Casting Part Problem

Posted in Custom Workstation

Okay, so I have an issue. I'm trying to make casts of the joints that connect the knees to the legs, or the hinges that connect the shoulders to the torso.

The problem is that when I cast them, they don't harden perfectly like the larger pieces. I've tried heating the mold to high temperatures, but the parts are still slightly flexible. I've noticed that a thin piece connected to a larger piece will harden correctly, but I don't know why.

I'm considering using a clear resin to cast the parts, but it takes 2 full days to harden correctly.

Does anyone have any advice on how to get the casts to harden properly? Unless they do, the parts are too fragile to use in custom figures.