For the final project, Ashley and I decided to work together!

Selection of chess piece:

We had quite a few ideas about what we wanted to CNC. However, many of them would have been difficult to cut in half and CNC (such as a squirrel king piece) due to the detail and curvature. We did want pieces that were interesting and intricate  so we scoured Thingiverse to find something to be approved by Dr. Wettergreen and Rachel. Based on that, we settled on until we found Kuchi Kopi from Bob’s Burgers!

To visualize how it would look, we printed the piece straight from Thingiverse without changing the size. It turned out to be enormous, especially because it is pretty wide.

Based on that, we decided to make our part about 7 cm. We printed out a 1:1 ratio to visualize how big that would be, then went ahead with the pre-processing of files.

Pre-processing: 3D-printing

To pre-process our 3D printed part, we first sliced the entire part in (almost) half with meshmixer. For 3D-printing, we kept the front of the piece since it had more detail and more curves, which would be harder to achieve with the CNC. After slicing, we added a base and pegs in Solidworks so that when molded, the two parts could fit together closely.

Pre-processing: CNC

For the CNCing, we used the back half of the piece. Similar to the 3D-printed piece, we added a base and pegs on Solidworks. To create the tool path, we used VCarve. We followed the video that Douglas posted on Canvas in order to create the tool paths in VCarve. At first, we tried Solidworks but it was too difficult and was causing some frustrations. VCarve was pretty simple to use and it was convenient to be able to download the Pro version on our own computers. From there, Ashely had to download the g-code on the computer nearby the Nomad and email to herself to cut on the Shapeoko.

3D-printing

With all of the experience we had with 3D-printing at the OEDK, printing our front half was very quick and painless! Here’s a look at our final part:

CNCing

CNC Maching was a headache. The roughing and finishing tool paths together was estimated to take more than 1 hr and 30 minutes on the Nomad. On the Shapeoko, it only took about an hour. We used a ¼ th end mill for the roughing path and the ⅛ th ball nose for the finishing. We wish we were taught how to extrapolate the things we learned on the Nomad to the Shapeoko. It was a larger system to get a handle of, but overall easier to use than the Nomad (and much more available). Based on the type of the wood, we were worried after seeing the completion of the roughing path. There were pieces of stringy wood everywhere, and it looked pretty rough overall. The way to change the bit on the Shapeoko was also difficult if you didn’t know how, but once we got the hang of it, we were able to CNC easily. The smoothing file turned out pretty great. Once that was done, we sanded the surface slightly to remove any debris left over.

 

Molding

To prepare the 3D-printed and CNC pieces for molding, we glued cardboard onto the sides to make a “container” that could hold the mold. 

We used the quick steps Dr. Wettergreen demonstrated in order to hot glue the four walls to the parts. (pro tip: make sure to put extra hot glue anywhere you might have doubts so the pseudo container does not leak!). 

When it came to molding, we messed up slightly in determining the volume needed. First we found the displacement of a 1:1 ratio 3D printed model made (80 mL). Then, we calculated the volume of the box, to about 1 cm above the highest point in the positive molds. Then we subtracted half of the volume of the chess piece to determine the volume needed to fill one mold. In total, we needed 360 mL overall. At this point, we didn’t consider the fact that our 3D-printed and CNC parts were slightly different sizes, and we had based our calculations on the smaller part. When filling our second mold, we were running about ~ 1 cm short. Thankfully, because the silicone has a longer working time (about 15 minutes), we were able to mix up a small batch and fill the last portion up. 

Once these molds were set, we were able to remove them from the positive molds. Because both sides were not the same size, they weren’t interfacing correctly when putting them together for casting. Therefore, we used an exacto knife to shave off extra areas. We also ended up cutting off the male pegs that would hold the two pieces together, since they actually ended up being male-male and female-female. During the processing of the files, we must have made a mistake in understanding which orientation was correct. To overcome this, we tried drilling holes and using pegs to keep them together, but because the molds were so flexible, it would deform when drilling and ended up with the molds not fitting together properly. Something interesting we noticed was how detailed the silicone was in getting the curves and sharp turns of the CNC or 3D printed piece.

Casting

The casting process was pretty fun. It was key to make sure that the sides lined up perfectly. It was a bit frustrating because after one piece was done setting, then you had to unravel the whole thing to begin the process again. This added small variability in the way each bear may look. However, because the set in about 15 minutes, casting each part was the quickest part of this entire project. We were also able to play around with the dyes to get fun colors. Here are our final pieces! 

Post-processing

For post-processing, we used an exacto knife to remove extra portions of the polyurethane where the two molds meet, and any extra parts at the bottom of the final chess piece. And now our final project is done! We were able to get a ton of new skills from this project, and our final parts turned out great.

Cost:

• Silicone: $10 for 300 ml
• Urethane: ( ~ 80 ml each bear * 8) = $36 
• Wood = (for 1 piece) $0.7
• Labor 15 hours * 7.25/ hour = $108.75
• Other items (PLA, Dye for casting, cups, gloves, popsicle sticks, rubber bands, carboard) = (free at OEDK)

 Total Cost = $155.44