[Bug?] non-continuous extrusion of inner wall on hollow cylinder

[ChaosBlades 0]

From what I can tell of the STL the wall thickness of this hollow cylinder is 1.2 mm which should be able to be divided by 3 with a 0.4 mm nozzle but I keep getting inconsistent extrusion causing a nasty effect on the outside of the print. The picture explains it better than I can. It does this on the same 2 sides of the cylinder regardless of how I have it rotated. I do not believe the cylinder wall thickness is thicker in these areas. I have looked through all the Cura settings and I have only been able to make it worse.

 

Just tried Prusa Slicer and it isn't doing this.

 

The STL has been attached. Can I get some community support in determining if this is a bug then I will submit an issue on GitHub? Let's see if all profiles do this or maybe it is a setting that is doing this.

 

 

I 'fixed' the issue by setting walls from 3 to 1 and also setting 100% concentric infill. Which isn't a fix at all for obvious reasons.

Edit: Also noticing when I do this it is extruding the outer wall, the inner wall, then the yellow wall... Then it is combing(?) back through the yellow wall after it is already printed before it starts a new layer. Turning combing off does not affect issue.

 

Edit: I meant Combing not Coasting, fixed. Actually combing was turned on and didn't affect issue.

IncenseTubeBoxThreaded-HQ.STL

Edited April 9, 2020 by ChaosBlades

[burtoogle 516]

This is all known behaviour for Cura. It cannot at this time make a good job of walls that are not close to an even number of line widths wide. I believe that the Cura devs are addressing this long standing deficiency.

[ChaosBlades 0]

So you are saying because it is 3 line widths instead of 4, that is the issue?

 

Do you know the GitHub issue number, so I can track progress?

[burtoogle 516]

12 minutes ago, ChaosBlades said:

So you are saying because it is 3 line widths instead of 4, that is the issue?

 

Yes.

 

13 minutes ago, ChaosBlades said:

Do you know the GitHub issue number, so I can track progress?

 

AFAIK, there isn't an issue on github specifically about this.

 

The PR that could form the basis of the solution is https://github.com/Ultimaker/CuraEngine/pull/1210

 

You can see from the comments there that it still has some way to go before becoming a reality.

 

[ChaosBlades 0]

In the situation I am talking about the wall thickness is 1.2 mm, the line width is set to 0.4 mm, and the number of lines is 3. So the line width should not vary, it should stay at 0.4 mm.

 

If the perfect world what I just said above would be true but thinking about it, I think it does need to vary the line width due to the nature of the STL and how circles are not perfectly round and some places are going to be slightly thinner than others.

 

In Prusa Slicer I can see it can vary the line width when filling out gaps between walls. I can also see some lines from my above pictures are no longer printed when I disable fill gaps between walls.

 

Edit: Setting Line width to 0.39 mm also 'fix' the issue.

Edited April 9, 2020 by ChaosBlades