Molds for resin casting replicas should be made from urethane or silicone RTV rubber since these have negligable shrinkage. Latex has a great deal of shrinkage and shouldn't be used.

If you are making a copy of the builder's plate, use it as the pattern. On the other hand, if you have to change numbers and dates, make an RTV mold of the original; use this to make an epoxy copy (polyester resin isn't recommended since it will poison a urethane RTV mold); apply the new numbers; and use the plastic replica as a pattern--it will endure enough pulls with a sand flask to fulfill your needs. For a production run, however, it won't work. There will be some shrinkage with the brass, about 3/16" per foot. With something as small a builder's plate this shouldn't matter.

Be sure to use a mold release with each step of the RTV mold making and resin casting process. Carnauba wax (paste floor wax) is best.

Pattern numbers are available from any foundry supply house: look in the Thomas Register or go to: http://www.thomasregister.com/ extablish and "account" and then do a search on foundry supplies, or check with your local pattern maker.

> Has anyone ever looked into cast resin or
> polymer for replicating plates for use on
> outdoor display locos (non-operational,of
> course!)
Any thoughts?

The two Baldwin Sharks operated on Michigan Northern with resin reproduction plates. We had a stack of them in the enginehouse to replace ones that broke or "disappeared". The only problem we had with the resin plates was skrinkage. The holes in the resin plates were slightly off from the bolt holes in the units. The stess the bolts put on the plates did cause some to crack. That was a problem that could have been fixed by drilling the resin plates with oversize holes. At the time the units were owned by Castolite Corp. which specialized in resin casting kits (and still does).

dsrc512@sd.value.net

> Any thoughts?

> The two Baldwin Sharks operated on Michigan
> Northern with resin reproduction plates. We
> had a stack of them in the enginehouse to
> replace ones that broke or
> "disappeared". The only problem we
> had with the resin plates was skrinkage. The
> holes in the resin plates were slightly off
> from the bolt holes in the units. The stess
> the bolts put on the plates did cause some
> to crack. That was a problem that could have
> been fixed by drilling the resin plates with
> oversize holes. At the time the units were
> owned by Castolite Corp. which specialized
> in resin casting kits (and still does).

And I vaguely recall chalked on the loco next to the plate "Want plate? See Engineer $15" and I think he had a box of them up in the cab.


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