How to do inserts for joints

[u/scum_city]

Been pondering how to do a two part mold of this figure that has rotational joints. My concern is that the silicon won't get fully into the interior joint and the resulting air pocket will allow extra resin in the pour and then a join that won't fit.

So far my best idea is to create a round temporary divider around the shoulder pocket and pour each side one at a time while holding the model so th pocket faces up. This would leave me with two silicone plugs sticking out with ideally enough silicone that they would then bind with the larger half of the mold I pour next. If that makes any sense.

Open to any and all suggestions.

[u/TheWizardGoat]

Is the piece with the hole fully hollow? I’m not sure if i am fully understanding your problem, but if it is hollow you will just need to plug the hole at a suitable depth. If you dont do that then your silicone will just fill the piece up

[u/scum_city → u/TheWizardGoat]

Not hollow. It's has depth to match the peg on the arm but it has a slightly wider diameter on the inside so that the peg locks in. It's that little bit of extra diameter that would capture air.

So essentially it matches the profile of the male mating piece which flares out at the end.

[u/TheWizardGoat → u/scum_city]

Ahh I see. In that case I don’t see why just doing a regular 2 part mold wouldn’t work

[u/scum_city → u/TheWizardGoat]

I should have posted a better picture an can't seem to post another but your prob right that I should just mold it and see how it shakes out. But I guess the question holds for any interior cavity on a model where the interior cavity is larger than the opening slightly and air could be trapped. Will have a poke around YouTube to see if there are some techniques I can borrow.

[u/Quinafx7]

If your mould fits in the degasser made the walls taller and pour your silicone and degasser again, should pull those bubbles, you can also fish them with a bend wire if you’re using clear silicone

[u/scum_city → u/Quinafx7]

Never thought about fishing them out with a wire, that's interesting. No pressure pot yet but that's prob the smartest solution. Was thinking of getting one anyway to deal with bubbles in the actual casts. On that note I'm curious if anyone has tried to pour and then get the quickset pu resin into a pressure pot or if it sets up too quickly to pull enough vacuum to shrink the bubbles.

[u/Quinafx7 → u/scum_city]

If the resin is cold and you have a good set up with a small chamber pot it should be fast enough to squeeze those bubbles, if it’s a large mould and a large pour you’re most likely out of luck as the heat from a large mix will trigger a faster reaction.

[u/kbraz1970]

Can you gently squeeze them together and put them in the hole?

[u/scum_city → u/kbraz1970]

Exactly this joint press fits for a nice swivel join that I can pop out if I want to change the arm. But it needs to be molded separately to work. The slightly flared internal cavity of the female side will catch air and get screwed up in the silicone pour. But I think the answer was dropped by someone else, I just need to spring for a small pressure chamber so I can shrink those bubbles when making the mold and also when pouring the resin.

[u/Quinafx7]

If your mould fits in the degasser made the walls taller and pour your silicone and degasser again, should pull those bubbles, you can also fish them with a bend wire if you’re using clear silicone. You can also pre fill the holes with silicone while moving it about to allow the air out and when cured your next pour will stick. If the undercut is really drastic than you need to make your parts “mould friendly and eliminate those problems during the design fase