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.
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wrote:

One of my suppliers: http://www.yarde.com/products.html https://www.yarde.com/catalog/class1struc.html https://www.yarde.com/catalog/cat48.html
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.
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wrote:

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.
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On Wed, 21 Mar 2012 14:04:08 -0400, Ed Huntress wrote:

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.
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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
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On Wed, 21 Mar 2012 13:05:05 -0500, Lloyd E. Sponenburgh wrote:

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.
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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
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On 3/21/2012 1:32 PM, Tim Wescott wrote:

You might look here: http://www.mdteam.com/index.php/products/aluminum-shapes-a-metal-sheets Macklanburg Duncan makes these aluminum extrusions and should be readily available through most lumber yards and box stores.
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That was already suggested to him a week ago... no bite. Odd, that, because MD makes a whole line of very standardized extrusions you've been able to buy since the early 1960's with no changes in the line.
Lloyd
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You should go to Hadco Metals to see what is/is not standard.
Architectural is sharp-cornered, structural is round-cornered. The heaviest in architectural is 3x3x1/4. If you need 4x4x1/2, AND you need a sharp corner, I don't think a machine shop would charge too much to square the inside/outside corners of structural.
And for what MSC/HD charge, you could get whole lengths from Hadco or other alum suppliers. PSC in PA will cut and ship UPS, nice people.
Btw, 4x4x1/2 is really hefty stuff. I've got 2.5x2.5x1/4 structural, and DATS hefty!!
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I have a machine shop, and I needed only 4' of the heavy angle, and the next morning.
Since I live in the boonies, not near any major cities, MSC was the supplier of choice. In truth, they were only about 20% more expensive than most on-line suppliers, once you figure shipping (which was a flat $8.95).
But the OP who asked the question didn't need anything that stout; I was ribbin' him about whether or not 4x4x1/2 would be big enough to heatsink one TO-220 transistor or regulator.
For standard architechtural shapes in small sizes, MD is the way to go.
LLoyd
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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
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On Wed, 21 Mar 2012 11:44:40 -0700 (PDT), Stanley Schaefer

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.
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On Wed, 21 Mar 2012 11:44:40 -0700, Stanley Schaefer wrote:

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.
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On 3/21/2012 10:21 AM, Tim Wescott wrote:

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
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On Wed, 21 Mar 2012 11:59:34 -0700, Paul Drahn wrote:

My requirements are not severe, thankfully.
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"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
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On Wed, 21 Mar 2012 15:28:34 -0700, PrecisionmachinisT wrote:

I should re-do my thermal analysis. (I.e., something more thorough than "use what's already there"). 1/8" may be thick enough.
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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.
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On Wed, 21 Mar 2012 15:59:46 -0700, PrecisionmachinisT wrote:

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.
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