Abstract: Pin holes are common machining features in mechanical manufacturing, their perpendicularity, cylindricity, surface roughness, and diameter are critical to machining quality. Common methods for machining pin holes include machine-tool reaming, magnetic drilling and reaming, manual reaming. When machine tools or magnetic drills cannot meet the machining requirements due to process or site constraints, manual reaming is generally adopted. However, conventional manual reaming methods have difficulty ensuring the required accuracy of pin holes. To address this difficulty, this paper investigates a manual reaming method under the conditions that the centerline of the hand reamer remains coincident with that of the pin hole and that the reamer and grinding tools move axially at a uniform speed while maintaining stable radial motion. Based on this method, a machining process is proposed to ensure the perpendicularity and cylindricity of the pin hole while improving the surface roughness of the hole wall without adversely affecting these geometric accuracy parameters. The feasibility of the proposed method was verified through practical machining tests. Furthermore, probability analysis was employed to compare the influence of manual reaming and manual grinding on the pin-hole diameter. The results show that the combined machining method of manual reaming and manual grinding provides better performance than manual reaming alone. The findings provide a reference for manual pin-hole machining under constrained working conditions or limited equipment availability.