What is the impact of a chamfer or radius on the mating part on the thrust capacity of a spiral retaining ring?

A radius or chamfer on the retained part creates a moment arm that induces a 'dishing' effect on the ring. The reduced thrust capacity $P_r$ is calculated by $P_r = P \times (1 - \frac{z}{t})$, where $z$ is the chamfer size and $t$ is the ring thickness. When the chamfer exceeds 50 percent of the ring thickness, the risk of the ring being 'cammed out' of the groove increases exponentially. For heavy-duty machinery, engineers should utilize a backup washer or specify a square-edged mating surface to ensure the load is applied perpendicular to the ring face.