pogo wrote:

I'd like to grind a 5/8" shaft on a motor down to 1/2", but have no real
metal shop - just a drill press & mitre saw.
Is there something like an inverted drill bit, that I could put in my drill
press and fits on the outside of the shaft to mill it down?

There are rotabroaches that are 1/2" ID but it would be nearly impossible to use
one in a drill press and have the shaft come out concentric with its axis. You
are in deep doodoo, pal. Suggest you buy a motor arbor that bolts on which
effectively does what you need, rather than wrecking your motor. - GWE