Design
I chose to do a one-sided mold of a ninja star! To begin, I followed the archshops tutorial on molding and casting to make sure my CAD design would be proper. Using Fusion360, I designed my ninja star:
Mill
I sent my design as a STEP file to Jen, who then spent quite a bit of time adding the right toolpaths in Mastercam. In essence, two drill sizes were used. A bigger one was first used to do a rough cut in order to get rid of the huge spacing (a smaller size would be more precise, but less efficient). The smaller one was then used in several iterations (e.g. create different layers) to smoothen out the edges to create the final cut.
Afterwards, we uploaded the file to the actual machine to mill the wax! Understandably, there were a lot of shavings to vacuum up.
Casting
Armed with the wax, it is now time to actually mold and cast! First, we create the Oomoo mold by doing a 1:1 mixture of compounds A and B. The compounds had surprisingly different viscosity levels. Next, we stir the mixture together well and shake the cup to make the air bubbles come up. After about 5 minutes of stirring and shaking, I carefully poured the mixture into the wax and left it there overnight to harden.
After it formed the mold, I mixed the dry plaster with water to form the solution to cast into the mold. The first time I tried it, I eye-balled the ratios, and I think I went with around 40/60 plaster to water ratio. This turned out to be pretty weak, as you can see below, with the star breaking right after I took it out!
Learning from the mistake, I did a 60/40 plaster to water ratio to make the mixture more structurally stable. I stirred and added plaster until the mixture was quite thick. Turns out, it did the trick! While the object still felt a little bit brittle/fragile, it still stuck together well.
