OT: Cold Molding Plastic ?

Polymer clay comes to mind. Its somewhat like a stiff modeling clay that hardens when you bake it in a toaster oven. Fimo and Sculpey are two brand names I know of. It can be found in craft stores or sometimes in the crafty aisle of your local Wal-get-co-mart.
It runs about 2 bucks for a 2 oz block. A 2 oz block is maybe a cubic inch or a bit less. When cured it is not as hard as epoxy. You can indent it with a fingernail. It can be trimmed with a sharp knife.
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Not OT if you're using it to clamp material!
1. Bondo 2. There are epoxy putties out there -- check auto parts stores and plumbing aisles at Home Despot 3. Hobby shops stock a bondo-like epoxy + microballons putty 3a. Better hobby shops will sell you just microballons.

Marine-Tex has an epoxy "putty" that might work: David

bondo or the bondo with fibergalss in it [tiger hair?]
Dave wrote:

I am thinking 'Plastic Wood' would break apart once cured as it has no support.
How about this.......
Have you got a chunk of MDF scrap lying around? Run it through a table saw/router/jig saw to make a quantity of 'dust'.
Mix the dust with the epoxy (I would go for the 24 hour cure type rather than the 5 minute cure to give more 'play time') and build your mold/block out of that. The addition of the MDF dust should give it 'body' and thicken it up so that it doesn't run away. You would still have to make 'walls' around the area though as it would still try to find it's lowest level.
You could also mix the dust with regular carpenters glue (PVA) and make a 'putty' that way but I doubt it would have the strength of the epoxy version.

What about making your own version of a Jeweller's Pin Vise? Take a look at the following link for an example

I think I would try Bondo first. I used to make router fixtures for vacuum formed parts from an acrylic base and use Bondo to hug the part.
Think about making a two piece box that has some pins to index each half and that way you can attempt to keep everything square. You might also put a small shim (tape) between the halves when setting the Bondo to allow for a little squeeze when you are attempting to machine.
Good luck,

something There is a thermoplastic material called Jett-Sett which you can soften in hot(160 degree F) water and mold into the desired shape to make fixtures, special shaped pliers jaws, hammer heads, custom tool handles, etc. It is reusable, warm it back up and remold it to another shape. You can mold it to the item to be held, remove the item and tweak the mold just a little and when the material hardens back up you can snap the item into the mold. I got some from a jewelry supply outfit called Rio Grande, but I see some for less money,$20/lb, from this place There is an array of holders that you can get to put in vises and on mandrels to use the stuff. There is a some discussion about it on the Ganoksin site.

There are several epoxy products that are available as a putty, to avoid the messy liquid epoxy problems, that can be formed into almost any shape. The thick consistency (kinda like a stiff clay) might not make it the best choice for molding though, for this situation where you'd like it to form to a weak plastic camera body. It would probably mold well if a stronger material were pressed into it.
The putty products I've used are packaged as a stick or log, with a grey outer layer and a black inner core. The amount to be used is cut off, and kneaded to attain a consistent dark grey color, then shaped. It sets fairly quickly, within a few minutes, and it adheres to almost any clean rigid surface. I haven't actually tried to extend the set time by reducing/removing one of the parts, or experimented with thinning the mix to make it more moldable, but these could be tried I suppose. Thinning it would be most likely be risky in your application, where the solvent would probably deform the plastic camera housing.
There were some good recommendations about adding a filler to a wet casting material. I dunno what types of fillers to suggest for liquid epoxies, but there are fillers available for several applications (one being the concrete patch epoxy products).
If I were trying something like you're suggesting, I'd consider trying to make a pair of jaws that hold the camera body top/bottom or left/right pairs. To form a jaw, I suppose I'd probably form a pocket to be filled with a pour of liquid epoxy, with some sort of clay. Setting the camera (protected by the plastic film) into the clay dam to a level where the molded epoxy would provide enough holding coverage (jaw shape) and also provide enough material below the jaw profile to make a strong part.
The amount to fill the pocket would be an estimated guess, as the camera will displace some material. The protected camera body could be placed in the mold dam (or suspended to a reasonable depth), and then the liquid epoxy could be poured into the clay dam. This probably wouldn't provide a good like-image due to the plastic film being creased and wrinkled. The part could be lined with a soft material to conform to the camera body, or more epoxy could be used to fill the creases.
Ideally, the mold and casting procedures would be done with something other than the actual camera body. If you intended to do numerous parts, maybe a plaster copy would be more practical, or a part made of similar material that could be coated with a release agent. Autobody fillers are cheap, soft enough to conform to another shape well, and fairly quick to set. There are types with finely chopped glass for reinforcement, as opposed to the product with long stringy fibers which can be difficult to work with. The dust or shavings from the reinforced products will make you itchy, and the dust isn't anything you'd want to inhale. An extensive cleanup of the machines and work area will be required.
Getting away from casting parts, you might also consider a metal clamp frame, with soft jaws made from something rubbery (those stick-on pads for instrument feet, for example). A Dremel cutter will shape soft materials quickly.
WB ..................