[BUG] Probe Z offset vs Home Z offset when using UBL (may only apply to DWIN display)

[TheAndr0id]

Did you test the latest bugfix-2.1.x code?

Yes, and the problem still exists.

Bug Description

This might be a feature request, it might be a bug. I've flipped back and forth and settled on a bug because I think it's not working as intended. Maybe.

First some background. I use UBL, and I never looked into any of the ABL forms as UBL just makes sense to me.

Just for clarity, I am talking about M851 XYZ Probe Offset vs Home Offsets.

I see the UBL probe data as a topology of the bed, I perform the 100(ish) probe points with Probe Z offset = 0, then use the G29 P5 C command to unify them down by the mean average. This gives a +- topology of my bed surface. I then use a 4 point adjustment probe before each print (G29 J2) to adjust the stored UBL data.

The issue I struggled with was how to handle nozzle changes. I wasn't looking forward to having to redo the UBL bed probe every time I switched to a different nozzle. Now it sounds obvious, but at the time realizing the how the home offset was going to work was a eureka moment. Change the nozzle, print a couple of bed leveling test patches and adjust the Home Offset Z value to taste. Done and done.

From my testing on an Ender 3v2 (DWIN) using UBL, I found that setting the Probe Offset didn't change the Z height at all, it only changed the probe values during the probing process. Changing the Home Offset did work dynamically during a print or otherwise. This all makes sense given the premise of UBL.

Here's the bug/feature request. Currently if a probe is configured then all of the UI settings show configuring the Probe Offset Z, not the Home Offset Z, even though the probe offset really doesn't make sense when using UBL. (Again, I don't know the other ABL methods so maybe this is also an issue?)

The DWIN interface has setting values in multiple places (Prepare, Control/Advanced, Tuning during print) and seem to utilize the HAS_BED_PROBE define to switch from Home Offset Z to Probe Offset Z. I've found switching these to HAS_ONESTEP_LEVEL switches this back(mostly - Tune menu is hard coded) to Home Offset Z.

I've found there are other changes needed for the edited values (Draw_Edit_Signed_Float2 vs Draw_Edit_Signed_Float3) and how the scaled values for Home Offsets are stored when changed under Advanced Settings. The Chinese language entries are a guess at best for me. There's also a minor issue where if Home Offset Z is set it also saves all settings to EEPROM (see HMI_Zoffset()). This could cause serious issues - by default UBL_SAVE_ACTIVE_ON_M500 is defined, and if this was done after the G29 J2 is run, your UBL stored mesh is now ruined...

Bug Timeline

old

Expected behavior

Mostly see the description above. I was expecting to be able to control the distance of the nozzle above the bed.

Actual behavior

Probe offset Z only impacts probe measurements not live distance between the bed and the nozzle. If any bed probe is defined all of the interfaces menu items switch to only being able to change the Probe Offset Z, not the Home Offset Z.

Steps to Reproduce

1. Enable UBL using DWIN (may be impacting other interfaces), compile, flash.
2. Visit menus see that all of them change Probe Offset Z not Home Offset Z.
3. Change Probe Offset Z and note nothing changes during an active print.

Version of Marlin Firmware

2.1.2.5

Printer model

Ender 3v2

Electronics

Stock

LCD/Controller

DWIN

Other add-ons

none

Bed Leveling

UBL Bilinear mesh

Your Slicer

Slic3r

Host Software

None

Don't forget to include

• A ZIP file containing your Configuration.h and Configuration_adv.h.

Additional information & file uploads

Configurations.zip

[classicrocker883]

i think that is the confusion then. Probe Offset Z vs Home Offset Z
correct me if im wrong but is the TL;DR basically...?:

Probe offset Z only impacts probe measurements not live distance between the bed and the nozzle. If any bed probe is defined all of the interfaces menu items switch to only being able to change the Probe Offset Z, not the Home Offset Z.

after changing the nozzle you should just need to just the Z offset, and by that I mean Home offset for Z.
if the Probe Offset for Z changes the actual probe point measurements then there's no need to touch that unless it is to change just a point right?

I found that setting the Probe Offset didn't change the Z height at all, it only changed the probe values during the probing process. Changing the Home Offset did work dynamically during a print or otherwise. This all makes sense given the premise of UBL.

I'm used to ProUI and the layout is more intuitive

[TheAndr0id]

I think we're on the same page, the feature/bug is what is accessible from the user interface. If bed leveling is used (any type) currently the interface only allows the setting of Probe Offset Z. This has no benefit until you do a full bed probe, which under UBL you don't normally do. Home Offset Z is dynamic and can be done at any time with immediate effect and this is much more useful when using UBL.

For instance I have one type of filament that doesn't like ambient temperatures greater than 25C - it won't stick to the bed (also warps). If I decrease the distance to the bed giving it a little more squish then it might be able to put down the first layer. I can dynamically tune the Home Offset Z at the start of the print to get things started, but in the current config that requires hooking up a serial cable to issue an M206.

[thinkyhead]

• The home offset in Marlin 2.1.3 is applied only at the end of G28 and then it is not touched or used again.
• The "probe offset" is not meant to override or affect the "home offset" which is not the same thing as "babystepping."
• Babystepping has two modes:
  • With BABYSTEP_ZPROBE_OFFSET your babystepping is seen as a correction to the probe offset and after you dial it in you can save it with M500.
  • Without BABYSTEP_ZPROBE_OFFSET your babystepping simply moves the Z axis without touching any coordinates in the firmware. It just physically moves the nozzle.

The designers of the DWIN displays made their choices. These can be changed if some options are hidden when they should not be. None of them apply babystepping to the home_offset.z.