Background <p>Many manufacturing processes introduce non-homogeneous distributions of residual stress (RS) in components. Accurate measurement of such stresses requires localized techniques with high spatial resolution, which presents a considerable challenge.</p> Objectives <p>This study presents an experimental procedure for mapping non-homogeneous RS using incremental hole drilling (IHD) with small-diameter end mills.</p> Methods <p>A multi-magnification stereo digital image correlation (stereo-DIC) system, equipped with parfocal zoom lens optics, is used to capture full-field displacements around drilled holes ranging from 3 mm down to 0.5 mm in diameter. Schajer’s optical formulation—based on displacement fields rather than local strain readings—is applied to quantify RS. The dependence of RS values on end mill diameter is analyzed as a benchmark to assess the reliability of the measurements.</p> Results <p>For IHD with small-diameter end mills, fluorescent speckling offers several advantages over conventional black-and-white speckling, including reduced noise, improved stability, and facile detection of the datum plane. Optimal drilling parameters for minimizing deformation are strongly influenced by end mill diameter. The Schajer’s optical formulation leads to high consistency due to its insensitivity to filter size, a common source of uncertainty in DIC-based measurements. Consequently, RS values show weak and unsystematic dependence on end mill diameter, reinforcing the robustness of the approach. Finally, non-homogeneous RS distributions of a dissimilarly welded 304 stainless steel block is mapped.</p> Conclusion <p>The proposed experimental method enables a reliable and high-resolution assessment of non-homogeneous RS distributions.</p>