First, we selected a hexagon-style knight chess piece from Thingiverse. We made sure the piece was symmetrical so that we could create two opposing positive molds from it.

Thingiverse File

Mold

During class, we split the knight in MeshMixer and removed one half. Then, we built a back plate using Fusion 360 and added 4mm thick positive prongs. We added sides to the base so that we could pour the silicone directly into the 3D printed pieces rather than using cardboard for sides. We lined up the chess piece with the base of the wall to create a pour hole. Then, we created the opposite half of the mold by inverting the prongs into holes and slightly increasing the diameter of the holes so that the prongs would fit properly. We then proceeded to print the two halves of the positive mold at 75%. Then we casted the negative silicone molds. We used a 1-1 weight ratio of yellow and green solution to pour our molds. 

Initial Fusion360 Files

When we took the negative molds out of the 3D printed positives, we realized that while we did correctly invert the prongs on the mirrored part, unfortunately we forgot to mirror the actual knight part of the file before 3D printing the file. To fix this, we mirrored the part in Solidworks.

Mirrored File in Solidworks

As expected, we had difficulty finding an open printer to fix the mistake. When we finally got on a printer, we resized the file to 75%, as we thought we had in the original prints. When the print was done, we realized that the original prints were actually resized to 80% not 75%. 

Final Mold

At this point, we were running low on days to complete the project and did not want to continue re-printing and wasting materials, so we decided to proceed with casting our chess pieces even though the two mirrored halves are slightly different sizes. If we were to do this project again, we clearly learned the importance of slowing down to double check the files we are printing make sense, and the settings we use on the 3DPrinterOS website are consistent between iterations if trying to make parts match previous parts. We were trying to hurry and get prints started when we had time in the OEDK between this class and finishing all of our other final projects, which ultimately led to more work for us. 

CNC

We started producing the CNC file during the in-class tutorial. However, we were not able to fully complete it. We followed the instructions provided to complete the file independently. As explained previously, we used MeshMixer to split the body and pre-process the file reducing the triangles to 10,000. Then, we uploaded the file into Fusion360 and created a Meshbody. We scaled the file appropriately, because when importing the body it was scaled up exponentially. 

Once the mesh was created, we entered the CAM menu. We had to download the easel tool package linked in the instructions. We followed the detailed directions to setup our piece. We created 2 separate setups. First, we made an adaptive setup which created the first toolpath using a basic drill bit ensuring it was long enough to cut through the material. Next, we created a smoothing setup which is a toolpath used to refine the cut choosing a smaller diameter, more precise drill bit. Finally, we imported the g-code into easel, which can be used to CNC our half-body.

Cast

We successfully produced 8 uniform hexagon-style knight chess pieces. We casted these pieces using our molds which were slightly mismatched in scale. Because of this, we had to align the shapes within the molds perfectly to achieve a cohesive look. We used wood blocks on either side of the molds and rubber bands to secure them in place. We let the pieces cure for ~15 min after removing them from the molds.

 After some trial and error, we successfully produced 8 consistent pieces. For post-processing, we used sandpaper to sand down the imperfections of the knight pieces. 

Post-Processing and Final Chess Pieces

Cost Analysis 

• Labor 8 hours at $15/hour = $120
• PLA ~$10
• Silicone mold ~$25 (cost high due to 2 mold iterations)
• Plastic casting liquid ~$25
• Rubber bands and scrap wood for jig ~$2
• Sandpaper ~$2

Total Cost ~$184

CNC not included in cost since we only produced the file not the piece. Fusion360 and 3D printers not included as they are included in OEDK access.