You might want to check the bobbin case for signs of "punctures" from a broken needle. This will shred thread for sure. This has happened to me more than once. If you do find a hole or groove in the bobbin case, you don't have to run to your dealer to immediately buy a new one. You can file the hole smooth with very, very fine sandpaper or emery board. You also might want to use a thread stand for your thread so it feeds from a vertical position. Also use a spool cap and check to be sure that the thread isn't getting caught in a sharp place on the edge of the spool (actually a spool cap should take care if that is the problem). Another possibility is that a small piece of thread could be caught in your tension disk. If you are brave enough to remove the top or side of your machine, you can probably see any small bits of thread and remove it with tweezers. My machine is also an embroidery machine and every time I have had a problem with shredding, it was one of these issues. If you haven't already done so, you might want to put in a new needle and a new bobbin. I hope some of these suggestions help. I know how frustrating this can be. Let us know if you find the cause and solution.