Gary, for a 2-pole motor (which these spindles normally are), your equation is technically right, but it’s much easier to times and divide by 60 (the inverse of .016667).
Hz x 60 = RPM; RPM / 60 = Hz
Note this only works for 2 pole motors. Some spindles are 4-pole and for those you would use 30 instead of 60 in the equation.
As far as the VFD settings, I can’t offer much help there.
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