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Setting up Harig SG with VFD - Useful RPM range???


Sep 16, 2015
I'm setting up my Harig 612 surface grinder with a VFD. I've already set the VFD to ramp up/down slowly (prevent shifting the wheel), but I've heard it is advantageous to have some control over the RPM of the wheel (works like increasing / decreasing the wheel hardness?).

What is the useful range to set the RPM parameters? The spindle is a direct drive, 3450 RPM, 1hp unit.

Wheels should never shift. There is clearance to the wheel mount diameter so a wheel that is loose enough to shift is way too loose to do any grinding.
I don't know where the notion came from, likely from the Tormach videos, lucky they did not get sued.
Wheels should be as tight as a normal guy can make them with a 6" long wrench with one hand on the wheel and the other hand on a 6" long wrench..and then a little tighter. I set the wrench end on a block and with two hands on the wheel make it a little tighter

3450 RPM for vitrified 7 or 8" wheels and 5,500 is ok for diamond wheels, two speeds.is enough.
Old timers would ramp up RPM when the wheel diameter got smaller, of for using cup wheels that list a higher speed.
OSHA says don't go over listed RPM.

A verified 7 or 8" wheel may blow up at 5,000.
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I leave the limits open to 100Hz on top end and wide open on the bottom. I have slowed down the wheel plenty of times to help prevent burning on things like hardened D-2.
Thanks for the info fellas. I'll do as you suggested as I plan on using a diamond wheel from time to time.