how to use this: http://www.quiltingboard.com/t-76366-1.htm
First to make a round bobbin
When you adjust your tension, stitch on the diagonal for several inches. Then take it out from under the presser foot and pull on both sides of the stitching on the diagonal. Your goal to have both top and bottom stitches break at the same time. Just keep playing with the tension until it is balanced.