Advice for making vacuumform buck?

I have a couple of parts for my MST3K Crow puppet that I want to vacuumform and I would like to know what would be the easiest and relatively cheapest way to make plaster bucks out of the parts.

I heard of a way to make a cheap mold is you make a negative mold out of plaster and that you use the negative mold to create the final plaster buck; this process usually results in the destruction of the negative. What's your opinion on that?

Thanks!

Depends on the parts.

Which parts?

depending on the part you can make a fiberglass negative. then a fiberglass, epoxy or resin positive. then the negative can be used again. you just have to make sure the part has enough "draft" so the negative comes off easily and inturn your positive pulls from your negative and your vaccum formed part pulls from your positive or 'buck"

micdavis said:

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Depends on the parts.

Which parts?

and this tray part:

kantgetnun said:

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depending on the part you can make a fiberglass negative. then a fiberglass, epoxy or resin positive. then the negative can be used again. you just have to make sure the part has enough "draft" so the negative comes off easily and inturn your positive pulls from your negative and your vaccum formed part pulls from your positive or 'buck"

Wouldn't the resin stick to the heated plastic? How expensive does fiberglass usually cost?

Well, to my eye, plaster doesn't look like a successful choice for the first two part. The tray should work if you cast in the plaster and make sure the buck bottom is dead flat. Otherwise the pressure of the vacuum will snap the plaster. Of the first two, the one on the left will probably destroy both positive and negative trying to get a buck of plaster out of the negative. The second one may work, however if you clay it up on the inside to the bottom of the rim. On the first, even if you did get a plaster buck, it would be rather thin at the top, and therefore, fragile. Also trying to pull vacuum formed plastic down into that one does not look good to me. The bottom of the inside would end up paper thin and probably web unpredictably in there.

A good cheap mold for casting plaster would be to make a latex mold a little over 1/8 inch thick and then back it with a plaster or fiberglass mother mold. That way it will release from your parts easily and can be reused.

Or alternitivly (to Oz's sugestions) you could use silicon , instead of latex , Ive found silicon a much nicer product to work with than latex

Sweet, thanks for the advice, guys! I'll go ahead and get some later this week.

MrSinistar said:

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Wouldn't the resin stick to the heated plastic? How expensive does fiberglass usually cost?

a decent mold release will keep the resin from sticking to the part. fiberglass fabric, matte and resin is cheap and available from any hardware, auto parts or department store

kantgetnun said:

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a decent mold release will keep the resin from sticking to the part. fiberglass fabric, matte and resin is cheap and available from any hardware, auto parts or department store

Sweet, I'll see if I'll get some fiberglass soon.

I got some plaster, latex, clay and mold release so hopefully this week, I'll make my first mold.