ORIGINAL: drcrash


Are you talking about vacuum forming directly over the existing body?

If so, I'd be worried that the plastic might warp. But if you don't support it (fill it with clay or something), it will definitely get crushed. Even a vacuum cleaner can apply about three hundred pounds of force per square foot of surface. (A vacuum pump can apply up to a ton of force per square foot.)

The usual thing is to cast plaster INSIDE the original piece of vacuum-formed plastic, using it as a mold, and vacuum form over the plaster cast. (You need to support the original with clay, or maybe in a sand box, or something, to keep it from distorting under the weight of the wet plaster. Wet plaster is heavy.)

If the original was formed over a male mold in the usual way, you actually get better detail that way---the side of the plastic against the mold captures the shape of the mold better. The other side is a bit more smoothed and rounded, by the thickness of the plastic (and usually a bit more).

This is a good idea for making "backup copies" of cowlings and other things that tend to get broken in crashes. When that happens, you can just pull another one over the plaster positive you saved. (Tip: make the plaster cast BEFORE you trim the flash off the original. The extra plastic around the edge helps keep it rigid during casting.)

Don't do this just to make a bunch of copies of somebody's commercial shape though. (That's not cool or legal.) But if you want to transform an original you own into (say) thicker or tougher plastic, it can be "fair use". (In my opinion, but maybe not their lawyer's. But if you're not selling them, or giving them away, they probably wouldn't care.)

The best application of this "recasting" is when you can buy a shape that's *close* to what you want, cast it, and modifiy the cast to make it *exactly* what you want. (Like adding scale details, or making it into a different version of the same make of plane, etc.)

ORIGINAL: DogbreathRacing

I use regular plaster of paris and pour it directly into an untrimmed body, when cured it makes a great plug. It does get warm but not enough to warp the body which can be cleaned up and used after making the plug.