Got a TECO N3 VFD to power the spindle motor for my old Hurco KMB1. I
was using a static phase converter on this machine, but the
acceleration ramp up to speed was excessive. The TECO is a 1ph in 3ph
out, and seems to work fine. I have it's I/O configured to accept the
Hurco's FWD/REV signals, and it outputs overload to the Hurco
control. Fine so far, but the braking from full RPM to zero is not as
quick as I might like.

I was hoping to not have to rely on the air operated mechanical
spindle brake, but with the N3's DC injection braking set to max., the
spindle takes ~ 3 seconds to stop without the mechanical brake. I
purchased the optional braking resistor, but it's not clear from the
manual if this really enhances braking over DC injection, or if it's
really more for situations like putting a constant drag on a play out
reel, or slowing a large inertia of some sort. Normally this machine
uses the mechanical brake for stopping at the bottom of a tapping
cycle, before reversing.

Max RPM is the other question. The motor is a 1800 rpm, but could be
dialed up to 3600 at 120 hz. This would save having to crank the vary-
speed belt drive up for smaller end mills, but if it's going to kill
the motor bearings I'm not going to try it. I did run it up to 2400
rpm for a few minutes and it seemed smooth and quiet. I'm guessing the
bearings on 1800 rpm and 3600 rpm motors are the same, and since it's
a 3ph motor there are no windings to throw. Also the Hurco control
board has an analog speed command which I could wire up. This could
be kinda nice, as the program could then control the spindle speed as
coded, instead or the present operator adjust. Setting the vary-drive
to a fixed speed, say 2500 spindle rpm @ 1800 motor rpm would allow me
to cover 500 to 5000 rpm using only the VFD. So far the VFD has not
spiked the 24 year old motor's insulation..