Dominic Doty

Chainless Challenge - Keyed Bike Hub

More Chainless 29 Apr 2012

The Chainless Challenge bike I worked on in 2014 utilizing hydraulic cylinders needed a custom keyed hub. This is the story of how I machined a bike hub from steel billet.

The 2014 bike was designed to use a pair of hydraulic cylinders to drive the rear wheel like a crankshaft. The rear wheel needed to have a gear train to create an overall gear ratio similar to a bike at about 1:2.7. The rear wheel needed to have a large pinion gear fixed to it outside the bike chainstays, so the rear wheel ended up needing to ride on a keyed 1.5” shaft.

Obviously keyed 1.5” hubs are not easy to come by in a bike shop, so I had to make one myself. I first rough cut a steel round to length and faced its end. To turn out the entire space between the flanges, I first plunged with a parting tool to create a narrow groove in the part.

Incomplete Hub

Then I used the groove as a starting point to turn the center out with a left hand tool, and when I neared final dimensions, came in with an ISO4 cutter (which is symmetrical) and turned down one flange, across the center, and then up the other to get a nice clean finish. I then drilled and bored out the center hole, and finally broached it for the keyway. I drilled the spoke holes on a rotary table on the mill. All said and done, removing that much steel is time consuming and tiring.

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