Be sure when you start winding you bobbin, that you stop once it has a good start and trim the thread that you were holding up to start it with really short. Sometimes if you don't this thread can get caught when the bobbin gets low and catch. Hope this makes sense. Be sure to check your bobbin case too to make sure you have not hits on it or rough spots that can catch your thread anytime. This happens when you have mis-threaded it by not having the presser foot up or missing the take-up lever. These two things are vital to any machine. Results = nest of thread in the bobbin area.