Jaegoor has it right, almost no one from stone age onwards did this sort of stone work by hand - water or pedal/handcrank powered grinding wheels were the rule of the day - and they could get pretty big. Using electricity instead of an apprentice to power said grinding is perfectly fine.
The stone RPM is, of course, slower with the historical way of doing things, but still much, much faster than doing it by hand.
As for what would they do if they didn't have a readily available helper or a water wheel, I suspect they wouldn't have bothered with grinding the stone.
Image from 1560s: