incomplete, imperfect, impermanent
Mark 4 is finally in the works!
I haven’t spoken much about Mark 4, so here’s a quick run down:
1. Increase the torsional rigidity of the frame.
I recently borrowed my friends carbon fibre bike, A specialized tarmac, and wanted to compare how that frame held up against my wooden bike. After riding both around, what I discovered was that the carbon frame was significantly stronger than the wood frame when dealing with torsional stiffness, don’t get me wrong, Mark 3 holds itself well when I’m stepping on the higher gears, but there is still some give. There has been talk about the importance of torsional rigidity, and it seems like there are two main arguments. One side argues that torsional rigidity matters, as the flex in the frame is energy that is lost, the other claims that although there is more flex, the frame returns the energy back and propels the bike forward. Either way, a more torsionally stiffer frame would be desirable.
How I’ve decided to deal with this, is to look at how composite materials are being used in other industries, for instance, looking at how skateboards, snowboards, ski’s and surfboards are made. These examples are great for research, as they are all initially made from wood and then further reinforced using either a torsion box, or carbon fibre.
As I had spare carbon fibre lying around, and a tonne of epoxy, I decided to give this a go. I routed out an internal groove in my frame, and then proceeded to line the internal structure with carbon fibre, as well as creating a larger diametre cross section in my frames, all with the hope of reducing torsion, only time will tell how this turns out
2. Australian woods
I wanted to design a frame that was constructed purely out of Australian timbers. The goal was to reduce the carbon costs of my bikes, while still creating something beautiful. The cost of growing native species and bringing them to my work shop would be significantly less than European birch or African mahogany grown overseas and shipped to Australia.
The woods I’ve chosen to work with, are Hoop pine, and Jarrah. I choose the hoop pine, as I’ve heard excellent things about it when it comes to strength, one of the main reasons why its used in plywood, The Jarrah was chosen due to its almost unmatched strength in Australian timbers, meaning I could utilize it in areas of the bike frame where large amounts of stress were likely to occur.
3. Custom Drop outs
With my geometry being quite unique, using OEM dropouts wouldn’t cut it anymore, so I decided I would design and fabricate my own custom dropouts for each bike. I’ve also added the extra feature of the dropouts being replaceable, meaning the ability to run any kind you want. Initially I was going to outsource the work to a laser/plasma cutter, but realising that metal working was a skill I wanted to pick up, I decided hand fabricating them would be the better option. This allows me to hone my skills not only as a wood working but a metal worker too. I am also able to add much more detail into my dropouts this way
I’m about half way through my build, and progress is looking good, here are some pictures, enjoy!