Answer
Shimming is used to adjust the installed height $H_1$ of a wave spring to ensure the preload $P_1$ falls within a narrow tolerance. Because $P = k \cdot (H_0 - H_1)$, even small variations in the housing depth or bearing width can cause significant $P_1$ errors. When using shims, it is vital to ensure the shim is flat and covers the entire contact surface of the wave spring crests. If a shim is too small radially, the spring crests may overhang, causing local bending and non-uniform loading. In high-speed spindle bearings, engineers often use a series of 0.05 mm shims to fine-tune the preload, measuring the starting torque of the bearing as a proxy for axial force. The shim material should match the spring material to prevent galvanic corrosion.
