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Discussion Starter · #1 ·
I got the idea to cast hopup arms from two part resin, and eventually start casting custom nubs into them as well (SCS/PSCS anyone?
)

First off, I need a mold. I was thinking of using plaster of Paris, considering its pretty cheap, and I couldn't source any RTV silicone. Yay? Nay?

Also, what would you guys want for nubs prongs, etc?
 

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Having been a professional model maker for many years and used to cast my own resin and white metal figures I'm gona have to say your gona have to find sum silicon bud.

Plaster of paris is highly rigid so would be a one shot wonder per arm you manufacture, making it totaly cost ineffective.

With silicon rubber you'll get hundreds from the same mould before it'll need replacing.

What you will probably also find is that you'll end up throwing about 50% away due to bad casting unless your very careful.

You'll gleen the best results from a 2 part mould but again you'll have to make sure you key the molds very carefully or you'll end up with one half out of kilter with the other.

The best place to source all you'll need, and more, is a model making supplier on the tinterweb ;)
 

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Discussion Starter · #6 ·
Heres and update: I threw caution to the wind, made a basic clay mold, poured epoxy into it. I had my measurements a little wrong, epoxy was a tad squishy, but I got somewhat the basic shape.

Vindi, do you have any guide that could lend me a hand? Im a total noob when it comes to this. Also, How what would the best way to make the silicone mold, the prongs are what im worried about.
 

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Try this http://www.resincasting.co.uk/

Havn't read through it myself but from what I have read it should point you in the right direction ;)

If your resin was still 'squishy' I'd say you either took it out the mould to early as the hardener hadn't finished doing its thing or you never put enough in to harden the resin all the way through before it stopped working.

If you want to speed the curing process up wack it under a hot lamp or another heat source of some kind for 15 - 20 minutes.

The RTV mould rubber is basicaly the same but alot thicker. I used to make my rubber former from lego bricks about half inch bigger all round than the thing I'm casting.

Don't forget mould release agent, you can use baby talc powder or I used to use liquid vasaline/petroleum jelly.

Another trick I learned on high detail moulding was to paint a little pre-mixed resin into the mould before doing the final pour.
 

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Discussion Starter · #8 ·
Thank you for the noob spoon


Im unsure on how to pour the RTV over the arm as the prongs make it a PITA.

I was thinking put the flat top of the arm facing away from the mold and pour on top, bot how would i get it out? RTV would seep through where the slider and pin go and hold it into the mold...
 

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I've been thinking about this problem earlier on and came to the conclusion I'd mould it on its side and use the tip I gave above about painting in some resin before the final pour into the bottom prong, Its the only reasonable way I can think of doing it.

Your other option it to not try casting the prongs 'in situ' and mould them as a solid lump giving the option for an extended high pressure nub for heavier bbs or the nub could be filed into the shape of preference at a later date.... just an idea :-/
 

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Discussion Starter · #10 ·
RTV is fairly flexible right? The prongs shouldn't be a problem then, ill just have to do some twisting.

But, Ill probably order some RTV tomorrow afternoon, so stay tuned
 
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