Strange change to Z-axis calibration between prints
 
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jrock
(@jrock)
New Member
Strange change to Z-axis calibration between prints

After first layer calibration my z-axis offset will be something like -1.500. 

I'll do a few prints and they are awesome.

I'll do another print, sometimes immediately after a successful print, and now the nozzle is too high. I'll do a live z-axis calibration and fix it up - now the offset is something like -0.750. Weird.

Then I'll do another print, and now the z-axis is way too low and the nozzle crashes into the bed. I can fix it with live z-axis calibration to raise it up (back to about -1.500) and the print continues and succeeds.

So this is pretty annoying. My bed is taking a beating from nozzle getting dragged along it.

There seems to be no rhyme or reason or pattern behind this.  It is suspicious that the change in z-axis height is about half - from -1.500 to -0.750 (approx) and it is always been about this much for the dozen or so times this has happened.

I am using Octoprint, but I am pretty sure this was happening before I started using Octoprint. I do not think it is temperature - I have the SuperPinda and I will often let things heat up before print start.

Anyone else have similar experience or know how to fix this?

Thanks!

 

Posted : 10/09/2021 11:43 pm
BogdanH
(@bogdanh)
Honorable Member
RE: SuperPINDA adjustment and test

Just few thoughts...

First, when asking for solution, it's always good if you also tell if printer is new (just assembled) and if your trouble started recently or it's there since beginning.

I assume all screws are tighten properly and that there's no wobble (print bed, Z and X axis). I also assume printer geometry is correct (all axes perfectly perpendicular!). Also check again, that SuperPINDA is fixed, so it can't move up/down.

First, make sure SuperPINDA height is correct. Manually move printhead down (by rotating Z shaft) to the point where nozzle just touches the print sheet. Now check distance between bottom of SuperPINDA and print sheet: it should be 1.5mm!

You can also check if SuperPINDA is working correctly (at least to some degree). Manually move printhead up so the distance between SuperPINDA and print sheet is about 5mm. At this point LED on the top of SuperPINDA will be lit. Now slowly move printhead downward and watch the LED. As soon LED goes off, measure the distance between bottom of SuperPINDA and print sheet: it should be about 2.3mm (for normal smooth PEI sheet). Difference of about 0.1mm doesn't matter and so distance of 2.2mm is still acceptable. More important is, that the distance to bed is constant (repeatable). That is, if you do that 100-times, LED must go off always at the same distance.

Now make 1st layer calibration. I expect Z-offset will be at about -0.800 for acceptable first layer. Repeat 1st layer calibration between each print. If it happens you need to make big adjustment, repeat process in previous paragraph and see if distance is still about 2.3mm. If not, I would assume SuperPINDA doesn't work correctly.

I hope that was of some help

[Mini+] [MK3S+BEAR]...
Posted : 11/09/2021 9:08 am
fuchsr
(@fuchsr)
Noble Member

Sure sounds like a loose Superpinda probe. Give the screw that's holding it in place a bit of a turn. And I assume the nozzle/printer block are tightly secured and not loose.

Posted : 11/09/2021 8:02 pm
jrock
(@jrock)
New Member
Topic starter answered:

Pinda's tight. Thanks for the input.

Posted : 18/09/2021 7:49 pm
jrock
(@jrock)
New Member
Topic starter answered:
RE: SuperPINDA adjustment and test

Thanks for taking the time to post!

My Mini's been working well for over a year, not a new assembly.

Everything is tight, and the SuperPinda is at the right height. The SuperPinda LED goes off at just over 2mm to the bed.

I did a first layer calibration. The z axis offset is -1.542. Though I have done first layer calibration in the past where the offset was closer to -0.750. Weird, eh? I'll remember to measure the height the SuperPindo LED goes off the next time I get bed crash, or if first layer calibration comes out drastically different.

Posted : 18/09/2021 8:09 pm
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