<p>This paper presents an end-effector and optimal force-tracking controls specifically designed for precision polishing of curved surfaces and narrow interspaces. A structure of the flexible elastic actuator (FEA), which combines a variable stiffness actuator (VSA) and a series elastic actuator (SEA) in series, is proposed. The FEA, along with optimal force-tracking control, enables the proposed compliant polishing end-effector to maintain a constant contact force with an object, even under disturbances and vibrations during polishing operations. The system exhibits rapid control response and high efficiency. Additionally, the SEA structure and the disturbance observer (DOB) can estimate the force acting on the polished surface without a force sensor, allowing for force control accordingly. Experimentally, the force estimation performance of the DOB and the force control performance under disturbance conditions were confirmed. The input torque was reduced by 46.5%, and the force control range was improved by 62.2% compared to the use of the SEA alone. It is expected that the proposed FEA and optimal force-tracking control will enable efficient and fast force control for precise polishing operations.</p>