Traced around rib form and cut rib blank, then tried to bend part using clamps on the work table surface. The result on the first side was uneven, so I switched to the bending brake. At this point I made my callculations using the new Bend Allowance spreadseet. That worked very well, so I completely changed my approach. For the other three ribs, I drew the dimensions directly on the metal (instead of tracing around forms), and the long sides of the other three ribs were bent using the brake, resulting in perfectly straight flanges. All that was left to do was to tweak the flanges to the correct angle (1 degree open or closed) and to bend the end flanges against the end of the rib forms. This turned out to be the only real use for the rib forms.