Originally Posted by
Craftnut
Prism is correct, if the timing is off the machine will not make a stitch, the threads won't lock together. I would floss out the tension discs like she said. Then check to be sure that the thread isn't catching on the side of your spool or cone, that is a common problem. When it catches, it won't advance through the thread guides, actually stopping the thread from moving for just a moment. Long enough to look like the tensions are tightening. The other place is to clean out the bobbin area. Lint can collect with machine oil to make gunk that looks like it is part of the mechanism, but shouldn't be there. Good luck! This
Google Search has some good links.
I have found that as thread prices go up, the spool quality goes down. I have learned to keep an emery board near my machine for smoothing the ends of the spools so they don't catch as the thread unwinds. Even with the large spool tensioner on the machine the little barbs catch, so I remove them gently. Worked for me when I had a similar problem.