Thread cutting via reciprocating arm with pockets and a trimming plate

Abstract

A thread cutting mechanism is added to a chainstitch sewing machine, including a trimming plate, fitted on the machine in alignment with the needle and looper and associated mechanism. A guideway in the bottom of the plate, extends along a path crossing the loops of the upper and lower threads. A slide moves in the guideway, and has an arm with a pointed free end extendable from the slide to move in and out of the guideway. Pockets formed along a side of the arm capture portions of the upper and lower threads in the sewing head, preparatory to forming a stitch. The slide is reciprocated when a stitching operation ends, extending the arm out of the guideway, pushing aside the upper thread and adjacent lower thread. The arm at its forward extension aligns the pockets with the upper and lower threads, so they engage within the pockets. When the slide retracts the arm draws the threads between the plate and arm. Knife edges on the plate and on an edge of the outermost pocket sever the lower and upper threads simultaneously upon completion of reverse slide motion to free the previously formed stitches from the portions of the threads engaged by the needle upper and the loop forming means. The end of the lower thread leading to the looper is retained to prevent its withdrawal from the looper head during starting of the next sewing operation. A slack portion is formed into the lower thread, upstream of its entry into the looper head. Tension in the needle thread is released during the trimming process to avoid additional tension being created during trimming/cutoff.