Teeth that mesh, off the printer and turning.
Pick the tooth counts and the tooth size (module) and the tool builds a gear pair, a rack or a whole planetary set, laid where they mesh — with the ratio and centre distance you need to design the rest.
Building the model…
Drag to orbit, scroll to zoom
Pitch diameter = module × teeth. Two gears only mesh with the same module and pressure angle. With a 0.4 mm nozzle keep the module at 1 or above.
Round holes through the web between the bore and the tooth roots, with at least 1.2 mm of material either side. A small gear without the room gets fewer or none.
Each tooth is thinned by this much on each side so printed gears turn freely. 0.1 mm suits most printers; a planetary set printed assembled wants 0.15–0.2 mm.
How it works
Involute teeth, checked by turning them.
Every flank is the involute of the base circle (pitch radius × cos of the pressure angle), in standard proportions: addendum 1 module, dedendum 1.25 module. Two gears sit at exactly module × (z₁ + z₂) / 2 apart. A planetary set's ring has as many teeth as the sun plus two planets, and is cut by the same involute turned inside out.
Helical and herringbone gears use the same section, twisted steadily up the face: meshing gears twist opposite ways, and a ring twists the same way as its planets. Each gear's phase is set so its teeth sit in the middle of the other gear's gaps right where they are exported.
Checked across 240 random sets — pairs, racks, planetaries; spur, helical, herringbone; three pressure angles; tooth counts at or above the undercut limit — with the mesh checker /tools/model-check uses. Every part had to be closed, meshing parts had to clear each other at rest, and had to collide when one was turned past the backlash — proof they really mesh rather than just sitting apart. Below that limit the tool shows a warning: in a run down to 6 teeth, a few planetary sets with tiny planets bound against the ring. Another 150 sets with random hubs, D or hex bores and lightening holes passed the same tests.
Which module should I use for printed gears?
With a 0.4 mm nozzle, module 1–1.5 for small gears and toy mechanisms, 2–3 for gears that carry load. Below module 1 the teeth are thinner than two extrusion lines and tend to break or fuse.
How much backlash do printed gears need?
Start with 0.1 mm per flank for gears printed separately and assembled, 0.15–0.2 mm for a print-in-place set. If the teeth bind, add backlash; if there is too much slop, take some away. Printers with a squashed first layer usually need a little more.
Why helical or herringbone teeth?
Helical teeth engage gradually, so they run quieter and carry more load, but they push sideways along the axle. Herringbone teeth cancel that push and keep the gears from sliding apart. Both print well on FDM, with no overhangs that need supports.