Sorry, I should have been more precise: when I speak about "machining" I
mean using the (mostly hand) tools I have (like most hobbysts): drill, cup
saw, conic drill bits to enlarge holes, jigsaw, files of any kind,
grinder... I never used a puncher. I usually make even the trapezoid holes
for mains plugs starting from a drill hole and working it out to shape with
a file: it's an hobby, after all, and the more time consuming, the better.
I did not mean that copper is a good material to be worked with industrial
tools, but I suppose this was not the scope of the thread... I happen to
have some friends working in some big factories, producing pressure vessels
and heat exchange equipments for refineries, but I never managed to get
access to the tubesheet drilling machine to "speed up" my hobby.

As per the ground reference: I did it in 2 or 3 units, welding the "grounds"
of the circuits to the points of the strips that were in turn bolted to the
frame plate. I do not understand why a bus wire should be a better "zero"
(ie. lower internal resistance) than a 3 mm thick plate, 12" wide by 16"
deep. (Obviously the abovementioned units were all power amps, I never did
this with phono stages..)

Ciao

Fabio



"Tim Williams" ha scritto nel messaggio
...
"Fabio Berutti" wrote in message
...
IMHO aluminum is too weak

Which is why you use thicker pieces. And as a matter of fact, 7075-T6 is
as
strong as 1018 cold rolled (and 2.7 times stronger and stiffer by weight).

and bends and sticks to the tools.

They sell WD-40, y'know... it's not just for displacing water anymore!
(No,
it never was, and never will be, a spray lubricant!)

Steel is too hard, particularly stainless...

They also sell this new wonder metal known as High Speed Steel.

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.

Nice.

I'd say that copper is the best of all in terms of ease of machining:

Gack choke sputter!!! Pure copper is about the gummiest thing you can
find.
(They say razor sharp tooling and milk for cutting fluid is the best you
can
do.) Copper alloys like brass and bronze generally machine well, but are
too "slippery" (hence their use in bearings) to cut with anything but the
sharpest tools.

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.

Or green, or blue. Unless you want that. In which case, toss it in your
litterbox for a week.

A further advantage of a 3mm copper plate is that it IS definitely a
ground
reference, at least for a power amp.

Not that using the chassis for grounding (unless done very carefully) is
ever a good idea, of course. This I know from personal experience...

Tim

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