The largest I've done is queen (only because I don't have a king sized bed). I quilt from the center outward toward the edges, bunching up the excess under the harp and constantly shifting the bulk as I move to a new area. I have an extra large table for resting the bulk of the quilt (both on the left and behind the machine) so that there is no drag, and I use Machingers gloves. Harriet Hargraves' book, Heirloom Machine Quilting, is a very helpful resource, as are Diane Gaudynski's books.