Building a Bamboo Bike - Part One: The Frame

Just as I announced in my last bike post, I jumped right into a bike-building workshop. The inspiration came from Arthur, my most recent warmshowers guest, who is riding around the world on his bamboo bike. He came to Mexico City specifically for one reason: to get to know BambooCycles, the bike shop specializing in bamboo frames, which is conveniently located just five minutes walking distance from where I live.

Though I had dropped in once to look at the place, and inquire about the cost of their frames, I never even thought about taking a course. In fact, I may never have done it hadn't it been for Arthur. In the end I'm glad that I signed up for the course, and remain grateful to my guest for sparking my interest. After roughly a week of off-and-on work, I can finally say I have completed a beautiful bamboo frame! So the next steps are a bamboo fork, a bamboo handlebar, and a set of other components that will complete a bicycle. For now, however, I want to present the highlights of the building process:

Starting out with Some Sticks

What is a frame, really? It's something to keep together the seat post (for the seat), the bottom bracket (where the cranks go), the headset (to attach the fork), and the dropout (for the rear wheel). All of these attachments require metal pieces, but the frame itself can be made out of bamboo. This wonderful material has numerous advantages: it's much lighter than steel, it won't rust, but it doesn't have the annoying rigidity of aluminum. Bamboo is a type of giant grass, so it's a fully natural, renewable product, and if grown sustainably it can have the added benefits of water management and habitat creation, mulch, (etc. etc.). From among the myriad of bamboo species, the one used for bike building is the Dendrocalamus strictus, chosen for its non-splitting properties.

Assembling the frame is really quite straight forward: we use strands of carbon fiber, glued together by epoxy resin, to keep the bamboo pieces and the metal fixtures together. For this reason, the parts of the bamboo that will be covered in carbon are peeled, and the rest is covered in a plastic wrap for protection. Eventually the carbon fiber will join all the pieces, as illustrated in the cross-cut frame, hung up at the shop for demonstration purposes.

A Dream of a Fixie

Depending on the type of bike, the frame can have various geometrical aspects, to give the rider the best position for speed, for climbing mountains, for a leisurely ride to the bakery, or performing mind-blowing tricks. At first I liked the Durango model because it was the most similar one to my Zorra Roja, the touring bike I built for my trip down the West Coast last year. But then I realized that riding around in Mexico City requires a different type of bike.

One of the many challenges this city poses, are discontinued bike lanes, or other factors that would force you to go through curved tunnels, where motorists are speeding through along shoulderless lanes. The alternative usually includes carrying your bike up and down pedestrian bridges, clearly the preferable option, especially if your bike is light, and stripped of any unnecessary components and accessories. Such a dream of a fixed gear bike is the Insurgentes model. Finally, I won't be the only horizontal dropout here!

image source

Putting it all Together

This part of the work could be the hardest, and most frustrating one... if you didn't have the assuring experience of the guys at BambooCycles. Fortunately, they know exactly where each piece has to go, and with their nifty frame-building-frame this precision work can be completed in a few minutes with doubtless exactness.

The fork and the wheel seen here are only used for measure, which is why they are covered in epoxy, just like the entire work surface. Once you get your hands into the sticky stuff, it becomes quite clear why the plastic foil is needed: it's simply unavoidable to get the resin onto everything! Needless to say, it's best to wear clothes that are on their last thread anyway.

Using shorter pieces of carbon fiber, immerse them in the resin mix, you stick the pieces together. Next, you use strands of medium length (approx. 10-20 cm) to cover the joints on the outside. Then you wrap them in a generous layer of long strands, similarly saturated in epoxy resin. This fiber looks a lot like hair! This realization has been brought up and discussed so much during the workshop, that I had to look into it.

After all, our hair (just like the rest of our body) is mostly carbon, and is known for its great strength. However, it seems like it is still no match for the carbon fiber. According to this source, carbon fiber can be 2-3 times as strong as our hair. Good to know. Still, in order to hold a bike frame together human hair may be just sufficient. I may come back to this idea for my next bamboo bike. Till then I'll let my hair grow a bit longer.

Most of the Work: Sanding, Sanding, and more Sanding

Once the joints have hardened, giving the frame the desired strength, you could say that most of the work is done... leaving only the non-essential cosmetic work. That may be true, but the sanding is actually what takes most of the time and energy in this frame-building process. And though it may not be strictly essential, skipping it would leave the bike in an ugly shape.

Take the head tube for example and observe the huge dents and holes all over it! These used to be air pockets between the strands of fiber. Though it is theoretically not inevitable, these kind of holes tend to appear regularly in all the carbon fiber parts. The solution is to sand it all down. At this point I should mention to cover as much of your body as you can, because this carbon dust can be quite itchy, especially when it gets onto your neck or arms.

If there are still remaining holes, even after hours of sanding, they can be filled with a mix of metal filler, hardener, and black pigment. As tempting as this method may seem, it requires another round of sanding, getting rid of the excess paste on the outside, making sure that you don't sand the pieces away that were supposed to fill the holes. The whole process may need to be repeated.

When all the holes are filled and the carbon pieces have taken on a nice shape, you can switch the sandpaper for one with a finer grain, and continue sanding away the scratch lines. Over a course of several hours I went from 36 to 100 to 230. Eventually the rough sanding becomes smooth polishing. At this point even the protective plastic layer can be removed, so the bamboo can be given a very gentle sanding.

Once all the sanding has given the frame a satisfactory look, the entire thing is covered in a generous layer of bee's wax. This is why even the bamboo got a light sanding, to open up its pores for the wax. It is recommended to repeat this last step regularly, as part of bicycle maintenance. The wax is absorbed into the bamboo, where it protects it from getting wet, or drying out. If kept up properly, a bamboo frame can have the longevity of frames made of other materials.

Well, that's how I built myself a bike frame of bamboo. Please stay tuned for the next parts of this series, where I document the building of the bike.