A bevel gear whose teeth curve across the face at a spiral angle, so more than one tooth carries load at a time and engagement is gradual. Spiral bevels run quieter and carry more load than straight bevels at the same size, and they are used in helicopter transmissions, machine tool heads and industrial right-angle reducers. They are cut on dedicated generating machines and finished by lapping the pair together or by grinding, then kept as a matched set.
Spiral bevel gear set on the tail rotor box is a matched pair, so if one's pitted, both go in the scrap.
Also heard as
- spiral bevel
Related terms
Bevel gear
A cone-shaped gear that transmits motion between intersecting shafts, usually at right angles.
Hypoid gear
A spiral-bevel-like gear pair with the pinion axis offset from the gear axis, standard in vehicle drive axles.
Lapping
Running a matched bevel or hypoid pair together with abrasive compound after heat treat to refine contact.
Contact pattern
The imprint left on gear teeth by marking compound after running, showing where and how the teeth touch.