Dec 19, 2010 at 8:38 am #1266725
I've made about a half dozen backpacks using variations on this basic frame shown below. The parts shown weigh less that two ounces total and are more than strong enough to transfer all of the pack's load to the waist belt.
The spars are Skyshark 400 carbon fiber. The corners are nylon barbed Ts.
I add padded a waist belt and shoulder pads and a 4000 cubic inch bag made of 1.9 ounce ripstop and come up with a frame pack ranging in weight from about 10 ounces to 1 lb total weight.
I've been using this basic configuration for about 10 years now. I've never had a frame (or bag) failure and have carried up to 40 lbs with it.
Thought the info might be of use to any of you contemplating a diy pack. I can provide more info if you have questions.Dec 19, 2010 at 8:53 am #1675627
Go inside the CF? and the CF doesn't split from the internal forces? Interesting.
Who makes them?
Nominal 1/8" OD? Or, What "sizing" number do I look for?
Thanks.Dec 19, 2010 at 9:17 am #1675629
Greg, i machine a small Al collar to stop CF 'split ends'.Dec 19, 2010 at 9:18 am #1675630
The nylon barbed fittings shown are sold as 3/8" od. I drilled them out so their id matched the od of the spars. The spars go inside the fitting. This is not how the fitting was meant to be used. Normally some type of flexible tubing would be pulled over the outside of the fitting where the barbs are located.
I have since moved up to fittings sold as 1/2"od. The fit is looser but it doesn't seem to affect anything crucial. The additional give might even make the pack and fitting less likely to break? I don't have to drill the 1/2" fittings. Their id is usually 3/8"…..plenty big for the spars. The extra room within the fitting also allows me to run webbings and/or cords through the fittings. These webs and cords tighten up the fitting/spar connection. The larger fitting would also make it easeir to make a temporary repair of the pack if a spar did ever break. One could insert a sturdy wooden stick, for example, by simply tapering the end to less than 3/8".
I plug the ends of the spars with a small piece of solid fiberglass or carbon rod glued in. So far no splits and no breaks. My 6'5" friend, 5'2" wife and I (5'8") have used these packs for hundreds of hours of backpacking without a single spar break. The orginal 3/8" nylon barbed fitting on my wife's pack had a crack in it after about 100 days on the trail. No cracks so far in the 1/2" fittings.
Here's where I get the spars:Dec 19, 2010 at 9:29 am #1675636
Chris HBPL Member
@nxpLocale: Upper Midwest
Those spars are .244 ID, 32.5" long weighing roughly 278gr = a standard (1/4") 8.5 grain per inch carbon arrow.
You can find carbon arrows with that same dimension even lighter than that, some of Easton's 500 and 600 spine arrows weight down into the 5.5gr/inch area.
Chances are if you head to your local Walmart's hunting section (provided they still have one) you'll find some arrows that are labeled 8.5gr/in on the side of them for roughly the same cost or cheaper.
Good idea with the barbed fittings!
CDec 19, 2010 at 9:44 am #1675640
I like the idea that the spars fit inside the fitting. It makes a lot more sense than a sleeve/barb on the inside of the CF.
The issue I have with staight stays is the tendency of the top of the pack to "lean away" from my shoulders.
Is there some magic spot on the back bottom or hip belt that minimizes this?
I would love to build/mod a 3000 ci pack under 1 # that sits close to my back. I haven't carried over 30# in quite some time, so this is a real tempting project.
This is great info. Thanks .Dec 19, 2010 at 9:52 am #1675642
I expermented with various aluminum, fiberglass and carbon fiber spars for the packs. They all work.
My wife carries about 20 lbs in her pack. Generic fiberglass tubing (about 1/4 od) works fine. They bend more than I like for 30+ lbs, however, so I use the skyshark 400s.
One could write a book about choosing spars. Factors include length, pack load, desired deflection, wall thinkness, shape of your back, etc. My strategy has been to find one that works (through trial and error) and stick with it. All of the fiberglass and carbon fiber options are light.Dec 19, 2010 at 10:03 am #1675645
The spars start out as straight but then bend when load is applied. The key is to find the right flexibility in the spar relative to the weight carried.
There are other factors also. The waist belt/frame connection, the location of the shoulder straps and the length of the spars all affect the curve of the frame. I've gone through a trial and error process over the last 10 years that included 1000s of combinations before I was satisfied. Even now I find that if I experiment with one thing it might affect the way the pack fits.
Having said all that I think the best thing I can do is take some more pictures and show you how mine is put together and how the spars form up when loaded.Dec 19, 2010 at 10:33 am #1675652
I think I understand what's going on.
Pics would be interesting, but not essential for me.
Thanks.Dec 19, 2010 at 11:49 am #1675669
John WestBPL Member
@skyzoLocale: Borah Gear
This looks really intersting. I have a light frameless pack that I use for trips under 4-5 days, but I have nothing that will hold enough for longer escursions.
Do you happen to have any pics of the finished pack? I would be really interested.Dec 19, 2010 at 12:54 pm #1675692
I've attached 3 pictures of older models. I don't have a picture of the one I'm currently using but it is similar.
The three pictured use aluminum tubing for the top bar. I'm currently using carbon fiber. The one my wife is wearing weighs about 10 ounces. The other two are just a little under a pound.
One of them has a front bag instead of shouder straps. The front bag does a great job of balancing the load front and back and also helps with bending the carbon fiber frame to match the curve of the back. With heavy loads I always use the front bag.
Total capacity of the bags with these three models range from about 4000 cubic inches to over 5000 cubic inches plus a top bar for strapping on additional items.Dec 19, 2010 at 7:29 pm #1675813
Ah ha, now that's an interesting design. I'm trying something similar myself with regards to getting the straps off my shoulders by having them come off a high bar, but i'm wondering, it looks like most of the weight is on your hip, how do you achieve some balance? Also if you are bending the stays with your back, doesn't that create pressure points. Mine will transfer some of the shoulder weight to just below the back of my neck, [it remains to be seen if thats a good idea or not, haha!]Dec 20, 2010 at 11:07 am #1675979
Yes, all of the weight is transferred to the hip belt. I injured my back a few years ago and try not to put loads on my spine above my waist.
I assume your question about balance refers to side to side balance? With conventional shoulder straps, even ones mounted high up, my shoulders are squeezed between the shouder staps and the vertical spars of the pack frame. It is very stable and easy to balance. With only a front bag hanging in front there is sometimes a little side to side sway. If it is more than I want I can cinch the front bag down using two straps that go from the bottoms of the front bag to the bottom corners of the pack frame.
Or are you possibly referring to front-to-back balance? The front bag is primarily aimed at addressing front-to-back balance. It reduces all of the leaning forward and straining that one often associaltes with heavy packs. Without the front bag I must lean forward to keep a heavy pack in balance. My wife has a very straight back and doesn't have much of a problem with front-to-back balance. She doesn't use a front pack.
Pressure points? The vertical frame stays usually touch my back just outside my shoulder blades. They don't cause me any discomfort to speak of, however. When I made a pack for a friend of mine he was concerned about the same thing but found it not to be a problem. If it became a problem one could loosen things up a bit or cover the vertical frame stays with some foam. The back does act as a fulcrom to some degree in the bending of the vetical pack stays but the primary bending force is the weight of the pack and the front bag. Stiffer vertical frame stays are harder to bend than more flexible ones and therefore put more pressure on the back where they touch.Dec 21, 2010 at 11:30 am #1676419
This reply is in response to your questions about how the vertical stay goes from straight to bent.
I've attached some photos to show you how the vertical stays bend under load. I removed the back bag and simulated load by pulling down on the stays with the front bag webbings.
I also attached photos showing how the bottom of the stays attach to the waist belt. Notice that the nylon barbed fitting rotates to adust to whatever angle the vertical stay is at. I tried simple pockets in the waist belt and they don't work very well. They resist the natural bending of the vertical spars.
Dec 21, 2010 at 11:39 am #1676422
That is very ingenious. The flex is amazing!
Thanks.Dec 21, 2010 at 12:02 pm #1676432
THAT! is a very cool design. Lots to be done with backpack design, i can see, if you google 'backpack design' all you see is different pockets & such.Dec 23, 2010 at 11:42 am #1677090
Here's a photo showing an aluminum top bar instead of carbon fiber. This top bar (with fittings) weighs about 1.3 ounces. Barbed fittings are 1/2". Thin walled tubing is about 5/8" od and something less than .6 id. (It is an old tent pole that Gerry used to sell.) The barb on the nylon fitting is slightly over 1/2" so the aluminum fits snugly.
The aluminum top bar has some advantages over carbon fiber top bars at a cost (weight wise) of about 1/2 to 1 ounce, depending on tubing and carbon fiber spar being compared. The advantages are (1)aluminum slips over the nylon fitting while the vertical carbon fiber spar fits inside it…….so the cross bar won't rub on the vertical stays. (2) Holes can be easily drilled in the aluminum to attach shoulder straps or other items. (3) The ends of the aluminun tubing can be lightly dippled to keep it from sliding off the nylon fitting. (4) The aluminum feels very solid when lifting a full pack by the top bar (psychological benefit).Feb 5, 2011 at 12:03 pm #1692876
@mikebiondoLocale: Missouri Ozarks
Dayrl, your pack frame intrigues me! Could you please elaborate on how you secure the spars to the fittings so the spars do not separate from the fittings? You mentioned in your original post about using webbing and/or cords:
I don't have to drill the 1/2" fittings. Their id is usually 3/8"…..plenty big for the spars. The extra room within the fitting also allows me to run webbings and/or cords through the fittings. These webs and cords tighten up the fitting/spar connection.
I'm guessing that you are running cord completely through the spars, and then through the fittings at each end of the spar. Have you ever had any problems with the spars slipping out of the fittings while on the trail?
Mike-Feb 5, 2011 at 12:35 pm #1692888
I have tried dozens of methods for tieing everything together so the spars don't slip out of the fittings, including, like you guessed, running cords through the spars and fittings(like shock corded tent poles). This system, however, prevents me from plugging the ends of the spars with small pieces of carbon fiber rod. I like to plug and glue the ends of the spars to prevent breakage at the spar ends.
Soooo, my current preferred method (for the vertical spars) is to connect the waist belt to the pack bag with overlapping omni velcro that runs through a loop on the waist belt and then back upon itself. It is secure and adjustable and is working very well. I just returned from a 4 day backpacking trip where I was carrying 30+ pounds of gear, going up and down ropes, sliding through mud, crawling over rocks, etc. and had no problems with the spars coming out of the nylon fittings. My wife was carrying about 25 pounds. My wife and I both used packs I made with the lightweight carbon fiber frame. Hers weighs about 10 ounces and mine weighs about 15 ounces (pack+frame+waist belt+front bag or shoulder straps).
The top (horizontal)spar can be kept in place with a piece of cord running outside the spar and tied to the two top fittings. I'm currently using an aluminum top bar (see previous photos) and that is kept in place by putting a few small dents in the aluminum tubing ends. I use a nail to do this. I place the small dents in the aluminum tubing ends so they can't pull away from the barbs on the nylon fittings.
I've designed the pack so it can be taken apart and put back together. This allows me to run the bags through the washer after each trip. I had quite a bit of mud and clay on my pack after this trip, for example. When taken apart the pack fits into a bag about the size of a tent pole bag.Feb 7, 2011 at 4:01 pm #1693728
@footeabLocale: Pacific Northwest
Love your frame. Gonna get me going for making my own based on what you have done I am thinking for a medium weekend climbing pack good for around 30-50lbs. Looks like a great way to be able to attach multiple pack bags and extra stuff etc.Feb 25, 2011 at 6:56 am #1701401
Very nice design and thank you for sharing it.
I think external frames will come back due to the low cost in CF.
You don't need shoulder straps the weight is balanced.
Have you looked into trying to reuse the frame tubes as tent/tarp supports?Feb 25, 2011 at 8:03 am #1701427
"Looks like a great way to be able to attach multiple pack bags and extra stuff etc."
Yes, the frame works well for lashing separate things on it. Here's an example I put together quickly for another person who expressed interest in lashing things to the frame. Please excuse the crude lashing. This was for demonstration purposes only.
I experimented with this about 20 years ago but gravitated to one big bag instead of multiple bags lashed to the frame. Big bags provide more volume per fabric area than small bags. Plus, I can always put three smaller bags inside the one big bag and doing so is quicker and easier than lashing them to the frame separately.
I have worked out a quick way of lashing any bag to the frame, however, using 1/2" webbing and quick release buckles. If that is of interest to you I can post a photo.
DarylFeb 25, 2011 at 8:31 am #1701446
I've done a lot of thinking about using the pack frame components for a tarp or a tent. So far I haven't made anything worth posting, however. Give me another 10 years.
Here are some thoughts on the subject, however, that may help you or someone else come up with a good application.
*The frame can be taken apart and put back together quickly so the potential exists to use the components in other ways in camp.
*If one wanted to day hike from camp and leave the tent up one could use the front bag as a frameless day pack. With the addition of a couple of buckles (.2 ounces) the back bag can also be used as a frameless day pack.
*The vertical carbon fiber stays would work well in a tent frame but they weigh less than 2 ounces total. Is it worth it to even bother taking the pack apart to save 2 ounces? One could simply view these two extra spars as back-up in case a tent pole breaks.
*My ideal tent/pack combo would be a one person tent that uses the assembled pack as the high point at one end of the tent and has a side entry. It would be mounted on the top of the pack frame and ready to erect at all times. After erecting it I could roll under it and then access the back bag's contents from within the tent. The front bag has quick release buckles so it would be detached and in the tent with me. I could go from hypothermic snow/rain storm to 70 degree warmth in less than a minute.
*The vertical stays on my pack are currently only 24 inches long. If I was to use the frame for a tent I would leave them longer (I think 32.5" is the standard length when you buy them). I've made an adjustable connection between the frame and the waist belt that would allow these longer spars to hang below my waist, out of the way.
DarylFeb 25, 2011 at 9:07 am #1701461
Still amazed at your work. I was looking for a curved member to attach from the rear stay around the should so another rigid member would attach to the front of the hip belt, but I think it would have to be aluminum. I don't have the ability to make carbon rods.
My other dumb thought, and nothing new here, would be to form the pack bag out of a tarp. I have not worked on the folding pattern. I will have to look for my origami books. The external frame opens up many possibilities.
Have you looked at http://www.aarnusa.com ?Feb 25, 2011 at 10:09 am #1701484
I've considered that curved shoulder member idea and even fooled around with it a bit. Haven't come up with anything worth posting, however. Aluminum is pretty easy to bend with hand benders. The current front bag system, hanging from the top of the frame, has been working well so I lost motivation on the curved member idea. I still think it is worth consideration, however.
The back bag I'm currently using is very simple to make. It is a 24" X 5' rectangle of fabric folded over itself to make a large stuff sack. So it does seem that it could be incorporated into a tarp. I use uncoated fabric but one could use coated fabric if he/she wished (most do). It would be fun to see what you might come up with.
Yes, I've seen Aarn's website and even corresponded with him briefly, via e-mail. His site does a good job of showing the benefits of a front bag. We came up with our packs independently and they are quite different, even though they share the same principal of a balanced load. My efforts have been more toward the lightwieght end of things. The pack I'm currently using, for example, weighs a little less than 1 pound and has similar capacity to Aarn's large size Natural Balance bodypack at 4.38 lbs (over 4 times as heavy as mine).
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