Author Topic: Weird z offset problem  (Read 124 times)

furious1y

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Weird z offset problem
« on: July 14, 2020, 04:43:05 AM »
Hi all,
just wondered if I can pick someones brain here.

I have 1.5 installed and working. I can check the mesh data, doesn't seem to vary much, only the usual stuff from having a removable bed with PEI.
The sprung steel isn't perfectly flat, but not much is :)

So, I'll print something. Have to restart to adjust the z offset a few times. Like this morning - kicked off a new print, no layer adhesion, had to lower the z-offset by 0.2mm, then prints fine.

Problem is... I have to do this every time. After each print, I make sure the bed plate is clean, ensure that its seated correctly, yet for some reason the mesh levelling doesn't seem to counter the bed being reseated and I have to do the z-offset again.

Am I missing something here? I'm taking this isn't normal, and surely the whole point of the mesh is to counter the geography of the bed, and if its 0.2mm higher or 0.2mm lower in any or all spots (z offset is usually -2mm +/- 0.3mm each new print), it should counter that?

Is there something I should be putting in the gcode to ensure it's using the mesh properly or to actually apply the offset?

Here's my start gcode for my slicer:
Code: [Select]
M280 P0 S60 ; Test Mode
G4 P500
M280 P0 S90 ; Stow Probe
G4 P200
;*** Start Preheating ***
M140 S{material_bed_temperature_layer_0} ; start preheating the bed
M104 S{material_print_temperature_layer_0} T0 ; start preheating hotend
M190 S{material_bed_temperature_layer_0} ; heat to Cura Bed setting
M109 S{material_print_temperature_layer_0} T0 ; heat to Cura Hotend
;*** End Preheating ***
G28 ; home
G29 A; ABL
M500
M117 Purge extruder
G92 E0 ; reset extruder
G1 Z1.0 F3000 ; move z up little to prevent scratching of surface
G1 X2 Y20 Z0.3 F5000.0 ; move to start-line position
G1 X2 Y200.0 Z0.3 F1500.0 E15 ; draw 1st line
G1 X2 Y200.0 Z0.4 F5000.0 ; move to side a little
G1 X2 Y20 Z0.4 F1500.0 E30 ; draw 2nd line
G92 E0 ; reset extruder
G1 Z1.0 F3000 ; move z up little to prevent scratching of surface

furious1y

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Re: Weird z offset problem
« Reply #1 on: July 22, 2020, 02:37:06 AM »
Well, I'm having some success after I found this particular gem:
https://github.com/MarlinFirmware/Marlin/issues/17166

I'd kind of mitigated the issue by getting the offset dialled in and working and then removing the G29, even though it defeated the point of having ABL.

Then I finally managed to put the right words into google to yield the above.

So, if anyone is getting weird fluctuating z offsets, try the following:
Code: [Select]
M420 S1 Z0
G28 ; home all axes
G29
M420 S1 Z5 ; Enable ABL using saved Mesh and Fade Height

In fact, you don't need the last line at all.