I started out joining batting by stitching by hand, then tried the tape, but have wound up using the zigzag. I use my walking foot with the widest zigzag setting and a normal stitch length, or just a little longer. Just butt the two straight edges together and stitch. Don't worry if there's just a little bulk where you're stitching because you won't notice it after it's in the quilt. Some people actually overlap the two pieces of batting just a little bit, and that works too.