79pmooney

Actually, the recess is not necessary for the chainrings. It helps with clearance with the chainstays and makes for a nice clean appearance. Chainring bolts are sized assuming the recess, so yes, we now need the recess. but not because there is any magic to the recess itself. I have a crankset where the outer ring sits only on the bolt and the recess is there but not used. Bolt extends past the chainring. There is a large washer and nut.

This works (very well) because the bolt is a tight fit with the chainring (and was a very interesting project). That crankset is a triple with 3 1/8" chairing for a fix gear chain. A short bottom bracket is used to bring the entire crankset inboard, both for chainline and to reduce the Q-factor for my knees. Inside chainring sits on the usual inside position of a double crankset. Middle on the usual outside position. Outer chainring is spaced out into the gap between chainrings and crankarm.

Crankarm bolts are standard 8mm stainless flathead bolts with a generous shoulder. The inside chainrings were countersunk for the flathead bolts. The bolts were brought out to the tight fit 10mm by fabricating sleeves that fit tightly over the bolt shoulders.

This was done by Dave Levy at TiCycles, an expert machinist on a very high quality milling machine. Not cheap. We were very conscious that extending the bolt out unsupported meant that any play at all would be quickly fatal. especially since it would be seeing the rigors of fix gear use.

Ben