I am starting a project to make a steel investment cast part. About 2" x 1" x 0.5". I'm thinking in the few hundred parts range, it will end up fitting in an assembly of mechanical parts in a machine, so here are my initial thoughts. 1. Shapeways makes a master. 2. I build a form and cast it in RTV silicone. 3. I got a little wax injection molder, so I shoot waxes 4. I send them off to a foundary to get cast in tool steel 5. I finish machine (reaming a pivot hole, and touching a surface grinder to clean up one edge). 6. Send out for heat treat. So, my questions I can think of are: 1. What material is best for my master? Presumably I want the best surface finish, though I could clean it up by hand. 2. Shrinkage. I assume 4%, though I would not apply shrinkage to my pivot hole, so it is 4% undersized, leaving enough meat for the reamer to clean up. What am I missing?