I have a Juki 9". As the quilt is being done it's rolled onto the take up roller, which is inside the throat of the machine, so the quilting area gets smaller. By the end of a queen quilt I have only a 5" wide area to quilt. That's not enough. I really don't think you'd be happy using your regular machine on a frame unless you were doing very small quilts.
I'm looking for an 18" machine. One I'm considering is the ABM Innova. You might want to check it out.