On Wed, 21 Mar 2012 12:21:57 -0500, Tim Wescott
wrote:

So, for my day job I'm working on a circuit board design to replace
something which features a heatsink made from aluminum angle. It's 1" x
1" x 1/4", with nice square corners everywhere (radius 0.02").

Up to now I've been blithely assuming that this is an off-the-shelf item
that I can get anywhere -- but it looks like it may be harder to get than
that. Worse, I'd really like to extend the heat sink another 1/2" or
even 1" under the board, while keeping the outside leg at 1".

So I want to specify something that won't have their mechanical engineers
muttering under their breath _too_ much about @#$% EEs with time on their
hands...

McMaster carries aluminum angle, but it describes the inside corner and
the inside ends of the legs as "rounded", without saying what the radius
is. I can handle a radius on the inside corner, but that radius on the
leg takes away from area that I want touching my board. Furthermore,
McMaster only carries angle with even-length sides.

So my questions a

Is there any commonly-available aluminum angle that has corners that one
wouldn't describe as "rounded"? From who?

If I must go with rounded corners, can I expect that there is a
standard? What is it? Is there a place I might find it on the web?
(Machinery's Handbook doesn't seem to list anything like that).

Is there any commonly-available aluminum angle with uneven leg lengths?
I'm specifically looking for 1" x 1.5" x 1/4", or 1" x 2" x 1/4". From
who?

Any notion of how much it might cost to have a machine shop take a larger
angle and whack it down? These need machining anyway: they have to be
cut to length, then drilled on both webs and tapped on one -- so it would
be a case of "while it's in the machine anyway, make one or two
additional cuts". Precision is nearly nonexistent: +/- 0.05" would be
fine, and finish wouldn't be a huge issue: as long as the edges are
deburred and the cut side isn't so rough that it draws blood when handled
things would be fine; I would expect that a decent shop with even a
minimal sense of pride would insist on a much better finish than
necessary to get the job done.
When I've needed sharp cornered aluminum angle in the past I've
ordered "architectural" angle. It looks like you may need to order 2x2
in order to get the 1/4 thickness. And the alloy is 6063T52. If I was
cutting the angle shorter I would probably use a 3" dia. slotting saw
blade in the mill and spin it really fast. That would leave a good
finish, be accurate, and be fast.
Eric