Likewise saw out a guide block for the slide valve rod and make it 1 inch wide, 2 inches long and 3¹⁄₄ inches high and drill a ³⁄₈ inch hole through the middle of the top of it lengthwise so that the center of the hole will be exactly 2¹⁄₄ inches from the back board to which it is fixed.
Next cut out a rocker arm of a ¹⁄₄ inch thick piece of wood and have it ³⁄₈ inch wide at one end, ³⁄₄ inch wide at the other end and 7 inches long; drill a ¹⁄₈ inch hole in each end and a 1¹⁄₈ hole 1¹⁄₂ inches from the large end; pivot the small end to the end of the slide valve rod with a machine screw having a nut on the end of it.
Cut out an eccentric rod ¹⁄₄ inch thick, ³⁄₈ inch wide and 8¹⁄₂ inches long, and drill a ¹⁄₈ inch hole at each end so that their centers will be exactly 8 inches apart: pivot one end of this rod to the second hole in the rocker arm with a machine screw as before. Saw out a pivot block 1 inch square and drill a ¹⁄₈ inch hole through the center of it and pivot the lower end of the rocker arm to it with a screw.
Make a connecting rod, to couple the piston rod to the crankshaft with, ³⁄₈ inch thick, ¹⁄₂ an inch wide at one end, ³⁄₄ inch wide at the other end and 9 inches long; whittle or plane down the small end so that it will fit easily into the slot in the end of the piston rod and drill a ¹⁄₈ inch hole in each end so that their centers are precisely 8¹⁄₂ inches apart.
The crankshaft can be made of a piece of ¹⁄₈ inch thick wire 13 inches long which must be bent to the exact shape shown at [D]; before it is thus bent, however, slip the wire through the hole in the end of the eccentric rod and then bend the crank on it.
Saw out a flywheel of ¹⁄₂ inch thick wood, 8 inches in diameter, drill a ¹⁄₈ inch hole through its center and force it on over the wire forming the crankshaft; then slip the end of the connecting rod on the other end of the crankshaft wire and bend it to form a crank.
The front end of the crankshaft must be supported by a pillow block just as it is in a real engine, but the rear end is held in place by a board screwed to the back of the base. This block is ¹⁄₂ an inch thick, 1 inch wide at the top, 2 inches wide at the bottom and 3 inches high; drill a ¹⁄₈ inch hole in the top of it exactly 2¹⁄₄ inches from the base line and slip this over the end of the crankshaft next to the connecting rod.
The last thing to be done is to make a base to mount the parts of the engine on; this is a sort of a shelf and it is built up of a board ³⁄₄ inch thick, 6 inches wide and 31 inches long for the base. Saw a slot in it ³⁄₄ inch wide and 9 inches long in one corner, 2 inches from one end and ¹⁄₂ an inch from the side; this is for the fly-wheel to set in.
Fig. 125f. the steam engine ready to demonstrate