I was intrigued by the metal casting posts from earlier in the year and wanted to give it a try. It’s worked pretty well so far, and I thought others might be interested in the process.
The first step was finding a suitable metal. I opted for this bismuth based alloy because of the low melting temperature (281 F) and it is lead free. This doesn’t take any special equipment - we used an old pot to melt it on a regular camp stove. Remember to wear safety goggles!
Next was making the mold. The approach we’ve been using is to sandwich layers of material together to create a void that can be filled. After trying different materials, acrylic seemed to give us the best results. In the picture below we have three layers of acrylic, one with the void and another with a 3D engrave, which are then sandwiched between two pieces of draftboard to spread out the clamping load.
I cut holes for screws to hold it together during casting, and to make sure the engrave was aligned correctly. The V-shaped notch at the top makes it easier to pour the material in. I also found leaving one of the plys taller than the hole created a lip that helped keep the material from sloshing out during the pour.
We dusted the inside of the mold with baby powder, which seems to help with bubbles. After putting the mold together, pouring the melted metal in and banging it a few times (again to help with bubbles), it looks like this:
After letting it cool, we opened it up:
We then melted and ground down the sprue hole, buffed it a bit on the grinding wheel, and got the little tokens below. I’d like the play a bit more with defocusing to get the engrave cleaner, but we’ve been pretty happy with the experiment so far. Hope this helps!
) One suggestion though; if you’re getting bubbles or you design has an irregular shape where air could get trapped, just add small vents for the air to escape.