Tips on rib straightening ?

[fairchild]

I am now making the nose ribs. I am finding that adjusting the edges to be flat seems pretty easy by adjusting the crimp on the fluits.
However - on some I have each edge straight but the two edges aernt quite parallel..... and the center between the holes is a little
depressed or raised (depending which side is up)

Anyone have any remembrance of where you work the rib to undo the flanged edges being non-parallel ? ( I havnt tried the "bob-stick" yet- as I am mostly
bending the hole flanged using the rubber pad in the press----) --- can the bob-stick used in the round flanges help ?

Tim

[S Lathrop]

Have you flanged the holes in the ribs? You should be able to flatten the rib as you do that process.

I used a different process than the Bob Stick to flange the holes through the ribs but in that process, I was able to flatten the ribs. I think that as you flange the holes, you can bring the rib back to flat.

[fairchild]

I press the blank in the press with a thick rubber pad------ that flanges the holes about 90% and bends the outer edges about 1/3 of the way.......
Then I work the outer edge over to about 80 degrees with a soft mallet..... then fluit the flange and run through the RV"corner" tool . I adjust the outer flange
several more times with another touch up with the fluit pliers and corner tool.....
The center flange seems to come out to 20 to 25 degrees without further attention. May have to tweak with bob tool to get to 30 degrees. (my wood die is 45 degrees....
but thats just how far the rubber is pushing it in....)

when I lay it flange-up on the table------ the area between the holes is up off the table about 1/16----
and on some--- when laid flange-down on the table----- I have a slight twist somewhere out in the middle --- the end of one edge is up off
the table about 1/8 ----- but each flanged edge is straight individually.... so there is a slight curve or cup in the center somewhere.....

so it appears that there is a tweak to be done in the center section somewhere---- the hole flanges would seem to be a possible place
to try----

Tim

[S Lathrop]

Here is the tooling I used for my ribs. This is an upset type die system that flanged the center holes. The reason I used this setup is because it tends to flatten the areas under the die. The edge flanges were formed over a slapping block and fluted. If you look closely at the finished flanges you can see that they are joggles with the inner edge parallel to the rib itself. The upset is 1/8th inch.

It may be more work that it is worth but if you made a wood from that would fit as my outer plate in my system and use that form to press the rib flat, you could then work the flanges to hold the rib flat. I expect that when you flatten the rib, the flanges around the lightening hole will distort and you can see where to tweak them to make the rib flat.

Hope this is helpful. I apologies for the poor explanation.

[fairchild]

I might try making a "plug" out of 2 layers of 3/4 wood or mdf. A round part about 1 inch bigger than the hole--- and another to
fully form the 30 degree angle. Glue them together and let the press push it into the die. The outer disc should compress the
perimeter outboard of the bend line and maybe re-establish flatness there. and the center would finish the bend the last 5 degrees.(to 30)
Might be worth trying. since my holes are 85% bent - the die should self center without much drama ( I think....)

Never tried a slapper-- seen them used on videos by tinman----

I considered putting recesses into my form for the crimps in the flange but I couldnt see how to do them all even and consistent.

Tim

[fairchild]

here are my latest ribs---- only real problem is the area inside red dotted line. getting a reflex-bend there (if you can see it---)
I believe it is the extension of the bend line from about 1.5 inches back from edge.(near the fluit) I think to eliminate this- I need
the bending there to be more compound--which means I need the metal to stretch some there--- Which I think means that I need
to bend the beginning several inches of the bend line deeper while pressing against the rubber pad. I think this might put more
"compound" into the bend there since the pressure from the rubber should hold and bend at the same time.

The below examples were bent about 1/3 the way in the press and finished with a small rubber bead blow against the form. All the bend
looks good except the first 1/2 inch at the front edge.

The 3-rd pic is how it looks just out of the press from the rubber pad only.

I am wondering if anyone else has had this little uncooperative spot at the front edge ?

Tim

[Chris In Milwaukee]

Since I pounded out my flanges with a hammer, I may be getting a bit more stretch than you with a press. But your ribs look perfect to me

https://bearhawkforums.com/forum/bearhawk-patrol-plans-build/21676-fluting-party?p=21703#post21703

[Bcone1381]

You probably know this area has the most curvature of any are that you will flange on the entire aircraft. That flange is fighting what you are trying to do to it. My nose ribs ended up with flat spots on the flange between the flutes right in that area. Thats unacceptable. My input comes from a failure, not success, so take it with a grain of salt.

If I were in your situation again I would go to my local EAA chapter, borrow their shrinker and try to shrink that flange area. Extra flutes might work, but If you can find someone with a shrinker, they may lend it out. I think you are ahead of where I was when I aborted my scratch build.

I like your bend radius, and the rubber press looks like its an industry best practice to me. Others who read this in the future, take note. Below is a link that shows the shrinkers capabilities.

http://allmetalshaping.com/showthread.php?t=17303

[Glenn Patterson]

We hammered over our flanges but I don't think it matters how the flanges were bent. Our ribs cupped slightly across the ribs so the valley was along the center length of the rib. We found if we pried with the bob stick on both sides of the lightening holes up the longitudinal center of the ribs that the ribs went flat with very little effort. Once we had the rib flat then we pressed the rib flat on the table with one hand and then worked the flanges. The flanges were squared up with a combination of tapping the edges with the poly dead blow hammer and if they resisted squaring up then press the flute a bit deeper as the flutes can do a lot to square it up. If the flanges are square then they are parallel.

We made our fluting pliers from a pair of vise grips that gave us good control over pressing in the flutes. The vice grips can be set and limit the depth so as we could tell when to stop before we hit the limits set in the vice grips. The flutes can go anywhere as long as it is not a rivet line. The areas of the flange with a tighter radius will need deeper flutes than a section with a more gentle curve. The flutes take up the excess material when the flange is bent as the outer edge length of the flange is a lot longer than the flange at its bend. The difference between the the inner and outer flange lengths is greater at a tighter radius so it takes deeper flutes to take out the excess material so the flange can square up. It comes easy after a couple ribs under your belt. If the flange is a long ways from square then start by setting the flutes deeper & then follow up with a bump or two to coax it square.

The shrinker stretcher jaws will likely mar up the aluminum more than a person would like. They are great for fabbing body parts for a car but I would be hesitant to use the shrinker on the aluminum as it is teeth biting into the metal to pull it together.

[Bcone1381]

Good point about marring up the aluminum.I hadn't thought about that aspect of the shrinker.

[fairchild]

went back and looked at my first 2 ribs..... they didnt have the little inflection bend at the front. I have 2 rubber pads - each about 1.5 inches thick.
On the first 2 I stacked the pads so I had 3 inches of rubber to push down into. Then I tried layered floor mats about 4 inches thick----
I think i will go back to the double 1.5 inches stack. I THINK- that was allowing me more push-in depth than just one pad alone.

Hope that fixes the problem.

Tim