The Stormtrooper Chess Piece by Rachel and Thomas | ENGI 210: Prototyping and Fabrication

For the midterm project we were tasked with creating chess pieces out of a mold comprised of two halves, one 3d printed and the other carved/CNC machined. We chose to create 2 storm trooper “bishops” as we liked the detail in the chosen piece and thought it would look good as a chess piece, also we thought the sizing of the piece as a bishop would be appropriate. We used a file off of Thingiverse for our bishop and worked on the two halves.

We first used MeshMixer to split our file into the 3D printed side and the CNCd side. We did not end up splitting our file exacting down the middle. The back of the trooper was less detailed so we determined that we should split the file to create a back “half” that would be easiest for the Carvey to cut.

Additionally, we realized that the arms of the trooper would be problematic for both the Carvey and 3D printing, so we chopped the arms off in TinkerCAD.

We then added the two halves onto blocks and included pegs that would allow for the halves to line up. Our front side file was simple to finish as we just needed to upload the file into 3dprinteros. Our first print came out beautifully and we did not have to worry about it. However, the CNC side still needed a lot of setting up to do. We followed the step by step materials provided in the Google Doc for this assignment to prepare our file in Fusion360.

Finally, we were ready to upload the g-code into Easel and start carving.

Due to the height of our wood piece and the length of the chosen drill bit, we had to forego using a fan. This meant that we had to take turns sitting in front of the carvey and stopping the Carvey every 5-15m to vacuum up the material. This proved to be very tedious, taking a carve that should have taken 3h to almost 4h. However, it was all worth it, as our rough cut ended up being very nice.

This is where things started to go downhill. We went ahead with the smoothing cut, but very quickly had to stop the machine because the fan on the drill bit had dug into part of the wood. With the help of Dr.Wettergreen and Callum, we were able to figure out that the smoothing cut’s machine boundary was not selected correctly and should have just been around the back of the trooper, not including any of the pegs. We quickly fixed the file and uploaded the g-code into easel and tried starting the smoothing pass. Unfortunately, we very quickly realized that the carve was offset so we shut down the Carvey immediately. Luckily our part was minimally affected and we decided to go ahead and use our part as it was.

To create the silicone molds from the two parts, we created cardboard boxes of indeterminate size using a generous amount of hot glue. For the CNC’d half, we chopped off the extra wood to simplify this process. We mixed together the two parts (A and B) of the silicone and poured the silicone into the boxes. Unfortunately, both of the boxes for the 3D printed part and the CNC’d part started leaking so we had to improvise. We ended up using duct tape and even more hot glue to try and plug up the leaks which proved to be effective.

The silicone molds came out nicely and we were able to move onto pouring the liquid plastic. We carefully mixed the two parts of the plastic and very quickly poured it into the mold (which had been held together by the lined up pegs and rubber bands. Our first two bishops came out very nicely, however, we noticed that the two halves did not line up perfectly. The CNC’d half seemed slightly larger than the 3D printed side. We believed this was due to the fact that we were not able to finish our smoothing pass. We decided to fix this small problem during post processing by sanding off the extra plastic.