How to Become an Engineer

by Frank W. Doughty

Next come the cylinders. These are to be an inch thick and three-quarters bore by two and a half inch stroke. They should be of the fixed slide-valve pattern, with double eccentrics fitted on the middle axle shaft, and reversing lever brought to quadrant on foot plate. They had better be bought ready made.

Fig. 27 shows their working. A A are the eccentrics, B the slide-valve rod with guide G attached. C C is the bed plate and D the balance weight, F the rod leading to quadrant and lever on foot plate. The cranks are put on outside the wheels and fastened by keys as in Fig. 20. The connecting rod T should be cut to the form shown in Fig. 28, and the ends squared out and a brass band fitted in with a hole drilled from top A to oil by and a set screw B to adjust the bearings perfectly.

If you wish to fit a force pump it should be placed centrally between the cylinders and be worked by an eccentric on the main shaft, but a pump on a model locomotive is next to useless unless it is also made to work by hand.

In Fig. 29, we have one which can be worked either way. A is the pump; B the eccentric on main-shaft to work it by steam power. To work by hand you have only to push up hook connection C, which disconnects it from the eccentric; and then by working the handle D, which is screwed into the bottom of the plunger C, the water is forced into the boiler. An extra stuffing-box at F will be required. G is the exhaust water pipe bent up to the back-pressure valve on boiler, and H the supply pipe carried on to rear of engine.

Two small blow-off cocks will be necessary on each cylinder to get rid of the condensed steam when starting. They can be connected with a tye-rod, and both worked from the foot-plate with a single handle. Now paint to suit your taste and put away to dry.

Next comes the boiler, which will need extreme care. For this you will require sheet copper an eighth of an inch thick.

First cut a piece 19 inches long by 16 wide and bend it round, forming a cylinder 5 inches in diameter. The cap must be closely riveted and the two ends hammered out into a flange outward, leaving the body of the boiler 17 inches long, as in Fig. 30. B is the shape of the piece to be next riveted on at after end. Now take another sheet 9 inches wide and hammer a half inch flange round it, so as to fit over the dotted line at A. Rivet them firmly together and also another piece in after end. It will then have the appearance of Fig. 31, and should be 4-1/2 inches deep from A to B, and forming a copper box 6 inches wide from B to C and 8 inches from C to D. Then rivet together another box to form the inner casing 4-1/2 inches wide by 6-1/2 inches long and 9 inches deep, the bottom to be hammered outward to the dimensions of B C C D, as shown in section Fig. 32 at A A. A hole is next to be cut out in the center of rear plate and also the rear part of inner casing which comes opposite to it, and 1-3/4 inches by 2-1/2 forming the furnace door.

A casting of that shape and 3/4 of an inch thick, which is the distance between the inner and outer casing B C, must be procured and drilled with holes every 3/8 of an inch and firmly riveted in position, as shown in Fig. 32 at D. Two pins should project on either side of the inner surface to support the fire-bars and ash pan, and the bars should be made of cast iron and small enough to get out easily by tilting up one side; they should run lengthwise of the engine.

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.