That little Skill is generally known as a toenail filer or fingernail grinder.
Normally it's used with thin snagging wheels a/k/a cutoff wheels in tight spots or to cut out cracks and defects.
These tools predate the common availability of compressed air and air tools, and are by comparison FAT, heavy and nasty to run. The smaller ones like your Skill also had short working lives generally because the bearings simply couldn't stand the workload.
Speed difference~
Well into the 70s grinding and abrasive speeds were normally quoted in Feet Per Minute.
A 3000 rpm spindle carrying an 8" wheel grinds at 75,360 fpm when the wheel is new. By the time the wheel is down to 6" it's only cutting at 56,520 fpm, barely 2/3 of the machine's design workload, and a pathetic use of a grinder, so yo put a new wheel on and go back to making money.
Your Skill spins a 2.5" wheel at 17,500 rppm delivering 137,375 fpm, an appropriate speed for cutting and snagging, but way faster than you could ever hold and turn a 6" wheel because of gyro effect. A 6" wheel spinning near 6,500 rpm would deliver about the same feet per minute, but few men could hold it and use it.
The gyro thing can get very nasty, particularly in places where there isn't much room for the grinder to get clear of the wheel if something goes south. If you get the chance to mount a 9" wheel on a standard angle grinder normally used with a 7" wheel give it a try. Changing the attitude of the grinder becomes more work than hanging onto the grinder.
