NCCER Sheet Metal Worker cheat sheet

OSHA general industry 29 CFR 1910 and construction 29 CFR 1926 both apply to sheet metal work; construction sites generally fall under 1926 Subpart M (fall protection) and Subpart E (PPE).

Fall protection is required at 6 ft or more in construction (1926.501); guardrail top rail is 42 in ±3 in, midrail at 21 in, and toe boards 3.5 in high.

Hand protection: cut-resistant gloves (ANSI/ISEA 105 level) are used when handling sheet edges; sheet metal cuts are the most common injury in the trade.

Ladder rule: 4:1 slope for extension ladders, 3 ft extension above the landing, and 300 lb duty rating for Type IA; inspect before each use.

Eye protection must meet ANSI/ISEA Z87.1; when grinding or cutting, a face shield is worn over safety glasses, not instead of them.

Hazard communication (29 CFR 1910.1200): SDS sheets must be accessible for every chemical on site, including sealants, adhesives, and solvents.

Hot work (welding, cutting, grinding) requires a permit, a fire watch for at least 30 minutes after work ends, and 35 ft clearance from combustibles (or shielding).

Lift technique: keep the load close, bend at the knees, and use two-person or mechanical lifts for sheet goods over about 4 ft × 8 ft; a 4 × 8 sheet of 24 ga steel weighs about 40 lb.

Sheet metal gauges are non-linear: 24 ga mild steel is about 0.024 in, 26 ga about 0.018 in, and 20 ga about 0.036 in; galvanized and stainless use different gauge tables.

Aviation snips are color-coded: left-cut (red) cuts counterclockwise curves, right-cut (green) cuts clockwise, and straight (yellow) cuts straight or gentle curves.

The hand seamer (hand brake pliers) forms flanges up to 1 in deep; the depth of the jaw sets the maximum flange width.

A box-and-pan brake forms boxes and pans with a removable finger section; a bar folder (bar brake) is for simple bends and hems.

A Pittsburgh machine forms the Pittsburgh lock (a folded seam with a pocket) used to join duct sections; a lockformer rolls the seam profiles.

A notcher (hand or powered) removes corners so flanges can be folded without interference; notches must be square and to the bend line.

A rotary slitter or power shear cuts straight lines; a nibbler cuts curves and cutouts without distorting the panel.

Crimpers reduce the end of a duct so it fits inside the next section; a beader (crimper/beader) adds stiffening beads to increase rigidity.

Architectural scales: 1/4 in = 1 ft means 1/4 in on the drawing equals 12 in actual; multiply drawing dimension by 48 to get actual inches.

Views follow third-angle projection in North America: top view above front view, right side view to the right of the front view.

A duct run's centerline elevation is usually given as the bottom of duct (BOD) or centerline (CL); confirm which before laying out hangers.

True length is found by developing the inclined line; a line appearing foreshortened in one view is true length in a view perpendicular to it.

Radial line development is used for cones and pyramids (round and square-to-round transitions); triangulation is used for twisted or oblique transitions.

Parallel line development is used for prisms and cylinders (rectangular duct, round pipe); stretch-out equals circumference (π × diameter) for round work.

Allowances: bend allowance = (π/180) × bend angle × (inside radius + K × thickness), where K is typically 0.33–0.50 depending on material and radius.

A takeoff/quantity sheet lists duct by size, length, gauge, and fittings; fittings are counted by type and size, not by length.

Bend deduction = 2 × setback − bend allowance, where setback = (inside radius + thickness) × tan(angle/2); this determines the flat pattern length.

Minimum bend radius for mild steel is roughly 1 × thickness; for aluminum it is larger, and for 3003 aluminum about 1–2 × thickness depending on temper.

Shear clearance is about 5–10% of material thickness; too little clearance causes edge cracking, too much causes burrs and rollover.

The Pittsburgh lock, drive cleat, and S-cleat are the standard longitudinal seams; a Pittsburgh seam is typically locked and then hammered or crimped.

Spot welding (resistance welding) is used on galvanized and light-gauge sheet; weld current, time, and electrode force must be set for the gauge.

Galvanized steel must be welded with adequate ventilation because zinc oxide fume causes metal fume fever; grind the coating back at the weld zone when possible.

Annealing (heating and slow cooling) softens work-hardened sheet so it can be formed further; work hardening occurs with each cold bend.

Layout marks are made with a scratch awl or fine marker; a prick punch marks hole centers, and a center punch is struck before drilling to prevent walking.

Hanger spacing for rectangular duct: SMACNA/industry practice is typically 8 ft maximum for horizontal rectangular duct up to 60 in wide, 6 ft for wider duct, and 10 ft for round duct; follow the project specification when stricter.

Hangers must be independent of the duct; do not support duct from sprinkler pipe, conduit, or other trades' supports.

Duct must not be used as a walkway or support for other trades; reinforcement (angle, T-bar, or tie rod) is required above certain widths per SMACNA.

Flexible duct: keep bends to a minimum, limit sag to 1/2 in per ft of span, and do not compress the duct; excessive sag and compression increase pressure drop.

Sealing: SMACNA Seal Class A seals all transverse joints and seams; Class B seals transverse joints and longitudinal seams; Class C seals transverse joints only.

Fire dampers are required where ducts penetrate fire-rated assemblies; they must be installed per the listed assembly and be accessible for inspection.

Volume dampers balance branch airflow; a balancing damper is set and locked, and the position is recorded on the balancing report.

After installation, duct systems are leak-tested per SMACNA leakage classes; test pressure and allowable leakage depend on the class and duct size.

Airflow equation: CFM = velocity (fpm) × area (ft²); for a 24 in × 12 in duct, area = 2 ft², so 1,000 fpm gives 2,000 CFM.

Velocity pressure: VP = (V/4005)² in w.c. for standard air (0.075 lb/ft³); total pressure = static pressure + velocity pressure.

Duct sizing: equal friction method holds friction loss per foot constant; velocity reduction method steps velocity down after each branch.

Friction loss in duct is found from a duct calculator or the ASHRAE friction chart using CFM, duct size, and equivalent length of fittings.

Equivalent length converts fittings to straight duct: an elbow may equal 30–60 ft of straight duct depending on radius ratio and velocity.

Aspect ratio = long side ÷ short side; keep rectangular duct aspect ratio at or below 4:1 to limit friction and noise.

Sensible heat equation: BTUH = 1.08 × CFM × ΔT for standard air; latent heat uses 4.5 × CFM × Δgrains (or 0.68 × CFM × Δgrains for lb/hr forms).

Static pressure budget: typical residential supply plenum is 0.1–0.2 in w.c.; total external static pressure for a residential air handler is often 0.5 in w.c.

Roof pitch is rise over run; a 4:12 pitch rises 4 in per 12 in of run, an angle of about 18.4°, and slope factor = √(rise² + run²) ÷ run.

Minimum slope for standing seam metal roofing is typically 3:12 for structural panels and 1:12 for some hydrostatic (architectural) panels; check the manufacturer's listing.

Standing seam panels use concealed clips; clip spacing and panel expansion must allow thermal movement (about 0.0000065 in/in/°F for steel).

Hydrostatic (architectural) standing seam uses a sealant and a folded seam and can go to lower slopes than hydrokinetic (structural) panels.

Roof underlayment: high-temperature self-adhered membrane is common under metal roofs; ice dam protection is required at eaves in cold climates per code.

Flashing types: step flashing at sidewalls, apron flashing at headwalls, and counterflashing set into masonry reglets.

Gutters are sized by roof area and rainfall intensity; a 5 in K-style gutter handles roughly 5,500 sq ft of roof at 1 in/hr rainfall (varies by manufacturer).

Fasteners: use screws with EPDM washers on metal roofing; overdriving crushes the washer and creates a leak point.

SMACNA publishes HVAC Duct Construction Standards (rectangular and round), Architectural Sheet Metal Manual, and HVAC Air Duct Leakage Test Manual.

ASHRAE 90.1 sets energy requirements for duct insulation and sealing; ASHRAE 62.1 covers ventilation rates for commercial spaces.

The International Mechanical Code (IMC) governs duct installation, clearances, and fire dampers; the International Residential Code (IRC) covers one- and two-family dwellings.

NFPA 90A covers air conditioning and ventilating systems in commercial buildings, including duct clearance to combustibles (typically 2 in) and duct material limits.

UL 181 lists factory-made air ducts and connectors; UL 555 covers fire dampers, and UL 555S covers smoke dampers.

Duct insulation R-value and thickness are set by climate zone in the energy code; R-6 and R-8 are common for supply ducts in attics.

Shop drawings and submittals must be approved before fabrication; a submittal register tracks the status of each product data sheet and sample.

Change orders must be documented in writing before extra work proceeds; keep daily reports, time cards, and photos for delay and change claims.