Double helical Gear

herringbone gears

double helical gears , herringbone gears similar, difference herringbone gears not have groove in middle double helical gears do. double helical gears overcome problem of axial thrust presented single helical gears using 2 sets of teeth set in v shape. double helical gear can thought of 2 mirrored helical gears joined together. arrangement cancels out net axial thrust, since each half of gear thrusts in opposite direction, resulting in net axial force of zero. arrangement can remove need thrust bearings. however, double helical gears more difficult manufacture due more complicated shape.

for both possible rotational directions, there exist 2 possible arrangements oppositely-oriented helical gears or gear faces. 1 arrangement stable, , other unstable. in stable orientation, helical gear faces oriented each axial force directed toward center of gear. in unstable orientation, both axial forces directed away center of gear. in both arrangements, total (or net) axial force on each gear 0 when gears aligned correctly. if gears become misaligned in axial direction, unstable arrangement generates net force may lead disassembly of gear train, while stable arrangement generates net corrective force. if direction of rotation reversed, direction of axial thrusts reversed, stable configuration becomes unstable, , conversely.

stable double helical gears can directly interchanged spur gears without need different bearings.