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Cura making a loop in air


Shrubbery
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Posted · Cura making a loop in air

My model has small overhanging / bridge type sections near a wall. They should be perfectly printable with continuous wall paths, but Cura (3.6.0) creates a loop path in mid air instead.

Is there a way to correct this behavior?

 

loop-in-air.thumb.png.fa2bed36b32dcfc872aaf45807a706d0.png larger-view.thumb.png.317d05ea7f48b48553a7edeb7c79524b.png

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    Posted · Cura making a loop in air

    Are they connected in the CAD design files? In similar designs I made, Cura just follows the outlines of each layer, and thus automatically connects these (but I am using an older version, so I don't know about the most recent).

     

    If not connected in the CAD, then what we see here is the desired behaviour: this is what we use to make supports and other parts removable, like gears or blocks in Rubic-cubes.

     

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    Posted · Cura making a loop in air

    Ah, interesting! That fixed it. Thank you.

    So Cura actually checks if vertices are connected in an object, and if not, it prints topologically separate parts separately like this? I assumed it would essentially just voxelize each object and then slice them as if they had been solid all along.

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    Posted · Cura making a loop in air

    I am not sure what Cura is supposed to do if the gap is *totally zero*, or if the parts overlap. Maybe one of the developers can answer that? (I am not a developer, and not related to Ultimaker.)

     

    But Cura can't know the intentions of the designer, so I think it is best if it treats models exactly *as they are*, without making assumptions.


    Usually I leave very small gaps between 0.1mm and 0.5mm for supports or for different objects that need to be separated, and these of course shouldn't fuse: that would be a nightmare.  :)

     

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    Posted · Cura making a loop in air

    This is even a feature.  You can add 0.01mm diameter cylinders (needles) of air in your print and cura will blindly print around them which can strengthen a portion of your print.  You need to make them at least as tall as one layer though or the slice may miss the needle.

     

    Cura takes an STL file which is a randomly ordered set of triangles.  When it slices it intersects a plane with EVERY triangle and gets a random list of line segments.  Cura than has to figure out which go with which and puts them together in loops.

     

    Now most of the work starts - now that cura has a random set of loops.  Cura doesn't think about voxels.

     

    There is some preprocessing to find overhangs and to note which areas are near a top or bottom surface.  But mostly cura thinks in 2 dimensional slices.

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