308A Fabrication Techniques 4

Question 1

What is an S-cleat and where is it typically used?

Accepted Answer

An S-shaped metal strip used to join the longer sides of rectangular duct sections together

Answer

An S-cleat is a formed strip of sheet metal with an S-shaped profile. It slides over the edges of two adjoining duct sections, connecting them along the longer (non-drive-cleat) sides of rectangular duct.

Question 2

When fabricating a round duct elbow, what is the 'throat' radius?

Accepted Answer

The radius of the inner (tighter) curve of the elbow

Answer

The throat radius is the inside radius of the elbow — the tighter curve. Combined with the duct diameter, it determines the centerline radius and the overall size and airflow characteristics of the elbow.

Question 3

What is the recommended overlap for a longitudinal lap seam on round duct?

Accepted Answer

3/8 to 1/2 inch

Answer

A longitudinal lap seam on round duct typically has a 3/8 to 1/2 inch overlap, which provides enough surface for rivets or screws while minimizing material waste and maintaining a smooth interior.

Question 4

What is the purpose of a 'standing seam' in sheet metal roofing and architectural work?

Accepted Answer

To create a raised, interlocking seam that sheds water and allows thermal movement

Answer

Standing seams project above the panel surface, creating a water-shedding joint that also accommodates thermal expansion and contraction. They are the premium seam type for metal roofing.

Question 5

What tool is used to set a Pittsburgh lock seam after the edges have been formed?

Accepted Answer

A hand seamer and mallet or a closing machine

Answer

After the Pittsburgh pocket and lock edges are formed and engaged, a hand seamer is used to close the seam flat, and a mallet is used to set it. Production shops may use a closing machine.

Red Seal Sheet Metal 308A Practice Test

Red Seal Sheet Metal 308A Practice Test

308A Fabrication Techniques 4