Servo tuning issues (Velocity mode driven from 7i77)

Adam,
Sorry about forgetting to include this info.
Lathe: Nardini FastTrace toolroom lathe.
Motors: DMM 86M-DHT 750W (no brake)
Drives: DYN4, 240VAC
Inertia: I could do a lot of calculation and find this, but I have no specs. How would I go about quantifying this without disassembling the machine and weighing the saddle/cross slide?
Reduction: 4:1, belts

As for temp issues, the servo does not actually have temperature feedback (or that's what I was told). The temperature is calculated within the DYN4 based on load detected. Odd, but maybe that works.

I set up the X axis as torque mode, and so far it's gone a lot smoother.

Attached is how far I've gotten in LinuxCNC. One thing that is persistent in all is the flatline f_error both before and after jog motions. Am I missing something here? Is it a tuning issue or an artifact of jog motions vs MDI?

(purple = vel-fb, overlayed on green = joint-vel-cmd, blue = output, red = f-error)

I'm on my phone so just a quick reply, but I think you want your output scale of -10 for full torque and -10 for minimum and 10 for Max. Look back at my screenshot.

As for inertia, I would say it's low. You have a 4:1 belt and 5tpi screw?

I had a spreadsheet I put together to calculate inertia, I will see if I can find it.

Also, the drive knows the current/voltage through the motor and the resistance of the windings. With these, they can calculate power loss as heat. I've never seen the thermal shutdown. Is everything hot or does it run cool? If it's hot, the motor could be too small for the axis.

When all the other tuning is done you can add some I term to remove the static error
(and you may be able to add enough to remove a significant amount of the motors torque ripple)

Beware that too much I term will cause instability with _large_ oscillations so reduce your following
error limits to something reasonable before playing with it. That said, it is good to find out how much is too much...

Edit: Also for torque mode drives you may be able to increase the servo thread rate to
2 or 4 KHz to get better performance (higher stable P and D terms )