Issue with Cura and thin layers. Cura is modifying the 3d geometry.

[DoktorAce 0]

Hi,

I'm printing using an Ultimaker S3 and Cura slicer 5.4.0. When trying to slice thin walls (like the one in fig. 1), the slicer is not following the 3d geometry and will produce some small wall deformations (fig. 2 and 3). Is there a way to force the slicer to follow exactly the position of the outer wall?

 

Thank you for your help 🙂

 

Fig. 1:

Fig. 2:

Fig. 3:

Edited October 16, 2023 by DoktorAce

[DoktorAce 0]

Also, this behaviour is not observed while using Orca Slicer with the same STL file.

 

[gr5 2,224]

It appears your CAD model has lots of inidividual, short planes on that outer wall.  So the outer wall is curved?  I'd try reducing the number of triangles output to STL in your CAD software.

 

Also there is some kind of resolution setting in Cura (I forget what it is called exactly) that might help if you increase the resolution but it might print worse because it will have more gcodes and many printers have problems if there are too many movements per mm (they stutter as the cpu can't keep up with the computations).

[DoktorAce 0]

23 minutes ago, gr5 said:

It appears your CAD model has lots of inidividual, short planes on that outer wall.  So the outer wall is curved?  I'd try reducing the number of triangles output to STL in your CAD software.

 

Also there is some kind of resolution setting in Cura (I forget what it is called exactly) that might help if you increase the resolution but it might print worse because it will have more gcodes and many printers have problems if there are too many movements per mm (they stutter as the cpu can't keep up with the computations).

 

Thank you for your answer. The outer wall is not curved, it is perfectly plane. Also, with the same STL, Orca slicer provides a perfectly plane sliced model. I will however try to reduce the number of triangle and get back to you.

 

I tried to use the resolution parameters in cura but it dit not help with this issue.

[GregValiant 1,344]

"Wall Transitioning Threshold Angle"

As the inner diameter approaches the exterior wall Cura is making adjustments to the line width.  At the default value of 10° - Cura stops extruding, makes a minor adjustment, and then continues with a single extrusion for the narrow part of the wall.  That will often leave a mark.

 

With the setting at 25° the situation is different and there is no "stop" to adjust the line width.

 

You can still see some slight variation there.  Whether those variations will show up in the print I don't know.

Cura is not "altering the geometry" but is making an adjustment to respect the geometry given the settings employed.

 

This is Cura 4.13.1 without the Arachne Engine Variable Line Width.  This is likely what you are seeing with Orca.

Edited October 16, 2023 by GregValiant

[DoktorAce 0]

14 minutes ago, GregValiant said:

"Wall Transitioning Threshold Angle"

As the inner diameter approaches the exterior wall Cura is making adjustments to the line width.  At the default value of 10° - Cura stops extruding, makes a minor adjustment, and then continues with a single extrusion for the narrow part of the wall.  That will often leave a mark.

 

With the setting at 25° the situation is different and there is no "stop" to adjust the line width.

 

You can still see some slight variation there.  Whether those variations will show up in the print I don't know.

Cura is not "altering the geometry" but is making an adjustment to respect the geometry given the settings employed.

 

This is Cura 4.13.1 without the Arachne Engine Variable Line Width.  This is likely what you are seeing with Orca.

 

Thank you very much for this detailed answer.

 

I tried to play with the "Wall Transitioning Threshold Angle" parameter and it helped a little but there was still a little bit of deviation compared to the stl file (which can be observed in your second figure). And unfortunatly this is still visible in the prints and still is an issue as it is happening in the most critical part of the design.

 

Thanks to your help, I understand now that this is a feature of the new slicer engine (Arachne). Is is possible to switch off this feature or should I go back to Cura 4.13.1 to print this design?

 

 

[GregValiant 1,344]

An "On-Off" switch for the Arachne Engine has been requested but there currently isn't one.

If it is a critical feature I'd go with 4.13.1.

 

This is from PrusaSlicer with Arachne turned on (there is a switch).

You can see the same thing happening as in Cura.  There is a line width adjustment being made.

 

And here I've flipped the switch and turned Arachne off.  I would say this is "altering the 3d geometry".

 

[DoktorAce 0]

I do agree that your last picture is a great example of geometry alteration 😉

 

I just tried with Cura 4.13.1 and I get the result that I was expecting. I will stay on this version untill the Arachne switch is implemented in the latest version of Cura.

 

[GregValiant 1,344]

You have the "Walls / Compensate Outer Wall Overlaps" turned off and the "Compensate Inner Wall Overlaps" turned on.  If you switch those around you will see that there are artifacts on the outer wall as Cura adjusts the line widths to accommodate that thin wall cross section.

So it is still a question of how you set up the slice.

This is 4.13.1 but with the "Outer Walls" compensated.  You can see that the artifacts re-appear.