How to Bend a Sheet Metal Flange

Standard sheet metal flanges are used for mounting accessories to duct work. Sheet metal flanges can be bent to any size, but there are two common types of flanges. The flange is designated by the direction that the flange bends on the duct. A "flange in" is, as the name describes, turned to the inside of the duct work and a "flange out" bends to the outside of the duct work. Both flange types bend the same way; the difference is how you lay out the bends for the flange versus the layout marks for the duct work.

Things You'll Need

• 26 gauge sheet metal cut to the size
• Scribe
• Tape measure
• Permanent marker
• Aviation snips
• Roll-forming equipment
• Sheet metal hand brake
• Combination square
• Wood or rubber mallet

Instructions

1. Set the scribe to 1 inch. Run the scribe along the edge of the ductwork that is going to receive the flange. Measure across the sheet metal with the tape measure and use the permanent marker to lay out the locations of any bends that will need to be made across the duct's sheet metal flange.

2. Cut a straight line with the aviation snips at each bend location that you marked in Step 1. The cut needs to extend the full 1 inch width of the 1 inch flange. Notch the corners of the flange that will require the seams for the connections on the side of the duct work.

3. Run the duct work through all roll-former equipment needed to place seam edges on the piece of duct work before you bend the sheet metal flange.

4. Place the edged sheet metal into the sheet metal hand brake. Slide the end that does not require the flange into the hand brake first, with the 1 inch scribe mark facing up. Align the 1 inch scribe mark with the top clamping leaf of the hand brake. Pull down the clamping handle on one side of the hand brake. Switch to the other side of the hand brake. Line-up the scribe mark with that side of the clamping leaf and pull the clamping handle on that side to completely secure the sheet metal in the hand brake.

5. Grasp the low handles of the hand brake's bending leaf. Pull the bending leaf up as you watch the sheet metal. When the flange is close to 90 degrees, lower the bending leaf and unclamp the sheet metal by raising the clamping leaf handles of the hand brake.

6. Pull the sheet metal forward of the clamping leaf 4 inches. Check the sheet metal flange for 90 degrees with the combination square. If the base and blade of the combination square both rest completely on the sheet metal and the flange, the bend is 90 degrees. If the bend is not 90 degrees, push the sheet metal back into place, clamp the metal back into the hand brake, and lift the bending leaf higher to tighten the bend of the sheet metal flange.

7. Check the sheet metal flange for square using the method described in Step 6. If the flange is still short of 90 degrees, repeat the process of clamping and bending to tighten the flange. Use the mallet to open up the flange if you go over 90 degrees. Hit the sheet metal flange lightly with the mallet. Hit the entire length of the flange with the mallet. The closer together you hit the flange, the more even the flange will look.

8. Bend the width and heights of the duct work. Assemble the ductwork with the sheet metal flange placed at the end of the length of duct.