Backpack modification

[Bryan]

I tried a Golite Jam2 pack and found that I liked most of its characteristics, but it made my back very hot and sweaty. So I recently purchased a Golite Lite-Speed pack, which has a ventilated back, a framesheet, and many more features that I like.

Jam2 pack

This pack is very comfortable, but unfortunately it’s much heavier than the Jam2. The Jam2 pack weighs 753 grams or 26 ounces, and the Lite-Speed weighs 1.19 kg or 42 ounces. So I set out to lighten the pack as much as possible.

Lite-Speed pack

By making small changes such as removing and shortening straps, I got the weight down to 1.1 kg or 39 ounces.

Removing the framesheet from the pack, I found that it is made of thick plastic with two aluminum bars and Velcro attachments. The plastic is flexible, allowing the aluminum bars to be bent to fit your back. This assembly weighs 308 grams or 10.9 ounces and is rather bulky as well. I decided to make my own framesheet using carbon fiber composite as is used in many high-performance applications from racing cars and aircraft to sporting equipment (including hiking poles).

The original framesheet, with its outline traced onto poster board and a measurement scale

In order to get the exact shape of my back, I took my photo from the side next to a measurement scale to allow me to reproduce the size exactly. Then I printed this photo using the scale to assure it was printed actual size. I cut out this photo slightly longer than the pack at the top and bottom. Next, I made some paper templates from this printout. (I could have just cut the printout instead.) I bent the original framesheet to this shape to ensure it was comfortable and to confirm the exact vertical position. Finally, I traced the templates onto two pieces of wood and cut them to match.

Printout of profile photo, templates and wood

Next, I cut out a piece of sheet metal and assembled it to the wood guides. This became the mold for the new framesheet.

Mold

I cut out two pieces of carbon fiber fabric and two pieces of plastic mold release of the proper size, and taped one piece of plastic over the mold. The carbon fiber fabric is cut on a bias of about 30 degrees. This allows the fiber strands in the two adjacent sheets to be oriented in different directions, increasing strength.

Carbon fiber graphite cloth

Now we’re ready to start making the framesheet. In the photo below you can see a scale (for accurately mixing the two-part epoxy), supplies for mixing and spreading the epoxy, rubber gloves, cans of epoxy and hardener, and a bag of cotton flox.

Supplies and equipment

Next, I mixed up some epoxy and applied it to each carbon fiber sheet. The goal is to get the entire piece wet on both sides using the minimum amount of epoxy. These sheets were then laid onto the mold in opposing directions and the second layer of plastic was added to the top. Adding the top layer of plastic enables squeezing even more excess epoxy out of the assembly, making it as light weight as possible.

First layer, with plastic

Once the 2-ply first layer was dry, the plastic was removed.

First layer, without plastic

Next, I cut out a piece of foam core to match the shape of the framesheet but about 12 mm or 1/2 inch smaller all around. The foam gives the assembly some thickness, greatly increasing bending strength while adding very little weight. I beveled the edges of the foam on all sides and cut another layer of carbon fiber fabric. This layer was not cut on a bias, so that it would be oriented in a different direction from the first two layers.

Foam core with carbon fiber cloth

I mixed up some more epoxy and used it to wet the carbon fabric. Then I added some cotton flox to the epoxy, which greatly increases its volume without adding any significant weight. This mix was used to wet the foam core on both sides. Next, the foam core and the top carbon sheet were added to the first two layers. Again a layer of plastic was added to the top. A thin sheet of aluminum, the opposing wood strips, and some weights were added to press everything together, and the assembly was allowed to dry.

Complete assembly in mold

After drying, the framesheet was removed from the mold and cured in an oven.

Freshly removed from the mold

Finally, the framesheet was cut and smoothed to its final form.

Finished

The finished framesheet weighs 219 grams or 7.7 ounces, saving 89 grams or 3.2 ounces. That may seem like a lot of trouble for a little bit of weight savings. But it’s far stronger than the original part, it’s thinner, it doesn’t have the ridges the aluminum stays created, it’s waterproof, it’s metal detector friendly, and it fits my back perfectly. And I had fun making it.

[robert_loken]

Wow Byan! I'm impressed. 89 grams is a good savings for a backpack. It really looked like fun to do the job too! Have you tested it on any trips yet? It would be interesting to hear how the fit feels when you have weight in the sack for longer walks.

Thanks for the recipy! At one point I thought I was witnessing Mythbusters - all the epoxy flying around :-)

[FreddyMusic]

A smart traveling man.

A good workman is known by his tools.

[Kim]

Great work Bryan. Reminds me of a famous handyman that used to attract a lot of viewers on Danish television

[edng]

wow thats impressive

i just dont have the tools to make this work

anyway for me a kilo off the beer belly is worth a 2kg lighter backpack ha ha!!

[Bryan]

Originally Posted by robert_loken

Have you tested it on any trips yet? It would be interesting to hear how the fit feels when you have weight in the sack for longer walks.

No, and the crazy thing is that when I get a chance to test the Lite-Speed pack, I'm going to try using no framesheet at all. I think I can cut down a sleeping pad to the right size to roll up inside the pack and give it some rigidity. After all, saving 308 grams is a lot better than saving 89 grams.

[robert_loken]

I see. 308 grams is an even better saving.
You'll be flying along the Great Wall! :-)