Has anyone had this problem? I bought a new Smart by Pfaff (not a cheap machine). I had a Queen top about half done when I got the new machine. I finshed that top and started a baby quilt. I had no problem pieceing the top but when I started quilting it the thread balls up on the bottom side. It might sew 6 foot ball up 6 inches then go back to working fine. This is the first time I have tried quilting (my 3rd top). If this keeps up I will just make tops. I have read on this board about thread I am using a cone of polyester thread from JA. I have changed needles, changed thread, cleaned and recleaned the bobin area, rethreaded several times. My daughter told me about pulling my bobin thread through to the top when I start. Done that. When it is acting up sometimes it will run slowly without my foot on the pedal. I am going to take it back to the shop but it is just a timing thing.