Why does the walls move front and back?  

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nickeh
(@nickeh)
Active Member

Hi,

why does the printer (MK3S, 0.6 nozzle, 0.3 layer height, PLA) not print a straight wall when the model is straight? I usually print objects that have all walls the same height but now when I needed to print with different heights I noticed this. I've checked the belts and they are around 280 in the belt test, so it should not be that (and also there is no variation when printing higher objects that have walls going all around). 

Thanks in advance!

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Posted : 11/12/2020 9:17 am
fuchsr
(@fuchsr)
Reputable Member

I don't know the answer but I'm curious what the experts here say because just yesterday I noticed the same with a large model I printed, like you with 0.6 mm nozzle, 0.38mm layer height, but PETG.

Posted : 11/12/2020 12:57 pm
nickeh
(@nickeh)
Active Member

Interesting, I haven't printed anything since the above print (so the comment about no variation on higher objects was true before this print). I now remember that there was an update pop-up (and I updated) when I started Prusa slic3r so maybe that did something?

This post was modified 3 months ago by nickeh
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Posted : 11/12/2020 1:25 pm
nickeh
(@nickeh)
Active Member

Did some more printing and as you can see it only happens when there are "non equal" walls, tried to load earlier snapshots of the configurations as well as a test with 2.3.0 beta 2, all produce the same error. Seem to be hardware and not software but what... Any ideas?

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Posted : 11/12/2020 3:25 pm
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(@-2)
Illustrious Member

You need to equalize the print speed for the layers involved. It will take a deep dive into your Prusa Slicer settings.

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 11/12/2020 11:18 pm
Extra Fox
(@extra-fox)
Eminent Member

I'm commenting here simply to subscribe. I experienced exactly this same thing on a largish, shelled print. It was a housing for a small LCD screen. I've had layer shifts before, but this was something entirely different, and exactly as you've photographed.

Aaron...
Posted : 12/12/2020 3:38 am
nickeh
(@nickeh)
Active Member

@-2

Ok, can you elaborate on that a bit? Exactly what should I look at and how do I know were the problems will be (without printing one for many hours that has problems first)?

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Posted : 12/12/2020 10:07 am
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(@-2)
Illustrious Member

If Prusa Slicer isn't doing what you want, try a different slicer, one that has a manual you can read and understand. But all of them require tweaking to get what you want, no two parts are identical and often require optimization for best results. Predicting where each will fail requires a crystal ball I don't know how to obtain.

ps: controlling print speed is a fundamental control for printing various plastics. you need to understand this aspect of printing, and all of the controls in Prusa Slicer are labeled, though spread out among the various profiles. Try using the print speed visualizer (those check boxes below the slice preview window).

This post was modified 3 months ago by --
It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 12/12/2020 6:12 pm
Extra Fox
(@extra-fox)
Eminent Member

So here's the thing about that. I use PrusaSlicer for everything and it works great. I've printed tons of things without much fuss and yet I printed this one model and got this:

 

Layer Contraction

Layer Contraction

 

This was PETG using a 0.4mm nozzle and 0.2mm layer height. The really weird part about this is that the layers are contracting and returning to normal on a seemingly random basis. I almost think this might be some sort of issue on the printer itself. There are a lot of variables here.

I'm still eager to see if anyone else has experienced this and if they might have discovered a cause. If only in their specific case as it could be the helpful lead to cracking this one open for others.

Aaron...
Posted : 12/12/2020 7:00 pm
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(@-2)
Illustrious Member

Lots of prior discussion on this...

https://forum.prusaprinters.org/forum/original-prusa-i3-mk3s-mk3-how-do-i-print-this-printing-help/buldge-when-print-reaches-solid-layers

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 12/12/2020 8:53 pm
Extra Fox liked
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(@-2)
Illustrious Member

Then again, you might have a loose pulley or belt that is allowing backlash.

Another variable is a worn nozzle that extrudes slightly thinner one direction than another, the same can happen with a bent heat break.

 

This post was modified 3 months ago 2 times by --
It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 12/12/2020 8:55 pm
Extra Fox liked
nickeh
(@nickeh)
Active Member

So I've spent the day doing maintenance to the printer and did a test print to check if anything has changed. This time with a corner of the object that made me see the problem in the first place, when only printing a part the problem moved to the lower part (to the right in the picture).

 

It then struck me that how wide are the walls (a model downloaded from thingiverse), it turned out to be 2mm (so it is 0.6*3 or *4) so I think the problem has to do with rounding. I replaced the 0.6 nozzle with a 0.4 and it looks much better... But looking to the right (the end of the wall) you can still see that the layers look different above the "foot".

 

To you others that had similar problems, check your dimensions and see if this can be the solutions to your problems also!

 

@-2 Thanks for the feedback, you got me thinking in the right direction 😉

This post was modified 3 months ago by nickeh
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Posted : 13/12/2020 3:26 pm
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