< 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.
Finished patterns.
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.
| TOP | BACK | NEXT |