Gear train

A line of involute gears that actually mesh, at the right spacing.

The gear train lays out a line of involute gears, each spaced from its neighbour at the correct centre distance so they truly mesh instead of just sitting near each other. Every gear shares the module and pressure angle (required to mesh), and the Properties panel shows the resulting ratio live. Helical gears alternate helix hand down the train so they mesh. The gears are separate printable bodies — print them and mount them on your own shafts.

Backlash is the small deliberate play between meshing teeth, and it is why the train turns after printing. Gears at the exact centre distance with full-depth teeth mesh with *zero* clearance — correct in theory, but a printer lays material slightly oversize, so teeth that only just touch will jam. With Keep teeth apart for printing on (the default), the backlash is raised to the smallest that leaves 0.15 mm between the printed teeth — a low pressure angle or a steep helix needs more than the 0.35 mm default — and the Print gap read-out shows what the plate will do. Where no printable backlash opens a pair — a small helical pinion, a very fine module — the toggle also sets that pair slightly further apart, never so far that its teeth stop handing on, and the Centres read-out shows the distance it builds. Raise it further for a coarse nozzle or a looser fit; switch the toggle off only for a tighter mesh than will print apart, such as a display model that never has to turn.

Find teeth for a ratio works the tooth counts out for you. Type the ratio as input turns per output turn (3 slows the output to a third), or give two speeds, and optionally which way the output turns, a tooth range, the distance between the input and output shafts, and the largest gear that fits. It proposes tooth lists, closest first, each checked for printing with the same Tooth tip and Mesh fit measures as the read-outs, and Apply writes one into the teeth as a single step. Middle gears are idlers: they change the direction and the distance, never the ratio, so a large ratio in a small space needs gears that share a shaft. When that is the only way, it shows such a compound train for information; the gear train can’t build one yet.

1. Open the Generate panel from the left sidebar and choose Gear train (under Gears & drives).
2. The gears drop in already spaced to mesh, with the ratio shown. The parameters open in the Properties panel, where you set them.
3. Enter the tooth count of each gear, in mesh order (two or more).
4. Set the shared module, pressure angle, thickness, and optional helix angle and bore.
5. Leave Keep teeth apart for printing on: it raises the backlash where your settings need it, so the gears come off the plate as separate parts. Turn it off only for a tighter mesh on purpose.
6. To get a particular ratio, open Find teeth for a ratio under the parameters, type the ratio (or an input and output speed), and Apply one of the tooth lists it proposes. Undo puts the old teeth back.