by mattb » Mon Aug 08, 2016 7:21 am
When doing a 2 part mold, I do pull my masters out before I paint the mold release. I've found the silicone can run into the smallest opening and it won't come out if there is no mold release. I paint the first part, then put my pieces back in their positions before pouring the second part.
Looks like the silicone is the Alumilite from Hobby Lobby. I find that stuff so soft and flexible that I can glue a driver torso to the bottom of a small plastic cup and cover it with alumilite. After curing, I can remove the cup and push the driver out of the mold. I then cast a one piece driver in that mold and the rubber stretches so much that the driver will come right out.
Another trick I have used for two part molds is to glue a piece of sprue or something similiar to your master so the air can be released when you push both halves together. Otherwise most of your parts will have air trapped in the mold cavity and it won't fill up with plastic.
The alumilite is so soft and flexible that I have been able to mold a Cox Chaparral driver in one piece.
You guys doing bodies will find that Shotguns process is especially great if you apply it to a body. You will make a thin body in one cast and the inside will have the nice finish the outside does.
The casting thread is really good and all of us learn a bit from each other and make what we need. It was much like this back in the 80's when we had to make our tires and plastic bits. We didn't have this great communication back then.