How to Choose the Right Material for CNC Machining: 2026 Engineer’s Guide
A practical guide to selecting CNC machining materials by application. Aluminium, stainless, titanium, brass, plastics — strength, machinability, cost and finish trade-offs explained.
Material selection is usually the single biggest decision affecting a CNC part’s cost, weight, machinability and end-use performance. This guide walks through the materials JLYPT machines daily and where each one belongs — written from the workshop floor, not from a datasheet.
How to think about material choice
Most material decisions can be reduced to four questions, in order:
- Mechanical requirements — yield strength, fatigue, stiffness, weight target, operating temperature.
- Environment — corrosion, chemicals, UV, food/medical contact, sterilisation cycles.
- Machinability and cost — how fast it cuts, how much the bar stock costs, what tooling wear to expect.
- Finishing and downstream processes — does it anodise, plate, weld, paint, glue?
Aluminium alloys — the workhorses
Aluminium dominates CNC work because it cuts fast, takes a beautiful surface, anodises in any colour, and weighs a third as much as steel. For most consumer and industrial parts, the question is which aluminium alloy, not whether to use aluminium.
| Alloy | Yield (MPa) | Best for | Trade-off |
|---|---|---|---|
| 6061-T6 | 276 | General-purpose: housings, brackets, fixtures | Moderate strength; most common |
| 6063-T5 | 215 | Extruded profiles, decorative anodised parts | Softer; slightly worse machined finish |
| 7075-T6 | 503 | Aerospace, motorsport, structural | Harder to machine, less corrosion resistant, anodises poorly |
| 2024-T351 | 345 | Aerospace skin, fatigue-loaded parts | Susceptible to stress corrosion; usually clad |
| 5052 | 193 | Marine, sheet-metal-style folded brackets | Lower strength but excellent corrosion resistance |
| MIC-6 / cast tool | 170 | Vacuum chucks, optical bases, tooling plates | Stable but heavy; rarely used for end-use parts |
Carbon and stainless steels
When strength, fatigue resistance or corrosion in aggressive environments matters, steel is the answer. Three families cover almost everything we machine:
Carbon & alloy steels
- 1018, 1045 — cheap, weldable, easy to machine. Good for shafts, jigs, low-stress brackets.
- 4140, 4340 — pre-hardened or heat-treatable to ~50 HRC. Used for gears, drive shafts, tool holders.
- Will rust without coating — plate, paint or oil.
Stainless steels
- 303 — free-machining, but worse corrosion resistance and not weldable.
- 304 — the default food/marine grade.
- 316L — superior corrosion resistance, medical-implant grade.
- 17-4PH — precipitation-hardened, ~40 HRC, aerospace and pumps.
- 15-5PH — similar to 17-4 with better transverse properties.
For surface treatment of steel parts, see our surface finishing services — passivation for stainless, black oxide for tool steel, electroless nickel for carbon steel.
Titanium and superalloys
Titanium and nickel superalloys are the answer when no other material works — typically aerospace, medical implants, downhole oil tools and high-end motorsport.
| Material | Strength | Density (g/cm³) | Typical use |
|---|---|---|---|
| Ti-6Al-4V (Grade 5) | 895 MPa | 4.43 | Aerospace structural, bicycle frames, surgical implants |
| CP Titanium (Grade 2) | 275 MPa | 4.51 | Chemical processing, marine |
| Inconel 718 | 1240 MPa | 8.19 | Jet engine hot section, downhole tools |
| Inconel 625 | 760 MPa | 8.44 | Marine seawater, chemical processing |
| Hastelloy C-276 | 690 MPa | 8.89 | Worst-case chemical environments |
| Monel 400 | 241 MPa | 8.80 | Seawater, hydrofluoric acid |
Brass, bronze and copper
Copper-based alloys are niche but indispensable for electrical, plumbing and decorative work.
- C360 brass (free-machining). Cuts like butter, ideal for valves, fittings, electrical components and decorative hardware.
- C932 bearing bronze. Self-lubricating; bushings, gears, marine fittings.
- C110 (oxygen-free copper). Best electrical and thermal conductivity; bus bars, heat sinks, RF.
- Beryllium copper (C17200). Springs, non-sparking tools, EMI gaskets — but requires careful handling due to dust hazards.
Engineering plastics
CNC-machined plastics fill applications where metal is too heavy, too conductive or too expensive. Sheet stock and extruded rod are routinely turned and milled to ±0.05 mm tolerances.
| Material | Strengths | Watch out for |
|---|---|---|
| Delrin / POM | Low friction, dimensional stability, machines cleanly | Difficult to glue; weak in UV |
| Nylon (PA6, PA66) | Wear resistance, gears, bushings | Absorbs moisture and grows ~2% |
| PTFE (Teflon) | Chemical inert, very low friction, –200 to +260°C | Soft, creeps under load |
| Polycarbonate (PC) | Optical clarity, impact resistance | Scratches easily; chemical sensitive |
| Acrylic (PMMA) | Optical clarity, easy to polish | Brittle, not for impact |
| PEEK | Aerospace/medical, –60 to +250°C, autoclavable | Very expensive (~$300/kg bar stock) |
| UHMW-PE | Wear resistance, chemical inert, food-safe | Difficult to machine to tight tolerance |
For micro-features in plastics — sub-millimetre walls, optical surfaces — see our micro-machining services.
Materials at a glance
A condensed reference for selecting a starting material based on your top requirement:
| Top requirement | Start with | Upgrade path |
|---|---|---|
| Cheap and good enough | 6061 aluminium | 7075 → 17-4PH |
| Strength-to-weight | 7075 aluminium | Ti-6Al-4V |
| Corrosion resistance | 316L stainless | Hastelloy C-276 / Monel |
| Wear resistance, low friction | Hardened 4140 + DLC coat | Tool steel (D2, A2) |
| Heat resistance (>500°C) | Inconel 625 | Inconel 718, Waspaloy |
| Electrical conductivity | C110 copper | Silver-plated copper |
| Thermal conductivity (heat sinks) | 6061 aluminium | C110 copper |
| Optical clarity | Acrylic (PMMA) | Polycarbonate |
| Food contact / sterilisation | 316L stainless | PEEK for plastics |
| Magnetic permeability needed | 1018 carbon steel | 4140 hardened |
| Non-magnetic (MRI rooms) | 316L stainless or Ti | Beryllium copper |
Material × finish compatibility
The chosen surface finish often constrains the material. Always check both before locking the design:
| Finish | Compatible materials | Not compatible |
|---|---|---|
| Type-II anodising (decorative + protection) | 6061, 6063, 5052 | 7075 (poor cosmetic finish) |
| Type-III hard anodising | 6061, 7075, 2024 | 5xxx series (some grades) |
| Bead blasting | Most metals and plastics | Anything that must remain optical |
| Powder coating | Aluminium, steel, stainless | Plastics (heat-sensitive) |
| Electropolishing | Stainless 316L, 304 | Carbon steel |
| Black oxide | Carbon and tool steels | Stainless (only specific grades) |
| PVD coating | Stainless, tool steel, carbide | Aluminium (substrate softens at coating temp) |
Read more about specific finishes in surface finishing and PVD coating.
Frequently Asked Questions
- Aluminium 6061 by a wide margin. Bar stock is cheap, it cuts fast (so machine time is low), and it accepts any standard finish. About 70% of JLYPT’s industrial work is 6061.
- Most yes, but with different tooling and parameters. Titanium and nickel superalloys need slower cutting speeds, sharper tools, and aggressive coolant. Magnesium needs special fire-suppression. We segregate certain workflows (e.g., medical-grade titanium) into dedicated cells to avoid cross-contamination.
- For practical engineering: Ti-6Al-4V slightly edges 7075 aluminium when fatigue is included. For pure tensile strength-to-weight, modern carbon-fibre composites win — but those usually aren’t CNC-machined from billet.
- Anodising colour depends on the alloy, the bath chemistry and timing. Same batch = good match. Different batches = small variation, especially on 6061 (worst case ~ΔE 3–5). Critical colour-matching jobs should be processed in a single batch with a witness sample.
- If the part will see continuous moisture, salt spray, or chemicals, go stainless. For dry indoor environments, plated/painted carbon steel costs much less. Outdoor non-marine: zinc-plated 4140 lasts 5–10 years cheaply.
- Often no. A 3D-printed Ti-6Al-4V part is a different material grade than a CNC-machined one (different microstructure, anisotropy, residual stress). For certified aerospace or medical work, the two are not substitutable without separate qualification. See our CNC vs 3D printing comparison.
- Yes — we maintain stock of common alloys (6061, 7075, 304, 316L, Ti Grade 5, Delrin, PEEK) and can source specialty materials with full Material Test Reports (MTRs) and certificates of conformance. For aerospace and medical work, traceability is included by default.
What is the cheapest material to CNC machine?
Can I machine all materials on the same equipment?
Which material has the best strength-to-weight ratio?
Will my anodised aluminium colour match between batches?
How do I know if my application needs stainless or just plated steel?
Are 3D-printed materials interchangeable with CNC-machined ones?
Can JLYPT source the material for me?
About the author
JLYPT Engineering Team
Senior CNC Application Engineers
Our application engineering team brings 15+ years of combined experience producing precision components for aerospace, medical, robotics and industrial automation customers.
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