Sheet Metal and Fabrication Flashcards

What is the standard gauge thickness for residential HVAC supply ductwork in low-pressure systems?

Answer: 26 gauge

26 gauge galvanized steel is the standard minimum thickness for residential low-pressure supply ductwork per SMACNA guidelines.

Which type of joint is used to connect two sections of rectangular duct end-to-end in the field?

Answer: S-slip and drive cleat

The S-slip and drive cleat connection is the standard field joint for rectangular duct sections, providing secure mechanical attachment.

When fabricating a 90-degree elbow for round ductwork, what is the primary advantage of a gored elbow over a stamped elbow?

Answer: Lower airflow resistance

Gored elbows have a larger radius and fewer abrupt direction changes, resulting in lower static pressure loss compared to stamped elbows.

What does the term 'flat pattern development' mean in sheet metal fabrication?

Answer: Laying out the 2D shape that will be bent into a 3D fitting

Flat pattern development is the process of calculating and drawing the unfolded shape of a fitting on flat sheet metal before cutting and forming.

Which hand tool is used to close the Pittsburgh lock seam on rectangular duct?

Answer: Hammer and bar folder

A mallet and a bar folder or hand seamer are used to close the Pittsburgh lock seam by folding the male edge into the female pocket.

What is the purpose of adding a standing seam reinforcement to a large rectangular duct panel?

Answer: Prevent oil-canning and panel flutter

Standing seam reinforcements stiffen large flat duct panels to prevent oil-canning (drumming) caused by pressure fluctuations.

According to SMACNA, what is the maximum recommended length for a flexible duct connector at a fan unit?

Answer: 12 inches

SMACNA recommends flexible duct connectors at fan units be limited to 12 inches to isolate vibration without excessive pressure drop.