I have a Pfaff GQ on a frame and have never had a problem with breaking thread ... until one day. I had finished a quilt and oiled, cleaned, changed the needle, thread and bobbin. Couldn't quilt more than 6 inches. Hadn't had a problem at all with the prior quilt. So, for 2 days I kept changing the needle, rethreading, new bobbins, cleaning oiling. The only thing I didn't do was to change the main thread - that solved the problem. I had never used that spool before (I only use that brand) and I haven't had a problem since. the mfg replaced the spool for me.