Dealing with Lower Thread Breaking - Sewing - as part of the expert series by GeoBeats. If the lower thread on your machine is breaking it is usually a function of what we call the bobbin. The bobbin is what controls what the underside of the seam looks like. And it is under the bed of the machine here. Most of the time when your lower thread is breaking it is because the bobbin itself is not inserted into it is spool properly. Double check that it is inserted properly, pull against the thread, make sure that it is coming off and then reinsert it. Once you have reinserted it you should be in good shape.