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Form blocks for the wing spars?????

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  • Form blocks for the wing spars?????

    Well while driving home from work my mind was on building, as usual. I came up with and idea that im just not sure about and wanted to ask people with more experience. Since 8’ metal breaks are hard to come by and way to expensive to buy, I started wondering if a person could make some form blocks out of MDF, radius the edges, and coat them with PC wood petrifier to make the spars. Now im not suggesting clamping the metal between the two blocks and hammering the edges over because I wouldn’t want to cause any undue stress to the spars but what I would do is to make a way to press the form block and metal in between two other boards that were spaced correctly to bend the flanges over the form block. Any thoughts?

  • #2
    Builders have created home-made brakes with varying degrees of success. You need a lot of rigidity to keep the bend straight. A steel brake that big will usually weigh over 1000 pounds.

    In the context of how much r&d you'll have to do, and how much aluminum you will go through in testing, it may well be worth a day's drive to borrow time a brake.
    Last edited by jaredyates; 07-05-2019, 12:03 PM.

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    • #3
      At one time I owned an 8 foot leaf brake that I did aluminum race car chassis on. It worked well. When it came to doing my spars, I found a shop in Indianapolis that had a big press brake. That was way more accurate than my leaf brake and the radius is exact. Also, the spars are the only job that requires that big a brake. I still have a 4 foot finger brakes and a 4 foot press brake.

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      • #4
        I made a brake using steel angles. Roughly followed a design from the Zenith forums. Used it on my .032 LSA spar webs with good results. Look in my thread John's LSA build for a few pictures.

        Google "Dave Clay bending brake" and you'll be able to see several variations. It was even featured in Sport Aviation several years ago.

        Good luck.

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        • #5
          Sounds like a press break is the way to go. Thanks for the replies fellas!

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          • #6
            Originally posted by Cameron Ramsey View Post
            Well while driving home from work my mind was on building, as usual. I came up with and idea that im just not sure about and wanted to ask people with more experience. Since 8’ metal breaks are hard to come by and way to expensive to buy, I started wondering if a person could make some form blocks out of MDF, radius the edges, and coat them with PC wood petrifier to make the spars. Now im not suggesting clamping the metal between the two blocks and hammering the edges over because I wouldn’t want to cause any undue stress to the spars but what I would do is to make a way to press the form block and metal in between two other boards that were spaced correctly to bend the flanges over the form block. Any thoughts?
            I have access to a brake so I'm not doing what follows .....but the thought has crossed my mind...

            i call it slam forming.....spar material sandwiched between 1 inch plywood with flange area sticking out.....the lip/flange of the spar is resting on another piece of plywood same length.....you drive up on the the wood with your car...forcing the whole edge down and formed in one fast slam form....

            was thinking of using a hot parking lot to put temp nails to hold the wood edges close....the drive the family car onto the spar sandwich.....

            patent pending...lol...
            Last edited by way_up_north; 11-13-2020, 10:53 PM.

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            • #7
              Well that was kinda the idea I had. I want the spars to be perfect.....cause.....they’re kind of important and I want this plane to last a long time. I just thought that a form block would make each spar the same instead of taking a chance of not lining one up on a break perfectly. Thanks for the information though.

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              • #8
                "the slam brake" I swear Ive seen my dad do stuff like that when I was a kid ! :-)

                Here is a variation on that idea--- Pieces of 3/4 ply -- double them so 1.5 thick. Use the wood hardener. Make a male and female half.
                Set up a couple of roller skate type conveyor tables. Make a steel wheel with a thick rubber "tire" a little wider than the dies. Put the wheel
                above the conveyor with some 1 inch threaded rod. It would be like a rolling mill. Have a gearmotor on the wheel. Make a pass from one end to the other
                as the dies roll--- move the wheel down about 1/16 on each pass--- back and forth---- at some point it should bottom out.

                Only problem is you would be left with bends that may not be bent quite enough. The finished angles would be hard to control/predict.
                would be like roll forming except without steel dies...….

                Im going with a press brake--- I think it is much more uniform than a leaf job. I think this might be the only critical bending on the whole plane.
                (IMHO)

                Tim

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                • #9
                  Thanks for the reply. I believe a press break is the way to go as well

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                  • #10
                    I'm presently sitting in my hanger designing 120" brake and when I'm done it will weigh around 1,000 lb. Not quite but it will be a piece of furniture forever in my hanger. And this exact idea that is mentioned in this thread came to my mind why not use form blocks to flange the spar? The more time you take and less force you use to bend this metal is the way to go. T3 is representative of a tempering process used to increase the tensile strength of the metal. I have to think more about this I know a materials engineer that I can consult.

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                    • #11
                      I did follow up on the forum block with a materials P.Eng. He advised it makes no difference to the material how it gets formed. It will simply crack if you screw it up. It is 2024-T3
                      However a friend who is an HVAC tech advised, & I quote "Good Luck Keeping The Spar Straight" It is easier to simply use a Brake. At the end of the day it is just money :-)

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                      • #12
                        Here is a press brake I made years ago to form wing skins for race cars. The skins are usually 6061T6 .032 thick because of they abuse they take on the front and low to the ground. The bottom of the brake is moved with bottle jacks I can set dial indicators to measure how far I move the bottom of the press to assure an accurate bend and to assure that the bend is even. This particular brake is only 4 ft. but it could be expanded to any length. The die part of the brake is adjustable and made from 2" square 1/4 inch wall tubing. The radius on the working edge has been polished.

                        I made something like this press out of wood to form the leading edges of my wing skins. I felt that is was important to have the wing skins drape over the ribs and not use the ribs to form the skins.
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                        Last edited by S Lathrop; 11-22-2020, 09:55 AM.

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                        • Sir Newton
                          Sir Newton commented
                          Editing a comment
                          Nice job 👍. Your brake is heavy duty. I have a fairly simple leaf brake in mind. Every spar has lightening holes in them. This fact solves the requirement of a heavy foot on the design. The plan is to use 1/2 bolts to secure the foot & material in place. I am hoping to get away with 3x3x1/4" angle for the leaf. We will see how it works soon enough.
                          Last edited by Sir Newton; 11-22-2020, 11:01 AM. Reason: Spelling as usual

                        • S Lathrop
                          S Lathrop commented
                          Editing a comment
                          I am going to double down on my suggestion about bending your spars on a press brake. Yes a leaf brake will get the job done but it will be slightly less precise. I just can not see that forming the spars over a forming block will give the accuracy that you need. One big issue with bending over form blocks is that it is nearly impossible to keep from stretching sections of the flange that you bend. When you release the part from the form block you will not have an edge close to as straight as the block.
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