In computer numerical control (CNC) production, product specifications are entered into machine software, and sensors automatically distinguish between conforming and nonconforming products, preventing mixing and shipment issues. Modern factories often use sensor-based automated measurement instruments to improve efficiency and reduce costs. Process capability indices (e.g., Cp, Cpk, and Cpm) quantify process variability relative to specifications, with Cpk widely used owing to its focus on aligning the process mean with the specification center. In this study, we explored product quality stabilization by using Cpk to analyze sensor data in lock manufacturing, stabilizing product quality, and verifying process stability after equipment maintenance to make the material inspections more accurate. We selected key dimensions of lock products for measurement, employing an image-measuring instrument for bi-daily sampling. Analysis results indicate that Cpk effectively reflects process stability. If the Cpk value does not reach ≥1.33, CNC lathe parameters are adjusted to enhance the Cpk value, demonstrating significant process capability improvement. Additionally, we innovatively applied Cpk to evaluate process capability post-equipment maintenance, ensuring that product quality meets the required standards. In summary, we demonstrated the practicality and effectiveness of Cpk in process capability assessment and improvement.