How do you fabricate an elbow sheet metal duct?

To fabricate an elbow sheet metal duct, start by measuring and marking the desired angles and dimensions on a flat sheet of metal. Cut the metal using shears or a plasma cutter, ensuring clean edges for proper fitting. Then, bend the metal at the marked angles using a brake or bending tool, and secure the seams with welding or rivets. Finally, apply a sealant to prevent air leaks and ensure a tight fit at the joints.