JC Wood Technology cheat sheet

Cell wall: cellulose microfibrils wound steeply in the S2 layer of the secondary wall give longitudinal tensile strength; lignin resists compression; hemicellulose bonds the two.

Reaction wood: compression wood forms on the underside of leaning softwoods (high lignin, brittle, excessive longitudinal shrinkage); tension wood forms on the upper side of hardwoods (gelatinous G-layer, high cellulose).

Heartwood is dead, extractive-rich, less permeable and usually more durable; sapwood is living, starch-rich, permeable and prone to stain, borer and insect attack.

Fibre saturation point is about 28–30% moisture content; above it no shrinkage or swelling occurs and strength is constant, below it strength rises as moisture content falls.

Equilibrium moisture content is about 12% at 20 °C and 65% RH and 8–10% in heated interiors; sorption hysteresis means the desorption curve lies above the adsorption curve.

Shrinkage from green to 12% MC: tangential 5–10%, radial 3–6%, longitudinal under 0.5%; tangential is roughly twice radial, which is why flatsawn boards cup toward the bark side.

Density is the best single predictor of strength and stiffness; a 10% increase in density gives roughly 20% more bending strength.

Kiln schedules set dry-bulb temperature against wet-bulb depression; too fast early drying causes case-hardening and honeycomb, too fast late drying causes surface checks and end splitting.

Softwoods are gymnosperms with tracheids only and no vessels; hardwoods are angiosperms with vessels - hardness does not define the group, since balsa is a hardwood.

Ring-porous hardwoods (oak, ash, elm) have large earlywood pores in a distinct band; diffuse-porous hardwoods (beech, maple, birch) have evenly scattered pores of similar size.

Knots: live/intergrown knots are bonded to the surrounding wood and sound; dead/encased knots are loose and downgrade the piece; a spike knot appears on a quartered face.

Seasoning defects: checks run along the rays, shakes separate between growth rings, case-hardening is locked-in internal stress, honeycomb is internal cracking from over-rapid drying.

Decay: brown rot leaves cubical, crumbly residue and mainly attacks softwoods; white rot leaves pale fibrous residue and mainly attacks hardwoods; both need moisture content above about 20%.

EN 338 strength classes: softwoods C14–C50 (C24 is the common structural carcassing grade, 24 N/mm² characteristic bending), hardwoods D18–D80.

EN 350 durability classes run 1–5 (1 = very durable) and EN 335 use classes run 1–5 (1 = interior dry, 4 = ground contact, 5 = marine); durability, use class and treatment must be matched.

Quartersawn stock is more dimensionally stable and shows medullary-ray figure; flatsawn stock is cheaper, available in wider boards and cups toward the bark side.

Grind plane irons and bench chisels at a 25° primary bevel and hone a 30° micro-bevel; mortise chisels take 30–35° to survive levering in hardwoods.

Waterstones around 1000 grit hone and 6000–8000 grit polish; flatten the stone on a diamond plate before each session so the bevel stays flat.

The cap iron sits flush on the iron with its edge 0.3–1 mm back from the cutting edge; it turns the shaving and controls tear-out on reversing grain.

Crosscut saws are filed with 60–75° fleam and a bevel across the plate; rip saws are filed square across with 0° fleam, and all teeth are jointed level before filing.

Saw sequence: joint the teeth, file the fleam, set each tooth about half the blade thickness to each side (less for rip), then side-dress on a stone.

Cutting rule: clamp the work, keep both hands behind the cutting edge, cut away from the body, and use a slicing action for paring cuts.

A sharp edge shows no reflecting line when sighted along the bevel; test by paring end grain or slicing thin paper.

Table saw: blade projection 3–5 mm above the stock, riving knife in line and within 8 mm of the blade, guard fitted, push stick for stock narrower than 300 mm.

Tooth geometry: ATB for crosscut and sheet goods, flat-top rip teeth for fast ripping, combination for mixed work; roughly 24–30 teeth for ripping and 60–80 for fine crosscutting.

Kickback control: stand to one side of the blade line, use a short rip fence for solid timber, and never trap the work between fence and blade without a push block.

Band saw: side guides and thrust bearing set about 0.5 mm behind the tooth gullets; blade width and teeth per inch set the minimum cutting radius.

Router feed: move the work right to left against the cutter rotation for a conventional cut; climb cutting is reserved for light finishing passes because it pulls the work forward.

Drill press speed rule: halve the spindle speed when doubling the bit diameter to keep surface speed roughly constant; clamp the work or use a drill vice.

Planer/thicknesser: 1–2 mm depth of cut per pass (3 mm maximum on large machines); never feed stock shorter than the gap between the feed rollers and always use push sticks.

Site practice: 110 V centre-tapped earth tools on a 30 mA RCD, M-class extraction for hardwood dust, and check NVR switch, brake and guards before every use.

Mortise-and-tenon proportion: tenon thickness about one third of the rail thickness, with a haunch above it to fill the groove and resist twist in framed doors.

Dovetail angles: about 1:6 (9.5°) for softwood and 1:8 (7°) for hardwood; tails are cut on the horizontal member and pins on the side of a drawer.

Dowel joints: dowel diameter about one third of the board thickness, spacing no more than 10× the diameter, end and edge distance at least 2× the diameter.

Carcass: a back panel housed in a groove or rebate at least 12 mm from the rear edge squares the box and resists racking; 18 mm MDF or ply suits sides and shelves up to about 750 mm span.

Groove, housing and rebate all remove section, so leave at least one third of the thickness remaining in the member carrying the joint.

Frame joints: haunched mortise-and-tenon at door stiles, barefaced tenon where the rail meets a flush face, bridle joint for exposed decorative frames.

Movement allowance: a solid panel in a frame needs about 3 mm clearance per 300 mm of width, fixed at one point only with slotted or oversized fixings elsewhere.

Glue-up sequence: dry fit, check that diagonals are equal, apply adhesive to both surfaces, clamp within the open time and re-check square before the cure.

PVA to EN 204: D2 for interior dry, D3 for interior with frequent short-term wetting or exterior protected, D4 for frequent wetting; polyurethane foaming adhesive is gap-filling and water-resistant; epoxy suits oily tropical woods.

Bond strength depends on joint fit of about 0.05–0.15 mm, clean freshly machined surfaces, timber at 8–12% MC and clamp pressure around 0.5–1 N/mm² for PVA.

Abrasive sequence 80 → 120 → 180 → 240; never skip more than one grit step, or the coarse scratch pattern will not be removed by the finish.

Aluminium oxide for general wood, silicon carbide for finishing and wet flatting between coats, zirconia for heavy belt sanding; stearated paper resists clogging under paint.

Finish selection: oil penetrates and is easily repaired, shellac dries fast but is not water resistant, polyurethane is durable but hard to repair, water-based acrylic has low VOC.

Raise the grain with a damp cloth, de-nib with 240–320 grit, and always sand between coats in the direction of the grain.

Preservatives: copper-based systems (copper azole, MCA) for exterior and ground contact, boron salts for interior protected timber; CCA and creosote are restricted, so check the use class.

End grain to end grain is never a sound glued joint on its own; the porous end draws adhesive away from the interface and starves the glue line.

First-angle projection places the view from above below the elevation and is standard in Europe; third-angle projection places it above; the truncated-cone symbol identifies which convention is used.

Line hierarchy: thick continuous for visible edges, dashed for hidden detail, chain/dash-dot for centre lines and pitch circles, thin continuous for dimensions and projection lines.

Dimension once only, either from a datum face or along a series of parallel dimension lines; never duplicate a dimension already given on another view.

Standard scales: 1:1 for details, 1:5 for joints, 1:10 for cabinet work, 1:20 to 1:50 for room layouts.

Setting out: mark face side and face edge on two adjacent jointed faces with arrows pointing to them, and take every measurement from those faces.

A working drawing set comprises general arrangement, plan, elevations, sections, detail views, cutting list and specification.

Design process: brief → research → specification → concept → development → prototype → evaluation, each stage producing an output that can be checked against the brief.

Typical tolerances are ±1 mm for joinery and ±0.5 mm for cabinet components; cumulative error is checked by comparing diagonals rather than by trusting a single measurement.

Hardwood dust is a carcinogen causing nasal adenocarcinoma; the 8-hour workplace exposure limit is 3 mg/m³ for hardwood dust and 5 mg/m³ for softwood dust, controlled by LEV first and RPE second.

Fine wood dust can explode when dispersed at roughly 30–40 g/m³; keep ignition sources out of extraction plant, earth ducting and fit explosion relief.

Noise action values are 80 dB(A) lower and 85 dB(A) upper; hearing protection is mandatory above the upper value and available on request between the two.

Electrical safety on site: 110 V centre-tapped earth tools, 30 mA RCD protection, PAT testing, and no defeat of guards or interlocks.

COSHH requires a safety data sheet, an exposure assessment and recorded control measures for adhesives, finishes, preservatives, solvent vapours and dust.

Fire classes: wood, paper and dust are Class A, extinguished with water, foam or ABC dry powder; CO2 is for electrical equipment, not for deep-seated wood fires.

Machine rules: NVR switch and brake working, guards in place, push sticks used, no gloves at rotating machines, eye protection and suitable RPE worn.

Workshop layout: separate machining, assembly and finishing areas, keep walkways at least 1 m clear, store finishes in a fire-rated cabinet and clear offcuts and shavings at the end of each session.

FSC and PEFC are the two main forest certification schemes; an on-product claim requires chain-of-custody certification through every stage of processing.

EUTR in the EU and UKTR in the UK require due diligence: species, country of harvest, legality evidence, risk assessment and risk mitigation before timber is placed on the market.

CITES Appendix I bans commercial trade in the listed species; Appendix II requires export permits - rosewood, true mahogany and ebony are listed.

About 1 m³ of timber stores roughly 0.9–1.0 tonne of CO2, so long service life, reuse and recycling keep that carbon locked up for longer.

Formaldehyde classes: E1 (≤0.124 mg/m³ in chamber testing), CARB Phase 2 and E0/ULEF low-emission boards; specify E1 as the minimum for interior board products.

Embodied impact is lowest for locally sawn softwood (roughly 0.1–0.3 kg CO2e per kg dry) and higher for MDF and plywood because of resin, drying and pressing energy.

Reclaimed timber and board reduce impact but must be checked for nails and fixings, lead paint, preservative residues and loss of strength or section.

Specification levers: certified and local species, durability matched to the use class, low-VOC adhesives and finishes, and design for disassembly and reuse.