Abstract: A thread chain guiding device provides a needle-thread-guide plate which extends underneath a throat plate by energizing a solenoid as needed. Thus, the needle-thread-guide plate pushes the needle threads twined around a lower looper outwardly away such that the thread chain is prevented from hanging on an inner chain-off finger when it is rotated counter clockwise. The needle-thread-guide plate is retracted during a normal stitching process by de-energizing the solenoid.

Abstract: A thread chain is prevented from hanging at an inner chain-off finger when it is turned back or rotated to the operator's side for holding and cutting. A needle thread, positioned at the front side of a lower looper, is guided by a needle thread restricting device, and a needle thread positioned on the back side of a lower looper is prevented from being hung on an inner chain-off finger by a thread chain guiding device provided at a throat plate so that enfolding back and tacking of the thread chain into the fabric material is performed well.

Abstract: In a two-needle overedge sewing machine, a thread chain guide recess is formed for positioning the thread chain at a given position on the throat plate so that the thread chain is spaced apart from the outer needle descending point. The thread chain guide recess may be made at a tip portion of an outer finger of the throat plate or at a tip portion of an outer finger of a presser foot. Furthermore, the thread chain guide recess may be formed by the combination of the outer finger of the throat plate and the outer finger of the presser foot. In an improved embodiment, a thread chain guide groove is formed in an upper surface of the outer finger of the throat plate so that the thread chain is substantially fully received therein.

Abstract: A thread tension control device for overedging sewing machines wherein each needle thread tension controller and each looper thread tension controller provide two springs designed to clamp two tension discs wherethrough a thread is passed. A slide plate, by its horizontal sliding motion, either causes the two springs to be active or causes one of the two springs to be released thereby obtaining either strong or weak thread tension. A workpiece end detector defines either an overedging process or thread chain forming process and sends a signal to actuate the horizontal sliding motion of the slide plate. Thus, the proper thread tensioning for each needle thread and each looper thread for either an overedging process or a thread chain forming process may be automatically adjusted.