Aluminum Angle

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 are:
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.
Reply to
Tim Wescott
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One of my suppliers:
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Yarde usually stocks the stuff shown in those pages. There's a downloadable pdf catalog somewhere on the site that shows more products, but not everything in it is stocked.
Reply to
Ned Simmons
For an application like that, note the variation in thermal conductivity for different grades and hardnesses of aluminum. 2024 T4 is around 120 W/m-K. 1199-O is twice that: 240 W/m-K.
I found out about the hardness/temper issue the hard way, semi-annealing a piece of 2024 to almost double its conductivity, only to find it drop back to the original value a couple of weeks later.
Reply to
Ed Huntress
Tim Wescott fired this volley in news:wOGdnZbV7Yqok_fSnZ2dnUVZ snipped-for-privacy@web-ster.com:
Tim, Have you checked smallparts.com? Most big-box home improvement centers and ACE hardware carry a good selection of aluminum angles, some with unequal legs.
I just bought 4' of 4"x4"x1/2" aluminum channel from MSC. They carry other sizes, but few with unequal legs.
On the MSC metal, the INSIDE corners (all) are rounded (ends of the legs as well as the crotch), but the outside corners are all square.
4x4x1/2" should be big enough for your little TO-220 sink, yes?
LLoyd
Reply to
Lloyd E. Sponenburgh
I'll take a look. It really needs to be something that's commonly available for machine shops, though, and for the entire life of the product -- I'm going to be specifying this to the manufacturer for whom I am designing the board; I'm sure they'd rather not have to send out a guy to dig through the racks at Home Depot for something that might disappear at any moment over the next ten years or so.
Reply to
Tim Wescott
Fortunately the thermal design is way over-specified -- but thank you for the reminder; I'll make sure to take hardness (and self-hardening) into account.
I was kind of thinking that hard enough for easy machining, but no harder, was what I wanted -- now I just need to make sure to pick an alloy that _stays_ that way.
Reply to
Tim Wescott
Rounded corners generally means that the stuff is extruded, you have to go to machined billets to get squared corners. And they're irrelevant either way for the heat sink function. The extruded hardware store stock will machine like bubble gum, from experience. The critical parameters for heat sinks are the surface area and heat conductivity. You probably won't get the last with any material from a mechanical supplier. There are heat sinks and extruded heat sink stock available from just about any electronic supplier, with mechanical AND thermal parameters. By the time you finish messing about with mechanical stock, you could have had the job done using the real deal. That's if you're doing a real job for real people and real money. If not, carry on...
Stan
Reply to
Stanley Schaefer
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
Reply to
Paul Drahn
Tim Wescott fired this volley in news:wOGdnZPV7YpZg_fSnZ2dnUVZ snipped-for-privacy@web-ster.com:
In that case, check with Macklenburg-Duncan, who makes all sorts of "standard" aluminum extrusions for consumer sales. Often as not, it's M-D aluminum you'll find in those big-box racks.
LLoyd
Reply to
Lloyd E. Sponenburgh
The common square corner angle (and tubing) is extruded 6063 and the stuff that looks like hot rolled steel angle is more often extruded 6061. But extruded in both cases.
Reply to
Ned Simmons
Well, real people, real money, and a quite real expectation that the board is going to bolt on in place of the one that it replaces -- and their heat sink is also their mounting flange.
So yes, I could put a stock heat sink in there and inform the customer that all they have to do is rework any unit that comes in from the field needing a replacement board -- but I don't want to do that.
Reply to
Tim Wescott
My requirements are not severe, thankfully.
Reply to
Tim Wescott
"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...
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Reply to
PrecisionmachinisT
I should re-do my thermal analysis. (I.e., something more thorough than "use what's already there"). 1/8" may be thick enough.
Reply to
Tim Wescott
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.=20
Reply to
PrecisionmachinisT
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.
Reply to
Tim Wescott
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.
Reply to
runcyclexcski
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
Reply to
etpm
For low /medium quantity volume production it may be cheaper in the long = run to just buy 1x1 square stock--cut away excess, drill / tap....flip = over, drill / tap / partoff into individual pieces.
Reply to
PrecisionmachinisT
just buy 1x1 square stock--cut away excess, drill / tap....flip over, drill / tap / partoff into individual pieces. He's looking for 1.5 x 1 x 1/4. If the parts aren't much more than 6 inches long then rectangular stock could be turned into angle as you suggest. And it would be fast. Modern carbide cutters for aluminum remove material in a hurry. Eric
Reply to
etpm

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