Herringbone gear

A herringbone gear, also known as a double helical gear, is a special type of gear which is a side to side (not face to face) combination of two helical gears of opposite hands.


Precision herringbone gears are more difficult to manufacture than equivalent spur or helical gears and consequently are more expensive.


Where the oppositely angled teeth meet in the middle of a herringbone gear, the alignment may be such that tooth tip meets tooth tip, or the alignment may be staggered, so that tooth tip meets tooth trough.


Solutions to this have included assembling small gears by stacking two helical gears together, cutting the gears with a central groove to provide clearance, and (particularly in the early days) by casting the gears to an accurate pattern and without further machining.
With the older method of fabrication, herringbone gears had a central channel separating the two oppositely-angled courses of teeth.


The logo of the car maker Citroën is a graphic representation of a herringbone gear, it comes from André Citroën's earlier involvement in the manufacture of these gears.