While faced with some free time, I decided to take a leap and fly to New York to take a class at the Bamboo Bike Studio. The studio offers a two day workshop giving you an option to build either a complete bicycle or frame only, from start to finish. I was interested in this class because not only do you end up with a very classy looking bicycle frame, but as a good introduction on building a composite bicycle frame, because the bamboo tubes are connected with carbon fiber.
The workshop is two very long days, and in our class we had 5 students and anywhere from two to five instructors, depending on the session. The studio is located in Red Hook, Brooklyn, New York in an old industrial / warehouse space now occupied by a few artists and the Bamboo Bike Studio. The workshop is about $650 for just the frame, and complete single speed bikes start at $900, which is a very good value considering the amount of instruction that goes into the class, and the fact that you leave with a brand new bamboo frame.
On the first day I woke up early and got to the studio at 7:00 am. I arrived with Aaron, another student, and met Piper, one of our very skilled instructors. Piper got Aaron and I started right away with a quick overview of the class, some initial paperwork, then it was off to our jigs to start putting the bikes together.
The first step in building the frame is to attach the bamboo tubes, which were prepared for us before the class started, to the foam blocks that create the backing for the carbon lugs. This is a surprisingly simple process involving shimming and hot-gluing the tubes to the foam. If you're reading this, you're probably thinking exactly what I was thinking: hot glue and foam? and you're supposed to ride that thing? Well, it's true that we did use hot glue and foam, but it's really more to hold the tubes in place for making the lugs, neither the foam or glue are structural.
After the tubes were in place, we got out our files, rasps and sandpaper and began to shape our lug cores. This is again a surprisingly easy process, but because it is so easy to file the foam it is easy to go to far, so a little restraint goes a long way. Ideally you want the shape of the foam to mimic the shape of the bamboo tube that it meets, as well as form smooth transitions between the tubes. This whole process took less than an hour.
After shaping the lug cores, the next step is to wrap the tubes, lug cores, and metal parts (BB shell, headtube, seat tube insert) with fiberglass. The fiberglass creates a bond between these parts below the layers of carbon fiber. It's as strong, but a lot heavier, and so only a little is used in the initial process.
Then the fun begins: wrapping your joints in carbon fiber. Though I worked for Trek for a number of years and new exactly how OCLV frames were assembled (once the tubes and lugs were made), I had never seen how carbon fiber is formed into these parts. I understood the basics: wet the material with epoxy, wrap, compress, and dry, but had no idea how simple the process is. So here's the rundown on carbon fiber, at least as it applied to this frame:
The material we used was 24k carbon fiber tow, which is a ribbon of 24,000 carbon fiber strands that is rolled onto a spool. The ribbon is about half an inch wide, but because there are so many small strands, it can easily be rolled into a thread or flattened and spread into widths much smaller or larger. This tow is wetted with a mixture of epoxy and hardener and tightly wrapped around the lug cores and tubes, which creates the lug. After the lug is wrapped in carbon, it is compressed with plain electrical tape and allowed to dry and harden for a period of time specified by the epoxy you use. That's pretty much it. Simple in theory, a little more complicated in practice.
So we wrapped the joints, one at a time, starting with the dropouts. We used anywhere from 20 - 60+ grams of carbon tow per joint (this weight does not include epoxy). The tow was prepared for us by the staff at Bamboo Bike Studio onto spools specific to the joint we were wrapping, and these numbers are based on years of research and test frames.
After the joints were wrapped, compressed and allowed to cure overnight, we unwrapped to reveal what appeared to be a bike! The carbon on the joints was rough, so the next hours were spent filing the joints smooth, the same way we did the lug cores. The idea is that each sharp corner creates a stress riser in the material, so the smoother your lugs are, the stronger they will be. This takes a long time, because the carbon / epoxy / hardener is very hard, but to play it safe most of this is done by hand. I did cheat a little and use the band file belt sander for some of the hard to reach corners.
Final sanding was done with 100 grit sandpaper, then the frame was wet down to see if there were any voids or areas that still needed sanding. The final step is to add one layer of epoxy / hardener to the outside of the lug - this is what appears as the clear coat over the carbon fiber.
That's pretty much it, you have yourself a frame. Or rather, in my case, a Christmas Gift for your girlfriend. I hope she likes it!
A special thanks to the staff at the Bamboo Bike Studio for making this class possible. The small staff there has a diverse set of skills and backgrounds but all understand the bike building process, and teach it in a clear concise way. If you ever have the opportunity to take this class, I highly reccomend it.
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