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Printer ignores z offset from PrusaSlicer  

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AnneVanLeyden
(@annevanleyden)
Eminent Member
Printer ignores z offset from PrusaSlicer

I have a MK3.5 + Revo. Since all Revo nozzles are slightly different in length, I have to use a different z-offset on each of them. For a long time, I wasn't aware of the z-offset setting in PrusaSlicer, so my routine was to set the live adjust z on the printer on each nozzle swap. 

When I read about the z offset setting in PrusaSlicer a few weeks ago, I set up the z-offset for each nozzle in PrusaSlicer. The live adjust z value on my printer is -0.500 and in my 0.4 nozzle profile I set a z offset of -0.380, making for an effective z offset of -0.880. This is the value that I get when doing a first layer calibration. This seemed to work perfectly. But not anymore.

When I open the generated gcode I can see the negative z-values, so on the PrusaSlicer side, everything is fine. The printer however seems to ignore these values and prints the first layer too high.

The problem isn't in the PINDA probe, since each time when I run a first layer calibration, it confirms the -0.880 value.

Are negative values being ignored by the printer because it assumes they will run the nozzle into the bed and damage it? Is this a setting I have to change somewhere in the printer? 

This topic was modified 6 months ago 3 times by AnneVanLeyden
Posted : 04/03/2025 1:49 pm
FoxRun3D
(@foxrun3d)
Illustrious Member
RE: Printer ignores z offset from PrusaSlicer

Don't know why the offset is being ignored. However, another idea is to repurpose the sheet profiles on the printer and use them for nozzle offsets instead of sheet offsets. 

Formerly known on this forum as @fuchsr -- https://foxrun3d.com/

Posted : 04/03/2025 3:27 pm
AnneVanLeyden
(@annevanleyden)
Eminent Member
Topic starter answered:
RE: Printer ignores z offset from PrusaSlicer

Thanks for the suggestion, FoxRun3D.

It is not only the z-offset that differs between printer profiles. Also nozzle size, standard/hardened/high flow. 

A bit overkill to define a complete new printer profile, while only the nozzle is different, but that is a less problematic PrusaSlicer issue. Once set up, you rarely have to touch these profiles.

Posted : 04/03/2025 5:51 pm
FoxRun3D
(@foxrun3d)
Illustrious Member
RE: Printer ignores z offset from PrusaSlicer

Not printer profile in slicer. The firmware on the printer should give you the option to create profiles for different sheets. I use it to store profiles for my satin and textured sheets. My suggestion was to use those instead for your specific live Z offsets. 

Formerly known on this forum as @fuchsr -- https://foxrun3d.com/

Posted : 04/03/2025 6:20 pm
AnneVanLeyden
(@annevanleyden)
Eminent Member
Topic starter answered:
RE: Printer ignores z offset from PrusaSlicer

Ah, sorry - I get it now.

Posted : 04/03/2025 8:47 pm
AnneVanLeyden
(@annevanleyden)
Eminent Member
Topic starter answered:
RE:

I made a small gcode file and indeed can confirm that the firmware will refuse to go below 0.

That gives me about the height of the first layer as wiggle room. The difference between my longest and shortest Revo nozzle is 0.15 mm, so that is enough.

The z-offset in PrusaSlicer can not be lower than the negative height of the first layer, usually -0.2 mm. By adjusting the live adjust z in the printer to be 0.2 mm lower, I could add 0.2 mm to all z-offsets and fix the issue.

This post was modified 6 months ago by AnneVanLeyden
Posted : 04/03/2025 8:58 pm
Brian
(@brian-12)
Prominent Member
RE: Printer ignores z offset from PrusaSlicer

Can you adjust the height of your pinda probe to make your shortest nozzle 0.  That way all of your other nozzles will have a positive offset? 

Posted : 04/03/2025 9:13 pm
AnneVanLeyden
(@annevanleyden)
Eminent Member
Topic starter answered:
RE:

The PINDA height is what you correct for with live adjust z. Changing the PINDA height would force me to also change the live adjust z with the same value and the net effect would be 0. It is all about relative heights.

If I would make my shortest nozzle 0, then it would crash into the bed on autohoming when I screwed in a longer nozzle. I thought about that, but it is not an option.

Luckily, the variation in nozzle lengths is within the 0.2 mm first layer, so I can just about dial it all in the way I wanted. I just had to configure a lower live adjust z on the printer and a higher z-offset in PrusaSlicer. The z-offset in PrusaSlicer can imo never be less than -0.2. Lower values are ignored by the printer. Which makes the pop-up description misleading because it talks about a -0.3 z-offset. Which can only work if you have a first layer height >= 0.3 mm.

This post was modified 6 months ago 2 times by AnneVanLeyden
Posted : 05/03/2025 8:01 am
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