Official Answer
Answer
The groove radius is the small fillet at the bottom corner of the groove. While a radius is necessary to reduce stress concentrations in the shaft or housing, an excessive radius significantly reduces the ring's thrust capacity. A large radius allows the ring to 'climb' the wall of the groove under axial load, inducing a dishing moment. The standard design rule is that the maximum groove radius $R_{max}$ should be no larger than $0.1 \cdot d$, where $d$ is the groove depth. If a larger radius is required for fatigue life of the shaft, a custom ring with a chamfer on its inner edge may be necessary to ensure the ring sits flat against the groove wall, maintaining the intended shear plane.
