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


"Tim Wescott" wrote in message
m...
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.

Good post!


"The socialist movement takes great pains to circulate frequently new labels for its ideally constructed state.
Each worn-out label is replaced by another which raises hopes of an ultimate solution of the insoluble basic
problem of Socialism, until it becomes obvious that nothing has been changed but the name.
The most recent slogan is "State Capitalism."[Fascism] It is not commonly realized that this covers nothing more
than what used to be called Planned Economy and State Socialism, and that State Capitalism, Planned Economy,
and State Socialism diverge only in non-essentials from the "classic" ideal of egalitarian Socialism. - Ludwig von Mises (1922)