The angle at which helical teeth are inclined to the gear axis, measured at the pitch diameter. Typical values are 15 to 30 degrees for single helical gears and higher for double helical. Hand describes the direction of the twist: viewed with the axis vertical, right-hand teeth slope up to the right. Parallel-shaft external pairs need equal angles and opposite hands, and the helix also sets the lead, the axial length of one full turn of the tooth.
Helix angle matches at twenty degrees but they're both right hand, these two will never mesh on parallel shafts.
Also heard as
- beta
Related terms
Helical gear
A cylindrical gear whose teeth wrap at an angle around the blank, engaging gradually for quiet, strong running.
Herringbone gear
A gear with two opposite-hand helical tooth sets side by side, so their axial thrusts cancel.
Helix deviation
How far a tooth's actual path across the face width departs from the intended helix, including crowning.
Contact ratio
The average number of tooth pairs in contact at once, which largely sets how smoothly and quietly a pair runs.