I've heard about a stuff called REmeltable casting rubber. I don't have budget to keep buying rubber so I want to know, where can I find remeltable casting rubber?

If you're living in the U.S., then you might be out of luck because I've been looking for these for a while, but they are only available in Europe. Unfortunately, I don't think they ship to the U.S. either. Even if they do, shipping would be too expensive to afford.

The nearest thing you can do to save money and re-use your rubber is to cut it up into tiny chunks and mix it in with your next batch.

No no no, don't use the stuff. I tried it and it is absolutely worthless. Airbubbles are all over the place, it makes a sticky mess, ruins FDM masters and there is no way to make a two part mold.

Forget it.

Have you actually tried this? Your experience would certainly be pertinent to this thread.

Mold-making rubber is usually a thermoset compound so I don't think the chunks would be capable of melting into the next batch. But the finely-ground chunks might make an excellent filler to extend the volume of a batch of rubber, as long as there's enough virgin rubber compound to fill all the spaces between the chunks.

Using old moulds as filler works surprisingly well.

Personally I don't see why you couldn't use anything as a filler, as long as the bits are small enough and the silicone solution is thin enough to flow and fill the space between them. Otherwise you waste 90% of the silicone just to fill a big void.

Alternatively, has anyone tried making moulds out of wax? Not quite so flexible, but fully reusable...

thanks all!

I think wax would be a no-no with most urethane resins like Alumilite and Smooth cast, because they generate a lot of heat. It would melt the wax!

I think what he means is not that they will melt in, but just take up space. The rubber bonds well to non-mold released rubber so as long as you keep it away from your part surface it is fine. I don't think finely grinding it is the way to go, you want your liquid rubber to be pristine next to your part.

I have used this idea, but I use it with larger chunks and slabs. I meant to document it with my Gigaminx project, but didn't get the right pictures.

The easiest way to think about it is for me to describe my slab method: Pour your liquid rubber until it just covers your part (2mm or so). Normally you would want a good 10mm over your part for strength, but this doesn't have to fresh rubber. Take a 10mm slab from a previous dead mold and lay it on your liquid rubber. Then pour a bit more to fill the gaps left (you have to leave a bit of room between the slab and box to drop it in...). I like to pour at least a tiny bit over the top to have a clean surface, but it isn't necessary.

Taking this approach further, you can drop in blocks and strips of old molds into areas where your parts are not (to help you fill your mold above your part). It will displace that much rubber which is a good savings if you do it well. I have made some of my Gigaminx mold halves with as little as 45ml (1.5 oz) of liquid rubber and about 2 oz (60ml) of old mold in blocks and slabs.

Reduce, Reuse, Recycle!

Dave

Yes I've done this a lot especially when I'm desperately low on rubber, or if I'm being too tight too pour a whole lot into a large cavity. I'll just throw a few chopped up pieces into the mix or I will push the pieces into the mold after some liquid has been added.

As you know, forgetting to use a mold release between two halves of a mold means that sucker is sealed for life. Same principle. Throwing in the chunks means they fuse with the new silicone.

Dave's right on the money. It's a space filler. So I don't throw out all my failures.

The way you say you lay your old molds on top of the liquid rubber sounds risky for the parts new mold you make because you say you only put about 2 mm of liquid rubber before that...
Is the solid old rubber more or less dense than the liquid rubber? because, unless it is less dense, I don't see how this is supposed to work...
If it is heavier it would simply sink to the bottom of the liquid and disturb the piece under it, which could ruin your mold.

Rubber is gooey stuff, and it won't sink fast if it is a different density (it should be the same). Remember that to sink it has to push a bunch of other OOMOO up through small cracks.
Also, even if it touches your part, it has been covered by liquid rubber and so it will probably have a thin skin of liquid rubber between your part and the old mold. If not, hey, it's rubber too

Dave

I finely chopped my old molds into 3-4mm^3 cubes and used it as a filler with excellent results. I will do it every time from now on.

Really it's not necessary to use "new" rubber on anything except the areas that will touch the parts being molded, + a few mm of cushion. Like Dave said, rubber is rubber and old+new rubber fuses perfectly once cured, so even if it touches a little it's no big deal.

Obviously the older the "filler" rubber is, the less you would want to use. Otherwise certain areas of the mold will be much more brittle than others and are more prone to tearing.

Is mold max 30 able to be cut up like oomoo, or is it too strong?

Any rubber can be cut no matter how strong.

Although I agree it's best not to use re-meltable rubber / Gelflex it isn't quite as bad as TomZ makes out. I used it to make a huge number of my early puzzles including my Golden Cubes- http://www.youtube.com/watch?v=VRMATodm2Bo . I never had any trouble with bubbles and it's very usable for certain projects. I would still advise against it though for these reasons-

1. It shrinks so is unsuitable for moulding mechanisms.
2. It needs to be heated very carefully or will give of smoke and unpleasant fumes (it does anyway a bit). I never did but you are supposed to use special heating equipment.
3. It's like boiling treacle if you get any on you.
4. The temperature required to heat it is high enough to melt many plastics including regular Rubik's Cubes.
5. It's less durable than silicone rubber and moulds need replacing more often.
6. It doesn't last for ever so you eventually have to replace it anyway.
7. Because of the temperature you need to use metal or foil boxes for your moulds and forget about plasticine.

When I started transforming puzzles I had never heard of silicone rubber so I had to make do with this stuff. I am much happier using silicone rubber now but it is far more expensive to use.