To the lady a few weeks ago who had a similar machine which shredded the cotton while sewing free motion (mine was doing that same thing) The mechanic found the culprit was the free motion foot (not threading, cleaning or anything else) The cotton was snagging on the little hole so he drilled out a new larger hole in the plastic and no more problem. And of course that explains why I never had a problem when I was just sewing with the ordinary foot. Didn't know about the Service Manual - sounds a great idea.