Generally the mold is made with silicone rubber, for it takes great detail from the original, and also gives a "non-stick" (or, rather poor stick) surface to a cast plastic. At the same time a mold from silicone rubber is not very durable, and gives you only a couple dozen or so castings.

However, most puzzle parts are pretty straight, and don't really have that intricate detail that needs to be reproduced precisely, like hair lines, etc. Can a mold be made from different material? What would that be? How long would it hold?

For example, can a mold be made from the same polyuretane resin that we use for casting? Would a mold release solution work so that a casting does not stick to the mold? Or can a cheaper resin be used for a mold?

I'd like to understand this deeper, so please forgive me if I am completely dumb on this. :-) Thanks!

There is also the possiblility of using polyurethane rubbers, however, you're usually casting polyurethane plastic pieces and you will need plenty of silicone spray to stop them from sticking. A missed spot will mean your mold and piece are basiccally ruined. I find that I get plenty of castings out of a mold. And the only reason it get's ruined it because I forgot to spray it first. Also when sites mention that silicone is sometimes not durable that is because of somtimes using large molds, with plenty of possibility of damage. You generally try to avoid small nicks in the rubber as that starts a tear.

I've found so far that silicone rubber / polyurethane plastic is the best thing for what we do.

Wayne, you talk about using two part moulds in your article, I have a couple of questions.

You don't seem to use pourers and vents like in the posted article. Do you use simple two part moulds, fill the two halves and bring them together? If so, how do you stop the resin pouring out as you close them? Don't you get a lot of resin leak between the two halves of the mould? Isn't there an issue with bubbles along the join line? How is the finish effected on the final piece? Do you need to sand them or just trim with a scalpel?

I understand it isn't practical to use vents etc on smaller pieces, I just wanted to pick your brain for tips. I have just got a bunch of parts from my stereolithography guy and I am going to have to make two part moulds.

Max

Yep, what I do is make a two part mold, no vents or anything like that.

I have both halves of the mold face up and fill them with resin. Actually you slightly overfill them. Depending on your working time, spend time removing any bubbles lock in sharp places out with a sharp steel or plastic tool (don't pierce the mold).

Use the tool to prod the liquid surface. When it becomes thick like a gel, it's time to get it together. Then it's all in the wrist. Quickly but carefully close on half on the other while trying not to capture air, and trying not to spill too much out.

Once the two halves are together, press from one end to the other sqeezing out more resin and bubbles along with it.

Do large pieces first because the cure quicker. Then move to smaller pieces.

It's a technique that you need to master after a few goes. Doing the closure right before gel time, helps a lot.

Wayne, I don't see this as a method for making hollow parts (i.e. caps). For example, a hollow polyhedra that has walls only. How do you do that, then?

I would still use the same method. Check the article I write on making the 2x2x2 rhombic dodec (http://www.twistymegasite.com/2x2x2dodec.asp. I made the pyramids out of card, and a two part mold to cast the card.

Maybe send me a drawing of the kind of part you're wanting to cast.

Anyone need some pigment?
I've got 2 cans of pigment (pint each i think)
one black, one blue. I also have a can of Synlube if anyone wants it. All i ask is that you pay the shipping. They are all sealed (execpt the lube). Cost me about $30