When sewing having sewing machines with a thread cut-off device, wherein the needle thread or upper thread, respectively, and the hook thread or lower thread, respectively, are automatically cut off at the end of the sewing action, there is the basic problem that the thread ends hanging down from the workpiece must be severed, i.e. the workpiece must be trimmed. The same applies to the thread ends at the starting point of the seam.

The back spindle is positioned on the side facing the main spindle via the work and in parallel to the main spindle. On the work side of back spindle is integrally fixed a machining chuck as a back spindle tool. A back spindle is disposable on a side of the work opposite the main spindle for holding a selected secondary machining tool selected from the plurality of secondary tools. The back spindle is selectively movable to enable the selected secondary machining tool to perform the secondary machining of the work.

In order to solve this problem it is known for household sewing machines to secure clamping and cutting plates pivotably to the fabric presser foot and to provide a pivotably supported knife below the stitch plate, i.e. directly below the stitch hole. These two knifes are actuated by means of two electro-magnets to be actuated simultaneously. In the numerical control automatic complex lathe of the present invention, the number of machining process which can be performed on the back spindle is increased by constructing the machine in such a manner that the back spindle tool can be changed. Thus the needle thread is cut off on the upper side of the workpiece and the lower thread is cut off directly below the stitch hole. With this thread cut-off device the cutting off of threads takes place in such a way that only infinitely short thread ends remain which need no more trimming.

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