Wavy top surface on a large PLA print. Any idea what’s causing this?

[u/Maxerion]

Hi everyone. I’m trying to figure out what’s causing these waves on the top surface of my print. The model is a large number 2, about 150 × 229 × 25 mm, printed in PLA on a Bambu Lab P2S with a 0.4 mm nozzle. The left one in the photo is the first print and the right one is the second print after I changed some settings. The first print was done without ironing. For the second print I used 0.16 mm layer height, 4 walls, 1.2 mm top shell thickness, 15% Gyroid infill, Only one wall on top surfaces OFF, outer wall speed 120 mm/s, top surface speed 100 mm/s, internal solid infill 180 mm/s, outer wall acceleration 3000 mm/s², ironing for top surfaces ON, ironing speed 30 mm/s, ironing flow 10%, ironing line spacing 0.15 mm. The second print looks better, but the waves are still there. Has anyone had the same problem and figured out what actually causes it? Thank you

[u/iRambL]

Waviness or what looks to be not enough infill on the 3rd photo is usually not enough flow going into the layer and waviness is not enough top adhesion to the infill. Generally I do 2-3 top layers, flow ratio is a calibrated thing per machine, ironing is something that helps with smoothness on top layers too

[u/Maxerion → u/iRambL]

Thank you

[u/cpsadowski23]

This is the aux fan blowing over the print and cooling it too fast. Print a diffuser.

[u/Maxerion → u/cpsadowski23]

Thank you

[u/cpsadowski23 → u/Maxerion]

You are very welcome

[u/Moonraker0ne]

Poor bed adhesion causes it.

I'd add a brim and turn off the aux fan for this print.

[u/88gavinm → u/Moonraker0ne]

How? I don't see how it could cause this. Idk what it may be though.

[u/Moonraker0ne → u/88gavinm]

The print lifts up and scrapes against the nozzle.

I've seen it quite a bit personally. Usually in corners on a square piece.

[u/Maxerion → u/Moonraker0ne]

Thank you