< Cylinders and Pistons >
I reported that I modified my engine from s-v to p-v. I will report about that in the next time. Here I introduce the cylinder blocks, cylinder covers and pistons. This is a sequence to the page "Wood Pattern for Cylinder Block".
Bolting face to the frame is finished in the four-jaw chuck.
The two bores are opened out from backside of the cylinder. First, the steam chest bore is opened to final diameter. Note a brass disk glued around the main bore for scribing center. I have to report a pair of angleplate and faceplate doesn't always give me a true square! It is worth testing by D.T.I. just before turning.
Next is the main bore. Only screws between the faceplate and the angleplate are slackened for centering, so as to keep two bores parallel. To minimize chattering, I prepared small boring tool with fat hexagonal steel bar. In this setting, face for the back cover is also finished. The opposite side (for front-cover) can be finished in four -jaw chuck, because the front face doesn't need to be strictly square to the bore.
Boring ports. The port has tilt in two directions. The angleplate between the vertical slider and the job can adjust direction. The cutting procedure is:
1) mill end of the port to be square
2) center and drill a series of holes into the steam chest
3) remove walls between the holes by a long endmill
The steam inlet is drilled and tapped.
The exhaust recess is formed by "rough-cut" endmill, and the passageways to the steam chest bore are slot-drilled in both ends of the recess.
Gunmetal castings for cylinder covers. Particularly the back covers need following accuracy.
1) All of center hole, inner register, chamber for the O-ring and thread for gland have to be concentric.
2) bolting faces for slide-bars should be parallel and same distance from the center.
I prepared a special jig to overcome such difficulties.
Chucking with outer spigot, the inner resister is cut and the center bore is drilled and reamed.
The special jig to finish outer side of the cover. After the jig was fixed firmly onto the faceplate, the center pin and the inner face are trued up.
When the cover is mounted onto the jig, the inner resister and bore become concentric and square to the lathe spindle. Then the O-ring chamber is bored and threaded. I left diameter of the O-ring chamber smaller than the thread. So when a gland is screwed into the end of the thread, the chamber will maintain correct depth.
The jig is mounted on cross-slider with a suitable packing. Then the bolting face for slide bars are cut to the correct depth. The job is just rotating 180 deg. in the jig without moving the saddle. Note a guide bar on the tail stock to ensure 180 deg. rotation, by pushing onto a finished surface.
The side arc of the cover is milled in the jig mounted on a rotary table. Such an operation as cutting a side and a bottom at a time, has a chance to capture the tool and spoil the job! Please take care.
I also prepared a jig to drill screw holes in the covers. The tapped holes in the cylinder are copied directly from the covers. Particularly for the back covers, the slide bar seatings are kept square to the frames by a try-square.
The piston glands of brass. If you adopt hexagonal shape here, you have to confirm that your spanner can slip into the space between the slide bars.
The piston is made of phosphoric bronze. Before finishing outer diameter, the piston rod is pulled into it. Deeper half of the hole and the same length of the rod end are threaded for pulling work. The remainder is adjusted to press-fitting diameter. Once the rod end catches up the thread in the hole, the rod is automatically pulled into the hole by turning lathe spindle by hand.
The spindle is chuck with four jaws and centered with a dial gauge to ensure concentricity. Then the diameter of the piston is finished to a nice sliding fit to each cylinder.
The groove of the piston is filled with graphited yarn.
Assembled cylinders waiting for the piston valves.