In Situ Evaluation of Drill Wear and Hole-Wall Surface Integrity Using a Wireless BT40 Instrumented Toolholder

Drill wear monitoring is essential for maintaining hole quality and avoiding unexpected tool failure, yet it remains challenging because of the enclosed cutting zone in drilling. This study presents an in situ monitoring method based on a wireless BT40 instrumented toolholder that synchronously measures axial force, torque, and two orthogonal bending moments during continuous drilling of 304 stainless steel with an 8.5 mm cemented-carbide drill. Tool wear progression, represented by the number of drilled holes, was correlated with drill morphology, SEM observations of the hole wall, and surface topography measurements. The results show that axial force reflects the increase in overall cutting resistance, torque provides information on torsional fluctuation, and the two bending moments are the most wear-sensitive signals because they capture radial load imbalance and asymmetric tool–workpiece interaction. As drilling progressed from the 10th to the 60th hole, bending-moment features increased markedly, while hole-wall roughness deteriorated from Ra = 0.589 μm to 2.528 μm and Rq from 0.760 μm to 2.916 μm. These findings indicate that the proposed toolholder provides physically interpretable features for drill-wear identification and tool-change warning.