7075 Al alloy pole/carbon fiber arrow/foam external frame w/ UHMWPE fabric + bag

Wowza, that’s all quite impressive. Would love to see some photos of the process.

Try
http://bushwalkingnsw.org.au/clubsites/FAQ/DIY_RNCPacks.htm

I think  the packs I have been using for over 10 years are what you are describing. But you do NOT need to reinforce the Easton arrow tubing. It is quite strong enough by itself.

cheers

Hi Nathan, here’s a pic.  The black coloring on the poles, i think, is not paint, but the extra thick Al oxide layer created by the hard anodization process–you should be able to see where it’s been removed, at least on the outside.  The white fabric that the poles are on is the UHMWPE fabric.

Well Roger, you were partly right.  For some reason, i decided to try to bend the poles more.  I think this time, i didn’t pull as slow, but pulled faster (almost jerked it) and broke one.  (thankfully these poles are only a few dollars a pop).

Btw Roger, what size poles do you typically use? (these are .49″)  And if i can break it somewhat easily with my hands and no tools, wouldn’t that argue for the carbon fiber/foam core?   We’re only talking about an extra couple ounces or so.

An old trick for bending Al tubes is to fill with sand before bending.  It may only provide limited support for these hardened Al tubes but will help spread out the bending forces to prevent localization.

If you consider the moment you put on the tubes when you bend from the ends, the force might seem small but in actual use the lever arm is small so you are unlikely to ever see such a high moment.  In other words, the tubes are plenty strong.

Hi Justin

Those pack frames use 0.344″ Easton tubing for the verticals and 0.313″ for the curved horizontals. The frame is then sprung by putting a panel of LenoLoc mesh across it and tensioning just a little.

To be honest, there’s rather a lot of technology gone into those frames. I developed a special bender to curve the tubing, and a press die for the joiners. No sand fill was used.  Yeah, probably took well over a year for all the work.

But the packs have been used on a number of 2-month and 3-month long Alipne walks in Europe, plus ski-touring in Australia (with crashes!), plus some rather rough exploration work around the cliffs and canyons of Wollemi NP in Aus. I have never had any fear that the frame would distort or be damaged – PROVIDED that the shoulder straps are correctly attached. If they aren’t, you are quickly history.

Cheers

Hi Clifford, i did pack them with sand before bending.  If you look at the first pic, the curved pole has vinyl end caps on it–that was used to keep the sand in them while i was bending them.

I think the problem was with the technique–previously, i very slowly and carefully bent them.  The next day, i was less careful and almost jerked pulled it.

I can see your point about the greater forces than typical being applied when i bend them by hand.  If it was more weight than just a couple ounces, for a lot more strength, i would probably skip the carbon fiber/foam core part.  But it’s so light and easy to do, i figure why not.

Your frames look very well designed and executed Roger, so i’m not that surprised by the amount of work/thought that went into them.  Unfortunately i have neither the funds, the time, and probably not the engendering capacity or know how at this point in my life, to do similar.

Considering how small the tubes are, and that you’ve put them through that kind of wear/tear, it’s impressive that they have held up so well.

Yesterday, i prepped the fabrics and put a coat of adhesive on one side of each.  Today, i put another coat of adhesive on, put the fabrics together, put a bunch of books on top and let it set and cure for a few hours +.  Then i took an iron on low and ironed it on the Silpoly side.  Let it sit for a bit more, then threw it in the dryer on medium low heat setting to speed up the curing.

Then i sewed it around the perimeter and then an X.  I don’t think the adhesive bonded very well though.

I’ve flip flopped on my choice of frame material. Now i’m going with the Easton Carbon Fiber FX poles.  I’m going to use some other different fabrics and make another pack with the Al poles i have.

Yesterday i put the frame together.  As mentioned, i’m now using the Easton Carbon FX poles.  I had bought the 90 degree Al elbows that normally go with them, but when thinking about it and trying different things, i noticed that the carbon poles fit pretty well inside the .49 Al elbows that i had ordered previously.  I figured going with extra strength of these elbows was a wiser idea.  I also like the carbon poles going inside the Al, rather than the Al going inside the carbon.  The Al has a little give/ductility which may help protect the carbon fiber during possible impacts. I’m also hoping that the foam core provides a bit of absorption and wall protection to the carbon fiber for impacts.

Most of the frame was epoxied together.  But, i took some 3+” spray foam and sprayed foam inside, so i wasn’t able to epoxy two of the connection points.  To make up for that, i took FiberFix and wrapped these connection areas the most with it.  I used some of the rest on some other joints, but the stuff doesn’t last long once unsealed.

Because i originally prepped the .49 elbows to be epoxied with the .49 Al poles, i had exposed areas where i had sanded off the hard anodization.  To give those areas of the Al a little extra protection, i wrapped them in some self adhesive silicone tape.

After the foam fully cured, the frame is surprisingly stiff for a simple, square structure.  I’m still wrapping it with dyneema or spectra cord, but i guess due to the foam/carbon fiber combo, i need it less for the structure/stability. It has a little flex/give but really is fairly stiff considering the simple structure with no cross supports etc.

So far, the frame weighs 7.5 oz.  The horizontal/vertical stringing with with dyneema cord will add maybe about an ounce.   The main pack material weighs 8.6 oz.  Tomorrow i plan to attach the frame to the pack material and start making and attaching the shoulder straps, hip belt, etc.  Might not finish since it’s a friend’s B-day tomorrow and i’ll be out and about later on.  Since the upper and lower poles are not being bent, i plan to sew some Evazote foam/fabric over key parts of the frame.  I’m guessimtating it to weigh around 1.5 to 1.75 lbs total after shoulder straps, etc are added.

Pic of the frame (it’s very slightly skewed and not fully level on one part):

I mostly finished the pack, except for sewing up the bag, some buckles, etc.

But, i’ve flip flopped again.  When sewing the shoulder straps on with a “Speedy Stitch” hand sewer, came to the conclusion that it wasn’t the best fabric combo to support such large thread.  Made me kind of concerned about the fabric’s durability in general.

Think i’m going to replace it with 420D Robic nylon from Ripstop by the Roll.  Seems to be a near bomber material at mid’ish weight.