Week 9

1. Designing a tensegrity desk

For this week, we are making something big with plywood, and I decided to make a tensegrity desk just to really understand the physics of it as it has always confused me and is not intuitive. By looking at common tensegrity desk designs, I decided to base my design off this “VIVO Anti-Gravity 12 inch Tabletop” (which is available on Amazon and is $39.99). By just designing new shapes for the arms and the two boards, I should be able to maintain the structure of it while creating something interesting. The arms look like actual, muscular arms to me, and it kind of look like the two arms in Genesis. This further inspired me to make the top board like a cloud and the bottom one like a mountaing, and I envision the two arms sticking out from the cloud and the mountain. I arranged multiple images in powerpoint to create a reference image, and imported it into Fusion as a canvas to sketch my designs on it.

After sketching the arm, the cloud and the mountain (which is actually referenced from the shape of 玉山 (the tallest mountain in Taiwan) but it turns out that the silhouette of it is not as iconic as the photo of it), I arranged them on the 4 feet x 8 feet stock plywood, and simulated the 2D contour milling.

My milling buddy is Cyrus, who had experiecne using ShopBot from previous sessions and is so nice to have him guiding me. 10/10 milling buddy. Although it is milling out what I’ve designed in Fusion, it is still very inspiring and is an impactful experiecne to see something big getting cut out. And this is nice plywood.

After getting the pieces, I sanded them down with sandpaper and drilled holes for M5 screws. I then screwed the two pairs of arms and used Gorilla wood glue to insert them into the slots on the two boards. I tested the slots on the mountain board with a dogbone design, but I’ve designed the slots too numerically correct and didn’t have enough interference, leaving too much of a gap so I used 2-part epoxy for that.

After leaving them overnight, the joints felt pretty strong and it’s ready for the final assembly, which is tensioning it with wires. I bought clear fishing wire from amazon, which should hold 19.5kg and should be strong enough. And I can always put multiple wires to make it stronger (foreshadowing). I made this temporary asssembly jig to keep the two pieces in place, and started by tensioning the middle, short wire as that’s the main supporting wire.

By tying the wires directly on the screws, I will be able to adjust slightly the tension of the wire, which is good if it just needs to be adjusted for a few cm, but is not enough for what I’ve encountered. The first assmebly was way too wobbly as the outer wires are too long, but it kind of worked! It was very exciting to me as I can see it standing, which at this point after tensioning the wires to try to balance it I have a much better understanding of it, but it still looks magical. I re-tied multiple wires multiple times to find the best way to level the top board, which is not very easy. After painfully adjusting the wires for almost an hour, it finally looks good and is pretty stable now.

And then the center wire broke 30 minutes before the class as I was testing its strength. And it turns out fixing the center wire is hard, as it has to really be in tension. I ended up hanging the whole thing with the top board so that the four outer wires are in full tension, and tried to tie the center wire as tight as possible. I wrapped 2 threads for the center this time, which should be twice as strong. I made it standing again in time for class show and tell, which is nice, but without enough time to adjust the outer wires properly the top board is a bit crooked. A better for tensioning this may be using a hook instead of tying knots so that I can measure the wire lenghts exactly. As suggested by others, using turnbuckles for adjustment might be good as well as I will have a larger range of adjustment than tightening the screws. It won’t look as clean though, so might need additional design to make them look intentional. I also plan to thread more wires in the middle to make it stronger and I can use it more freely.

Update after class

After bringing it to the show and tell, I cut the center wire so that it collapses and is easier to carry back home, which is still quite bulky and convinced me to take the Tech shuttle back to Ashdown for the first time. I then mangaged to make a very sketchy assembly jig with anything square and heavy that I could find, which happened to be my bass amp and my microwave.

I re-tentioned the center wire with six threads to make sure it’s sturdy enough. I also took the opportunity to level my desk by adjusting the length of the four outer wires. The tensioning process is still tedious even after gaining much more experience and kind of knowing how to do best. After an hour, a cut on my right index finger by the fishing wire and lower back pain, I finally tentioned it to a point that is tight and level, and I am very happy about it. It takes up quite a bit of real estate but totally worth it. I put the lamp I got from good will on it and it is now a nice center piece in my room.

2. Group Training with Dan

To get properly trained for using ShopBot, we get a group training with Dan to mill some test dog bone joints pieces. The user guide by Alfonso is a detailed guide on how to set manufacture settings properly in Fusion and operate ShopBot safely and correctly.