(Using Cura 4.5.0)
I ran across this behavior, which I'm sure is correct, but I would like to know what Cura is thinking...
Relevant screenshots are collected in the attached .jpg.
I modeled a simple cylinder sitting on a box in Blender. They are two separate objects but meant to be printed as one object (they are not boolean'd together or anything). The bottom face of the cylinder has the same z coordinate as the top face of the box.
Both objects were exported together to a single .stl. (Select both objects and export selection).
(To be clear in what follows below: I always expected Cura would print these two objects as a single object. That is, I never expected to get two loose objects off the printer! I know that Cura seems to do its own union of multiple objects before slicing)
Now, when sliced, I thought that the four top-layers of the box would have been completed before any sign of the cylinder showed up. But it seems the cylinder starts appearing in the first top-layer of the box. The screenshots will show what I mean. It is not like the cylinder ends up printing 4 layers shorter. Rather, it looks like Cura is somehow anticipating the start of the cylinder 4 layers ahead of time.
I am happy with the behavior, but just want to know why it happens as it may affect structural decisions in future prints.
Thanks!