I’m not normally one for superflous veneers, but when given the opportunity to pimp my bamboo bike even more I just couldn’t resist. With 2 hubs in tow (one new, one old), I measured the diameters between the flanges and got to work chamfering, splitting, gluing and sanding these bamboo veneers on. I’ve coated them in beeswax to protect them from the elements. I’ll need to reapply that every so often.
Two layers of top coat later and the frame’s all finished! It’s not the smoothest of finishes. There’s a few carbon fibre/cat hairs stuck in there and imperfections of my sanding back are clearly visible. Still, it’s just a prototype and doesn’t look too bad from afar.
The final processes haven’t been without drama though. During the drying process a few hairline cracks appeared on various parts of the frame. To mitigate further crackage I’ve wrapped the affected areas in carbon fibre tow (which are the black bands you can see on the down tube and chainstays). The cracks are caused by the expansion of the bamboo at high temperature during drying (ie. around 80 degrees). I don’t expect it to crack any further, unless we get a severe heatwave…
It’s now off to the shop to get parts fitted. Hooray!
Today I put the last 2 layers of carbon on the seat-tube and then finally got to unwrap all the tubes and sand back the joints and bamboo.
Here’s what she looks like now:
The only things left to do now are:
- Drill a hole in the rear bridge for caliper brakes to mount
- Bind a small amount of carbon around one of the rear stays, which has developed a hairline crack during the build process.
- Coat the entire frame in “clear coat” (an epoxy based varnish)
- Put on parts!
Today I’ve put the first of the final touches to the frame – a carved bamboo head-tube Cognitive logo. It’s a bit simplified, but that’s ok as it will probably change down the track anyway.
The only things left to do now are two more layers of carbon on the seat tube and then to unwrap all the tape, sand it back properly, and add some final clear coat as a protective varnish layer.
I’m continuing to wrap the bottom bracket joint today. I’ve now done a total of 9 layers, which I’m pretty sure will be enough for a sturdy and stiff BB.
After wrapping up each series of layers in cling wrap and PVC tape I place it inside my homemade autoclave. It gets up to 80 degrees C in there, with just a regular old hairdryer. 30-40minutes is all it needs at that temperature to cure the epoxy enough that the wrapping can be removed. It will continue to cure at room temperature over the next few days.
The headtube’s pretty much done so I’m now starting work on laying up the bottom bracket area. It’s a much more complex shape to work with, which made the template cutting all the more fun. I’ve figured out a better way to make the templates is to wrap smaller pieces of cloth around each part, then stick them together with tape, then cut strategic slits to remove it from the frame. Then lay that all flat and trace over it to make one bigger template. I also add areas of overlap around where the slits were cut to add strength to those areas.
Here’s some pics of the finished headtube and the first layer of the bottom bracket: