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What I do not understand..... bed-mesh related

Mike Eitel

Well-known member
Just a silly request:

1. I do homing. all fine
2, I run a quad gantry leveling. all fine , adjusts better than the size of a hair.
3. I run bed-mesh. all fine, the distortion is not too big and my resulting prints are ok.

But then I made the mistake to look more in detail to the result of bed mesh.... and get puzzled....

My QGL worked out better then 0.01 .. But bed mesh shows values in the corners much bigger then the expected 0 ( or around 0.01 ) ????

That makes no sense for me.
In my understanding the gantry is mechanically adjusted to be equidistant to the 4 bed corners.
( if you start with one artificial miss-adjusted corner you see the correction by eye)

So how can it be that a bed-mesh is not near to zero in all 4 corners.

I'm very curious to see my wrong thinking


Mike Eitel

Well-known member
Amazing quite some reads, but no comments.

A'm I the only that has this discrepancy between 'adjusred' bed and afterward measured gantry?


Well-known member
It's a good question and I am no pro about the topic. But if you look at the bed mesh the corners are not at the same height. It's not even possible because every bed will be slightly warped I would guess.
Please don't as why QGL does not put the left upper corner more down to compensate...


Mike Eitel

Well-known member
So you have exactly the same effect.
And naturally the beds are never plane.
Maybe one of the geniuses that wrote this good SW will read that and can explain.. ;-)


Active member
Maybe the corners (probe points) of the bed_mesh and the corners of the quad_gantry_level are not in the exact same locations?

If they are not in the exact same location, and the bed+magnet+steel+PEI sheets are not perfectly flat, then the slightest difference in probe point location will likely result in a Z diff between the corners of a bed_mesh and the corners of a quad_gantry_level.

Perhaps it's worth to try and see if the deviations are reduced when the corner probe points are made exactly the same?

To make them the same, as I understand it:
* Set the [bed_mesh] "mesh_min" value to the same as the first entry (1 of 4) in the [quad_gantry_level] "points"
* Set the [bed_mesh] "mesh_max" value to the same as the third entry (3 of 4) in the [quad_gantry_level] "points"

Maybe something like this, temporary settings while debugging:
mesh_min: 25,25
mesh_max: 325,325


Mike Eitel

Well-known member
I played with these values and also regarded the distances to the joints (outside of bed - 60,-10 and 410,420)
I even tried to remeasure these values and also believe to understand their existence.

And no, changing the 4 bed-measured-points did not change the behavior.