Here's what I found out:
- The problem could be caused by the wrong type of bobbin--for instance putting a Singer bobbin in a Brother machine. These machines both use clear plastic bobbins that are almost, but not quite the same size.
- The problem could also stem from a poorly wound bobbin. If the bobbin is not winding perfectly smoothly and evenly, it will probably cause tangles at some point in the bobbin's use.
- The bobbin has to be placed in its case with the thread end running in a clockwise position.
- The tension of the top thread has to be correct.
- The machine has to be threaded correctly with no steps missed. (The problem here is that as your machine is galloping along sewing, the thread may come loose from the guides without your knowledge.)
So, I re-threaded the whole shebang, wound a new bobbin and started again. I am pretty sure the problem was a combination of poorly wound bobbin and the top thread had come loose from one of the guides. Even still I am training myself to check at the beginning of each stitch run to check and make sure the thread tension looks good on the back of the project.
Thanks to all those folks on the World Wide Web who post information about how to solve problems and fix things that are broken!