"He Wears Black and Has a Beard"

CBIIweek: day 2

Toby Roworth

Aug 7, 2013

I needed a week off work to take a break. I also needed to make the distance between the saddle and the pedals bigger on my bike. So cue "CrapBike II week" (CBIIweek for short), in which I modify my bike a bit.
Today, thanks to a lack of rain, I got a lot more done - in fact I got enough done to roll the chassis down the road, with only minor bads happening. If all goes well tomorrow I should have it ready for painting, leaving the rest of the week to build a trailer, or do some van work - maybe even both.

After welding the inner headstock to the seatpost (it's not often bike builders say that), the outer headstock to the old down tube and the front (now rear) forks to the old top tube I could lay it out to get a feel for size. After deciding on where to cut the V-joint in the middle, I got to work with the angle grinder and did some fishmouthing.

Then I set about welding the two halves of the bike together,as strongly as possible, as the mid point is quite a likely place for failure to occur. I was a bit generous with my cuts, so the wheels have ended up an inch or two closer together than I'd like. However, this helps keep the wheelbase short, which is good somehow. And if it really shows up as a problem during test rides I can reverse the rear forks with about twenty minutes ~(as is traditional) of grinding and welding.

At this point I took it for a test ride, quite aware of its many potential points of failure. However, I generally came off well - more in the video below:

Afterwards I started work on the bracing of the structure - any engineer over the age of nine knows you need triangles to make strength, rather than just tubes with their ends welded together.


I got some quite nice weld beads on the centre brace, as shown above (ignore the middle, which was a lot trickier than I expected, as the tubes were different sizes, and seemed very keen to melt).

Now I just need to add a couple more braces - one for the headstock and a pair for the rear forks - before I can try and work out how to build the seat, something I've not yet considered in detail...