My current bike is a Condor Pista single speed. I use it for everything from my daily commute into London to the 110 mile King of the Downs ride every year. To be honest I don’t know why i’m building a new one, because I love my Pista, but it’s always fun to have a project. Conveniently Condor have a full frame spec for all their frames on their website so it was just a case of finding my frame size and reading off the dimensions.
I drew a whole series of curvy frames where the top tube blended into the seat stays. However, once i started to work through the actual construction I realised that the curved tubes would be much harder to form as you obviously want the wood grain to run along the length of the tube. Renovo achieve this by laminating the frames in 2 directions around curved templates to get vertical stripes but curved tubes. Sounds tricky, so straight tubes it is then. It also turned out that using straight tubes minimised material wastage and hence the cost of the wood (the cost of the wood was looking like it could jeopardise the project at the point i made this decision).
I work in an engineering office, so I have access to CAD software that I use regularly. I put the basic frame geometry in and started fleshing it out with the shape of frame that I had in mind. I knew that the frame was going to be around 50mm wide with a 60mm deep down tube, 40mm top and seat tube, 20mm round stays and i’d aim to get the whole lot formed to a 5mm thick tube. These numbers weren’t entirely plucked out of thin air and i’ve written a bit more about it in Why Wood. I also spent some time looking at the various high end carbon fibre frames that all have the same style of oversized, thin walled tubes to maximise stiffness but minimise weight.
The frame was going to be built up from vertical layers in 2 halves and then bonded together like the Renovo frames. I found some really useful photos of Renovo frames during construction that helped focus my design.
You can see in my CAD drawing, i’ve left in some solid bands inside the tubes where my bottle cage mounts are going to go and to provide some internal stiffeners like the Renovo frame above. The one part of the design that I was struggling with was how to join the different straight sections of wood together. Renovo use a very neat finger joint at each of the joints that you can see here
I don’t have a finger joint cutting tool for my router and they tend to be quite expensive, so I came up with an alternative (in retrospect this decision added a lot of time to building up the frame but i feel quite happy with the strength of the joints). At each of the main joints you can see i’ve left it solid in the CAD drawing. The idea was that each layer would be fully lapped onto the next over the full length ot this solid region with each layer running in the opposite direction to give the joint strength. It is probably easier to see this in the construction pics .
Wood – I’ve never worked with exotic hardwoods before so there was quite a bit of homework to be done here. My goal was something like this frame which uses wenge, maple and padauk hardwoods.
Rather than copy it verbatum, I wanted to understand why they had used the different woods that they had chosen. I’ve written about some of what i’ve learnt about the different woods that are suitable for bikes in Why Wood? but the short version is that the woods chosen for the bike above are all both dense and stiff. That means that you can build a fairly thin walled frame that will be light, stiff and still dent resistant.
I contacted a whole range of UK hardwood suppliers for quotes and ended up placing my order with Timberline hardwood specialist. They were very helpful and helped me get the wood I wanted for a lower price than many of the other suppliers.
I ended up running with 2 x 10mm thick maple central layers, 6mm wenge and 10mm bubinga outer layers. The bubinga is very similar to padauk in material properties but is slightly browner and seemed to be more readily available from the suppliers I spoke to.
Other parts – The bottom bracket, head tube and top section of seat tube are all formed from aluminium inserts glued into the frame. I scoured the streets for a discarded aluminium frame that could be used as a donor bike. After a couple of weeks of keeping my eyes open for suitable candidates, I noticed a Kona racing bike frame locked to the bike racks next to my house. The bike had been stripped of EVERYTHING and the rear stays had been bent till they were touching each other. There’s no way anyone was coming back for it. 10 minutes later with a hacksaw I was the happy new owner of 2 halves of frame (well it was easier cutting through the frame than the lock!)
I used West System epoxy to glue all parts together which i got from The Fibreglass Shop in Brentford. I also picked up some 25mm wide 175gsm fibreglass tape to use for reinforcing the frame at the aluminium to wood joints.