Point- Surface-Origin, PSO, macropitting occurs at sites of Geometric Stress Concentration, GSC, such as
discontinuities in the gear tooth profile caused by micropitting, cusps at the intersection of the involute profile
and the trochoidal root fllet, and at edges of prior tooth damage such as tip-to-root interference. When the
profile modifications in the form of tip relief, root relief, or both are inadequate to compensate for deflection of
the gear mesh, tip-to-root interference occurs. The interference can occur at either end of the path of contact,
but the damage is usually more severe near the start-of-active-profile, SAP, of the driving gear.
An FZG-C gearset (with no profile modifications) was tested at load stage 9 and three pinion teeth failed by
PSO macropitting. It is shown that the root cause of the PSO macropitting was GSC created by tip-to-root
interference.