A singer sewing machine sews with two threads: an upper and lower thread. The upper thread comes from the spool and is threaded through the eye of the needle of the sewing machine. The lower thread comes from the bobbin, a small spool of thread that's loaded under the slide plate of the machine. Although most issues with a Singer's bobbin are solved by referring to the owner's manual, knowing how to troubleshoot issues on your own is useful.
Threading the Needle
The bobbin mechanism of a Singer sewing machine will not work properly if the sewing machine is not properly threaded. A blunt or dull sewing machine needle cannot pick up bobbin threads. Therefore, an important first step in threading a Singer is ensuring the needle is sharp. Change the needle or purchase a new set, then thread the machine according to manufacturer instructions.
Winding the Bobbin
Irregular stitches may occur if the bobbins thread is not wound evenly onto the bobbin spool. If so, rewind the bobbin. Avoid winding the bobbin spool too tightly because it will not fit into the bobbin case. Use the correct type of bobbin and fill the bobbin with the same type of thread used in threading the upper threads.
Threading and Inserting the Bobbin
A common issue with bobbin threads breaking when using a Singer sewing machine may be caused if the bobbin case is not threaded correctly. Singer sewing machine bobbin casings are loaded into the bobbin shuttle by either a front or top drop-in loading method. The bobbin is inserted into the bobbin case so that it turns clockwise or counterclockwise, depending on the type of Singer. In general, whether counter or clockwise, insert the bobbin by placing it into the case leaving a 3- to 4-inch tail of thread outside the case, then pulling the thread through the slit in the case and underneath the tension spring. Inserted the case into the shuttle.
Cleaning the Bobbin Shuttle
Lint, thread and other foreign matter accumulates inside the bobbin case and shuttle. Once this happens, the machine may jam, bobbin threads may break and the sewing needle may not catch the bobbin threads. Clean the bobbin case and shuttle using a lint brush, pair of tweezers or your fingers. Afterward, lightly oil the sewing machine oil to ensure smooth operation.
Adjusting the Bobbin Shuttle
Irregular or loose stitches are sometimes caused when the bobbin's tension is out of sync. Adjust the tension to solve the problem. Bobbin tension is controlled by a screw located on the bobbin case. Use a small screwdriver to adjust tension by turning the screw clockwise to increase tension and counterclockwise to decrease tension.