<p>Large-scale machining centres play a critical role in aerospace manufacturing, where tight tolerances are required for components made from materials with limited machinability. During operation, ambient temperature fluctuations—combined with heat generated by motors, guides, and moving axes—induce thermal expansion or contraction of structural elements. These deformations lead to deviations of the cutting tool from its nominal position, resulting in volumetric inaccuracies. While thermal effects are present in all machine tools, large machines are especially prone to asymmetric, spatially localised deformations, which complicate compensation strategies. This study proposes an experimentally validated methodology to isolate and quantify the thermal influence of individual heat sources on volumetric errors in a large five-axis machining centre. The method integrates a dense in-situ sensor network (comprising IDS and thermocouples) with targeted heating sequences and rapid artefact-based validation. The results identify critical sensors and optimal placement for error estimation, validate the feasibility of linear superposition under multi-axis heating, and highlight asymmetric deformation effects. The approach enables efficient model simplification and offers practical guidance for thermal compensation in large-scale industrial machining environments.</p>