Abstract: The results of experimental studies to determine the influence of the parameters of reverse surface plastic deformation (SPD) on the deviation from roundness (Δround) of cylindrical parts made of steel 45 are presented. To implement the proposed method of finishing and hardening processing, a device for reverse circular motion of the working tool was developed. Based on the results of experimental studies and using the PyCharm computer program in Python, the optimal hardening modes were determined, which provide the smallest deviation from the roundness of cylindrical parts. © 2023, Allerton Press, Inc.