[139] How to build model steam engines and all other kinds is explained in my new book Engine Building for Boys, published by Small, Maynard and Co., Boston, Mass.
To the end that this may be done the cylinder and steam chest are split-down the middle lengthwise so that the inside of them can be clearly seen and the movements and functions of the piston and the slide valve in these parts will be clear.
Make the cylinder first and the easiest way to do it is to saw out two disks of wood for the cylinder heads of ³⁄₄ inch thick stuff, 4¹⁄₂ inches in diameter and bore a ⁹⁄₁₆ inch hole through the center of one of them for the piston to slide through, as shown at [A], [C] and [F] in Fig. 125. Turn, or whittle out a piece of wood for the stuffing box,[140] 1 inch in diameter and ¹⁄₂ inch long, and bore a ⁹⁄₁₆ inch hole through the center of it and glue it to the center of the cylinder head so that the holes are exactly in a line as shown at [A] and [F].
[140] A stuffing box on a real steam engine is to keep the steam in the cylinder and steam chest from leaking past the piston rod and the slide valve rod.
Fig. 125a. working drawings for the demonstration steam engine. cross section side view of the engine
Next saw out two rings of ¹⁄₄ inch thick wood, make the outside 4¹⁄₂ inches in diameter and the inside 3 inches in diameter, see [C], and glue one of the rings to each end of the cylinder heads. Now cut out of a sheet of thin cardboard, or better of tin, a piece 5³⁄₄ inches wide and 6 inches long; cut two holes ¹⁄₂ an inch in diameter and have the center of each hole ¹⁄₂ an inch from one of the long edges and ⁷⁄₈ inch from each of the short edges as shown at [D].
The next thing on the list is the piston and the piston rod. For the piston, saw out a disk of wood 3 inches in diameter and bore a ¹⁄₂ inch hole through it in the center. The piston rod is simply a piece of wood ¹⁄₂ an inch in diameter and 12 inches long; cut a slot in one end ¹⁄₈ inch wide and ¹⁄₂ an inch deep and bore a ¹⁄₁₆ inch hole through it as shown at [C]. Put the piston inside of the cylinder, slip the piston rod through the hole in the cylinder head, smear some glue on the end of it and fit it into the hole in the piston.
The steam chest is next in order; for it use ³⁄₁₆ inch thick wood and saw out four pieces 2 inches square; two of these pieces are for the heads of the steam chest, as shown at [A] and [B], and in the center of one of them drill a ³⁄₈ inch hole for the slide valve rod to go through. Turn, or whittle out, a piece of wood for the stuffing box ¹⁄₂ an inch in diameter and ¹⁄₂ inch long, bore a ³⁄₈ inch hole through the center of it and glue it to the center of the steam chest head that has the hole in it as shown at [A], [C] and [F].
Saw two holes 1¹⁄₂ inches square out of the other two 2 inch square blocks and glue these to the steam chest heads. Now make a trough of ¹⁄₄ inch thick wood, or of cardboard or tin, 1¹⁄₂ inches square, outside measurement, and 2³⁄₄ inches long; this is for the sides of the steam chest; as shown at [A] and [F].