Manufacturing data typically flows one way (CAD→CAPP→CAM→CNC), expanding as it approaches the shop floor through technologists’ know-how and parameter choices. Using the CAM-Connect module integrated with Mastercam, we automatically extract these CAM settings and export a structured process description (STEP/STEP-NC XML) for scalable analysis. This paper introduces a practical CAM-driven method to identify and quantify non-productive motions in 3-axis milling. We focus on vertical auxiliary motions: Z-axis approaches, withdrawals, retracts and safe-height traverses. Auxiliary distances and times are reconstructed by interpreting CAM option logic, including clearance modes and retract/feed-plane definitions. The method is applied to 242 industrial milling operations comprising 2912 toolpaths. After excluding special drilling cycles and extremely short operations, auxiliary motion averages 7.96% of total operation time. Moreover, 14.5% of operations exceed a 15% auxiliary-time share. While rapid and feed auxiliary distances are similar, feed-executed auxiliary segments generate about 96% of auxiliary-motion time. The findings provide actionable diagnostics tied to CAM decisions and support systematic auditing and improvement of machining processes.