[modelman]

Pricer-the blue mold you have pictured for your track pads looks simple enough and should work just fine. The tumbler is the nightmare to me. I would not ever try to cast a part like that. And yes, air is always a problem with a pour mold. Vent holes will only do so much. You may need a shaker table but with a part that complex I think injection molding is the only way. This is a very interesting project and I wish you good luck. And like you said, trying things is how you learn so I say go for it!!