I sometimes have the problem too. Most often its the tension, but I've also found that the wrong needle size can do throw things off too. Grrr. I HATE machine sewing but do it because I love cats - the only sewing I do is to make blankets for the shelter kitties. I made a few and they've requested more. I was ready to toss the machine through the window (like lynnestankard ), but hey, who can refuse to make more when the kitties love them so much?