How to choose the right metal for your CNC part.

The 7 dimensions that drive material choice.

Material selection for CNC parts is a constrained optimization — you're minimizing cost while meeting seven performance requirements. For most parts, only 2–3 of these actually constrain the choice. Identify yours first, then pick the cheapest material that satisfies them.

Starting defaults by use case.

When to pick aluminum — 60% of parts.

Aluminum is the default CNC material because it combines low density, good machinability, corrosion resistance, and reasonable cost. Most brackets, housings, enclosures, mounts, and structural frames should start as aluminum and only move up if there's a specific reason.

• 6061-T6 — the baseline. Good strength (276 MPa yield), excellent weldability, anodizes cleanly. Use for 80% of aluminum parts. See full spec →
• 7075-T6 — when 6061 is strength-limited. Yield 503 MPa, but 2.5× the material cost, slightly lower corrosion resistance. See full spec →
• 5052-H32 — sheet-forming grade. Excellent corrosion resistance (marine-rated), lower strength than 6061. Mostly for bent/formed enclosures.
• 2024-T3 — aircraft-skin grade. Similar strength to 7075 but better fatigue resistance. Poor weldability, poor corrosion (usually clad).
• 6063 — extruded heat-sink grade. Better surface finish in anodizing, lower strength than 6061.

When to pick carbon or alloy steel.

Steel comes in when you need strength at 3–4× the density of aluminum and low cost. Heat-treatable alloy steels are the default for shafts, gears, and load-bearing machine parts. Plain carbon steels are for jigs, fixtures, and non-corrosive structural use.

• 1018 mild steel — lowest cost, easy to machine, easy to weld. Use for non-heat-treated brackets, fixtures, and jigs. No corrosion resistance — paint or plate.
• 1045 medium carbon — can be flame-hardened on surfaces. Used for shafts, keys, and gears in non-corrosive service.
• 4140 (42CrMo4) — the default alloy steel. Heat-treatable to ~45 HRC. Used for shafts, connecting rods, tooling bodies, and anything that sees cyclic load.
• 4340 — 4140 with more nickel. Better impact toughness; use when 4140 is underperforming in fatigue. More expensive.
• A2 / D2 tool steel — air-hardening, very wear resistant. For dies, punches, stamping tools, wear plates.

When to pick stainless steel.

Stainless is the answer whenever moisture, washdown, food, blood, or mild chemicals are involved. It's 2–3× harder to machine than aluminum, so expect 30–80% higher part cost for the same geometry.

• 303 — free-machining austenitic. Has sulfur added for cleaner chips; use for turned parts in mild environments. Avoid if corrosion is critical or if welding is needed.
• 304 / 304L — general-purpose stainless. Good corrosion in food, beverage, pharmaceutical, and most outdoor environments. See full spec →
• 316 / 316L — added molybdenum gives chloride resistance. Use for marine, coastal outdoor, and all sour-service environments. See full spec →
• 17-4 PH — precipitation-hardening. Can be aged to ~1200 MPa yield. Used where high strength + corrosion are both required (aerospace fasteners, pump shafts).
• 420 — martensitic. Hardens to 50+ HRC. Used for cutlery, surgical instruments, corrosion-resistant dies.

When to pick titanium.

Titanium's sweet spot is when you need stainless-equivalent corrosion resistance but at half the density. It's 4–6× more expensive than stainless and harder to machine, so it shouldn't be a default — but it's excellent for weight-critical, biocompatible, or chloride-aggressive applications.

• Grade 2 (commercially pure) — low-strength titanium. Best formability and corrosion resistance. Used for chemical process parts, marine heat exchangers, and biocompatible non-structural devices.
• Grade 5 (Ti-6Al-4V) — the titanium workhorse. Yield 830 MPa, biocompatible, weldable. Used for aerospace structural parts, orthopedic implants, race bike components. See full spec →
• Grade 23 (Ti-6Al-4V ELI) — extra-low interstitial. The medical-implant version of Grade 5. Slightly lower strength but better toughness and fracture resistance.

When to pick nickel alloys.

Nickel superalloys earn their cost when you need strength at temperature above 500°C, or aggressive corrosion resistance in oil/gas service. Expensive to buy and machine — budget 8–12× the aluminum equivalent.

• Inconel 625 — solid-solution-strengthened. Best weldability, service to 980°C. Used for chemical process vessels, exhaust components, subsea manifolds.
• Inconel 718 — precipitation-hardened. 1240 MPa yield in aged condition, service to 650°C. The dominant alloy for aerospace hot-section parts and O&G downhole. See full spec →
• Hastelloy C-276 — extreme chloride and acid resistance. Used in chemical plants, chlor-alkali, wet FGD scrubbers.
• Monel 400 / K-500 — nickel-copper. Best choice for seawater service at moderate temps.

When to pick copper or brass.

Copper alloys win when electrical or thermal conductivity is the primary requirement, or when you need non-sparking / non-magnetic behavior.

• C110 (OFHC copper) — pure copper, best conductivity. Used for bus bars, electrodes, heat sinks, RF components.
• C360 free-machining brass — the fastest-machining metal. Used for fittings, fasteners, connectors, small electrical components. See full spec →
• C260 cartridge brass — drawn/formed. Used for ammunition cases, deep-drawn parts.
• Beryllium copper (C17200) — age-hardenable copper. High strength + high conductivity + non-sparking. Used for springs, electrical contacts, and oil/gas non-sparking tools.
• Bronze (C932 / C954) — excellent bearing properties. Used for bushings, thrust washers, worm gears.

When to pick machined plastics.

Plastics machine cleanly on CNC and make sense for electrical insulators, low-load structural parts, and chemically aggressive environments where metal won't survive.

• Delrin (POM acetal) — best general-purpose machining plastic. Low friction, dimensionally stable, easy to cut. Used for gears, bushings, small structural parts. See full spec →
• PEEK — high-performance. 250°C continuous service, chemically resistant, biocompatible. Expensive. Used for medical implants, aerospace brackets, semiconductor wafer carriers. See full spec →
• PTFE (Teflon) — lowest friction, chemically inert. Soft, hard to machine to tight tolerance. Used for seals, bearing surfaces, chemical process parts.
• Ultem (PEI) — high-temp, high-strength. Flame-retardant, dimensionally stable. Used for aircraft interiors, electrical housings.
• Nylon (PA6, PA66) — tough, wear-resistant. Absorbs moisture (swells slightly). Used for gears, wheels, bushings.
• UHMW / HDPE — low-cost. Low friction, impact resistant. Used for wear strips, guides, non-structural parts.

Material-overspec traps we see most often.

Quick reference chart.

For a printable version, see our materials library index which includes all of the above with linked detailed spec pages.

Relative cost is per finished part with identical geometry (machining + material), benchmarked against 6061 = 1.0×, production quantity 100 parts.