About this project
A plate with two identical counterbored holes, printed with the pockets on the bed. The left ceiling is the plain circle the CAD gives you. The right one uses the sequential-bridging trick: the first layer over the pocket is a slot, the second is a square, and only then does the hole go round, so every strand lands on something.
Why the plain one is hard
The ceiling of a counterbore is an annulus. The slicer bridges it as a circle, and the strands that reach the through-hole have nothing to land on at their inner end. They droop, and the hole's first layers come out ragged.
What the fix does
Layer one bridges wall to wall across the pocket, leaving a slot the width of the hole: two straight, anchored bridges. Layer two bridges across that slot, anchored on layer one, leaving a square. Layer three is the round hole, and the only unsupported material is the corner overhang readout, a fraction of a millimetre. The two sacrificial layers cost nothing: the hole is still open through them.
Set the layer height
Each sacrificial layer is exactly one layer thick, so layerHeight has to match the slicer, and the pocket depth should be a whole number of layers. Slice it and step through the layers above the pocket to confirm the slot, square and circle land on three consecutive layers.
What to look for
Print it, turn it over, and compare the two ceilings. Then put a screw through each.