In response to my note about using a 1/4" dowel impregnated with valve grinding compound to grind out pits on cones for hubs, both Mark Bulgier (off-list) and John Thompson made a thought-provoking suggestion:
They both suggested using an extension of this method to grind pits out of BB spindles. Even if the bb spindle is too fat for the chuck, it's certainly feasible to thread in an 8 mm bolt, and cut off its head, leaving a couple of cm. to be chucked in the drill. Even though the drill press rotating normally will tend to thread the spindle up against the chuck, I'd find myself more comfortable with a stop nut locking the nut against the spindle.
I'd also want some bearing at the lower end, something like the tailstock on a lathe. There's a fair amount of mass being spun around, and it might be a bit off-center. That won't affect the grinding (since the dowel and your hands let the grinding "track" the surface. But I'd hate for this to get away from me. Just something in case the bolt in the chuck gets fatigued. My drill press only has a few speeds, ranging from very fast to much too fast, and I'm cautious.
Thanks to John and Mark!