I have had this problem to some degree across many different printers. Does it have a name? And a solution?
This top surface should be flat and uniform but it deforms due to what is on the other side, like it kind of shrinks:
The inside is like this:
That’s from a few things. Basically it’s from variations in print speed, time between visiting those points on each layer as the layers change and the different cooling/shrinkage that gets you.
There’s hints in the wiki but keeping the build area warm with caveat on too warm, and using chamfers to remove step functions in the features behind the surface. That helps get a more gradual change in layer times as well as helping to disguise steps from more or less cooling between layers.
In addition to what MZip said, it’s commonly referred to as a “Benchy Hull Line” – on the benchy model, this effect is mostly present on the line where the “top surface” of the deck is printed, which slows it down quite a bit in comparison to the one above and below it. So that layer gets more time to contract and cool relative to the others.
It’s hard to give exact answers to remediate because it is a combination of being unique to your model, infill-allowed areas or not, time and temperature, shrinkage characteristic of the filament, etc.
Some of that can also due to the top and bottom surface patterns one chooses. Monotonic vs Rectilinear. Nozzle is squirting out a bead just like a caulking gun, except smaller. Color, surface pattern, material choices can both hide or accentuate the patterns.
Thanks folks!
Just putting a name to it, “Hull Line”, helped me to learn more about it. Annoyingly there seems to be no quick or easy fix. The model can be adjusted, could be environmental, could be in part with print settings. I did find this YouTube video good though: https://www.youtube.com/watch?v=ITighzYPTTs
