Can you let me know what the lowest usable spindle speed will be?
You can run the spindle all the way to 0 RPM.
Follow up question
Is there a high/low belt/pulley system? Or is it fixed at a doubler (1:2 overdrive per specs)
With only an ER20 collet, not sure I could ever runs tools large enough for very low RPMS (shell mill, etc.) so likely a non issue
From all the documentation I can find it is only 1:2.