This happened to me once before. I had wound a bobbin with bottom line. I had to bring it into the dealer. They didn't tell me how they fixed the problem, I just know the bobbin was off when I got it back. I learned something, here. I was not aware to wind the bobbin slower when using poly thread.

I have two Vikings and want to thank you for this post. I love my machines, but have had problems with the bobbin winder too.

Thanks for sharing...learn something useful here everyday. :) :)