I find drilling easier than grinding.
I usually drill a small hole, like 1/8th, followed by a larger one closer to the size of the rivet. I find they punch out faster if that larger hole is all the way through the frame, but not the rivet.
Good sharp bits and some lubrication make it go fast. Last time I had a bunch to do I used two drills so I didn't need to swap bits, but could just keep moving.
Then a punch smaller than the hole will drive the rivet right out.
