Not sure if this is the way everyone does it, but here's how I bend the flanges:
1. I pre-flute the flanges prior to bending the flanges over. I just align the fluting pliers with the fluting depressions in the edge of the blocks. I find this makes the flanges bend MUCH better (fewer warps and wrinkles).
2. After bending them over I bang on the side of a screwdriver, set into the flutes, which sets the flutes a the proper depth.
All of this is using a non-metal hammer, of course.
Got 14 ribs bent tonight (not the lightening holes, though).
Pre-fluting prior to bending the flanges over
After bending over the flanges, I bang the side of a scredriver with the hammer .
