The Process:

In the final project for EDES 210, our team of three included Kyle Tam, Ellena Jeon, and Ryan Purdy. We were tasked with casting 2 3D chess pieces. We selected the 3D model we would use to cast our piece. At first, we planned to cast a model of the Empire State Building, but since the Empire State Building was previously done multiple times, we decided to change our chess piece file to Ditto. Ditto is also way cuter than the empire state building:)

Once the model was downloaded from Thingiverse, we sliced it in half using MeshMixer. We exported each half of the model as an STL and brought each file into SolidWorks. We added a base with pegs and holes to each model and then exported these positive pieces as STLs.

We printed one of the positives on a Bambu FDM printer, and the other was cut out of wood using the CNC mill. Before we cut, we needed to prepare a toolpath for the cut in VCarve, which included a rough pass that would remove most of the wood and a finishing pass that would add more detail with a ball mill. Once the file was prepared, we started the cut on the Nomad CNC. The rough pass ran successfully, but the finishing pass could not reach the lowest point of our cut without scraping the walls of the piece. We were forced to stop the cut early, but the finishing pass had already detailed the actual model adequately so we could move forward.

Now that both positive pieces had been created, we began creating the negative molds. We built a cardboard box for the 3D printed positive to provide a barrier for the mold covered in a copious amount of hot glue to guarantee a watertight seal. Then, we estimated the required volume for the mold and mixed the silicone accordingly. The mold was calculated by measuring our mold’s width, height, and length. Then, we subtracted the volume of the Ditto. The whole mold was 12 cm x 7 cm x 3 cm = 252 cm3, and our pieces were 6 cm x 4 cm x 2.5 cm = 60 cm3, which was divided by half to account for the fact that the half Ditto is shaped like a triangular prism. Therefore, the volume of our piece was 30 cm3, which makes the volume needed for our silicone mold to be (252 cm3 – 30 cm3)/2 = 111 cm3. After pouring the mixture into the mold, we left the mold to cure overnight. We then repeated the same process for the CNC positive piece.

Below are pictures of our silicone molds being created:

Once both molds were complete, we discovered a major mistake: the pegs and holes in each base were in the wrong positions, so the two pieces were incompatible. To bypass this, we cut off the pegs and aligned the two molds as best as we could without them. Because the silicone material is not rigid, the mold still fits nicely together, but there were still some misalignment issues when we began casting the chess pieces. The two molds were at slightly different scales, which we only realized after casting the first piece. However, these inaccuracies could be easily addressed through post-processing. 

We made sure our calculations were correct by re-measuring the size of our piece. We determined that 60 mL was the appropriate casting mixture to fill our mold using similar steps we took to measure the piece for our silicone mold. We divided this by half (30 mL) to determine the required volume of parts A and B. Because the mixing beakers are not accurate in terms of volume, we measured out 30 mL of water using a graduated cylinder, poured it into the beaker, and marked the point where it hit the 30 mL line to have a more accurate measurement of the material so that we do not waste any material. We poured the 30 mL of part A into a bigger tub and then poured 30 mL of part B, starting the timer for 2 minutes simultaneously. We set the timer to 2 minutes because that is the time before the casting material begins to cure. We waited 8 minutes for our piece to cure completely. We witnessed the material becoming hot as the reaction happened, which was pretty cool. After a total of 10 minutes, we were able to pull our piece out.

Because of how large our piece was, we had to confirm with the TAs and Dr. Wettergreen to limit the number of our pieces to 2 pieces. So, we repeated this casting process for the second piece, adding a blue dye for a fun color to part A this time. Finally, our 2 Dittos in white and blue are ready for post-processing.

To post-process, we used an exacto knife to smooth out the misalignment and sandpaper to smooth the roughness. When designing our mold, we also created a bottom stand for the Ditto to stand correctly, which was cut out with a band-saw. 

Cleaned up workspace:

Cost Analysis:

• Silicone mixture 111*2 = 222 mL  222mL = 0.0317006gal
  • 0.0317006gal*$145.00 = $4.43 (AeroMarine)
• Wood Block for CNC Machining $2.98(lowe’s)
• CNC Machine Rental $60*1.5 = $90 (practical Machinist) 
• 3D Printing Rental 25*4 = $100 (texas filament supply)
• PLA filament $13.98 (amazon) 
• Casting Material 60 * 2 = 120 cm3 = 4.05768 oz 
  • 4.05oz*$40.99/64 = $2.59 (amazon)
• Labor: 10hours * $15 = $150

total: $362.98