The Boy's Own Book of Indoor Games and Recreations / A Popular Encyclopædia for Boys

by C. Stansfeld Hicks; John Nevil Maskelyne; Gordon Stables

The upper end of the pillar is bored through at right angles to the flat at the bottom (see [Fig. 2]). Through the top a piece of brass tubing about ⁵⁄₈ in. long is fixed, generally by soldering; this is the bearing for the crank-shaft. The crank-shaft itself is a piece of steel wire bent to the form required. The fly-wheel is fixed to one end, and prevents the shaft coming out of the bearing, the bend of the arm serving the same purpose at the other end.

Fig. 3.

Fig. 4.

The cylinder itself is shown at [Fig. 3], and also in [Figs. 1] and [2]. The piston, piston-rod, and bearing which fits the crank-pin are shown in [Fig. 4]. It will be evident that the dimensions of this engine are microscopic. The bore of the cylinder is ⁵⁄₁₆ in., and the barrel itself is often made of triblet-drawn brass tube. The enlarged part at the bottom is a casting with a flat face, as shown in [Fig. 3], on one side. Some makers use a casting for the entire cylinder, but the tube is perhaps the cheaper method of making. A piece of good tube is sufficiently accurate in the bore for use as bought, so that the trouble of boring the cylinder is dispensed with. The base, for the tube to fit in, is bored to the external diameter, and the tube fixed with solder. The lid or cover is fixed only by being snapped on. Its object is only to guide the piston-rod.

A reference to [Fig. 3] will show the working of the oscillating valve. The face of the pillar is shown on the right. On this, a is the hole from which the live steam issues, and b is the exhaust hole. These holes are technically called ports. The hole c is bored through the pillar, and takes the trunnion, or pin on which the cylinder oscillates. [Fig. 2] shows this trunnion-pin prolonged and having a nut on the end. A spiral spring around the trunnion, between the nut and the pillar, keeps the valve face in close contact with the pillar face. Again, turning to [Fig. 3], the holes in the cylinder on the left are:—c, into which the trunnion is screwed; and d, the steam-way.

When the cylinder is in the position shown in [Figs. 1] and [2], the port-hole d ([Fig. 3]) is over the solid metal between the holes a and b. On turning the fly-wheel the crank draws the piston out very slightly and inclines the cylinder sideways, bringing the port d over a. The live steam from the boiler at once enters and forces the piston upwards, and on the crank reaching the highest point the cylinder is again vertical and the hole d is mid-way between a and b. The momentum of the fly-wheel carrying the crank round brings the hole d opposite b, and allows the steam to escape. There is no force to keep the engine going during this part of the time except the momentum of the fly-wheel. When the cylinder again inclines to the opposite side d comes over a, and force is again applied under the piston. This will keep the engine going.

The single-action oscillating cylinder, being supplied with steam at one end only, exerts power only during half the revolution of the crank. The return stroke is dependent entirely on the momentum of the fly-wheel, which also has to drive the steam out of the cylinder. Steam only acts in the lower part of the cylinder, and as there is no power tending to force off the cover, it may be simply snapped on like the lid of a pill-box. The piston, [Fig. 4], has for its head a disc of brass, with a V-shaped groove in its edge. This is packed with hemp or lamp cotton, to make it fit the cylinder steam tight. The rod is a steel wire about ¹⁄₁₆ in. diameter; it is fixed in the piston by riveting, to save the trouble of screwing. The end of the rod has a small piece of brass fixed on to it which fits on the crank-pin.

The crank itself is all of one piece; a straight length forms the shaft; it is bent at right angles to form the throw, and a piece bent from this, parallel to the shaft, forms the pin. This is the most simple way of making a crank, and when large quantities are made the wire is bent upon a template. A better type of crank is made by using a steel rod for the shaft, a brass arm riveted on to it, and a steel pin riveted into that. In the portion of this chapter devoted to the horizontal engine will be found a more complete description of such a crank.