The Excelsior Project, 7: The Crank

Start of the pattern-making process. This is a rocker from the bottom of the front fork, to be cast in 4140, machined, then heat treated. I made the pattern a little "chunkier" for added strength. The distance between the centre lines of the holes was lengthened .044" to allow for shrinkage: 1/4" per foot. All surfaces to be machined were also built up slightly. It now goes to the pattern maker to be mounted on a board to suit the foundries' specifications.

Yes, you can still buy Excelsior parts. This remanufactured crank arm didn't have the shoulder in the right place, so a new tube was turned on the lathe, split in half, and Tig-tacked in place. That "thing" on the top left is a spigot, used to hold the crank in the four-jaw chuck for machining.

The crank after machining. Notice the collar was brazed after tacking. Also notice the flaw in the casting. Not good. This is 4140, a tough and hard steel. The chips are small and curled; you can't get that with a cheap steel.

Even after moving the shoulder all the way to the left, the crank still wasn't long enough to clear the bevel drive, so the middle section was turned down to fit a seamless DOM (drawn over mandrel) tube. It needed to be a 1/2" longer. This is OK for the prototype, not production.

Bronze bushings (not shown...) are machined up as spacers to position the side-to-side positioning of the cranks. Must remember to look for a pair of 1919 pedals...


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