On Fri, 20 Sep 2013 12:36:51 -0700, anorton wrote:

"Tim Wescott" wrote in message
...
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 http://www.wescottdesign.com


Epoxy looses a lot of its strength and toughness if it is queezed into
too small a gap. It also delaminates with changes in temperature more
easily. I think what you ideally want for this applications is one of
the Loctite 6XX series of retaining compounds. Mcmaster sells them in
small sizes. They have them for different gap sizes and temperature
ranges etc. Once you bond cylindrical parts with these, they do not
come apart.

In other applications, epoxy peel strength on anodized (or naturally
oxidized) aluminum is not very high unless it has been roughened or
etched.

So, 603 or 609, or maybe 620 if what I'm considering counts as "high
temperature"?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com