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 & Software
http://www.wescottdesign.com