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I've noticed my Ender 3 V2 printing odd little bubbles of material on curves. Is this over-extrusion? I'm using Creality PLA at 210 °C with a bed temperature of 60 °C

3D printed model with bubbles on the side

The opposite side of the same print, with no problem in the curve. Yes, I do have lifting at some corners, but this seems to be a different issue.

The opposite side of the previous model with no bubbles

This was printing a center-finder


It's a bit hard to see but here's the same blister-like look on the handles of a grabber-toy. Lighting makes it a bit hard to see, as does printing in black.

A different 3D printed model with bubbles on the sides

I have calibrated my E-steps; initially, it was extruding 95.5 mm when told to do 100.0 mm. By changing the printer's numbers, it's now pushing through 100.1 mm when requested to do 100.0 mm. Is that my cause?

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  • $\begingroup$ Possibly related to 3dprinting.stackexchange.com/questions/13805/… $\endgroup$
    – Criggie
    Oct 23 at 4:25
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    $\begingroup$ Does the nozzle move through that section at a uniform smooth rate when printing, or does it slow down and speed up eratically? This looks to me like the fallout of bad interaction between acceleration/cornering profile, the stock firmware's lack of linear advance, and numerical imprecision in model or slicer output making what should be curves into fine jagged details. $\endgroup$ Oct 24 at 1:21
  • $\begingroup$ @R..GitHubSTOPHELPINGICE good thinking - I watched a second run of the same center finder, but at 70% not 50%, and the motion looks smooth throughout the whole print. I do have the stock firmware on it, an update is in the plans. What makes no sense is that the opposite curve is perfect. $\endgroup$
    – Criggie
    Oct 24 at 6:02
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After much faffing about, I've discovered that OctoPrint is the cause, or specifically running it on underpowered hardware.

I originally thought that OctoPrint sent the job to the printer's internal SD card and it printed from there.

That is incorrect, OctoPrint feeds G-code to the printer. And since I'm using a sub-standard Pi B+, it does not have the resources to keep up.

By attaching a webcam, I doubled down on the resource contention and made it worse.

Own work

Basically, the OctoPrint minimum-spec is there for a reason, disregard it at your own risk.

The test object can be found at https://www.tinkercad.com/things/1vjIJXoQkde and has 5 half-barrels with different segment counts. I originally noticed that the smoother curves suffered worse, and was testing that.

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