308A Fabrication Techniques

Question 1

What is the primary purpose of a Pittsburgh lock seam in sheet metal ductwork?

Accepted Answer

To create a strong, airtight mechanical joint without welding

Answer

The Pittsburgh lock seam creates a strong mechanical connection that is airtight and does not require welding. It is the most common longitudinal seam used in rectangular duct fabrication.

Question 2

What is the maximum gauge of galvanized steel that can typically be formed on a standard hand brake?

Accepted Answer

22 gauge

Answer

Standard hand brakes are typically rated for forming galvanized steel up to 22 gauge. Heavier gauges require power brakes or press brakes to achieve clean, accurate bends.

Question 3

When using a slip roll former, what determines the minimum diameter of a cylinder that can be formed?

Accepted Answer

The diameter of the upper (adjustable) roll

Answer

The minimum cylinder diameter is limited by the diameter of the top roll. The sheet metal wraps around this roll, so the cylinder cannot be formed smaller than approximately the roll's diameter.

Question 4

What is the purpose of 'beading' on a round duct fitting?

Accepted Answer

To add rigidity and strength to the fitting and provide a point for connection

Answer

Beading adds structural rigidity to round duct fittings and creates a crimped edge for inserting into the next duct section. It reinforces the fitting against collapse and provides a positive connection point.

Question 5

What is the correct procedure for notching a corner on a sheet metal pattern before forming?

Accepted Answer

Remove a precise amount of material based on the seam type and material thickness to allow clean folding

Answer

Proper notching removes exactly the right amount of material so that when edges are folded, they meet without overlapping or leaving gaps. The notch size depends on the seam allowance and bend radius.

Red Seal Sheet Metal 308A Practice Test

Red Seal Sheet Metal 308A Practice Test

308A Fabrication Techniques