I recently stumbled upon Bamboo Bicycles. I’ve spent a couple of days investigating this on and off now. There seem to be two major vendors at the moment, both related to the same man. Calfee Design appears to make Bamboo bicycles in the US, and then there is a separate factory in Ghana that makes bicycle frames. Also there is one guy in Australia making Bamboo Bikes, but he’s only producing about one frame a year.
Bamboo bikes, like traditional bikes, seem to come in a wide variety of styles and frame designs. There are only a few rules that all of the bikes seem to follow:
- Use natural fibers instead of carbon for joint wrapping (hemp, twine, etc)
- Grossly overbuild the joints
- Use metal dropouts
- Use a metal seatpost
- Use a metal fork
The biggest long term problem seems to stem from using carbon fiber wrappings, which apparently don’t expand/contract at the same rate as the wood and cause cracks after a period of several years. This is easily remedied by using hemp fiber or a similar fibrous binding material to match the expansion rates of the Bamboo, with the added benefit that when done right (and with dark fibers) the end result joint can look like burled walnut.
The other immediate problem is that the joining where the seat tube meets the seatpost clamp, cracks can occur. This joint is expected to carry the full weight of the rider at an angle that causes leverage on the joint. It appears that this is the only place where sizing your bamboo properly seems to really matter – you need to be able to epoxy a small piece of metal seat tube inside the bamboo that fits snugly enough
How to build Bamboo Bikes: Actual construction seems simple enough. Devise a jig of the appropriate dimensions, cut bamboo to length + 1″ on either side. Toast the bamboo using a butane torch, once to dry the bamboo, and after cooling completely, a second time to toast it. Removing the bamboo skin may improve the asthetics considerably.
Once the Bamboo is ready, roughly cut the ends of bamboo in a concave, semi-circular fashion to fit flush with the other pieces. While still in the jig, roughen the joint areas and glue together the entire frame using expanding glue (Gorilla Glue). This will fill many of the gaps left during the fitting process and provide the initial strong bond. Let sit overnight.
Once the glue has cured, the bike should be strong enough to release from the jig and place upright. Mix a batch of slow-set epoxy and mask off the bamboo not involved in the joint to improve finish. At this point you can start tightly wrapping the joints, literally painting on the epoxy overtop of the fibers. For the best “burled” pattern, wrapping motions should be somewhat random, as if you were lashing together the bamboo without the aid of epoxy. Judging from pictures it looks like they are using a Size 20 (1/2″ to 3/4″ art brush) to apply epoxy resin directly to the bamboo and fibers. Don’t be afraid to go overboard here, you want to overbuild your joints to prevent stress fractures in the future.
For final finishing, fill in gaps by cutting pieces of hemp cord to size and paint them in. Cover the entire joint with an extra layer of epoxy and then wrap with black electrical tape (sticky side out) to level the surface. Remove the electrical tape when the epoxy becomes tacky to firm (not completely cured).