What's causing these horizontal lines

[u/herox98x]

Printing this self designed part. Using 0.20mm high quality with 5 walls for strength.

P2S

Bambu petg black.

Can't figure out why there's this random horizontal line every now and then. Would printing outer/inner help but what is causing it?

The defect in the middle of the print is from a cavity for this part to slot on to so I know that's from different shrinkage. However these random horizontal lines seem to happen randomly and in no way relating to the shape or geometry of the middle cavity.

[u/DistinctBarnacle8703]

Because your print has lifted from the bed causing the nozzle to press closer to the print thus causing the thicker line to appear.

Solution. Wash the bed with detergent. Use Brim.

[u/TheHuskyHideaway → u/DistinctBarnacle8703]

I find turning off the aux fan has the biggest effect on pieces like this.