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Update following advice from @R..GitHubSTOPHELPINGICE in the comments - I've increased the Z-offset from -2.97 to -3.10 and all now appears to be much better.

  • Printer: Ender 3 V2 with heated glass bed
  • Slicer: Cura 4.11
  • Temps: extruder 215 °C, bed 65 °C first layer, 60 °C remaining (works the best for the filament I'm using, lower for other filament).
  • Filament: 3DTomorrow UK PLA Filament - Anthracite Grey - 1.75 mm (But happens with all others too e.g. ERYONE, ZIRO)
  • Summary: On the first layer, every time the printer starts extruding to the bed after a move, the first approx. 10 mm doesn't stick, but the rest sticks perfectly.

The issue, as an example, I'm trying to print a case for a Raspberry Pi which has air vents on the bottom. When the print starts, it does the line down the side which the first ~ 10 mm doesn't stick, but the rest does perfectly. It prints the skirt, which again the first ~ 10 mm doesn't stick, but the rest does, then when it gets to doing the vent slots, the same again.

The photo hopefully shows what I'm trying to explain.

Initial extrude not sticking

When printing a raft, again the first ~ 10 mm of the extrude doesn't stick, but the remaining does.

Raft initial extrude does not stick but the rest does

Once the raft is printed, the first layer sticks to it perfectly well

First layer sticks to raft without problem

The bed is pretty level, I'm using a BLTouch to assist and has been cleaned with alcohol before the print. Bed has been levelled and the Z-offset calibrated to -2.97.

I have Enable Retraction on, 5 mm, 45 mm/s speed. I've tried increasing and reducing these, increasing/decreasing print speed, manual Z-axis offset fine adjustments, etc.

I did think First 3 mm prints poorly, then fine after that was kind of the same issue, but there's no discussion of the issue being for every touch of the bed within the same print job.

Any advice would be appreciated. I've loitered this community for quite a while and lots of Google searching hasn't come up with any suggestions (there's actually very little I could find on this kind of troubleshooting).

Aubs
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    From the pictures it looks like the distance between your bed and nozzle is too great. Note that "automatic bed leveling" **fundamentally cannot** help you get this right because it depends on a quantity it can't measure, the Z offset between the bed leveling probe and the nozzle tip. At best it can help you get the distance *consistent[ly wrong]*. – R.. GitHub STOP HELPING ICE Dec 11 '21 at 18:04
  • This is also consistent with raft fixing the problem, since the raft has extra wide extrusions in the first layer whose width will just vary if the leveling is wrong, and after that, all print heights are just relative to the top of the raft. – R.. GitHub STOP HELPING ICE Dec 11 '21 at 18:05
  • Thanks for the comments. before the photos, I had calibrated the distance from the nozzle to the bed - initially with a piece of paper, then by live calibrating. The Z-offset was -2.97 IIRC. I'll double check it, and confirm once it's finished in a few minutes. – Aubs Dec 11 '21 at 19:34
  • @R..GitHubSTOPHELPINGICE - Thank you. I did have it at -2.97 from manually levelling as it was printing, but have since gone down further to -3.10 and it's doing much better. I honestly thought it looked too close at -2.97, but how wrong I was! If you want to post that as a solution, I'll happily mark it as an answer. Could have saved myself and you lot time and effort if I'd have just pushed it that little bit more! – Aubs Dec 11 '21 at 21:43

1 Answers1

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From the pictures it looks like the distance between your bed and nozzle is too great. The way I see this is that the extrusion lines that should be pressed against each other have small gaps between them, and look rounded rather than flat. The only other way this could happen is with severe underextrusion/wrong esteps-per-mm, but that seems unlikely.

Note that "automatic bed leveling" fundamentally cannot help you get this right because it depends on a quantity it can't measure, the Z offset between the bed leveling probe and the nozzle tip. At best it can help you get the distance consistent[ly wrong].

This is also consistent with raft fixing the problem, since the raft has extra wide extrusions in the first layer whose width will just vary if the leveling is wrong, and after that, all print heights are just relative to the top of the raft.

R.. GitHub STOP HELPING ICE
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  • Your assumption about under extrusion / e-stepping is correct, I had already calibrated that to +/- 0.1 mm over 100 mm. Thank you for the guidance here, you were spot on. – Aubs Dec 12 '21 at 02:31