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Combing AKA "Avoid Crossing Perimeters"

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I believe the "Enable Combing" is supposed to prevent the print head from passing over perimeters, but in some cases it doesn't work quite right. This may occur on other models, but it is very prominent on a bladed disc like what I am printing.

Instead of staying 'on print' at all times, the print head jumps around between the blades, and leaves them full of holes. Hop + retraction could take care of this without having to go give up the optimum path, but for this specific application it would result in bulging mid-blade.

Is Cura not detecting the spaces between blades as "holes" and therefore not avoiding themb? because I do have combing enabled.

Link to STL: http://www.justbeamit.com/58fd6




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Looking at a model I'm slicing right now, it does appear that Cura doesn't consider the outermost perimeter loops as acceptable regions to comb through, and so, as a result, it has no other option but to jump across the model to reach areas separated by touching outer perimeter loops.

Not optimal in your case, but maybe not the worse case scenario either, considering the large-ish amount of oozing that happens during long comb moves anyway.

BTW, your STL link is broken.


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"because I do have combing enabled" :shock:

Are we talking Cura?

Could not find it in 13.06 or 13.04 ( the older versions I've uninstalled), or a "secret" version?

When you give it a try in 13.04 pretty sure it retracts on the 'blue' lines. I would use Infill>perimeter>loops for print sequence


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Actually, this is kinda expected (but possibly unwanted) behavior. Having a nozzle traveling on the outer perimeter scars the outside surface, so instead of traveling on top of the outer perimeter Cura opts to retract and move the shortest distance instead of trying to comb a thin area.


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Hmm, I see what you mean about the oozing, but that assumes that it should indeed jump around between far away blades. If the move was from one blade to another, it wouldn't be so much of an issue. I see what you mean about how the outer perimeter might not be sufficient for Cura to consider travelling over, although considering it's wide enough to have infill, I'm not sure why. For larger parts, I've seen Cura 'comb' over some pretty large distances.

The STL I used in my first post is a newer, untested version of a previous turbine disc that I *did* print a few months ago. I can't for the life of me remember if I used Cura or Slic3r, let alone which version, but I recall there being no jumping around and the parts came out flawlessly. I'll upload a photo later showing how the new one started printing, and how there are blade chunks missing. There was indeed some stringing as well.

I've attached the older (successfully printed) STL. The screenshot below shows how sometimes some pretty big jumps are made (although often times it's just from one blade to another).

I feel as though the best way to print a part like this, in theory, would be to print it as a series of perimeters with no rectangular infill.




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