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wietschebehr
(@wietschebehr)
Active Member
Bed Level Correction workings

Hi,

I have a bed level that has a dip in the center. The surrounding areas seem to be fine and on the same level. No mechanical issues. I've even loosen the center screw a bit with no effect. I've printed no less than ten 3 X 3 grids as described in https://help.prusa3d.com/en/article/bed-level-correction_2267. They all pretty much look the same with level adjustments made almost to the allowable limits. The middle square always have gaps between the strings, where the outer blocks have too much squeeze.

I would like to find clarification on the Bed Level Correction workings, as I am not getting the results expected when adjusting the front, back, left and right heights at the same time.

Does the bed react to adjustments like a solid plane, i.e. raising all sides by the same number also lifts the middle up by that same number, or is the center fixed at your Live Z adjustment height and the sides can go "up" or "down" independently of the middle, where the middle is not "moving" making the bed virtually convex or concave? Hope my question makes sense...

I have a suspicion that it acts like a solid rigid plane and not possible to remove a dip in the center.

Kind regards,
Wietsche

Posted : 16/02/2021 2:21 pm
JoanTabb
(@joantabb)
Moderator
RE: Bed Level Correction workings

are you using 7x7 Mesh Bed Levelling (tests  49 points on the bed.) if not, turn it on in the LCD Settings menu.
For Bed Level Correction, consider the centre fixed and consider the changes as acting on the perimeter

regards 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 : 16/02/2021 6:04 pm
wietschebehr
(@wietschebehr)
Active Member
Topic starter answered:
RE: Bed Level Correction workings

@joantabb

Thanks Joan!

Thanks for coming to the rescue. Ive post a reply to one of your other answers on another thread, but then saw it was a very old thread, and reposted my question as a new topic. But I think you have noticed that.

No I am not using 7x7. I will turn it on and re-evaluate the print pattern.

How does this make a difference to the Bed Level Correction? Or do you think it might not be neccesary to do manual correction at all once 7x7 is activated? I just want to understand the technicalities and how this work. There is limited info on this topic and I am totally confused how this should work. I would like to avoid things like the Nyloc Nut mod and keep things standard om my new MK3S+ printer if possible. 

Kind regards, Wietsche

 

 

Posted : 16/02/2021 7:17 pm
JoanTabb
(@joantabb)
Moderator
RE: Bed Level Correction workings

I only use bed level correction on my Mk2 printer, which doesn't have 7x7 mesh bed levelling

my other printers don't seem to need it, once they are on 7x7 mesh bed levelling, 
Please allow magnet compensation and set the number of test probes to 3

regards 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 : 16/02/2021 7:50 pm
wietschebehr
(@wietschebehr)
Active Member
Topic starter answered:
RE: Bed Level Correction workings

Hi Joan,

The 7x7 setting made a difference of getting more uniform results, but not fixing my problem.

I combined with the 7x7 grid and 3 probes per point, I increased the distance on all 4 sides to +50. That is half of the allowable adjustment range per side. This seems to have brought all the squares down to the same level. They were all now under-squished roughly by the same magnitude. Clear visible gaps between extrusion lines.

I then did a couple of First Layer calibrations and had to lower the nozzle from -1.58 to -1.69. This seemed to me very large. And that brought about a huge difference vs the previous 11 times I tried the Bed Level Corrections with almost no success or effect to my squares. I cant explain why the Bed Level Correction with the 3x3 grid had little to no effect before, even though I had the sides up to +90 points adjusted at some point.

I think there might be some work needed with this calibration and maybe a debug session to see why there is such a big difference. The grid size should not by my understanding interfere with the manual Bed Level Correction settings.

I have now printed the 9 squares single layer test pattern with 9 perfectly flat and strong squares, that adhere properly to my whole printer bed.

Thanks for your help and I hope this info helps other users with saucers for printer beds.

Do I maybe have a defective printer bed or aluminum bed undercarriage? Should I contact Prusa Support to send me a new printer bed assembly? Especially now that it is clear that the 7 x 7 Mesh Bed Leveling feature could not even compensate for my dished surface? I don't think this is an acceptable error margin, or is it?

Kind regards,
Wietsche

Posted : 16/02/2021 10:10 pm
JoanTabb
(@joantabb)
Moderator
RE: Bed Level Correction workings

Are you using the Prusa First later calibration tool? 

If you are, try 'Life Adjust Z My  Way'

https://forum.prusaprinters.org/forum/original-prusa-i3-mk3s-mk3-assembly-and-first-prints-troubleshooting/life-adjust-z-my-way/

regards 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 : 16/02/2021 11:57 pm
wietschebehr
(@wietschebehr)
Active Member
Topic starter answered:
RE: Bed Level Correction workings

@joantabb

Hi Joan,

Yes, the normal tool on the printer interface. 

I will do that thank you!

See attached pics. Not joking about trying very hard to get the Bed Level Correction thing working...

Multiple Bed Level Correction Failed attempts

Kind regards, Wietsche. 

This post was modified 6 months ago by wietschebehr
Posted : 17/02/2021 8:17 am
JoanTabb
(@joantabb)
Moderator
RE: Bed Level Correction workings

as you are really only interested in the perimeter of the build plate when changing bed level correction, 
I make a gcode with a single large patch say 240 x 200 x 0.2mm  and use concentric infill, then the printer tries to print from the outside towards the middle, 

I make sure the build plate is absolutely clean, because you will be printing in the areas where you often handle the build plate... typically front and side edges... 

and set the printer, to start printing. within a couple of laps, you will know whether you need to make any adjustments 
so you can stop the print,  make an adjustment, clear the old print and restart the next print, quite quickly.

when you get a reliable print say 10mm wide, all around the perimeter, check your live Z, and is all is well, then try one of your fancy eleven square print matricies.

 

regards 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 : 17/02/2021 12:05 pm
wietschebehr
(@wietschebehr)
Active Member
Topic starter answered:
RE: Bed Level Correction workings

@joantabb

Thank you Joan! That is a great idea! My "fancy" matrices is the one recommended in the Prusa online guides and the only good guide I found. But next time I'll use your suggestion. Would waste far less filament.

Thanks for your help and insights. I made a good print today, so I am hoping all is well an fixed now. For a change my prints stick very well to the bed. I think the warped bed had a much more severe impact on my prints than I thought. The Prusa default Live Z calibration test square is on the edge of the bed where it was almost at it's highest area of my bed. So my Z was never perfectly dialed in at the middle, until now.

Thanks again!

Kind regards,
Wietsche

Posted : 17/02/2021 7:18 pm
JoanTabb
(@joantabb)
Moderator
RE: Bed Level Correction workings

We try to please... 

🙂

 

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 : 17/02/2021 7:31 pm
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