Will my gear teeth print?

The Tooth tip figure, what it measures, and which control to reach for when it turns orange.

Whether a printed gear works comes down to one number, and it is not the tooth count. It is how wide the tooth is at its narrowest point, measured against the thinnest wall your printer can lay down.

An involute tooth widens from its tip to its root, so the tip is the narrowest part: if the tip clears your minimum wall, the whole tooth does. That is what the Tooth tip row reports, and it measures the tooth the generator actually drew rather than a rule of thumb — so the figure and the shape cannot drift apart. On a multi-part assembly it reports the worst tooth in the set, because a gearbox is only as printable as its thinnest tooth.

Which control to reach for, in the order that measurably works:

- Module up is the strongest lever, and the only one with no effect on meshing beyond size. Module 1 to module 2 roughly doubles the tip. - Backlash down gives width back directly — at module 1 with 12 teeth a tooth measures 0.53 mm at 0.15 mm of backlash and 0.62 mm at zero. Zero backlash binds when printed, so lower it rather than removing it. - Pressure angle down, which is the opposite of the classic advice. At 12 teeth a tooth measures 1.15 mm at 20°, 0.79 mm at 25° and 0.37 mm at 30° — thinner than a 0.4 mm nozzle can lay down. - More teeth helps least. At module 2 a 4-tooth gear measures 0.57 mm and a 30-tooth gear 1.39 mm — barely twofold across the whole range, which is why a tooth-count rule was never the right check.

What about undercut? The warning this replaced said that gears under 17 teeth undercut at 20°, and told you to raise the pressure angle. Every part of that was wrong for these gears: they are drawn so that undercut cannot occur, tooth count was the wrong axis, and raising the pressure angle made the printed tooth *worse*. It fired on four of the six shipped defaults, which is the sign of a rule measuring something other than what it claims.

Pulleys are measured differently, because their teeth are not involute at all — they are what is left between belt grooves or chain-roller seats, so the row reports the narrowest material between two pockets. On a fine pitch that can be genuinely small: a GT2-2M pulley at 20 teeth leaves about 0.18 mm at the bottom of the groove, so a coarser profile (GT2-5M, HTD-5M) or more teeth is the fix if the teeth need to survive handling.

1. Insert any toothed part — a gear train, planetary, rack and pinion, herringbone, worm drive or pulley.
2. Look at the Tooth tip row in the Properties panel: it reports the width of one tooth at its narrowest, in millimetres.
3. Compare it against your printer’s minimum wall, which the row does for you — it turns orange under one wall and red under half of one.
4. If it is too thin, raise the Module first. Lowering Backlash and lowering the Pressure angle both help too, in that order.