The paper presents determination of dynamic cutting force coefficients by direct measurements of instantaneous cutting forces during vibratory cutting. The method exploits a special test rig consisting of a dynamometer supported by flat springs. The dynamometer with the cutting tool vibrates in the feed direction during orthogonal cutting. The measurements of the dynamometer acceleration allow elimination of the inertial forces influence on the feed force measurements. Thus, a direct measurement of instantaneous cutting force, uncut chip thickness and vibration speed allows determination of the dynamic cutting force coefficients dependence on cutting conditions and the tool wear.