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herringbone gear[′her·iŋ‚bōn ‚gir]
a spur gear with V-shaped helical teeth. The mutual inclination of the tooth segments on opposite sides compensates the axial thrust produced by single helical gears. Herringbone gears afford smooth operation and increased load-carrying capacity, which are characteristic of helical gear transmissions in general. They are used in medium-size and large transmissions, including special transmissions operating at pitch-circle velocities up to 200 m/sec (turbine reduction gears).
Continuous-tooth herringbone gears (Figure 1,a) require special equipment to machine the teeth. Double helical, or conventional herringbone, gears (Figure l,b) have a gap, or groove, where the two sets of teeth meet; they may be made on ordinary gear-hobbing machines, but the width of the gear wheel must be increased by the width of the groove g. Transmission through two pairs of helical gears with opposed teeth (Figure 1,c) enables the space between the gears to be used for another transmission.