The study objective. The increase in the construction of buildings, structures, and the development of natural resources requires the involvement of machinery used for drilling boreholes and wells. For these purposes, boring machines of various action types, including rotary and impact, are used. Many of boring machines are already obsolete, have bulky working equipment with a large number of connected parts. The task to which the paper is devoted. The authors propose a mechanism of rotation-but-impact action of a fundamentally new design, confirmed by a positive decision for getting a patent. In the proposed design of the rotary-impact mechanism, the rotation of the drilling rod is carried out by moving the rotary coupling along it. Research methods. The theoretical studies of the proposed mechanism of rotary-impact action are based on modeling the excavation works by the working bodies of boring machines. The novelty of the work. The theoretical studies carried out by the authors of the design of the rotary-impact mechanism made it possible to simulate not only its operation, but also to evaluate and calculate the kinematic and dynamic features of its individual elements. The study results. Based on the conducted studies, the correlations of various parameters of the rotary-impact mechanism are established, depending on the value of friction factor between the contacting surfaces and the mass of the impactor. The assessment of the motion path of the rotary-impact mechanism lug made it possible to identify the features of the constructive execution of the guide rod with the guidance of the eccentricity, which excludes the blocking of the lug at the moment of tranferring from the vertical to the inclined direction. Conclusions. The conducted studies allowed qualitatively and quantitatively assessment of the change in the geometric parameters of the rotary-impact mechanism during excavation works by the rotational impact method and evaluate its parameters depending on the change, for example, friction factor, the diameter of the rod, etc.