Fig. 133. Under part of machine
using a vibrating shuttle.
Fig. 134. Diagrams showing
proper tension.
237. Bobbins. There are two styles of bobbins used on lock-stitch sewing machines—the shuttle bobbin (Fig. 135) and the round bobbin (Fig. 136), depending on the particular type of machine used.
Fig. 135. Shuttle bobbin.
238. Shuttle Bobbins. In shuttle bobbins, there is a long iron spool on which the thread is wound. This is put into the bobbin with the twist in the direction indicated in the book of directions for the machine being used, and the thread is drawn thru the slits and holes in the bobbin which govern the tension of the lower thread (see Fig. 135).
Put the shuttle into place and draw the thread up over the feed plate (Fig. 137). The machine moves the shuttle backward and forward, and as this happens, the needle is timed to drop down, leaving a loop of thread in such a position that the bobbin passes thru it. In rising, the needle pulls the loop up tight, and as it has passed thru the cloth, this cloth comes in between the thread from the bobbin on the under side and the thread from the spool on the upper side, which have been interlocked by the bobbin having passed thru the loop of thread from the spool as the needle carried it down below the cloth. This is called the lock-stitch (Fig. 134). The spool bobbins also pass thru the loop left after the needle has passed downward.
