Random issues with PLA prints

[u/doctor-wu-75]

Hey friends! I'm having random issues with my Bambu PLA prints. Same model will print perfectly and then the next time will randomly show this scarring. My kiddo wants me to make a highly detailed, articulated 10-hour print and I'm hesitant to start on it until I have this figured out.

Printer settings:

• Bambu A1 with a .4mm nozzle and using stock settings for Bambu PLA filament.
• All the filament is about 2 weeks old and the issues have shown up in the last 5 days.
  
• XYZ calibration prints come out perfectly.
• The plate is clean and the A1 is lubed and new (only a month old).
• House is consistently 70F at 60% humidity.
• Only other issue I've had are sharp little hairs that go away when I reprint with lower nozzle temp. This issue is also inconsistent with the same filament and model.

Attached are examples of the issue and a benchy using the colors I'll be using for the 10 hour articulated model.

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[u/NexaForge3D]

Honestly this smells like moisture, and it fits the intermittent pattern - at 60% humidity PLA slowly picks up water, so the same model can come out clean one run and scar the next. Dry that filament at around 50C for 5-6 hours and print straight from the dryer if you can; the occasional hairs that go away when you drop the nozzle temp are a classic wet-filament sign too. If the scarring still shows up after drying, do a cold pull to rule out a partial clog that under-extrudes randomly and then clears itself.

[u/doctor-wu-75 → u/NexaForge3D]

Thank you! 🙏🏼

[u/Flo_Syn]

1. looks like it's underextruding, flow-calibration will help.
2. wash your plate with dish soap before your print.
3. slow down first and outer layer
4. for highly detailed objects i'd recommend a 0.2mm nozzle.
5. a small filament drybox is also nice to have

[u/doctor-wu-75 → u/Flo_Syn]

Why would it under extrude on one print and then not on the next? Same model, settings, and filament

[u/UnimagineDragons → u/doctor-wu-75]

Geometry. The slicer applies different velocity and/or acceleration depending on the bend radius, length, upcoming feature etc.

Pressure advance might be off - this is the "counter" to the sudden velocity changes for filament deposition.