18aa367c_ooting_Sewing_Machine_Problems__Symptom
[Root Cause] Bobbin has not been fully inserted in bobbin case. Bobbin has been incorrectly threaded. Bobbin does not turn smoothly in bobbin case. Lint in bobbin case or shuttle. [Corrective Action] Securely install bobbin into bobbin case. Correctly thread bobbin case. Check to see that bobbin has been wound evenly. Clean bobbin case and shuttle. [Symptom] 
Bobbin thread breaks.
Troubleshooting Sewing Machine Problems
Symptom