One must be careful using rotary power tools to polish locks. They will quickly round over edges that should remain sharp, and dish out screw and pin holes. I start with small bits of course emery cloth or sandpaper and work my way finer.
-Ron
Yeah, for lock plates you need to work them on a flat surface. I have a set of diamond hones that work great for that.
I just did a pan this way. It looks great. The Dremil has few uses, this is one though. It makes a mess of any polished exterior surface you will see. But, for this use, a concave trough, it works great. Put the lock plate in a vice. Use cratex wheels, Brace your hand, and go slow. You can easily get a perfect semicircle in the pan and a wire edge corner.
Almost all other metal polishing should be worked with files then backed paper or stones.
I own lots of cotton wheels and polish-o-ray. I mostly use them to sharpen kitchen knives these days. With few exceptions I don't polish gun parts that way, anymore.