UM3 prints well with AA0.4, not so with AA0.8... ?

[jnhg 0]

I am at a loss here, hope someone with better knowledge than me has some advice.

I am trying to print with an AA0.8 print head at 0.2 and 0.3 mm layer height to speed things up but the results (surface finish) are pretty bad.

Everything is fine when I swap in an AA0.4 print head.

I have tried to print with Inofill PET and Polymaker PETG with the same awful result. I have mostly used PET/PETG materials before, with good results.

I have tried the factory recommended settings for both and have varied temperature, print speed, fan speed and flow rate, one at a time. Things monstly get worse, so the recommended settings are probably fine, they work for 0.4mm, so no surprise really.

I have cleaned the nozzle, pull looks good. I have dried the filaments and I have tested both head positions. I can't see or hear anyting strange with the extruders.

I have not used this print head much since I got it, I never got it to work well and thought I needed to spend some time on it to get it right. Well now I have spent quite a lot of time...

In close up it looks to me like some kind of inconsistent extrution or as if something moves around. I have looked for something loose but can't find anything strange.

What am I missing?

The tube on the left is 0.4, on the right 0.8.

[jnhg 0]

Update:

I found this article:

https://community.ultimaker.com/topic/29632-getting-better-cylinder-walls/

And followed the suggestion to disable compensation of wall overlaps. There was a considerable improvement. I also set Z seam alignment to "shortest".

I could then lower the temperature from 233C, which was the best looking before this change, all the way down to to 215C which is more in line with the factory suggestions for Innofil. That seems to be the sweet spot. I could also crank up the speed to 70mm/s which makes the switch to 0.8mm really worthwile.

In other words, I was really on the wrong track, There was no issue with materials, mechanics or print cores, the problem was with Cura (4.5) and obscure settings...

The prints now have a surface finish good enough for my use.

Thanks to hazedav and iccherry for their work in solving their similar issues.

I am really happy to leave this behind me...