On Thursday 24 January 2019 08:41:47 Todd Zuercher wrote:
I have a fair amount of experience with high speed spindles. And I've
found that most are incapable of running much below about 1/3 of their
rated speed for any length of time, and cutting anything at those
speeds is certainly out of the question. If you don't believe me,
start your 18k rpm spindle at 4000rpm and then check the current
readout display on the VFD, and you will be shocked at what numbers
you see displayed (I'd venture a guess that it would be close to about
200% of rated amps on the motor name plate).
This would indicate the Volts/Hz ratio is not set right.
This might make the spindle accelerate better, but if set up
properly, you should not see excessive current at low
speeds. Some drives have multiple breakpoints, so the V/Hz
curve can have multiple slopes between those points.
We have a really off-brand mill at work that has an 18000
RPM spindle. You can run it all day at 1000 RPM with no
heating. It really lacks torque at all speeds, obviously
designed for high speed, but won't burn anything up.
Jon
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