Sri Lanka NVQ L3 Carpenter cheat sheet

Personal protective equipment for carpentry: safety helmet, safety boots, eye protection when cutting or nailing, hearing protection above 85 dB(A), dust mask (FFP2 minimum) for timber dust and silica-bearing concrete dust.

Wood dust is a carcinogen (nasal cavity and sinuses); Sri Lanka's Factories Ordinance and its Woodworking Machinery Regulations require local exhaust ventilation and dust control at machines, not only a mask.

Hand-arm vibration syndrome risk: keep exposure to percussive and rotary tools under the 5 m/s² A(8) action level where a vibration meter is available; rotate tasks and report tingling or numbness.

Portable circular saw kickback: the guard must close freely, the riving knife must be fitted and aligned with the blade, and the workpiece must be supported on both sides of the cut.

Abrasive wheel and cutting-disc speed: never fit a disc whose marked maximum speed is below the machine's no-load speed (rpm); the disc may burst.

Ladder rule 4:1 - the base is set out one unit for every four units of height, and the ladder extends about 1 m (3 rungs) above the landing point.

Scaffold working platform: minimum 600 mm width for general use, fully boarded, toe boards and guardrails at 1 m and 0.5 m, and no work from the top guardrail.

Timber preservative and solvent safety: CCA-treated timber dust is toxic - cut outdoors or with extraction, wash hands before eating, and never burn offcuts (arsenic fumes).

Waste hierarchy in practice: reduce offcuts by cutting lists, reuse formwork and packing timber, recycle clean wood, and segregate solvent, paint and preservative containers as hazardous waste.

Crosscut saw tooth geometry: crosscut teeth are filed with a bevel (knife-edge) to sever fibres; rip teeth are filed square (chisel-edge) to chisel fibres along the grain.

Hand saw set: the set (kerf width) must exceed the blade plate thickness to prevent binding; too much set gives a wandering, rough cut.

Sharpening angles: plane irons commonly honed at 25° primary bevel with a 30° micro-bevel; a chisel honed at 25–30°; a steeper bevel (35°+) suits hard, abrasive timbers.

Try square checks 90°; mitre square checks 45°; a sliding bevel transfers any angle. A square is only trusted after it is checked against a true straightedge (flip test).

Spirit level accuracy is quoted in mm per metre (e.g. 0.5 mm/m); check it by reversing it end-for-end on the same surface - the bubble must read the same.

Plumb-bob and line: a plumb line gives vertical reference over height; a chalk line gives a straight reference over distance and is snapped, not dragged.

Portable circular saw depth of cut: set blade projection to about 5 mm more than timber thickness to reduce exposed blade and splintering.

Drill and bit selection: twist bits for metal, masonry bits with carbide tips for concrete, brad-point bits for accurate holes in timber, Forstner bits for flat-bottomed hinge recesses.

Machine maintenance rule: isolate and lock off before changing blades or belts; check guards, cables and plugs (RCD protection) before every use.

Timber moisture content (MC) = (wet mass − oven-dry mass) / oven-dry mass × 100%. Interior joinery is normally specified at 8–12% MC; structural timber at 15–20% or less depending on exposure.

Shrinkage is anisotropic: tangential shrinkage is roughly twice radial; longitudinal shrinkage is negligible. This causes cupping, bowing and twisting on drying.

Seasoning methods: air drying (slow, to about 15–20% MC) and kiln drying (controlled, to 8–12% MC, also sterilises insect eggs).

Strength grading: visual grading checks knots, slope of grain, wane and fissures; machine grading measures stiffness (modulus of elasticity) and assigns a strength class.

Softwood vs hardwood is botanical (conifers vs broadleaved), not a hardness statement - balsa is a hardwood, and some softwoods are harder than light hardwoods.

Plywood: odd number of veneers, grain of adjacent plies at right angles; exterior grades use WBP (weather-and-boil-proof) glue. Blockboard and laminboard have a core of strips.

MDF and particleboard swell on wetting; MDF machines and finishes well but has low screw-holding on edges - use confirmats or dowels rather than edge screws.

Timber defects: shakes (separation along grain), checks (drying cracks across rings), knots (branch bases), and fungal decay requiring MC above about 20% to progress.

Preservative and durability: heartwood of naturally durable species resists decay better than sapwood; sapwood is permeable and must be treated if exposed.

Scale reading: 1:50 means 1 mm on the drawing represents 50 mm in reality; multiply drawing dimensions by the denominator to get real sizes.

3-4-5 method for a right angle: measure 3 units along one line and 4 along the other; the diagonal must be 5 units (Pythagoras: a² + b² = c²).

Building rectangle check: diagonals of a true rectangle are equal - measure both diagonals and adjust until they match.

Datum: a fixed reference level or line from which all heights are set; record it on the drawing and mark it physically on site.

Setting-out lines: use a builder's line and profiles (batter boards) offset from the excavation so the line survives digging; transfer marks with a plumb-bob.

Drawing types: plan (view from above), elevation (vertical face), section (cut through), and detail (enlarged part). Hidden work is shown by dashed lines.

Dimension conventions: dimensions in millimetres on building drawings unless stated; give overall dimensions and a running chain of dimensions, never both duplicated inconsistently.

Levelling: a level instrument or water level transfers a level; the staff reading subtracted from a known reduced level gives the new level.

Tolerance and checking: re-measure critical settings (door openings, roof pitch, floor levels) before fixing; record as-built deviations.

Formwork loads: fresh concrete exerts hydrostatic pressure ≈ 24 kN/m³ × height, reduced by setting time, pour rate and temperature; design props and ties for the actual pressure.

Formwork must be: accurate in line and level, rigid, joint-tight to prevent grout loss, and treated with a release agent before the pour.

Striking times depend on concrete strength gain, not a fixed clock: soffits and props to slabs/beams stay until concrete reaches the specified strength (often 70% for props, per specification).

Vertical faces (columns, walls) can usually be struck after 24–48 hours if the concrete is hard enough not to be damaged, but must be re-propped where required.

Camber: long spans are set with a slight upward curve to offset deflection under load.

Props and bracing: props are plumb, on firm sole plates, and braced in both directions; wedges allow fine adjustment and controlled lowering.

Formwork tolerances: check plumb of columns, level of slab soffit, and alignment of beam sides before concreting; once poured, correction is expensive.

Reuse: clean, oil and stack formwork flat; damaged faces cause surface defects; plywood face quality determines the finish class of the concrete.

Boxing out: openings, sleeves and blockouts are fixed to the formwork so they cannot float during vibration.

Roof pitch = rise / run (or rise / span × 2). Pitch angle = arctan(rise/run); a 30° pitch has a rise/run of about 0.577.

Common rafter length = √(rise² + run²); add for eaves overhang and subtract for ridge thickness as required.

Rafter spacing follows purlin and sheet/tile module (commonly 400–600 mm centres); purlin spacing follows the covering's span capability.

Roof components: ridge board, common rafters, purlins, wall plate, hip rafters, jack rafters, valley rafters, collar ties, and barge boards.

Hip roof: four sloping planes; hip rafters run from the corners to the ridge; jack rafters shorten progressively. Valley: internal intersection of two roof planes.

Ceiling joists tie the wall plates and resist rafter thrust; collar ties near the ridge resist uplift and spread.

Corbel/overhang and birds-mouth: the birdsmouth notch seats the rafter on the wall plate; the seat cut must not exceed one-third of rafter depth.

Roof covering and ventilation: provide ventilation at eaves and ridge so moisture from below does not condense on the underside of sheets.

Setting out a roof: establish wall plate level and square, mark rafter positions on the plate, cut a pattern rafter and test-fit before cutting the set.

Door leaf sizes: standard internal door 762 × 1981 mm (2 ft 6 in × 6 ft 6 in) or 838 × 1981 mm; external doors usually 838 or 914 mm wide.

Door frame clearance: allow about 3 mm at each side and top for the leaf, and 8–10 mm clearance at the floor for internal doors (undercut for ventilation).

Hinge selection: butt hinges for flush doors; hinge positions about 150 mm from top and bottom, with a third hinge on heavy doors.

Door swing and handing: the hand is determined by which side the hinges are on when viewed from the opening side; fire doors must swing in the direction of escape and be self-closing.

Window types: casement (side-hung), awning (top-hung), sliding sash, and fixed; opening sashes need a drip and a weather seal.

Glazing safety: glazing in doors and low windows must be safety glass or protected; glass must not be relied on for structural support.

Ironmongery: locks, handles, closers and stays must align with the door thickness and stile width; check backset and centres before mortising.

Joinery joints: mortise and tenon for frames, dovetail for drawer boxes, dowel or domino for butt joints, and loose tenons for speed.

Setting out a frame: mark the face side and face edge, work from a single reference, and check diagonals for square before assembly.

Floor joist sizing depends on span, spacing and loading; solid timber floorboards are laid with a small gap (about 1–2 mm) for expansion and secret-nailed through the tongue.

Timber floor moisture: boards should be at service moisture content (about 8–12%) before laying; a vapour barrier or ventilation is needed under suspended floors.

Suspended timber floor: sleeper walls or hangers support the joists; provide ventilation openings in the external wall to prevent rot.

Ceiling systems: direct-fixed boards to joists, or a suspended grid; plasterboard joints are staggered and taped/skimmed; fixings at 150–200 mm centres on edges.

Partition types: stud partition (timber or metal studs, plasterboard), block partition, and glazed screens; studs at 400 or 600 mm centres to suit board width.

Acoustic and fire partitions: add insulation, double-layer boards, and seal all gaps; fire-rated partitions require tested systems and correct fixings.

Skirting, architrave and trims: fix after the finish is applied; mitre external corners and scribe internal corners for a tight fit.

Finishes: sanding sequence from coarse to fine (e.g. 80 → 120 → 180 grit), then seal; knots in resinous timber need knotting solution before painting.

Level and fall: floors are set level; wet areas need a fall to the drain, typically 1:80 to 1:100.

Quantity take-off: measure net lengths/areas from drawings, then add wastage allowances - typically 5% for timber, 10% for sheet materials and tiles.

Area of a rectangle = length × width; volume = length × width × depth; convert units consistently (1 m² = 10,000 cm²; 1 m³ = 1,000,000 cm³).

Timber quantity is often expressed in cubic metres: volume = cross-section (m²) × length (m) × number of pieces.

Formwork area is measured as the contact area of concrete with the form (soffit + sides), not the total area of plywood used.

Labour estimation: output rates (e.g. m² per carpenter-day) × quantity gives labour days; add allowance for supervision, breaks and weather.

Programme logic: sequence work so wet trades (concrete, plaster) precede dry finishes; formwork striking time constrains the cycle.

Bill of quantities structure: description, unit (m, m², m³, nr), quantity and rate; the rate covers labour, material, plant and overhead.

Cost control: track material wastage against the allowance; offcut reuse and accurate cutting lists reduce loss.

Site planning: material storage off the ground and covered, access routes for deliveries, and a cutting area away from traffic.

Toolbox talk: a short pre-task briefing covering the task, hazards, controls, PPE and who is in charge; record attendance.

Permit to work: required for hot work, confined spaces and work at height; the permit states the precautions and the time limit.

Method statement: describes the sequence, plant, materials, supervision and controls for a task; the risk assessment identifies hazards and who may be harmed.

Reporting: near-misses and defects are reported to the supervisor immediately; an accident book entry is required for injuries.

Instruction chain: receive instructions from your supervisor; if an instruction is unsafe, stop and raise it - the right to refuse unsafe work.

Drawing communication: always work from the current revision; record changes on site instructions and confirm verbally agreed changes in writing.

Team coordination: agree the setting-out datum and face-side marks with the next trade so that work aligns; protect finished work from others.

Cultural and language awareness on site: confirm understanding by asking the person to repeat the instruction back; use sketches and simple terms.

Housekeeping: clear offcuts and dust at the end of each shift; keep walkways clear and store materials so they cannot fall.