Was in a workshop that the instructor not only had us use the little brush, she said to put a few drops of sewing machine oil on the end of a Qtip and wipe that around in the bobbin case and areas that you can't reach with the brush. You'd be surprised how much that will pick up for you. Do NOT blow into the machine--it pushes all of that deeper inside where it can't be removed at home! Remember to clean the grooves on the feed dogs, too, especially if you've sewn nappy fabric like flannels or fleece.