Print-in-place hinges fail for boring, specific reasons: the gap was smaller than the slicer could resolve, the vertical gap was not a whole number of layers so the first layer over it drooped and closed it, the barrel wall above the bore was thinner than three extrusions, or the pin sagged across its unsupported span and touched the bore. This app models all four and shows you which one you just broke. The three clearances are separate on purpose, and conflating them is the usual mistake. Radial clearance is pin surface to bore surface, and it decides whether the joint spins. Axial clearance is knuckle face to knuckle face, and it decides whether the knuckles fuse into one lump. Rotation clearance is the gap between one leaf's plate and the other leaf's barrel, and it decides whether the hinge can swing at all. A fourth number, the vertical clearance, is the radial one promoted up to a whole number of layers, because a vertical gap your slicer cannot resolve is not a gap. Print it flat, exactly as it exports. The pin axis lies in the layer plane, so bending loads run along extrusions instead of pulling layers apart. A hinge printed with the pin standing vertical shears at the first tug. Calibrate first-layer squish before you print one: over-squish is the single most common cause of a seized joint. Defaults come from published designs that people have actually printed, not from intuition. Nothing published works below 0.10mm per side.