Tooth thinning, addendum and dedendum geometry changes to avoid under cut or interference. If the pinion or gear is modified, the mating gear will also require modification or change in the center distance.
The following tooth forms may require modification to avoid under cut or interference.
· 11 teeth or less with 25 degree pressure angle.
· 17 teeth or less with 20 degree pressure angle.
· 31 teeth or less with 14.5 degree pressure angle.
Machinery’s Handbook has a section on this subject titled “Increasing Pinion Diameter to Avoid Undercut or Interference”.
Tooth thinning may be accomplished by selecting the supported ANSI/AGMA standard. Along with tooth thinning/thickening the addendum and dedendum changes accordingly. As the tooth thickens on the pinion, the addendum increases and the dedendum decreases in size. Conversely, the gear tooth thins and the addendum decreases while the dedendum increases in size. The whole depth remains constant.