The cranks should be at right angles to each other, and the throw of the crank half the distance of the cylinder stroke.
For instance, say the cylinder being a 1-1/2 inch stroke, the distance between A B (Fig. 8) will be three-quarters of an inch, you must then ease the size of the crank at A to prevent the piston knocking the cylinder ends.
Fig. 9.
The cylinders you had better buy ready made or have them made for you. Get a pair of oscillating cylinders of three-quarter inch bore and inch and a half stroke. These will drive your engines several miles an hour.
Fig. 9 gives an underneath view of the frame work and the place to put the cylinders in. They must be supported by two lugs, A A, screwed to the bed plate B, which must have a piece cut out on either side to allow the driving wheels C, to work in, as at D; because, being larger than the others, they project beyond the top of the bed plate, as shown in Fig. 2.
Next screw on by means of the hook F, the buffer beam, previously cut from a piece of mahogany, 5 inches long, half an inch thick and one inch deep, nicely squared and sand papered. Drill a hole at G, and pass the shank of the hook through the beam and piece of brass in front of the frame, screwing up tight with nut H.
For buffers you may take two brass, flat-headed screws, and attach them to the beam half an inch from either end, allowing half an inch projection.
Now polish everything smooth and bright. Next warm the model over the gas—don't let it get hot—and carefully lacquer it with a small brush taking care not to go over any part more than once. The spokes of the wheels must be painted, the buffer beams varnished and the cylinders painted, leaving the covers and flanges bright. Now put away your work to dry, covering carefully from dust.