Mold Making & Casting, Part 2

A pictoral guide to pouring resin into a rubber mold to cast a part.
By Ro Annis

This picks up where part one left off.

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Illustration 1: Here’s the mold all ready for action. I use a couple of rubber bands to snug it together and put a funnel into the “pour in” area.

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Illustration 2: here is the resin. A lot of people use Alumilite. Its OK, but very brittle. I’m using, what I think is a much better resin, called “Smooth-on”. Its easier to cast, demold and work.

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Illustration 3: I’ve mixed one side of the resin into a graduated cup. This resin is mixed 1:1 by volume (not weight). I’m adding some black pigment so that I’ll have grey parts. Smooth-on is normally snow white. It is impossible to discern any detail in anything cast in this color.

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Illustration 4: Mix well.

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Illustration 5: The mold is put in a pressure pot and the resin is poured into the funnel. Be quick here, as the resin has a short working time.

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Illustration 6: Before the lid goes on (you’ve got to be quick because this stuff kicks in about 3 minutes) you can seen a clean spooge coming from the vent. That is good. Means air is getting out so resin can go in.

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Illustration 7: Lid on tight. (This is the little pressure pot).

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Illustration 8: The resin in the cup is starting to kick. Keep it nearby, that way you know whats going on inside the pot.

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Illustration 9: OK, now its about 30 minutes later. Ready to demold the part. Notice that both vents have spooged quite nicely.

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Illustration 10: Peel it open gently so as to not break or distort the castings….

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Illustration 11: Wheels! Jim will be so happy. You can see how the resin goes in, flows through the sprues and up and out the vents. Just have to pour a bunch more….

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Illustration 12: This is an open face mold for some other doo-hickey. I put it here to show a simpler type of mold for simpler parts.

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Holy Cats! Will you look at the time.
Time to “think like a Bubble” in part 3…