Live Z increases from print to print - software bug?  

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pn2
 pn2
(@pn2)
Active Member

My live Z correction was around -0.6mm.

To inspect bed levelling (the bed is not as flat as I would like), I connected a computer with octoprint.

Now my live Z adjustment keeps increasing (becomes more negative) with every print. It almost seems like I have to add the original correction on top of what I already have. In the end I was around -3.2mm. I then resetted the printer, and now am at around -1.3mm, which is twice what I originally had.

This seems like a bug somewhere. I am not sure whether it is related to connecting octoprint, I now have removed the USB cable and the printer is "independent" again, but still my Z adjustment seems too large.

And yes, I "paralleled" the Z axis by running it into the top limits, but this did not help.

Any idea what might be going on here?

Posted : 08/11/2018 9:01 am
BillCampbell
(@billcampbell)
Reputable Member

Did you run a first layer calibration after disconnecting Octoprint? There is a code in that routine that tells the printer to save the value to EEPROM. If you need to do that, return live Z to 0 before you start or you may ram the bed with your nozzle.

Bill
Tagaytay City, Philippines
Founder member of Philippines Prusa Printer Owners FB Group
Sponsor Pillars of God Academy in Bacoor...
Posted : 09/11/2018 2:15 pm
pn2
 pn2
(@pn2)
Active Member

Did you run a first layer calibration after disconnecting Octoprint? There is a code in that routine that tells the printer to save the value to EEPROM. If you need to do that, return live Z to 0 before you start or you may ram the bed with your nozzle.

No, I did not. But I do not understand why I would have to do that... And how is this related to Octoprint?

My understanding is that the reference surface is determined by the 9-point PINDA measurement at the beginning of each print. Then, to this reference surface the live Z setting is added. Isn't this correct?

The live Z also is "remembered", so it seems to be stored in EEPROM.

Posted : 10/11/2018 4:15 pm
Texy
 texy
(@texy)
Reputable Member

There are at least two bed levelling plugins that octoprint supports- which one are you using?
Texy

Posted : 12/11/2018 3:59 pm
BillCampbell
(@billcampbell)
Reputable Member



My understanding is that the reference surface is determined by the 9-point PINDA measurement at the beginning of each print. Then, to this reference surface the live Z setting is added. Isn't this correct?

The live Z also is "remembered", so it seems to be stored in EEPROM.

Live Z is the calibration that measures and sets the exact Z location where your printer will consistently produce a 0.2mm thick first layer. You say the live Z is remembered, but your symptoms say only the LCD setting is being remembered.

The 9 point sensing routine run before every print checks that the current readings are within tolerance to the readings stored during XYZ calibration and stops the print if they are outside set parameters. It does not change z height, it maps the bed warp.

Bill
Tagaytay City, Philippines
Founder member of Philippines Prusa Printer Owners FB Group
Sponsor Pillars of God Academy in Bacoor...
Posted : 15/11/2018 7:07 pm
pn2
 pn2
(@pn2)
Active Member

Live Z is the calibration that measures and sets the exact Z location where your printer will consistently produce a 0.2mm thick first layer. You say the live Z is remembered, but your symptoms say only the LCD setting is being remembered.

This is exactly what I say, and if this is the case, this would be a software bug, right? In particular the "run-away" from print to print indicates something is wrong.

The 9 point sensing routine run before every print checks that the current readings are within tolerance to the readings stored during XYZ calibration and stops the print if they are outside set parameters. It does not change z height, it maps the bed warp.

The Z axis has no end switch, and I am pretty sure that the Z homing is done with the Pinda probe (how would it be done otherwise?).

I also would be surprised if the 9-point Z calibration would not be re-measured before every print (and the measured values used for the print). That is the whole point of the discussion about whether it should be done before or after bed warming etc. What is certainly only done during XYZ calibration is the calculation of X/Y axis deviations from 90 degrees, and where the pinda poiints in the bed actually are. But this is not what we discuss here.

Posted : 16/11/2018 7:08 am
pn2
 pn2
(@pn2)
Active Member

There are at least two bed levelling plugins that octoprint supports- which one are you using?
Texy

The one I use is called "Prusa Mesh Map" and I installed it from here ( https://github.com/PrusaOwners/OctoPrint-PrusaMeshMap/archive/master.zip )
by entering this URL in the OctoPrint plugin manager.

I used it to visualize bed unevenness while making adjustments with thin spacers.

Posted : 16/11/2018 7:12 am
sandra gabriela.p
(@sandra-gabriela-p)
New Member

Hi pn2, could you fix this problem? Because I have the same problem and I couldn't fix it yet. I'm going crazy reconfiguring the pinda in every print.
Thanks in advance.

...
Posted : 05/02/2019 12:42 am
sandra gabriela.p
(@sandra-gabriela-p)
New Member

I forgot mention that I don't use octoprint.

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Posted : 05/02/2019 12:43 am
nicolas.b
(@nicolas-b)
New Member

I am facing the same problem... After reading your posts, I am not sure this helps to solve the problem.

Is it possible to know what is really the problem and how is it possible to fix it?

Thks

 

NB

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Posted : 28/09/2019 6:30 pm
joan.t
(@joantabb)
Veteran Member Moderator

If you are struggling with Live Z, I suggest you use the process devised by Jeff Jordan in this thread 
https://forum.prusaprinters.org/forum/original-prusa-i3-mk3s-mk3-assembly-and-first-prints-troubleshooting/life-adjust-z-my-way/

At the bottom of the first threadm there is a zip file containing three Live Z routines, 
One for PLA, 

One for PETG

And One for ABS

run whichever of  those is appropriate, and your printer should be Ok!

 

Joan, 

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 28/09/2019 9:53 pm
nicolas.b
(@nicolas-b)
New Member

@joantabb

Thanks Joan. I'll give a look. NB

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Posted : 29/09/2019 6:55 am
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