Week 6 - Casting and Molding

Chintan Vaishnav


I decided to create a mold for casting a lego block of the dimension of a real lego.

I had to dramatically scale down this ambitious idea: going from two part mold to one, and from perfect lego block to a paper-weight version (albiet of the actual size). The challenges were many.

Original Blocks

Mold for Milling (Top Piece)
Mold for Milling (Bottom Piece)


Only milled the top piece. Had to mill twice. The first time around, did not have the room for creating a base for the mold, so changed the drawign to create a base, and re-milled.

I used 1/8 inch ball-shaped endmill. This required to set the offset on the Fab module to 0.5 (when creating path) or in order to avoid a wavey surface. I learned about this later, so my mold will be wavey.

Finally, there were two people waiting to use the milling machine, so did not mill the bottom piece.

Milled Wax (Top Part)

Creating the Mold

This turned ito a huge mess. I first mixed the Oomoo in two parts, but may have had my proportion for Part A and B of the material (which should be 1:1) slightly off, or so I thought. The resulting mixure was very viscus and did not flow at all. I pushed it over the wax, but then realized there was no way to get rid of the air bubbles trapped. Then, out of panic, I tried to clean off the Oomoo from wax block, which turned into a mess. I then realized that I can just let it sit while I make another mix of Oomoo and remove the one on the wax block once it has settled, as it would come off easily.

Silicon mess after thick Oomoo mix

The second mix of Oomoo wasn't much better. I was sure I had the right proportions this time. The resulting mix was still too thik. I concluded that it was mostly because I was using the last scrappings of Part A and Part B bottles, and that the temperature in the lab was a bit chilly (Charles pointed me to this possibility). I now stuffed the wax block anyways to make a mold, despite suspicion that many air bubbles may be trapped.

After two hours, I removed the silicon from wax. The mold had air bubbles, but it wasn't as bad as I had imagined.

Mold with some air bubbles


I casted the one-sided mold with hydro stone. The mold had a slit on one side so the hydro sand was flowing out slowly.

Cast in Progress