For our final project, Eli and I decided that our chess piece should be the Google Chrome dinosaur (the game you play when you have no wifi).
First, just to test out the sizing, we printed out a model we found on Thingiverse:
We ended up slightly modifying the design, adding a base so it could stand on its own better.
After our sizing was checked, we designed and 3D printed the first positive.
This was our initial version, but based on advice from Dr. Wettergreen, we brought the pegs in closer to the piece and added more air channels near the mouth and arms. After reprinting, we glued cardboard around the positive to make a mold and poured in silicone. Our first mold half looked like this:
After this, we designed the CNC positive half in VCarve, made the tool paths and cut it out:
We then made a box around the wood and filled it with silicone again to make our second mold half:
Now that we had both our molds, we got to casting. We used ~30 mL of each part of the polyurethane cast and rubber banded the mold together. Unfortunately, our first go at it was not the best:
The main issue was a distortion around the dinosaur’s head, which we determined to be from the mold being too thin in that area, lacking structure. It took some trial and error, but we ultimately found that gluing a piece of wood to that part of the mold kept it straight.
We also had some issues with leaking, and considering the only polyurethane available when we casted was the one with a 30 minute set time, a bad casting wasted a lot of time. To get every cast as good as possible, we would push both mold halves together, rubber band them, hot glue the bottom (top of dinosaur) to ensure a good seal and structure near the head, and then use two pieces of wood to apply an even clamping. We’d also tilt the piece after pouring to get the polyurethane to fill the arms and mouth as best as possible.
Some of this might have been overkill, but considering a few extra minutes in clamping could prevent another 45 minutes in cleaning and casting, we thought it was worth it. In the end, we got 4 castings that we are pretty proud of.
Here are the 3D printed halves:
And here are the CNC’d halves:
Here is our cleaned workspace at the end
Here is our cost breakdown:
Wood: ~$2
Silicone: 200 mL x 2 molds x ($44 for 1800 mL) = $9.7
Polyurethane: 60 mL x 6 casts (including testing) x ($36 for 950 mL) = $13.65
Labor: ~20 hours each x $11/hour = $440
Total: $465.41
