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I'm trying to diagnose a print issue that looks like a missed layer (sorry, first-time printer here)

side-view and top-view

Specs:

  • Printer: QIDI Tech X-Plus (direct drive).
  • Material: PLA.
  • Extruder temp: 200 °C.
  • Bed temp: 60 °C (70 °C first layer).
  • Print speed: 60 mm/s (actually 48 mm/s on non-infill because of min_layer_time).
  • Retraction distance: 2 mm.

Started from a new printer: I was getting imperfect prints (lesser version of this, functional part) and contacted QIDI support. They eventually replied that my bed was too low but I had since lowered the bed on a misdiagnosis. They supplied a slightly modified G-code but that also failed in a similar way.

Since then, I've been raising the bed bit by bit to try to fix this issue. I don't care about the little whiskers much, but the solid "connecting lines" are a problem.

Questions:

  1. Is this actually a bed-leveling/height issue?
  2. What is this defect called (whatever the cause)? I've been googling but can't find something that looks like this.
  3. Is there a better way of fixing bed height issues than just printing->tweaking bed height->printing?

I'd appreciate any help diagnosing this issue - even if it's just the name of this problem. I have no experience disassembling/looking at hardware but I could always give it a shot.

Update

As per comments I took a look at coasting and ran some tests. I first re-leveled the bed manually (I'll call that height=0). I don't want to add tons of pictures so I'll show the baseline, and "bad" refers to similar failure as above.

+--------+--------------+------------+-----------------------+-----------------+--------------+-------------+
|        | Combing      | Coasting   | Retraction distance   | Extruder temp   | Bed height   | Results     |
|--------+--------------+------------+-----------------------+-----------------+--------------+-------------|
| Test_1 | infill only. | off.       | 2.0 mm.               | 200 C.          | 0.           | Baseline.   |
| Test_2 | infill only. | off.       | 2.0 mm.               | 200 C.          | +0.05 mm.    | ~ Baseline. |
| Test_3 | off.         | off.       | 2.0 mm.               | 200 C.          | 0.           | Bad.        |
| Test_4 | infill only. | off.       | 1.5 mm.               | 200 C.          | 0.           | Bad.        |
| Test_5 | infill only. | off.       | 2.0 mm.               | 190 C.          | 0.           | TBD         |
+--------+--------------+------------+-----------------------+-----------------+--------------+-------------+

(+/- 0.05 mm height achieved with clicks of "fast leveling")

Test 1 external view: test_1_out

Test 1 internal view: test_1_in

Update

I think I've confirmed an under-extrusion problem. Here is a top layer printing I stopped partway through.

test_5_top_layer

This looks exactly like Simplify3D's Guide. So I manually pushed through, removed, and re-inserted the filament - and cleaned the nozzle with a brush.

I then ran a new print and noticed a clicking sound in the extruder (I don't know if it's new or if I simply noticed because I was focused on under-extrusion problems) - the print failed in the same "dragging" way as above, but the top layers were slightly better.

I'm now going through the list of possible causes of clicking extruder + under-extrusion.

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    $\begingroup$ It looks like the layer wasn't missed but failed to adhere and instead got dragged around until it stuck in the wrong place. This might be due to underextrusion at the start of the wall line, due to having lost (oozed) material elsewhere just before starting it. You say your retraction is 2 mm. Is your machine direct drive or bowden? If bowden that's way too low; minimum is around 5 or 6 mm. Also "combing" can cause this problem. $\endgroup$ – R.. GitHub STOP HELPING ICE Apr 23 at 21:41
  • $\begingroup$ @R..GitHubSTOPHELPINGICE it's direct drive (as per the printer specs). If combing is the same as coasting then it is enabled. Slicer coasting: coasting replaces the last part of an extrusion path with a travel path. The oozed material is used to print the last piece of the extrusion path in order to reduce stringing.. I think they're different? $\endgroup$ – Antoine Zambelli Apr 23 at 21:48
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    $\begingroup$ No, combing is not the same as coasting, and coasting is a very harmful option and probably the cause of this. It inherently causes underextrusion (total extruded material will be less than the nominal mass of the object). Turn it off. If you have stringing it means your retraction settings are wrong, not that you want to underextrude to compensate for it. $\endgroup$ – R.. GitHub STOP HELPING ICE Apr 23 at 21:51
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    $\begingroup$ I managed to get one much better print with: combing (infill only), no coasting, otherwise same specs. But since then it started having the same problem with every variation of parameters I try (no combing, retraction distance 1.5 mm, bed height + 0.05 mm) - any other ideas apart from coasting? I was thinking maybe turning off retract after layer change? $\endgroup$ – Antoine Zambelli Apr 24 at 23:21
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    $\begingroup$ I don't follow - with same settings, it went back to producing bad results? BTW you never answered if your printer is bowden or direct drive. That makes a difference to recommendations for this. $\endgroup$ – R.. GitHub STOP HELPING ICE Apr 25 at 1:01
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I managed to confirm the dragged layers were mostly due to under-extrusion.

I had a faulty extruder (clicking sound) and once I swapped it out it was greatly improved.

It's worth noting I also had a slight z-wobble issue so that could have played a role.

Hopefully this can help somebody out as I hadn't seen this kind of symptom in any of the print quality guides.

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