Mesh Bed Leveling behavior.  

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Baklin
(@baklin)
Estimable Member

Not sure if this is a problem or what to do with this.

The Bed leveling doesn't always work the same way. Sometimes it probes the bed at all nine places quickly and another time it probes some  places different. Than it moves Z higher on some points.

At the moment I use different parts for the x-ends, but it did the same with the stock parts.

And it doesn't always do it or in the same places. Where do I start fixing this if that is possible?

I have added a zip file with a video (could get the video to upload to the forum)

In the video you can see it is doing normal probing only on the right side. When I now use the 7x7 mesh it will do that on the 2 points on the right side only.

 

meshbedleveling.zip

Posted : 10/11/2020 7:01 pm
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(@-2)
Illustrious Member

Bed leveling is controlled by the slicer, which has gcode in the Printer profile. Within the Custom G-code: Startup G-code: is the bed leveling command. It will look something like this:

G80 N7 R5; mesh bed leveling

 

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 11/11/2020 12:57 am
Baklin
(@baklin)
Estimable Member

I haven't changed that from the default. It is still "G80 ; mesh bed leveling"

 

The way I see it that just tells the printer to do it's bed leveling the way it is set in the menu.

It does that too. When I change between 3x3 and 7x7 that printer does that before each print.

 

But why does it during the bed leveling probe some points quickly with hardly any z movement and others with much more z movement (looks like almost 2 mm to me and doing that 3 or 4 times)

This makes the bed leveling take more time. No that it matters that much on the total print time, but it looks strange to me that the bed leveling handles points differently.

Posted : 11/11/2020 12:39 pm
Neophyl
(@neophyl)
Famed Member

The bed levelling works on the process of detecting metal with the pinda probe.  That is achieved magnetically.  Anything that disturbs the magnetic field can cause the firmware to not be sure of the reading so it can repeat or perform a different process.  The magnets of the bed for instance or even motor currents causing magnetic fields.  

You might try adjusting your pinda slightly lower so it can get a more positive reading and redoing your live z height if it bothers you that much.

Posted : 11/11/2020 1:08 pm
Neophyl
(@neophyl)
Famed Member

Btw what version firmware are you using ?  I found this over on github https://github.com/prusa3d/Prusa-Firmware/pull/2447   where they fixed an issue in 3.9.0. 

Its basically what I mentioned about current disturbing the Pinda probe so they turned bed heating off during levelling to make it more stable. 

Posted : 11/11/2020 1:15 pm
Baklin
(@baklin)
Estimable Member

I think I have figured it out already. I Took out the Igus bearings for the Z-axis. I didn't like them there but put them in because the original bearings run very rough. Now I have put in new normal bearings and things work like they should.

Looks like the rough bearings and the Igus bearings didn't let the Z move freely. That would explain why it did the weird probing mostly on the left side. Maybe that side would stick a bit more and give different readings that made the printer try several time to get a consistent reading.

Posted : 11/11/2020 1:19 pm
Neophyl
(@neophyl)
Famed Member

@baklin

That sounds like a pretty logical hypothesis.

Posted : 11/11/2020 1:28 pm
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