Odd behavior with SuperPINDA  

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Siafu11
(@siafu11)
New Member

I recently upgraded my printer to the MK3S+ kit and have noticed that certain points cause the Z axis to raise a few millimeters higher on one or two of the 5 point averaging procedure during mesh bed leveling. This behavior only seems to occur when the bed is heated (85C), and never happened with the PINDA v2 sensor. I am currently running 3.9.2-3556 firmware.

Is this expected behavior with the new sensor?

I have also noticed some deviation between sensor readings at room temperature vs heated bed

Ambient:

Num X,Y: 7,7
Z search height: 5.00
Measured points:
0.15500 0.12300 0.12750 0.14200 0.09550 -0.00750 -0.06000
0.16350 0.12200 0.08700 0.04550 0.04050 -0.00750 -0.08650
0.17000 0.12100 0.09350 0.06300 0.03700 0.00200 -0.08150
0.11800 0.10200 0.07300 0.07600 0.04212 -0.01350 -0.08300
0.14600 0.11600 0.10750 0.08463 0.06900 0.01850 -0.06200
0.12750 0.12050 0.11350 0.08600 0.07600 0.03000 -0.05350
0.15350 0.14050 0.15150 0.12000 0.10950 0.03250 -0.05050

85C:

Num X,Y: 7,7
Z search height: 5.00
Measured points:
0.13400 0.20150 0.25550 0.27350 0.19850 0.02800 -0.13750
0.24650 0.28750 0.30550 0.28100 0.24100 0.12600 -0.06250
0.30500 0.34750 0.36450 0.32737 0.29550 0.19350 -0.00150
0.28700 0.34250 0.36050 0.36850 0.29612 0.19550 0.02650
0.28350 0.34350 0.38150 0.35088 0.32500 0.21000 0.02550
0.20950 0.29400 0.33400 0.32850 0.29300 0.17300 -0.03100
0.10350 0.19300 0.24250 0.23400 0.20100 0.05700 -0.15550

Is this range of deviation normal?

I am aware that those values indicate an unlevel bed, but my main concern is that the ambient readings are borderline within spec, whereas the 85C readings are outside of spec.

 

As an aside, if anyone knows of a good way to level the bed (say, 0.1mm thick washers?), I'm certainly open to advice there.

 

Posted : 20/04/2021 11:38 pm
Clarmrrsn
(@clarmrrsn)
Honorable Member

Perfectly normal, started doing it on my mk3, there is an article on mesh bed levelling that explains the process.

I found that my bed had around a .3mm variance accross the bed, manually levelling to within .02 fixed it for me.

My new MK3s+ started doing this after 5 weeks or so.

Also worth double checking there is no play in the Y axis, I readjusted the bearing clips while levelling the bed as well and has not done it since.

Make sure you have tightened the bed screws correctly as per the manual and not over tightened, also do it when the bed is heated to 55, this can improve things if the bed is warped, can also be a bent frog (can be straigtened manually and checked with s strsight edge)

But it is nothing to worry about.

This post was modified 4 weeks ago by Clarmrrsn
Tank you very much!...
Posted : 21/04/2021 12:12 am
Siafu11
(@siafu11)
New Member

Thanks for the tips.

When I rebuilt the Y-axis I followed the manual very carefully, however I often struggle with the concept of "overtightening" without the aid of torque values. That said, my torque wrench only goes down to 10 in-lbs, which I suspect may be too much for this application.

As for the new (MK3S+) bearing clips, should the clip bottom out against the frog, or should their be a gap between the bottom of the clip and the frog? I noticed that my clips are a bit shorter than expected and it appears as though the flange won't sit flush against the frog no matter what.

Posted : 21/04/2021 3:45 am
Clarmrrsn
(@clarmrrsn)
Honorable Member

@siafu11

I would not use a torque wrench for tbe bed screws, I toyed with the idea, and as they are m3 you are looking at max 1.25ft/lb, however this is into aluminium and not taking into account the pcb, which could crack if overtightened, just use the short and of the allen key and give it a good nip up but dont go mad.

As for the bearing clips nip them evenly until the bearngs just stop moving with your fingers (so you cant rotate or slide the bearing), dont overtighten them, this could warp the frog.

If you find the frog is bent from new, speak to Prusa, they may replace under warranty, check it with a straight edge.

Other option, do the nyloc mod, will bring a warped bed to within around .02 if done correctly

https://www.reddit.com/r/prusa3d/comments/bp440f/full_guide_to_doing_nylock_mod_if_you_havent_you/

This post was modified 4 weeks ago 2 times by Clarmrrsn
Tank you very much!...
Posted : 21/04/2021 8:23 am
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