How do you solve PLA corner-curling short of printing really, REALLY slow?

  • I've been trying a lot of different things to combat corners curling upward in the first few tens of layers after the bottom skin. To be clear, I'm not talking about corners of the first layer printed on the bed, but rather the points of the outline in layers above the base where direction of print motion changes discontinuously (discrete corner) or abruptly (turn with very tight curvature). Here's an image I found (not mine) that demonstrates:

    print with curled corners next to one without

    And a pic during print of the type of curling I'm talking about:

    curling corners during printing

    And some previous worse prints:

    2 dodecahedra with very warped edges, one with minor distortion to one edge, shown bottom-up

    My go-to worst test case for this now is a 20mm tall hollow dodecahedron with 0.8mm shell (hollow geometry, not just empty infill; 0% infill on a non-hollow model does even worse, shown above). For everything else I've tried, I've mostly been able to sovle the problem with combinations of

    • Improved cooling fan duct

    • Lowered bed temperature or unheated bed (but this is a tradeoff; it seriously hurts first layer quality and increases risk of non-adhesion)

    • Disabling Cura's overhang detection mode (non-uniform print speed causes a huge increase in the curling due to latency of extrusion rate response)

    • Increasing motion acceleration limits or decreasing speed limits (also mitigating the latency in extrusion rate response)

    but I can't get all 5 edges of the worst-case dodecahedron completely warping-free without just heavily slowing down the print; during print it's obvious that the curling at the corners in each layer is the source of the warping. Increasing Cura's cool_min_layer_time to 10 seconds (default is 6, and I usually get by fine with 3-4.5 for most things) mostly but not entirely solved it, and going much slower than that seems likely to introduce other surface artifacts from extremely slow extrusion.

    Are there any additional tricks I'm missing for solving this? I'd like something that's easy to leave on all the time or at least to automate, as opposed to hacks like adding in a junk tower off to the side to waste time between layers.

    My printer is an Ender 3 with stock gear except for improved fan duct. The problem was worse with the stock fan duct.

    Hi, please provide us with the types of PLA (opaque, transparent, filled) and vendor, and, equally important, what temperatures you're using, what print speeds, etc. I've successfully printed various thin-wall objects without any deformation at the corners.

    @CarlWitthoft: It seems worst with real "natural" PLA (supposedly no additives, clear), but also happens with opaque blue and probably others (I could try if needed). I'll add some pics and further details in the question

    Someone commented then deleted the comment that I haven't yet added pics. I've had my printer hacked up for a few days and been busy with other things, but I do intend to get back to this. It looks like the problem *might* (fingers crossed!) actually be soolved by Marlin 1.1.9 with linear advance; I just tried to reproduce the problem for a pic and got a perfect print. If I can confirm that setting K=0 makes it come back, I'll write up a self-answer based on that.

    Still having trouble reproducing it really bad, even with linear advance turned off and bed temp back up to 60°C. Either Marlin 1.1.9 fixed some subtle problems with synchronization of extrusion with motion vs the stock firmware, or there's some environmental issue like ambient temperature or humidity. I'll try later and see if I can reproduce with some clear/natural PLA which seemed to be more problematic, and see if I can find some examples from my scrap box showing the warping.

    OK, it reproduces easily with plain clear/"natural" PLA. Added pics.

  • While I tried a lot of things to solve this, including tuning temperature, fan, speed, etc., ultimately the single biggest factor that causes or prevents it is the state of Cura's Outer Before Inner Walls (outer_inset_first) option. With outer walls first, I don't have the problem at all. With the default (inner walls first), I have it to varying degrees depending on geometry and a lot of other factors.

    I don't have a good explanation for why this happens so I'm asking a new question about it.

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Content dated before 7/24/2021 11:53 AM