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Fluting the other direction

Polar

Polar

Active Member
I have all the ribs in my emp flattened, and all the flanges squared up, but I've left this one for last.





It's the top rib on the rudder and it's curved considerably more, and in the opposite direction, than all the other ribs were. I've watched every video and read every article I can find on fluting and they all show the use of flutes to address curves the direction opposite to this. I've squared up the flanges on this piece, but haven't done any fluting, so I can't 'unflute' something to try and push this end back down.

I considered repeatedly fluting then flattening those flutes, like a shrinker stretcher, but I'd be worried about cracking the flange. When I do that to a sheet of aluminum I have to anneal it first. I'd rather not take the acetylene torch to this part. Yet.

I'm sure there's a way to do this, but I can't seem to find it on the Google box.
 
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I don't remember this being an issue, but I may have bent it over the edge of a table, moving the tabled edge 1/4" at a time over a 3" length.

Stretching can be aided with a squeezer, flat sets with a squeeze and move technique - overlapping the set squeeze areas. Be careful, a little adds up.

Practice then choose something that works for you.
 
I tried to bend it over the edge of my workbench, but it's much too stiff. Bending those two flanges without any relief slots anywhere is pretty tough without getting the press involved!

I'll try squeezing and straightening. My concern is work hardening, but I'll try to not overlap the flutes as much as possible.
 
You need to very gently and gradually and evenly stretch the outside edge. Fluting effective shrinks the edge by gathering up material. You have to do the opposite, but very slightly. If you overdo it 2024t3 will crack, but it looks like you hardly need any stretch at all.

It's a harder thing to explain than to do and you need specific tools, and it would be very easy to ruin the rib if you have never done it. I will try to find a youtube video that demonstrates this.
 
https://youtu.be/WdPmp0ZYPAg

Here Kent White is stretching an edge massively with a pneumatic hammer. The top die is flat (think body hammer) and the bottom die is radiused (think "heel" dolly). He is stretching the edge enough to make a full circle. You need to turn your part one or two deg at most. So a few light taps with a hammer on some curved surface will do it. They have to be VERY light taps so you leave NO marks or it will crack.

So I mention this video simply to illustrate the principle of stretching the edge. You don't need this machine!
 
Thank you for the detailed reply. I actually have a planishing hammer, but obviously it's too much machine for this little part. The hammer and dolly method is a good idea. I'll give it a try when I'm back in the shop.

Thanks again
 
First, can you confirm your order of operations? It looks like those ribs have already been dimpled. The order of operations should be straighten, fit, drill, deburr, dimple.

Second, it appears that (measuring from the tip of the rib) you have flutes between the 3rd and 4th holes and the 5th and 6th holes. If that's the case, flatten those flutes and your rib will straighten out. Flutes are only necessary when you need them - you don't always need to flute a rib between every pair of holes.

Third, maybe you haven't fluted the rib. If not, it may be that your dimples are acting like flutes. Make sure you get a good firm dimple on the flanges - a slightly under-formed dimple can create a fluting effect because the area around the dimple is not smashed flat.
 
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Kyle Boatright said:
First, can you confirm your order of operations? It looks like those ribs have already been dimpled.
Click to expand...

This part actually comes dimpled from vans, which probably added to the deformation. I put a couple of flutes into the flange, and then flattened the flute back out, trying to stretch the flange and push the end back down. It didn't move much though, and I didn't want to repeat that process for fear of cracking.
 
Dimpling it will lock in the shape to some extent, making it harder to straighten. It doesn't look that bad. You can't force it into position 1 cleco at a time?
 
Get going - do something

Polar said:
This part actually comes dimpled from vans, which probably added to the deformation. I put a couple of flutes into the flange, and then flattened the flute back out, trying to stretch the flange and push the end back down. It didn't move much though, and I didn't want to repeat that process for fear of cracking.
Click to expand...

Either it will or won't. Posting won't fix it and if it is not fixed you won't assemble it. Get going!! Take a 3/4 wide strip of material and squeeze it centered 1/3 across along one side. Measure the change in straightness. Settle on a plan, then squeeze to extreme and see if it cracks.

I don't think the part is 2024, but if it is, it is already dimpled bent and holes punched in it. It is not THAT brittle. Likely 6061 with T6 after bending - even less prone to brittle failure.

It is easy to paint yourself in an imaginary corner, and just as easy to imagine a way out. Make the project true to its heritage - experimental - so experiment. Do something -if it breaks , do something else.
 
Time to do something else

Well, it was going ok until it wasn't.

I was close, but it cracked.



I was slowly squeezing small flutes, then tapping it back flat. The top of my welding table is 3/8" plate, so I was squeezing the tip of the rib on to the corner of the table (which barely fit between the flanges) and tapping the flutes flat.



It was going ok, slowly, and I was trying to keep the flutes from overlapping, but eventually there was a very definite pop. The crack runs right down into the radiused inside corner, so it's now scrap. Oh well, I ordered 2 extras, just in case.

I carried on and got it reasonably flat without further cracks, so the process works. I'll just have to go a bit slower next time.

 
Sorry to see a failure. Curious, Cody, why did you flute it then bang it back out? It needed to be stretched, but don't see any reason to bend it (flute) first. Hammers are good ,but the part will assume the surface finish of the hammer and anvil. I think the fluting was the base cause of the cracking. Either hammer/dolly or squeezing will compress and stretch the edge slightly and curve the part back straight.
 
The jaws on the fluting pliers look identical to the anvils on a power hammer, or a pullmax. Squeezing material around the corners of the jaw IS stretching it. I used a squeezer near the middle of the rib, but closer to the point of the part the yoke wouldn't fit between the two flanges. The fluting pliers would though.
 
Fluting and then hammering it out is asking too much of that alloy and temper. You can bend it once without cracking but that's about it.
 
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