For the boiler tubes some hard drawn brass tubing three-quarters of an inch in diameter will be required. Cut the pieces slightly over 17 inches long, then drill 10 holes in the inner plate as at E, Fig. 32, and in the position and arrangement shown in Fig. 33. These tubes should have a wire ring brazed on about a quarter of an inch from either end, and then being placed in their respective holes in the tube plate, the projecting portion is to be headed back with a flange, or you can fit them in as already shown in Fig. 16 by each being double screwed and nutted. These tubes allow the smoke and flame to pass through from the furnace to the smoke box, M, Fig. 20, and so away up the smoke stack, and by the large surface they expose to the fire, help to raise steam very quickly. In some engines as many as 300 tubes are fitted.
The steam supply pipe and regulating lever handle should now be made and placed in position, and Fig. 34 shows the shape to make it. A B are the front and rear plates of the boiler, C is the supply pipe bent with a screw end downward, after passing plate A, and then upward into the steam dome, where it should be securely fastened into a cross-piece. D is the tap or valve which can be turned on or off from the foot-plate by means of the long rod, F, ending in the lever handle, G.
The rod must be fitted with a stuffing-box, the same as those used on the cylinders, and packed with cotton wick to prevent loss of steam by leakage. When all this is complete, the forward end of the boiler can be furnished with a tube-plate riveted on and the tubes flanged over.
Now the boiler must go to a practical brazier, and be properly brazed. Cut the hole for the steam dome, and let him braze it on at the same time. If the job is practically done, your boiler can be heated red-hot without fear.
Meanwhile buy your pressure gauge--it wants to be one and a half inches in diameter--and let the brazier test your boiler to 100 pounds steam to the square inch capacity.
Should it burst you will have to make another. If not you need thereafter have no fears.
Now make the smoke box, which should be three inches deep and of the shape and dimensions shown in Fig. 35. This and the smoke-stack can be made of iron, hammered up to shape and finished with a brass ring. The smoke-box can be screwed on the forward flange or boiler.