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Old 06-24-2017, 03:12 AM   #1
lakeracer69
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Default Dave's cheap sheetmetal brake

Has anyone built one of these? I need to bend up some .025 6061T6 sheet for longish parts. I have a plan to use 4 X 4 X .250 angles for the brake parts. I want to make it around 9 feet long. It looks like he used aluminum MS hinge on his.

I was looking at continuous hinge online and was wondering what size to use. I'm thinking of something steel with a 3/16 pin diameter. Is that overkill? I know even thin stuff is hard to bend without deflection when it's long.

Here is a URL of his brake http://www.biplaneforum.com/pdfs/brakeplans.pdf


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Old 06-24-2017, 04:47 AM   #2
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Just curious. Have you tried a good siding brake? You can rent them inexpensively and I found I can bend my aileron coves pretty well with one (0.016 2024 T3). 0.25 maybe on the outside edge of the lighter duty (0.030) but they seem pretty capable. Heavy duty ones go to 0.040 soft al. Throat depth of 19 inches. Be easier than making a brake.


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Old 06-24-2017, 12:43 PM   #3
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I thought about that. Rental ones are banged out for the most part. Also in my research I found that there is a good deal of deflection as you go towards the center so you don't get the same bend and radius in the center as the ends. Also looks like the material thickness is probably too much for the brake.
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Old 06-24-2017, 03:14 PM   #4
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I checked out the Home Depot ones and they look like new heavy duty brakes. a little more money than the average rental price though, The let me test a scrap piece and it worked pretty nice. just need to plan all my work out to minimize the rental time.....
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Old 06-24-2017, 04:38 PM   #5
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Don't underestimate the force required to do a long bend in aluminum. Deflection in the brake will cause all kinds of problems if trying to do precision bends. If you have access to a commercial shop with a brake, and they will let you work with their guys, do it. A commercial brake like used for duct work will have a sharp die, not what we want for aluminum aircraft parts. It is however, easy to make it work. Cut some strips of aluminum. Bend one of them, move the top die back (they are usually easily adjusted), leave the strip you bent in the brake and bend another around it. Repeat this as needed to increase the radius to what you need. I built a 10' brake out of 6" "I" Beams, to bend the flanges on .040 6061T6. I need to use 3 - 5/8" dia threaded rods to keep the top I beam (die) from flexing up! I ground & filed a nice 1/16" radius on the edge of the I beam flange, and have a stack of 1/16" & 1/8" that I bent to stack up for radius shims to bend bigger radiuses.
If bending a long channel, like an aileron spar, you will find the ends will bend different than the middle because there is no material past the end helping to resist the bend, and because of flex in the brake. That usually will cause the middle to have a slightly bigger radius when done. A bigger radius won't hurt, but it will also mean the overall width of the spar will be different in the middle than at the ends. I took some spar blanks to a well known aircraft kit factory and asked if I could use their heavy duty brake to bend them, the owner said sure, but cut them in half and after bending rivet them together, there is no way to bend that long accurately. Unacceptable!
So back to my shop to experiment, ( because we are building experimentals). Some trial is needed to learn your Brake's "errors" , and you can expect to scrap a spar or two. Part design, Brake flex, and how it's loaded all are variables. Bend a spar and measure it to find the error. With our brake, to bend a 9' spar, we now clamp the part at both ends and pull the center about 1/32" then clamp the center. We are in effect springing the spar, opposite to the error, and to the same dimension, as the brake puts in it, the resultant spar comes out straight and true. We have bent hundreds of accurate spars this way.
Bending Brake Shims.jpg  
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Old 06-24-2017, 04:56 PM   #6
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I get deflection bending a 90 degree full length of .025 2024t3 on my american made 16ga. 48" brake. If you build a brake I recommend building as beefy as you can. If you buy a brake buy a 12 ga. When I want to do some really nice bends I go to my buddy's shop that builds custom Swifts. All his brakes are 12 ga. You can buy a brake on craigslist, build an airplane, then sell the brake and not lose a penny on the tool.
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Old 06-25-2017, 01:18 AM   #7
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Quote:
Originally Posted by garyg View Post
I checked out the Home Depot ones and they look like new heavy duty brakes. a little more money than the average rental price though, The let me test a scrap piece and it worked pretty nice. just need to plan all my work out to minimize the rental time.....

Just take your aluminum to the store and keep "test driving" it
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Old 06-25-2017, 01:29 AM   #8
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Originally Posted by TxSkyBolt View Post
Just take your aluminum to the store and keep "test driving" it
yeah, when it gets to final pieces though it looks way to obvious.....

The good ones are pretty solid tools though. Need to keep under 0.025 to 0.030 soft. I was bending 0.016 2024 T3 (springing stuff needing a huge overbend).

I tried to get a regular shop to bend them (S1-11 aileron coves) but their machines just leave marks on thin sheet metal so I gave up. I figured out to make them using the siding brake and a homemade box for the curve.

Most of the these home built brakes and the cheap smaller Harbor Freight brakes need a lot more than just bolts on the end to keep the clamp metal from bowing on long pieces.
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Old 06-25-2017, 02:18 AM   #9
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They're not long but I've seen some good work come from Harbor Freight brakes. They are like every other tool you buy there. You have to fix or repair it first. I know one guy that built a new leaf with the radius he needed, he also rounded off the original hold down for a more acceptable bend. With the usual 20% off coupon you can walk out of there well under 200 bucks and go home and make airplane parts.
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Old 11-11-2017, 03:01 PM   #10
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Ok, The brake as I built it works fine. I bent an 8 foot piece of .025 6061 T6 with a .125 radius ( with the grain for obvious reasons ) and it came out perfect. I would think .032 would be the limit though for this brake. For a couple of hundred bucks and no headaches from the local HVAC sheetmetal benders I have a very useful brake. I used 1/8 monel blind rivets. Follow the guys directions and you'll have a useful brake too.
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Old 11-11-2017, 03:54 PM   #11
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Now make some ribs so I can see how that process works!


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