Fundamentals: The Fabrication Shop
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: “Did you have any fabrication classes at the trade school you attended?”
ACE: “Sure. We learned how to fabricate a number of different fittings.”
1NATE: “OK. Let’s see how much you remember. What would be the proper gage thickness for a residential exposed rectangular duct over 14 inches using galvanized sheet metal?”
2NATE: “What would be the proper gage thickness for a residential enclosed rectangular duct 14 inches or less using galvanized sheet metal?”
3NATE: “What is the purpose of a cross break on the metal?”
b) Added cross-section area for airflow.
c) Reduced rigidity.
4NATE: “All right, Ace, I’m going to give you four drawings of the ducts we have to fabricate. I want you to tell me what size pieces of metal we will have to cut out to make the ducts. Each section of duct is made of two pieces. Remember, we will be using a machined Pittsburgh corner locking system, and the tolerances we will use are 15/16 of an inch for the lock side (or pocket, as some call it) and 1/4 of an inch for the flange side (or single edge). What size should each of the pieces be for the first section?”
a) 28 x 48 inches
b) 28-1/4 x 48 inches
c) 28-15/16 x 48 inches
d) 29-3/16 x 48 inches
5NATE: “What size should each of the pieces be for the second section?”
a) 26 x 48 inches
b) 26-1/4 x 36 inches
c) 27-3/16 x 36 inches
d) 27-3/16 x 48 inches
6NATE: “What size should each of the pieces be for the third section?”
a) 22 x 24 inches
b) 23-3/16 x 24 inches
c) 22-15/16 x 24 inches
d) 22-1/4 x 24 inches
7NATE: “What size should each of the pieces be for the fourth section?”
a) 19-3/16 x 12 inches
b) 19 x 12 inches
c) 18 x 12 inches
d) 19-15/16 x 12 inches
8NATE: “What would be the tolerance for the lock side if we had to make the Pittsburgh by hand?”
a) 15/16 of an inch
b) 1 inch
c) 1-1/4 inches
d) 1-5/16 inches
NATE: “Looks like we’re ready to cut up the metal. We’ll work on the fittings after we have the straight ducts cut out.”
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) c; 2) b; 3) d; 4) d; 5) c; 6) b; 7) a; 8) d.
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 email@example.com (e-mail).
Publication date: 10/28/2002