A cylindrical gear with teeth cut along a helix, typically at 15 to 30 degrees to the axis. Contact starts at one end of each tooth and sweeps across the face, so several teeth share load and engagement is smoother and quieter than on a spur gear. The price is an axial thrust force that the bearings must carry, and an external parallel-shaft helical pair needs opposite hands at the same helix angle.
Swap the spurs for a helical gear set and the whine will drop, but you'll need thrust bearings on the countershaft.
Reverse the drive direction or the hand of the helix and the thrust moves to the other bearing, so check which one is rated for it.
Also heard as
- helical
Do not mix it up with
- Spur gear: Spur teeth run straight along the axis and produce no thrust, but engage all at once and run noisier.
Related terms
Spur gear
A cylindrical gear with straight teeth parallel to its axis, the simplest gear for parallel shafts.
Helix angle
The angle between a helical gear's teeth and its axis, along with the hand, right or left.
Herringbone gear
A gear with two opposite-hand helical tooth sets side by side, so their axial thrusts cancel.
Contact ratio
The average number of tooth pairs in contact at once, which largely sets how smoothly and quietly a pair runs.