[BUG] Z probe offset ignored unless UBL is enabled

[nelsongraca]

Did you test the latest bugfix-2.0.x code?

Yes, and the problem still exists.

Bug Description

Running latest code from bugfix-2.0.x branch, can't test latest release since there is a fix to avoid watchdog restarting when saving UBL mesh.

If I set probe offset M851 Z0 and run G28 and then G0 Z0 the distance of nozzle to bed is around 2mm, if I set the Z offset M851 Z-1.5 then G28 and G0 Z0 the nozzle to bed distance is still around 2mm when should be 0.5mm.

If I then run G29 P0, G29 P2, G29 P3 (until the mesh is complete) G29 S0, G29 A. When I home with G28 and then G0 Z0 the distance of the nozzle to bed is 0.5mm.

G29 T shows a grid full of values around -1.5, I assume the grid is having the offset subtracted.

Current config attached.

More info or tests ask.

Bug Timeline

No response

Expected behavior

No response

Actual behavior

No response

Steps to Reproduce

No response

Version of Marlin Firmware

hotfix-2.0.x

Printer model

Ender 5 Pro

Electronics

Stock Creality 4.2.2

Add-ons

BL Touch connected to the 5 pin connector

Your Slicer

No response

Host Software

No response

Additional information & file uploads

No response

[nelsongraca]

config.zip

[nelsongraca]

Something I just tested enabled Z_MIN_PROBE_USES_Z_MIN_ENDSTOP_PIN and disabled USE_PROBE_FOR_Z_HOMING and changed the black and white wires from the dedicated bl touch connector to the Z switch, now everything works as expected.
The reported problem no longer happens, I wonder if it's some different behavior due to this config.

[strayr]

I ran into this as well. A G29 J will get it to print correctly, but it makes calibration prints that don't need UBL a but annoying. I could rewire my printer to solve this, but it appears to be a regression from 2.0.7.2 behaviour

[strayr]

A followup, G29J gets me a first layer on the bed, but my prints are stretched upwards by the Z-offset over the UBL fade distance. That's usually about 2mm for most bl-touch style setups over a default of 10mm which not only makes prints way off size wise but also look awful. I didn't notice the height was wrong until I compared it against the same print done with 2.0.7.2 era bugfix.

This change is recent and affects everyone who uses a probe on dedicated pins, so the default install for ender 3 users.

A better summary is "Z offset is applied to mesh not home position when USE_PROBE_FOR_Z_HOMING is enabled, and it breaks everything"

[strayr]

This also looks like the same issue #21584

[thinkyhead]

Whenever there are homing or leveling issues, we now ask everyone to follow a standard procedure to gather more information so that we're not just taking stabs in the dark. Here is the boilerplate:

• Download Marlin bugfix-2.0.x to test with the latest code.
• Enable DEBUG_LEVELING_FEATURE and M114_DETAIL and re-flash the firmware.
• Connect to your printer from host software such as Cura, Printrun or Repetier Host.
• Send M502 and M500 to ensure your Configurations are applied.
• Issue the command M111 S247 to enable maximum logging.
• Perform a G28 to do your standard homing procedure.
• Do a G29 to probe the bed. This will also enable bed leveling.
• Copy the log output into a .TXT file and attach it to your next reply.

Repeat this procedure, if needed, to demonstrate inconsistencies. From these logs we should hopefully get a better idea of what's going on with your machine.

[strayr]

Thanks for that @thinkyhead
I've just found another and was working on documenting it, i'll redo with detailed logging. Going to have to make a quick conversion harness so i'm not rewiring connectors when chaning how the probe is wired, but something has gone really sideways.

[spikedsoft]

I have the same problem when I use bilinear leveling.

I do the Leveling with G29, then Home with G28, Move to Z0, disable the Soft-Endstops, move down to the correct Z height and set that height as the Z-Offset with M851, but then after another G28 and Move to Z0 it is at the position where it was before, ignoring the offset. Even if i set something extreme like M851 Z10 it doesn't make any difference.

When using UBL it works (after G29 J, withouth G29 J it's the same problem)... But i guess with the same caveat reported by strayr.

Attached is my config as well as the output from the procedure you requested.

Marlin_Config_Debug.zip

Let me know if you need more information. Also feel free to contact me on your Discord if you want, i'm loged in as "spikedsoft" on your Server.

[strayr]

Ok, ive spent a lot of time on this trying to replicate, bugfix as of 3am today and 2.0.8 release work independent of how i configure my probe.
I think i managed to replicate it by not doing an M502 M500 after flashing firmware at some point but couldn't reproduce reliably.
I need to get in the habit of dumping "good" settings by M503 to a text file, and just running that as gcode on fresh firmware. And getting better at git so i can go back to an old firmware and config and know what it was built off.

[spikedsoft]

Here is an update after receiving Discord Support:

The problem in my case has been that I used the regular Z-endstops instead of the probe for Z-homing. After changing it to use the probe it works as expected now.

The reason i was using the endstops is that the printer uses dual Z motors and dual Z endstops and i liked the automatic synchronization i got by using the endstops. I now enabled Z_STEPPER_AUTO_ALIGN instead and that works as well.

However, it makes things a bit slow, having to do G34 every time before the print.

Is it intended that the probe Z-offset is only applied when the probe is also used for homing?

[no-trick-pony]

Here is an update after receiving Discord Support:

The problem in my case has been that I used the regular Z-endstops instead of the probe for Z-homing. After changing it to use the probe it works as expected now.

The reason i was using the endstops is that the printer uses dual Z motors and dual Z endstops and i liked the automatic synchronization i got by using the endstops. I now enabled Z_STEPPER_AUTO_ALIGN instead and that works as well.

However, it makes things a bit slow, having to do G34 every time before the print.

Is it intended that the probe Z-offset is only applied when the probe is also used for homing?

Do you by any chance know if this is a new issue (or a version where this still worked for you)? On my machine with Marlin 2.0.6 (which is now ~1 year old) z-probe offset is ignored as well with BL touch, ABL_BILINEAR and dual z-motors. I can literally set any value for z-probe offset, save it, do the leveling, save that, print, and it will start printing 0.5mm too high, as for every print. I am using the z-endstops as well (mostly for synchronization and because I trust them more to not fail and cause a fatal crash). Right now I am looking through open and closed issues and this is the closest one I found so far. Since this issue here apparently concerns my exact setup, updating to the newest version of Marlin seems pointless as well. Not sure what to do.

[spikedsoft]

Do you by any chance know if this is a new issue (or a version where this still worked for you)? On my machine with Marlin 2.0.6 (which is now ~1 year old) z-probe offset is ignored as well with BL touch, ABL_BILINEAR and dual z-motors. I can literally set any value for z-probe offset, save it, do the leveling, save that, print, and it will start printing 0.5mm to high, as always. I am using the z-endstops as well (mostly for synchronization and because I trust them more to not fail and cause a fatal crash). Right now I am looking through open and closed issues and this is the closest one I found so far. Since this issue here apparently concerns my exact setup, updating to the newest version of Marlin seems pointless as well. Not sure what to do.

I don't know if it's a new issue.. The original Chiron firmware didn't have the problem but i don't know how that was configured...

However, I also got a bit annoyed at having to run G34 before every print.... I found a solution that works for me.. Instead of tuning the Z-probe-offset, i now tune the Z-home position. I figured that out after quite a bit of trial and error... I never read about this method anywhere before so maybe it's wrong.. Use it at your own risk... :) But so far i didn't have issues and I can finally use the Z-endstops again in combination with BL-Touch leveling...

In order for this to work, you should make sure that your Z-home position is at 0 at the beginning (check it with M503).

Here is the procedure i do for leveling:

1. Heat up the bed, and manually level it via the 4 leveling screws...
2. Home and move to Z0 - G28 / G90 / G1 Z0
3. Now use Babystepping to move the nozzle to the correct zero position. Remember the displayed Z offset.
4. Update the Z-home by negating the value from step 4 - M206 Z<Value from step 3 * -1>
5. Run ABL

After step 4, you can test if it homes to the correct height.. But keep your finger on the power switch in case it crashes the bed... :) If it doesn't go to the position you previously set and you have soft Z endstops enabled, you may have to disable them...

After running that procedure, it should be approximately correct.. If it's not perfect, you can fine-tune the Z-home position by first resetting it to 0 (M206 Z0) and then doing a first-layer test print. While it's printing, babystep the Z-position until you're satisfied and again note the displayed Z offset. Then set the Z-home position again like in step 4...