Pressing flanges in the ribs.^20h

Going back to the situation with "underpressed" ribs.

A year ago, I noticed that my replacement main ribs have very flat webs, making their stiffeners essentially useless. Other builders also noticed that problem, and Van's response at the time was that this should not cause any safety or maintenance issues.

However, looking a bit more at my ribs, and comparing them to the properly pressed ones (three outboard ribs or my scrap stack of laser-cut ribs), I see that they have much lower resistance to buckling when force is applied between the top and the bottom skins.

So I decided to press ribs using a set of dies and punches that can be compressed with bolts. Here is an example of the tool I designed for the smallest lightening hole.

And this is how the tool is used on the rib.

Here is what flange looks like after pressing.

Here is what the large hole tool looks like.

For the beads I designed a fixture that would position punch and die relative to the lightening holes. The 3D-printed punch and die are backed by a steel C-channel (to spread the pressure along the die), then these two C-channels are pressed by two (or four in the case of biggel holes) C-channels that run from one lightening hole to another. To position C-channels relative to each other I used a rivet as a locating pin. All the holes in the C-channels were drilled on my milling machine with DRO, so they are relatively precise.

The whole contraption locks on the holes with very little movement, and what is more important, the punch and the die are located one against another.

And the end result.

Overall, I like the end result -- the ribs "feel" more like the ones that are properly pressed (with the feel adjusted for "split flanges"). I took the technique (pressed dies) from the scratch-building toolkit, which is why I was comfortable doing it.

The whole procedure, including the design of the tools, took me about two weeks total.