Another blog post coming at you from Cole and Serena after midnight? So unexpected. At least its not being written in class though, right? It’s our last one so please enjoy.

For our final project, we were tasked with making a chess piece using machining, molding, and casting.

Part Selection

For our final project, we wanted to choose something awesome yet simplistic. We decided a rook was the best way to go to achieve this — it’s radially symmetric and still an interesting shape. We grabbed “Torre Ajedrez” off of thingiverse — apparently it looks like the Stanley Cup?

MeshMixer

Next we opened the Torre Ajedrez stl file in mesh-mixer. Our main goal here was to fill in the little window cuts in the top of the part to make it machinable, and to cut the piece in half and export it as a binary stl file so it could be opened in Fusion 360 as single body. We used a plane cut and with lots of skill and dexterity rotated the plane cut exactly 180 degrees so it divided the piece in half along the long axis.

Next we had to decide the number of triangles we wanted our binary stl to have. I think we started with something insane like 100,000. This led to frozen screens, lagging programs,  frustration, keyboard banging and more than a few curse words (see here for reference on our mood).  We calmed down (eventually) and went back to the drawing board where we changed the number of triangles to 15000. Still more laggy than we would have liked but improvement nonetheless.

Fusion 360

Fusion 360 was hands down the best part of this project!!! <3 <3 :))))))) HA lol no. We went through way too many versions of our design (see pic below).

Here’s a brief overview of our eons-long battle vs Fusion 360.

First, switching the view: We spent a long time messing with axes and trying to follow the directions, but later realized the key was orienting the axes in an acceptable manner and then right clicking the top of the view cube and selecting “set as top view”. We set this view as “home” and all was well. Honestly, this took us an entire class period to figure out.

Next, we extruded the block that the piece was to sit on, along with an air channel and pins and holes to connect the two molds together when casting. This all sounds pretty tame but I guarantee you Fusion 360 made this miserable for us (most likely because we still had too many triangles).

Once we had the model the way we liked it, we moved into the CAM prep portion. We chose to do two cuts — a rough and a smoothing. The rough cut took care of removing most of the material. It used a ⅛ inch ball drill bit, a step down size of 0.1 inch, and a feed rate of 7.5 in/min (about ⅕ of the original 30 in/min). The smoothing cut consisted of parallel cuts in a cross hatch pattern to smooth out the surfaces and further define the contours. For this we used a 1/16 flat drill bit, with the same-ish step down size and feedrate.

Carvey

With the CAM files on hand, we took them to the carvey via easel. We chose to do a test cut on a block of wood initially. Turns out boundaries of the cut were too close to our stock, and the carvey ended up carving outside of the bounds of the wood, rendering that cut useless for creating a mold. We let the cut run for a little longer however to see how the step down and feedrate would work when cutting around the piece itself. An overall summary of what we learned from this trial cut: move the cut further away from the edge and center the piece in the middle of the cut so that we would only have to make one mold (yay for symmetry!).

On to the final cut — but out of wax this time. We thought this might come out cleaner and cut easier than the wood. It cut SMOOTH LIKE BUTTA. Really mesmerizing to watch, too. The first rough cut took about 1.5 hours and the smoothing cut took about 1 hour (we sped up this process a bit by upping the feed rate when the carvey was making straight passes along the planar surfaces, and only slowed it down to normal speed for when it passed over the holes or the piece itself.

Molding/Casting

From here on out, everything was pretty straightforward. To create the mold, we poured the silicone mixture into the wax part. We put this in the vacuum pump to get all the air bubbles out of the mold to make it smoother. We poured two molds in total.

In terms of casting, we strapped the two molds together using wooden blocks and rubber bands. The molds were lined up really well with respect to each other because Cole is really good at being a perfectionist and won the Eclipse award for “most likely to measure something to the 0.0001 inch” award for a reason. Thank god though because the chess pieces came out nearly perfectly. We poured in grey, orange and blue, and then decided to do a marbled piece just for the heck of it.

Post Processing

Post processing was pretty easy with such clean parts. We used an exacto knife to cut off the edges of the base that had overflowed slightly, sanded these edges, and sanded the bottom to be flat.

Overall, we are pretty happy with the way our pieces came out. We realized that a little more effort towards the beginning of the process (getting the CAM file right, using the right materials, vacuuming, etc) really helped down the road in minimizing the amount of trials to get the pieces right or post processing necessary to make the pieces look good.

That’s all folks.

Peace, Love, and ENGI,

-Serena and Cole