What is the effect of 'Groove Chamfer' on the thrust load capacity of a spiral retaining ring?

A chamfer or radius on the groove edge significantly reduces the thrust load capacity of a spiral retaining ring. The chamfer acts as a ramp, facilitating the 'rolling' or 'dishing' of the ring out of the groove. If a chamfer of width $c$ is present, the effective thrust capacity $P'$ is reduced by a factor: $P' = P \cdot (1 - c/t)$, where $t$ is the ring thickness. Engineering drawings must specify 'square corners' for the groove, or if a chamfer is necessary for manufacturing, its size must be strictly limited (typically $< 0.1$ mm). If a large chamfer is unavoidable, the designer must specify a 'Heavy Duty' ring with a larger radial wall to provide more contact area and counteract the rolling moment.