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Odd first layer behaviour

Discussion in 'Troubleshooting' started by Red Submarine, Apr 5, 2014.

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  1. Red Submarine

    Red Submarine Active Member

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    I don't know why this happens, but routinely, when I print with ABS or PLA my bottom layer is terrible. Without adjusting anything, it will start weak on the first few strands, then squish the next bunch and then when it moves to the other side of where it started it's perfect. I can see when I move the head on the X axis that the bed is bowed a bit, but that doesn't explain why the strands all print differently... I have no bed adhesion issues but this does make the underside of my prints look all melty when they come out.

    (sorry for the blurry pic, cell phone of a moving bed, but you can see how it is thin in the middle, too squished to the right, and after it has picked up and come down for the left side it's perfect)
    photo(4).JPG
     
    #1 Red Submarine, Apr 5, 2014
  2. Red Submarine

    Red Submarine Active Member

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    Also, why does my ABS slurry bubble like that? I've noticed that it doesn't bubble if I spread it really thin or add more acetone to the mix, but it is an odd phenomena.
     
    #2 Red Submarine, Apr 5, 2014
  3. Mike Kelly

    Mike Kelly Volunteer

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    what temp are you applying the ABS slurry? I lay it down at 70+c so the acetone boils away as I lay it. Gets a relatively smooth placement.

    My wife thinks it looks like a ghost busters explosion.
     
    #3 Mike Kelly, Apr 6, 2014
  4. tesseract

    tesseract Moderator
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    the problem you are having is directly related to the initial height of the z axis and the fact that you bed is not level
    the filament should be slightly flattened out as it gets put down on the bed surface as you can see in this first layer example-text.jpg

    this was done with a very accurate initial z height and a bed made level with my bed levelers mod.
    It only take a very slight difference in the distance the nozzle is from the bed to create the difference you are seeing. I have seen the same exact issue in some of my prints and to me it mean I am just a bit too close the middle few lines where it looks slightly rough is the prime clue for that just raising it slightly will correct that.

    The key is when I say slightly I really mean slightly usually less than 1/16 of a turn of the screw will fix it and not mess up the other layers that look good
     
    #4 tesseract, Apr 6, 2014
  5. Red Submarine

    Red Submarine Active Member

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    Lol, the immortal "first layer example" pic. I've seen it all over this forum and it is very useful. I get why it oversquishes, but it does not explain why two strands, right next to eachother but laid down at different times, have different characteristics.

    Mike, I lay it on cold. I ended up just adding more acetone to the mix and have no issues now.
     
    #5 Red Submarine, Apr 6, 2014
  6. tesseract

    tesseract Moderator
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    that would indicate some small extrusion type issue that could be related to the temp or retract rates and speed depending what it is ding right as teh bad patches start but on the hole for me at least if I raised it a tiny bit things cleaned up
     
    #6 tesseract, Apr 6, 2014
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