[MrForbes]

My guess is that trying to ream the hole in the inner race of a ball bearing is not going to be easy.

If you give more info about how you're planning to use the shaft, etc, maybe we could offer some useful suggestions.

btw we are using a couple of shafts to run some mechanisms, we're just using cheap 3/8" hex aluminum shaft which we turned the ends to fit into a standard bearing. This is for moderate torque use, not in the drivetrain.