We begin by cutting out of 1/20-inch sheet brass a piece shaped as in Fig. 60. Parallel to the long edges, and 3/8 inch away, scribe bending lines. Join these by lines 5/8 inch from the short edges, and join these again by lines 1/4 inch from the bending lines. Cuts must now be made along the lines shown double in Fig. 60. Bend parts CC down and parts BB upwards, so that they are at right angles to parts AA. The positions of these parts, when the piece is applied to the cylinder, are shown in Fig. 62.
One must now make the bridge pieces (Fig. 61, a, a) to separate the inlet passages from the exhaust. Their width is the distance between the bent-down pieces CC of Fig. 60, and their bottom edges are shaped to the curvature of the cylinder barrel. Finally, make the pieces bb
Fig. 57. Vertical section of cylinder.
Fig. 68. Wall-piece for steam chest, with gland and valve rod in position.
Fig. 69. Valve plate.
Fig. 60. Piece for steam ways.
Fig. 61. Valve plate and steam ways in section.
(Fig. 61), which form part of the top of the steam ways.
The following order should be observed:(1.) Solder the piece shown in Fig. 60 to the cylinder barrel by the long edges, and to the cylinder supports at the ends. This piece must, of course, cover the steam ports in the cylinder.
Fig. 62. Cross section of cylinder and valve chest.
(2.) Put pieces aa (Fig. 61) in position, with their tops quite flush with the tops of BB (Fig. 62), and solder them to the cylinder barrel and sides of the steam-way piece.
(3.) Solder the valve plate centrally to BB, and to the tops of aa, which must lie between the central and outside ports. Take great care to make steam-tight joints here, and to have the plate parallel to the standards in one direction and to the cylinder in the other.
(4.) Solder in pieces bb. These should be a tight fit, as it is difficult to hold them in place while soldering is done.
(5.) Bore a 5/16-inch hole in the lower side of the central division and solder on the exhaust pipe.
The contact part of this is cut out of flat sheet brass (Fig. 63), and to one side is soldered a cap made by turning down the edges of a cross with very short arms. The little lugs aa are soldered to this, and slotted with a jeweller's file to engage with notches cut in the valve rod (see Figs. 58 and 62).
The next thing to take in hand is the fixing of the crank shaft. This is a piece of 3/8 or 1/2 inch steel rod 5 inches long.
The bearings for this may be pieces of brass tubing, fitting the rod fairly tight. By making them of good length--1 inch--the wear is reduced to almost nothing if the lubricating can is used as often as it should be.
Each bearing is shown with two standards. The doubling increases rigidity, and enables an oil cup to be fixed centrally.
The shape of the standards will be gathered from Fig. 53, their outline being dotted in behind the crank.
Cut out and bend the standards--after drilling the holes for the foot screws--before measuring off for the centres of the holes; in fact, follow the course laid down with regard to the cylinder standards.
Make a bold scratch across the bedplate to show where the centre line of the shaft should be, and another along the bed for the piston-rod centre line. (Position given on p. 138.)
Bore holes in the bearings for the oil cups, which may be merely forced in after the engine is complete.
The crank boss may be made out of a brass disc 2-3/4 inches diameter and 3/16 inch thick, from which two curved pieces are cut to reduce the crank to the shape shown in Fig. 53. The heavier portion, on the side of the shaft away from the crank pin, helps to counterbalance the weight of the connecting and piston rods. In Fig. 54 (plan of engine) you will see that extra weight in this part has been obtained by fixing a piece of suitably curved metal to the back of the boss.
The mounting of the crank boss on the shaft and the insertion of the crank pin into the boss might well be entrusted to an expert mechanic, as absolute "squareness" is essential for satisfactory working. Screw-thread attachments should be used, and the crank-shaft should project sufficiently to allow room for a flat lock nut. The crank pin will be rendered immovable by a small lock screw penetrating the boss edgeways and engaging with a nick in the pin.
Place the two bearings in their standards and slip the crank shaft through them. Place standards on the bed, with their centre lines on the crank-shaft centre line. The face of the crank should be about 3/8 inch away from the piston rod centre line. Bring the nearer bearing up against the back of the disc, and arrange the standards equidistantly from the ends of the bearing. The other bearing should overlap the edge of the bed by about 1/8 inch. Get all standards square to the edge of the bed, and mark off the positions of screw holes in bed. Remove the standards, drill and tap the bed-plate holes, and replace parts as before, taking care that the lubricating holes in the bearings point vertically upwards. Then solder bearings to standards.
If any difficulty is experienced in getting all four standards to bed properly, make the bearing holes in the two inner ones a rather easy fit. The presence of the crank-shaft will assure the bearings being in line when the soldering is completed.
Fig. 63. Parts of slide valve.
The standards and bed should have matching marks made on them.