A backlash error is a motion error that occurs when changing the direction of gears.
Backlash error occurs when, after reversing the direction of rotation of the thimble, the tip of the screw does not immediately begin moving in the opposite direction but remains stationary for a portion of the rotation.
Cause of backlash error:
It occurs as a result of screw thread wear and tear.
When there is a gap between the driving tooth's trailing face and the driving tooth's leading face behind the driven gear.