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Nose rib technique

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  • Nose rib technique

    Good day all; been a busy summer and haven't had a chance to post much or work on the Bearhawk. I have been working through ribs at a snail's pace... I'm up to five that I consider airworthy, but another seven that are going in the scrap pile. I was at 3 and 7, so perhaps I'm turning a corner... I was worried I was going to end up making three planes and keeping one. I have a few questions on what I'm considering to be "airworthy" ribs, but I'll save those for later.

    Right now, my question is about the nose ribs. Four of those seven rejects are nose ribs, and I have yet to get one right. The problem seems to occur when I bend the outer flange around the formblock. I get a "crease" with a bend radius that is too extreme. It's not the radius on the formblock - that's pretty generous - it looks like somehow I'm not able to set the radius while hammering the forward part of the flange. See the pictures attached to the message. I thought perhaps that my relief hole wasn't big enough in my first two, so I made it larger, but that didn't seem to make much difference.

    I'm about to cut another set of blanks from a 4x4' sheet of 2024 T3 0.025 (I'm starting small until I get my process worked out), which includes another 4 nose rib blanks. I'm going to try a much tighter clamp right by the leading edge of the flange on the formblocks as I'm hammering, and may try to use the nose of my plastic mallet to set the radius (see last image attached - the rib there in the formblock is a center rib, and I've been using the plastic mallet to set the radius, and finishing with the deadblow mallet).

    Any thoughts on what else I should try? I don't really like to use the plastic mallet much, as it's a little too hard and I don't want to work-harden the metal too much. That said, it seems to do the trick on my last three center ribs for setting the radius.

    Many thanks for reading!
    4-Place Model 'B' Serial 1529B (with many years to go...)

  • #2
    I used a raw hide hammer with the ends mostly flat. The hammer is about 1.5 to 2 inches in diameter and is not weighted. The edges are curved gently (mainly from age and use).

    I start the flange by folding the metal over the slapping block. I make several passes to get the metal the full 90 degrees. After I have the metal folded over the block, I then work the metal to make the fold follow the slapping (form) block. I use a home made tool called a slapping file. It is an old file ground smooth and the edges rounded. It is bent up at the tip and bent up at the handle end enough so that a round handle can be welded to the file. Using this tool, I can hammer the flange and not leave any hammer marks. It also tends to flatten the area I as I hammer.

    As I hammer, I want to see the metal bend at the edge of the block. I strike metal as close to the form block as I can. Because the face of my hammer is largely flat, I get the bend to start at the edge of the form block.

    The small dents I can see in your flanges are places where you have stretched the metal and that is not something you want to do. The hide hammer will not dent the metal as easily as what you are using.

    If you go much slower and move the metal more slowly you can get rid of that curl right at the relief hole. Also, if there is any flex of the backing plate that holds the metal against the from block, you will not get a good bent at the flange.

    Hope this helps.

    I finished my ribs using the fluting pliers. Having notches for flutes in the form blocks would have been helpful but I used a single form block for all the ribs. I felt that this would assure better accuracy. I used the fluting pliers to flatten the ribs. I also used a thin piece of wood that had the same radius as the ribs to further form the flanges. Between the fluting pliers and the piece of wood I was able to flatten the rids and have a good 90 degree bend on the flange.
    Last edited by S Lathrop; 10-31-2019, 06:01 PM.


    • #3
      Use a fluting pliers early and often as you're working the bend over.


      • #4
        What Marcus said. You got to shrink the edge as the rib is formed.

        Imagine yourself as the piece of aluminum that is being formed into a rib. Look carefully at the second photo. The the rib starts out flat and the ribs outer edge has a certain distance measurement. As you (The Rib) start to get formed the flange around the form block, the distance of the edge doesn't not change. Now your (the rib) stressed, and so you form a wave in your edge to accommodate the compression feelings. But the builder kept on trying to mash the rib into position and you (the Rib) had no choice but to fold back onto the face of the rib. The pressure and force had to go somewhere.

        So, if the builder can but some flutes into the edge, it will take up some distance along the edge and relieve the pressure. When the pressure on the edge is relieved and the waves will lesson, and there will be no need to fold back onto the face to accommodate the compressive pressure along the shrinking edge. Ribs looks awful at this stage of the forming. Think about the stresses being built up and how to relieve them and you'll do fine.
        Brooks Cone
        Southeast Michigan
        Patrol #303, Kit build


        • #5
          I agree with the use of fluting pliers early in the process due to the aggressive curvature in the nose rib. Of course the sandwich should be heavily clamped; I used a jaw-horse with additional MDF sheets sandwiched and additional clamps near the edge. I used two hammers, one smaller hammer held tight to the backer board, striking the smaller hammer with the dead-blow early on to ensure setting the radius around the form block.

          Before starting, I cut valleys (troughs) into the form block so that the flutes would have a place to lay down into. I avoided direct hammer hits near the edges of the valley troughs. The amount of fluting is limited at first and carefully set to be perpendicular and aligned to ultimately lay down into the troughs. As the flange bends over additional fluting is done to take out the waves...
          Bearhawk Bravo #1508B - Scratch Build (wings)
          Northern Idaho


          • #6
            Here is another view after it is folded over...
            Bearhawk Bravo #1508B - Scratch Build (wings)
            Northern Idaho


            • #7
              Thanks all. I do use fluting pliers, but only after I have roughed out the flanges and the ribs are out of the formblocks. I did that based on the Bearhawk Book and Eric Newton’s manuals. I’ll try fluting while I form the initial nose flange. I have noticed that several of you on this forum have flutes cut into your formblocks - now I see why!

              Some specific replies...

              S Lathrop - I have never heard of a rawhide hammer. I have a new tool to search for! Regarding the initial stretching of the metal - I have noticed it with the plastic mallet (less so with the softer face on the deadblow mallets), so I’ve only been using the plastic mallet with the small nose to set the radius. I figure there has to be some stretching of the metal - forming is inelastic deformation - and though it initially looks bad, the final product post-adjusting (deadblow mallet, hand seamer, fluting pliers, magic) has ended up looking pretty good to me. You say the small dents/stretches are “not something you want to do.” If I’ve done this for what I’m considering to be my three “airworthy” center ribs, are you saying those should be considered for the scrap pile as part of the learning curve? I’m on the wrong device to post pictures, else I’d post some of the final product. I’ll try to upload some pics later. No matter what, I’ll still be looking for a softer hammer from now on.

              kilohotel - In your picture, it looks like your flutes are cut into the smaller of the two formblocks. I’ve been using the smaller formblock as my backup block, and hammering the flanges towards the larger primary formblock. That means I don’t initially get a 90-deg flange due to springback. I’ve been following the process in the Bearhawk Book to get to 90 degrees - placing the rib web side down and hammering the flanges against a clamped 2x4. (Well, that plus the hand seamer and fluting pliers.) Can you comment a bit more on your process?

              it seems there are a lot of techniques - but then again, I started the slow build to learn! Many thanks to you all for your thoughts and comments.
              4-Place Model 'B' Serial 1529B (with many years to go...)


              • kilohotel
                kilohotel commented
                Editing a comment
                The green (flute) and red (rivet) marks in my pictures are on the backer board. The little channels for the flutes to lay down into (once the get there) are cut into the edge of the form block. I posted a longer discussion (and link to pictures) about my rib forming process on 4/22/19 under Rib Forming & Bob Stick issues thread..

            • #8
              Search VansAirforce for a neat little homemade tool for bending flanges to 90 degrees.


              • #9
                Thanks Jim - I found this thread:


                Some of the pics don't show up anymore, but I get the idea. Is this tool common among Bearhawkers?
                4-Place Model 'B' Serial 1529B (with many years to go...)


                • #10
                  S Lathrop - as noted above, I have never even heard of a rawhide hammer. Seems like a great idea. I found some weighted ones on Amazon... anyone have any experience or recommendations?

                  (Original URL was too long, so I went to TinyURL):

                  (if you want to preview where the link takes you):
                  4-Place Model 'B' Serial 1529B (with many years to go...)


                • #11
                  A little late now, but you may want to switch to one of the control surface ribs and hone your craft there. They're smaller, simpler and way easier. I found the main nose ribs to be the most difficult of the set.
                  Scratch building Patrol #275
                  Hood River, OR


                  • nborer
                    nborer commented
                    Editing a comment
                    Totally agreed. That's the process I took. I started with a 4x4 sheet of .025 and cut out all of the different rib types to try my technique. I screwed up the aileron ribs (2), but then got the two flap ribs to come out well. I then set my sights on the nose ribs, and screwed up the first two. I then moved on to center ribs, and work-hardened the metal on one of them before getting the next three in good shape. I went back to my last two nose rib blanks and then got the results shown above. So, I think I have the process down for all but the nose ribs. I'm cutting another 4x4 sheet now with another 4 nose rib blanks (plus a number of others) to try again...