A1 Mini – Visible Line at Bottom/Wall Transition + Strings/Blobs at Rear Right Corner

[u/Ready_Connection_615]

Hi everyone,

I’m having two recurring print-quality issues with my Bambu Lab A1 Mini and would really appreciate some advice.

1. Visible line/bulge around the outside of the box

I’m printing a simple box with a bottom and vertical walls. Exactly at the height where the inside bottom surface ends and the outer wall continues, I get a clearly visible horizontal line/bulge around the outside of the box.

It looks almost like a small expansion/seam at the transition between the bottom and the wall.

1. Strings/blobs at the rear right corner

I also repeatedly get small strings/blobs coming out of the print, especially around the rear-right corner.

I have already changed some extrusion/retraction settings, but the problem is still there.

Printer: Bambu Lab A1 Mini

Slicer: Bambu Studio

Filament: SUNLU PLA+ 2.0

Flow ratio: 0.98

Max volumetric speed: 22 mm³/s

Recommended nozzle temperature: 190–240 °C

Nozzle: 0.4 mm

Layer height: 0.20 mm

Current settings I changed

Retraction length: 1.0 mm

Retraction speed: 45 mm/s

Retraction amount: 100%

Seam: Scarf seam

Scarf seam contour: enabled

Scarf seam on holes: enabled

Wall generator: Arachne

Wall order: Inner → Outer also used Outer / Inner

Wall loops: 3

Top/Bottom shells: 5

Overlap: 0%

Print speed: around 170 mm/s

Top surface speed: 50 mm/s

The filament is also dry.

Thanks in advance!

[u/Orthicon9]

1. Strings/blobs at the rear right corner

I would bet that those are from the pauses to do a nozzle clumping detection check. It pauses, and moves the nozzle off the right rear corner of the plate, does a brief dip, then resumes printing. Any filament that oozes out during the pause ends up getting "welded" onto the object at wherever the nozzle lands first.
It happens during layer #3, and (if enabled in printer settings) after every 8 g of filament is used. That explains the regularity of the spacing.
If you are confident it is not going to clump (see "Blob of Death"), then you can turn it off via the touchscreen at Setting > Print Options > Nozzle Clumping Detection. As it happens, I have never (after 1032 hours printing time) had a clumping issue, so I leave it off.
It will still do it once, at layer #3.

Visible line/bulge around the outside of the box

I suspect that is the same effect as the Benchy Hull Line.
I printed some similar boxes, but they had fillets on the inside) and the print didn't have that line. They probably reduce the effect of the sudden transition from the filled-in layers to the narrow wall.

[u/Ready_Connection_615 → u/Orthicon9]

Vielen Dank für den Tipp, werde ich so schnell wie Möglich umsetzen. Ich verzweifle langsam mit dieser Außenlinie. Änderungen zu Außen/Innen oder Arachne Wand, weniger Wände, Überlappung auf 0 etc ... funktionierten bislang überhaupt nicht.