Stitch Formation
From Groz-Beckert®
Needle Thread Loop:
The first step in producing a stitch on a sewing machine is the formation of the needle thread loop. This step is always the same regardless of the type of stitching being produced, or the nature of the machine being used.
Proper formation of this loop depends on the tendency of the thread to bulge away from the needle as it is drawn upward after reaching the lowest point of it's stroke – due to inertia and friction against the material through which it passes.
Any interference with the formation of the needle thread loop will result in faulty stitch formation. One of the most common conditions is that the material stitched is not held firmly by the presser foot at the point where the needle passes through, allowing the material to flag, or move upward with the needle as it rises. Either no loop is formed at all, or the loop is formed too late. Skipped or broken stitches result.
Correct setting of the needle is necessary for the forming of a good loop. At the proper height, with the eye at ninety degrees to the direction from which the point of the shuttle (or hook, or looper) enters the loop, the needle is positioned for normal loop formation.
Since the thread tends to form an equal loop on each side of the needle, a guard is used to push the loop through to the side from which the thread is taken by the stitch forming mechanism (shuttle, hook or looper). Correct setting of this guard is necessary for good loop formation.
Please note Formation Pages listed below have large diagrams.