I'm probably late in this response since I've gone to Orchid Digest.
I don't think you're being unclear in your instructions at all. I
think your casters are just terrified of messing up the RTV mold,
destroying your original wax and having nothing to show for it.
They have a reliable casting systems so they are pretty much
assured of successfully
casting your wax and having a metal model to work with. That's
obviously the route they've taken.
Many of us have worked with complicated metal models that took
several attempts before a good production mold was made. Just
imagine having just one shot to make a production mold with a
precious hand-carved wax or a single milled or RP produced wax that
won't survive the molding process. Also, a lot of the RTV molding
materials aren't as easy to cut as vulcanized rubber. They can't be
pulled and stretched as much or cut in corkscrews as easily.
Complex molds can be very difficult to guarantee in RTV.
You have several options:
(1) You can have them use a ZERO shrink rubber and mold the single
accurate casting and go from there and see if you can get more
acceptable results than the 10% smaller castings. In addition, you
might look into more technical investments like those used in dental
casting since those have very, very minimal shrink since casting
crowns and dental appliances require exacting fit.
(2) You can absolutely absolve them of any responsibility if they
don't successfully RTV mold your wax. You will have to take on ALL
the risk and not penalize them for destroying your wax (the
assumption is that you use good jobbers and they do everything
professionally possible to insure success). If you're running on a
deadline, again, you accept all the risk if things don't work out.
If you're not willing to accept this risk, how can you expect them
to? It makes perfect sense for them to hedge their bets to the best
of their ability and to at least be assured of giving you
(3) You can carve your wax larger to compensate for the 10%
shrinkage so your job shop can cast your wax, mold the resulting
casting and produce the end result castings you desire in the
proper size, assuming you've compensated correctly in making your
(4) If you can produce waxes via CAD/CAM and send multiples as
backups for the RTV mold making process, your jobbers may feel more
secure in attempting to follow your instructions to RTV mold the
original wax and make subsequent waxes and casting directly as you
desire. (NOTE: Not all RTV products are zero shrink so you might
want to find out what RTV material your jobbers use.)
(5) If none of these options are acceptable, you'll have to do
everything yourself. At least you'll have total control and complete
responsibility and I don't mean this is a sarcastic, judgmental
way. I do a lot of things myself simply because I don't want to be
in a position to regret an outcome that I didn't retain control of.
(It's sort of like the old question, "Do I set the horrendously
expensive center stone that could destroy my business if I crack it
or do I send it out to a setter?" ) Also, it doesn't help work
relations to blame someone else when bad things happen because they
do from time to time. Whenever we job something out, we ultimately
accept the risk. In the final analysis, I think your jobbers are
doing what they think is best and most responsible. They think they
are looking out for your interests as well as their own.
I hope my suggestions help in some way and good luck with future