Last Updated: March 2026

CNC Machining Materials Guide: How to Choose the Right Material for Your Part

Material selection is one of the most consequential decisions in CNC machining. The right choice affects mechanical performance, surface finish, machinability, cost, and lead time. This guide covers every major CNC machining material with properties, typical applications, and selection guidance — so you can make the right call before uploading your file to Rapid Manufacturing for a quote.

Quick selection guide:
  • • Lightweight + strong: Aluminium 7075-T6
  • • General structural + low cost: Aluminium 6061-T6
  • • Marine / food / medical: 316 Stainless Steel
  • • Maximum strength-to-weight: Ti-6Al-4V
  • • Bearings / bushings / gears (plastic): Delrin (POM)
  • • High temperature plastic: PEEK

Aluminium Alloys

6061-T6

Density2.70 g/cm³
Tensile Strength310 MPa
Machinability⭐⭐⭐⭐⭐ Excellent
Relative Cost$
Typical Uses: Structural components, enclosures, brackets, fixtures, prototypes
Notes: Most common CNC aluminium. Best balance of cost, machinability, and mechanical properties. Good weldability and anodising response.

7075-T6

Density2.81 g/cm³
Tensile Strength572 MPa
Machinability⭐⭐⭐⭐ Very Good
Relative Cost$$
Typical Uses: Aerospace structures, high-load fixtures, bicycle components
Notes: Highest-strength common aluminium. Not weldable. Hard anodises well. Choose when strength-to-weight is critical.

5052-H32

Density2.68 g/cm³
Tensile Strength228 MPa
Machinability⭐⭐⭐ Good
Relative Cost$
Typical Uses: Marine, sheet metal, chemical tanks
Notes: Excellent corrosion resistance, particularly in marine environments. More commonly used in sheet metal than CNC machining.

Stainless Steels

304 Stainless

Density7.93 g/cm³
Tensile Strength515 MPa
Machinability⭐⭐⭐ Moderate
Relative Cost$$
Typical Uses: General engineering, food processing, architectural, chemical
Notes: Most widely used stainless. Good corrosion resistance. Work-hardens during machining — use sharp tools and appropriate feeds.

316 / 316L Stainless

Density7.99 g/cm³
Tensile Strength515 MPa
Machinability⭐⭐⭐ Moderate
Relative Cost$$$
Typical Uses: Marine, medical, pharmaceutical, food grade, chemical processing
Notes: Adds molybdenum for superior chloride resistance. Required for most food-grade and marine applications. 316L has lower carbon for better weld corrosion resistance.

17-4 PH

Density7.78 g/cm³
Tensile Strength1,170 MPa
Machinability⭐⭐⭐ Moderate
Relative Cost$$$
Typical Uses: Aerospace, defence, medical, high-strength fasteners
Notes: Precipitation-hardened stainless. Combines high strength with good corrosion resistance. Available in multiple condition states (H900 through H1150).

Carbon & Alloy Steels

1018 Mild Steel

Density7.87 g/cm³
Tensile Strength440 MPa
Machinability⭐⭐⭐⭐⭐ Excellent
Relative Cost$
Typical Uses: Shafts, pins, brackets, general structural parts
Notes: Low carbon, excellent machinability. Not suitable for heat treatment beyond case hardening. Will rust without surface treatment.

4140 Alloy Steel

Density7.85 g/cm³
Tensile Strength655–1,035 MPa
Machinability⭐⭐⭐⭐ Good
Relative Cost$$
Typical Uses: Gears, shafts, tooling, dies, high-load structural parts
Notes: Chrome-molybdenum alloy. Can be heat treated to high strength levels. Often supplied pre-hardened (4140 PH) for direct machining.

Titanium

Grade 2 (CP Ti)

Density4.51 g/cm³
Tensile Strength345 MPa
Machinability⭐⭐ Challenging
Relative Cost$$$$
Typical Uses: Chemical processing, marine, medical implants, heat exchangers
Notes: Commercially pure titanium. Excellent corrosion resistance. Lower strength than Grade 5. Biocompatible.

Ti-6Al-4V (Grade 5)

Density4.43 g/cm³
Tensile Strength895 MPa
Machinability⭐⭐ Challenging
Relative Cost$$$$
Typical Uses: Aerospace structures, medical implants, high-performance motorsport
Notes: Most commonly used titanium alloy. Outstanding strength-to-weight ratio. Requires slow speeds, heavy coolant, and sharp carbide tooling.

Engineering Plastics

Delrin (POM / Acetal)

Density1.41 g/cm³
Tensile Strength68 MPa
Machinability⭐⭐⭐⭐⭐ Excellent
Relative Cost$
Typical Uses: Gears, bearings, bushings, electrical insulators, food machinery
Notes: First choice for most plastic machined parts. Low friction, excellent dimensional stability, easy to machine cleanly.

PEEK

Density1.32 g/cm³
Tensile Strength100 MPa
Machinability⭐⭐⭐⭐ Very Good
Relative Cost$$$$$
Typical Uses: Medical implants, aerospace, high-temperature, chemical resistance
Notes: Premium engineering plastic. Service temperature up to 250°C. Biocompatible. Only choose PEEK when the application demands it — very expensive.

Nylon 66 (PA66)

Density1.14 g/cm³
Tensile Strength82 MPa
Machinability⭐⭐⭐⭐ Good
Relative Cost$
Typical Uses: Gears, bearings, structural housings, automotive components
Notes: Higher continuous temperature than Delrin (~120°C). Absorbs moisture, which affects dimensions — use if temperature matters more than dimensional stability.

PTFE (Teflon)

Density2.20 g/cm³
Tensile Strength25 MPa
Machinability⭐⭐⭐ Good
Relative Cost$$
Typical Uses: Seals, bearings, chemical-resistant parts, electrical insulators
Notes: Lowest friction of any engineering plastic. Poor structural strength — use only for sealing or non-load-bearing applications. Excellent chemical resistance.

Material Selection Decision Tree

Need lightweight + highest strength?→ Aluminium 7075-T6 or Ti-6Al-4V
Need lightweight + good strength + low cost?→ Aluminium 6061-T6
Need corrosion resistance + marine/food/medical?→ 316 Stainless Steel
Need general corrosion resistance at lower cost?→ 304 Stainless Steel
Need high strength steel that can be heat treated?→ 4140 Alloy Steel
Need maximum strength-to-weight (aerospace)?→ Ti-6Al-4V (Grade 5)
Need plastic bushing, bearing, or gear?→ Delrin (POM)
Need plastic, temperature >120°C or medical?→ PEEK
Need plastic with chemical resistance + low friction?→ PTFE
Need electrical conductivity + machinability?→ Copper C101 or Brass C360

Not Sure Which Material to Choose?

Upload your STEP file to Rapid Manufacturing. Our free DFM analysis includes material recommendations based on your application requirements and budget.

Get a Free Quote with DFM Review

Frequently Asked Questions

What is the easiest material to CNC machine?

Aluminium 6061-T6 is generally considered the most machinable common engineering material. It cuts cleanly, tolerates high spindle speeds, produces short chips, and has minimal tool wear. This also makes it the lowest-cost material to machine on a per-hour basis.

What is the difference between 6061 and 7075 aluminium for CNC machining?

6061-T6 is the most common CNC aluminium. It offers a good balance of strength (tensile strength ~310 MPa), machinability, weldability, and corrosion resistance at moderate cost. 7075-T6 is significantly stronger (tensile strength ~572 MPa) and is used for high-performance applications like aerospace structures. It machines well but is harder to weld and costs more. If you need maximum strength-to-weight ratio, choose 7075. For general structural use, 6061 is usually the right choice.

Should I use 304 or 316 stainless steel?

304 stainless is the standard choice for most applications — it offers good corrosion resistance, strength, and is cost-effective. 316 stainless adds molybdenum, which significantly improves resistance to chloride corrosion (seawater, marine, chemical environments) and is required for most food-grade and pharmaceutical applications. 316 costs ~15–25% more than 304 and is slightly harder to machine.

Is PEEK worth the cost for CNC machined parts?

PEEK (polyether ether ketone) is one of the most expensive engineering plastics — typically 10–20× the cost of Delrin per kilogram. However, it is justified when you need: (1) continuous service temperatures above 150°C, (2) chemical resistance to harsh solvents, (3) biocompatibility for medical implants, or (4) very high mechanical strength from a plastic. For most applications below 100°C that don't require chemical resistance, Delrin (POM) is a much more cost-effective choice.

Can Rapid Manufacturing machine titanium?

Yes. Rapid Manufacturing has suppliers capable of CNC machining titanium, including Grade 2 (commercially pure, used for chemical and medical applications) and Grade 5 / Ti-6Al-4V (the most common aerospace and medical implant grade). Titanium is significantly more expensive to machine than aluminium or steel due to its low thermal conductivity and tendency to work-harden, so tolerances and surface finishes should be carefully specified to avoid unnecessary rework.

What plastic should I use for a bearing or bushing?

Delrin (POM / Acetal) is the most common choice for CNC machined bearings and bushings. It has a low coefficient of friction, excellent dimensional stability, machines cleanly, and is significantly cheaper than alternatives. For higher temperatures or chemical environments, Nylon 66 or PTFE may be more appropriate. For very demanding applications, PEEK or filled grades (PTFE-filled Delrin, carbon-filled PEEK) are available.

How do I specify material on my CNC drawing?

Specify the material grade explicitly on your drawing title block or notes — e.g., "Material: Aluminium 6061-T6 per ASTM B209" or "Material: 316L Stainless Steel per ASTM A276". Avoid vague callouts like "aluminium" or "stainless" without the grade, as this can lead to incorrect material selection. Rapid Manufacturing's DFM review will flag any ambiguous material callouts.