Bonding ALU rods to tubes – What adhesive?

First of all, how are you preparing the surfaces for bonding? You will want to roughen up the surfaces a little so you also get a little mechanical bond. Then you can use something like 30-minute epoxy to bond the parts together – you will have a 30-minute working time and it will take 24 hours to cure. Adding some chopped up fiberglass to the epoxy will add strength. This is stuff I've learned from building and flying RC sailplanes.

If you are breaking the superglue bond then you should reconsider the design.
I was repairing an early proto pack in the Pyrenees for a few weeks, until I finally figured that one out. Once I reconfigured the harness (at 2,000 m in the tent), it worked for ever after – maybe 6 years or more.

> Taking the parts to a welder is not a good option either
It's actually a disaster waiting to happen. The welding will destroy the very high temper of the tubing!!!

I can recommend Loctite Black Max for the application, once you have sorted out the design.

Cheers

Can you braze/solder it? Not as strong as welding but still quite strong. Just takes a little blow torch and some flux coated filler rod. Naturally if it has to be connected while still installed in the fabric this won't work without some major precautions but if you can mark the locations first then remove for brazing you'll be in good shape.

Otherwise there are several adhesives that will work. eng-tips.com has a lot of great manufacturing info. This thread should give you some ideas. Specifically the preparation of the surfaces is critical. I suspect the inside of the outer-larger tube needs special attention to ensure it's cleaned well and abraded properly.

http://www.eng-tips.com/viewthread.cfm?qid=40718

I would use JB Weld epoxy and definitely rough up the surfaces.

> Can you braze/solder it?
Braze aluminium? If only.
And the heat would destroy the temper.

> the preparation of the surfaces is critical
It helps of course, but really you want a design which is not on the knife-edge.

Cheers

When I glued Al tubes into carbon fibre walking poles I used a two part resin glue (Araldite). This is still working after 400 mls.

"…By shear strength is meant the amount of force required to rotate the rod in the tube after bonding."
I rather doubt that epoxy will work if super glue did not. It might, because it is slightly flexible, but I seriously doubt it. There does not seem to be any shock involved which is where epoxies really help. The biggest problem is the oxides (that form on Al in air almost as quickly as you clean it off.) It is almost impossible to bond aluminum to aluminum for high strength applications because of that. The stresses will eventually work it loose, I'm afraid. It is not actually a clean bond, you are bonding the glue to aluminum oxide which is bonded to the aluminum. Many of the two part epoxies are not very moisture resistant. They will soften and loose strength if they remain wet for any length of time, too, but not likely a problem.

The twist of the rod will cause it to momentarilay excede any glue I know of. Perhaps designing in a region of torsional flex will work?

The proper use of adhesives usually is not to let the actual stresses to be applied through the adhesive. Though this is common with modern adhesives, every now and then, you run into a situation, such as yours, where following the "rules" works.

Try gently tapping the two pieces into an out of round configuration. This will add mechanical strength to the joint, rather than relying on the glue, alone. You probably have to do both pieces together, but they do not have to be identical. Be careful with the tempered stuff, it could crack with too much deformation, though you should be able to get a small amount…a small amount will work. You might notice some elongation around the inner. I believe you can ignore that, unless it is a lot. Some of the alloys are quite hard.

After they are bonded and in place, the glue will act in two directions. It will pull the parts together under loads as the metal tries to deform back to "round", hence not allowing that motion, and, prevent the twisting motion as in the origonal stress. The glue will also act as a continuous "shim" around the rod segments preventing any movement against the mechanical lock. I believe you will find the joint has about 50%+ more strength. It is likely worth a try. But, even using this technique, you might look for another solution. Roger is correct in suggesting a redesign.

I suggest you try Oatey Epoxy Putty. Surfaces to be joined should be roughened with sandpaper, emery or file as per directions. Wash hands after use.

It's easy to use. Just cut off amount needed, knead in palm of hand and then form around and inside joint where the 2 pieces meet.

I've used the putty and like how it performs. Give it a try on your project. Use scrap cutoffs for a trial run.

Perforate the end of the 1/4" rod so the putty will have some holes to enter for better bonding 1/16" deep would be nice.

http://www.mrsupply.com/product.php?productid=63996&gclid=CODxz_zE47YCFaxaMgod6RAA1Q

Epoxies are strong enough and far better than any super glue/cyanoacrylate for shear stresses. Surface area is important, so covering as much tubing as possible and getting a complete bond are the key. If you can extend the overlap on the tubing, so much the better for the strength of the joint. Of couse you will add weight if you go too far with the overlap, but something like three inches would be better than one. The joint can be stronger than the tubing.

I've seen very large boats built with epoxy and properly done, the wood will fail before the adhesive does.

Cyanoacrylate glues are great for light stuff like electronics assembly, but not for stuff like this. Try a test joint with epoxy— you will trash the tubing before the joint fails.

Wow! Thanks for all the suggestions.
Sounds like the Loctite Black Max and an Epoxy that has some flexibility need testing. Was also thinking of those little packages of epoxy that Easton sells with its 'HIT' shafts.

Wondering why nobody commented on urethane adhesive.

Will post if the solution is found. Otherwise, back to the drawing board as Roger mentioned.

Have you thought about crimping the tube. Using a file you can make a groove all around the rod. If you then apply pressure to the tube it will deform the tube to match the rod. A well done crimp might exceed the strength of of all glues. You might have to experiment with different rode shapes and crimping methods to find the best way for your application.

If Cyanocrylic failed I doubt you will get good results with any hard epoxy. In some cases a soft flexable glue might out perform hard glues because it can flex with the parts without the bond failing. At work some time ago a guy was trying to bond aluminum to teflon for some experments. Nothing worked even Cyanocrylic failed. I suggested he try silicon rubber. the bond he got with it wasn't that great but it lasted a lot longer then anything else and he was able to get his data.

Roughing the surfaces of the to parts to bond is always a good idea.

OK, three test samples are set up:
1. Elmers Glue-All Max, PU glue
2. Epoxy glue for Easton HIT connections for arrow points to shafts
3. Hysol 2-part PU, "FV"

These were just what was lying around, and have something to recommend them.
The PU expands while drying and is a little flexible after setting, and the Easton is for an application that receives a lot of pressure on the joint.

Tomorrow night, will put the rods in a vise, and see if the bent tubes will twist at the joints.

Could also try the epoxy putty, the 5 minute epoxy that dries a little flexible, and the Black Max suggested by Roger. BTW, the last is a rubberized glue, so Roger was perhaps thinking along the same lines as the most recent poster. Am running out of trash pieces to run tests on, though.

As suggested earlier, the Easton 340 tubes can't be messed with. They are ultra high temper, as noted by Roger, and would be weakened and more subject to breakage if 'folded, stapled or mutilated.' That includes crimping, etc.

Like the idea about boring small pits near the ends of the rod. May try that if all else fails.

BTW, these tubes are being used for side-arms on a 'Jackpack' suspension that folds a partial (no buckle) hip belt to cradle around the hips. Here's a photo of the first prototype sidearms next to the frame. It is called the 'ANT' frame because it has six legs:

The super glue was used on the sidearms in the photo, and failed. The position of the U-shaped ALU rod in the tubes controls the position of the sidearms next to the hips, and once set, must remain constant and unwavering.

This was easy when heavier 5/8" ALU tube was used in the past, and could be bolted to JanSport fittings at just the right angle. It's the use of much lighter materials that presents so many issues. The payoff, though, would be reducing a 6 lb. pack and frame to one weighing 2 to 2.5 lbs.

A possible last resort may be to find or make clamps that go over and around the sidearms, and lock them in the desired position. The rubber T fittings (cut to an 'L' shape) in the photo have been replaced with nylon PEX ones. Small screw hose clamps tightened around the tubes in those fittings might work, but would be uglier than he**.

Yet another solution might be to reinforce the tubes at their other ends, the ends that go into the fittings, with ALU rod, glue it, and drill a small dia. hole through the fitting and tube to hold a pin or bolt that would prevent the tubes from rotating in the fitting. Or maybe just drill and screw in a small sheet metal screw through the fitting and tube into the short piece of reinforcing rod in the center.
But as was noted, these approaches will weaken the tube. Maybe heavier L fittings at this location would compensate somewhat for that.

Thanks again for all your suggestions.

Cheerio!

It was a surprise to find that neither urethane glue created any real bond, the Hysol 2 part being even worse than Elmer's. Didn't even have to put the parts in a vise to separate them.

The Easton HIT epoxy did better, but once the rod fitting was put in a vise, it didn't take much rotating of the curved Easton 340 tube to separate them.

Instead of trying more adhesives, decided to use cable clamps and a small ALU plate line tightener (similar to the plastic ones originally made by SMC) to create a bar clamp between the tubes. The bar is about 1/8" thick, 1/2" wide, and cut down to a little under 1.5" long. Of the 3 original line tightener holes, the outer two were threaded with a high grade steel self-tapping screw. Ordered 5/16" nylon cable clips from Grainger's to place on each end of the bar and tighten with a short wide pan head screw into the tapped holes.

This assembly will go between the tubes close to the U-shaped rods, and if the clamps can be made tight enough around the Easton tube, will prevent it from rotating. The bad part is the weight – the two clamp assemblies will add about a half ounce total. The good part is that the clamps can be loosened to readjust the cant of the sidearms. Will look around for a good epoxy glue for the rods, but not expect it to contribute much to the rigidity of the sidearms.

Am becoming a real doubting thomas about the reliability of adhesives. They are OK for holding ferrules in tent pole sections, and gluing reinforcement patches on silnylon tarps and flies. That's been about it so far, and is the reason I'm leaning toward the sewable 10-15 denier coated nylon and polyester fabrics coming out to use rather than Cuben. Hope to have more to post about these fabrics, and about the pack after seeing how they fare in hard use this summer.

edited…crimping wont work :)

You could also make a sort of coupling out of slightly larger tube, tap 2 holes to use a set screw on the two pieces you are trying to bond. You will not twist that off.

> You will not twist that off.
Ahhh … give me 5 seconds and I will have it off.
Well, OK, maybe 3 seconds.
Sorry, but.

Cheers

Am thinking that James M has a good point about trying to bond through oxidation.
The irony is that due to the softness of the rod, if the fit of the rod in the tube is tight enough, they can be made with some twisting to bind tightly together – but not likely in the right position.

Am hoping that ordinary cable loop clamps of Tefzel or Nylon will latch tightly on to the E340 tube when tightened. Should know in a day or two.

If not, one other option might involve the ferrules that come bonded by Easton somehow into the tube. Wonder how they do that. Tried boiling to separate the ferrules as Roger suggested on another thread, and no effect at all. As mentioned above, I have cut off the end of the ferrule protruding from each tube, and drilled out the ferrule to accept the quarter inch rod (with enoough allowance to avoid binding).

The inside of the ferrule might also be tapped to accept an aluminum bolt, and some kind of fitting placed over the ends of the tubes and tightened in place with the heads of the bolts. As with all my screwed together gear, medium (blue) threadlocker fluid would also be used. The Easton 7075 is fairly hard stuff, and should hold a thread.

Will hold on that until I see how the clamps work. Am trying the plastic ones first, but if they don't work, there are rubber covered metal ones available in the right size on line. They are a lot bulkier and heavier, though.
Thanks.

P.S. Am also thinking of that English King who lost his horse in battle and said, "My kingdom for a horse" (according to Wm. Shakespeare). It's the unexpected glitches that sometimes seem to make a plan run totally amuck.

"If not, one other option might involve the ferrules that come bonded by Easton somehow into the tube. Wonder how they do that. Tried boiling to separate the ferrules as Roger suggested on another thread, and no effect at all."

Boiling would only work if the glue is sensitive the temperatures around 100C. many glues out there will actually handle higher temperatures. You might have to heat the parts to 200 to 300C to get any glue to faille. But heat might change the strenght of the aluminum. I don't know what temperature is needed to weaken the metal.

I am guessing ferrules are probably press fitted in. Meaning the outer diameter of the ferrule is slightly wider then the out er tube inner diameter. A press fit has the ferrule under compression while the outer tube in under tension.

When you are dealing with a press fit applying heat will only work if the two parts expand due to the heat at different rates. If both parts are made of the same metal both parts respond the same to heat and no gap will develop between them. However if one part was ceramic and the other part was aluminum heat could easily separate the two parts because the two parts respond to heat differently.

Hi Sam

Have a look at the first pic on
http://www.bushwalking.org.au/FAQ/DIY_RNCPacks.htm

That shows the 'clips' I developed for pack frames. They are pop-riveted together, and Black Max is used as the glue. 28 kg on one of these Easton arrow frames (full ski gear ++). But they ONLY work when the load is correctly applied. Twist the connections too much and the glue shears.

Cheers

Roger,
I've always been curious about what you use to craft the T-fittings on your frame.
Now I know there are pop rivets involved. As posted in the past, I'm pretty much sold on nylon T-fittings made from barbed hose/tube Tees from plumbing suppliers.
They can often be drilled out to fit tightly over the Easton 340s. It takes some mixing and matching with Tees,tent tubes and drill bits to get the right combinations. If the backband or other design component is going to hold the tubes in place in the Tees, it sometimes may not be necessary to bond or fasten them to the tubes.

Well, the problem in the OP appears solved. Tried the J-B Weld, suggested by Dale W, and found that it really locked the bent aluminum rods into the drilled out ferrules in the Easton 340s, using about an inch of overlap. Best of all, it was sold at Walmart, so no expensive mark-ups or shipping from an online industrial hardware supplier. The grip is so strong, it may not be necessary, or worth either the trouble or weight, to install the cable clips screwed onto an aluminum connecting bar. Also, there was plenty of working time with the J-B Weld, unlike even the slowest setting cyanocrylics. On to the next problem – they seem to crop up like hydras.

Thank you all.
Sam F.

Glad you solved the problem.

Didn't occur to me until just now but Larry Penberthy (MSR) dealt with a similar problem many years ago on some tent poles.

He solved it by notching the free end of an inside ferrule at the tip. He then put a pop rivet through the tubing into which the ferrule fit. The pop rivet fit into the notch of the inside ferrule and kept the tubes from twisting.

Larry Penberthy doesn't post much anymore.

–B.G.–

> I've always been curious about what you use to craft the T-fittings on your frame.

I made up two steel production jigs. The first bends the Al rectangle into a U-shape. The second forms the U-shaped aluminium into the T-shape. The second one needs a medium-sized press though. Then I pop-rivet it together. I did poke the steel nail-heads out and re-press the pop-rivets as well.
The joiner just slides neatly over the Al tubing, so I assemble the pack frames in a jig (for size and squareness), and apply Black Max.

Yeah, … too much spare time. :-)

Cheers

Roger,
I like the way you make things from scratch.
Sort of a survivalist version of MYOG.
Reminiscent of the public TV show with the guy who made wooden furniture the way they did hundreds of years ago. The first few shows were about making the tools to make the furniture. Some of the pieces were pretty good looking, solid stuff.

Forgive me for always looking for the quickest, easiest way, though.
The reason for that is not enough time. Just want to get the gear done and get out there. Doctor's orders – more exercise.