Stitch type 607 while suitable for seam elongation, may not always offer the softest seams.
This stitch type uses over 30cm of thread for every 1cm of seam, almost half of this total amount going into the lower looper thread. With this amount of yarn placed in the looper expectations are that these seams are soft but even when the softest sewing yarns are used in the looper the sewn seam itself may remain rough to the touch.
This roughness is due in the main to the loops of needle thread that show on the underside of the material. Other reasons for roughness in the seams include but are not limited to, fabric, unbalanced stitching on seams produced under this stitch type uneven sewing while over sewing.
Figure 7 showing the needle loops produced in a flatseam