Official Answer
Answer
As a wave spring is compressed toward its solid height, the sine-wave geometry flattens, causing a slight increase in the outer diameter ($D_{out}$). This radial expansion $\Delta D$ can be approximated by $\Delta D = \frac{0.02 f (D_{out} + D_{in})}{N_w^2}$, where $f$ is the deflection. In high-tolerance bores, failure to account for this expansion can lead to binding or interference with the housing wall, which introduces parasitic friction and alters the spring rate. Precision designs in medical devices using 316 Stainless Steel require the bore diameter to be at least $D_{out} + \Delta D + \text{clearance}$ to maintain a linear load-deflection curve and prevent wear on the housing.
