April 22, 2014

Adding Gears to the Oar Bike

Over spring break I added a cassette, rear derailleur, and shifter to the carbon bike.  The shifter and derailleur were taken off my now unused bamboo bike, while the cassette was scrounged from MITERS.

When I milled the dropouts for the original frame, I did not add a derailleur hanger.  To attach the derailleur, I machined a clamp-on hanger.  This was shaped out of some aluminum bar stock with a bandsaw and some files.  Brief aside: I think files are one of the most underrated metalworking tools.  Especially on soft metals like aluminum, files can remove material remarkably quickly, but can also make smooth, elegant edges.  Bandsaw and filing this part took way less time than CAD and CNC milling this thing, which would be an alternative for making such a weirdly shaped object.  Granted, precision was of little importance here.

The hanger clamps to the old dropouts with a small bolt and nut on the other side:

For cable stops, I removed the cable stops from a broken carbon fiber frame Nick pulled out of the trash last year.  These were epoxied in place, and then riveted to the frame, which was their original attachment method.

While I was at it, I also added cable stops for the back brake, to replace the single length of cable housing that ran down the frame.  These were tacked with epoxy, and then fixed by wrapping with carbon fiber tow.  I figured the brake stops, since they see all the tension in the brake cable, should have pretty beefy attachments.