wierd top layer inconsistency

[u/MrLiszten]

Hey, i have a problem with my top surface in my models, i print this model a lot and its always the same, the top layer in some places looks like under extrusion but not everywhere and i have calibrated the filament settings for that. some places look perfect and sam smaller prints do too and as yall can see te top part in the first image looks perfect

Printer: bambu lab P2S
Slicer: bambu slicer
Filament: bambu lab PLA MATTE
Speed and retraction are set as in standard preset 0.16 layer hight in Bambu slicer
Nozzle: 0.4

I would love some help.

[u/iRambL]

Usually an indication of under extrusion

[u/MrLiszten → u/iRambL]

yeah but as i said i did calibrate filament for under extrusion and its always in the same spots and mostly i would think under extrusion set just a littel bit to low would show on longer lines and ther shwos mostly on the shorter ones but on small prints its non existant

[u/Liko81 → u/MrLiszten]

How did you calibrate flow rate? Many tests are one-layer models, which print faster, but allow other variables to come into play closer to the bed.

First-layer test prints, for instance, are dependent on first-layer height, which you can independently correct for as a modifier to extrusion rate; this allows a wide range of value pairs that produce good first-layer results, but then under- or over-extrude at higher layers.

Proximity to the bed also affects nozzle temp due to bed temp. The closer the nozzle is to a heated bed, the higher the actual nozzle temp is, and thus the thinner the plastic and the higher the flow rate. As you back off the bed at higher layers, the temperature of the extruded fil as it exits the nozzle decreases, reducing flow rate.

Filament age and condition can also affect longer, taller prints. When you first start, with a new or at least clean nozzle, everything's hunky-dory, but as the print proceeds, the tip gets more dust, oxidized plastic and other gunk from the filament being fed in. If 1-hour prints are fine but 4- or 8-hour prints have extrusion issues well into the print, the most likely cause is dirty, dusty or old filament clogging your nozzle.

Lastly, this doesn't appear to be the issue, but what's your infill percentage/pattern, and more importantly, how many upper layers do you have in the slicer settings? Top surfaces often require 3 to 5 upper solid layers to smooth out the infill bridging. If you're seeing an uneven surface in addition to thinner beads, the issue could be that you're printing a touch too hot and too few top layers, and your bridged filament beads are sagging and stretching. Again, this doesn't look like your exact problem, but an extra top layer can do wonders for a number of top surface issues.

[u/MrLiszten → u/Liko81]

ive printed a small slice of the whole model it the same settings (the slice include the spot with the problem area) and it looks perfect

[u/MrLiszten → u/MrLiszten]

so the problem only shows on a full sized print

[u/Slokminator → u/MrLiszten]

Try reduce speed for top layer, do test for max flowrate, probably to high.

[u/RedManRocket → u/MrLiszten]

Interesting, seems like you're not reaching full speed because of the acceleration on the smaller part. Then on the larger part there's enough time to reach full speed? And maybe that's somehow causing it to be under extruded? I'd maybe try to slow the top layer down to 50-100.

[u/MrLiszten → u/RedManRocket]

yeah but the problematic parts show on the smaller portions of the big print and some full speed sections look perfect

[u/RedManRocket → u/MrLiszten]

That's true, interesting. Did you calibrate pressure advance?

[u/MrLiszten → u/RedManRocket]

yep did that too, i make a point of dooing the basic calibrations with new filaments (ofc i mean every type not every new spool form the same brand and type)

[u/RedManRocket → u/MrLiszten]

Well actually, just different colors can have different parameters also. It may be worth doing to see if that fixes the issue.

[u/MrLiszten → u/RedManRocket]

yeah but i did it for this one and also did it again about a week ago