Use probe to set z offset?

I have a delta (FLSUN QQ), so there are end stop switches at the top.

Let me first say I don’t entirely understand which config values determine where the bed (z=0) is. [stepper_a/b/c] position_endstop probably? But there’s also [delta_calibrate] height0 which is around 0 when I use the paper method and around 2.3 when I run DELTA_CALIBRATE with the probe. I don’t know what this value represents.

Running DELTA_CLIBRATE is also said to “invalidate the results of probe calibration” but to run DELTA_CALIBRATE I also need to have a calibrated probe. Does that mean I need to calibrate the probe, run DELTA_CALIBRATE and then calibrate the probe again because it was invalidated?

This much was to give you an idea of what level of understanding I have, on to my actual question:

I got a BLTouch mainly because I want to switch between different beds, some things I print on glass and some on FR4, so the thickness of the bed varies.

I totally expected there to be a command that probes the bed and either sets z=0 to be at that height or adjusts the “Z Offset” accordingly.

But now I cannot find such a command, what am I missing?

The klippy.log.

That happens when you instantly delete the template when you open a new General Discussion thread.

Please attach the klippy.log to your next post. If it is too long you can zip (compress it).


I didn’t think the log is of much use when my question is about understanding the documentation. Anyway, here it is. (37.0 KB)

I dare to say, that all your questions are answered in the documentation, you already quoted:

Calibrating the Z-Offset is a completely different thing, as it determines the distance between the probe’s tip and the nozzle to obtain the first layer height.
The process is described here: Probe calibration - Klipper documentation

I just wanted to confirm that the correct setup procedure is then: “Guess” somewhat appropriate delta values, calibrate probe, delta calibration, calibrate probe again.

That is the probe z-offset, which to my understanding is a completely different thing than the Z Offset. I mean this Z Offset (screenshot from fluidd):


I think this latter Z Offset is also sometimes called “babystepping” or that might be another separate thing, not sure.

I also don’t know if this Z Offset is the setting that I need to adjust when I swap out the build plate.

And last and foremost I don’t know what command I should use to re-determine the z=0 point using the probe after I swap out the build plate.

Correct, at least under the assumption your probe has an offset to the nozzle. Otherwise, not needed.

If you home Z with your probe, then the build-plate plays no role as the relevant distance is determined between the trigger point of the probe and its distance to the nozzle.
The build-plate could play a role of course when it comes to a bed mesh, as you cannot be sure that different build-plates have the same “topology”.

I think that is exactly what I want to do, isn’t it? Currently the “Home” button drives the head to the top until it hits the end stop switch and I’m guessing from there (z=377.23) it will use the delta calibration values to know where the build plate (z=0) is? Instead I want it to determine z=0 using the probe. How can I do this?

All is described here: BL-Touch - Klipper documentation

Do you mean the paragraph that starts with “If the BL-Touch will be used to home the Z axis”? I don’t see anything else on that page that could be relevant.

The mentioned paragraph tells me to remove position_endstop in the [stepper_z] config section, which I obviously don’t have. I could try removing position_endstop from all three stepper sections and see what happens, but that config setting is in the part that explicitly says DO NOT EDIT THIS BLOCK OR BELOW. The contents are auto-generated..

AFAIK Deltas typically do not home to Z via a probe because they need to rely on exact alignment of the 3 towers and this can only be achieved via endstops.

But then again, I’m no delta expert, so users with a Delta might shed more light into it.

you wouldnt want to do that.
you need to home at least once when turning on the printer.
just imagine you forget putting the probe in before homing… BAM

well, you could reverse the switch from NO to NC and it will stop homing immediately after starting

A delta homes to the endstops at the top of the rails.

ah maybe I misred it

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