A cylindrical gear carrying a right-hand and a left-hand helix on the same blank, forming a V pattern. The opposite thrusts cancel inside the gear, so high helix angles and heavy loads are possible without big thrust bearings. A true herringbone has the two halves meeting at the apex, while a double helical gear has a groove between them for tool runout; both are common in turbine drives, rolling mills and marine gearing.
Mill drive is a herringbone gear set, so one shaft has to float axially, lock both and you'll load up the bearings.
Only one shaft in a herringbone train is located axially; the others float so the two helices can center themselves.
Also heard as
- double helical gear
- double helical
Related terms
Helical gear
A cylindrical gear whose teeth wrap at an angle around the blank, engaging gradually for quiet, strong running.
Helix angle
The angle between a helical gear's teeth and its axis, along with the hand, right or left.
Bull gear
Shop name for the biggest gear in a drive train, usually the slow, heavy output gear.