I just finished my first MYOG project: a cuben backpack to use in my PCT thru-hike attempt this year. The other MYOG forum posts here were quite useful sources of design and technique tips, so I wanted to share a few details of my project.
My goal was to create a lightweight frameless pack that would be durable enough to withstand a PCT hike and spacious enough to fit a 10 degree sleeping bag and bear canister. The resulting product is a 6.4 oz frameless pack that seems to be able to hold and distribute a 30 lb load comfortably. The materials are 1.43 oz cuben from ZPacks and 1/4 inch closed cell foam from an old Gossamer Gear sleeping pad, with some webbing from Quest Outfitters.
The main design inspiration came from the ZPacks Zero pack I used on my AT thru-hike last year, which was basically a dry sack with arm straps and side pockets. The main changes I made were increasing the capacity of the main body and side pockets, adding a beefier hip belt, and adding side straps to optionally attach to the roll top. I also reinforced the attachment of the top of the arm straps to the back of pack, since this seemed to be the weak link in my ZPack and first prototype.
My process was to create three prototype packs out of cheap rip stop nylon from JoAnn fabrics (they regularly have 50% off coupons) and use these prototypes to hone my previously non-existent sewing skills and the details of the design.
Some things I learned from the prototypes:
Getting the exact location of the hip belt was tricky. I knew my torso size and knew the right position of my previous, webbing only hip belt, but using this to determine the correct position of a differently sized and shaped hip belt still took trial and error.
Determining the right amount of elastic shock cord to use in the side pockets was also surprisingly tricky. Too little and the pockets are too tight (and the elastic compresses the pack when empty), too much and everything is loose. For these pockets I found that I needed heavier weight shock cord provided enough tension to hold an upright Platypus in place without compressing the fabric of the empty pack.
By making the wing-style hip belt in three pieces I was able to hide any visible seam, which I think looks much better than the prototypes where I made the hip belt out of four identically shaped pieces of cuben.
I put the seam of the side pockets is on the inside of the pockets, which was a huge pain to sew. Now I know why the ZPacks side pockets have seams on the outside of the pocket.
Rainbow colored thread is fun!