Custom SAR Pack Project: Harness part 1: shoulder straps and kydex framesheet

I made some decent progress on the custom SAR pack project this week. I've completed the left shoulder strap, so I can show you the process I use to do straps, since the right will be identical, and I've gotten the framesheet molded. Part 2 of this, whenever I finish it, will be the hipbelt and back cushioning panel of the harness.

Completed shoulder strap

First step in doing the harness is to cut foam, which I detailed in my last post. Next, I cut the orange 'surface' part of the covering fabric. For this I use a lightweight ripstop nylon called HyperD from Ripstop By The Roll. Good folks, and I highly recommend them if you're working a DIY gear project. They've got everything from silnylon to dyneema to Cuben fiber, they're very knowledgeable, they ship promptly, and they send you free thread. What's not to like?

Cutting forms

On to the cutting of material. I traced out the foam parts of the hipbelt and shoulder straps, then cut with about 3/4" of extra material around each one as a seam allowance. Pretty straightforward, yes?

Next step is to sew all the stuff onto the surface of the strap before it's attached to the foam, so that all the seams don't have to pass through the foam and make a hash of things. I run a strip of 1" web down the length of the strap for structural purposes, terminating in the buckle that I'll use to adjust the strap. This would be more straightforward with a straight shoulder strap like on a cheap school backpack, but with contoured straps, you end up using several pieces of webbing to follow the contour.

Center webbing and buckle

Next I add several rows of PALS webbing for the attachment of pockets and gear, a concept I nicked from the military. If you're not familiar with PALS, here's a couple pages that explain it: Explanation, Attachment system styles

PALS pinned on, laying open

PALS stitched together

I made a few atypical choices with the PALS. First, rather than 3 strips of webbing 1" apart like the mil spec, I used 5 strips immediately together, similar to Blackhawk Tactical's "strike" PALS system. This allows more fine-tuning of the height of attached pouches, but that's not the main reason I made that choice; I plan to attach the sternum strap directly to the PALS webbing using a C-shaped plastic clip, and idea I stole from 5.11 Tactical's Rush 72 bag. I wanted a little more precise vertical adjustment than standard PALS would allow.

Sternum strap attachment (both ends)

 Rather than just stitch the webbing flat to the surface of the strap, I elected to fold it under so it's firmly connected to the center piece of webbing instead of just the thin, relatively flimsy ripstop nylon, particularly the inner row. The reason for this is twofold; first, my GPS receiver rides on one of these panels, so a secure attachment is important to me. Second, the sternum strap issue mentioned above.

Next, I attached the loadlifter straps, which are simply stitched to the surface of the shoulder strap rather than on some fancy adjustable slider like you see on many packs at REI. In my experience, the sliding loadlifter attachment just migrates its way rearward under tension, and thus does more harm than good.

Hydration routing. Loadlifter can be seen as the grey strap in the upper left.

Additionally, at this point, I added channels on the shoulders. Pictured is the routing for my hydration system, which is a simple tube made of the orange HyperD. Once the shoulder straps are mated with the pack, this tube will pass through the pack body and so connect to my reservoir. I find this arrangement a little cleaner than several velcro or elastic ties connecting the tubing to the shoulder strap. On the left shoulder is a similar system for the microphone/speaker handset of my 2-way radio, but that one involves a zipper. I'll go into more detail later on when I finish the rest of the radio pouch.

Attachment to pack

The final surface addition is the green webbing and velcro mess you see above, which is the attachment point between the shoulder strap and the pack. I intend to cut slots in the framesheet and attach the shoulder straps directly to the framesheet, and so they need to be removable in case I need to pull the framesheet in order to fit the pack into a sewing machine for repairs or modification later on down the road.

I settled on the velcro attachment as the most secure thing I could come up with that didn't involve bulky plastic hardware. The end of the green webbing is covered on both sides with 'loop' velcro and the hook velcro at the base wraps around it and around itself. Honestly, I think the stitching will fail before the velcro.

underside of orange material and foam

Next step is pinning the HyperD to the foam. I push pins into the foam at an angle so that they hold the fabric in place without sticking all the way through the foam and stabbing my fingers.

Pinning black backing on inside edge

stitching black backing on inside edge

 The next step is the initial attachment of the black backing material. I honestly don't know what this stuff is, but it's stretchy, soft, and dries fast. I'm guessing some kind of polyester. I just had it laying around in one of my drawers of random fabric.

First I cut out an outline with a generous (about 1.5") seam allowance. Most of the excess gets trimmed later, but it's good to have to cover 'oh, shit' moments during sewing. Next I lay the fabric on top of the strap. Not under it where it's supposed to end up, but draped on top of all the attachments I just finished working on. I then stitch it to the HyperD right at the edge of the foam.

I chose to hand stitch this portion since it's...fiddly. It would be very easy to accidentally sew through something you didn't intend to if you were doing this part with a machine. Once stitched, I fold it under.

Smooth and pretty

Next comes my absolute least favorite part of the entire process. Unfortunately, I can't seem to come up with a better way to do this. See, what you want is a nice smooth surface, as seen above. Wrinkles in the lining fabric will absolutely ruin your day after eight or ten miles on the trail. Getting that nice smooth surface is a job of work, with much cursing and gnashing of teeth.

I fold it under, roll it to hide the raw edge, and just pin the hell out of it. Below you can see 29 pins holding together 20-ish inches of strap liner. It makes me a little crazy to do, because it takes a dozen attempts to get the wrinkles all out. Once pinned, I stitch it in place with a whip stitch, like the toe of a moccasin, then stitch through the entire strap in a couple places to keep things from shifting.

Approximately all of the pins. Ever.

thoroughly sick of pins and sewing, thus unwilling to start repeating the strap liner process with the right-hand shoulder strap, I decided to build the framesheet instead. I'll get to the other strap some other day.

The only way I know to do this with the tools I have access to is using kydex, which is a heat-moldable plastic sheet that's mostly used to make holsters for handguns, knives, lights, and ammunition magazines. I've seen examples online of people using various other materials such as carbon-fiber for framesheets; maybe one day when I'm feeling adventurous I'll give it a go. The advantage of the kydex, however, is that I can reshape it using a heat gun, so if the shape I ended up with doesn't quite work out, I can poke at it until I'm happy.

I ordered a 12" x 24", 0.080" thick kydex sheet from an Amazon-affiliate seller for about $15 shipped. As is typical with this material, one side is glossy smooth and the other has a texture. I neglected to take pics of the raw material straight out of the envelope, but it's a black sheet of plastic. Use your imagination.

Heating and folding

To give the frame some rigidity, I chose to fold the edges in, 1" on top and bottom and 2" on either side. My original plan was to stick the thing in the oven and soften the entire sheet all at once, but I found out it didn't fit in my oven, so I had to use the heat gun. However, I think it would have been hard to control if the whole thing had been malleable at once, so this is probably a better approach. As it was, wielding the heat gun and folding required more hands than I'm in possession of, so I pressed my girlfriend into service helping hold things in place.

Edges finished

Next I had to shape the panel to fit the contour of my back; as any EMT student can tell you, being pressed against a flat board for any length of time does not for happy times make. Rather than reinvent the wheel, I used a framesheet from another pack as a model to shape this one. Before heating it to change the contour, I wrapped duct tape around it so that the edges wouldn't unfold. I just realized that I don't have any pictures of this part, and I'm not wrapping duct tape around the thing just for the Kodak moment.

My lovely assistant, with the finished product

 As a final touch, I curved the top edge, so the corners angle forward, toward the wearer's head. This is to counter the tendency I've seen in other packs I own of the framesheet to fold back as tension is applied to compression straps. The final product is very rigid against bending, but it twists pretty freely. We'll see how it works out when I get the rest of the pack done and have something to put it in, but I'm cautiously happy with how it turned out.

Orange spice tea in a mason jar. Because reasons.

 That's all for tonight. Auf Wiedersehen.