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The object on the right is a basic C channel, the outer surface should be smooth but the first ~5 mm of filament is missing after every layer change. In this example, the missing filament is reasonably consistent and extreme. The object on the left (from the same print) has a seam where the filament is also missing but it was not a layer change so it is only missing 1-2 mm.

enter image description here

But when printing a benchy the gap is not as large and has different lengths. The other side of the Benchy looks great, this side has all of the seams on it.

enter image description here

Details

  • Anet A6 direct drive
  • Marlin firmware with the latest Octoprint
  • Heated enclosure, glass bed @ 60 °C
  • eSun PLA, have used many cheaper brands all with the same issue
  • Printing at 210 °C but have tested 180-220 °C

When printing an army of Benchys, I thought this was a retraction issue and test all sorts of settings with small increments but did not fix the issue. It was after printing this C channel that the issue was more clearly highlighted.

Things that I have attempted to resolve this

  • Geomerty calerbration
  • Extruder calerbration
  • Filament temperature range tests
  • Retraction distance and speed towers
  • Retraction distance and temperature towers
  • Disabling retraction (worth a short) - Disabling retraction during only Z hop (did nothing)
  • Different version of Cura
  • Different filament brands

Can not seem to figure out what the issue here is and have run out of ideas on what to do next.

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Several things to try:

  • Dry your filament. Wet filament can have trouble resuming after retract due to moisture absorbing all the heat and slowing the melt, and can also drastically increase internal oozing, leading to missing material later.

  • Adjust Cura settng "Max comb distance with no retract": set very low, around 1mm. Having this at the default (unlimited) causes serious oozing inside the model leading to missing material on the next extrusion path. You'll want to turn on "Connect infill lines" when changing this or you'll introduce a lot of extra retractions that will make your prints very slow.

  • If using Linear Advance make sure it's not set too high. Some users get carried away calibrating it for pretty corners, but if you go too high, you'll end up with serious underextrusion wherever the toolpath slows down. It needs to be set as close to perfect as possible, erring on the side of a lower K value rather than a higher one if unsure.

  • If your printer has a Bowden extruder system (I believe yours does not relevant to OP's printer), check that all the tube fittings are holding the tube snug and that it does not move in/out on retract/unretract. If there's play in the tube, this can make retraction and unretraction ineffective, causing all sorts of artifacts that can be similar to those of having bad retraction settings, but that can't be fixed by changing settings.

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    $\begingroup$ The question says it’s direct drive, i.e. no Bowden tube. $\endgroup$
    – fectin
    Commented Jun 17, 2022 at 14:15
  • $\begingroup$ @fectin: Sorry, I missed that. Just googled for anet a6 and it seemed to be Bowden. $\endgroup$ Commented Jun 17, 2022 at 15:10
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    $\begingroup$ No problem, just trying to help improve the answer :) $\endgroup$
    – fectin
    Commented Jun 17, 2022 at 15:11
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Posting my own solution here

The seams are printing normally now and the solution was simple. The extruder gear was not gripping the filament correctly during retractions and was slipping as a result. Figured this out because the gear seemed to be dirty, which made me think 'how could it get dirty?'.

There was an adjustment that compresses a spring that holds the filament against the extruder gear, it just needed some adjusting.

Thank you to everyone for your ideas, I was close to quitting with this printer.

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    $\begingroup$ Thanks for revisiting your question and posting your own solution! This is very much appreciated. Please remember that after 48 hours you can even accept your own solution. $\endgroup$
    – 0scar
    Commented Jun 30, 2022 at 10:20

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