Gluing Aluminum

This is out of curiosity:
How good of a bond can one achieve with epoxy to aluminum? How good can one achieve with epoxy that ordinary folks can mail-order, vs. what folks
who have the ear of a Locktite sales rep and applications engineer can achieve? How good can one achieve with JB Weld?
An Internet acquaintance has a scale model airplane that needs a driveshaft driven by an 049 engine (that's a bitty one that swings a 5" prop, not a humongous one that swings a 12" prop -- 1/20th cubic inch, not 1/2). His current driveshaft uses a solid aluminum rod, and is heavier than he'd like.
Because of the way the plane balances with the current shaft, every gram he takes out of the shaft takes out more than two grams from the plane, because he's currently got a buttload of weight in the nose.
I'm thinking that one could machine ends out of aluminum, then plug them into a thin-wall (.035"), 1/2" or 5/8" diameter tube made of 2024. I'm also thinking that bonding everything with epoxy would be a valid way to go -- but I'm not so sure about the epoxy in a part that's going to be subject to lots of vibration in at least eight of the six available degrees of freedom.
Threading such thin wall tubing makes me think that it'll just break.
Welding makes me think it'll never happen.
Soldering???
--

Tim Wescott
Wescott Design Services
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If it were me, I'd try Loctite Bearing retaining compound, being very careful about fit, curing time, etc.
Tim Wescott wrote:

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On Fri, 20 Sep 2013 14:03:50 -0500, Tim Wescott

I'm sorry I won't be around to discuss this further, but here are a few points to consider:
1) You're talking about shear loads, at which epoxy is very good.
2) The amine curing agents for epoxy, which are the ones we can get at hardware stores and marine supplies, give you the lowest temperature tolerance and rarely exceed 5,000 psi in cured epoxy. You can achieve 10,000 psi with other curing agents, but you'll have to Google "epoxy curing agents" and spend some time looking around. Amine cures are good for around 180 deg. F. You can get another 40 deg. out of other agents.
3) With aluminum, the surface treatment is everything. They glue airplane wings together by applying a phosphoric acid anodize. You can get about the same strength by doing a good scratch-in job. Maybe someone here can help.
4) With a high performance epoxy, you want a 0.003" - 0.004" clearance, or your strength will be a fraction of what it can be.
Good luck!
Ed Huntress
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On 9/20/2013 3:46 PM, Ed Huntress wrote:

I want to but in here - But - first hand stuff.
What Ed said. Then... Appropriate primer before epoxy.

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On 9/20/2013 3:03 PM, Tim Wescott wrote:

<snip>
Everybody here has stayed on the adhesive train! I say use a mechanical solution. Pin or swage it together!
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On Sat, 21 Sep 2013 17:17:13 -0400, Tom Gardner wrote:

Good thought, but:
If I did this I'd be using relatively thin wall tubing; pinning would either rip out, or require me to use thicker tubing than I want.
Swaging would, I'm pretty sure, vibrate off as the tubing stretched.
Shrinking the tubing onto the end, followed by shrinking a collar on, might work -- but that's extra weight, and I think I'd rather try glue.
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Tim Wescott
Wescott Design Services
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On 9/22/2013 6:10 PM, Tim Wescott wrote:

I see.
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Shrink and shrink means no clearance, which means STRAIGHT.
A glued high speed shaft seems a bit dicey to me, balance-wise.
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On 9/24/2013 9:03 PM, snipped-for-privacy@snyder.on.ca wrote:

I just have the mechanical gene when it comes to fastening. Not that adhesives don't have their place, but moving parts have a whole set of dynamics on a joint that adhesives alone will eventually fail...in my world. For this application, I think that maybe a mixture of adhesives and mechanical fastening would work.
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On Fri, 20 Sep 2013 19:17:47 -0400, Ed Huntress

JB Weld outperforms West System where high temperatures are concerned. OTOH if I understand the question I would also vote for the 6xx retaining compounds (Vibratite make Loctite equivalents and are cheaper). One thing to note: They hold differently on different metals, e.g some are weaker on brass than on steel. The data sheets are useful here.
Michael Koblic, Campbell River, BC
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On Friday, September 20, 2013 12:03:50 PM UTC-7, Tim Wescott wrote:

A little late but I would go with 6061 and have the assembly dip brazed. Maybe too costly...
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There are airplanes made of glued aluminum alloy. It's quite a process, but for a model airplane one can use a slow-curing epoxy cured at 180 F.
Clean the surfaces to be glued *very* well, to eliminate all grease and wax, and the surface oxide. I'd use wet/dry sandpaper in windex, or the like. Like real TSP from the paint store.
Beware acetone - most has some oil in it.
Design the assembly do the gluelines are in shear, not peel. Do not expect butt joints to work.
Joe Gwinn
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