The road wheels are made from two castings, cartridge ball bearings and
Holding wheel castings to a mill table is quite difficult, so
I first made a custom jig that I bolted to the rotary table. The jig has a recess
that fits the wheel outside diameter, and has 4 each 10-32 threaded holes for clamping
The back side of each wheel half is first bored for a press
fit of a cartridge ball bearing.
Then 10 equally spaced holes are drilled for wheel lugs,
which will hold the wheel assemblies together.
The top two wheels in the photo are outside wheel halves
after drilling and boring are complete. The lower two wheel halves are inside
The next piece that each wheel needs is a plate that clamps
the teflon seal against the inside face of the wheel. I started by cutting squares
of 0.09" aluminum sheet and drilling center holes. These plates were then
bolted onto an arbor and turned on the lathe to the appropriate outside diameter.
Finally, the bolt pattern is drilled through the seal plates.
At left, a stack of seal plates is drilled simultaneously on the rotary table.
The next step is to cast a neoprene tire onto each wheel
half. At the bottom of the photo is a male mold that I used to make modelling clay
molds for each tire. The mold was turned from a block of aluminum. On the
plywood board are three molds that have been formed, and three wheel halves. A
single bolt has been installed in each wheel so they are easier to handle.
Note that it
is impossible to form the modelling clay molds unless the aluminum plug is first swabbed
with silicone release agent. Modelling clay really likes to stick to aluminum.
The three wheel halves in the molds after pouring the
flexane. The photos dont show a couple of steps:
1) The wheels need to be
degreased and the flanges roughed up.
2) Flexane metal primer is applied
3) Flexane rubber primer is applied
4) and then the wheels are inserted into the molds for the urethane pour
The final step is to grind the urethane to final dimension.
I drilled and tapped a bolt circle onto a lathe faceplate so I could mount the
wheel. In the photo you can see a diamond file being used to turn a wheel, using a
tool holder as a steady rest.