<p>Variable-helix cutters exhibit excellent dynamic cutting performance due to the geometrically non-uniform cutting edges with different helix angles. Consequently, they are increasingly used in the machining of complex and weakly rigid structures, which are often made of difficult-to-cut materials. Accurate mechanical modeling of the machining process is the foundation for chatter suppression. However, existing studies on variable-helix cutters generally do not consider the influence of the variations in helix angles, and the modeling process often neglects the cutter run-out effect, both of which lead to an accuracy loss. To address this issue, this paper first establishes a variable-helix milling force model with multi-group cutting force coefficients (CFCs). Building upon the derivation of the trochoidal motion equations for different helical edges, the run-out effects on the instantaneous uncut chip thickness (IUCT) and the entry/exit of the helical edge into/out of the workpiece boundary are considered. Subsequently, for the developed force model, a new method for calibrating the multi-group CFCs and run-out parameters based on a force data sliding matching strategy is proposed, which includes a direct full-parameters optimization strategy and an indirect few-parameters optimization strategy. The proposed calibration method has a high degree of automation and requires only one to approximately two groups of cutting experiments. Finally, a series of experiments are conducted to validate the force model and calibration method. The experimental results show that the theoretically predicted forces closely align with the experimentally measured forces.</p>