My spindle will happily run for over an hour before getting slightly above luke warm and thats cutting not just spinning. That said I don't run it without water but in the past I have had too when the pumps broke etc so if yours is getting hot then somethings definately wrong.? If it's getting above warm in just a few minutes then I suggest something is wrong. Check the VFD settings to make sure the Amps or volts are correct.