Answer
Dishing is a deformation mode where the retaining ring is forced into a conical shape by the axial load. This happens when the moment created by the thrust load (acting on the middle of the ring) and the reaction force (acting at the groove edge) exceeds the ring's torsional stiffness. The 'Dishing Angle' $\theta$ can be approximated by $\theta \approx \frac{P r_{mean}}{E I}$. As the ring dishes, its effective OD (for external) or ID (for internal) changes, eventually allowing it to 'walk' out of the groove. Failure analysis often shows the ring has become permanently warped into a 'saucer' shape. To prevent this, engineers can increase the thickness $T$ of the ring, select a higher-modulus material, or use a 'heavy-duty' series ring with a larger radial wall to increase the moment of inertia.
