Casting and mold making in the Bay Area

I live in San Francisco and am thinking of having Sierra Pacific
Casting Inc. cast some pieces for me--I just found them on the web but
they seem to have good prices and have been very friendly in answering
my questions. However, while they can make molds of metal pieces and
wax (cold RTV mold), I was told that the original wax piece often
breaks during the process (sometimes in many places--basically it
sounds like you lose the original).

I have had silicon molds made in the past and the original came out of
the mold looking fine--just a few scratches from cutting the mold
open. I am not very familiar with the RTV mold.. is losing the
original wax fairly normal? Are there other ways of doing this that
would be easier on the original? Or any other companies that can do
this a different way?

Also, the mold making appears to be the lowest-tech part of the
process (no large machinery involved).. I was looking at the Rio
Grande catalog and eyeing the different mold mixtures and am thinking
maybe I should just do this myself. The problem I would have then is
no wax injector... but SPC says they can inject copies from whatever
mold I provide and cast these. I don't have much experience with molds
and making wax copies, but is there much touch-up involved?--Is this a
feasible solution (having them make the copies and cast directly
without me meddling)?

thank you in advance for any help!
cheyenne

cheyenne weil wrote:
I live in San Francisco and am thinking of having Sierra Pacific
Casting Inc. cast some pieces for me--I just found them on the web but
they seem to have good prices and have been very friendly in answering
my questions. However, while they can make molds of metal pieces and
wax (cold RTV mold), I was told that the original wax piece often
breaks during the process (sometimes in many places--basically it
sounds like you lose the original).

If You have a waxform with different undercuttings and You stretch the
rubber by cutting, the mold will break very often.
If it´s a flat piece, problably nothing will happen to the mold.
I think it´s fair to warn the customer.

--
Heinrich Butschal
Gutachten, Projektmanagement
www.butschal.de

"cheyenne weil" wrote in message
...
I live in San Francisco and am thinking of having Sierra Pacific
Casting Inc. cast some pieces for me--I just found them on the web but
they seem to have good prices and have been very friendly in answering
my questions. However, while they can make molds of metal pieces and
wax (cold RTV mold), I was told that the original wax piece often
breaks during the process (sometimes in many places--basically it
sounds like you lose the original).

[If you're worried about that, cast the original wax in metal first. You run
the risk of losing the piece entirely if the casting fails, but that's not
likely if you have the pros do it. Sierra Pacific is really very good at
this.]


I have had silicon molds made in the past and the original came out of
the mold looking fine--just a few scratches from cutting the mold
open. I am not very familiar with the RTV mold.. is losing the
original wax fairly normal? Are there other ways of doing this that
would be easier on the original? Or any other companies that can do
this a different way?

[Silicone rubber is an RTV (Room Temperature Vulcanizing) rubber. The wax
will break on demolding if it's a complex piece, but if it's simple it will
probably come out okay. But if you've got the mold, you can easily shoot
another wax- so what's the problem?]

Also, the mold making appears to be the lowest-tech part of the
process (no large machinery involved).. I was looking at the Rio
Grande catalog and eyeing the different mold mixtures and am thinking
maybe I should just do this myself. The problem I would have then is
no wax injector... but SPC says they can inject copies from whatever
mold I provide and cast these.

[They might come out better if the mold was professionally made and
(especially) cut and vented. There's some technique to this that makes a big
difference in how well the molds work.]

I don't have much experience with molds
and making wax copies, but is there much touch-up involved?--Is this a
feasible solution (having them make the copies and cast directly
without me meddling)?

[If you're really interested in the process, and are determined to master
it, it's possible to get proficient at this. But it will take some trial and
error to get it right. If you just want the parts produced in the most time
and cost-effective manner, let them do it for you.]

thank you in advance for any help!
cheyenne

[Good luck, Cheyenne!]

Andrew Werby
www.unitedartworks.com