Abstract: A camless automated thread cutting system for an electronic lockstitch pattern tacking sewing machine having a sewing needle driven by a main shaft and having a knife mechanism in proximity with the needle for cutting thread at the end of a pattern sewing cycle. The cutting system comprises a pneumatic cylinder for mechanically engaging the knife mechanism through a mechanical linkage in the machine, a solenoid-actuated air valve in fluid communication with the pneumatic cylinder, a programmable logic controller (PLC), and a pair of independently adjustable discs mounted on the main shaft of the sewing machine and operatively coupled to a proximity sensor which supplies an electrical signal to the PLC. The PLC is responsive to a machine signal indicative of the end of a sewing cycle and to the proximity sensor signal for generating a control signal for actuation of the valve so as to initiate and subsequently terminate a knife movement sequence at the end of the sewing cycle.