[Cura 5.1] Pathing for infill jittery constantly backtracking - causes catastrophic print issues

[Botagar 0]

Good existence all~!

I've been getting back into 3d printing after taking a few year hiatus but all my prints with any kind of infill have all failed due to infill tracks being built up to the point of overflowing with plastic.

When i play the path journey after slicing, I'm noticing that the paths near the walls seem to jitter and in the interior, there are times when the path will go over the same spot up to 3 times. Attached in the gcode produced from my slicing. If you look at around layer 170 (it happens on all layers with a large area of infill, 170 shows it well) you'll notice the jitters and backtracking I'm talking about. I've also attached the original stl (It's from https://www.thingiverse.com/thing:2759439 ).

I'm looking at my cura settings and I just cant see anything that would obviously cause such behavior.

 

I don't know if its relevant, but my printer is a Creality Ender 3 Pro with Micro Swiss direct drive extruder.

 

Any help here would be appreciated.

 

Cheers~!

CE3PRO_BLOKHEAD_hf.3_30.21.gcode BLOKHEAD.hf.3.30.21.stl

[Botagar 0]

I've recorded a .gif of the layer playback and attached the project file as well.

 

 

Any hints or tips?

 

Thanks~!

CE3PRO_BLOKHEAD.hf.3.30.21.3mf

[GregValiant 1,248]

I can tell you what's going on, but not why.

This is an image of your layer at Z=12.0.  The circles are drawn around what appear to be simply the ends of extrusion lines.  (I know my red text sucks but I'm too lazy for a re-do.)

 

The text indicates how many ENTIRE lines are within each circle.  It does not count the full lines that extend outside of the circle.  In a normal situation the count should have been either ZERO or ONE complete line within the circles.

You can see that in the top right circle there are 27 line segments piled on top of each other all at the same Z.

You may have found something here.  @nallath could you take a look?.  It appears that there is a lot of wasted motion going on and I don't see anything in the Cura Preview because all the lines are colinear.  It sure looks like this is what's happening in the OP's GIF video.

Cubic Subdivision Infill.

("Gradual Infill Steps" = 5 but is not visible with Cubic Subdivision.)

 

[Botagar 0]

Thanks for having a look Greg. I didn't realize it was that bad.

I want to note that i see the behavior on all models i slice that has non trivial infill, not just this one.

[GregValiant 1,248]

When you select the "Cubic Subdivision" infill pattern the setting "Gradual Infill Steps" gets hidden but it's value remains the same.  In your case it is set to "5".

I'm wondering if Cura is using the value even though it appears it should not.  I noticed that the setting "Cubic Subdivision Shell" that becomes available appears to have little to no effect.

Slicing the model as received (no changes) resulted in a file 854,528 lines for the print and 50021 seconds print time.

Slicing the model with Gradual Infill Steps at 0 resulted in a file  574,721 lines for the print and 36131 seconds print time.

That's 300,000 more moves (and ~3:45 longer to print) in a file that I would have thought would be simpler with less moves.

I also checked the 2nd file I sliced by reading it into AutoCad.  There are very few double/triple/quadruple lines.  It would appear that is where a large part of the difference between those two files is.

 

So one thing you can do to make a difference is to enable "Grid" as the infill pattern and then set "Gradual Infill Steps" to "0" and then switch back to Cubic Subdivision.  That's how I got the file size down.  

[Botagar 0]

Thanks @GregValiant!

The model is printing now as I would expect after dropping the Gradual Infill Steps to 0 like you outlined.

 

This does appear to be a legit bug then.

How does one submit a bug report? Is this forum thread it?

 

Cheers again!

 

[GregValiant 1,248]

Bug reports are made on GITHUB.  That 3mf file is a good example so you can just ZIP it and post it along with your video GIF and verbal report.  I'm one of the "greeters" there so I'll add a comment and my CAD workup as well.