We are at the final project! John and I (Anna) worked together to CNC, mold, and cast a bishop as our chess piece. We picked a file off of Thingiverse for a simple bishop piece by lylebclarke that looked like a cartoon of the eponymous religious figure.

However, we realized that the Thingiverse file, being created in Tinkercad, had a low number of polygons, resulting in a blocky .stl file. Therefore, we decided to recreate the piece in Tinkercad and make use of cross-platform compatibility with Fusion 360.

Once we got the file properly transitioned to Fusion 360, we started going about making a test cut. We split the piece down the seam using Meshmixer, and named one half ‘left’. The other side, due to an argument involving relative perspective, was dubbed ‘other left’ given that the bishop would regard it as his left. This name stuck throughout the design process. The handmade Fusion 360 tutorial Dr. Wettergreen was a lifesaver for going through the new program and preparing gcode.

Next, we tried running the foam cut, to confirm that we have the settings properly calibrated and the file properly prepared. (Spoiler: they weren’t.) At first, the Carvey’s dremel bit hovered uselessly in the air above the foam and wiggled around. Turns out, the origin of the block in Fusion 360 needs to be at the top corner of the stock, rather than the bottom. Once we sorted that out, we ran it again and got the photo at the left: the sad circle. The block of foam was at the awkward no man’s zone between clamp sizes on the Carvey, meaning that we couldn’t really clamp down the block. To solve this, we hot glued the foam to a sheet of 1/4″ plywood and clamped that down with side clamps, as well as raising the foam up enough to be clamped. Finally, we were able to get successful contact.

Before running a full cut, we wanted to add our extra features (alignment pins and pour hole). However, none of the 3D modeling software we had used so far felt like it would allow us to efficiently add these features. Therefore, John decided to use Google Sketchup (since the Pro free trial works with .stl files) to add the features. Finally, we used these new files to run a complete foam cut of Other left, shown below.

We ended up using 2 passes for our wood carves, a roughing pass with a 1/8″ fishtail bit to remove the bulk of the wood, and a smoothing pass with a 1/16″ fishtail bit (since we don’t have any 1/16″ ball end bits yet) to smooth out the contour lines. Due to scheduling conflicts during finals week, John and I decided to each carve one half independently and reconvene for molding and casting.

I hung out with the Carvey for the hour-ish it took to run the roughing pass, and found it full of sawdust. I figured I should clear that out, so I removed the block and brushed/knocked most of the debris out before carefully putting it back in the Carvey and running the ~20 minute smoothing pass. The bit seemed to be digging into the piece, but I guessed that was getting it closer to the true form of the bishop. Here is the piece without detail around the collar after the roughing pass, and more defined after smoothing.

John then ran his piece independently, after coordinating the settings. As the smoothing pass started, I walked by (because I live in the OEDK) and we weren’t even sure his smoothing pass was making contact with the piece. In fact, it was- the proper amount. At this point, we realized that the Left side (mine) had cut too deep into the wood, creating new contour lines along the parallel pass, while his had smoothed the original, leaving some of both the original and parallel contours.

Finally, we had reached molding and casting! The first step was to mold the wooden positives in a silicon rubber. In order to avoid having too thin a mold at the highest point, we added foam walls on top of the block to expand the volume. Unfortunately, there was still some sawdust stuck in the notch of the hat that carried through into the mold, and ultimately, the casts.

We began casting using the quick-setting material in order to quickly iterate through the first trials. We found that in addition to the hat, the mold is not perfectly aligned from the outside, and that in the process of being milled, the alignment pins came out a different size from the holes.  This meant that we had to align the mold by eye each time to line up the piece, especially the cross.

Squished boi: We found that a clamp around the wood supports deforms the mold. Let’s not do that. Rubber bands instead!

Yellow one: He’s Yellow- not quite gold. But we improved his hat by using the Japanese pull saw to remove the sawdust nub. 

Mint boi: How about marbling? Stir the solution together, then add a drop of dye right before pouring. It almost worked, needs more mixing.

Fire boi: Can we make a light purple base with red marbling? Apparently not, but at least we got this really cool effect! We upped to two drops of marbling dye and some swirling before pouring.

Smoky boi: What about black on white? Apparently not. Not enough dye and/or swirling.

Indigo boi: Let’s try a darker color, maybe a deep blue. or purple. so indigo. Add some black marbling; it can’t hurt, right? Also, sanding the base changed the color. Let’s do that to the cross!

Great! Now we have two good pieces, so let’s try something more… dangerous.

Speedy boi: John has a bold idea; let’s try doing the clear material, vacuum out all the bubbles, and add a shoot of black dye. Black marbling should work eventually, right? Wrong. Also, he’s a bendy boi. That can’t be good.
So we need a tighter hold on the mold, to prevent the explosive leaking. Also, we should make sure the vacuum chamber actually creates a vacuum; we should close the valve earlier. Maybe that’s why the surface is so bubbly?

Sled boi: One more try for the clear with dye effect; maybe green will work better, along with other procedural improvements. It didn’t.
So the mold itself is too porous, resulting in aeration at the outer edge of the piece in the vacuum; in order to get the desired effect, we would need a mold that is non-porous.

 

Clearly, there was some iterative prototyping involved. As we went, we learned how to better align the halves of the mold, and continued experimenting with marbling techniques. The vacuum chamber runs were a good experiment, but ultimately show that our mold is insufficient for the process. Based on a quick test with a mold of a picture frame, having fewer air holes and a larger surface area exposed help the product significantly, although we ultimately still did not achieve the desired effect.

Overall, we successfully created our pieces from start to finish, including but not limited to: CAD, CAM, molding, casting, and marbling. However, we would have liked to improve upon several stages. For one, the bishop’s collar is too thin to be effectively machined or to be sturdy in the final product. Secondly, we wish we had removed the sawdust more thoroughly before molding, especially in the nook of the hat. Finally, the smoothing pass difficulties resulted in two very different textures (which you can see in the picture above). I have now learned to not to remove a piece halfway through. The end product, however, was satisfying, with two bishops exemplifying rich color and a beautiful marbling.

And with that, we and our illustrious psalter of bishop bois bid you adieu!

ENGI 210: 10/10 would recommend. (We two and all our bishop bois approve.)

Cost estimate: $∞ + $141.12

Machine time: $50;  5 hours of machine time on Carvey ($10/hour)
Materials: $91.12; Silicone rubber mold: $30, Wood: $2, Casting material: $34, Dyes: $15 for 5, Rubber bands: $0.12, Foam Core: $10
Time: $∞; During finals week, our time is priceless.