This is the story of Jeff and Brendan’s creation of eight moai chess pieces.

The Process:

We started by looking through Thingiverse and found a model for a moai chess piece that was posted by “SmileyBee.” After downloading the file, we uploaded it to a CAD software and developed the first positive that was to be 3D printed. We decided to 3D print the face of the moai because it was the most detailed section which would be best completed with the precision of the 3D printers rather than the CNC. We added a back plate with holes that would fit the two silicone pieces together, and then added walls to create a space to pour the silicone into. The process of 3D printing went smooth, and that positive was complete.

3D Printed Positive

Next, we moved on to creating the positive for the back of the moai using the CNC and a wood block. We created an stl of the back side of the file a plate that contained holes to fit into those created on the front side, and then inputted the file into VCarve and adjusted the settings for the cut using the recommended options in the assignment file. The CNC was going to cut straight into the wood, so we did not need to add walls as we would already be cutting a hole to pour the silicone into. We downloaded the VCarve files using the computer by the Nomad CNC, and then used the Shapeko to actually perform the cuts. We started off using a 1/4″ bit with a flat end to perform our roughing cut which took approximately 45 minutes.

Result of the first roughing cut.

Then, we used a 1/8″ ball nose bit to perform the finishing cut. However, during the first few minutes of the finishing cut, we noticed it was drilling deeper than it was supposed to, and the shape was not coming out correctly. After pausing the cut, we noticed that the bit was slightly loose and, as a result, was moved slightly lower than the height we placed it at during the cut.

First failed CNC cut

As a result, we started the same roughing and finishing patterns, but this time we made sure that we had placed enough of the bit into the clamp so that it would not move during the cut. Both our roughing cut and finishing cuts took 45 minutes each. During the cut, we had to pause it and use a file on the left hand corners so that the CNC could drill to the proper depth for the holes without the clamp hitting the sides of the wood, which was a successful strategy. After this cut, we had our back positive.

Finished CNC part

With both positives ready, we began the process of creating our negatives using the silicone molds. We filled the positives with the silicone mixture, and then left it to harden overnight, and when we arrived the next morning the negatives were complete.

Complete silicone molds

The final step was to complete the casting with the polyurethane. We wanted to create 4 gray pieces and 4 white pieces, so we combined 25ml of each part for the solution and mixed in black dye for the gray pieces, and white dye for the white pieces. We held the molds together with rubber bands and then filled the mold with the solution and let it dry and cool for approximately 20 minutes.

Polyurethane in the mold

We repeated the process until we had 8 pieces. Once the pieces came out, there was excess polyurethane around the space where the two molds met, so we used 220-grit sandpaper to smooth those down, and then the pieces were complete.

Final Pieces

Reflection:

We were satisfied with how the pieces turned out, but there are some things we learned from this project that we would do differently next time.

• Leave room for error in parts that need to fit together, and make sure to account for different tolerances for different methods of machining. We made the holes for the molds to fit each other exactly, but because the 3D printing and CNC methods were not exact, the holes did not fit one another. Luckily, they were able to stay together securely and in the right place by using the rubber bands.
• Ensure that the CNC bits are over half of the way into the clamp so that they will not sink during the cut, but also check to make sure that it is long enough to reach the depth that you need for the cut without any interference.
• When reserving equipment for a specific time period, plan out and ensure that we are fully prepared to use the equipment. There were multiple times when we reserved the CNC machine and then realized that we were not fully ready to complete the cuts, and ended up never attending the session. In order to stay on pace and maintain organization, in the future it would be helpful to plan out what needs to be done when on the equipment to be most efficient.
• When working with partners, it can be useful to plan and delegate tasks that can be done individually to specific partners, and not put both people on a job that doesn’t need two sets of hands. Some of the tasks for this project such as pouring the polyurethane did not require both people to be present, so, after reflection, we realized that it can be helpful to delegate beforehand who does what task to make the process more efficient, as we decided this last minute for some tasks which resulted in wasted time that could have been used on another task.

Overall, the project went felt like it went smoothly and we are confident that we could complete similar projects in the future with relative ease.

Cost Estimate:

3D print piece – (approx 50g at $0.04/g) = $2.00

Wood – 2″x4″x8″ pine = $4.00

Shapeko CNC Machine (2 uses @$10.00/use) = $20.00

Silicone Mold – $25.00

Polyurethane (for the 200ml of both solutions) – $20.00

Miscellaneous Supplies (popsicle stick, rubber band, cups, dye) – $8.00

OEDK Overhead Costs (staff, tools, etc.) – $20.00

Labor (10 hours combined at $20.00/hr) = $200.00

Total Cost: $299.00