New Project

A couple of years ago I built a bamboo bike. This was based on a kit from the Bamboo Bicycle Club – you can either go on a weekend course with them in London, or for quite a bit less money, they send you a kit in the post. I opted for the latter, and built a bike frame from the box of sticks, epoxy resin, hemp cloth, assorted stainless steel inserts, and bottle of beer that turned up:

Setting out the jig

Setting out the jig

Mitred joints

Mitred joints

 

Mitred Joints

Mitred Joints

 

Tacking in place

Tacking in place

 

Rear Triangle

Rear Triangle

 

Rear triangle

Rear Triangle

Layup with hemp cloth & epoxy resin

Layup with hemp cloth & epoxy resin

 

Cured lugs - bumpy finish!!

Cured lugs – bumpy finish!!

 

Lugs after MUCH sanding & fettling

Lugs after MUCH sanding & fettling

 

Finished bamboo bike

Finished bamboo bike

 

On the whole, it was an immensely satisfying process, and taught me a whole lot about how to put together a bike frame. Ever since, I’ve had a hankering to do another one, using my new skills on something a little different. The method for building the lugs in situ would work just as well with other composites, and I think the next logical step is carbon fibre. I was thinking of building myself a new touring bike from a titanium tubeset.

But then I got thinking… I’ve always wanted a recumbent. It’s taken me a year or so of mulling over designs, sketching and thinking, scrapping the whole idea, and then coming back to it after some 3am inspiration. But here’s what I’m going to build:

Recumbent bike

Recumbent bike

It’s based on a couple of scrap frames I saved from the skip. The green is a late 1980s / early 1990s Dawes Discovery, in either Reynolds 530 or chrome-molybdenum, while the yellow is a Paul Donohue road bike in Reynolds 653. The rear triangle is from a no-name full sus mountain bike, and the forks are from a late 1980s kids bike, though I may see if I can stretch to a set of Brompron forks instead. The wheels are 26″ on the back, and 16″ on the front. The drive uses a tandem chainset for the BB at the front, with the chain running down the left side of the bike to a second BB. This may seem to complicate things, but means I can run a cheap single speed chain over that enormous length. The second BB takes the drive back to the right hand side, and will have a 9 x 3 setup. The steering will be under-seat, with a joystick on either side, and cable connection to the forks (yes, I’ll build this as a dual-system for redundancy). I may also add a set of parking wheels, so I can stop without having to unclip… Oh, and I haven’t fully made up my mind, but I’m probably going to make the seat rather than buying one. This will connect to the frame via rubber bushes at the front, and a suspension damper at the back.

Construction will be similar to the bamboo bike, but with some changes:

  • I think it’ll be jigged vertically rather than horizontally. This will make it easier when doing the layup
  • I’ll fill the acute angles with epoxy putty & smooth them to a sensible radius. This will make it easier to get wrinkle free layup
  • The layup will be with two different materials.
    • The main structure will be from around six layers of carbon fibre tape. So unlike the hemp I used on the bamboo bike, there’ll be no cut & fraying edges to fret over
    • On top of this, there’ll be a cosmetic layer of carbon fibre cloth in a twill weave. This will drape & conform well to the complex shapes, but will still need a lot of care to get right. Most of the joints will need two accurately cut pieces to achieve a uniform finish.
    • Rather than going straight to the PVC tape for compressing the composite while it cures, I’ll then add a layer of release film, a layer of plasticine (or similar), and then the PVC tape. I’m hoping this’ll give a much smoother as-cured finish, requiring a lot less work to get cosmetically satisfactory results

All this is going to be quite involved, and there will be many experiments and trials along the way. And once this is done, maybe I will build that titanium-carbon bike after all.

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Posted in Bike Build

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