Herringbone Gear (module 2, 24 teeth)

A herringbone gear — two opposed 20° helical halves meeting in a V at mid-height. Module 2, 24 teeth, 48mm pitch diameter, 52mm over the tips, 14mm face, 6mm bore, 20° helix. This is the part in the library that is genuinely awkward to buy: cutting a herringbone on a hob takes two passes and a run-out groove for the tool, which is why commercial ones are expensive and usually double-helical with a gap down the middle. Printed, the V costs nothing — it is just where the twist turns round — and there is no gap. Worth the trouble for two reasons: a helical tooth comes into mesh gradually along its length instead of slapping into contact all at once, which is quieter and smoother than a spur gear; and a single helix pushes a thrust load down the shaft that a bearing then has to carry, whereas mirroring it cancels that against itself and leaves the gear self-centring. It meshes with another of the same hand and module. Nothing on it leans more than the 20° helix angle, so it prints flat with no support. PETG or nylon for a driven gear.

from £6.84example, in PLA