Remember, however, that the larger you make the engine the more expensive the castings and materials will be.
Should you persevere, however, and by good fortune succeed, you will have a model locomotive that would cost you two or three hundred dollars to buy ready made. If you have a lathe and can turn the wooden models for the castings yourself, use sheet iron for the frame-work, etc., where possible; the total expense will not be so very great.
Begin your work in the same way you did on the other model. If you want a bigger engine than the one shown in Fig. 20, there would be no trouble in increasing the measurements, which we are about to give, proportionately, remembering that Fig. 20 is drawn to an eighth-inch scale.
Make your dimensions as follows: Length over all, 3 ft. 2 in. Length of bed-plate, 3.5 in. Width of bed-plate, 9 in. Diameter of driving wheels, 8-1/4 in. Diameter of leading wheels, 5-1/4 in. Gauge--that is width of track on which model can run--6-1/2 in. Cylinders, 1-3/4 in. bore by 2-1/2 in. stroke. Length of boiler, including smoke box, 28 in. Diameter of boiler, 5 in.
Cylinders of the above dimensions will drive the engine at a high rate of speed, with from 30 to 50 lbs. of steam.
In Fig. 20, the different parts of the engine are lettered, and it will be well for the boy who desires to make a locomotive like it to compare the following description with the cut, before he does anything else.
A is the smoke stack and B the steam blast used to increase the intensity of the fire worked by rod C running through the hollow hand-rail D and ending in handle F. G is the steam-dome, which with the safety valve is the same pattern previously used. H is the extra safety valve, worked from the foot-plate. I is the steam whistle, K wind guard, L starting lever, M smoke-box with door, N O spring buffers; P is the line-clearer or wheel guard. Q are the leading wheels, R R the driving wheels, S is one of the cylinders with piston rods and guides bolted to frame and showing double connecting rod at T T. U U are the springs which support the weight of the boiler, etc., on the axle bearings. The spring or rear wheel does not show, being inside the safety guard and hand-rail V. W is the back pressure valve, through which the water is thrown by the force-pump into the boiler, and X is the blow-off tap to clear the engine from all water after having used it. Y shows the side of the ash-pan.