Casting question

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

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.

Ray Haddad spake thus:

I forgot to say that it's not just a plain block, but has a slot cut in it to clear a screw boss in the loco, so it'd be tricky to try to get plastic wrap around it.

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.

Jim Bright

I got a reference to this groupie named Cynthia Plastercaster, but she was doing 1:1 casts, not models.

1) You don't mention draft angles - are the sides of your master perhaps too parallel? 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.

Cheers, John

You might use sheets of lead flashing (not as easy to find as it used to be, however) or lead shot glued together. Avoid the casting altogether.

On 26 Jan 2007 12:35:04 GMT, I said, "Pick a card, any card" and snipped-for-privacy@nyx.nyx.net (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.

-- Ray

If it is a 'one-off' casting, have you thought about doing a lost wax casting? Shape the wax make a plaster mold around it to contain the lead then pour.

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 vice.

Regards, Greg.P.

Don't do that - the fumes from the battery acid given off will do nasty things to the cat and any other living creatures in the vicinity.

I read some earlier postings and saw the one about a slot to clear a chassis screw - make the casting without provision and drill and chisel a suitable depression to suit. Lead is soft!

. . . but you have to find old ones with lead shot, not steel.

I recommend

for tools and materials.

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 home. Thanks.

Cheers, John

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.

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