Hi everyone,I'm plans building a 750 and at the point of making flaperon spars.I built a 9 foot brake out of solid birch and piano hinge.The brake is very strong and dead straight.I clamped in the blank and bent the flanges as per plans,the only problem is when I removed the part it looked like a banana!All I did to fix it was put some small crimps in the flange but I don't feel comfortable doing this.I then tried again but this time I made a form block the correct size and formed using a mallet just like the ribs.Once again the spar looked the same.Anyone have any suggestions?

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Comment by Travis Corbin on October 13, 2009 at 8:37pm
Hi Dwayne. I'm one of 6 friends plans-building 750's in Lethbridge. Looking forward to having another 750 in Alberta skies. Cheers.
Comment by Robert Haines on July 25, 2009 at 10:58am

I too built a piano hinge break for my scratch building project. A friend of mine owns a commercial HVAC shop so I was also able to try his 8' break and 8' press brake. If bending long thin strips, I ended up with a curve on any of the breaks I used.

What I did find that also worked (I'm respectfully supplementing Ron Lendon's post) is to leave the material wide and then cut the angle off. If I need to make a batch of 4' x 3/4" x 3/4" L's for example, I'll start with a 4' x 16" piece, bend one or both sides, and rip off the 3/4" edge. Then repeat.
Comment by Ron Lendon on July 7, 2009 at 9:05pm

Bending metal always requires what I call qualifying. Here is the process I use for a 90 degree bend on a long strip.

1st. Over bend so the center area (middle of the length) is close or just over 90 degrees.

2nd. Open the bend using tools, dead blow hammer that won't mar the surface, and a piece of round stock inside the bend (presently using 1.875" PVC about 18" long)

3rd. Start at the ends and hold the part over the PVC and hit it with the hammer to open the bend. Check the angle every 1" and work the piece to get it correct.

4th. If you need to close it back up, just hold the flange down against the workbench and strike the other flange with the hammer where you need to move the metal.

Some the this adjustment/qualifying can be done with your hands also, wear gloves. Check often and get the angle correct first, you will find the banana shape will disappear when the angle is right.

Hope this helps,

Take a look here: http://mykitlog.com/users/display_log.php?user=rlendon&project=113&category=0&log=21203&row=605
Comment by Dwayne Roos on July 7, 2009 at 11:57am
Hi guys,I was a little disappointed with the first two results.This morning I got looking at the spars and realized that I formed them both on the same side.When I received my sheet it was sent rolled,thought that might have something to do with my problem.So I took another parts blank but I flipped it and hoped for the best.Guess what,it came out perfectly staight,couldn't believe it.Later to day I'll try another one to see if I get the same results.
By the way I was notified that this is supposed to be in the discussions area so please go there to continue.
Thanks Dwayne
Comment by Carlos Sa on July 7, 2009 at 10:58am
Dwayne, the "banana effect" always happens, just in varying degrees depending on the tool and material thickness. For longer parts, I went to a local airplane kit manufacturer and rented their brake for a day. Even those parts have a bit of a bow.
This is not a problem, provided that when you assemble it, you make sure it is straight.
I don't like the crimping idea myself - I would check with ZAC.

Good luck
Comment by Chris Aysen on July 7, 2009 at 7:56am
Dwayne - Sometimes material grain direction plays an important role; especially when it comes to bending. The plans probably does not mention this but thats OK because on most parts it does not affect the integrity and function of the part; exception, main leaf gear. I completed a 701 from plans and ran into some of the same problems on those very same parts. Crimps are not a bad thing just use as few as possible on the spars. It is more important for you to figure where your rivets will be and place the crimps in between. The skin fitting flat on the spar (make sure to deburr) is much more important than having to put a few small crimps. Additionally, make sure you hold the proper sizes on the parts (widths, lengths, etc.).

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