I gluing 2 pieces of metal together there a 3 things to remember;

#1 surface area
If you can use a 1" sq plate with a hole in the corner instead of the
standoff it will have 20 times the glue joint area.

#2 tooth
Rough up the joint surface with 80 grit sandpaper, it increases the
surface area and randomizes the shear angle so it will not pop off easily.

#3 Chemical coupling
Epoxies work best when they are able to chemically bond with the metal.
This is tough on aluminum because the oxide surface on aluminum is almost
completely inert and will form immediately on exposure to air. The solution
is to put a drop of epoxy on the area to be glued and rough the surface of
both pieces to be glued with sand paper through the epoxy. This protects the
surface from exposure to air. Then, wipe off the dirty with epoxy with a DRY
paper towel and apply some fresh clean epoxy and bond as usual.

Paul K. Dickman

Dave Marsh wrote in message ...
Hi,

I need to space off a PCB by 0.25" behind a small (4" x 1" x 0.06" thick)
anodized aluminum front panel for an electronics project. The PCB contains
the push buttons that protrude through holes in the front panel.

The PCB has M3 holes drilled for fastening purposes but I can't put holes
in
the front panel for appearance sake. I need to fasten the PCB strongly
enough so there is no danger of it coming loose when the user presses one
of
the buttons.

My idea so far is to glue 4 metal hex spacers to the back of the aluminum
panel. I can then bolt the PCB to that. Alternaitevely the same kind of
idea
but glue the flat heads of 4 countersunk M3 screws to the panel instead
(I'm
thinking the contact are of a screwhead will be greater than that of a hex
spacer with its central thread hole).

The hex spacers are made of nickel-plated brass. The screws could be zinc
plated or stainless steel.

So far I've tried an epoxy ("plastic steel" by Draper) with the hex
spacers.
Initially it seemed ok, but with a small amount of leverage the spacers
came
away.

Could someone please suggest whether I would get better adhesion on the
anodized aluminum with the zinc screws, stainless steel screws or the
nickel-plated hex spacers? What epoxies would you recommend? I've also been
advised that curing the epoxy will improve the adhesion - does this make a
big difference?

Many thanks,

Dave