I wasted a few bucks on a cheap drill bit sharpener that was much better at ruining bits. Since I'm a cheap ******* and don't like to throw things away, I finally figured out a good use for it.
It DOES do a nice job fixing the end thread of cut bolts, screws, and threaded rod.
https://youtu.be/AC0KdRw4ff0
WARNING: Always wear appropriate proper eye, face, hand... protection when grinding or working with moving machinery. If you don't know, learn first or don't do it.
Nice use of a useless tool used for something useful! I've always found if you thread a nut on the rod or screw first, then cut it, you can run the nut to the new cut end. Once you have it at the end, unscrew it until the new cut end of the screw is inside the nut. Then just lay the nut on a hard surface (steel preferably) and hit it with a hammer on 2 or 3 sides. The threads in the nut will dress the newly cur end of the screw. It also works on threads anywhere on a threaded rod or screws: Just run the nut to the bad threads and lay it on a hard surface and whack it with a hammer a few times. It will restore any bad threads. Just need to make sure the nut is harder than the all thread or screw.