Errors of modified spur gears results in meshing interference or meshing clearance at the position of mating teeth coming into or out of contact. Based on the analysis of the relation among tooth deformation

normal profile modification and manufacturing error of tooth profiles

investigation is made on geometric interference or meshing clearance

which occurs when the mating teeth commence to approach or recess contact along the path of contact. Formulae are deduced to calculate the maximum meshing interference or meshing clearance for the mating teeth with gear contact ratio less than 2 or 3. It will be useful for studying the meshing state of modified spur gears and correcting the modification parameters for modified spur gears.