About this project
Three bars with the same cross-section, printed three ways on one plate: FLAT on its wide face, EDGE on its narrow face, and UP standing on a foot. They are deliberately separate bodies. Print them together so they share every setting, then snap each one by hand and compare.
What differs
Nothing about the bars. Everything about the layers. In FLAT and EDGE every bead runs the length of the bar and carries the bending load itself; the bondsFlat readout is zero because no layer bond crosses the load path. In UP the load crosses a bond at every layer, and the bondsUpright readout counts them from the bar length and your layer height. Each of those bonds is a weaker interface and a small notch.
The notch
Set notchDepth above zero for a 90 degree V at mid-length on the tension face of each bar. It moves the break to a known place and lets you compare notch sensitivity: on UP the notch coincides with a layer line, which is what a real part's layer lines do at every sharp corner.
Sizing
3 mm thick PLA snaps by hand; 5 mm wants pliers. The foot keeps the upright bar from wobbling while it prints, and the validator complains if the bar gets tall for it.
What to look for
How much harder FLAT and EDGE are to break than UP, and where UP breaks: it will be a layer line, clean across, with the bead pattern visible on both faces. Then print the set again at a higher nozzle temperature, or with the fan turned down, and feel whether UP moved.