Development of a laser-guiding-type deep small-sized hole-measurement system: Measurement accuracy

In this study, a system for measuring small-sized holes with a 17–21 mm diameter and 1000 mm length was constructed. The system comprises a laser interferometer to detect hole accuracy, a probe connected to a measurement bar, and an optical apparatus for detecting the probe attitude (position and inclination). The probe was supported by supporting pads. A steel workpiece with 18 -mm diameter and 800 mm length was used for the performance test. During the experiment, errors were found in terms of hole deviation and roundness profile. Further experiments, using new experimental apparatus and analysis, revealed the causes of errors: electrical noise that increased with time, two periodic stylus swings in the longitudinal direction of the hole per rotation of the measurement unit, and the excessive spring force pushing the tip of the stylus, causing a large frictional force with the hole wall, etc. If these errors are corrected, high accuracy in the measurement of hole deviation and roundness can be achieved.