1. Field of the Invention
This invention relates to a needle plate for a sewing machine which forms double chain stitches, and more particularly to a needle plate for guiding a thread loop making the stitches on the underside of fabric round and soft.
2. Description of the Prior Art
Double chain stitches appear on the underside of fabric as a looper thread is laid in triple and tacked by the needle thread at every stitch, and each stitch can be varied according to sewing conditions, especially by the balance of the thread tension between the needle thread and the looper thread. That is, when the tension of the needle thread is high, the looper thread is divided into three parts and the stitches look round and soft as shown in FIG. 5, and when the tension of the looper thread is high, as shown in FIG. 6, the looper thread becomes like a rope, as if made of two threads. The former stitches are called balloon stitches, which are used in stretchable knit fabrics or other soft-hand materials, while the latter stitches are used in stiff and less stretchable woven fabrics. However, when the tension of the needle thread is increased in order to obtain balloon stitches, the supply of needle thread for making the stitches decreases, and puckering may occur in the sewn product. On the other hand, if the tension of the looper thread is reduced to be less than that normally used with the needle thread, since the tension of the looper thread is initially set at more than several times lower than that of the needle thread, there is a lower limit for loosening the looper thread, and, if set too low, may give rise to skipped stitches or other sewing defects.