I tried to do what you are working on. The best way I figured of doing it was to go into face mode. Select the face you want to manipulate. Hit the "insert" key and move the rotation axis and snap it to the line by holding the "C" key to the line or angle you want it to bend on. Then make sure you go straight to the rotate tool, if you go to the translate tool and the skip to the rotate tool the axis resets for some reason. This is the best way I found. Make sure you're in gimbal mode when you rotate it.