Daniel,
Cool pack you made… similar ideas. You're totally right about the "compression creep" that occurs if the load sags to the bottom of the dry bag – I've found that careful packing keeps the dry bag shaped properly, but I've been thinking about ways to fix this (I was considering putting cord locks on the lower half of the draw cords).
Regarding volume… Up to around 70L seems OK but the suspension might get overloaded if it's not just 70L of pillows. At the lower end, when things are fully compressed the bag still needs to be about 25L for it to not have too much slack in there.
John,
I've been selectively ignoring questions about the "lazy Susan" hipbelt attachment point – not because I'm trying to be obstinate but because I'm not quite sure how much I should guard that "secret" right now. I would like to share as much info as I can however so perhaps others will be inspired to build packs as I've been by all of BPL's great contributions and open sharing. Let me try to answer your other questions:
I can't take a photo of the frame sheet because it's sewn in – I originally thought of creating a velcro closure so I could remove it, but ultimately I knew that personally I never would and sewing it in made it more secure and simpler. However, you're correct that the load lifters are attached right at the top of the stays, and the stays actually are removable: I left the top edge of the pack open above each stay and since the load lifters are connected to the back of the "sandwich" layer of pack material, they are then pulled forward over the holes above the stays, effectively pinning the stays in place – works great and is a simple solution. I'll try to take photos of that and the stays themselves later. Any other pics you'd like to see?
I "bound" all the edges of the frame sheet with a layer of duct tape to prevent the sharp plastic edges from wearing into the dyneema – I suppose if you're really fancy you could sew grosgrain webbing all the way around the edges of the frame sheet, but since no one is ever going to see it, and really it's just an extra precaution anyway, it seemed like a good, lightweight method.
One other tip I'd like to share: Originally I couldn't fit the spacer mesh-foam-gridstop-webbing combo under the presser foot of my sewing machine, so I sewed all the bar tacks on the straps prior to assembling the straps. This made things look really neat, but ultimately I found that the sleeve that is formed around the foam core would rotate a little under load and this wasn't good. I since took the straps to a friend with a better sewing machine and sewed additional bar tacks all the way through every layer, thus pinning the foam in place – problem solved! But even with the friend's $$$$ Viking machine, fitting such thick material under the presser foot was difficult. To solve the problem, I would lower the feed dogs, slide all the materials into place, raise the feed dogs, and then I had to press the fabric down using my hands to "fool" the machines computerized sensors into thinking the fabric was thinner than it was (otherwise a "presser foot is too high" alert would prevent sewing). Once the first stitch was sewn, the machine was OK and I could sew the bar tacks as normal. BTW, I'm using 3/8" CCF as suggested by Chris Zimmer.