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Figure 2-75.—Dovetai1 lock seam | Up
Steelworker Volume 02 - Building manual for how to work with steel | Next
Metal Screws |
for the job. If the notch is made too large, a hole will
be left in the finished job. If the notch is too small or
not the proper shape, the metal will overlap and bulge
at the seam or edge. Do not concern yourself too much
if your first notches do not come out as you
expected—practice and experience will dictate size
and shape.
A SQUARE NOTCH (fig. 2-76) is likely the first
you will make. It is the kind you make in your layout
of a box or drip pan and is used to eliminate surplus
material This type of notch will result in butt comers.
Take a look around the shop to see just how many
different kinds of notches you can see in the
sheet-metal shapes.
SLANT NOTCHES are cut at a 45-degree angle
across the comer when a single hem is to meet at a
90-degree angle. Figure 2-77 shows the steps in
forming a slant notch.
A V NOTCH is used for seaming ends of boxes.
You will also use a full V notch when you have to
construct a bracket with a toed-in flange or for similar
construction. The full V is shown in figure 2-78.
When you are making an inside flange on an angle
of less than 90 degrees, you will have to use a
modification of the full V notch to get flush joints. The
angle of the notch will depend upon the bend angle. A
modified V notch is shown in figure 2-79.
Figure 2-76.—Square notch.
Figure 2-77.—Slant notch.
Figure 2-78.—V notch.
Figure 2-79.—Modified V notch.
A WIRE NOTCH is a notch used with a wire edge.
Its depth from the edge of the pattern will be one wire
diameter more than the depth of the allowance for the
wire edge (2 1/2 d), or in other words, 3 1/2 times the
diameter of the wire (3 1/2 d). Its width is equal to 1
1/2 times the width of the seam (1 1/2 w). That portion
of the notch next to the wire edge will be straight. The
shape of the notch on the seam will depend on the type
of seam used, which, in figure 2-80, is 45 degrees for
a grooved seam.
Most of your work will require more than one type
of notch, as shown in figure 2-80, where a wire notch
was used in the forming of a cylindrical shape joined
by a grooved seam. In such a layout, you will have to
notch for the wire edge and seam.
JOINING AND INSTALLING
SHEET-METAL DUCT
After the sheet metal has been cut and formed, it
has to be joined together. Most sheet-metal seams are
locked or riveted but some will be joined by torch
brazing or soldering. Lock seams are made primarily
by the forming processes that have already been given.
Figure 2-80.—Wire notch in a cylindrical layout.
2-27
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