the strap; a hole must then be bored for the shaft at a proper distance from the real centre of the sheave. The strap is very simple, and should be readily understood on reference to the woodcut, it being simply a ring, made in halves, with lugs or ears to bolt them together, and a boss to take the eccentric-rod. The width of the strap must be the same as that of the groove in the sheave, and its internal diameter should correspond with the external diameter of the groove.

FIG. 24.

Fig. 24 represents the valve-spindle: one of the ends is filed to a flat on opposite sides, leaving shoulders which butt against projections on the back of the valve, and between which the flat end is placed. Another method would be to cast a small boss on the back of the valve, and screw the spindle into it. I am almost inclined to think that the latter plan is the more preferable. The other end of the spindle is fitted with a joint for connecting it with the eccentric-rod. The length of the spindle is 2 in. from the end to the centre of the pin in the joint, and its diameter about in.

A few words as regards the fly-wheel. I should advise that it be made as large as convenient (in order to carry the disc over the dead centres), the moving force or inertia of which maintains continuous rotary motion.

The next process will be to erect the engine. The first thing to be done will be to line or mark out the bed-plate. X X is the centre-line of the cylinder and piston-rod, &c.; Y Y, centre-line through sole of guide; z z, centre of shaft and plummer-blocks. Centre-lines must also be scribed on the cylinder and pedestals themselves. Particular attention must be paid to the fact that the cross centre-lines must be at exactly right angles with the longitudinal lines. First fix the cylinder, then the bearings, and then the guide.

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Setting the slide-valve is by far the most difficult part in erecting; and, as suppose few of my readers could do it properly themselves, I should advise

them to secure the services of some mechanic, who would quickly do it for a small trifle.

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Lastly, but not least, the boiler (Fig. 25), requires our consideration. The easiest way that I can suggest of making it is to procure a piece of copper or brass tube, 8 in. external diameter and 16 in. long; this will form the shell, A. B is the fire-box, and should be made out of a piece of sheet copper, brazed up with a piece of 2-in. brass pipe, E, fixed into the top of it, terminating in a bell or trumpet-shaped mouth; the length of this pipe may be about 20 in., and it will form the chimney. C is a brass plate, in. thick, soldered into one end of the boiler, having through the centre of it a hole to allow the chimney to pass through; this should be soldered in the first of all. The fire-box must next be fixed in, and the chimney soldered or brazed into it, after being passed

through the hole in the top, a small bit of solder being run round the joint to make it tight. D is a short piece of brass tube, 8 in. internal diameter and 2 in. long, soldered round the bottom of the boiler to form the lamp space. The safety-valve, F, lever, G, and weight, H, can easily be made on reference to the illustration, which is drawn to scale. K K are gauge-cocks, to try the quantity of water in the boiler; the top one should be screwed at 2 in. below the top of the boiler, and the lower one 8 in. from the bottom of the water space in the boiler. L is a blow-off cock, fixed quite at the bottom of the water space, for the purpose of emptying the boiler. The gauge-cocks K K are so arranged that when the boiler has its proper quantity of water in it, steam will issue from the upper and water from the lower cock. M is the steam-pipe leading to the engine. To fill the boiler, unscrew the safety-valve, and pour in the water by means of a funnel until it reaches to about 3 in. from the top. The steam can be got up by means of either a spirit-lamp or gas-jets; the latter are preferable on account of the much larger amount of heat which is given off. The steam-pipe may be in. or 3 in. diameter.

OSCILLATING ENGINE.

For the benefit of my readers who might not be able to make the foregoing engine, I append directions how to make the simplest kind of engine that can

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possibly be made. It is a simple modification of the high pressure engine, usually known as "direct-acting," in which the cylinders (a single one in our case) oscillate; at the same time it is the weakest. As an oscillating this is but one of a class, as many of our largest marine engines are built on the oscillating principle, the recommendation being the small compass in which they can be stowed.

The term "oscillating" is obtained from the fact that the engine while working rocks or vibrates from side to side, which motion is imperative, on account of its possessing no connecting-rod. This will be seen better on reference to the drawings Figs. 26 and 27, which represent a front and side elevation of a single-acting engine. A represents the crank-shaft, to which are attached the fly-wheel, B, a driving pulley, C, and the crank, D, which communicates with the piston-rod, E, by means of the cross-head, F. G is the cylinder; H, the standards or supports for the shaft, A; I, the boiler; K, space under boiler for spirit-lamp or gas-jet; L, set-screw for keeping the cylinder close against the boss, M; N, an opening in the fire-box, to admit air necessary for the proper combustion of the gas or spirit-lamp flame; 0, a safety-valve; P, the blow-off cock, for drawing the water out of the boiler; Q, an inlet or plug for feeding the boiler; and R, a small bracket for carryin; the set-screw, L.*

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Of course the cylinder should be our first consideration. On reference to the detail drawings (Figs. 28 and 29), it will be seen that the body, A, is to be in. diameter, with a flange, B, on the top end, 1 in. diameter and in. thick, while the flange, c (if I may so call it), on the other end, is to be in. deep and 14 diameter, the entire length being 1 in. The cylinder is to be bored out from end to end with a 3-in. half-round boring-bit, and should be perfectly smooth. After this has been done, turn the top surface of the flange B perfectly true and square with the bore. This being a very important item, care should be taken to have it nicely done. Then one side of the lower flange must be filed away perfectly level and parallel with the bore. Exactly in the centre of this, drill a small hole and screw in a short piece of fine steel wire, F. This must project about one-eighth of an inch from the flat surface. On either side of this pin, drill an -in. hole, E E, through to the bore. The cylinder will be completed by soldering or brazing (soldering is the easiest, but brazing is the strongest method) into the bottom of it an end made of 4-in. brass. If a pattern be made for the cylinder-cover (Fig. 30), a great deal of trouble will be saved, as well as time and trouble, which latter is no small consideration. It may, however, be made in the following manner: procure a piece of brass, 13 in. diameter and 4 in. thick; in the centre of this solder a smaller piece, in. diameter and in. thick. A hole must now be bored the exact size of our piston-rod, viz., in.; drive the metal disc on a mandril and turn it up to the size shown in the drawing, with a shoulder accurately fitting the inside of the cylinder and in. thick.

FIG 30.

The plan and elevation are drawn to 3-in. scale, or quarter size, and the details to 6-in scale, or half size. Fig. 34 showing steam-ports in standard is engraved full size.

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