Using current as cutting force indicator?

[Jonathan]

Do you think that the Current reading as produced by the VFD is a good indicator of cutting force or is there a better way to measure or derive cutting force? Sorry I know little about how these motors actually work and I'm assuming it will use more current under higher load?

As a first approximation, yes the spindle will draw more current as the load increases. The problem is the motor efficiency changes with load and speed, so it's tricky to estimate the actual torque output, though not impossible. If you subtract the no-load current from the current whilst cutting, that's a good start. But if you're more interested in not overloading the spindle, then just looking at the phase current as a proportion of the rated current is sensible.

I'd almost forgotten about that thread discussing linking torque to feedrate, but I've got a bit further with my motor drive I will use in it so it wont be too long now.