www.TK560.com

[Asok]

My friends and I are going to be doing some clay sculpting and then wanting to make vacuum formed copies of it. What is going to be the best way to make the molds for it? I have seen different people use different items to make the molds, so I am not sure what to use. If buying something like resin from Smooth On is the best way and just costing a little more, that is okay. Suggestions?

Thanks,
Bill

[jegner]

Good to see you over here!

As for my opinions, MDF, wood, bondo are cheap, easy to find and use, and hold up well for most hobbist needs. Plaster of paris, in a ratio of 10:1 mixed with portland cement makes a decent short run material. It sets up harder than regular Plaster of Paris, and is pretty easy to carve, and shape. Not good for long runs, but for test runs etc. it works great. UltraCal30 is a commercial version.

There are some other materials that work, like anchoring cement, but that stuff sets so hard, it will never crack! Good for a final buck mold, but not good as a sculpting material.

Jim

[drcrash]

It sounds like you want to sculpt in something(s) easy to sculpt, then mold and cast the actual buck for vacuum forming over from that.

That sounds like a good plan to me. Any sculpt that you spend a lot of time getting right is worth making a mold of to save the shape. You can work from intermediate casts, and if they turn out well, you can make a new mold from that. Or if one breaks, just cast another one. Cool.

The usual way of doing that is to use 2-part silicone or urethane to make the intermediate mold, and cast polyester or epoxy resin in that to make the buck. Everybody loves 2-part silicone, but it's kinda pricey. Molding urethanes are somewhat cheaper, but still not cheap, and urethanes are a bit nasty---you have to be very careful with mold releases, because urethanes are just about the stickiest thing in the world.

One cheaper way of doing silicone is to use silicone caulk for the intermediate mold. There are a couple of ways to do that, and a bunch of variants. You can search up info about that on taxidermy sites. (For some reason, taxidermists seem to be the people who mold with silicone caulk the most. I guess maybe because they make a lot of molds for one-offs, and it'd be unreasonably expensive to use 2-part silicone for a mold you're only going to use once.) I can elaborate on that a bit if you want, but I don't have much actual experience with it.

On the casting side, epoxies are nicer than polyesters, but polyester is cheap so people use it a lot. (E.g., Bondo brand products from auto & hardware stores.) Be careful about breathing the fumes---polyesters are pretty toxic.

You might be interested in some tips I compiled from various sources and some limited experience. Check out posting #6 in this thread over on thedentedhelmet.com:

http://www.thedentedhelmet.com/forums/showthread.php?t=16584
_________________
Paul (a.k.a. Dr. Crash)

Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com