On 07/21/2020 12:14 PM, Matthew Herd wrote:
Hi Rob,
Thanks for the insights. I suspected something along these lines, even if I
might have other problems with noise. I can confirm, the spindle stops way too
slowly and definitely more than 10 revolutions pass before stopping. Long
story short, I can’t readily run the machine in back gear and the slowest I can
go at 60Hz is 560 RPM without backgear.
I do not use backgear or belt reduction when doing small
taps (2-56 up to 10-32). I do the smaller taps at 1000 RPM,
and maybe 600 for the 10-32. So, the motor is running quite
slowly at these speeds, maybe 15 - 20 Hz. This makes it
much easier to stop and reverse the motor. I DO have a
braking resistor on the VFD. You can actually use stovetop
heating elements for this (look in the back of any Haas
machine.)
I’ll play a bit more with how quickly I can stop the spindle with a braking
resistor or I’ll attempt to get the HAL file to engage the mechanical brake to
help transition faster. Nonetheless, 10 revolutions seems fairly ambitious
based on my best guess of how long it might take to stop the spindle even with
a braking resistor. That’s about 1 second, but should be achievable.
Currently the VFD is configured based on the fastest stop time for max RPM, and
there doesn’t seem to be a way to decrease stop time for different inertial
loads (i.e. lower gear ratios/spindle speeds). However, I understand that the
braking resistor should decrease stop time by approximately an order of
magnitude based on some reading I did yesterday.
My machine (Bridgeport with 1J head) can reverse in a
fraction of a second, probably 2 revolutions from 1000 RPM.
Jon
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