On Thu, 22 Mar 2012 11:38:15 -0500, Tim Wescott
wrote:

On Wed, 21 Mar 2012 22:10:34 -0700, PrecisionmachinisT wrote:

"Tim Wescott" wrote in message
...
On Wed, 21 Mar 2012 17:57:10 -0700, runcyclexcski wrote:

On Mar 21, 7:06 pm, Tim Wescott wrote:
On Wed, 21 Mar 2012 15:59:46 -0700, PrecisionmachinisT wrote:
"Tim Wescott" wrote in message
...
On Wed, 21 Mar 2012 15:28:34 -0700, PrecisionmachinisT wrote:

"Tim Wescott" wrote in message
...
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.

"Structural" is generally 6061 and it has an inside fillet
whereas "architectural" is generally 6063 and has sharp corner.

That said, your problem probably isn't going to be finding it
with sharp corners, rather, it's going to be finding it in your
desired (1/4) in wall thickness.

Suggest try this link you just might just find something...

http://tinyurl.com/6vwjdzj

I should re-do my thermal analysis. (I.e., something more thorough
than "use what's already there"). 1/8" may be thick enough.

Additional mass does not increase thermal radiation capacity, it
only increases the amount of TIME that it takes for the unit reach
thermal equilibrium--which is only appropriate for something that
has a rigid duty cycle...otherwise you're only asking for trouble.

If you want to INCREASE BTUH CAPACITY, then either increase airflow
or increase the total amount of surface area by milling grooves or
by adding fins.

In this case the mount/heatsink's job is to carry heat from the board
to the frame of the machine. Extra thickness would, indeed, carry
that heat from the board to the mounting flange more effectively --
but I don't think that is the worst offender in the temperature-drop
sweepstakes.

--
My liberal friends think I'm a conservative kook. My conservative
friends think I'm a liberal kook. Why am I not happy that they have
found common ground?

Tim Wescott, Communications, Control, Circuits &
Softwarehttp://www.wescottdesign.com

Does the heat sink have fins? you did not seem to mention fins in the
OP. When I had to custom make heat sinks I got a bunch of roughly
matching ones (1x1 seems like a popular size) and shaved them down to
my desired size with a grinding mill (using a regular mill bends the
fins all over the place). heat sinks usually have square corners.
Digikey as you probably know has all sorts of heat sinks. I got my
batch off ebay for dirt cheap, probably from a hi tech company
liquidation.

No fins. It's really a "heat conductor", or perhaps just a thick
bracket that conveys heat. I don't know what you might call it -- but
it's not a device to better match the thermal impedance of a solid with
the thermal impedance of the air.


"heat spreader" is the engineering name I've seen occasionally applied
to parts having that function...

I'm too busy to dink around with new projects for the foreseeable future
but you might want to ask Eric for a ballpark quote...simply make from a
solid bar...

Thanks. "Heat spreader" is, indeed a term that I remember now that
you've joggled my memory.

Tim, take a look at this:

http://www.midamericaextrusions.com/...ock-shapes.pdf

Look at "Angle Unequal Legs–Square Corners," page 14

--
Ed Huntress