First layer underextrusion issue on A1 I cant solve

[Elothan]

I have a A1 Combo, and I is constantly giving me underextrusion/gaps, similar to Bad first layer on a1 mini

At first I figured I need to tune flow (both % and k), but no luck.
This is leading me on a chase where I cant nail down the culprit.

So far I have tried:
Flow calibrations, even at 1,08 it does this, and obviously overextrudes elsewhere.

Changing nozzles (from 0.4 SS to 0.4 HS)
Checking extruder gear for debris (none there, but cleaned for good measure)
Checking and tightening the 4 screws on the “artificial stone”

Manually tramming the bed.

Swapping between 3 different buildplates, and the sides on each. (both stock and 3d party) They are all offcourse clean.

Tried reducing volumetric speed, even tho it was nowhere near maxing out, no change.

Tried 5 different filament manufacturers, including bambu, esun, filamentum, flashforge and prima creator.

Tried both PLA and PETG

The issue seems to be less visible the narrower the layer lines get, but do not disappear, and do not always appear in the same spot.

Size of objects seems to not matter, as I have seen it both on 150mmx150mm squares, and 15x60mm squares.

I have not tried replacing the extruder gear yet, as I do not have a spare.

I am included thinking that the issue is somewhere in the printhead rather than the bed, but I am at a loss for what it could be.

It has acted like this since I got it a few weeks back.

Any suggestions are apreciated.

[igi82m]

The nozzle seems to be too far from the bed.

[Elothan]

It is not, thats the weird thing.
The bed is both manually trammed, and the spots where it underextrudes are not tied to specific spots on the bed.

If it were, it would at least be somewhat consistent to where it was.

I am leaning more toward extrusion gear related, as it can manifest anywhere, no matter the size of the actual print.

[Elothan]

Looks like @igi82m igi82m might have been on to something…

Seems like there is a dip in the plate.

[Elothan]

Currently testing out shimming it with paper to see if it makes a difference, and it does… But its quite a lot and not even good yet.

The heated bed seems almost twisted, not that I have any idea how that could have happened during manufacturing.

[Arhmitzis]

Hi, try to change Z offset:

[Elothan]

Thanks

While not 100% perfect, it at least got me a lot closer to something acceptable by going .002 lower.

I really miss proper babystepping on these machines.(from the UI)

[Elothan]

Sadly, that only worked partially and is not a proper fix, and no response from Bambu customer service…

Edit:
After pestering them more they agree that the bed needs to be replaced and sending me a new one.

[Elothan]

After several weeks it now appears fixed.
I got a new extruder from Bambu, and during dissasembly of the old I noticed that some of the fan wires were flattened and squeezed between the extruder unit and the casing, causing the extruder to not sit entirely straight. When putting in the new one I took care to reroute the wires wires properly, and upon
testing it now works flawlessly.

This was a though one to fix, but at least I have some pare parts to show for it after replacing both the bed and the extruder.