On Sat, 01 Nov 2008 09:56:09 -0400, Ed Huntress wrote:

"Larry Jaques" wrote in message
...
On Sat, 01 Nov 2008 01:23:16 -0500, the infamous Tim Wescott
scrawled the following:

On Fri, 31 Oct 2008 22:59:53 -0600, F. George McDuffee wrote:

On Fri, 31 Oct 2008 21:38:22 -0700 (PDT), Dar
wrote:

I need to make a bunch of molds in sandcast bronze and would like to
know the kind of sand
to get for finest detail/smoothest finish . They won't be complex ,
or even 2 part sand molds, probably just bronze poured onto a flat
cope that has an depression in it and a dam built around the
depression .

thanks

DS
I would consider plaster molds for best detail

see
http://www.modernsculpture.com/bronze.htm

I've only ever used plaster molds (a long time ago, molding bullets for
miniature cannon out of solder. It's a wonder I'm still alive).

Were they still wet and exploded on you? There's a very good reason
the molds are seasoned in the furnace, Tim, as you found out.

It's not just "seasoning." First you have to dry out the free water.
Then you have to drive off a percentage of the chemically retained
water. That's called "calcining." For casting zinc or aluminum, it
doesn't take much. For casting brass or bronze, it's critical, and
requires more heat.

It's not something to do by guess and by gosh. Those things can explode
in a serious way. Furthermore, ordinary Plaster of Paris will not do for
casting brass or bronze. You need special high-temperature casting
plaster.

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.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html