How to Fold Metal Duct Seams
There are many types of seams for duct work. The Pittsburg lock and pipe seam are two of the most common types. The Pittsburg lock is used mainly on rectangular duct, while the pipe seam is used primarily for round duct. Does this Spark an idea?
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Things You'll Need
- Sheet metal
- Hand break
- Wooden or rubber mallet
- Three-eighth pipe seam tool
- Hammer
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Instructions
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Pittsburg Lock
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1
Calculate the size of the metal that you need for your duct and add 1/4 inch for the single edge and 1 5/16 inches for the Pittsburg lock.
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2
Insert the metal into the break, leaving 1/4-inch stick out past the toe of the break. Break up 90 degrees. This forms the single edge.
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3
Take the sheet of metal out of the break and flip it over. Reinsert the metal into the break, 1/4-inch edge first until only 1 5/16-inch sticks out past the toe. Close the break and with a rubber or wooden mallet, hammer the metal sticking out over the bottom leaf down 90 degrees against the bottom leaf of the break.
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4
Break the metal over 90 degrees as far as the break will allow. With a mallet, tap the edge down to form a "Z."
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5
Open the break and slide the "Z" under the toe of the break and close the break to flatten the "Z."
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Remove the sheet metal from the break, flip it over and reinsert into the break 1/4-inch first until the flattened "Z" sticks out just past the toe of the break and close the break. This will kink the flattened "Z" up slightly. With a mallet, tap the "Z" down flat. The Pittsburg lock is now formed.
Pipe Seam
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Using a 3/8 pipe seam, allow one and a half times the width of the pipe seam, or 9/16 of an inch, on each side of metal to form a seam.
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Mark a 3/8 inch on one side to be seamed. Insert the metal into the break, leaving the 3/8 inch stick out past the toe of the break. Break up over 90 degrees as far as the break will allow. Open the break and slide the bent edge under the toe and squeeze it together slightly to form a hook. Do not flatten.
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9
Take the metal out of the break and flip it over. Reinsert the metal with the edge just formed first. Leave 3/8 of an inch out past the toe, break over 90 degrees, open the break, slide the edge under the toe and close the break slightly, forming a second hook. One hook should be facing up on the metal and the other down.
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Roll the metal to your pipe size, being careful not to flatten the hooks. Hook the two edges into each other and slide the pipe on a stake, pipe or other hard-rounded surface. Using a 3/8 pipe seam tool, place the tool over the seam and tap it down with a hammer, flattening the seam and forming a pocket so the seam can't open.
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