Red Seal Sheet Metal Worker cheat sheet

Personal protective equipment (PPE) minimum: safety glasses with side shields, hearing protection where noise exceeds 85 dBA, cut-resistant gloves when handling sheet metal, and steel-toed boots.

Sheet metal edges are sharp; deburr all cut edges before handling. Use gloves and never wipe away chips with bare hands.

Lockout/tagout (LOTO) is required before servicing or clearing jams on powered equipment such as shears, brakes, and roll formers.

Hazard communication: consult Safety Data Sheets (SDS) for chemicals such as solvents, adhesives, and coatings; follow WHMIS/GHS labeling.

Ladder safety: maintain 3-point contact, set at 4:1 slope, and secure top and bottom. Do not stand on the top two rungs.

Fall protection is required when working at heights of 3 m (10 ft) or more in general industry; guardrails, safety nets, or personal fall arrest systems.

Hot work (welding, cutting, grinding) requires a fire watch, clear combustibles within 11 m (35 ft), and a permit where mandated.

Manual lifting: keep loads close, bend knees, and avoid twisting. Use mechanical aids for sheet goods over 25 kg (55 lb) or large panels.

Orthographic projection: third-angle projection places the top view above the front view and the right side view to the right; first-angle places top view below front and right side to the left.

Line types: object lines (visible edges) are thick continuous; hidden lines are short dashes; center lines are long-short-long; dimension lines have arrowheads at ends.

Scale: verify drawing scale (e.g., 1:50) and never scale dimensions from the drawing; use stated dimensions.

Title block contains drawing number, revision, scale, date, and approval signatures; always work to the latest revision.

Specifications define material gauges, finishes, fasteners, and installation standards; they complement drawings and take precedence where noted.

Layout: use a baseline or datum; transfer dimensions with dividers or trammel points; verify square by 3-4-5 method or diagonal measurements.

Welding symbols: arrow points to joint; tail contains process; reference line holds symbol; size and length placed left and right of symbol.

Architectural symbols: door and window tags, section markers, elevation markers, and material hatches must be cross-referenced to schedules.

True length lines are found by rotating a line to parallel the reference plane in auxiliary views; use for triangulation and radial line development.

Parallel line development applies to prisms and cylinders; stretch-out length equals circumference (π × diameter) or perimeter of base.

Radial line development applies to cones and pyramids; divide base into equal parts and project to apex; true lengths from apex to base points.

Triangulation development applies to transition pieces (square-to-round); divide surfaces into triangles and find true lengths of each side.

Bend allowance (BA) = (π/180) × bend angle × (inside radius + K × thickness), where K is the K-factor (typically 0.33–0.5).

Bend deduction (BD) = 2 × outside setback − BA; outside setback (OSSB) = (inside radius + thickness) × tan(bend angle/2).

Flat pattern length = sum of flange lengths − bend deductions for each bend; verify with trial bend on scrap.

Allowance for seams: add material for Pittsburgh, double seam, or grooved seams as specified; typical 10–15 mm (3/8–1/2 in) per seam side.

Galvanized steel: zinc coating weight measured in g/m² or oz/ft²; do not weld without removing zinc and providing ventilation (metal fume fever risk).

Stainless steel: use dedicated tools and non-contaminating brushes to avoid carbon steel contamination and rust; 304 for general, 316 for corrosive environments.

Aluminum: soft and prone to galling; use lubricant when cutting or bending; do not install in direct contact with steel without isolation to prevent galvanic corrosion.

Gauge systems: U.S. Standard Gauge for sheet steel (e.g., 24 ga = 0.024 in / 0.61 mm); galvanized sheet uses galvanized gauge; aluminum uses Brown & Sharpe.

Hand tools: aviation snips (left, right, straight), hand seamers, deburring tools, dividers, trammel points, and prick punches.

Power equipment: squaring shears, box and pan brakes, slip rolls, rotary machines, notchers, and power hammers; inspect guards before use.

Measuring tools: steel rule, tape measure, protractor, feeler gauge, and calipers; verify calibration and zero before use.

Fasteners: self-drilling screws (TEK), pop rivets, blind rivets, and welds; select based on material thickness and joint strength.

Shearing: blade clearance approximately 5–10% of material thickness; too much clearance causes burrs and edge cracking.

Bending: minimum bend radius depends on material and temper; for mild steel, typically 1× thickness; for aluminum, larger to avoid cracking.

Springback: overbend to compensate; springback increases with higher yield strength and thinner material; test bend a sample.

Roll forming: set roll gaps to material thickness; use lubricant; feed sheet squarely to avoid twisting.

Notching and nibbling: remove corners for box and pan work; keep clearance between blade and die to prevent jamming.

Circle cutting: use a trammel or circle cutter; center punch the pivot point; cut in a steady clockwise direction for aviation snips.

Edge treatment: deburr with a file or deburring tool; fold edges (hem) to eliminate sharp edges on exposed work.

Heat control: when welding or cutting, use clamps and heat sinks to minimize distortion; alternate stitch welds on thin sheet.

Rivet selection: diameter should be at least 3 times the thickness of the thickest sheet; hole size matches rivet diameter; grip length covers total material thickness.

Self-drilling screws: select length so threads engage at least 3 full threads in the supporting member; do not overdrive and strip.

Seams: Pittsburgh seam for rectangular duct; double seam for cylindrical; drive cleat and S-cleat for joining duct sections.

Welding sheet metal: use low heat input, skip welding, and backstep to control distortion; clean surfaces to bare metal.

Adhesive bonding: surface preparation is critical; follow manufacturer's open time and clamp time; test bond strength.

Fastener spacing: follow SMACNA standards; typically 50 mm (2 in) from ends and 150 mm (6 in) on center for duct seams.

Dissimilar metals: isolate with tape or gasket to prevent galvanic corrosion; especially aluminum and steel.

Inspection: check joint tightness, fastener engagement, and sealant application; leak test ducts per specifications.

Flashing: lap joints in direction of water flow; minimum lap 75 mm (3 in) for roof flashing; sealant at laps.

Rain screen principle: provide drainage plane, air barrier, and ventilation behind cladding to manage moisture.

Metal roofing: fasten with screws with EPDM washers; drive until washer just contacts panel; do not overdrive.

Thermal movement: allow for expansion and contraction; use slotted holes or clip systems; typical 1 mm/m for steel, 2.4 mm/m for aluminum over 100°C range.

Wall panels: install with proper backup, shims, and sealant; maintain weep holes at base for drainage.

Clearances: maintain required clearance from combustible materials for flues and chimneys as per code.

Anchorage: use corrosion-resistant fasteners; embedment depth per manufacturer and code; test pull-out if required.

Quality: verify plumb, level, and square; check weathertightness before closing in walls.

Duct sizing: use equal friction method or static regain; velocity limits for noise: 5–7 m/s (1000–1500 fpm) in main ducts.

Duct sealing: seal all transverse joints and seams; use mastic, tape, or gaskets; SMACNA Seal Class A for high pressure.

Hangers and supports: spacing per SMACNA: 2.4 m (8 ft) for rectangular duct, 3 m (10 ft) for round; support at joints.

Flexible duct: limit length to 1.5 m (5 ft) and avoid sharp bends; sag reduces airflow.

Fire dampers: install at fire-rated penetrations; must be inspected and tested after installation.

Equipment vibration isolation: use spring isolators or neoprene pads; align shafts and belts; check rotation.

Refrigerant piping: follow manufacturer's sizing; insulate suction line; pressure test with nitrogen.

Condensate drains: slope 1% (1/8 in per ft) to drain; install trap; test for leaks.

Air balancing: measure airflow with anemometer or pitot tube; adjust dampers to achieve design flows within ±10%.

Pitot tube traverse: measure velocity pressure at points across duct; average and convert to velocity: V = 1096 × √VP (ft/min) or V = 1.29 × √VP (m/s).

Static pressure: measure at fan inlet and outlet; compare to fan curve; check for duct leaks or blockages.

Leak testing: duct leakage test per SMACNA; pressurize and measure leakage; allowable leakage depends on seal class.

Commissioning: verify installation against design, test equipment operation, and document results in commissioning report.

Hydronic balancing: use balancing valves; measure flow with ultrasonic or differential pressure; adjust to design flow.

Controls verification: check sensor calibration, actuator operation, and sequence of operation; trend data.

Safety: lockout/tagout during testing; wear PPE; ensure guards in place.