Picture above shows a typical pack frame that I have used to make a half dozen external frame packs and to add an internal frame to a travel pack. I've been experimenting with it for about 10 years.
The one pictured weighs 1.7 ounces. Black pieces are carbon fiber or fiberglass tubes (can't remember which for this frame) and the white things are nylon plumbing fittings drilled out slightly to accomodate the tubing.
I thought this might be helpful to some of you contemplating the design of a lightweight pack. With this basic skeleton all of the pack's weight can be transferred to the waist belt. I've made packs ranging in total weight (pack, frame, straps and waistbelt)from 12 ounces to 1 lb with volumes up to 5000 cubic inches able to carry up to 40 lbs.
Thanks to phat for showing me how to post a picture.