A precise mathematical representation of long overhang boring bars is essential for predicting chatter and increasing productivity in internal turning. Most studies simplify the bar as a classical clamped cantilever, an assumption that often leads to significant discrepancies when compared to experimental modal measurements. In this work, we propose an improved modeling approach that incorporates the effect of tool clamping by representing the support region as a Winkler foundation with constant stiffness [1, 2]. The bar is modeled as a multi-span Euler–Bernoulli beam partially supported by this elastic foundation, providing a more realistic description of the boundary conditions observed in industrial toolholders. The proposed model is evaluated through numerical simulations and validated experimentally using modal analysis for several industrially relevant overhang ratios (L/D = 3…9). Natural frequencies, mode shapes, static and dynamic stiffness, and Lehr damping are analyzed and compared with results from both the traditional clamped-cantilever model and the experimental data. The findings demonstrate that the Winkler-based model yields substantially improved agreement with measurements, particularly for higher modes and long overhangs, where the influence of clamping flexibility becomes dominant. The study shows that neglecting the elastic support leads to overestimated stiffness and inaccurate prediction of the dynamic response of the boring bar. Incorporating the Winkler foundation significantly enhances the fidelity of the model and directly improves the accuracy of the resulting stability lobe diagrams (SLDs). The approach provides a more reliable framework for understanding vibration behavior in deep internal turning and offers valuable insights for the design of optimized anti-vibration tools and toolholders. REFERENCES [1] Cazzani, A. On the dynamics of a beam partially supported by an elastic foundation: an exact solution-set. International Journal of structural stability and dynamics 13, no. 08 2013. DOI: 10.1142/S0219455413500454. [2] Winkler. Die Lehre von Elasticitaet und Festigkeit (in German). Prag 1867 (H. Dominicus), pp. 182-184.