That is uncontrolled RPM and it’s why I don’t use an electric grinder because you can helicopter a burr right quick, just like that.
I found the same thing you did, in that the foot control doesn’t have enough control. It’s like trying to grind with a toggle switch.
Air is a PITA, but once you get a way to control air speed it’s easier. And I can use an electric grinder, I just don’t like it as well.
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You can see the little lever that controls air speed. I had a round one, but it wore out and that was all I could find. If I’m not careful I bump it and either **** the air off or it goes WOT. So I have to be careful.
Regardless of air or electric, you need some way to control speed that isn’t a toggle switch.