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Around 30% into a large print I had to cancel as the layers of the print were not full layers and looked very stringy. Here's a couple pictures of what it looked like.

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I have a feeling that it may be because of my retraction settings either being too high or too fast as this section it was printing had to use a lot of retraction. My retraction settings are 40mm/s for 4.5mm. I was printing at a pretty slow speed (around 55mm/s), and I'm sure confused on why it's not extruding properly at certain times. If anyone has any idea on what is happening and how to fix it it will be gladly appreciated!

I have an Anycubic Delta linear printer with a Bowden extruder, I use white 1.75 mm PLA at 200C, .4mm nozzle

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  • $\begingroup$ Maybe try reducing your printing speed to 30 mm/s. Are your settings appropriate for the filament diameter? What is the diameter of the filament that you are using? Nozzle size? $\endgroup$
    – Greenonline ♦
    May 31 '17 at 6:34
  • $\begingroup$ What material type, temperature settings, etc? $\endgroup$
    – Carl Witthoft
    May 31 '17 at 13:04
  • $\begingroup$ This looks like missing extrusion due lack of filament feed. The feeding gear needs more traction. Retraction I recommend 80mm/s for 2.0mm $\endgroup$
    – Fernando Baltazar
    Sep 29 '17 at 23:06
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It appears that at a certain point, you're running into issues with the extrusion being a bit too viscous / melted causing it to over-deposit or string (fail to retract completely). It also looks like this issue gradually gets worse as you go. This really feels like nozzle over-heating to me.

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My troubleshooting steps would go like this:

  1. Make sure my cooling it set correctly and fan is working properly. The nozzle doesn't adjust its temp for changes in extrusion speed. At times the printer has to rely on the cooling to get the extrusion leaving the nozzle to an ideal deposition temp, which is far lower than the temperate of the nozzle.

  2. Check my tool paths to make sure I'm not starting to return to the same X/Y position too immediately when I reach certain layers, not allowing the previous layer to fully solidify. Consider tweaking the slicer or printing at a lower temperate.

  3. Check if there's a lot of variance in print speeds for different tasks (shell, infill, etc). It can be hard for some printers to maintain the right temp for the extrusion about to be deposited if the speed changes too rapidly. If your printer has been heating extrusion rapidly for quick movements and then the speed slows way down, it can struggle to keep the subsequent slow filament from getting overcooked, as it can't instantly cool the nozzle even with proper cooling. Bring the various extrusion speeds closer together.

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  • $\begingroup$ Your point #1 sounds incorrect. The temperature of the nozzle doesn't generally get changed with changing extrusion speed, and the general advice for cooling fans is to avoid hitting the nozzle with the flow, as it's intended to cool the extruded filament only. $\endgroup$
    – Tom van der Zanden
    Oct 1 '17 at 7:21
  • $\begingroup$ What you said is correct. And admittedly the way I wrote that is a bit misleading... the cooling primarily affects the temperature of the extrusion, not the metal of the nozzle. However, the nozzle is always far hotter than the melting point of the PLA. So if the PLA spends more or less time in the nozzle without effective cooling just outside the nozzle, it will still be past its ideal deposition temp. $\endgroup$
    – Robert Nelson
    Oct 1 '17 at 10:28
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Try using 20 mm/s and 3.9 mm for your retraction and that should help. Also, what is your fan speed at?

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  • $\begingroup$ Are you able to offer a bit more explanation on why 20mm/s and 3.9mm would make an improvement? How did you come up with these magic numbers? Also, please note, that to request clarification from the author ("what is your fan speed at?"), you should leave a comment on the original question rather than posting an answer. $\endgroup$
    – Tom van der Zanden
    Oct 3 '17 at 19:45
  • $\begingroup$ I got the numbers from my personal experience and that is just what worked best for me after trying a whole bunch of different retraction settings $\endgroup$
    – TECTEC3 Studios
    Oct 3 '17 at 20:51
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It seems your printing temperature is too high. If there's a tiny space between the nozzle and the Teflon tube, high printing temperature will lead to a partial clog. And this will lead to under extrusion. Try lowering printing temperatures and printing speed. And also check whether there's a gap between the Teflon tube and the nozzle.

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