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.
Jan Heine, Seattle