308A Fabrication Techniques 2 — Questions and Answers
Question 1: What is a 'snap lock' seam used for in sheet metal fabrication?
- Joining two pieces of heavy plate
- Connecting round duct sections longitudinally with a self-locking seam that snaps together (Correct answer)
- Attaching insulation
- Connecting electrical wiring
Correct answer: Connecting round duct sections longitudinally with a self-locking seam that snaps together
A snap lock seam is a longitudinal seam used on round duct where one edge hooks over the other and snaps into a locked position. It provides a quick, secure connection without additional fasteners.
Question 2: When operating a power squaring shear, what safety device prevents the operator's hands from entering the cutting area?
- Safety glasses
- A holddown or finger guard assembly (Correct answer)
- Steel-toed boots
- A face shield
Correct answer: A holddown or finger guard assembly
Power squaring shears are equipped with holddown mechanisms and finger guards that physically prevent hands from reaching the blade area during operation. These are critical safety devices.
Question 3: What is the purpose of a 'bar folder' in sheet metal fabrication?
- To store metal bars
- To make narrow folds and hems on sheet metal edges for seams and safe edges (Correct answer)
- To fold reinforcing bars
- To measure bar stock
Correct answer: To make narrow folds and hems on sheet metal edges for seams and safe edges
A bar folder creates narrow folds on the edges of sheet metal, typically for lock seams, hems, and edges. It produces consistent, uniform folds along the entire length of the metal edge.
Question 4: What is 'grooving' in sheet metal work?
- Cutting channels in the metal
- Flattening and locking a grooved seam by closing the folded edges tightly together (Correct answer)
- Creating decorative lines
- Removing burrs from cut edges
Correct answer: Flattening and locking a grooved seam by closing the folded edges tightly together
Grooving is the process of closing and flattening a grooved (lock) seam using a hand groover or a grooving machine. It mechanically locks the folded edges tightly together.
Question 5: What is the correct sequence for fabricating a rectangular duct section?
- Bend first, then cut to size, then add seams
- Cut to size, form seam edges, notch corners, then bend to shape (Correct answer)
- Weld all joints, then cut to size
- Install hangers first, then form the duct around them
Correct answer: Cut to size, form seam edges, notch corners, then bend to shape
The correct sequence is to cut the blank to size including seam allowances, form the seam edges (Pittsburgh pocket and lock), notch the corners, and then bend the blank into its rectangular shape.
Question 6: What is 'burring' in sheet metal work?
- Creating rough edges
- Turning a narrow flange or edge on the end of a round pipe or disc (Correct answer)
- Removing rust from the metal
- Applying a protective coating
Correct answer: Turning a narrow flange or edge on the end of a round pipe or disc
Burring is the process of turning a narrow flange (typically about 3/16 inch) on the edge of a round disc or pipe end using a burring machine. This flange is then used for wiring edges or creating seams.
308A Fabrication Techniques 2
What is a 'snap lock' seam used for in sheet metal fabrication?