[BUG] Mesh bed levelling grid offset

[Gixy31]

Printer model

MK3

MMU model

No-MMU

Firmware versions

3.14

Upgrades and modifications

None

Printing from...

SD Card

Describe the bug

Since several upgrades, the mesh bed levelling grid is offset by sevral cm to the left, i.e no more centered on the bed. This has been already signaled in the forum, but still not answered. It is clearly a firmware bug, probably an incorrect offset parameter for this type of printer. Please correct this as the bed levelling is thus inconsistent.

How to reproduce

nothing to do, just perform mesh bed levelling on a MK3 printer.

Expected behavior

Grid centerd on the bed, which is no more the case.

Files

No response

[Gixy31]

Video sent to support team, without reaction, no answer here neither, what a useless community...

[github-actions]

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[Gixy31]

Just an update to avoid closing...

[3d-gussner]

@Gixy31 I assigned this issue to myself so the stale bot will not close it.
As this is not a trivial issue, we gonna need some time to look at it.

Do you have by chance an idea with which version this changed?

[3d-gussner]

I just printed a 250x210x0.2 two perimeter square (no bottom or top layers) without a brim or skirt.
On my MK3S the

• left line is about 3mm from the sheet edge
• right line is about 1mm from the sheet edge

My XYZ cal. details
Y distance from min
Left: 11.83mm
Right: 11.80mm
Skew 0.07°
[0;0] point offset
X 0.44mm
Y 1.33mm

[3d-gussner]

Printed a tiny 0.8 x 0.8 x 6 "tower" centered on the bed using the MK404 sim. To monitor the position I used M155 S1 C5 to autoreport the temperature and positions. The tiny moves of this tower where very very close to the center by 0.xx mm. The differences are related to the XYZ cal values that the MK404 SIM has.

[Gixy31]

Hi,
The problem isn't related to normal printing, but only to the mesh bed leveling function, which is offset to the left of more than 2cm! Printing is OK, but the right part of the sheet is never measured, even with the 7x7 grid. In the 7x7 configuration, I even had situation where there were only 6 columns...

[3d-gussner]

@Gixy31 Thanks for clarifying the issue. We will have a look into this.

[3d-gussner]

I went back to v3.12.3, v3.9.3 and even back to v3.8.0 and the Mesh bed leveling always ends at X 205 position. With the PINDA x offset off 23 the PINDA is at 228 X position.

1/9 X at 1 --> PINDA X 24
2/9 X at 103 --> PINDA 126
3/9 X at 205 --> PINDA 228

I don't understand when did this change?

Also the PINDA at 2/9 is at X 126 which is nearly middle of the 250 on X. Very good compromise between print area 250 and X axis ~255 length (Belt test).
250 / 2 = 125
~255 / 2 = 127.5
Avg = 126.25

Since several upgrades, the mesh bed levelling grid is offset by sevral cm to the left, i.e no more centered on the bed.

[Gixy31]

Exactly the same here. In fact, the grid is centered compared to the PINDA position, as in the past, I don't remember up to which firmware version, it was centered compared to the nozzle position, say something like 23 at 1/9 and 227 at 3/9, so PINDA at 46 at 1/9 and 250 at 3/9.
Now I understand that it is probably what is wanted and that the previous behaviour was not correct, as what is important is the PINDA position, not the nozzle, right?

[3d-gussner]

@Gixy31 The PINDA measures at positions 24 , 126, 228 on X and 6, 108, 210 on Y. These positions represent best the needed Mesh for the nozzle and the bed.

Also the magnets are an issue and the positions of the probing points are limited see also PavelSindler#1 and here #1607 (comment)

I used the MK404 SIM and G80 (3x3 and 7x7) and M420 to get the mesh for this example, as these values are reproducible, while real PINDA values will very a bit.

The measured points are different between 3x3 and 7x7 BUT the difference to the center of the bed are identical with both methods (front-left , left , rear-left, rear, rear-right, right , front right, front).