Bear with me for a moment, because I’m not sure how to describe this problem without just describing a part I’m trying to print.

I was designing a part today, and it’s basically a box; for various reasons I wanted to print it with all the sides flat on the print bed, but have bridges between the sides and the bottom to act as living hinges so it would be easy to fold into shape after it came off the bed. But when I got it into PrusaSlicer, by default, Prusa slices all bridges in a single uniform direction–which on this print meant that two of the bridges were across the shortest distance, and the other two were parallel to the gap they were supposed to span. Which, y’know, is obviously not a good way to try to bridge the gap.

I was able to manually adjust the bridge direction to fix this, but I’m kinda surprised that the slicer doesn’t automatically choose paths for bridging gaps to try to make them as printable as possible. I don’t remember having this issue in the past, but I haven’t designed with bridges in quite a while–it’s possible that I’ve just never noticed before, or it could be that a previous slicer (I used to use Cura) or previous version of PrusaSlicer did this differently.

Is there a term for this? Are there slicers that do a better job of it? Is there an open feature request about this?

Basically just wondering if anyone has insight into this, or any suggestions for reading on the subject.

Thanks!

  • monotremata@lemmy.caOPEnglish
    3·
    15 days ago

    Basically this: https://imgur.com/a/VjUTVaq

    The blue sections have no support material below them and are printing as bridges, but in the default behavior, PrusaSlicer just uses the single, global “bridging angle” setting to decide which way to print layers on top of these sections. The perimeters on these sections are printed correctly to make the shortest path across the gap, but the rest of the lines making up those bridge layers are printed to match the “bridging angle,” which here means that two of the bridges are printed so they are supported only by those two perimeter bridges themselves.

    Please ignore the details of the print itself, as I’m a little braindead today and this is a print that won’t actually fold together correctly as designed. But the issue of bridges orienting poorly is more general than this particular design.

    • Sphks@lemmy.dbzer0.comEnglish
      3·
      15 days ago

      Can you try to change the geometry so that the different bridges are not consecutive in their corners ? It looks like the slicer is just trying to make one big bridge (in one direction) instead of 4 bridges in 4 directions.

      • monotremata@lemmy.caOPEnglish
        3·
        15 days ago

        Oh, you’re totally right! I knew I was a little braindead today. Thanks so much! It absolutely already does the thing I’m asking for, it just got confused because the edges of the bridges were close enough that their anchors overlapped.

        Bridging working normally: https://imgur.com/a/U7yqZU3

        Thanks!

        • HewlettHackard@lemmy.caEnglish
          2·
          13 days ago

          Interesting, it took me a while looking at your images to figure out why the original design didn’t work. The problem was that there was no solution that could avoid at least one extremely long bridge, and that bridge also forced the adjacent bridges to be “wrong” (though maybe if it printed the super long bridges first, it could’ve made the rest short).

          I don’t have much to add besides being surprised the problem was more interesting than it first seemed…and I don’t accept that you were being an idiot because it want immediately obvious to me either. Or I am one too :)

          • monotremata@lemmy.caOPEnglish
            2·
            13 days ago

            The “idiot” part comes in where I encountered this problem, and didn’t even stop to consider whether this might be specific to this model, or even try something as basic as turn the model on the print bed, which wouldn’t have fixed the slicing, but would have told me my assumption about how the “bridging angle” setting worked was wrong. Instead, I leapt straight from “huh, this model sliced in a weird way” to “this basic slicer feature is designed in a bizarrely poor way and I’m the first one to ever notice,” and posted about it on social media.

            So I appreciate the sentiment, and I’ll leave the post up as it I agree it’s a mildly interesting and counterintuitive result, but I still maintain I acted kinda dumb. :)