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Old 08-12-2017, 06:44 PM   #1
chiru
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Default Fittings bending

Hi all,
I gave my fittings for bending to a specialized company but they used a too small radius. For me that's a No Go for 0.090 thickness.
Do you think there is a way to repair the fittings ? For example by welding the corners or adding some external or internal reinforcement ?
Thank you for your opinion.


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Old 08-12-2017, 08:06 PM   #2
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Well that sucks.
No.
Also, since they used a dead sharp radius if the flat pattern was per plans the hole locations will be off.
Sometimes it's better to make the holes after bending. I know, I know in this world of lasers and water jet cutting those words are herasy, but that approach avoids this sort of discomfort.


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Old 08-12-2017, 08:23 PM   #3
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Are they cracked? Usually they crack at the ends, especially as you did not polish the edges prior to bending, or crack on the outside of the bend somewhere along the length.

By chance is the material 4130A (annealed). There is a bit of that floating around.

Do some research on minimum bend radii for 4130. You may find the material to be more malleable than what is intuitive and the bend radii you have there to be OK.

I'm reluctant to advocate for using them, but I think those fittings may get welded along the bend line anyway upon being attached to the fuselage, so does the bend radius matter that much?

On a personal / human factors note, I find if I put stuff-ups like this aside for a week or more and then pull them out after a cooling off period, the path forward becomes a lot clearer. i.e. no big deal or there's no way I'm putting those on my plane!

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Old 08-12-2017, 08:41 PM   #4
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They are already bent, weld the corners and see. If the outside is welded, it's not going to matter. If they are bolt on I would be more concerned.
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Old 08-12-2017, 09:07 PM   #5
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As an observation I'd like to point out the legs are not equal.
The top picture, the legs are supposed to be the same length.
They bent them wrong.
Put a bolt in it and check if the bolt is parallel with the flat part of the bracket. Shud be. Bettin it ain't.
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Old 08-12-2017, 10:28 PM   #6
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Not just put a bolt thru it, put on the spar and then put the bolt thru it.

I vote start over. Not that I know that much but those look some hard bends waiting to crack. I would assume they would bend new ones on the house.
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Old 08-12-2017, 10:33 PM   #7
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This version is the first with holes done before bending. As I didn't like the result I cut them again and asked for another bending with a larger radius. But they did it wrong again ...
The symmetry oh holes is not a problem as I have one version with no holes.
My concern is about the potential cracks. The radius is below the tolerance, from what I read in several documents. The weld won't go along all corners, that's why I try to find an alternative solution to creating them from scratch third time.
It's the wings and landing gear attachment. I don't want to play with that. If you think the reinforcement welding I suggested doesn't help, I will create them again.
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Old 08-12-2017, 10:44 PM   #8
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The 'official' reason for the lower rear spar fitting AD on the Pitts is that the parts were incorrectly bent and I suspect that means the radius was too small. To my mind there's no point to saving those parts, in the long run it will only be a source of concern for you.
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Old 08-12-2017, 10:45 PM   #9
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I think if you try to do a weld on the inside corner, I am sure the spar will not fit correctly. There is not a lot of extra room on the inside.
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Old 08-12-2017, 10:55 PM   #10
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Ok, thank you for your advices. I will do them again. It's just a mess for bending correctly a 0.090 4130 but there is always a solution.
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Old 08-12-2017, 11:02 PM   #11
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That part is suppose to have a 1/4" radius in the bend.
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Old 08-12-2017, 11:19 PM   #12
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It is possible to make a punch and die that will form the bend from hardwood. The punch will need to be the thickness of the spar plus the spar plates and the wing spar attach straps. You will also need a block that has a cutout in it the width of the punch plus the metal thickness. (Two times the metal thickness in this case.) The bottom of the die can be square cornered. The punch should have the desired radius on the corners and the die will need to have a radius at the top to allow the metal to be drawn down into it without too much starting force. The die will have to be deep enough to hold the finished part to get good form and you should be able to provide enough force with a good bench vise but an arbor press would be better.

This is a bending die I made to form the aileron hinge parts but the idea is the same.

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Old 08-12-2017, 11:57 PM   #13
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Old 08-13-2017, 12:59 AM   #14
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Don't be discouraged. You've got a good looking project and you are getting to the most rewarding part.
It can be expensive, frustrating and time consuming trying to get non aviation folks to understand our standards and why we must adhere to them.
You can bend metals tighter than the recommended bend radius...sometimes without cracks. But their physical properties (strength, fatigue life) will be diminished.
You can't trust your life to something like that or compromise your project by using it.
I bent all of my steel in a simple break with the correct bend radius and performed the final trim and drilling after.
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Old 08-13-2017, 01:23 AM   #15
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Default Bent parts

Looks like they used the wrong punch ( male die on a press brake ) . Did you give them specs for the bends ? On the holes matching after bending , I'd opt for 1 hole then drill the other after its bent .
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Old 08-13-2017, 01:49 AM   #16
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It is much easier to make new fittings now than after they are welded on and you decide you are not happy with them or are worried about their airworthiness !

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Old 08-14-2017, 01:44 AM   #17
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Christian,
It takes so long to build these biplanes i forget how i bent the fittings but here is a post where i tack welded the fittings in assembly with the wings rigged.
http://www.biplaneforum.com/showpost...57&postcount=8
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Old 09-11-2017, 07:23 PM   #18
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Same problem, different piece. The rudder horn was also bent with a too small radius. As I have several pieces, I tried to weld one in the corners.
As there is no direct load on the bend I think that could work. Any thoughts ?
Thanks
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Old 09-11-2017, 11:41 PM   #19
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Mine were just welded on, much simpler than bending.
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Old 09-12-2017, 12:13 AM   #20
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Your pieces have been "bottom" bent or have been "coined".

Remake your flat patterns and take them to someone who has an "air bender", more commonly called a press brake, which has a vee-shaped bottom die. A good metal fabricating company can take your radius, degree of bend, and material type and give you correctly formed parts.

This is not rocket science. Your current fabricator is using the wrong bending process... the pieces need to be air-bent.

The male "punch" should have an end radius no smaller than the minimum recommended bending radius for your material (you can easily find that in charts on the web). The punch radius does not need to match your inside radius... in fact, it will correctly be quite a bit smaller.

The vee opening of the female "die" is calculated as follows:

(inside radius X .7071) X 4.85 = Vee opening.

I.e., (0.20" X .7071) X 4.85 = V
0.1414 X 4.85 = 0.69" Vee opening.

You may find this, and much more information about bending, by googleing "content by steve benson fabricator.com"



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