I have been evaluating 2.2kw 220V ER20 80mm water cooled spindles for my Onefinity.

From what I have been told it is best not to operate Chinese spindles below 10k rpm. The German Mechatron spindle will operate with constant torque down to 6k and can be run as low as 3k with no damage, albeit with much reduced torque but still usable.

So, does someone know what the physical difference in the Chinese spindles that causes them to have less turndown as compared to the German manufacturer?

I want to occasionally machine some brass and the turndown would be helpful.