For your final evening entertainment give a thumb-nail lecture on steam and the steam-engine.
You will find every one is interested in steam because it is one of the great prime movers but there are very few people indeed who have any idea of how a steam engine works.
If you will do exactly as I tell you, you can talk on and demonstrate the principles of a steam engine so that, whatever the age of your listeners, they will know, when you are through, exactly how and why a steam engine runs and develops power.
The engine I shall tell you how to build is not a model that runs by steam,135 but one made almost entirely of wood and the purpose of it is not actually to produce power but to show exactly how it works.
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, 4 1/2 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,136 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.
135 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.
136 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 4 1/2 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 5 3/4 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 1 1/2 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, 1 1/2 inches square, out-
Fig. 125B. End View Of The Engine. D. The Crank Shaft. E. The Rocker Arm
side measurement, and 2 3/4 inches long; this is for the sides of the steam chest; as shown at A and F.
Bore a 1/2 inch hole in the center of the top of the trough; this hole is for the intake port, that is the opening through which the steam flows from the boiler into the steam chest. Bore three 1/2 inch holes in a line in the middle of the bottom of the trough as is also shown at A and F. The two holes nearest the ends are the ports to let the steam into and out of the opposite ends of the cylinder, and the central hole, or port, is the exhaust port C.
Fig. 125C. Top View Of The Engine
Next make the slide-valve; use 1/8 inch thick wood and make it 3/4 inch high, I inch wide, and 1 1/2 inch long on top and 2 inches long on the bottom; the bottom, as you will observe at A and E, is cut out so that it will cover one of the cylinder ports and the exhaust port at the same time and you need put only one side on it.
The slide valve rod is a piece of wood 1/4 inch in diameter and 11 1/2 inches long. Whittle or plane one end flat and drill a 1/8 inch hole through it. This done, set the slide valve in the steam chest; slip the slide valve rod through the head and glue it to the slide valve.
Now make four tubes or pipes of cardboard or tin 1/2 an inch in diameter, and have two of them 1 1/4 inches long and the other two 3 inches long; when you have formed all of them cut a strip 1/2 inch wide out of each one lengthwise; the purpose of which is to show that they are hollow.
When you have the tubes done glue, or otherwise fix, one of the short ones into the intake port of the steam chest and the other short one into the middle, or exhaust port in the bottom of the steam chest; then glue, or fix the two long tubes into the end holes, or ports, of the steam chest and the holes in the cylinders.
Saw out a guide block for the piston rod to slide through, 2 inches wide, 3 inches high, 3 inches long on top and 5 inches long on the bottom as shown at A and C, and bore a 3/8 inch hole through the middle of the top of it lengthwise so that the center of the hole will be exactly 2 1/4 inches from the base line.
Likewise saw out a guide block for the slide valve rod and make it 1 inch wide, 2 inches long and 3 1/4 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 2 1/4 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 1 1/8 hole 1 1/2 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 8 1/2 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 8 1/2 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 2 1/4 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.
Screw a back to it 1/2 an inch thick, 10 inches wide and 3 inches long; this must be perfectly rigid and if necessary you can brace it with angle blocks. Finally glue four legs 1 inch square and 2 1/2 inches long on the corners of the base-board.
Fig. 125F. The Steam Engine Ready To Demonstrate
To put the engine together, or assemble it as it is called, screw the cylinder to the base-board, then glue or screw the piston rod guide block to the base; the slide valve rod guide block to the back board, and the pivot block for the rocker arm to the base-board.
Drill a 1/8 inch hole in the back board 2 1/4 inches up from the base-board exactly 16 1/2 inches from the front cylinder head; put one end of the crankshaft in the hole and slip the other end of it into the pillow block; see that all is in a line and that the flywheel clears the sides of the slot in the base-board. Then it is all done and will look like F.
Now if you will turn the flywheel around with your hand, or better, belt a small electric motor to it, you will see exactly how the slide valve opens first one port in the cylinder and then the other and that when the port is open which gives a clear path for the steam to flow from the steam chest to the cylinder, the other port is connected to the exhaust pipe, when the used steam passes into the open air.
When you know all about it you are then ready to give your last evening divertisement and for the time being to say Good-by.