< Valve Liner 1 >
Before assembling the cylinders, I fixed
the cylinder block onto the chassis temporary.
A horizontal concavity under the cylinder
block fits into a vertical concavity on the
chassis, only it has a little play.
A stretcher over the bogie truck is once removed from the chassis and drilled for screws.
The stretcher is fixed in the chassis again, the cylinder block is positioned, then the cylinder block is drilled through proper two holes. After that both parts are removed and combined with pins. Finally the rest of holes are opened. The cylinder block has tapped holes. It means the screws are put in from underneath.
The cylinder block is temporary fixed. Incidentally, the prototype doesn't have such a stretcher. The cylinder block is directly bolted onto the chassis. The bolts are put from inside to outside. Also the cylinder block holds the bogie truck directly. In the model, I employed the stretcher so as to ease assembly.
Following the prototype, I chose piston valve
for the engine. My first engine William has
piston valves without piston rings. This
time I want to use piston rings because the
model is very big. So the valve liner must
have lines of holes in circumference for
the steam ports. I started with the liners.
I designed the valve liner divided in front and back pieces. It needs six pieces for the three cylinders. The inner liner is longer than the outer liners. Middle section (steam inlet section) of a pair is called "basket". That's only spacing the outer working section. Both I.D. and O.D of the basket don't need to be precise. I utilize the basket as a chucking part for cutting the outer working section. That's the reason why I divided the liners. From outside to inside, the lines of holes are for steam outlet, steam port and steam inlet. The steam port holes must be rectangle.
If I made the liner from a round bar, I must cut plenty of metal to bore a large tunnel. So I prepared cylindrical castings in gunmetal. First, the basket section is cut. It has smaller O.D. and larger I.D. than the working section.
Reversed and chucked in the basket, the working section is temporary finished. Next, I divided the circle and scribe radial lines in the lathe. Note a paper band around the three-jaw and an indicator on the headstock so as to divide the circle in equal angle.
The job is reversed again and a guide groove for the steam port is cut.
The liner is clamped in the machine vise in desired angle by the radial lines. Then the four holes are opened. The hole for steam port is drilled and cut rectangle by 2mm end mill. Tiny fillets remain in four corners, but they can be removed easily with a fine rectangle file. Totally I have to open 60 rectangle holes and 180 round holes!
I spent two weeks for the operation. Here I reach the time limit of the report.