I finally finished my new pack. 25.5 ounces. I used pretty light materials, so durability could be an issue, but should be OK if I'm careful with it. I had the materials on hand except for the actual fabric, so it didn't cost too much to make. Like all DIY projects, I'm now thinking how I could have done it better
The light blue material is 2.2oz HEX70XL ripstop from Ripstop By The Roll (actual weight 2.73oz/sq. yd.). This material has a somewhat heavier coating than most similar material, which gives it a slightly rubbery feel and also makes it harder to pin. I don't think I'd use it again.
The black material is 200d coated nylon oxford (actual weight 2.95oz/sq. yd.)
The mesh is 2.6oz/sq. yd., which is pretty lightweight
The hipbelt and shoulder straps are 1/2" closed cell foam and the inside surfaces are a soft shell fabric.
The lumbar pad is a sandwich of 3/8" open cell foam, 3/8" closed cell foam, and .032" fiberglass (thin PC board material without the copper.) The fiberglass distributes the weight, as the bottom of the stays are directly behind the lumbar pad.
The back pad is 3/8" open cell foam and 1/8" closed cell foam. I used Carl Havens brand waterproof fabric adhesive to laminate the lumbar pad, back pad, and to glue the soft shell material to the foam (no longer available but 3M 77 adhesive is similar, I think.)
The stays are 0.1"x0.5" 7075-T6 aluminum. The regular aluminum from the hardware store bends too easily in the half inch width. The 7075 is springy and will flex quite a bit without bending. Harder to bend into shape, though.
There's a zippered pocket above the mesh panel on the front that's about 8" deep and runs the whole width of the pack. The pocketitself is internal, just the pack material folded over itself.
The lid pocket is 11.5"x8"x3" and will extend upward to accommodate the 8" silnylon extension collar (not shown in picture). The lid pocket only weighs 1.6oz., so I decided it was worth it.
Overall dimensions are 11.5" wide, 8" deep, and 23" tall, from the bottom to the top of the stays. These are rectangular dimensions, so when actually loaded, it bulges out slightly. I think the main pack is about 2500 cu. in. or 40 liters, not counting the extension collar.
Here's a link in case the picture isn't visible:http://i350.photobucket.com/albums/q438/WilliiamGK/Blue%20pack_3%20views_zpsruzximul.jpg