If you want mirror polished flats a disk grinder is the way to go…..I have 6 in my shop from 3" up to 9" Don't use the big one cept for rough grinding with 60 - 220 grit, I use the smaller ones for doing the flats on everything with the finer grits. We take the flats to 2000 grit with these, then when we hit them on the buffer it only takes a swipe or two……the fact of making things flat works really well with the disk grinder…..all of ours have foot pedals on them to start them up and only have up to 1800 rpm motors. The smaller ones run slower and have one with a reverse switch on it to run in either direction. We use a lot of bolsters on our designs so flat is a must…..only way to get things flatter with as good of a finish would be to lap the parts.
So, yep, would highly recommend one (or more) especially the smaller diameter disk……saves on paper and multiple disk setups allow you to go from one grit to the next without having to change the paper.
Oh yeah, almost forgot…..all of ours except for one is mounted horizontally, not vertical.
Thats how we do it…..good luck with it….hope this helps.
John I.