Best material for a master to be investment cast

Discussion in 'Finishing Techniques' started by ShootingSight, Jul 4, 2012.

  1. ShootingSight
    ShootingSight New Member
    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?