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The article presents the results of monitoring the drilling process. Vibroacoustic sensors were used to observe spindle vibrations. These signals were subjected to a Huang decomposition and a Fourier transform. Results for various conditions were studied and classified with help of Fourier spectra and the envelope curves. Using the additional results of numerical simulations sources of vibration were identified. We considered four types of drills which were diversified in terms of geometrical parameters of blades. The study was conducted in cooperation with the manufacturer of tools.