NOTE: Within a heating system, the use of
fiber-class duct is restricted by the adhesive
used to affix the protective outer coating to the
fiber glass. Check the specifications and ensure
that it will not fail when exposed to heat over
To fabricate a rectangular/square duct, you must
first measure the duct board accurately. Next, the
grooves must be cut. Ensure they are at the proper
locations and cut straight because this allows the board
to be folded to create the desired rectangular/square
shape. When cutting the board, you will need to leave
an overlapping tab that is pulled tight and stapled (fig.
2-104, view A). Tape is then applied and the joint is
heat-sealed (fig. 2-104, view B). Joints between
sections are fabricated by pulling the shiplap end
sections together and finished by stapling, taping, and
heat sealing the joint (fig. 2-104, view C).
The very nature of fiber-glass duct requires that it
be supported with 1-inch by 1/16-inch galvanized
steel strap hangers. These must be supplied or
fabricated to fit the duct precisely whether the duct be
rectangular/square or round. Rectangular/square ducts
up to 24 inches (span) can be supported on 8-foot
centers. Ducts larger than 24 inches must be supported
on 4-foot centers. For round ducts the supports must
not be less than 6-foot centers.
Some of the safety precautions applicable to
sheet-metal tools and equipment have been mentioned
throughout this chapter. Here are a few additional
precautions that should be carefully observed when
you are working with sheet metal.
1. Sheet metal can cause serious cuts. Handle it
with care. Wear steel reinforced gloves whenever
2. Treat every cut immediately, no matter how
3. Remove all burrs from the metal sheet before
attempting to work on it further.
4. Use a brush to clean the work area. NEVER
brush metal with your hands.
5. Use tools that are sharp.
6. Keep your hands clear
of the blade on all
7. A serious and painful foot injury will result if
your foot is under the foot pedal of the squaring shears
when a cut is made.
8. Do not run your hands over the surface of sheet
metal that has just been cut or drilled. Painful cuts can
be received from the burrs.
9. Get help when large pieces of sheet metal are
being cut. Keep your helper well clear of the shears
when you are making the cut.
10. Keep your hands and fingers clear of the rotating
parts on forming machines.
11. Place scrap pieces of sheet metal in the scrap
12. Always remember to keep a clean shop. GOOD
HOUSEKEEPING is the key to a safe shop.
13. Do not use tools that are not in first-class
condition-hammer heads loose on the handle, chisels
with mushroomed heads, power tools with guards
removed, and so forth.
14. Wear goggles when in the shop.