Building on the initial success of casting pewter into laser cut forms, I spent some time this afternoon prototyping some coins, with the ultimate goal of creating limited edition thank you gifts for special guests and benefactors.
I created the file for the laser cutter using Illustrator, reversing the text on the face plates, and adding a sprue and two vents into the middle piece, which is sandwiched between the two outer squares and defines the outline of the coin.
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Here are the pieces, cut out of 3mm plywood….
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…and the first pour.
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Not bad, but with some voids up near the ears and some loss of detail in the letters.
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I decided to melt this one down, and make some changes to the forms to try and get the metal down into the mold faster.
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There are apparently formulas for sprue sizing, but I just decided to try making at a wee bit bigger. I also increased the size of the original vents, and added a couple more.
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Better, but still some detail loss up near the top.
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For the next iteration, I decided to flip the outside plates upside down, the thought being that any detail loss at the bottom of the coin would be less noticeable than at the top. I also remembered to char the detail plates – a thin layer of carbon seems to function as a release agent.
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Success! I removed the sprues and vents using flush cutters, and performed an initial polish with fine steel wool.
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A really good prototype in hand, I decided to try different kinds of wood for the forms. Here’s walnut.
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Not great. Next, I found a small scrap of fine-grained wood – not sure what, exactly – but I only had enough to engrave the plates, so I used the standard birch middle piece.
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The metal picks up the grain of the wood, and this being a much finer grain, the result was a very shiny and smooth surface. Definitely an avenue worth exploring in future versions.
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I did one more test, spraying ingot release spray on the detail plates. This caused the metal to boil and bubble, resulting in an interesting (but unusable) outcome.
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Really pleased with the prototype coin, and I’m excited to continue perfecting this technique, and to finding other applications for molding metal using multi-part laser cut molds.