IMO, if its set up correctly, a disc sander can save you tons of time and effort on everything from finish grinding to flattening items. My first thought is that the grinder you described is WAY TOO FAST. I suspect that it would likely burn about anything you tried to grind on it. I've had several disc sander/grinders in the shop over the years, and had similar results until I plunked down the cash for the machine that Rob Frink sells. Its a variable speed (VFD), (reversable) 1 HP model, with a 9" X 1 degree beveled disc......and is a completely different machine than any of my previous disc grinders. Speed is the key. I rarely run this machine more than 30% speed, and the 1 degree beveled disc allows me to grind any length blade. For the way I do things, I use the disc mainly for finish grinding, with 9x11 sheets for the abrasive.... and it saves me a ton of time on finishing a blade.....and NOTHING will allow you to grind truer flats. Another improvement I made was to wire mine with a foot switch, which means I can position a blade on the disc, then step on the switch.....which means I don't have a disc spinning around while I'm trying to position the blade for grinding.
It makes flattening bolsters, handle material, or facing guards a breeze. Just about anytime I need a good true flat on something, I go to the disc grinder.
As I said, speed is the key to usefulness on a disc.....a slow rpm makes it very useful....too fast and it becomes a "charring" machine.
