Weird lines on layer 4 of every large print

[brent113]

@ctaddey

Can we do a special raft that will compensate the calibration matrix…

That is what all rafts do. I have posted before about why rafts are the way they are. Specifically to your question, it’s the base layer spacing that give it the flexibility to conform to the surface of the build plate by giving space for extra filament to flow into as a raised area on the build plate displaces filament.

@brent113

A raft cross sections looks something like this:

The initial layer is very tall, with gaps. This allows under or overextrusion caused by height changes in the bed to have a place to flow into, or sit on top of. Middle and upper raft layers refine these gaps into a more flat surface. There is then an intentional air gap for the first model layer so that it does not strongly bond to the raft. This is a strong negative if you expect the bottom surface of the model to be as smooth as if it was printed directly on the surface, but in exchange it’s easier to remove and will be flatter than the bed. This air gap, which leaves more circular filament extrusions, is compensated for in the model’s second layer with an intentionally smaller Z height increment.

That image is excerpted from this more detailed Cura support article: Support Community