Einstein Bust and Cold Casting

[jaco...@gmail.com]

For my first project I decided to make this bust of Einstein https://www.thingiverse.com/thing:966908 . I used a 3" X 3" cylinder of machinable wax. The file is an stl and seemingly limits me to 3+2. Due to the file size limit on the PNC I had to break it up into 24 tool paths between 3 different end mills (the stock single flute end mill and a 1/16" ball nose and finally 1/32" ball nose).

The PNC vice wasn't able to grip the wax well enough before it would just sink in so I used this method I saw on NYC CNC. https://www.youtube.com/watch?v=r6DCvtcU8_M
In short you apply a layer of painters tape to your B table, apply another layer to the bottom of the wax. Apply superglue onto the wax tape and then place the glue side down on the B table. To align the cylinder I moved the end mill to be perpendicular to the cylinder axis to be used as a proximity guide and jogged the B axis by 90 degrees, moved the cylinder, rotated another 90 degrees, adjusted, etc until it looked centered. I used a 2" stainless steel cylinder to weight it down for a hour.

After I was done machining (~16 hours splits over 6ish days), I used a two part silicone mold mix and made a negative of the wax Einstein. I then used a two part epoxy and mixed in fine bronze powder (2 parts epoxy to 1 part bronze). Poured the mixture into the silicone mold and pull out the cold casting the next morning. Several tutorials online made it seem easy to polish the cold cast bronze, but I discovered that due to it's density and my poor mixing skills that the bronze powder settled unevenly and the face was very hard to polish at all. After a few hours with mineral spirits and Brasso I settled on what you see in the below photos. I may try to cast another one as air bubbles are present all over the cast.

https://imgur.com/a/JodevDV