Week 7

This week, I explored molding and casting.

Mold design

At first, I wanted to make a dice with a skewed expected value depending on the roll axis, i.e. 1 across from 2, etc.

However, after molding the die, I realized that I could not do this with only two mold parts. I decided to go for a simpler design: a ring.

I used the Roland SRM20 to mill a block of wax. The rough cut took about 2 minutes, and the final cut with a 1/64" bit took about 20 minutes. Even though it was a very small design, it took a substantial amount of time because milling is subtractive.

The Oomoo was easy to use, and I did not use measuring cups and instead eyeballed the 1:1 mix ratio. After 75 minutes, the mold was complete and immediately ready for use.

I used a small clamp to hold the parts together and poured a bismuth alloy (melting point ~280F) into it.

I only had to wait one minute and the cast was complete!

I still have to remove the sprue and vent attachments.

Tips for the week

• One/two part molds really restrict your design
• Start with model, then make mold, then make mold for mold, all as different components
• Remember to add sprue, gate, and registration
• Rough cut with 1/8" xy only, final cut with 1/32" or 1/64" takes much longer
• Stepover 0.5, Speed 10, Remember to rotate STL if needed
• Beware collet length and that milling machine home is a lot higher
• Use compressed air and needle (for holes) to get rid of shavings
• Stir oomoo back and forth, not circular
• Use a clamp to hold two part mold together