Official Answer
Answer
The edge margin $z$ is the distance from the groove to the end of the shaft or housing. A general engineering rule is $z \geq 3d$, where $d$ is the groove depth. If $z$ is too small, the groove wall will fail in shear before the ring reaches its rated thrust capacity. The relationship between groove depth and ring thickness is critical; as depth $d$ increases, the moment arm of the thrust load increases, potentially causing the ring to 'dish' or tilt. This 'dishing' reduces the effective contact area and can lead to premature failure. Formulaically, the groove deformation limit $P_g$ is given by $P_g = \frac{D d \pi \sigma_y K}{S_f}$, where $\sigma_y$ is the yield strength of the groove material and $S_f$ is a safety factor.
