Jan Heine wrote:
I need to make (or have made) a new axle for a BB. The BB has tapered roller bearings, so there is no need for hardened ball races. Effectively, this looks like a modern cartridge bearing BB axle.
Requirements are: Must be OK to machine and thread (crank bolts). Must be safe to use - it's for a tandem, so the forces can be significant.
I suspect 4130 Cromoly is a good material, but I really don't know much about materials. Any help appreciated.
Many years ago, I made a couple of bb spindles in the Princeton U. student shop, using a Bridgeport to cut the spindle flats. There was one little problem, one that I still have as a reminder: On a 1-off basis (as opposed to a production run), jigging or other methods to assure that the flats match on the two sides is not intuitive. The "prototype" has maybe a 165 agnle between the crank arms instead of 180. After breaking off one scarce metric tap, I rebored oversize and used an SAE thread, which lightened the spindle a bit (wow!) and made life easier.
BTW, I know of one machine shop in Seattle that has some experience with exotic stuff, contact me offline if interested (I don't know if they have time now).
harvey "strictly amateur" sachs mcLean va
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