"Don Foreman" wrote in message
news
On Sat, 01 Nov 2008 11:07:44 -0500, Tim Wescott
wrote:


Do you know of any references on how to do it right? I've got a project
in mind (that probably needs to wait 10 years) that could be done quite
well with plaster cast aluminum, I think.

Google on investment casting. Jewellers do this routinely with high
melting point metals like gold, silver and even platinum.

The stuff to use is investment casting plaster.
http://www.gp.com/build/product.aspx?pid=5901

It can be found at jewellers' supply places. Once the mold is made,
it needs to be "burned out" or calcined at about 1200F long enough to
"burn out" the wax and also to drive off excess moisture.

With ally you'll probably need quite a tall sprue to get enough
pressure to get molten metal into the smaller internal features -- or,
use a centrifugal approach.

Just be aware that investment molds typically have much less of a venting
problem than cast plaster molds do, because they're a lot thinner. I should
say "gas porosity" rather than venting, actually.

--
Ed Huntress