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.

Could just make your lines curve instead of being straight too?

using a walking foot is an easy way to make easy curves. just move the quilt to the left then the right as you sew along. have fun!!

I did a king size on my dinky mechanical Brother. I did stitch in the ditch. The middle was tricky but I wasn't deterred and was happy with the results.

Definitely get some Machingers gloves (or similar) - they will make a HUGE difference to how sore your shoulders get! And I second looking at Diane Gaudynski's books.

And I second nativetexan's point about walking feet - much much easier to work with than leaping straight into free motion quilting, and you can do quite a bit of curvy quilting with a walking foot.

You can definitely make a beautiful quilt with two plain sheets, some thin batting and a bunch of straight lines: simple, clean, elegant. If it were me I would do that, and then (if I liked machine quilting) I'd move on to experimenting on a smaller quilt, where there isn't as much bulk to fight!

Alison

PS And I do all my machine quilting on a Kenmore mechanical domestic machine from the early 1980's - I have done several king size, quite a few queens and countless little 'uns - and I am entirely self taught. You can so do this!!

You could always just tye it. That is the easiest method I know. I grew up sleeping under quilts that were 2 sheets and batting, tyed with yarn.