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A Threshold for smallest structures

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Posted · A Threshold for smallest structures

Cura is dropping lines which are smaller than the nozzle size. That is correct, but some software has a small variance in export.

If I build an object with the 0.4mm nozzle in mind, than some of the structures are missing, bec. some of the values in the STL export could be minimal thinner than the 0.4mm (values like 0.39999...).

Could we have some kind of threshold for the minimal line thickness?

I would prefer a very small threshold in the slicer, instead of adding ~0.001mm(or so) to all my 0.4mm structures.

Or is it ok, to set the nozzle size in cura to something like 0.39999mm? Could this have some side effects?

Daid has answered on this in an other thread some weeks ago. But I can't find it (used google with "site", too). :(

I want to second the request of the original poster.

 

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Posted · A Threshold for smallest structures

Cura rounds things to the nearest micron. So 0.3999999 would become 0.4 again.

The nozzle-size effects the line-widths, printing lines smaller then the nozzle size can be done, but doesn't always give great results.

 

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Posted · A Threshold for smallest structures

Hi Daid,

good to know, that there is some rounding. Then this is not the problem. :(

Sorry to say that: But then there must be a bug. :(

I have created some bridge test. Build in FreeCAD 0.14RC1.

I have checked the STL in Blender, there are all values for the missing lines perfect 0.4mm.

Here with 0.41mm the preview in Cura:

Lines Ok 41

That is how it should look.

 

Here the preview with 0.4mm:

Lines Bug 4

There are some missing lines.

It would be nice if you could take a look at my test files (STL):

http://www.vrchannel.de/UM2/line_ok.stl

(The file with 0.41mm lines)

http://www.vrchannel.de/UM2/line_bug.stl

(The file with 0.4mm lines)

Tests above are sliced with 0.08mm, initial layer 0.16mm. Interresting layers are 35 and 36.

Would you need a simpler test?

Should I write a bug report? (If you could confirm the bug)

----

EDIT: OT: Can I change the title of the thread?

---

EDIT2: Hmm Strange. A smaller nozzle size (tried 0.38 - 0.39999) has no effect on the missing lines. They are still not there. ?!? Bad STL? In Blender and in Cura "Normal-View" it looks ok.

 

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Posted · A Threshold for smallest structures

Ah, I found the parameter.

The reason is the shell thickness. The lines are there with a shell thickness of 0.79999mm (instead of 0.8mm)

So that is the parameter where a threshold would make sense.

For now I'll use the 0.79999mm for shell thickness. Are there some side effects with that?

 

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Posted · A Threshold for smallest structures

For now I'll use the 0.79999mm for shell thickness. Are there some side effects with that?

 

No. I've used shell thickness of .3mm with nozzle set to .4mm. You can get a little bit of underextrusion at this severe setting but things come out okay. Using .79 or .39 for shell thickness will be fine. .3 is okay but you will notice reduced quality. Playing with these values is very useful for printing thin walls.

Also note that if you have .4mm for nozzle, and .3mm for shell, the infill is still printed with .3mm spacing and flow rate. This seems strange, but I don't mind as long as I understand what's going on. I guess it would be nice to be able to print the infill at .4mm width and shell at .3mm.

 

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