Casting story: success

Finally I was able to cast my masterpiece: a little block o'lead, made to fit in an empty space in a Rivarossi diesel loco to improve traction.
Phew!
In the hopes that someone may benefit from my many mistakes, a short chronicle.
I had made a nice wooden pattern (master) to start. My first attempt at making a mold from it, described in an earlier posting, was a failure: I tried to cast it in plaster, but between the lack of adequate draft (a sloping angle that lets you pull the master out of the mold) and the wood sticking like crazy to the plaster, it was no go.
So here's what I did:
1. Made an RTV (room-temperature vulcanizing) silicone mold from the master.
2. Made an RTV casting from the mold. I now had a soft rubber copy of the master.
3. Used the RTV casting to make a plaster mold. (Same as step 1, just different materials.)
4. Cast the lead part in the plaster mold.
It's a roundabout way to do it, but it worked.
Boy, that RTV is kewl stuff. And it lasts *far* longer than the container says it will (6 months): I've had mine for I don't know how long, at least 3 years. It still mixes and sets up perfectly. Makes a pretty blue rubber mold of whatever you put in it.
Even making the second RTV mold was a hassle. The first attempt failed because I cast it too soon after making the mold, and the casting just stuck to the mold like glue. The second time, I waited overnight.
One hint: bake plaster molds well to drive off the water before casting lead in them. I found that a few hours at 250 (F) was sufficient.
Another hint: mold release wax is your friend here. Coat whatever you're casting or molding liberally with the stuff.
Next time, I'll make something worthwhile, not just a stupid block of lead. Like those faux Greek columns for that little depot I'm working on ...
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David Nebenzahl wrote:

Most low-temperature alloys and pure tin or lead may be cast in molds made from RTV silicone rubber. There are several types available, choose one that can best handle the heat. It gives much better castings with crisper details than plaster, and the rubber can take negative draft angles.
Again, see http://www.tiranti.co.uk/ for a great range of supplies.
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Erik Olsen
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Erik Olsen DK spake thus:

Thanks for the link.
That requires special RTV (RTV-101); I just have the regular stuff.
Yes, I suppose I could try that. I'd actually tend towards using traditional metal-casting techniques, like sand casting. There's an active foundry (steel) near here, and I plan sometime on going by there and seeing if I can get a small quantity of casting sand to play around with.
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