I read other posts and see there’s some limitations to getting 90 degree corners… but I don’t understand why. I assume it’s to avoid a bulge? Is there a way to force a 90 degree turn at the corners to avoid this roundness? It’s causing an extra retract to fill in the missing space created by the roundness… and call me picky, but I want a perfect, rectangular top surface.
Since it looks like [visually] those line widths are changing, you could try changing from arachne → classic, as well as different top surface patterns to see if it solves in a more uniform manner.
Assuming you only care about the top surface, you could attempt to hide all top lines by enabling [and tuning] ironing.
If you’re wanting to have crisp corners on outer walls, your nozzle’s aperture is circular and incapable of extruding like that, best you can do is reduce diameter (0.2mm nozzle) but even then, its still gonna be rounded due to physics
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Thanks for the response. Seems like I was already using Classic. And it’s the same behavior when the model is designed as a multiple of the line width and prints with equal lines.
I’m interested in finding a way without ironing. And sure, something like rectilinear would avoid this, but concentric looks nice with this particular design.
The outer walls are fine… it’s the rounded corners of the lines in between the walls. They start to increase in radius from the inner wall. And you can see it switches back to the 90 degree turns closer to the outer wall, but then needs to fill the gap created by the rounded corner of the previous line.
Seems silly to me… it does the inner/outer walls and some others at 90 degrees, why won’t it do all the lines between them the same way?
I think it’s just a wall generator thing. When tracing that inner part, it encounters a 270degree turn, so it draws an arc… When tracing that outer part, it encounters a 90 degree turn and tries to keep it close? And then repeat times 6 till the walls collide.
Have you checked how “only 1 wall on top” and a variety of top surface patterns look? They can sometimes surprise.
Thanks. With your suggestions, I think now I’ve tried every possible setting 
I guess ironing or changing the top surface pattern it is!