Radius Braking

I need to bend some .125 5052. It doesn't have to be a sharp bend, but I do need a net of 90 degrees. If I tried to brake it to 90 on the brake with
the standard apx(0) radius it will tear. 45 is about as far as it will bend easily. I have not been very happy in the past with two close 45 degree bends. It seems to harden further back then you would expect.
I was thinking of trying about a 1/2" radius by:
Cutting a wide notch in some 1/2" black iron pipe (apx 1" OD give or take). Slip the pipe over the ends of the fingers. Adjust clamping force and distance. Adjusting the fingers on my brake back so that the edge of the bending part (table? apron?) + .125 is tangential with the leading face of the pipe when all is clamped down. Bend (with some help) to 90+ in one continuous motion.
I was figuring a light coat of oil on the bottom face of the aluminum sheet to help it slide against the apron.
Has anybody tried it? Will my pipe finger caps just go flying?
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wrote:

You might want to read http://www.thefabricator.com/article/bending/bending-basics-the-fundamentals-of-heavy-bending It has some information on for bending radius that might be of interest.
Admittedly it has been a long time since I actually bent aluminum plate but as I remember it for thick aluminum plate we usually tried to anneal the bend line - smoke the area with an oxy-acet torch set very rich then lean out torch and carefully burn the soot off the plate.
The bend radius was set by adjusting the distance from the edge of the Brake's clamping plate to the bending plate. I'm not sure for thick plate but we certainly bent 1/8"sheets using a conventional sheetmetal brake without any additional bits and pieces.
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John B.
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Bob La Londe wrote:

I put a fairly sharp 90 degree bend in 1/8" aluminum. I used to try to anneal either 6061 or 5052. There is a grade of 5052 that is bendable at 1/8" thickness, but even if it sits around too long, it hardens and then you get tears when you try to bend it. So, I do all this bent stuff in 3003. That is a lot softer, so may not be desirable, depending on how the part is used. But, the 3003 bends VERY nicely, with essentially no inside radius, at 1/8" thickness.
Jon
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On 4/05/2016 11:09 AM, Bob La Londe wrote:

If you have some thinner material around less prone to cracking, make some 'wrappers'. Cut strips maybe 2" wide, a bit longer than your bend. Bend back tight against the upper fingers. You now have a larger radius. May not take much extra radius to get a crack free bend. Also try to avoid bending parallel to material grain.
Jon
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THAT is a clever idea.
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Yeah... that is, actually!
I have a finger brake, because I do a good deal of 'box' work. But I have occasion to do radiused work. Hmmmm....
The idea of bending 'stuff' to a new radius works. But I think I can machine "radius noses" for my brake fingers, also.
Lloyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

I can certainly do that, but I want to keep all my fingers. I thought about making a second set, but I am jealous of time spent on fiddley stuff and of burning thru stock to do it. Pipe is cheap, which is where my original idea came from. Still it would take a little time. Throwing a piece of smaller stock on and using it to make a radius uses minimal stock and minimal time. If a larger radius is need I can just back up the fingers a smidgeon and wrap a second one around the first. There are usually plenty of pieces of .0625 (which brakes nicely) in the drops at my local metal vendor.
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Ahh... nah... I'm talking about little add-on tips to my existing fingers that could be secured (at worst) with a set-screw into the TOP surface of a finger.
I don't want to have to make all-new fingers for my brake, either! Too much work for too little return.
Lloyd
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Bob La Londe wrote:

You can even do this with heavy card stock, like they make posters out of.
Jon
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On 5/05/2016 8:20 AM, Bob La Londe wrote:

Credit that one to my college work experience classes at NASA Ames. Hardly anyone ever using the finger brakes, but we were taught how. One class project was an aircraft sheetmetal style box. Press brakes were constantly in use, so I did mine on the finger brake. Was a touch out of tolerance in a few places, but got points for getting as close as I did on the brake. About .015 out on a couple bends IIRC...
Jon
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    Since you don't mention this, I'm not sure whether you already know, but aluminum sheet has a "grain" resulting from the rolling which formed it. If you bend in parallel with the grain it will tear a lot sooner than if you bend at a 90 degree angle to the grain.
    I don't know whether this will make enough difference for what you are trying to do. You are working with thicker aluminum than my brake can handle. :-)
    There is also the trick of annealing it (you don't mention the temper). You don't mention what temper you have, but if it is anything other than the fully-annealed state, you can improve the bendability by (assuming you have an oxy-acetylene torch) first putting a deposit of soot along the intended bending line with just the acetylene flame, and then bring up the oxygen and move along the seam heating it until the soot goes away. At this point, it should be about as bendable as you can get for that alloy. Bend it soon, because the aluminum re-hardens (though not fully) with time. Again, I don't know whether this will make enough difference or not.

    Hmm ... I think that the pipe would crush on the part under the fingers.
    If you're going to do this more than once, I would suggest making an alternate set of fingers with the radius machined into the tips. (Likely with a radius end mill.)

    Oil -- or a wax, perhaps that which is used as a bandsaw lube.

    I'm more worried about the radius being crushed out of them on the first close
    Just my thoughts above.
    Good luck,         DoN.
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