"Fabio Berutti" wrote in
:

IMHO aluminum is too weak and it's not so easy to work 'cause it is
too soft and bends and sticks to the tools. Steel is too hard,
particularly stainless... a guy here in Milan made a 6550 PP amp out
of a large rectangular (reversed) oven pan, some 4-5 mm of AISI304. I
suppose it's .. well .. robust.
I'd say that copper is the best of all in terms of ease of machining:
just remember to paint it with a protective transparent lacquer as
soon as You finish polishing it with sandpaper, or it will get brown
in a wink. A further advantage of a 3mm copper plate is that it IS
definitely a ground reference, at least for a power amp.

Ciao

Fabio
Aluminium comes in a number of different grades. Some varieties (like
the type used to some cheap sheet ali) indeed are weak and are nasty to
machine (kinda like cheese). Extrusions tend to be made of better stuff
(though it would pay to check with your supplier as to what you are
getting - there is a 4 digit number that applies to ali which defines
its characteristics). I love it for chassis making!. You can anodise it
all sorts of nice colours.
http://homepages.kcbbs.gen.nz/moby/6A3.jpg
M