Now take a clock spring and cut it into shape, as at D, Fig. 26. The top piece requires to be made hot with your blow-pipe, then the ends turned over to hold the pin B. Each piece of spring must be a little shorter than the one above it, and the ends neatly tapered, all to be inclosed in the brass band F, which has a small hole drilled at F to hold the end of the pin by which the pressure is directed on to the axle boxes, as shown in Fig. 20. A hole is also to be drilled in the bed plate over the center of each axle box to allow the pin to pass through, and also a smaller one an inch and a half on each side for the support A, Fig. 26, to screw into. Now all can be fitted into position. 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.