Figure 2-70.Assembly of a Pittsburgh lock seam
Figure 2-71.Closing a Pittsburgh lock seam
Figure 2-72.Layout of a 1/4-inch Pittsburgh lock seam.
STANDING SEAMS are used for joining metals
where extra stiffness is needed, such as roofs, air
housing, ducts, and so forth. Figure 2-73 is a cross
section of the finished standing seam. Dimensions and
rivet spacing will vary with application.
Standing seams used when stiffening is required
are as follows: The SPREADER DRIVE CAP, the
POCKET SLIP, and the GOVERNMENT LOCK (fig.
2-74) are seams frequently used in large duct
construction where stiffeners are required.
The DOVETAIL SEAM is used mainly to join a
round pipe/fitting to a flat sheet or duct. This seam can
be made watertight by soldering. Figure 2-75 shows
the pattern for forming a dovetail seam and an example
of its use.
Notching is the last but not the least important step
to be considered when you are getting ready to lay out
Figure 2-73.Cross section of a standing seam.
a job. Before you can mark a notch, you will have to
lay out the pattern and add the seams, the laps, or the
stiffening edges. If the patterns are not properly
notched, you will have trouble when you start
forming, assembling, and finishing the job.
No definite rule for selecting a notch for a job can
be given. But as soon as you can visualize the
assembly of the job, you will not have any trouble
determining the shape and size of the notch required