Barry,
  Yes, aluminum gets an oxide film  after sanding or any
other cutting operation.  However, epoxy should bond to the oxide just
as well as to bare metal, perhaps better.
  ALL surfaces in an ordinary ambient (room temperature) are covered
with a layer of water from 1 to several molecules thick.  One of the
rules for making an adhesive work is that it is necessary for the
adhesive to wet the surfaces.  Epoxy and water don't mix and so epoxy
will not wet a wet surface.
  Chris Chapman's recent discussion on this net suggests ways of
improving adhesion.  Raising the temperature can do a pretty good 
job of reducing the adsorbed water layer.
Bob Barns


barry lotz wrote:
> 
> Sean Thomas
>    2¢   I have not been running my  SMT8 style verticals for very  long so the
> hinge contition has not had adequate history. I use an additional brass clamp
> ~.125" from the hinge(just enough to allow clearance from the perpendicular
> clamp. The hope was that it would take most of the tension. Aluminum has an
> oxide coating at the surface (which makes it hard to weld in an air
> environment). Could this maybe contribute to the bond issue. From what I've
> heard, if one sands aluminum that the oxide forms almost immediately.
> Regards
> Barry
> 
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