This thesis validates a numerical model for the modal analysis of high precision spindle assemblies, focusing on the challenges that arise when several mechanical components interact within an integrated system. While numerical modal analysis is reliable for isolated parts, significant discrepancies appear when analysing full spindle assemblies, especially in axial modes or in configurations with preload and floating bearings. These differences stem from an incomplete representation of bearing–housing boundary conditions in SKF SimPro Spindle. Since bearing stiffness strongly affects the eigenstructure and the Campbell diagrams, inaccurate constraint modelling reduces the reliability of numerical predictions. This issue is relevant for industry, where numerical tools are increasingly expected to reduce or replace time consuming experimental modal tests.