I’ve recently decided to build a cyclocross frame for the first prototype. I figure if anything’s going to test out the durability of a frame it’ll be a cyclocross race. That and it’s the only sort of bike I don’t own that I’ve always wanted (apart from a recumbent, unicycle, downhill, fixie, penny farthing …).
Here’s how it’s looking so far (ignore the colours, I just like designing in red/black/white):
As you can see there’s lots of angles, lengths and diameters to figure out. The BikeCAD above only is only showing the basic frame dimensions and angles, not any of the mitre lengths or tubing diameters.
The main issue to solve with using bamboo is tyre clearance for the chain and seat stays. I’m picturing that the diameter of this bamboo will be slightly larger than a steel/alu/carbon bike in order to get the greatest stiffness. To help overcome the larger than normal tube diameters I’m using a 73mm bottom bracket as well as a wider than normal seat stay attachment angle. If that doesn’t alleviate the problem I’ll try using skinnier bamboo, but fill it with expanding foam filler, which I’ve been told increases stiffness markedly.
The drop outs, bottom bracket, seat tube sleeve and head tube have all been ordered and are on their way. Soon it’ll be mitre time!
I’ve flown up to Queensland this week to see Bamboo Australia and their amazing supply of bamboo.
Arrived there today and spent a good 3 hours breaking the ears off the lovely staff and asking possibly too many questions. Here’s my good buddy Nat at the entrance to the farm:
Here’s the cutting shed, where I gathered various sizes of Tonkin and Aurea species bamboo poles and had them cut to 70cm long each (mainly so they’ll fit in my bag, but also because the bottom tube is never really any longer than this).
I came away with about 20kg of poles, both green and dried, as well as 5 pairs of bamboo socks and the bible of bamboo: Bamboo, The Gift of the Gods
Here’s hoping it’ll make it back to Melbourne without splitting from the various temperatures and humidities of flight.
Today we started the process of learning about how to make joints with bamboo. Using a Dremel we cut mitres into the 3 bits of wood and then stuck them together with an epoxy paste. Once that’s dry we’ll start the lay up process with sisal twine, followed by epoxy resin. This mini project will result in a simple 3 joint bike stand. You can see in the first picture where the rear wheel of the bike will slide into.
Testing the mitred joints:
Applying epoxy paste:
Letting the epoxy dry. We’ve temporarily lashed it together with some sisal:
Titanium seems to top the list in CO2 footprint… ouch!
I’ve been researching bio resins for use in the bamboo frames and discovering a whole beautiful world of people making resins out of things like soy. There’s an interesting PDF here that details the environment costs and benefits of creating such resins.
I’ve contacted Bioresin to see if their products have made it to market yet, and whether or not they’re available locally. Let’s hope so!
I’ve selected the 7 culms (fancy word for a bamboo pole) for the first frame. Here’s a pic of them laid out into the respective parts of the frame:
And here’s a view of the thickness of the downtube:
I also ventured to my local hardware store and picked up some epoxy resin, glass coat, borax, beeswax and some other glues and finishes to test the curing and joint making processes with:
I haven’t managed to find Boric Acid anywhere yet thou. I suspect I’ll be able order it online somewhere, or it might be available at a chemist.