As far as I know T&S machines use only plastic bobbins. The bobbins I'm using have been working fine in my 648 and I've tried 3 different ones with the same results. I will check again though. It just occurred to me if the bobbin is unscrewed a bit that could cause the problem I'm experiencing. Thanks Barny. I'm downloading the user's manual now from Singer but it's going to be a while longer before it's finished.
Rodney