Fundamentals: Fabricating Fittings For Ductwork

November 24, 2002
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The work: Substituting while the sheet metal duct fabricator is on vacation.
The apprentice: Allen Charles Edwards (ACE) — first-year mechanic.
The technician: N. Arthur Thomas Egan (NATE) — 15-year HVACR veteran.

NATE and ACE are working in the shop while the duct fabricator is on vacation. They will be fabricating fittings for various jobs according to the field drawings.

NATE: “Ace, we have to fabricate the fittings for the duct layout we’ve been working on. We have to make four fittings, which are listed below. There are also rough sketches of the fittings, which are labeled A, B, C, and D.”

NATE: “I’ll do the pattern layout and cut out the fitting pieces. You tell me which pieces are for what fitting and then cut the proper notches. Remember, we are using the Pittsburgh locking system, which has a tolerance of 15/16 of an inch for the pocket. The curved (flanged or single-edge) surfaces have a tolerance of 3/16 of an inch, and the straight edges have a tolerance of 1/4 inch.”

Match the following numbered pieces (1 through 9) with the proper fitting (A through D) below.


18-1/2 inches top, 14-1/2 inches bottom, 24 inches high


19-7/8 inches wide, 9-7/16 inches high


40-7/8 inches wide, 9-7/8 inches high


9-7/16 inches wide, 9-7/8 inches high


24-1/16 inches wide, 9-7/8 inches high


Curved piece, 20-3/8 inches wide


48-1/2 inches top, 44-1/2 inches bottom, 24 inches high


22 inches wide, 19-7/8 inches high


Curved piece, 8-3/8 inches wide


20- by 8-inch flat (sometimes called a Broadway) elbow with a 6-inch radius throat and radius heel.


18- by 8-inch riser elbow with a 6-inch radius and radius heel.


20- by 8-inch to 18- by 8-inch side flat transition that is 24 inches long. It is made in two pieces.


18- by 8-inch to 14- by 8-inch on center line transition that is 24 inches long.

Please remember no question appearing in these articles is on a NATE exam. These questions and dialogue are my creation alone. The NATE Technical Committee does not review the article content, and the committee has the final decision for the use of a question on the tests. Interpretation of codes, regulations, and standards comes from my experience as a technician and a contractor. Different jurisdictions have varying interpretations. The particular area a job is being done in will dictate which viewpoint is to be properly used. I learn a lot from your commentary and try to incorporate information into the next article, so please continue to comment.

Patrick L. Murphy
Director of Technical Development

Answers: 1) d; 2) b; 3) a; 4) a; 5) c and d; 6) a; 7) c; 8) b; 9) b.

Murphy is director of technical development, North American Technician Excellence (NATE). If you have any further questions or comments on this Fundamentals quiz, contact Murphy at (e-mail).

Publication date: 11/25/2002

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