How many scratch builders out there ? you are all going to need them----

[fairchild1934]

how many of you out there have all ready done this ? And how many of you are there that will have to do it ????
Is anyone trying to figure this out ?

I can get a 3 sided box bent ok I think---- its bending those flanges cleanly that is the problem. Tried an oak insert - but as expected-- you cant get a clean bend because the material wont keep a clean, sharp corner to bend against.

I am beginning to think it might be easier to ben those flanges all the way to 90 degrees. Anyone see a problem with that ? (in stead of 30 or 45 degrees. )


I tried making a steel version of the Bob-stick. That worked but it was hard to support the other half and force it to bend at the intended bend line. More of a bow than a bend with a bend line. Kind of a lumpy mess----

Tim

 

[SpruceForest]

Delrin works fine, while anything harder than aluminum is going to have to be very well polished on the interior/contact surfaces. I used mine extensively for flattening ribs and even did a few lightening holes just to see how bad they turned out (not bad...), but the hydraulic press technique detailed elsewhere resulted in far less residual stress in the ribs even where the approach is used ONLY for lightening holes. Spare rib done with press, Bob stick for straightening, the Vans Air Force flange straightener, and the usual fluting pliers.

Even with snips, hammer, and Bob stick, you'll likely get something better than what I've seen out of Cessna when it comes to wing ribs. Also - don't discount what can be learned by doing a half-dozen throw-away ribs... I have a box of them in the shop, and it was cheap tuition on the way to acceptable aircraft parts. The first ones were mild big-box aluminum to test out the process, and moving to 2024 generated more scrap, but what I learned got used on all 160 patrol ribs, so a half dozen 'wasted' rib blanks was money well spent.

 

[sjt]

If the question is how to make 90 degree flanges : I saw Vans aircraft versions of this tool






p.s. make that lever very very long.

 

[sjt]

All ribs when first made start out as potato chips. The first rib takes one hour to straighten. After doing 15 ribs it takes about 2 minutes per rib.


I use an mdf form with the proper edge radius .
Then I might give a hint as to where I want the flange flute

The cheapest and way to bend flange is with a $7 hammer form harbor freight:




There are youtube videos on solving potato chip
https://www.youtube.com/watch?v=mI9yARLfmU0



This bearhawk builder is always helpful
https://www.youtube.com/watch?v=_F7jObc0ajA



I myself used this method:
https://www.google.com/search?q=rib...ate=ive&vld=cid:6ba71a02,vid:pIvFpVV6kIQ,st:0

 

[fairchild1934]

sorry----- im NOT talking about aluminum wing ribs------ I AM talking about the steel control surface ribs. ( I have that process figured out well- I can make those all most flawless now-)

I didnt seem to get any useful responses in the other post-- so I thought I would ask it again---- from a different point of view.

I made a steel version of the bob-stick to turn the flange. But it does not work well because its nearly impossible to support the work on the other side of the bend line.

I am starting to think what we need is a special pair of pliers -- with 3 handles. A pair of outward pushing jaws having the jaws to be able to swivel a little---
and another 3-rd lever that turns over the flange while the other jaws apply pressure from inside out as an opposing force against the flange bend line.
Have the jaws about 2 inches wide--- so you could work your way from one end of the rib to the other.

Tim

 

[fairchild1934]

PS----- could possibly have used piper control surface ribs--- as they are about the same cross section shape as Bob's--- but basically none of them are the correct length. ( they are only about 15$ each- not not too expensive)

 

[sjt]

I have not gotten to that point for steel. My plan was to use my press to to hold. The press will hold no matter how hard I hit.
I might have to upsize the hammer.

 

[sjt]

b-spot has a video

https://www.youtube.com/watch?v=ki8_gRa5mTk&t=17s

I used up my oak stock and will have to get more.

 

[fairchild1934]

I think I watched B-Spots videos on that but I think he only showed the profiled stab ribs. They dont have the inward flange on them that make the complication in forming. but I will watch again just to refresh-- as his videos are very, very good..... liquid gold !

 

[sjt]

I am not sure if my drawing is the same.
On the patrol drawing 24
"Ribs may have lighting holes cut out after forming"

The holes might be made on a drill press

material .032 1018 steel

I think you are referring to section A-A




for some reason I can not draw it with ascii characters
3/8
______
/ *******|
********|
********|
********| 7/8
********|
\____ _|


If you do not have a hydraulic press maybe using a finger brake with all but one finger removed.
Maybe use finger to clamp a short length of 5/8 x 3/8 piece of steel that will hold rib while bending the lip.

 

[fairchild1934]

I watched B-Spots video. Unfortunately -- he just skips that step and does not bend the flange on his.
Stan--- just holding the rib is not exactly the problem--- its supporting the part you dont want bent-- and getting a nice bend line in stead of a frumpy, curvy
mess (which is what I am getting--) It like using a metal brake without using the hold -down bar on the other side of the bend line.
If I use something to bend it a few inches at a time- even gradually--- you end up with stretch ripples in the edge- no matter how gradually you do it. (like with using 2 inch seaming pliers)

im getting frustrated that no one seems to know how to do this ...... is no one making the flange ? or have most people just bought the ribs from avi ? The lofted ribs wont be a problem because they dont have the bent flanges.

Tim

 

[Rob]

I am a little confused on what you are asking. Are you asking about the 45 on the rudder and elevator ribs? I bent everything in box brake. Really not an issue. Here is a sample piece I did awhile back for another project. Bend radius is a little off because didn’t take the time to adjust set back. But you get the idea. Bent sides up into a U channel. Put edges back in and bent the 45. No form blocks are needed for these ribs.

 

[sjt]

Rob,
On one of the drawings it lays out the option of using 025 4130 instead of 032 1018.

Which one did you use?
stan

 

[Rob]

*** 1018 .032 ***

 

[sjt]

I think Tim is building a patrol. The patrol rib was always different then the original 4 place.
If I am not mistaken, all bearhawks now have profiled tail feathers.
The original 4 place was a pure rectangle.

It might be a good idea to bend an 045 exactly as the above pictures - and then add the airfoil curve.

 

[sjt]

Also, it occurs to me that the section AA on Bob's drawing was an artifact of the original rectangular profile tail feather.


______
/




\____ _|


maybe Bob would allow the 45 lip to be omitted on the updated tail feather design that is an airfoil shape.



The 45 seems like something that would help resist a torsional twist in the long direction. That would not be my first guess as the loads it would experience.

There is a T5 4130 tube welded internal to the control surface that would prevent a twist along the long direction anyway.

​

 

[fairchild1934]

Just to clarify-- the airfoil shaped ribs dont have the turned-edge--- only the "flat" ribs in the rudder and elevators. The stab ribs are the curved ones- and those are made on form blocks and dont have the turned lip. The parts Im trying to mfg are the exact ones in Rob's two pictures. Maybe i'm trying to turn
that lip at too much of an angle. Cant turn it too far in the brake because it its the hold down bar on the trailing edge end if it turns too far. im still on the struggle bus trying to get the widths exactly right at front and rear (template vs bent steel)

I found that Cleveland Aircraft tool has an edge forming tool that has two rollers welded to a vise grip designed for turning a flat on edges. Unfortunately it's shafts are facing the wrong way to get it inside the box section-- and the whole thing is too big and they dont make a Jr. sized one.

Rob: did you taper the width of the turned edge as it goes towards the small end ? That seems to be what the material wants me to do----
im using a 1/4 or 5/16 hold down bar on the brake--- so when you insert the 3 sided shape to make that final shallow edge bend-- the hold-down is about hitting the material before you start the bend. if I tapered the lip a bit that might relieve that interference.

I have a sheet of .025 4130 from spruce I have not cut into yet. I am currently using (possibly practicing on ) .030 1008 from the box store. Seems to be bending well (cross grain bends)

PS---- I think at some point they went to lofted ribs on all the models for the stabs. (instead of just round tubing) But all the rudder and elevator ribs have non-curved steel ribs with turned flanges.

 

[geraldmorrissey]

Can you get down to 1/2" wide on the narrow end?

 

[sjt]

I do not think the edge forming tool will work on steel. It turns down just a little on 2024

Maybe go to online metals and buy a 3/8x1/2 bar and a 3/8x3/8 bar. Tig weld them together and use that as a form block. You might be able
to sand the taper. I could not find a 3/8x7/8 bar.

Also, the procedure for closing the 2024 trailing edge by using a brake that might work for a much shorter piece of 1018.


I know the B-B secton is tapered but a brake can apply pressure on just one side. There is no need to pull both levers the same amount.

this is what my 2024 trailing edge form process looked like:

 

[Rob]

No mine does not taper. Same 3/16" wide complete length.

I have used hold down bars in the past also. But not all the brakes I have are the same. I have 3 different brakes. All with different upper clamping bar angles, and different leaf widths. Some things like this I am able to bend in one brake but not the others. So YMMY...

I my opinion you are getting a little too worried about it. I some cases the small end might get tweaked a little in multiple bending steps. You just need to go back and bend back in shape with duck bill pliers or hammer and dolly work to straighten back out. You just need a little turn down. Just a little turn down with add strength. But your just after a turn down to have a soft edge for fabric. You could just turn down with smooth duck bill pliers. Sometimes just a small bend to get a straight crease started makes it easier to finish bend with pliers. You can get it straight. Just take your time and work bending a little at a time back and fourth the length of rib. You can also straighten with a body hammer and dolly. If its not perfect it wouldn't be noticeable since the fabric shouldn't be touching the turned down edge.

 

[fairchild1934]

I may be trying to make the
turned edge a little too wide. I was doing like 1/4 wide. I think its more important to have a nice clean uniform bend line than to have the flange be wider.

I am getting closer now to getting a good one------

will try to post some pics if I can remember how----

Tim

PS
I started out doing a 4 place---- but the overhauled O-320 I had seemed to be trumping the IO -360 that I didnt have----- (bird in the hand---)
along with the current IO-360 and O-360 core prices------- (not to mention O-540 core prices-)

 

[fairchild1934]

I think I just made a good one. width at each end about right--- the flanges look adequate----- and reasonably neat.


then there are the practice ones----




too wide--- too narrow--- flanges at 90 degrees----- completely closed ready to weld up seam---

 

[fairchild1934]

another question------ do we make the rudder counterbalance rib flat like the rear ones ? or do we make it a curved one to match the curved one on the stab that it kind of nests with. ??? I would guess flat---- but I don't think the plans say explicitly ----- maybe I need to look at B-Spot's video one more time ----

OK -- watched B-Spot again--- he uses a curved and formed over wood rib. So that's what I will do.
i would think flat would work - just wouldn't look as nice how the contours match at the gap. His videos are GREAT !

tim

 

[Camflyer]

Have you got Eric's manuals? That's another detailed resource

 

[geraldmorrissey]

The "turn down flange" on the non contoured Patrol factory ribs is .125 wide.

 

[sjt]

1/8 inch suggests the 45 turn flange is just to protect fabric covering.

 

[SpruceForest]

Those hor and vert stab ribs have additional form stiffness by virtue of that curvature; the straight C-section ribs benefit from that turned edge in gaining some additional resistance to buckling failure (although 90 degrees would be better, but tougher to fab in a home shop). I suspect that 45 degree turn is primarily structural, given a 15 degree tweak or chaffing tape would do for fabric chafe considerations and would be a bit easier to fab. That 45 degree tweak seems to suggest Bob wanted a bit more stiffness without appreciable weight gain.

 

[fairchild1934]

I think my bends are more like 30 degrees----- I would like 45 degrees - but on the little end-- there is no place for the lip to go during the bend.
the hold down plate is about 1/4 thick--- and even at 30 degrees--- I have to flex it open to get the hold-down inside it. The only other way I see to bend it might be sheet metal pliers. But that will turn the nice smooth bend line into a wiggly mess. So I resist trying that. I tried that on the first 4 I did that became scrap.

I am making the flange about 3/16 wide. Any narrower than that -- and the work wants to pop out from under the hold down plate while bending. The only other method I can see would be to make a metal insert for each rib--- and then fold the lip to 90 degrees (or whatever) and then slide the insert out the end.

One other way I thought of -- would be to block up the open ends of the rib and fill the rib up with cerrobend low melting point alloy. Try to fill it right to the bottom edge of the bend line. Once it cools and hardens---hold the outsides of the rib with bardwood blocks work the lip over against the hardened alloy. Then either slide the plug out or throw it into a pot of boiling water to get it ready to recast. I remember this stuff has a pretty dramatic miniscus when liquid. That might work against you if you were attempting an exact 90 degree bend. But might work for less servere bend.

(cerrobend and /or cerrosafe are low mP alloys of busmuth-lead used to bend copper tubing without kinks in the tube from a sharp bend. The one I used melted at about 195 degrees F. Its useful for many things. I used it when I worked at the radiation therapy place at the hospital. We had it in a 5 gallon stainless steel coffee urn. You just depressed the tap and if poured out like water. Still hot enough to burn you though)

Yes I bet thats right that the imperitive for the bend is firstly for fabric chafing and cutting. Another way to make them stronger-- would be when the rudder is all done-- to carefully fill each one with some high density 2 part expanding foam. that would give the bent flanges quite a bit of extra strength
against the 3 sided shape from collapsing on its self. You might have to pick a foam that would be compatible with the fabric glue (doesn't melt it)
i expect to be using stewarts-- so I dont think stewarts glue would hurt it being water based...... anyone tried foam inside for strength ?