This problem has plagued me off & on for years, and I see plenty of posts from other users with the same issue. It has reared its ugly head again, and I started posting in reply to another user's post on the same problem before I noticed he was posting in the general forum, and not the Troubleshooting forum, where I think this belongs.
Here's the original thread I replied to: viewtopic.php?f=8&t=15579
It includes a couple factory files and photos of the problems I've been seeing. I'll try to summarize, and then throw some new info into the mix.
Basically, I'm getting gaps between inner perimeter passes. The defects are repeating layer upon layer, so you end up with a delamination between the perimeters. I've have experimented with a very wide range of settings for thin wall behavior in the Advanced tab, without any effect.
I'm running a 0.35 mm nozzle and a 0.40 mm extrusion width, using eSun PLA+ filament on a MakerGear M2E printer. I'm using S3D version 4.1.2.
Here's a picture of a small chunk of a larger model that I've been using to test things:
I've managed to improve things a bit since this. I changed to a new spool of filament, re-calibrated my extrusion multiplier, adjusted the temperature, etc. and that got me here:
Still lots of gaps. I posted this with my factory file in the other thread, and the user "airscapes" was kind enough to take a look at it, and provided me with a modified version he felt should work better. He changed a number of thin wall setting in the Advanced tab, decreased the number of perimeters from 3 to 2, and changed the print order to inside-out. His settings produced the following results:
I still have gaps, pretty much just as bad and in the same locations. There are gaps that didn't show up well in this photo because I couldn't get the camera lined up exactly vertical over multiple areas so the backlighting would show through. I did notice that the gap appears between the last perimeter and the 2nd to last. In my 3-perimeter process, the gap is between pass 2 & 3. Airscape's process with 2 perimeters has the gap between 1 & 2.
The section where the gaps occur is 2 mm wide, which a 0.4 mm extrusion width should fill exactly, with no thin wall treatment required. I modified the model so the problem area was only 1.9 mm wide, and that made no difference.
It looks like it's underextruding, but if I print a 3 perimeter test cube, the walls come out 1.2 mm thick exactly, with no gaps.
I did a search, and found lots of posts complaining about this issue, but no fixes. One user indicated that the problem started with 4.1, but I haven't gone back to 4.0 to test that theory. Several other users have posted that the problem does not occur in other slicers, and if I don't come up with a fix soon, I will try PrusaSlicer, although I really prefer S3D.
I think the three photos hits my attachment limit, so I will post a factory file in a separate reply.