Official Answer
Answer
If the surfaces between which a wave spring is compressed are not parallel, the load $P$ will not be distributed evenly across all wave peaks. This leads to 'point loading,' where one wave is compressed significantly more than the others. This imbalance causes a tilting moment on the assembly and can lead to localized stress exceeding the material's fatigue limit. Mathematically, the load variation $\Delta P$ is proportional to the parallelism error $\delta$ multiplied by the spring rate $k$. For precision optical assemblies, mating surfaces should be ground to a parallelism within $0.001$ inch to ensure uniform axial force and prevent optical axis deviation.
