On 3/21/2012 10:21 AM, 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.

Several years ago a former customer was modernizing the design of his
product and the new design required a heat sink. I researched heatsinks
and found a company that would make any designed heatsink and in any
quantity. They also had lots of information on their web site relating
to the type of aluminum used for heat sinking. It's not off-the-shelf
aluminum.

The customer began to realize the cost of updating his product and just
killed the whole product. So, other than machining a prototype of his
heatsink, I never went any further.

I don't know if the heatsink company is still in business or not.

Guess your heatsink needs to fit the heat produces and dissipation
requirements and possibly it's low enough that common extruded would
work. You can always shorten one side of an angle.

Paul