You are right but there is one other very important issue here ... age is
also a big factor in bond line strength. If you test your three samples in
three years time you will see different results. Some of the effects of poor
surface preparation don't show up for years. In other words you can prepare
samples in different ways now and test them and get similar shear and peel
strengths. If you test those same samples in three years you could see that
one has lost a lot of its strength and the other has retained most if not
all.

A very complex issue and no something that can be encapsulated in a simple
posting. Best to follow established process specifications. Companies like
Locktite (who now sell Hysol adhesives) have data sheets on their web sites
that you can download. Just get them and follow them with a lot of care.


"Ron Webb" wrote in message
...

2. Next there is the issue of surface preparation. If the plans say
prepare
by running with 80 grid paper then it is fairly clear that the guy who
wrote
the plans knows little about what he is doing ! Epoxy metal bonding is
reliable if the surfaces are prepared properly but from what you have
said
I
doubt that is the case.

I recently did some testing with West Systems and aluminum. I used 3 test
strips, side by side. 1" wide fiberglass tape, 3 inches of bonding
surface
on 6061.

The first strip was applied with no surface impression at all.
The second strip was applied after sanding with 80 Grit
The third was sanded and etched with an etch (Duramix 4925)

The first strip came off with maybe a pound of force, pulling on the end
of
the fiberglass tape.
The second strip (sanded) took maybe twice that - it still came right off
The third (etched) strip never did come off, I tore the fiberglass tape It
stood up to at least 30 pounds in shear!

Surface preparation makes a BIG difference!.