I also have a Singer 401, as my one and only machine. It is great for sewing and piecing, but I have tried quilting, and the bobbing thread seems to tighten to the point that the fabric won't move anymore, until the bobbin thread snaps. Any advice? I've tried almost every combination of thread tensions, and I don't THINK it was the feed dog plate catching....
Maybe one of those universal screw-on cover-plates would work better than the built-in raised plate?