Cant get flat walls on this print - any ideas?

[levelhead 0]

I am getting pretty good at troubleshooting and solving problems but my latest print has an issue I can't wrap my head around. The print is a 6mm high plaque with a 45 degree chamfer starting halfway up.

For some reason there is a bulge all the way around the side when the chamfer starts. I haven't seen this before and small tweaks to speed, temp etc don't seem to make a difference. One or two of the corners have very minor curling (1 layer high maybe) that I would expect would cause something like this but the ridge goes all the way around the perimeter of the print.

The only thing I see in layer view in Cura is that at the start of the chamfer, the printer starts doing a thin zig-zag fill inside the wall to support the next layer (see photo). I am not sure why that movement would cause such a large bulge though.

I am using Ultimaker Silver PLA at 205-210 degrees (60 deg. bed) at .15 layer height and 45-55 mm/s print speed.

Any ideas?

[burtoogle 510]

It's hard to tell from the photo but does the wall slope inwards beneath the bulge? Is the bulge the correct diameter and it's the wall below that has shrunk inwards making it look like there is a bulge?

[levelhead 0]

I was wondering if the wall sloped inwards a bit myself. I checked as best I could and it looks like there might be a very slight slope on that wall but at the same time the bulge is still sticking out more than any inward slope. I printed a similar item with no chamfer right after this one and the wall was perfectly straight. I have not have issues with walls before so I don't think it is the Ulitmaker (2+ ext.) itself but might be something in the slicing?

[zerspaner_gerd 379]

Here is a similar German post:

https://ultimaker.com/en/community/49485-oberer-rand-bzw-uberhang

But no solution

[geert_2 557]

What happens if you print the infill at a different density, or 100% filled? (Or just a small test part of it, to not waste too much material.)

In my experience, any sudden changes in layer area to print give clearly visible markings on the outside, especially on small models, due to changes in cooling time for that layer.

So, if the infill pattern changes halfway, I guess that could cause this effect too. Further, a change in pattern could also give a change in support, and thus be visible too.