The article provides a deep analysis concerning the formation of surface roughness on details, processed with an edge tool, the existing customaries about determined and probabilistic component in the calculations of its height. While final polishing with supply not more than 0,05 mm of the roughness value does not coincide with the calculation by more than 30...50 % upwards. Analyzing the reason for such an unconformity, the attention was drawn to the operative parts nonuniformity motion, especially finishing processing regimens. The «stick-slip» phenomenon, known as the slip-stick phenomenon or simply stick-slip, is the spontaneous jerking motion that can occur while two objects are sliding over each other. Assessment methods for motion smoothness in operative machine parts were considered. The results of preliminary studies related to the influence of saddle (toolhead) feed nonuniformity to the surface roughness. It was found that jerking motion with light (fine) feed of the operative parts in cutting machines provides a significant influence on the formation of roughness on the processed surface, increasing it by more than 50 percent.