Neu's come with a flat shaft right??

[glassdoctor]

Smooth shaft on the Neu.

If you grind a flat spot, keep debris from getting into the motor. One good way is to use a good strong ziplock bag, etc.... put the motor in it and poke the shaft out though the bag. Then maybe even tape around the shaft to make sure it's sealed good. Grind it with a cutting wheel or sanding drum and take your time.