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  1. #1

    Bumps at 90 degree corners, not every layer, looking for opinions

    I went ahead and printed a 20mm calibration cube using my maker select. I noticed that on the corners there are very tiny bulges in certain layers but not all. it also seems the imperfections are not throughout that entire layer just the corners. This is zoomed way in and is barely perceptible by my blind human eye but I could see it since the filament is so shiny. Tried a white PLA and the result was exactly the same but more difficult to see due to the color and lack of sheen.

    Make select
    1.75 PLA @ 190C/60C
    60mm/s
    .200 layer height

    Thanks guys!

    Dave
    Attached Images Attached Images

  2. #2
    Technologist
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    Jul 2017
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    Blobbing at corners or any place with a sudden change in direction (i.e. where motors need to stop or start on a dime) often causes this kind of (inconsistent) blobbing. The reason for this is that pressure builds up in the extruder, while this is fine when the print head is moving and it needs to keep extruding, when it suddenly stops for a moment (like at a corner) that pressure causes some extra filament to ooze out.

    A couple of possible fixes. Try 'pressure advance' or a similar setting some firmwares/slicers have to combat this sort of thing. Secondly, try upping your jerk in firmware, this lets the printer get moving faster and shortens the time spent stopped at the corner so less filament oozes out and creates the blob. Upping jerk can have a negative impact on print quality with regards to ringing and skipped steps though so it's a trade off.

    That being said, I can't see the thumbnail so I'm guessing based off the 'blobbing at corners' description.

  3. #3
    Sorry I did not get an email notification to this. The images are not working for you? I am using Simplify3D so I can check that. Would retraction speed or distance have any effect?

  4. #4
    Super Moderator curious aardvark's Avatar
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    you don't generally retract at the corners. So, unlikely changing retraction would have any effect.

    have to admit, it's never bothered me, so never looked for some way to change it.
    I'm always impressed how sharp a corner is made with a round bead of plastic :-)

  5. #5
    So this isn't an atypical issue? If not I'm good with it. Wasn't sure if this was impending doom or not

    Dave

  6. #6
    Technologist
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    Not impending doom, but it shouldn't be happening, prints shouldn't have gaps. It's likely a settings issue, try different slicers or slicer profiles, see if that fixes it.

  7. #7
    Engineer ralphzoontjens's Avatar
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    Yeah you definitely want this to be tighter. See if you can attain settings to lower the pressure on the print a bit, for example flow settings.
    If you used the same brand of filament for both tests, it can just be a less viscous filament blend.
    The overall best solution is to add radii to your sharp corners.

  8. #8
    Super Moderator curious aardvark's Avatar
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    what gaps ? he just said he didn't have perfectly sharp corners.
    Ah I see - yeah the layers are not particularly even.

  9. #9
    Technologist
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    My bad, I think I was thinking about/replying about the other thread with the under extrusion. Bumps are usually fine, but can mess with you when you need two parts to fit together.

  10. #10
    Yeah I agree on the fitment between two items. I will try slicr and simplify3d and see if the bumps are different. I can't see them being much different really. I've printed a few since then and the lines across the entire layer have been resolved but still have some corners a bit bumpy. I was hoping there was one particular setting I could play with that would help this.
    I have increased temp to 205 as I wasn't happy w/ layer adhesion at 196. The temp tower looked best at 196 but it just wasn't as strong as i wanted it to be.

    Dave
    Last edited by TTVert; 02-03-2018 at 12:36 PM.

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