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Gauge
(@gauge)
Active Member
Bed leveling fails

You can see in this photo that the mini fails to auto bed level front to back.  I just got this and I'm not sure what to do because you can't adjust this like you can in the other printers.  It is very easy to tell that the level isn't working.  The front is slightly too close (just so) and the back basically isn't touching at all.  Nothing I can seem to do fixes this.  Loosing bolts etc etc.  It seems to be in the leveling algorithm itself.  Can anyone help me?  I can't fix this because the problem appears to be with the bed leveling and there is no way to fix or do it manually.  Please advise.

auto bed leveling fail

Posted : 02/06/2021 1:50 am
cwbullet
(@cwbullet)
Illustrious Member
RE: Bed leveling fails

Have you tried goning -0.030 lower?  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 02/06/2021 9:29 am
Gauge
(@gauge)
Active Member
Topic starter answered:
RE: Bed leveling fails

@cwbullet

I can't go lower.  It's hard to see in the photo, but the front is as low as it can go without blocking the nozzle and dragging.  "Perfect" is somewhere between the first two rows.  I said this on github, there is not currently a method of fixing y calibration issues on the mini.  For now I'm going to try to put paper towel strips under the steel sheet in the back to see if it's possible to do a manual correction that way.  If it is, I'm a software engineer, so I'll fork the firmware and adjust the bed correction myself.  This is something that should be available on the unit itself, like with the MK3 IMO.  It's new firmware though for the new buddy board, so I suppose it's reasonable it hasn't been done yet.  If I can figure out how to adjust the calibration of the bed level in the firmware with some hard code I will report back how to do it.  Heck, if I can figure out their UI maybe I will make a pull request to add in bed level calibration 😀

Posted : 02/06/2021 11:43 am
cwbullet
(@cwbullet)
Illustrious Member
RE: Bed leveling fails

@gauge

Then, I would contact support via chat.  If you cannot go lower, you need their help determining you next option.  You have tried everthing I can suggest. Either you have assemmbled somethign wrong and you bed is warped.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 02/06/2021 12:33 pm
Gauge
(@gauge)
Active Member
Topic starter answered:
RE: Bed leveling fails

Well, the paper towel was a dumb Idea because the pinda probe activates off the steel sheet.  Going to try G81 bed correction in prusa slicer.  Maybe if I do -1 front and +1 rear I can get close?

Posted : 02/06/2021 12:52 pm
Gauge
(@gauge)
Active Member
Topic starter answered:
RE: Bed leveling fails

I sent support an email.  We'll see where it goes.

Posted : 02/06/2021 2:13 pm
cwbullet
(@cwbullet)
Illustrious Member
RE: Bed leveling fails

@gauge

Email is not an efficient and is rarely successful.  Use the chat box from the shop.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 02/06/2021 3:27 pm
Daryl
(@daryl-2)
Trusted Member
RE: Bed leveling fails

You state:  "You can see in this photo that the mini fails to auto bed level front to back."  Are you saying when doing Mesh bed leveling it does not complete the leveling procedure (all 16 sample locations)?  Or is it that the printing is not consistent across the bed?

BTW - if you use or plan to use OctoPrint, Bed Visualizer is a great plugin.  Here's a pic of my recently completed Mini+ bed level readout:

Posted : 02/06/2021 11:45 pm
Gauge
(@gauge)
Active Member
Topic starter answered:
RE: Bed leveling fails

I worked with support for 4 hours, the front and back of my bed are off by a full millimeter, which is apparently not within spec.  We couldn't fix it and they are giving me a refund.

Posted : 03/06/2021 12:33 am
Daryl
(@daryl-2)
Trusted Member
RE: Bed leveling fails

@gauge

Sorry to hear it.  The Mini is really a remarkable printer, hope you'll give it another try.

Posted : 03/06/2021 2:01 am
cwbullet
(@cwbullet)
Illustrious Member
RE: Bed leveling fails

@gauge

Glad to see you were able to come to a solution.  It is rare but lemons do occur.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 03/06/2021 2:12 am
Gauge
(@gauge)
Active Member
Topic starter answered:
RE: Bed leveling fails

So, an update on this.  Firstly, the return process for Prusa is horrendous.  It is 100% designed to make you give up and not return it, which is what I did because the requirements/process is really just dumb.  As a software engineer, I can tell you, this is what happens when you put an engineer in charge of systems non-engineers will use.

I decided to fix the issue myself.  Using pronterface, and silicone sleeves around the bed nuts, I was able to slowly manually level the bed.  These are what I used, Bed leveling silicone.  I cut them roughly in half with an exacto knife.  The hole him them is just large enough you can push it on the bed nuts between the heater bed and the carriage.  They are made to "squeeze" so you can level a bed with the resistance.  Doing this I was able to get my bed level to within .1mm.  I was not able to get the bed perfectly level because the bed itself is not flat.  I got to a point where the numbers were so close and the adjustments to be made were in odd spots (not linear), so I left it alone because it was "close enough".

Some thing I have discovered.  The PINDA probe algorithm doesn't work very well.  It's not broken, it just never worked well I suspect.  The algorithm in the firmware BARELY compensates for bed level data.  I'm sure it does something, but my bed is level to within .1mm and it can't fully compensate for that.  Luckily .1mm is good enough to basically not even have correction and still get prints that are good enough with just a Z offset.  The other thing I have discovered is that this is a major flaw in the design IMO.  The design of this printer, and in fact all prusa printers, assumes that the Y assembly is so precisely engineered, that it could not have any flaws large enough that the PINDA probe can't compensate.  Judging by my experience, and the experience of many others on this forum, that is NOT THE CASE.  Again, what happens when you leave an engineer in charge, my stuff can't break mentality.  The probe compensation in the firmware is so poor, I honestly would want to see code debug statements as proof that it does anything at all.  I want to stress, my probe does work, and is incredibly precise, as pronterface bed leveling readouts have confirmed for me.  To me this is a firmware failure.

For now, with some extreme pain, time, and trial and error, I have the mini printing pretty well.  I won't ever buy another prusa now that I know what I know and that the return process is terrible and designed to make you quit.  Maybe I got a lemon, but I seriously doubt it's just me looking at the forums.  This is a major flaw IMO, and one that most people will not be able to fix because there is no way to compensate for it.  So many things can cause the Y axis to not be flat, and all of them have to be 100% perfect for this machine to have a good first layer level.

Only came back to post this solution for others, so that there is some option for them to pursue other than a refund.

Posted : 02/07/2021 4:22 pm
BogdanH
(@bogdanh)
Reputable Member
RE: Bed leveling fails

It seems, the worst scenario happened in your case: Y-axis not perpendicular and bed not flat (enough). I really can't comment on how effective PINDA firmware algorithm is, because I had no such initial troubles with my Mini. After I adjusted Z-axis (non-perpendicular) geometry, prints were ok and so I didn't care to check other parameters. That is, I'm quite sure none of axis are 100% perpendicular and bed probably isn't perfect either.. so PINDA must be effective within certain range.

About how Mini is designed.. yeah, I hear you. On one side, Prusa did a good job with chosen materials, I think. For example, deciding for two 10mm rods on Z axis for such small printer. But the way elements are assembled together, Mini is still quite fragile in my eyes. That's especially the case for how Z-axis is connected to mainframe: if not careful, Z-axis geometry can be lost by just moving printer few times. One can easily understand why's that, if checking the procedure for adjusting "Z-axis not perpendicular to bed". Saying that, I can't imagine putting some "carry" handle on Z-axis for moving the printer.
But then, we shouldn't look at Mini as being some industrial machine -it is only home hobby printer. And as such, it's quite good in my opinion.

Support... yes, there's a difference between friendly and helpful.. what else to say.

Glad you managed to make Mini running fine for you and thanks for sharing your experience.

Mini+ with Bondtech upgrade & modified firmware...
Posted : 03/07/2021 8:28 am
Piasecznik
(@piasecznik)
Active Member

My Z axis compensation works for sure. I have perfect printouts for just one layer for entire bed area but I know that left side of the bed is lower than right side and I can see how it is being compensated when printhead moves left right doing same layer but Z axis lead screw turns anyway.

Posted : 29/07/2021 10:54 pm
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