Tree support "Infill" going through model

[jumper4412]

Cura Version

5.6.0

Operating System

Windows 10

Printer

Creality Ender 3 V3 SE

Reproduction steps

Added a sphere in mid air to test supports
enabled tree supports with 10% density and lines pattern

Actual results

Two support pattern lines are going straight through the model

Expected results

The support pattern lines ended going through when the interface started, should not start again after the interface ended

Add your .zip and screenshots here ⬇️

Curasupport.zip

[jumper4412]

[HellAholic]

Hey @jumper4412 ,
Please attach a project file so we can investigate the issue. A Gcode just shows the same information as your screenshot in this case and cannot help with identifying settings/parameters that cause the issue.

[jumper4412]

Sorry, forgot about the project file! I dont have the file from the original request, but i was able to reproduce it, screenshot and files attached

Curasupport2.zip

[HellAholic]

Thanks for the file and report, I can reproduce the issue.
If I reset to default settings for the layer height, then the support lines don't go through. So without an investigation, the suggestion would be to take a look at the print settings (combination of tree support and the settings) to see if anything pops out. I'll add a ticket for investigation.

If I drop the model to build plate, same settings don't result in the issue.
Or if I select normal support.

[jumper4412]

Many thanks!

[HellAholic]

Internal reference: CURA-11875

[ThomasRahm]

That is a interesting bug.

Issue lies in the function filterFloatingLines. The support lines around the object are not be supported, causing the hole in the support area to be removed. Seems there is a check missing to ensure that there is no model inside the hole that is removed. Basically there are two possible solutions.

1. Keep the holes always if there is a model area inside of them. Solves this, but can cause floating lines if infill density is 0%. Causes support to be kind of useless here in this case with 0% support density. I don't like this.
2. Only keep holes with model areas inside it if the support infill rate is larger than 0. Avoids above issues, but I have no idea if the support areas are used for travel/retractions down the road (potentially causing other issues as a model part may be inside the support area). I like that even less.

I think a proper solution would be to generate a different density support area below the hole. I do this now in my cradle branch, but I don't think that this branch will be good to merge before the next version.

Example of a different density support area below the hole

@HellAholic
Here is the commit to my cradle branch that fixes this (approach 1): ThomasRahm/CuraEngine@ae25532
I have seen that a 5.7.2 is planned, so I am not sure if I should be doing a pull request to fix this in the 5.7 branch or main.
If you want this fix liked above as a pull request please let me know if it should target main or 5.7.
(edit: Just seen the 5.7.2 released 12h ago, so that answers that question)

@jumper4412
Now that I know what caused this I can describe a workaround for this issue: One can ensure the hole in the support structure gets connected to the outside of the support structure. E.g. by placing a support blocker.

[nallath]

Fixed for 5.8