Advanced manufacturing technologies have enabled the production of computer-optimized components with complex internal geometries, efficient fluid transport and cooling, and weight reduction. Polishing these channels is an essential post-processing step to attain precise geometric tolerance and reduce surface roughness, improving fatigue life and corrosion resistance. Conventional polishing methods for complex geometries struggle to maintain uniform performance in long, and tortuous channels and often use harsh acids which negatively impact the environment. HydroFlex has been shown as an effective internal polishing methods with increased adaptability and performance in highly complex geometries. Key to HydroFlex operation is the generation and maintenance of orbital motion, describing the orbit of the grinding wheel around the internal contour of the channel due to grinding, fluid, and spindle forces acting in the grinding zone. In this study, the spindle force was modeled using minimum potential energy method to determine the spindle position and contact point(s) throughout a complex workpiece. Experimental validation utilized a highspeed camera for shaft position and orbital motion capture, and a force sensing to determine the spindle force during orbit and no-orbit conditions. Results indicated that the model was able to predict the shaft position with visual contact point accuracy. A spindle force threshold of 0.19 N was found to overcome the orbital motion. These results suggest that MPE can be used to predict the spindle position and grinding condition based on threshold force for given spindle and workpiece properties.