This tutorial shows how to cut and assemble sheet metal snap lock duct pipe for a residential heating and air system. Also see this related sheet metal duct installation project.
Snap Lock Duct Pipe
Snap Lock seam round sheet metal duct pipe is available in prefabricated sections. A 5 foot section of 12 inch diameter 30 gauge snap lock pipe is shown here:
The duct pipe is shipped with an open seam so it can be cut to fit if needed. Cut the pipe before closing the seam. The snap lock tongue and groove seam forms a permanent joint that cannot be undone.
How to Cut Snap Lock Sheet Metal Duct Pipe
Decide which end of the duct pipe is to be cut off: the crimped end (shown here) or the smooth end. The crimp band is for fitting two sections of pipe together. Because I’m fitting this piece of duct pipe between two elbows with crimped ends per my ductwork diagram, the crimped pipe end will be cut off. (See this project if your situation is different and you need to manually crimp the pipe.)
Measure and mark the length of pipe around the pipe. Make the marks close together for accuracy:
Cut the snap lock duct pipe with tin snips following your measurement marks. The 30 gauge pipe is easy to cut:
The completed pipe cut:
The tin snips will pinch the snap lock groove, insert the tip of a screw driver to open the groove to the normal width:
Assemble Snap Lock Duct Pipe
The snap lock sheet metal duct pipe is ready to be assembled. The groove side is on the left with the locking dimples, the tongue is on the right:
The 12 inch diameter duct pipe is braced between my feet and rounded, then the tongue is inserted into the groove starting at the end:
Work down the pipe and press the seam together:
The Gray Metal South, Inc. No. 301 galvanized duct pipe shown here snapped itself together when 1/2 the pipe length was joined by hand. Nice! (I’ve worked with the more crudely made dryer and bathroom duct galvanized pipe that had to be forced together the entire length, so this was a pleasant change.)
The assembled snap lock duct pipe:
Closeup of the snap lock pipe seam. The groove is on the left, tongue on the right. The tongue is locked in place by the series of dimples that prevents it from backing out:
See the How to Install Round Sheet Metal Duct for the complete ductwork installation project.
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