This article presents a method for calculating the working body of a cultivator in the form of a rotary knife drum. Since the knives on the drum are arranged radially, the ends of the knives under the translational movement of the rotary drum describe the trajectory of successively located arcs. As a result of the theoretical calculations conducted, three types of trajectories were obtained, depending on the value of the kinematic parameter. It was established that with an increase in the depth of the cultivated soil, the kinematic parameter increases. This indicates that high-quality tillage is ensured when the rotary knife drum moves along an elongated trajectory.