HY VFD and spindle at low speed

[Neale]

I agree as far as the motor is concerned, but the VFD has various torque-related settings and corresponding parameters, including things like voltage-frequency linking which can boost torque at lower speeds by increasing applied voltage - useful during acceleration if the motor has load on it at startup. I think - I'm still trying to understand the manual and the various settings available. I'm also aware that there must be some kind of feedback system as there is a set of PID parameters that can be modified, which implies feedback. Given that the speed is notionally determined by VFD output frequency, modified to some small extent by slip, I assume that this feedback system will boost applied voltage and hence current to increase torque if the sensing system believes that the motor speed is too low due to applied load on the spindle. Maybe - it's guesswork on my part at this stage!

One thing that does seem to be true is that increasing depth of cut and hence spindle load by a small amount (0.4mm to 0.5mm) seems to smooth things out slightly, which agrees with my thinking that any feedback mechanism in place, governed by the PID parameters, is tuned on the basis of a more heavily-loaded motor than I am presenting, or at least the parameters are not really optimised for the speed/load combination I am using.

I know that the display can be switched to display motor current, so I'm going to have a look at that tomorrow, running the motor at various speeds. Assuming that the displayed value is actually an accurate representation of motor current!

Trouble is, the rate of cut is low enough that I am standing there vacuuming up chips for long enough that my mind starts speculating on what's going on; I need to keep my "engineer" hat on long enough to just get on with it while it's working!