SOLVED slic3r messed up(?) infill when using various layer heights

  • Hi Forum 🙂
    I am printing a spool holder and decided to increase the layer height for the purely cylindrical part in the middle to 0.4 mm -- the rest is 0.3 mm -- to speed up the print a little.
    For that I used the "Layer Height Table" in the settings menu of the part. The layer heights come out as expected: 0.3 for the first 13 mm, then 0.4, then 0.3 for the last 10 mm.
    However, in the range with the 0.4 mm layer height, the honeycomb infill was not printed properly -- rather only one direction of diagonal zigzags was printed for one layer and then the other (90° rotated) zigzags for the next layer (looking from the top it did not even look like the two patterns would combine into a honeycomb, but i might be wrong).

    Do you have any idea what might have went wrong and which setting I should check?
    (I already made sure that the "combine infill every ... layers" setting was set to the default 1).

    Thanks a lot! 😃

  • Moderator

    Try a different infill pattern that doesn't alternate the pattern on every layer, maybe cubic.

  • @printHorst What size nozzle are you using? You can't print 0.4 mm layers with a 0.4 mm nozzle...

  • Hey @mrehorstdmd , thanks! You might be onto something -- yes, it's a 0.4 mm nozzle. However, I set the layer height to 0.4 in slic3r (for the middle range of the part) and it did print with that layer height. I just measured it with a caliper and there are exactly 10 perimeter traces within 4 mm.

    @Phaedrux also thanks 🙂 -- I think you might have misunderstood: I did not set it to alternate. With the prints before, it printed the complete hexagonal infill for every layer ("as expected"). With this print that I described here, it only did a zigzag in one direction for every 2n-th layer and 90° turned for every 2n+1st layer and thus the infill was sagging.

    btw.: the part still came out nice (except for some pretty bad "ooze seam"(?) which is the next thing i will figure out 😉 ) and is currently holding my spool -- so the 0.4 perimeters were fine, just the filling was messed up.

  • When you print with a 0.4mm nozzle, you want the layer thickness to be approximately 1/2 of the nozzle diameter so that the profile of the line of plastic being laid down has a flat top and bottom. That increases the bond between the lines of plastic and makes for strong prints. 0.25-0.3 mm is the upper limit of layer thickness with a 0.4 mm nozzle, and 0.3 mm is really pushing it. If you try to print a 0.4 mm layer using a 0.4 mm nozzle, there's no squish, and theoretically, the only contact between the layers is a thin line making for a very weak print. The reality is that the plastic coming out of the nozzle will slump until it cools and that will lead to very uneven, sloppy looking lines, and a weak print.

    You also can't print lines that are narrower than the nozzle diameter for similar reasons.

    I suggest you reconsider the infill pattern. Honeycomb and some of the other nice looking 3D patterns aren't especially strong and they print slowly because the direction keeps changing. If you want strong infill that prints fast, try grid or triangles. Both are composed of long straight lines (good for speed) and all lines occur on every layer so strength is maximum (assuming you don't try to print 0.4 mm layers with a 0.4mm nozzle!). As an added bonus, they won't shake the snot out of your printer while they are printing.

    Honeycomb and some of the other 3D patterns are good for prints in which the infill is going to show by intention, and for marketing photos if you're selling 3D printers or kits.

  • Alright, thanks, that makes sense. I can just tell you my anecdotal "evidence", namely that despite the supposedly too high layer height and the messed up infill, the spool holder is really strong (I tried to break it b/c I thought it might not be strong enough).

    Regarding my original question: I think I understand now that you are probably both right! I just looked at my gcode at and I see that the full hexagons are indeed printed along two alternating diagonals (Which is what @Phaedrux wrote and rather I misunderstood them) + then it might make sense that with a high infill speed and too high layer height it just did not manage to squeeze out enough filament and thus the infill was sagging? (Still, perimeters are fine, but they are printed more slowly.)

    Honeycomb and some of the other nice looking 3D patterns aren't especially strong and they print slowly because the direction keeps changing. If you want strong infill that prints fast, try grid or triangles

    Thanks a lot! 👍

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