Small Bike (part I)

The Small Bike (creatively named…) is a project I finished March 2009, but I haven’t gotten around to documenting anything until now. I built it because I had a set of 12″ wheels and I wanted to build a bike. I can’t weld aluminum (hoping to change that soon!), so I decided to make the entire assembly clamp together, where a 2″ square tube serves as the main structure. Many of the parts were waterjet and then machined. The rest is a mix of modified or off the shelf bike and scooter components.

I started with trying to figure out how to make dropouts. Tubing seemed like a good choice for the actual structure supporting the wheels, but I needed to figure out a structural way of securing the dropouts. My first idea was to machine individual dropouts that would then be pressed or bolted to the end of every tube. But this comes out to a lot of machining, and turning of parts that are not totally round. Anyway, what I did end up going with is shown below.

I turned a solid cylinder that fit the ID of the tube I used, drilled a hole for the wheel axle, and then milled away half the cylinder. The I cut a channel and a flat in the tube. There aren’t too many dimensions here that are tightly toleranced, so I got away with just eyeballing a lot of it. Features that need to be perpendicular to each other where just machined one after the other without unclamping the part in between.

The main ‘body’ of the bike is a 2″ x2″ square tube. I made a clamp to connect this tube to the front end assembly which includes the front fork stuff and the tube that holds the headset. The clamp is kind of composed of two clamps – one that actually holds the headset tube (press fit into the square tube), and another that provided added support for the walls of the square tubing. The bore for the head tube is angled slightly (just eyeballed it to look right) , and the bolts are not.

The disassembled front end is shown below.

From the top left:

– black off-the-shelf stem, attached to the telescoping handle bar tube of a razor scooter (I made a homemade stem later, more on that soon!).

– headset tube: regular length of tube with the ends bored to fit 1.125″ headset

– fork tube, with fork brackets and front wheel. Fork tube is a normal tube turned down

The razor scooter stem clamps on the end of the fork tube. This is definitely the weakest link on the bike. When I first made it, it would inch up all the time after a few bumps. Now, a bit of Loctite later, it mostly stays tight against the headset so that the bearings don’t rattle.

This assembly just clamps into the headset clamp mentioned above.

more to come soon!