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  1. #1
    Engineer-in-Training
    Join Date
    Jul 2014
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    Ontario, Canada
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    257

    Curling Overhangs

    Hi all,

    I'm having a weird issue which is really making me feel like a dummy tonight. When printing objects with an overhang, even a slight overhang, the layers begin to curl, specifically in the corners, and can get quite pronounced. I've checked my extrusion rates, and it seems to be within reason, and checked other settings as well. I'm wondering, is this really down to my quick print cooler not providing decent cooling, or is there something I'm missing? I usually print PLA, around 190-200ish, 0.4 nozzle, 0.35 layer height and for this specific print, a 40mm print speed (though i have printed up to 85-90mm). My extrusion rates seem pretty good (marked 50mm on my filament from the base of the extruder and then extruded 50mm and measured difference)


    Any ideas?

    IMG_20140921_173949.jpg

  2. #2
    Super Moderator Roxy's Avatar
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    Apr 2014
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    Lone Star State
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    Quote Originally Posted by MiniMadRyan View Post
    Any ideas?
    This is a common problem. It happens even without overhangs. There are number of ways to address the issue, but no perfect solution. Everything from using different plastics, fans, lower bed temperatures, higher print speeds, etc, etc.

    I think I'll move this where you will get more responses (and more expertise) on the topic.

  3. #3
    Staff Engineer printbus's Avatar
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    May 2014
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    Highlands Ranch, Colorado USA
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    Add printbus on Thingiverse
    If you watched this while it was printing, I bet you saw the soft overhangs being pushed down as the nozzle moved along. Layers aren't cooling enough in between and you're printing on soft PLA. Like Roxy said, a lot of things can come into play here. In addition to what she mentions, you could force more layer cooling time by printing multiple copies or items at the same time. Another trick would be to increase the minimum print speed and increase the minimum layer time in the slicer, making sure it is allowed to move the nozzle off the print for a while if it has to in order to meet the minimum print speed and minimum layer time.

    I've even salvaged the tail end of a few prints by following the nozzle with a flat bladed putty knife to pull some of the heat out of the PLA while the blade has it held flat. I've also used a light stream of air out of a compressed air can to help cool off delicate parts of a print - at least before I implemented a serious print cooler.

  4. #4
    Engineer-in-Training
    Join Date
    Jul 2014
    Location
    Ontario, Canada
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    257
    Thank you both! Oddly enough, your comments about the putty knife was exactly what I was doing for my last print, not ideal, but it worked. I truly didn't think my cooling solution was that inadequate, as my old Printrbot had a very similar solution and I don't recall having many issues with that. I think I will implement the solution you came up with Printbus, as using a blower fan is much more ideal space wise than the traditional one. Just have to find one locally now!


    Cheers

    Ryan

  5. #5
    I have been having overhang curling problems with PLA. I found the solution. The curling is caused by the deposited layers not cooling quickly enough. So according to Newton's law of cooling, cooling is most rapid when the temperature above the base temperature is largest. So I have started using an extrusion temperature of 230C with the bed at 30C. This works like a charm.

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