No, it's got nothing to do with American Idol or Broadway.
I've googled and looked at bunches of sites without finding what I'm
looking for, so I'm throwing myself on the mercy of the court of Usenet
(in other words, I'm desperate and am asking here as a last resort).
OK, here's the deal: I'm trying to make the simplest casting in the
world, basically a chunk o'lead to put into a diesel (Rivarossi E8) to
weight it down. Made a really nice master out of wood. Tried to make a
plaster mold with it: of course, even though I'd oiled the wood
thoroughly, it stuck to the plaster so tightly I had to bust the mold to
pieces to get the master out.
So here's my question: I know how to make the casting once I get my
plaster mold (be sure to dry to mold to remove all moisture, etc.,
etc.). What I'm having trouble with, obviously, is making the damn mold.
(It only needs to be a simple 1-piece mold, so I don't need advice on
making full molds, parting lines and such.)
Anyone familiar with casting here who can help?
Vaseline? Grease? Pull it out as the plaster is setting?
It occurred to me that I could also go down to the local foundry (yes,
there actually is one in town here, still functioning) and try to score
a little bit of casting sand. Or is there some easier way to make a
plaster mold from a wood master? The trick is trying to extract the
master from the mold after the plaster sets.
On Thu, 25 Jan 2007 20:32:18 -0800, I said, "Pick a card, any card"
and David Nebenzahl instead replied:
Lay plastic wrap over the wood and pour the plaster over it into a
large ring with the wood in the center. When you take it out, peel
the plastic wrap from the plaster. If a bit of it stays, so what?
Just pour the lead anyway and the plastic won't hurt a thing.
I use Pam, baking spray for most castings. Works a treat.
Ray Haddad spake thus:
Hmm; don't like the plastic idea so much (what with the inevitable fold
lines and all). Pam sounds more promising. Are you saying you use it as
a mold release agent for masters?
I thought soaking (literally) my little wood block in motor oil for
several hours would do the trick. Evidently not.
You might try a layer or two of aluminum foil. You should be able to adapt
it to the shape of your master pretty well. Be sure you don't have any
undercuts or your master won't draw -- better to have a slight taper. I've
done it myself and it has worked quite well.
here as a last resort).
1) You don't mention draft angles - are the sides of your master perhaps
2) Googling yielded a thread amongst potters with some ideas at
My own experience with plaster moulds for casting lead has not been
good - I never seemed to be able to get the plaster dry enough to avoid
generating steam when I poured in the lead resulting in voids, or causing
the mould to crack - I'm probably too impatient. I therefore make most of
my lead weights in wooden moulds and avoid the master step. To avoid
getting voids, I keep the wood as dry as possible and don't use any release
agent. I don't usually worry about draft angles and instead make the mould
partially disassembleable to remove the finished casting. As you describe,
I find that for simple weight shapes, I usually can design an open top 5
sided mould to allow a simple pour of the lead. Geezer
Geezer spake thus:
After I retrieved my wooden master and looked at it more carefully,
turned out it had a negative draft angle. I reworked it with a file and
am going to attempt another mold with it.
Also found my official wax release agent, which I'm going to schmear
over the master in hopes it'll keep the plaster from sticking to it.
Yes; a few hours of baking at around 300° or so should do the trick.
Good morning David;
I took a machine shop course in High School, and it contained a small
foundry. Those who used it generally melted down pistons for the aluminum
which was subsequently poured into blank moulds. I recall people using
casting sand sprinkled with bone meal dust. The only other alternative is
to scavenge lead-acid batteries, cut the lead slats to size and solder them
together. It's been 30 years and my travels have had little to do with such
projects since. Sorry if I can't be of more help.
On 26 Jan 2007 12:35:04 GMT, I said, "Pick a card, any card" and
firstname.lastname@example.org (John Purbrick) instead replied:
I was going to suggest shotgun pellets (or small split shot fishing
weights) and epoxy but that's a permanent addition to the shell.
Works great, though, when you need to add it without too much fuss.
Why not just make the mold out of wood?
I assume it's just a shaped block? It needs to split some way to get the
casting out so something like a profile cut in timber of the right
thickness can have ply/hardboard sides screwed on which can be removed
for casting extraction. Finish shaping with a coarse file/rasp in a
Good afternoon Greg;
Good point, as it's nasty stuff with which we wouldn't fare much better
than the cat. I was thinking of the scenario of the acid already removed
and the cells soaked in a sodium bicarbonate solution before bringing it
Frank A. Rosenbaum spake thus:
No, but if what I'm doing doesn't work, I may try that: I've always been
curious about lost-wax casting.
I guess my mold would be simple enough that I could just pour the lead
in on top of the wax and let it flow out, right?
Plaster tends to blow up unless it's been baked forever. I have made simple
molds (for lead) from wood. The wood gets burnt but a little water keeps
the fire from starting. Make sure the lead has set before adding any liquid
or it will explode. Safety glasses and a leather welders apron help while
doing all this.