A progress report:  On the second attempt I cast a decent-looking
drive wheel using Devcon Flexane 80 (the first try had air bubbles).
No softener was used and the result looks and feels like the rubber in
an automobile tire.

I machined the master from Teflon and made the mold from plaster of
Paris.  It takes up to seven days to reach full strength.  More anon.

Fritz Gellerman