The difference between the measured and design tooth trace along the face width, called lead in US shop practice. It is divided into total, slope and form components. A helix slope error loads one end of the tooth and causes edge loading, while form errors show up as waviness. On spur gears the design helix is straight along the axis, apart from any crowning or end relief.
Helix deviation is the same slope on every tooth, so it's the lead setting on the machine, a wobbling blank would swing it around the gear.
Also heard as
- lead error
- lead deviation
Related terms
Helix angle
The angle between a helical gear's teeth and its axis, along with the hand, right or left.
Crowning
A slight barrel shape along the tooth face so contact stays centered despite misalignment and shaft deflection.
Edge loading
Tooth load piling up at one end of the face width because of misalignment or deflection.
Trace
The printed plot of a tooth's measured profile or helix from a gear checker, read against tolerance bands.