I am making an action figure of a character in my 3D software as I was going to make his elbow and shoulder joints similar to these pictures. What I need help with is to figure out how to mold and cast these kind of parts. The two part casting for the shoulder I don't understand and can't wrap my head around it. Because once its molded and casted, there is a pin that is holding that disk in place in the shoulder but how did they mold and cast around the disk?? Also for the pictures of the Bicep and Forearm, what is the process for molding them? I imagine they would be two part molds but just not sure how to approach the holes that have a mushroom shape in them. How in the world could you mold that hole inside so when you cast the part you can capture that mushroom shape? Help would be much appreciated! Thanks a lot!