Team: Scott Fessler, Haruto Sasajima

The goal of this assignment was to cast a chess piece using a combination of CNC machined and 3D printed molds.

Our first idea was to create Barad-dûr from the Lord of the Rings franchise as a rook piece. We decided to use a model of the tower on thingiverse that we liked. The model is found here: https://www.thingiverse.com/thing:3026187. Since it was a fairly detailed piece, we had to make edits to the model ourselves in Fusion 360. One edit we had to make was to eliminate parts that would be impossible to CNC, such as the outer wall that stuck out from the tower. To solve this issue, we first cut the tower in half and then mirrored it, so the tower was made by the two back halves as seen in the picture below.

Since this tower is designed to be a dice tower, there were large noticeable holes at the top of the tower. We tried several methods from using the mesh tool, patch tool, and using a sphere to block out the hole. However, none of these methods proved to be effective and we decided to create an entirely different piece instead.

We then found this model and decided to use it as our knight piece. It has the torso of the greek playwrite Menander, but the head of a horse. To check the level of detail and whether it could stand by itself, we 3D printed the complete piece which can be seen below.

The 3D print turned out well, and it was time to move on to creating our molds. Because our knight piece was not symmetric, we first had to split our piece in half to create a front half and back half of our mold. We followed the instructions given to us on Canvas to create positive molds of our halves. We decided to use the 3D printer to create a positive mold for the front half of the piece, because it was significantly more detailed than the back half. We used fusion 360 to add the base, pegs, and pour hole to our halves.

Since the front half mold was going to be 3D printed, the back half mold had to be created on the CNC machine. We used Fusion 360 once again to create a gcode of our back half that Easel could understand and use to mill our mold.

After setting up the gcode, we were ready to put it into Easel for use in the Carvey.

We ran into issues with the Carvey as well. One of the screw holes for the clamp was completely stripped, meaning we couldn’t set up the calibration clamp correctly. We ended up having to duct tape the clamp to our piece of wood to prevent it from moving around during the milling process.

Our CNC mold turned out quite nicely.

Using cardboard and silicone rubber, we were able to make negative molds out of silicone rubber using our CNC’d positive mold. We set up cardboard walls around the mold and let the silicone rubber dry inside them. After it had dried, we were able to pull out the silicone to get our negative mold.

We also 3D printed our frontside half. Using the exact same process as we did with the backside, we used cardboard and silicone rubber to create our negative mold of the front half. It also turned out very cleanly like the back half.

Finally it was time to put the two silicone molds together to create a complete negative mold for our entire piece. We ran into a problem here as the pegs didn’t end up matching up with each other. We ended up using an X-acto knife to cut off the pegs because they served no purpose. We then carefully lined up the molds and poured in our liquid plastic for our piece. We used rubber bands to hold the molds together. Our first mold turned out pretty well, but there were small air bubbles near the mouth.

Overall, we were pretty excited and surprised with how well our first mold turned out. We tried several other attempts afterwards but it went by pretty quickly because of how fast the plastic would harden. Our two main problems that we experienced during these trials were air bubbles and misalignment. Sometimes when the plastic would expand it would misalign our molds. Air bubbles were also an issue if we weren’t careful when pouring the plastic into our molds. We tried solving these issues by pouring in the plastic at a slower rate, and physically holding the molds together instead of just relying on the rubber bands. After several attempts, we were finally able to get two casted horses that we were satisfied with.

It was now time to post-process. We used the belt sander to quickly sand down the pour hole and then used some rasps and sandpaper to smooth out the shoulders and sides. The picture below shows what the horses looked like after post-processing. We decided not to paint it anything because the white plastic already gave off a “marble” texture that we liked.

Overall, we are very satisfied with how our knights turned out. The details came out very cleanly and it stands very stably as well. We learned that casting the pieces using two separate molds is a lot trickier than we initially thought, and from our mistakes we were able to further our knowledge on the process of casting and molding.

Cost Analysis:

PlatSil 73-25 Silicone Rubber: $286.00

EasyFlo 60 Liquid Plastic: $123.00

2 in. x 4 in. x 96 in wood: $31.80

https://www.homedepot.com/p/Alexandria-Moulding-Douglas-Fir-S4S-Mixed-Grain-Board-Common-2-in-x-4-in-x-96-in-Actual-1-5-in-x-3-4375-102X4-DM096C/206876539

PLA: $2.07

Prusa: Free OEDK use

Carvey: Free OEDK use

Labor: 18hr ($12/hr) = $216

Total: $658.87