Bridgeport V2XT Z-axis jumping

[CarrowMac]

I have been upgrading a Bridgeport V2XT. My initial test ran went well, but I noticed the z-axis was getting progressively deeper as the program ran. By the end, the Z was programmed to be at -.625" but the actual depth was -.75". Other than that, it ran perfectly. Then yesterday, I was adjusting the z-axis and it started bouncing. Now, it bounces all the time unless I turn the feed rate down under 10 ipm.

Any suggestions on how to get it back to running smoothly? And to get the z-axis to stop slipping?

I'm attaching a link to the video of the bouncing and the most recent report.

https://youtube.com/shorts/3giN_QQwVB0?feature=share

Thanks,
'Carrow

[cnckeith]

maybe a loose pulley? Or a loose encoder. (Less likely ) What make model axis servo motor is installed on this machine?

[cnckeith]

Pull the belt covers off and start looking for lost motion. Pulleys slipping on the shaft etc

[polaraligned]

Looks like it is busting out into oscillation. Try tuning the axis.

[cncsnw]

My guess is a loose encoder. Look inside the motor cap.

[CarrowMac]

Pulley looks good, encoder is connected well, axis is tuned. It will now hold at 10 rpm, but any faster than that and it starts bouncing again.

any suggestions on what to check next?

[cnckeith]

photos and fresh report.zip

[cncsnw]

Do your X and Y axes move smoothly and under control?

If so, what happens if you swap connections (both power and encoder) between X and Z? Does the Z motor fast-jog smoothly using the X controls, or does it still oscillate? Does the X motor still fast-jog smoothly using the Z controls, or does it oscillate?

What are your current PID values? We will be able to see them in your Report when you post it.

I am guessing these are SEM motors, maybe MT30M4-28 models. I have not had any major problems tuning them in the past, with new 2000-line (8000-count) encoders. On some machines I have used reduced PID gains (ca. Kp=0.6, Ki=0.001, Kd = 1.2) to quiet down a tendency to jitter and buzz while sitting still.

What is the resolution (line count) of your new encoders? We will be able to see that in your Report when you post it.