# Plastic molds / Making plastic parts?



## greenLED (Jan 9, 2007)

I have some of that polymer you boil into liquid form and (am not afraid to use it). I want to make (somehow) a "clear" (midly translucent is just fine) plastic casing for my PT Eos.

Do you guys have any advise/ideas on how to make a mold to shape the plastic?


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## highorder (Jan 9, 2007)

you could make a plaster cast of the light, and use it as a pattern, or cobble something together in the shape of your light...

I would pour plaster or an epoxy into a Play-Doh mold, probably in halves.


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## DonShock (Jan 9, 2007)

I bought some of this Por-A-Mold to make some copies of some parts, but haven't had a chance to try it yet. It's a 2 part polyurethane that is meant to be poured around an existing part. Once it sets up, you can remove the original part and then fill the mold with whatever to make a copy.


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## greenLED (Jan 9, 2007)

Thanks for the ideas, guys. What I have handy is Shape Lock. My plan was to use that for the final part, but I'm not sure how it'd work for making the mold. Part of the problem is that the Eos case is sort of a concave shell and I'm not sure how to assemble a mold with that shape. What I'm trying to replace is the outer plastic casing of the Eos.


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## jch79 (Jan 9, 2007)

If you want help in funding the final project, I'd be happy to help - I think we have the same interests with this project, and although I might not be quite as handy as I'd like, any way I can help, I'd like to. I'm going to go home and stare at my EOS and think of what exactly can be done.

-john


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## hikari (Jan 10, 2007)

You might try using High Temperature RTV ("Silastic" by Dow Corning). It is a two part, room temperature vulcanizing silicone rubber compound. We use it to make molds for deep sea trolling lure heads and the lead inserts. If you get the High Temp version, it would more than handle the liquified plastic I would think (because we use it to make molds to pour molten lead into). I'm not sure if this would be suitable for your purpose--since there would still be some finish work required after removing your workpiece from the mold. The stuff works great for making molds to pour resin or lead into--you get extremely accurate reproductions with virtually no mold release issues.


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## LED Zeppelin (Jan 15, 2007)

I used to be heavy into plastic model kits, and had a guy that would cast custom parts for me from resin. The method was as Hikari described.

A two or more piece mold will need to be made dependent on the shape of the piece and how it will release from the mold. If it were a cup, you'd pour the outside shape, let it cure, then fill the inside using some release agent between the mold parts so they can be separated. 

The process can yield incredibly detail and accuracy, with the most common problem being pinholes from trapped bubbles. Depending on the shape and viscosity of the poured material (the resin is like milk), runners will need to be cut into the cured mold to allow the material to fill the cavity and air to escape.

Alternatively you could spread the material around the mold, then squeeze the mold together, but this is not as reliable or accurate.

There are methods to eliminate the pinholes also - by using a vacuum chamber to evacuate the air, then filling the mold by opening a valve while the mold is still under vacuum.


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## Any Cal. (Jan 15, 2007)

Some people use latex to make molds for plaster. Use a release on your case, then paint it on. You can use pieces of paper to add strength once you have a couple coats on it. The latex will stretch, so it needs to be reinforced a little. High relief molds will require the mold to be cut in order to retrieve the part, but it can be put back together later.


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## lrw2 (Jan 15, 2007)

dental alginate is another option to look at, though I don't know how it holds up to boiling temps.


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## greenLED (Jan 16, 2007)

:thinking: This sounds like it may be more complicated than what I expected... :thinking:


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## IsaacHayes (Jan 16, 2007)

That stuff doesn't pour easy does it punk? I think for a 2 piece mold you'll need something pour-able. Maybe 2-ton epoxy or some acrylic resin kit or something?


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## hikari (Jan 18, 2007)

lrw2 said:


> dental alginate is another option to look at, though I don't know how it holds up to boiling temps.



...and dental alginate does not have an extended life. It dries out and falls apart after a while.


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## will (Jan 18, 2007)

There is some stuff that Model Train people use to mold various parts. The mold is a rubbery stuff that can be peeled away from the molded part. 

How big is the part you want to mold? - how many are you making?


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