Set the scribe to 1/2 an inch. Mark each side of the two 12 1/2-inch pieces of sheet metal with the scribe. Cut the corners where the lines cross with a pair of aviation snips. Scribe a 1/2-inch line on one of the 14 1/4-inch sides of the 14 1/4-by-49 3/8th inch piece of sheet metal. Set the scribe to 1 1/8th inch. Mark the remaining three sides of the 49 3/8-inch long sheet metal.
Remove all the corners where the scribe lines cross. Cut the corners with the aviation snips, 1/8th of an inch on the outside of the scribe line to the point of intersection of the scribe marks. Measure over from the edge of the sheet metal on the side with the 1/2 inch notch with the tape measure. Mark the metal at 12 1/2 inches, 24 1/2 inches, and 36 1/2 inches. Rotate the sheet metal and mark the other side with the same dimensions. Notch each mark from the edge of the sheet metal down to the 1 1/8th inch scribe line.
Inspect the Lockformer Pittsburgh Lock Model 20 roll-forming machine. Manually check each bolt on the guard to ensure that the guard is properly secured. Examine the metal guide for loose screws and signs of wear.
Turn on the Lockformer by pressing "Start." Listen for mechanical parts that are improperly aligned or binding. Grinding and squealing noises coming from the Lockformer are signs that the roll head is misaligned or over-tightened.
Align one of the 1 1/8-inch notched sides of the 49 3/8-inch piece of sheet metal with the Lockformer metal guide. Hold the metal flat against the guide with one hand and support the end not being formed with your opposite hand. Push the sheet metal slowly under the guide, keeping your fingers away from the guide entrance. Rotate the sheet metal and continue to run the 1 1/8-inch notched sides through the Lockformer.
Align the 1/2-inch scribe side of the 49 3/8-inch piece of sheet metal with the guide on auto-flange attachment and slowly push the metal into the flange former. Repeat the process with the eight edges of the two 12 1/2-inch square pieces of sheet metal.
Bend the 49 3/8-inch long piece of sheet metal at the 12 1/2-, 24 1/2- and 36 1/2-inch marks in a sheet metal hand brake. Insert the 1/4-inch flange into the Pittsburgh seam and seat the flange with the 3/8-inch flat bar. Peen over the top of the Pittsburgh seam to lock the sheet metal together.
Open the edges of the Pittsburgh seams with the regular screwdriver. Place the 12-inch finished square pieces of sheet metal into the Pittsburgh edges on the ends of the ductwork you assembled in Step 6. Set and peen the flanges to lock in the two ends.