Are we really sure we are tackling the right issue?
We all know from experience that the UM2 can deliver good results, however for some strange reason sometimes underextrusion happens.
As an example, I printed a box yesterday which was perfect for the first 15 mm height, after that the walls were extremely underextruded. No problem in the feeding mechanism at all to be found.
Today I printed a small variation of the same box and it came out perfect.
The difference was that the first box had internal chamfering up to 15 mm. and above that only 1mm (!) walls. With a 0.4mm nozzle it might be hard to provide these 1mm walls.
The design of today had 1.2mm walls and came out perfect.
So is the first issue because of the extruder or is there a small bug in Cura, not providing enough filament to the nozzle for the 1mm walls?
So what is the rootcause of the issue, are we tackling the right issue here?
I made some pictures, but have not been able to share it in the forum yet. But might not be necessary for you all because you encounter the same issue?