FIELD: manufacture of machine tools, namely for cutting variable-pitch screw surfaces. SUBSTANCE: hydraulic step motors used in screw-cutting circuit and in pitch increase circuit are kinematically joined by means of lengthwise feed lead screw respectively with lengthwise motion rest and with summing mechanism in the form of differential with cone gear wheels. Each step hydraulic motor is controlled by means of separate hydraulic impulse generator. EFFECT: simplified design, enhanced accuracy due to reduced length of screw-cutting circuit in the result of extracting several mechanical links out of said circuit, lowered metal consumption. 1 dwg
