Prusa Mini + "Mesh Bed Leveling Failed?"  

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alancart
(@alancart)
New Member
I just received my Prusa Mini + (my second Prusa mini). I assembled it but ran into issues when trying to do the first layer calibration. The mesh bed leveling kept failing at the 4th point. The mesh bed leveling was able to run through the entire bed if I initiated it from the Calibration menu but would always fail when leveling in the first layer calibration. I have tried several things but have not had any luck. Here is a more detailed list of the things I've tried:
 
  1. First layer cal [Mesh bed leveling failed at 4th point] https://photos.app.goo.gl/px9nYajADVV4Q7AA8&source=gmail&ust=1613612670739000&usg=AFQjCNHjwuga2ISmVutBH9KYPtCl5TMUj g">(VIDEO)
  2. Tried Mesh bed leveling from the calibration menu [Unsure if successful or not but is able to go through all 16 points] 
  3. Checked the Super PINDA probe was connected properly [Looks good]
  4. Checked no tight zip ties or kinks on the wires [None]
  5. Checked Super PINDA height [It was too high out of the box, about 2 credit cards high when the nozzle was on the print bed, readjusted per Prusa instructions]
  6. Tried First layer cal again [The same result, mesh bed leveling fails at 4th point]
  7. Upgraded FW to 4.3.1 [Mesh bed leveling only does 4 points (front row) but allows the first layer calibration procedure to start]
  8. First layer calibration [Started printing at about 5-7mm off the print bed, started lowering the z height but then noticed that it was only that high on the left side of the bed and would go down to the bed on the right side. Prompts me to think there is still something wrong with the bed mesh leveling]
 
Not sure where to go next after this. I didn't have any similar issues with my other Prusa Mini. Any help would be appreciated.
Posted : 17/02/2021 1:51 am
Rbals
(@rbals)
New Member

I had this issue to. The fix that I found that worked was:

1: Loosen (Don't remove) the 3 screws that hold the ZX axis arm to the Y axis base. (M3x40, M3x20, M3x12)

2: Fold/cut a piece of paper 80mm x 13mm x 1.5mm dimension.

3: Flip over the printer (on its side) to access the bottom.

4: Wedge the paper between the both frames underneath where the 2 bolts meet. (M3x40 and M3x20)

5: Tighten the bolts in the Prusa recommended order. (Step 17 in the Manual)

6: You can measure the distance between the left and right side of the upper X axis guide rail to the bed using the depth end of a digital caliper. 

I measured mine first and I had a 3mm difference. After I had a .2mm difference. You can also print a space to replace the paper when the printer is up and running. I would change the thickness tho cause the paper is more compressible than the plastic. 

Posted : 17/02/2021 3:45 pm
alancart
(@alancart)
New Member

I think you may be on to something. Moving the extruder manually around the build plate I see that its height over the build plate changes drastically. From the photo below, the extruder is at its highest point at #1, #2 is slightly lower (could be the same), at #3 is at its lowest, #4 is a bit higher than #3. Not sure if its the build plate or X-axis that is off.

Another way of looking at it:

The extruder is close to the Z-axis. Extruder nozzle is touching the build plate:

The extruder moved to the center in the X-axis without changing Z-axis position. The extruder nozzle is now about 1mm off the build plate:

The extruder moved to the furthest point away from the z-axis. The extruder nozzle is now about 3 mm off the build plate:

 

Given that all four corners are slightly different, my guess is that the misalignment is both on the X-axis and the Y-axis.

Higher resolution images

Posted : 18/02/2021 3:27 am
SeanR
(@seanr)
Active Member

I put a single piece of painters tape on the outside edges of the magnetic  plate and then re-leveled the bed.  One on the right side one on the left.  That's been very successful for me.

Posted : 23/02/2021 7:57 pm
Dmitry
(@dmitry)
New Member

Well, I have just assembled my new MINI and was facing a similar issue with bed leveling. 

I found that overtightening the screws during the kit assembly Step 19 Final tightening leading to uneven X-Z angle. In my case, it resulted in the height difference on the left and right side = about 2-3 mm. If you are new to 3d printing, you might not see this.

So watch carefully mesh bed leveling. The SPINDA has a red led inside. Passing each point should blacken the red led for a moment. I would assume, this means the SPINDA sensor value turning 0 to 1. It should happen at all 16 points. Until you managed all of them, it makes no sense to start 1st layer calibration. If it is not blackening, then it is not reaching the sensor working distance to the bed. Unfortunately, the printer software is not catching the event properly and just stopping the mesh leveling.

I do not like to insert anything (paper/plastic) between the assembly as suggested above. So I did the following - while moving the print head over X-axis (I used the software option), I was adjusting the screws (blue and green) until the distance between bed and nozzle became equal on the left and right sides. Even after that the printer overall stays as one piece and feels sturdy.

After that, the mesh leveling test was always successful and the 1st layer test was ok as well.

Hope it helps others as I came to this thread while looking for the solution and figured out mine in parallel.

Posted : 05/03/2021 1:19 pm
SeanR
(@seanr)
Active Member

OK, so recently contacted support and I have to adjust my reply.  It is possible to believe you completed the layer one test and still not be correct.  So let me share with you what support had me do.  Download the Prusa logo (unable to locate).  Print the first layer only.  Continue to lower the extruder until there is zero separation in the first layer.  Because you can adjust the extruder real time during the print I only had to do this twice before everything was correct.

*Note:  The first layer should be smooth on the bottom when you peal it off the bed.  If there are gaps, then you are still not there.  Also, I noticed that the pla does shift a bit after it has been laid.  So once the layer is done peal up the that part.  Inspect, rinse and repeat as required.

**Note:  I ended up removing all the mods to the printer by the time I was done fixing the z layer height.  I have also been printing with zero fails since that time.  I can now start a print make sure it starts off good and walk away.  Another error I was making was cleaning the bed while it was hot.  That turns out to cause a lot of issues as well.  Clean the bed with hot soapy water to correct.

Firmware:  4.3.1
Printer:  Mini+

Posted : 05/03/2021 5:45 pm
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