Answer
Multi-turn wave springs, particularly those used in bearing preloads, require precise diametrical clearances to prevent binding. During compression, the mean diameter $D_m$ of a wave spring increases slightly due to the flattening of the waves. The expansion is governed by the relationship $\Delta D \approx \frac{0.051 \cdot (f^2 \cdot n^2)}{D_m}$. Consequently, if the spring is constrained by a housing (bore), the outer diameter $O_D$ must be sized such that $O_D + \Delta D < Bore_{min}$. Conversely, if the spring is located on a shaft, the inner diameter $I_D$ must remain larger than the shaft diameter throughout the full stroke. Failure to provide this 'expansion room' results in friction against the walls, leading to hysteresis in the load-deflection curve and potential galling of the mating surfaces.
