<p>To meet the demand for high-efficiency, multifunctional processing equipment in modern manufacturing, this paper innovatively proposes a configuration synthesis method for a variable-mode parallel machining mechanism based on Finite Instantaneous Screw (FIS) theory. Focused on grinding and cutting tasks for large-scale components, a variable-mode parallel mechanism is developed to achieve multiple uses with a single machine. The expected motions of grinding and cutting are unified through finite screw modeling, and a synthetic framework for limb motions is constructed using the screw triangle product operation. A reconfigurable static platform with R joint combinations is designed to replace P joints, enabling dynamic adjustments without changing the number of limb joints. Fifty-four feasible derived limb structures are synthesized, and a single-drive planar four-bar linkage is integrated as the reconfigurable platform to reduce control complexity and enhance rigidity. Theoretical and configuration validations demonstrate that the proposed variable-mode parallel machining mechanism offers motion flexibility, structural stability, and engineering practicability, providing an innovative solution for developing multi-task machining equipment.</p>