CNC Material Selection Guide
Which metal or plastic should your part be? Start with the one-page matrix, then answer five questions. No email gate, no download required — but there's a PDF if you want it by the CAD station.
One Page, Twelve Materials
Cost is relative stock cost ($ = cheapest). "Machinability" is how happily the material cuts — it drives cycle time and price as much as the metal itself.
| Material | Machinability | Cost* | Corrosion | Strength / weight | Best for | Watch-outs |
|---|---|---|---|---|---|---|
| Aluminium 6061 | Excellent | $ (cheapest) | Good (anodises well) | Very good | Brackets, enclosures, prototypes | Soft — watch thin walls & thread depth |
| Aluminium 7075 | Good | $$ | Fair (prone to SCC) | Excellent | Aerospace, high-load parts | Anodising looks patchy; less corrosion resistant |
| Stainless 304 | Fair (work-hardens) | $$ | Very good | Moderate | Food, medical, marine | Work-hardens & gummy chips — slower feeds |
| Stainless 316 | Fair | $$$ | Excellent (marine) | Moderate | Marine, chemical duty | Higher cost; same machining caveats as 304 |
| Carbon / mild steel | Excellent | $ (cheapest) | Poor — needs coating | Moderate | Jigs, structural, high-volume cheap | Rusts — plate or finish it |
| Titanium Gr5 | Poor (springs back) | $$$$ | Excellent | Excellent | Medical, aerospace, corrosive | Tool wear, chip-fire risk — slow & costly |
| Brass (C360) | Excellent (best) | $$ | Good | Moderate | Fittings, connectors, decorative | Free-cutting grade is a dream; soft |
| Copper | Fair (gummy) | $$ | Good | Moderate | Electrical, thermal parts | Burrs easily; spec it for conductivity, not load |
| POM (Delrin) | Excellent | $ | N/A (chem resistant) | Low | Gears, bushings, fixtures | Static, warps if clamped wrong, tight tol hard |
| PEEK | Good | $$$$ | Excellent (chemical) | Good | Medical, semiconductor, high temp | Expensive; needs sharp tools & high temp |
| Nylon 66 | Good | $ | N/A (chem resistant) | Low | Wear parts, insulators | Absorbs moisture (swells) — tight tol risky |
| ABS | Good | $ | N/A | Low | Housings, prototypes | Low temp, not for load |
* Relative stock cost, not per-part price. Final part cost is material × machinability × how much you over-specify — see the cost breakdown.
How to Choose, Step by Step
Answer top to bottom. The first "yes" usually decides it.
Will it see weather, salt, chemicals or food?
Yes → 316 stainless or titanium (metal) / PEEK (plastic). No → aluminium or steel and move on.
Is weight critical — aerospace, robotics, handheld?
Yes → 7075 aluminium (cheap) or titanium (best strength-to-weight, costs more). No → any metal fits.
Must it conduct electricity or heat?
Yes → copper, aluminium or brass. This often overrides everything else for electrical parts.
Highest cost sensitivity, no corrosion worry?
Yes → carbon / mild steel, then plate or paint it. Cheapest path to a strong part.
Does it need to be non-metal — insulate, low friction, chemical?
Yes → POM or nylon for everyday; PEEK only if it sees real heat or aggressive media. ABS for cheap prototypes.
Material FAQs
Which CNC material is the cheapest?
Carbon / mild steel is usually the cheapest stock, followed by aluminium 6061 and then engineering plastics like ABS and POM. Stainless, titanium and PEEK climb quickly because of both material and machining cost.
Which material resists corrosion best?
316 stainless steel and titanium grade 5 resist corrosion and salt spray best among metals. For chemical or high-temperature duty, PEEK outperforms every metal. 6061 aluminium is fine indoors once anodised.
What is the strongest material for its weight?
Titanium grade 5 has the best strength-to-weight of the common CNC metals, with 7075 aluminium close behind at a fraction of the cost.
Can I machine plastic instead of metal?
Yes — POM, nylon, PEEK and ABS machine cleanly and suit insulators, wear parts, fixtures and prototypes. The catches: plastics move with moisture and temperature, so hold tight tolerances only where the function needs them.
When should I specify PEEK?
Only when the part sees sustained heat above ~150°C, aggressive chemicals, or a medical / semiconductor environment that demands the combination. For most parts PEEK is over-specified and you pay 20–50x the material cost of a sane alternative.
Does the material affect what tolerance I can hold?
Indirectly. Metals are dimensionally stable, so tight tolerances are straightforward. Plastics absorb moisture and shift with temperature, so a ±0.02 mm call on a nylon part can drift after a humid weekend. State tight tolerances only on the dimensions that actually matter.
Not sure which grade your part needs?
Send the STEP and tell us what the part does. We'll name the cheapest material that meets the duty — not the one with the biggest markup.
Related: All Materials · Aluminium vs Stainless vs Titanium · Aluminium CNC · Brass CNC · Plastic CNC · Cost Calculator