UBL and Z-Offset: Manual probing of points where probe can't reach

I'm using 10-points (x and y) UBL with an inductive Z-Probe. The Z-offset is -1.9mm and everything is working fine except one thing:

My bed is bend a little at the corners. As the probe sits on the right side of the needle, printing at the corners is pretty much compensated with UBL on the right side of the bed.
But: The probe can't reach to the edge on the left side. UBL automatically fills in the 2 points along the X-axis that the probe can't reach with "G29 P3 T".
And they are pretty good calculated too, except the 2 outermost points on every corner.

Now finally the question:
How to probe these points manually with UBL considering my Z-Offset? I can't probe with needle +1.9mm in the air...

Edited 4 time(s). Last edit at 03/08/2018 07:32AM by LichtiMC.

If you have an inductive probe, the Z_PROBE_OFFSET_FROM_EXTRUDER will be positive and not negative.

You can move the nozzle to the corner and do a G29 P4 R to edit the points in that region.
Raise or lower the mesh points as appropriate.
Then do a G26 and see if the filament looks correct everywhere.
If not... Move the nozzle to the 'bad' areas and do another G29 P4 R.

Nope it's negative.

And yes I know that it's possible using the G29 P4 command, but I would really like to have a solution where the nozzle moves as I change the points on LCD.
But I guess there isn't one.

Edited 2 time(s). Last edit at 03/12/2018 11:49AM by LichtiMC.

You can turn on UBL_MESH_EDIT_MOVES_Z, but you still should use the LCD Panel to see how much you have moved the mesh point.

Quote
Roxy
If you have an inductive probe, the Z_PROBE_OFFSET_FROM_EXTRUDER will be positive and not negative.

I can't think of any situation where a positive Z_PROBE_OFFSET_FROM_EXTRUDER makes sense unless you can probe without the nozzle in place (like E3Ds new tool-changing design). The actual physical position of the probe is pretty much irrelevant - only the triggering point matters and if the triggering point is above the tip of the nozzle (which a positive Z_PROBE_OFFSET_FROM_EXTRUDER implies) then you're pretty much guaranteed to have the nozzle hit the bed when probing. In fact I would recommend adding a sanity check to ensure that Z_PROBE_OFFSET_FROM_EXTRUDER is negative.

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MMcLure
In fact I would recommend adding a sanity check to ensure that Z_PROBE_OFFSET_FROM_EXTRUDER is negative.

I would recommend you rethink the issue.
And if necessary... discuss with people that have inductive and capacitive probes.

Quote
Roxy
I would recommend you rethink the issue.
And if necessary... discuss with people that have inductive and capacitive probes.

I have an inductive probe. My Z_PROBE_OFFSET_FROM_EXTRUDER is -1.35 and everything works perfectly. The bottom of my probe is about 2.5mm above the tip of my nozzle, but because the trigger distance (around 4mm) is larger than the distance between the probe bottom and the nozzle tip it results in a negative Z_PROBE_OFFSET_FROM_EXTRUDER. If Z_PROBE_OFFSET_FROM_EXTRUDER was positive, it would mean that the probe trigger point is higher than the nozzle tip and that would make the nozzle hit the bed when probing.

Edited 1 time(s). Last edit at 04/14/2018 06:23PM by MMcLure.

Honestly, I think if the setting name were changed to "Z_HEIGHT_AT_Z_PROBE_TRIGGER_POINT" and its sign was changed (so in my case I'd use 1.35 for it) it would make much more sense and be easier to understand.

Yes, probably ... though it would'nt be dangerous if you by accident set a positive nr. as Z_PROBE_OFFSET_FROM_EXTRUDER.
I did so and realized soon, that the nozzle would move away from the heatbed in the opposite direction I wanted it to.

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MMcLure
I can't think of any situation where a positive Z_PROBE_OFFSET_FROM_EXTRUDER makes sense unless you can probe without the nozzle in place (like E3Ds new tool-changing design).

Think of foldable probes...

Edited 2 time(s). Last edit at 04/14/2018 06:52PM by LichtiMC.

The one reason I can see for a positive Z_PROBE_OFFSET_FROM_EXTRUDER is the case where you have a spring-loaded nozzle with a switch where you actually need the nozzle to go "under" the bed to trigger the switch. But in the great majority of cases Z_PROBE_OFFSET_FROM_EXTRUDER will be negative.

Quote
LichtiMC
Think of foldable probes...

The probe should still trigger before the nozzle hits the bed, right? In which case Z_PROBE_OFFSET_FROM_EXTRUDER would still be negative. Unless I'm misunderstanding what you mean by "foldable probe" - I'm assuming you mean something like a probe that gets moved into place by a servo and then can be stowed out of the way.