Runaway Z axis

[caskscob]

For the last week or so I have not had a problem moving the mill with the pendant, or manually through the CNC12 control panel.

Today however, I am moving the Z down to set my part zero location and when I stopped moving the dial on the pendant the mill kept going! Not only did it keep going, it sped up and crashed my drill center through the piece before I could stop it. After that I am testing it and it just keeps acting like it is lost. I tried moving using the control panel and same thing. I rebooted the system, same thing. Basically I can move the X and Y without issues, but the Z has a mind of it's own.

Can anyone tell me what is happening here?


Link to the video: https://share.icloud.com/photos/0QiIT-g ... 8n30QNh8fg

[caskscob]

I noticed now that when the Z is doing whatever it wants, the DRO is not showing that the Z is moving! I switched the motor driver (CL86) with another one that I have for a 4th Axis not yet installed. It does the same thing so it's not the driver module.

[caskscob]

Well... I replaced the encoder cable and it is still doing it. I switched CNC12 to the encoder screen and I can see the encoder counts for the Z axis changing normally. When the position on the Z gets below -9.0" it starts acting weird. When it is moving on it's own the encoder is counting properly but the DRO is not showing any change in the Z position! This has to be the ACORN board right?

[caskscob]

Looks like I discovered the issue. There's something up with the motor compensation table for the Z axis causing the issue. On a hunch I turned off compensation on the Z axis and now it doesn't go off on it's own. I'll have to examine the table to see if there's anything obvious.

[tblough]

Chances are if it's moving on its own and the Acorn DRO is not changing, then the Acorn is not commanding the moves. It's either noise or something wrong with the axis drive. Swap the drive with one of the other axis and see if the problem moves with the drive.

Acorn is an open-loop system so if the axis moves without the Acorn commanding it, the DROs will not update regardless of what the motor encoder is doing.

[martyscncgarage]

Always post a fresh report when asking for help.
F7 Utility, F7 Create Report

Pictures of the machine, motors/drives, and more importantly your control cabinet would be helpful.
Follow this post for better help: viewtopic.php?f=20&t=383

Marty