Describe the effect of housing bore tolerance on the performance of a wave spring with a high 'expansion factor'.

A wave spring's performance is highly sensitive to the housing bore diameter $D_h$. If the bore is at the minimum tolerance limit and the spring's radial expansion $\Delta D$ is high, the spring's outer edge will exert significant radial force against the bore. This introduces a friction force $F_f = μ \cdot N$, where $μ$ is the coefficient of friction and $N$ is the normal force against the bore. This friction adds to the axial load required to compress the spring, leading to inconsistent assembly preloads. Engineers must specify $D_h$ such that $D_h > D_o + \Delta D$ at the maximum material condition (MMC).