Hitachi ne-s1 and motor stall

[challenger]

I have a Hitachi ne-s1 inverter powering my Burke horizontal mill. The mill has a lima gear motor that's 3-ph 1/2ho and twelve available speeds when combining the gears and 3 pulleys. My problem is that I'm turning down a brake rotor which requires lower rpm than the lowest available through the motor/pulley combination. I have the inverter powering the mill but it will stall the motor. I have it set up for the proper kw, hp, number of poles (6-1200 rpm motor) and automatic torque control. Is there another setting I'm overlooking?
Thanks

[J Tiers]

When you slow the motor (and spindle) with the VFD, you lose power in proportion to the reduction in speed, AND you get NO advantage in torque (both same issue, really). Half speed means half power vs normal.

When you slow the spindle with gearing or belts, you preserve essentially the SAME power, and the torque is INCREASED by the reduction ratio. So 5x slower means 5x more torque and same power as before..

There is no setting that will get around that, it is just a mechanical fact. The only way to avoid the issue with a VFD system is to use a much larger motor and VFD, so that even when you lose power at slow speeds, you still have enough.