You say it sews wonderfully for a bit, but then top thread tangles. I'm wondering how many stitches or how far it stitches before catching. It seems like this has happened to me but it is only a few stitches good. That was a case when I hadn't gotten the bobbin and bobbin case inserted correctly.
Another possibility could be that it happens when pushing or pulling the fabric so that it doesn't finish the stitch.
Something else that has happened to me is that the thread has jumped around and out of the proper thread path (out of the check spring).
Are you using a cross wound spool of thread or parallel wound? If the parallel wound, are you using a spool pin felt under the spool of thread? Does the thread spool have a notch in one end? Some remove the notch, I just turn the spool the other way.
Janey - Neat people never make the exciting discoveries I do.
Last edited by OurWorkbench; 08-13-2018 at 05:21 AM.