tl;dr: STL export has two quality settings, a distance (deviation/chord height) and an angle. Whichever one is tighter decides your quality, and the other does nothing. Past a certain point, finer settings make files 10x bigger with no change a printer can reproduce. Background: I build a STEP/STL conversion tool (stlfixtool.com), so I needed to know which export settings actually matter instead of guessing. There was a great post here a while back showing that slicer STEP import is often worse than a good STL export. This is the follow-up question: what makes a good STL export? The test: - 3 shapes: a 20mm cylinder, a filleted 40x30x15mm box with a hole, and an organic torus/cylinder blend - Each exported at 5 linear deviations (0.1 to 0.001 mm) × 3 angles (0.5, 0.3, 0.1 rad) = 45 STLs - For every STL, I sampled 20,000 points on the mesh and measured their distance to the exact CAD surface. That's measured error, not the number in the settings box. Cylinder results: - linear 0.1mm, angle 0.5: 32 segments around the circle, 0.048mm max error - linear 0.1mm, angle 0.1: 126 segments, 0.003mm max error - linear 0.01mm, angle 0.5 or 0.3: identical, 100 segments, 0.005mm - linear 0.001mm, any angle: 315 segments, 0.0005mm Organic shape results: - linear 0.1mm, angle 0.5: 5,096 triangles, 0.092mm max error - linear 0.01mm, angle 0.3: 38,624 triangles, 0.0099mm, 1.8 MB - linear 0.001mm, any angle: 378,420 triangles, 0.0011mm, 18 MB What I learned: Neither setting is "the quality slider". Whichever is tighter is the one in control. At a loose linear setting, changing only the angle took the cylinder from 32 to 126 segments and cut the error 15x. At linear 0.01, angles 0.5 and 0.3 produced identical meshes, because the linear limit was already tighter. Once linear was very fine, the angle didn't matter at all. So if you crank one slider and nothing changes, the other one is the limit. That's why "I set it to high quality and it still looks faceted" happens. There's a point of diminishing returns. On the organic shape, going from 0.01 to 0.001mm linear made the file 10x bigger (1.8 MB → 18 MB) to remove about 0.009mm of error. That's well below what an FDM nozzle reproduces. All you get is a slower slicer. Where to find these settings: the names vary by CAD program (deviation, chord height, tolerance, refinement, angle). Look for one distance setting and one angle setting. Footnote: the raw mesher output for the filleted box has non-manifold edges where three fillets meet in a spherical corner. It's a raw tessellator artifact, unrelated to the settings, and a normal export pipeline cleans it up.   submitted by   /u/Tiny-Cap-3388   to   r/3Dprinting [link]   [comments]