Thread trimming device for a lockstitch bar tacking sewing machine

摘要

A thread trimming device for a lockstitch bar tacking sewing machine is equipped with a thread trimming unit comprising a detecting member which is rotatably supported by a sewing machine body and has a detecting portion, a first position detecting means which is fixedly mounted on said sewing machine body in such a way as to be capable of facing the detecting portion of the detecting member and which produces a thread trimming signal for starting thread trimming when the detecting portion approaches thereto and a driving unit for driving a thread trimming cam link in such a way as to bring the contact portion of a thread cam link in contact with the cam surface of a thread trimming cam for trimming a needle and a bobbin threads based on the thread trimming signal. As a result, the mechanical components thereof becomes simple in structure and easy in adjustment, and those relating to the thread trimming operation are improved in durability. The torque of an arm shaft is reduced and equalized, so that it is possible to equalize a stitch pattern and finish a well-balanced sewn product.