308A Blueprint Reading for Sheet Metal 2 — Questions and Answers
Question 1: What does a 'revision cloud' on a blueprint indicate?
- A weather symbol
- An area of the drawing that has been changed or modified from the previous version (Correct answer)
- A decorative border
- An area that is not to scale
Correct answer: An area of the drawing that has been changed or modified from the previous version
Revision clouds are drawn around areas that have been changed from the previous revision of the drawing. They alert the reader to modifications and are accompanied by a revision letter or number in the revision block.
Question 2: On an HVAC plan drawing, what does a rectangle with an 'X' through it typically represent?
- A fire extinguisher location
- A ceiling diffuser or supply air outlet (Correct answer)
- A structural column
- A return air grille
Correct answer: A ceiling diffuser or supply air outlet
On HVAC plan drawings, a rectangle with an X inside it is a common symbol for a ceiling-mounted supply air diffuser. The symbol may also include CFM values and a designation number.
Question 3: What is an 'isometric drawing' and how is it useful for sheet metal work?
- A flat 2D drawing
- A 3D pictorial drawing showing three sides of an object at equal angles, useful for visualizing duct routing and fittings (Correct answer)
- A drawing at double scale
- A cross-section view
Correct answer: A 3D pictorial drawing showing three sides of an object at equal angles, useful for visualizing duct routing and fittings
Isometric drawings show three dimensions of an object at 30-degree angles from horizontal. In sheet metal work, they are invaluable for showing duct routing, fitting orientations, and how components connect in 3D space.
Question 4: What does the abbreviation 'GA' or 'ga' represent on a sheet metal drawing?
- Galvanic action
- Gauge — the thickness of the sheet metal (Correct answer)
- Galvanized area
- General arrangement
Correct answer: Gauge — the thickness of the sheet metal
GA or ga stands for gauge, indicating the thickness of the sheet metal to be used. For example, '24 ga' means 24-gauge steel. The gauge number is inversely related to thickness — lower numbers are thicker.
Question 5: What is the purpose of a 'material list' or 'bill of materials' (BOM) on a sheet metal drawing set?
- To list the workers assigned to the project
- To itemize all materials, quantities, sizes, and specifications needed to fabricate the job (Correct answer)
- To show the construction schedule
- To list inspection requirements
Correct answer: To itemize all materials, quantities, sizes, and specifications needed to fabricate the job
The bill of materials lists every item needed for fabrication including material type, gauge, quantity, sizes, and specifications. It is essential for ordering materials and estimating costs.
Question 6: What does a 'break line' (zigzag line) indicate on a sheet metal drawing?
- A weld location
- That a portion of the object has been removed to save space on the drawing, and the actual length is longer (Correct answer)
- A bend line
- A section cut
Correct answer: That a portion of the object has been removed to save space on the drawing, and the actual length is longer
Break lines indicate that a long, uniform section has been shortened on the drawing to save space. The actual dimension is noted, but the middle portion is removed so the drawing fits on the sheet.
308A Blueprint Reading for Sheet Metal 2
What does a 'revision cloud' on a blueprint indicate?