Wood, Metal & Composites

Wood is where almost everyone starts, and for good reason - it is cheap, widely available, forgiving to cut and pleasant to handle. In digital fabrication you rarely use raw solid timber; you use engineered sheet goods, because they are flat, stable and standard-sized. Plywood is thin veneers cross-laminated for strength in both directions and is the fablab workhorse - laser-cut for screens and models, routed for furniture. MDF (medium-density fibreboard) is dense, uniform and edge-machines cleanly, making it ideal for CNC-milled moulds, jigs and painted joinery, though its dust is fine and must be extracted. Acrylic and other plastic sheet behave like sheet goods on a laser and belong here in practice.

Machining notes: wood is anisotropic, so mind the grain - climb versus conventional milling changes tear-out, and delicate laser cuts run cleaner along the grain. It burns and chars on a laser (a feature or a flaw depending on the look), moves with moisture, and can hide voids and knots that ruin a precise cut. Its great virtue is forgiveness: a slightly-off joint still crushes home, glues, sands and paints. Typical uses span the whole workshop - models, prototypes, furniture, formwork, interior screens and the moulds other families are made on.

Wood also rewards learning its grades and thicknesses, because standardisation is half of what makes it easy. Sheet goods come in predictable thicknesses (though a nominal 18 mm sheet is rarely exactly 18 mm - always measure before you cut mating slots), and plywood grades range from rough structural to cabinet-quality birch with few voids, which matters enormously for a clean laser edge. Solid timber still appears for finish and strength, but it moves most with humidity and hides the most surprises, so for precise digital work the engineered panels win. The everyday reality of a fablab is a rack of ply, MDF and acrylic sheet, a laser and a router - and that modest kit, worked well, covers a genuinely large share of real fabrication.

Metals give you strength, stiffness and durability nothing else matches, at the cost of harder, slower, more hazardous machining. The three you meet most are aluminium (light, soft enough to mill fast, corrosion-resistant - the default for machined parts and structure), mild steel (cheap, strong, weldable, the backbone of frames and brackets, but it rusts), and brass or stainless (for finish, corrosion resistance or precision). Sheet metal is a world of its own: cut on a CNC laser, plasma or waterjet, then bent on a press brake - which is exactly where spring-back from the last lesson bites.

Machining metal is unforgiving. It generates heat, so you run coolant or air blast, clear chips so they do not weld to the tool, and pick feeds and speeds for the specific alloy - too fast and you burn the cutter, too slow and you rub and work-harden. Joining is usually welding (fusing with heat, a skilled and hazardous process), fastening or riveting, rather than glue. The hazards are real: sharp swarf, hot work, bright arcs, fumes - all demand training, guarding and PPE, and none should ever be run unsupervised. The payoff is parts that carry real load, hold tight tolerance and last for decades.

A composite is two materials working together: strong fibres (carbon, glass or aramid) carrying the load, held in a matrix (usually an epoxy or polyester resin) that bonds them and transfers stress. The result is astonishing strength and stiffness for the weight - which is why boats, aircraft, car bodies and high-end architectural shells use them. But composites are not cut from stock the way wood and metal are; they are built up over a mould by layup: fabric plies are laid in chosen orientations, wetted with resin (hand layup, or vacuum infusion for quality), then cured, often under a vacuum bag or in an oven.

This is where digital fabrication usually enters - not making the finished part, but CNC-milling the mould (from tooling board, MDF or foam) that gives the part its shape and surface. The fibre orientation is a design variable: plies at 0, 45 and 90 degrees tune stiffness along different axes, so you engineer the layup, not just the shape. The trade-offs are serious: composites are labour-intensive, the resins and dust are genuine health hazards demanding ventilation, gloves and respirators, and cured composites are very hard to recycle - a point the sustainability lesson returns to. Use them where light-and-stiff truly matters, not by default.

Most projects do not choose one family - they combine them, letting each do what it is best at. A pavilion might have a milled MDF or foam mould (wood family) that casts a fibreglass shell (composite), hung on a welded steel frame (metal), with laser-cut ply fixtures inside. The skill is matching each part to the right family by asking four blunt questions: How much load must it carry? How much does weight matter? What finish and durability does it need? And what is the budget, in money and in labour?

Rough guidance: reach for wood and sheet goods when it is a model, a prototype, interior joinery, formwork or a mould - cheap, fast, forgiving. Reach for metal when it carries real structural load, must last outdoors, or needs tight tolerance and machined precision. Reach for composites only when strength-to-weight or a complex doubly-curved shell genuinely justifies the labour and the health and recycling costs. And remember the previous lesson: within each family, the specific material still behaves its own way under the tool. Family gets you most of the way; the individual blank gets you the rest.

A useful habit is to sketch the assembly and colour each part by family before you detail anything - it forces you to justify every expensive or hazardous choice. If a part is metal, ask what load or durability earns that cost; if it is composite, ask what a milled-mould-and-layup truly buys over a simpler material. Often the honest answer downgrades a part to plywood, and the project gets cheaper, faster and easier to recycle for free. The families are not a hierarchy with composite at the top; they are a palette, and good making is spending each material only where it pays.

Each family carries hazards that scale with how serious the material is, and treating them casually is how people get hurt. Wood and sheet goods: fine dust (MDF especially) is a respiratory hazard and a fire risk near a laser, and routers throw chips and can grab - use extraction, guarding and eye protection. Metals: sharp swarf, hot chips, welding arcs and fumes, and machines with enormous force; press brakes and mills demand training and never a wandering hand. Composites: uncured resins and hardeners are sensitisers and irritants, fibre dust from trimming cured parts is hazardous to breathe, and both need real ventilation, gloves and respirators.

The through-line for this whole course applies: fabrication is supervised, trained, PPE-protected work - never run a laser, spindle, welder or layup unsupervised, and defer structural, fire and code sign-off to engineers and authorities. Respect for the material and the machine is not caution for its own sake; it is what lets you keep making. The best makers are the ones still working, with all their fingers and their lungs, decades in.