How to Cut Ducting
- 1). Mark the length that you need to cut the duct with the tape measure and permanent marker.
- 2). Place the base of the combination square tight against the side of the duct. Align the top edge of the square's blade with the mark you made in step 1.
- 3). Rest the tip of the permanent marker against the top edge of the combination square's blade. Drag the tip along the blade to mark a line on the duct. Extend the line around the duct by relocating and re-aligning the combination square.
- 4). Align the hacksaw blade on the line you made around the duct (in step 3) with the longitudinal seam of the ductwork. Cut completely through the seam. Remove the blade from the cut, and proceed to step 5. For duct board, insert the knife into the duct, on the line, and cut around the perimeter of the duct.
- 5). Measure 1/2 of an inch over from the cut you made in the previous step onto the piece of duct that you will not be installing, and make a mark with the marker.
- 6). Make a second cut with the hacksaw on the 1/2-inch mark.
- 7). Pry the seam apart between the two hacksaw cuts with a flathead screwdriver.
- 8). Cut the two flared out pieces of seam with a pair of aviation snips.
- 9). Align the double cut on the permanent marker line you placed on the ductwork earlier, with the lower edge of the double cut blade aligned with the line.
- 10
Run the double cut along the marked line until you return to the notched seam. Discard the drop-off piece of duct that you will not be installing. - 11
Mark the location of the duct accessory if required. Use the combination square to keep the lines straight. - 12
Place one corner of the flathead screwdriver onto the duct, in the center of your marked hole. - 13
Hit the tip of the flathead screwdriver with the hammer to drive the tip through the duct. Stand the screwdriver vertically, and drive the tip of the screwdriver an additional 4 to 6 inches. Push the screwdriver toward the duct and twist the screwdriver to raise one side of the cut. - 14
Cut out from the screwdriver cut with the aviation snips, starting from the edge of the cut you raised in the previous step. Cut out to a marked line, and turn the snips to follow the line. - 15
Pull up on the center section of metal as you perform the cut to keep pressure from the snip's blades. Keep forward pressure on the snips and avoiding cutting with the very tip of the snip to reduce "fishhooks." Fishhooks are shards of metal that are razor sharp and can pierce your skin easily. - 16
Discard the metal when you complete the cut.
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