how to reconstruct a small shaped plastic part ?

[sdowney717]

the plastic is not the glue able kind.
What I was thinking was how to create a female mold of the part, then perhaps create a rubber duplicate?
Is there a liquid rubber, how about the kind tool handles are dipped into?
I suppose a hard reinforced fg epoxy part could be made.
the part needed is thin, only about 1/8 inch thick and is actually shaped to hold a phone headset on the bottom.

I cracked it by laying something heavy on it.

[Bob Cleek]

Plastic resin casting kits are made for replicating parts of all types. Check them out at http://www.micromark.com/casting-and-molding-supplies.html.

I don't know if an injection molded "springy" plastic clip can be replicated by casting, but if it can, MicroMark will have the stuff. They're quite a "toy store" in any event.

[coelacanth2]

What is the part used for? Can it be "tacked" together temporarily? If it is made of a light, springy, strong metal, will that be a problem? If the answer to the above is yes, call a local dental lab that does the frameworks for removable partial dentures. I have repaired several of my son's toys with Chrome-cobalt cast from the plastic that was temporarily repaired.

[S B]

Most of the stuff is glueable, you don't have the right glue.

[JimConlin]

Are you wanting to cast a part that is just a shaped cradle for something and doesn't need any great strength?
Could you mix up a light plastic bag of microsphere fairing putty and push it into the shape you want, perhaps using the object that's to be cradled? After it cures, you can reduce the mass by sanding or sawing, or add more bog.
Hell, there's no reason not to use Bondo for something like this. It's cheap.

[Thermo]

I used to make custom fiberglass and resin pieces for the costume industry, mostly using various polyester resins.

I'd sculpt/tool the object in tough plasticine clay (dry, oil based clay, the kind that got harder when cold, not 'sculpy' or pottery clay) and when it was right I'd build a mold right on that part by barrier-coating it in vaseline and covering it with "bondo jelly" (poly resin mixed with silica.)

The silica 'jelly' mix would catch most of the detail and fill any small gaps. It sort of makes a 'gel coat' on the inside of the mold. To complete a mold, I would always back that up with a few layers of glass mat cloth and poly resin for rigidity.

If a mold was to be in several parts, you need to build up a flange to put bolts in. Once the mold was done, it needed to be polished inside to about 2000 grit, waxed thrice with mold wax, and spray coated with PVA release agent. (PVA dries to a "peel-able" vinyl film, separating mold from part.)

The hard part was putting the goop/glass in the mold to make the part. If you are making a fiberglass 'ball' for instance, you'd better make two half-balls and glue them together later, or you'd have no way to get the glass into the mold. Sometimes with small parts, you'd have to just put a lot of goop in the mold, and then bolt them together, letting a bunch squish out, but leaving all the voids filled inside the mold.

Something like a mask would be easier, since it's open-backed, and as simple as filling a 'bowl' with layers of glass and resin. A fancy ,stylized button would be more difficult, because all sides need to be finished.

For a bracket or something, there's a lot to be said for just taking a bigger piece of plastic and some sharp tools and cutting off anything that doesn't look like your old part.

[Nicholas Scheuer]

The rubber molding medium you are considering is RTV (room temp vulcanizing)Silicone rubber.

Silicone sealant out of a caulk tube works, but is higher in viscosity than pourable molding silicone. You need a "release agent" on the pattern in order to keep the silicone from adhering.

Moby Nick

[soba]

If you make a female mould and want to use silicone RTV, it's easy without specialized release agents.

Simply fill a bucket with water and add a healthy dollop of dish soap. Caulk a pile of silicon right into the soapy water. Now you can pull off a glob in the water, and mash it into your mold...the soap acts as a release agent. Works like a charm...we use it to make Hallowe'en masks and prototype metal parts. Best of all, because it cures flexible, you can make undercut moulds....

[Woxbox]

Any why not just whittle it out of a piece of wood? Much nicer looking than plastic.