This week I decided to make a chess piece: a pawn.
I first designed the piece in FreeCAD. After reading a lot of online tutorials, I realized the best way to make a shape with complicated contours like a pawn is to use the "Loft" function in FreeCAD. This function can take several two dimensional shapes along the Z-axis and connect them into a smooth solid. To make the pawn I made 12 concentric circles of various diameters and then moved them along the z-axis. I then used the Loft function to connect them. Afterwards, I also added a sphere to the top.
Making this piece entails making two identical molds so I needed to somehow cut my piece in half. I added a rectangular prism that covered half of my design. I then added protruding borders around my piece for the mold. I also added four spheres for marbles within my mold but outside my piece. This was a trick we were shown in section for aligning two molds.
I milled a block of wax using the Shopbot in the Harvard Science Center basement. I attached the block to a piece of scrap wood using a hot glue gun and then attached the scrap wood by drilling in screws.
I used a 1/8 inch end mill to make my piece using first a rough cut and then a finer final cut.
The design came out well, although I had to clean it up a bit with a knife.
I made my rubber mold by pouring liquid rubber (Oomoo 25 rubber silicone) into my mold and waiting 2 hours.
I then took out the first mold and pouured Oomoo in again to make my second mold. I put marbles into the first mold.
After another 2 hours, with both of my rubber molds ready for action, I was finally ready to cast my piece. I used SmoothCast Color Match liquid plastic.
After pouring some into each of the two molds, I taped the two molds together (aligining them with the marbles) and poured some more plastic through the top hole. I then waited 30 minutes and took my piece out of the molds. The outline of the figure was made, but it wasn't solid inside, largely becuase the plastic leaked out before hardening.
I also tried it with Drycast but had the same issue as it leaked out. Exhibit A: A Mess
