Effects of the Shapes of Presser Foot and of the Loop Guard on Thread Looping

Abstract

Photographic pictures have been taken of thread looping of an industrial sewing machine using three kinds of presser feet and six kinds of fabrics to investigate how the shapes of presser feet and the loop guard affect thread looping.
The pictures have shown that :
(1) A form of typical loop with the loop guard conforms to a lemniscate inclined by about 13°to the scarf side of the needle.
(2) The width of typical loop (Y_g) with the loop guard is given by :
Y_g_??_Y+d·tan13°
where,
Y : the width of a typical loop without the loop guard, and
d₀ : the distance from the lowerside of a throat plate to the meeting point of a shuttle hook.
(3) The flagging, which causes the skipping stitches, can be prevented by using a proper shape of presser foot that press fabrics down tightly, even when the sewed fabrics tend to flag.