< back

Bonus: Composites

One Failure and One Success

January 2016

[Written May 2016]: This "bonus" post has been a long time coming. Looking back, I'm amazed that I was able to publish these detailed weekly posts on such a tight schedule. As planned, I did explore composites a bit in January, even though our run of HTM(A)A did not formally cover them. I ended up undertaking two composites projects with varying degrees of success. The first was a "proof-of-concept" attempt to use the basic materials available in the shop to make a magazine and/ or mail holder. This project was pretty unsuccessful, and was approached with a somewhat lukewarm attitude. The second project was using composites to make the joints of a bamboo bicycle. This project, as would be evident to anybody who has read about my other HTM(A)A projects, was much more personally motivated, and ended up being much more successful and fun!

Kim and I worked on the first project together. The first step of the process was creating a mold to wrap the composite fiber around. We decided to make something very simple: a hanging shelf/ folder that could hold mail or magazines. Our mold for this form was simply three rectangular pieces of cardboard that we taped together using masking tape. We also thought the masking tape would project the cardboard from the epoxy. After wrapping the mold with masking tape, we covered it in one layer of the release film.

After prepping the mold, we used scissors to cut out 5 identical rectangles of burlap. We also prepared epoxy by mixing it in a 2:1::A:B ratio. We applied the composite by coating/ soaking the pieces of burlap in the mixed epoxy, and then layering them over the mold and smoothing them down. This was an extremely messy process - we wore gloves and put down plenty of butcher paper. The burlap layers did not "take to" the mold as well as I'd expected; instead of lying flat and hugging the mold, they seemed to want to peel away and come loose from the mold.

After applying all 5 layers of burlap, we used the perforating tool to make another release film from Saran Wrap. We applied this film to the outside of our composite, and then wrapped the whole thing in cotton to absorp the excess epoxy. Finally, we left the composite under a very heavy metal sheet to compress it while it dried.

After letting the composite dry for a few days, we returned to unwrap it. Unfortunately, neither release film worked particularly well. On the exterior surface, we were able to peel away some of the cotton (and in those places, the composite looked great!), but in lots of other places, the epoxy had soaked through to the cotton and the cotton was stuck to the outside surface of the composite. We also were not able to remove the cardboard mold from the interior of the composite; despite the release, I think there was a lot of friction between the mold and the composite, and it was also a difficult shape to extract. In retrospect, we probably should have designed a mold that would have been easier to extract. In any case, even though it wasn't particularly successful, this was a quick project that gave me a better idea of the composites process.

My second composites project was much more successful! Through HTM(A)A, I met David Wang, who started a company called Bamboo Bicycles Beijing, which runs workshops guiding people through the process of making a bamboo bicycle. David ran a few of these workshops at MIT over IAP, and kindly offered to do a one-on-one workshop with me where I could learn how to make a bike and we could work on improving/ streamlining parts of the production process using skills/ tools/ ideas from HTM(A)A. The workshop was really fun and a great way to practice my HTM(A)A skills in a new context. We did a fair amount of wood-working and measurement, but the part of the process relevant to this page is that we created composites for each joint of the bicycle frame!

After measuring, cutting, and preparing the pieces of bamboo for the frame, we tacked them together using quick-drying epoxy to hold it together while we worked. We also wrapped the body of the pieces with Saran Wrap to protect them from the epoxy. The next day, we formed a composite around each joint using carbon fiber "ribbon" and epoxy. Safety considerations were very important here since we were using carbon fiber and epoxy; we wore masks, safety glasses, gloves, aprons and protective sleeves on our arms. That said, we were not cutting the carbon fiber that often or grinding it, since it had already been wrapped as carbon fiber ribbon onto spools. The danger of working with carbon fiber is that loose fibers can get caught in your lungs; grinding or cutting carbon fiber releases these fibers, so we tried to minimize these actions (we did not grind carbon fiber at all) in addition to wearing safety gear.

To create the joints, we prepared the epoxy in a 2:1::A:B mix, lathered the carbon fiber ribbon in epoxy, and then wrapped the carbon fiber around each joint in a weave meant to maximize strength. After wrapping the carbon fiber and completely covering each joint, we wrapped the composite tightly in electrical tape to compress the composite while it dried. After letting the composite dry for 24 hours, we removed the electrical tape and the Saran Wrap from the frame. I finished my frame with polyurethane. I have yet to actually equip my frame with bicycle components, but it's on my list! This project was a practical and fun application of composites that was also of great personal interest!