Need advice on making a mold

[Stilgar]

I need to make a couple (2) copies of some small pieces of a styrene model. The pieces are about 1 inch by 1/4 inch. I need (hopefully) this process to be failrly simple and easy.

I was wondering if I could just make a simple mold from clay, or liquid latex and then inject if with some hadware store bought epoxy resin.
One minor issue is that I all ready know I have to make some manual modification after it is casted (I need to drill out some areas on the piece). I am worried that most epoxy will cure too hard to easily modify.

Any advice on information on how to do this or a better way to do it??
Simpler the better....

Thanks in advance.

Stilgar

[macfrank]

I need to make a couple (2) copies of some small pieces of a styrene model. The pieces are about 1 inch by 1/4 inch. I need (hopefully) this process to be failrly simple and easy.

If the parts have a flat side and not too detailed, you can use Silicone putty It works like a charm. To cast, I guess epoxy might work, or maybe super glue + talc (although I've never tried this) or nail repair acrylic powder . It's expensive, but the resulting plastic has about the same hardness as styrene.

Frank

[Shinnentai]

One minor issue is that I all ready know I have to make some manual modification after it is casted (I need to drill out some areas on the piece). I am worried that most epoxy will cure too hard to easily modify.

I've cast detail bits in epoxy before. Epoxy is tougher than most resins used to cast kit parts, but its still easaly workable with drill bits and cutters. You'll just be looking at a little more deburring is all. Biggest concern is viscosity: the stuff is thick like honey, so preventing/getting rid of air bubbles can be tricky. For this reason it's really best used in open-faced molds.

For ultra-cheap molds, there's always silicone bathtub caulk. Just make sure that A) you get stuff marked "100% silicone", and B) your parts master is non-porous, and if painted and/or puttied, free of water based or weak solvent based paints/putties, as the carrier solvents in the caulk can dissolve some of them enough to bond the silicone to the master. If the caulk is too thick to brush on without trapping air, it can be thinned with naphtha.

It's cheaper & works better than latex, but takes a long time to dry, and gets quite fumey in the meantime.

[tonyG2]

For a cheap resin alternative to the more common polyurethane resins you could try the two part automotive resins that are used with fibreglass reinforcement (the brand over here I have used is by Davis).

On the plus side, it is cheap and reasonably low viscosity so it pours well into an open faced mold. On the downside, when set it tends to be brittle and doesn't withstand rough treatment plus it can remain sticky for a long time.