Sheet Metal Exam Essentials Review

Overview

Video tutorial covering review material for Sheet Metal 308A Certificate of Qualification exam, focusing on practice questions, technical concepts, safety procedures, and exam strategies. Instructor emphasizes critical thinking, careful reading of questions, and practical application of sheet metal trade knowledge.

Exam Strategy & General Tips

• Eliminate obviously incorrect answers first to improve odds (50/50 remaining).
• Read all four answer options before selecting; questions often contain trick wording.
• Draw diagrams when visualizing spatial problems or layouts.
• Practice math problems repeatedly to build speed; aim for ~60 seconds per calculation.
• Consider requesting an exam reader/assistant if reading comprehension is challenging (allowed with accommodation request).
• Questions test "best practice" methods, not necessarily fastest or cheapest job-site shortcuts.

Pattern Development Methods

• Common question: identify which pattern development method applies to specific fitting types.

Materials & Metalworking Specifications

• MRI exam room metal: Aluminum (non-ferrous, non-magnetic for magnetic resonance imaging environment).
• Pharmaceutical lab ductwork: Stainless steel or nickel (nickel is component of stainless).
• Galvanic corrosion: Aluminum and copper corrode fastest when in contact (most dissimilar metals).
• Drill bit angles: 118° for mild steel/galvanized; 135° for stainless steel.
• Cold chisel angle: 70° (some sources say 60°; confirm with current instructor).
• Sheet metal break capacity: If rated for 16-gauge mild steel, can cut stainless steel 4 gauges higher (20-gauge).
• Highest melting point: Stainless steel or steel (among common sheet metals).

Fire & Safety Systems

• Fusible link melting point: 165°F (standard for fire dampers in walls and floors).
• Fire damper orientation: Vertical dampers in walls; horizontal dampers in floors.
• Fire damper attachment: Use #10 screws to secure to sleeve.
• Commercial kitchen exhaust: Install cleanout door (CLE note) wherever duct changes direction.
• Near-miss incident response: Fill out near-miss report with supervisor immediately (or discuss at next safety meeting if company protocol differs).

HVAC & Ductwork Systems

• Opposed blade dampers: Used on supply air grills for volume control.
• Splitter dampers / single-blade volume dampers: Used inside ductwork branches to control airflow.
• Vestibule ceiling tile popping up: Install air relief damper or air transfer duct (not increased supply air).
• Restaurant kitchen odor/smoke in dining area: Increase exhaust fan speed or decrease makeup air supply to maintain negative pressure in kitchen.
• Noisy return air grill: Slow air velocity; may require larger return air opening or damper adjustment.
• Insufficient CFM (good RPM): Change fan pulley size (not motor); increase motor pulley for more CFM, decrease fan pulley size for higher speed.
• Climate control placement: Locate on return air side, before coil, center of space (not near exterior walls).
• Direct expansion coil system (blow-through): Fan installed before coil, blowing through it (standard furnace configuration).

Dust Collection System Order of Operations

• Explosion relief vent location: Positive pressure side, top of duct; some sources indicate side of cyclone (confirm with current materials).
• Dust collection duct takeoffs: Always on tapered section at 30° angle; 5:1 ratio (5 inches length per 1 inch diameter change).
• Duct bottom profile: Flat bottom on fittings prevents material accumulation.

Roofing & Flashing Procedures

• Batten seam: Best roof seam for expansion/contraction; install cleats first, use chalk line for alignment.
• Batten seam bend sequence: Smallest to largest bends (e.g., hooks before larger folds).
• Parapet wall waterproofing: Cap flashing (coping) at top; counter flashing at bottom.
• Gooseneck orientation: Point away from prevailing winds.
• Square-to-round seams: Groove seam for body; elbow edge for collar connection.
• Copper roof over galvanized: Use continuous felt strips (full coverage, not single strips).
• Copper roof permanent seal: Solder joints (like plumbing).
• Standing seam allowance: 3× material thickness (same as S-lock collar).

Lagging (Duct Insulation) Procedures

Order of operations for insulation installation:

1. Pins – Weld or attach pins to duct surface.
2. Glue – Brush adhesive onto duct.
3. Insulation – Apply insulation material.
4. Clips – Secure with retaining clips over pins.

• Bottom-sides-top: Order for lagging duct with metal jacketing (bottom sheet, side sheets overlap bottom, top cap covers sides).
• Mechanical fastening: Use stainless steel gear clamps or banding straps (tape alone not acceptable).
• Smoothing wrinkles: Use trowel for exterior finish (possibly sponge cloth for adhesive).

Service & Troubleshooting

• Thermostat beeping: Change filter (homeowner-level maintenance, not motor or CFM adjustment).
• Rooftop unit first check: Inspect filter (most common issue is clogging).
• Coil freezing cause: Insufficient airflow over coil (usually dirty filter).
• High limit switch repeatedly tripping: Insufficient airflow; dirty filter most common (electrical issues possible but less likely in exam context).
• One zone colder than others: Check for broken damper motor in that zone (not dirty filter if only one zone affected).
• Cracked heat exchanger symptom: Customer reports watering/burning eyes (carbon monoxide leak).
• Startup checklist: Remove shipping blocks before powering unit; complete startup report documentation.

Metalworking Protection & Finishing

• Stainless steel warping prevention: Use chilled copper block, lead block, or brick to pull heat away (or tack weld in sequence rather than continuous welding).
• Kitchen exhaust (16-gauge black iron): Use high-temp gasket at seams (not food-grade silicone).

Gas Venting & Piping

• A-vent / B-vent: Double-wall pipe (one has insulation, one has air gap).
• C-vent: Heavy-gauge galvanized stovepipe.
• Z-vent: Stainless steel (premium option for boilers).
• Crimped end orientation: Slopes back toward gas appliance so condensation drains back to unit.
• B-vent through roof: Sections lock together without screws; rain cap (China cap) locks on at top with male/female connection.
• Gas fireplace vent slope: Slope back toward unit (1/4" per foot for boiler breaching).
• Gas pressure measurement: Use U-tube manometer; formula involves difference between columns.

Cutting & Forming Operations

• Nibbler: Punches out crescent-shaped pieces.
• Cutting painted metal: Cannot use plasma cutter (requires clean metal for contact); use sawzall, snips, or hole saw.
• Cutting drywall (unknown obstructions): Use utility knife with blade set shallow (1/2 inch) to avoid hidden wires/pipes.
• Blanking: Shear operation that cuts shape out of roll stock or coil strip.
• Squaring shear operation: Blade pushes metal to left while cutting to ensure square edge.
• Chop saw setup for angle iron: Position angle directly under center of blade.

Mathematical Formulas & Calculations

• Blowpipe elbow centerline radius: 2.5× duct width.
• HVAC elbow centerline radius: 1.5× duct width.
• Corrugated decking stretch-out: Use Pythagorean theorem (a² + b² = c²) if rise and run given.
• CVA triangle: CFM ÷ velocity (FPM) = area (sq ft); convert to diameter using πr² backwards (÷π, √, ×2).
• SOHCAHTOA: Identify hypotenuse (longest side), determine adjacent/opposite relative to angle, select sine/cosine/tangent formula accordingly.
• Circular duct circumference: π × diameter.

Specialized Equipment & Procedures

• Anemometer: Measures air velocity; if dropped, compare readings to previous measurements at same location to verify accuracy (before sending for calibration).
• Builder's level: Sets precise elevations for installations (e.g., ceiling panels at specific heights); more accurate than 4-foot level for long runs.
• Caddy clamps (I-beam hangers): Must attach to top flange of I-beam or between corrugated decking and beam (not bottom flange, which causes tension on structural member).
• HRV flex duct connection: Secure with tie straps and proper tightening tool (not just screws and tape).
• Hollow mandrel vs. blow horn: Recognize tooling shapes for forming operations.

Key Terms & Definitions

• Lagging: Metal protective covering over duct insulation.
• MRI: Magnetic resonance imaging (requires non-magnetic materials).
• Batten seam: Expansion-joint roof seam with raised profile and cleats.
• Box-and-pan brake (finger brake): Allows bending of box sides without crushing by using removable finger segments.
• WHMIS symbols: Include toxic effects (T with star), corrosive, flammable, etc.
• Crane signals: Thumb = boom; finger = cable/line; up/down/in/out motions communicate direction.
• Nesting: Computer optimization of cutting patterns to minimize material waste on plasma/CNC equipment.

Action Items / Next Steps

• Practice mathematical calculations daily (CVA, SOHCAHTOA, area conversions) to build speed.
• Review order-of-operations sequences for lagging, sign installation, duct insulation, and dust collection.
• Memorize material specifications table (drill angles, fusible links, rivet protrusion distances).
• Draw diagrams for spatial problems (pipe slopes, ductwork transitions, vestibule pressure issues).
• Confirm current exam-specific details with instructor (cold chisel angle, explosion relief vent placement).
• Request exam accommodations early if reading assistance needed (ministry/Red Seal office requires advance notice).