The spring is best made from clock-spring, and cut to shape as at D. The top-piece requires to be made hot with your blowpipe, and then the ends turned over to hold the pin B. Each piece of spring must be slightly shorter than the upper, and the ends nicely graduated off, and when ready held together by the brass band F, which has a small hole drilled at F to hold the end of 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 bed-plate over centre of each axle-box to allow 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. They can all be fitted into position.
Fig. 27.
The cylinders come next, and should be, as previously mentioned, an inch and three-quarters bore by two and a half inch stroke. These should be of the fixed slide-valve pattern, with double eccentrics fitted on middle axle-shaft, and reversing-lever brought to quadrant on foot-plate, as I will show presently, and for the method of making them I will again refer you to my article on the [Model Launch Engine], and will simply give you in [Fig. 27] the modified form necessary to suit a locomotive, in which A A are the eccentrics, B slide valve-rod, with guide G attached; C C the bed-plate, D the balance-weight, and 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].
Fig. 28.
The connecting rods T should be cut to the form shown in [Fig. 28], and the ends squared out and a brass bush filled in with a hole drilled from top (A) to oil by, and a set-screw B fitted to adjust the bearings perfectly.
Although these little things give extra work in fitting a model, they add considerably to its finish and lessen the friction.
If you wish to fit a force-pump, it should be placed centrally between the cylinders, and be worked by an eccentric on main shaft, but a pump on a model locomotive is of very slight use unless it is arranged to work by hand also.
