a few postscripts

[E R Swanson <ers@xxxxxxxxxxxxxxxxxxxx>]

While it might be possible to make a urethane casting of a Spud part, I'd
be leary. The key problem is probably structural stability-- e.g. what
happens when heat hits the replacement component from a day in the sun.
Warpage is a problem with urethane, and also shrinkage. Most of the copy
processes using urethanes result in a minute amount of shrinkage, and if
you have parts that have pins etc, you may have to remachine or modify the
part to make it fit.

If you did a sooper dooper mold and did an epoxy/fiberglass replacement
part, with glass matting-- e.g. like building a boat or a bathtub, it
should be fine re stability. However, the cost in time to do such a job is
worth more-- to me anyway-- than the cost of a parts Spud for salvage... 

Lastly, to make an RTV mold for a part-- if you do it the right way--
requires a vacuum pump that will pull 29 inches of mercury pretty damn
fast, you betcha! You can also try to sort of debubble it by pouring the
mixed RTV from up high in a thin stream, but that's marginal. 

Post lastly, mold releases are another gotcha. Many don't actually work. 
Best stuff I've found when you're building a two part RTV mold is plain
old Vaseline. Never fails. Nothing much sticks to set RTV, so I generally
brush a little talc (wear a real mask with high filtration, not one of
those paper mesh throwaways. For a short run, nothing at all also works
when doing the actual urethane casting. 

I was asked to compile all this stuff, but too much going on at the
moment. It would make an interesting paper.

Elliott