I've been using UBL for a long time now and I'm on the Marlin 1.1 bugfix branch.

In my configuration.h file, I have ENABLE_LEVELING_FADE_HEIGHT defined. The default fade height is 10 mm. So once the Z is >= 10, no more bed leveling compensation will be done.

This is easy to see. If you set UBL active, then after homing raise the carriage to Z=10.0, and execute moves around the build area, you won't see any visible Z compensation happening. If you move to Z=2.0, you will see the Z compensation working.

So, let's say I just homed, so I'm at X0, Y0, and Z2. Now I raise the carriage to Z10, and do a G1 X185 Y185. There was no change in the Z compensation on that move. Now if I lower the print head to Z0, does the Z compensation get applied? If it does, then theoretically, I should be able to check that point with my feeler gauge and it should still be the same as when I did the initial mesh calibration.

Also, if I want to do some G29 P4 fine tuning of the mesh, should I deactivate UBL first and re-home before attempting this, or does the code automatically figure it out?

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brucehvn
So, let's say I just homed, so I'm at X0, Y0, and Z2. Now I raise the carriage to Z10, and do a G1 X185 Y185. There was no change in the Z compensation on that move. Now if I lower the print head to Z0, does the Z compensation get applied? If it does, then theoretically, I should be able to check that point with my feeler gauge and it should still be the same as when I did the initial mesh calibration.

UBL was written such that it is the destination coordinate of a move that is important. Whether the source is corrected or not... The destination coordinate is corrected (if UBL is active). So... Changing things does not always impact what you see on the nozzle.
But the nozzle will be corrected after the first move. If you want to see the correction for the current location, you can jog .1mm to the left. And the jog back .1mm to the right. And the nozzle will be in the 'corrected' location.

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brucehvn
Also, if I want to do some G29 P4 fine tuning of the mesh, should I deactivate UBL first and re-home before attempting this, or does the code automatically figure it out?

No... That is all handled for you. And in fact... most people prefer the nozzle does not move during a G29 P4 edit (in the Z direction). The nozzle is only moving around the bed to show you which point is being edited. Once it is at the point being edited... The number on the LCD Display is what is important. You are moving the mesh point up or down by what is shown on the display.

Edited 1 time(s). Last edit at 08/26/2018 11:15PM by Roxy.