Fab Academy – Molding and Casting

By: Rob Adams on March 25, 2013

Casting and Molding

I was particularly interested in doing the casting and molding this week, and I was fairly pleased with the results, considering it was my first time. The biggest challenger was designing the mold. I wanted to make a mold for a dog biscuit, since one of my businesses is a pet magazine, and last weeks lecture brought to mind making a food safe mold. Since I wanted to have the words DOG and HUMAN imprinted on the bones (to indicate what type of treat), I was trying to figure out how to make a positive mold in the machineable wax, and keep the words correctly positioned. I spent way too much time thinking about this basic question, to the point of confusing myself. So I decided to proceed with a design and see what would turn out.

I used TinkerCAD for the design work and then imported the file to Modela Player, since that computer does not have Fab Modules installed. In the process of setting up the file to being milling, I pushed NEXT, thinking thast would take me to the next setting, but instead started the milling process with a 1/8″ bit. I decided to let it continue and as it turned out, the mold looked OK, aside from some tool marking (I think this was because I had set the bit too low). I did a second run with the finish setting, which removed the tool markings.

Next I mixed the Oomoo and made the flexible mold. I had a bit of extra rubber, so I also made a mold of a 3d printed lego shield, set inside a round tin. Despite the directions indicated 75 minutes wait, in 120 minutes, I felt the molds were no longer sticky and removed them. As seen above, the bones mold came out well, but the lego one did not. I think that this was because I tried to remove it before it was ready.

I did not have Hydrostone or Drystone on hand, so I opted for plaster, with decent results. One of the bones broke in the middle because, again, I had not let it dry enough. I think my big lesson of the week is: double the expected drying time – probably a good rule for most things.

I enjoyed this weeks lesson more than the others, and look forward to experimenting with other forms of casting and molding, especially with different substances.