DGG said:

This post contains updates and corrections to information presented in
my original Delta 46-756 lathe review.

The VFD controller information, in particular, is relevant to
Powermatic and Jet EVS owners as well, since it turns out they all
come from the same factory as the Delta units. Primary differences
lie in the varying degrees of eloquence in implementing the units into
the final product.

Don't care? Don't own one? Stop here...
Otherwise, on with the show...

The original post discusses problems with runaway motor speed
and failure to remove motor drive when the stop button is pressed.
Additional info as follows.

These findings are applicable to all AC motor/VFD setups.
Additionally, I am now able to reproduce the fault at will.

The process of exploration reveals that the motor rotor is a rich
source of EMF which is induced by the harmonic rich pulses from the
VFD Drive. It seems to be aggravated by the 10kHz carrier rate
chosen. Imagine my surprise when I discovered that there is up to 45
volts of crap present on the rotor, and current up to .5 amps. The
unpowered-state resistance of the rotor to ground varies from 0 to 125
ohms. I would hazard a guess that bearing erosion or fluting is a
potential problem since the only path to ground for this potential
lies in the bearings themselves. A prudent consideration on any VFD
setup that does not use a specialty motor would be some sort of rotor
grounding mechanism. A graphite tipped grounding strap which rides on
the end of the rotor shaft, for instance; similar to almost every VCR
head drum motor ever built.

But this is not the only source of my immediate problem, however.
Apparently, the controller is working as advertised, but excessive
regeneration is causing the controller to hang in an infinite state of
overvolt protection while waiting for the DC Bus voltage to subside
before decelerating the motor. The feedback from the freewheeling
motor never subsides, so the controller just sits and waits. How do
you reduce regeneration? Well, one way is to apply a load - and sure
enough, placing heavy pressure on the handwheel causes the controller
to respond and continue on to decelerate the motor.

So, what is the cure? That's a tougher question, since any meaningful
changes would probably require rewriting register settings in the
controller and/or the addition of a zero phase reactor and/or shielded
motor feed wiring - which would most likely nullify their picky-ass
warranty. But since any number of replacement controllers are
probably going to respond in the same way, the fix is probably not as
straightforward as replacing a defective part. So we end up in a
Catch-22 situation that has probably resulted in loads of these lathes
being shipped back as terminally defective. And I'll be darned if I'm
waiting until January of next year for a part that probably won't fix
anything, or paying for the modifications out of pocket. I've got at
least two hours in the project already - not counting the interface
and VFD familiarization.

The thing that gets me, however, is that I bought a lathe to turn
wood, not to troubleshoot in lieu of the seemingly dysfunctional R&D
team at Block and Wrecker, or to sit for 3 months+ waiting on a fix.
This could get ugly... ;-)