< Wood Pattern for Cylinder Block >
The supplier disappeared before I get the vital castings, cylinder blocks. So I decided to do an important modification, replacement of the slide valve by the piston valve. After re-designing the cylinders, motion plates and valvegears, I designed a wood pattern for the cylinder blocks according to following policy.
- Using hard wood to stand up to machining
- Being integrated from elemental parts
- Preparing "core prints" so as to form the main bore in the casting
- Splitting along vertical center line of the main core
- Every side face has a 5 degree "draft angle"
- Maintaining 1% larger volume than the final size so as to counter shrinkage
I tried cutting two kinds of wood with the miller. The left is Japanese cherry wood which I used for the pattern and the right is ordinary white wood. You can achieve 0.1mm accuracy with the cherry wood.
The main core of the pattern is turned from a pair of wood plates glued together in both excess part. As wood is too soft to hold between the centers in the lathe, I glued brass washers to each end of the wood.
Machined parts ready for assembly. They will be glued together on a surface plate, pattied, smoothed by emery cloth and lacquered.
Halves of the patterns. The pins should be loose enough to be pulled out easily.
"Core prints" are also prepared from a pair of wood plates.
Finished core prints
Gunmetal castings from the pattern. It is more difficult to find out a foundry shop suitable for us than making the patterns.
This CG is of an advanced core which I gave up for its difficulty. The main bore and the piston valve bore are connected by the gates with large section, which greatly improve the exhaust speed. Only the castings can form such a cavity.