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Choosing a material for your CNC part

Material affects three things at once: how the part performs, what the stock costs, and how long it takes to machine. Here's how the common UK options stack up so you can pick with confidence.

Aluminium — the everyday choice

6082 / 6061: the workhorses. Great strength-to-weight, corrosion-resistant, and they machine quickly — which keeps cost down. Ideal for brackets, housings, jigs, enclosures and general prototyping. 7075 is a stronger aerospace-grade alloy that costs more; use it when 6082 isn't stiff or strong enough. Aluminium also anodises beautifully if you want colour or extra surface protection.

Stainless steel — corrosion & strength

304 is the general-purpose stainless: tough, corrosion-resistant, food-safe. 316 adds molybdenum for marine and chemical environments. Both are strong and durable — but they machine slowly and are hard on tooling, so parts cost noticeably more than the equivalent in aluminium. Choose stainless when you genuinely need the corrosion resistance or strength.

Steel — structural & hard-wearing

EN1A (free-cutting mild steel) machines easily and is cheap — good for non-critical fittings and studs. EN8 is a medium-carbon steel with more strength for shafts and general engineering. EN24 / tool steels are stronger again and can be heat-treated, at higher cost and slower machining. Most steels will rust unless plated or painted, so factor a finish in.

Brass & copper — detail & conductivity

Brass (CZ121) machines superbly — clean, fast, excellent for fine detail, fittings, valve parts and anything decorative. It's more expensive per kilo than steel but the easy machining offsets some of that. Copper is chosen for electrical and thermal conductivity but is gummy to machine, so it carries a premium.

Plastics — light, insulating, cheap to cut

Acetal (Delrin) is the go-to engineering plastic: stiff, low-friction, dimensionally stable — great for gears, bushes and manifolds. Nylon is tougher and more wear-resistant. POM, PEEK and acrylic cover higher-temperature, high-performance or clear applications. Plastics are light and electrically insulating, and cut fast — though thin features can flex.

"Relative cost" combines stock price and how long the material takes to machine — a cheap metal that cuts slowly can still make an expensive part.

More: What CNC machining costs → · Which CAD file to send → · Tolerances & finishes →