Servo Spindle - Step & Dir vs PWM?

Working on tuning my lathe spindle and it occurred to me that I've got all the hardware in place to use PWM instead of step & direction.  Right now I've got the drive in step & dir position mode.

I'm using Andy's caxis.comp to switch between spindle and c-axis mode.  It's not going smoothly - the spindle speed isn't right (about half the RPM I'd expect) and the servo isn't positioning gracefully.  Fair amount of over/undershoot.

Just installed a much higher resolution spindle encoder in the hopes that helps me tune the PID values.

For your servo experts out there...is there any benefit to changing the drive to PWM velocity-mode?

I believe it'd basically just be a Mesa firmware change, some drive changes, and changing the INI config (plus tuning).

Drive PWM specs below:

 

If the RPM is wrong in step/dir mode it seems like this
would just be a stepgen (or encoder if you are using encoder feedback)
scaling issue.
 

PCW wrote:

If the RPM is wrong in step/dir mode it seems like this
would just be a stepgen (or encoder if you are using encoder feedback)
scaling issue.


 

 
I have almost certainly hosed up the scaling.  I am using encoder feedback, but it's made complicated by a difference between the motor encoder count being different from the spindle encoder count, plus a not-quite-standard belth ratio.

In the other c-axis thread I've discovered that I'm going to have to work around two different units using the same stepgen scale (revs vs degrees).  It occurred to me that if the drive is in velocity mode then stepgen units are no longer an issue.  500rpm is 500rpm, whether it's in spindle mode or axis mode.