I have a 1600P and love it. If I start shredding thread, my first thought is always the needle. In fact, while I am at it, I take the machine apart, clean completely and oil it, just on general principles, but the needle is usually the main problem. If you have shreded a bunch of thread, there are almost certainly shreds in the machine. Also, I was advised by the repair guy in my dealership to slow down a bit on FMQ. Titanium needles last a lot longer.