Fabrication Techniques Flashcards

What is the maximum recommended aspect ratio for rectangular ductwork according to SMACNA standards?

Answer: 8:1

SMACNA recommends a maximum aspect ratio of 8:1 for rectangular ductwork. Higher ratios increase friction losses, require heavier reinforcement, and are less efficient than lower aspect ratios.

What is the purpose of 'planishing' in sheet metal fabrication?

Answer: To smooth and flatten metal by hammering it between a flat hammer and a planishing stake or anvil

Planishing smooths and work-hardens sheet metal by striking it with a smooth, flat-faced hammer against a smooth stake or anvil. It removes hammer marks and produces a uniform surface finish.

When fabricating a round tee fitting, what is the 'saddle' or 'fish mouth' cut?

Answer: A curved profile cut on the branch pipe that matches the curvature of the main duct it connects to

The saddle or fish mouth cut creates a curved profile on the end of the branch pipe that precisely matches the curvature of the main duct, allowing a tight fit at the intersection.

What is the function of a 'brake die' or 'nose bar' in a press brake?

Answer: To determine the inside radius of the bend being formed

The brake die or nose bar (upper tool/punch) determines the inside bend radius. Different die profiles produce different bend radii, and the correct die must be selected for the desired bend specification.

What is 'joggling' in sheet metal work?

Answer: Creating a small offset step in the metal so overlapping pieces remain flush

Joggling creates a small offset or step in sheet metal equal to the material thickness. This allows two overlapping sheets to lie flush at a lap joint, maintaining a smooth surface.

What personal protective equipment is mandatory when operating a power squaring shear?

Answer: Safety glasses, hearing protection, and no loose clothing or jewelry

Operating a power squaring shear requires safety glasses to protect from flying metal chips, hearing protection due to noise levels, and the absence of loose clothing, jewelry, or gloves that could be caught in the machine.