How does the use of a shim or spacer affect the load-deflection characteristics of a multi-turn wave spring assembly?

Shims are used to calibrate the Work Height $H_w$ and compensate for tolerances in the housing and shaft. Since $P = K(L_{free} - H_w)$, a small error in $H_w$ leads to a significant error in $P$. By using a precision-ground shim, the assembly's stack height can be controlled to within $\pm 0.001$ inch. In multi-turn springs, the shim also provides a flat, parallel bearing surface. Without a flat surface, the 'wave' of the spring may not seat properly, leading to an 'off-center' load or 'tipping' moment, which induces non-uniform stresses and potentially causes the spring to 'snake' or buckle sideways within the bore.