Built my first bamboo bike this summer. Built it up as a fixie because I unfortunately didn't have enough clearance to fit a freewheel due to the bulky joint at the dropout. Anyway, here is version 1.
After about 125 miles or so, I heard a distinct crack while I was riding it. It was still rideable so I got home and inspected it then. I couldn't find a crack on any bamboo pole or at the joints. I could feel that the bottom bracket was a little more flexible than before though.
I thought I would repair it. Since I was going to go through the trouble of grinding down the joint, I thought maybe this would be a good opportunity to replace the seat tube entirely. The first time around, I actually glued the seat post directly into the bamboo. I wanted to do it correctly this time around. I finally found a piece of bamboo that would work and proceeded to grind down the joint at the BB and the seat tube cluster. You can see my flickr to see more shots of the process. Here is the repaired bike:
After I had finished the first fiber/epoxy layer on the new joints, the new section of bamboo split in the middle section from node to node. I put the bottle cage mount with fiber wrapping it to try to inhibit the crack from growing and to cover it up.
Anyway. After about 90 kilometers on the repaired bike, it became too flexible to ride. On closer inspection I noticed that major cracks had formed at the down tube / head tube joint and at the top tube / seat tube joint.
It's hard to see in the second picture because I didn't finish the joint as nicely as the head tube. The crack follows the miter of the top tube.
My question for you guys is why? I'm not sure why these joints have cracked. What am I doing wrong? Could cold weather affect the epoxy enough to cause these cracks? While using the repaired bike, I left it outside at all times. The temperature ranged from about 0C to 18C in about 1 weeks. I had a minor crash that put a little bit of damage on the right side of the head tube. Could that have been enough to initiate a crack through the epoxy? Would it be worth it to grind down the two cracked joints and rewrap them? Or will there just continue to be problems due to something I did wrong? It is really frustrating that I can't get this bike to work. I would love any and all help.
TL;DR I built a bamboo bike that broke. Then I repaired that bike and it broke again. I don't know why.