Choosing the Right Material for CNC Machined Parts

Material selection is one of the most critical decisions in CNC machining.
The right material ensures that the final part performs as required, meets design tolerances, and balances cost, durability, and machinability. Whether you’re producing prototypes, aerospace components, or industrial tooling, each material comes with specific mechanical, thermal, and chemical properties that directly influence the success of your CNC project.

This guide walks you through the key considerations when selecting materials for CNC machining and offers a breakdown of common metal and plastic options.

Why Material Choice Matters in CNC Machining

Choosing the right material affects:

• 🛠️ Machinability – Impacts cutting speed, tool wear, and surface finish

• 💵 Cost – Varies by raw material price and machinability-related time

• ⚙️ Mechanical performance – Strength, toughness, wear resistance

• 🌡️ Thermal properties – Heat resistance, expansion, conductivity

• 🧪 Corrosion resistance – Suitability for environmental exposure

• 📏 Tolerances – Ability to hold tight dimensional accuracy

• 🧩 Assembly and compatibility – Interaction with other components or fasteners

The best material is the one that satisfies both functional and manufacturing needs—without overengineering or overbudgeting the part.

Key Factors to Consider When Choosing a CNC Material

Here are the primary factors engineers and machinists consider:

1. Application Requirements

• Is the part structural or cosmetic?

• Will it face wear, heat, moisture, or chemicals?

• Is the part static or dynamic (moving)?

2. Tolerance and Surface Finish Needs

• How tight must tolerances be?

• Is a smooth finish needed for mating surfaces?

3. Production Volume and Budget

• Low volume may justify more expensive materials

• High volume demands cost-effective options

4. Post-Processing and Secondary Operations

• Will the part be welded, anodized, or painted?

• Does it require threading, engraving, or polishing?

Most Common Metals Used in CNC Machining

Metals offer strength, durability, and precision. Here’s a breakdown of widely used options:

🟦 Aluminum (6061, 7075)

• Advantages: Lightweight, corrosion-resistant, good thermal/electrical conductivity

• Best for: Aerospace, automotive, electronics, enclosures

• Machinability: Excellent; fast cutting speeds and good chip evacuation

• Surface Finishes: Can be anodized or bead-blasted

6061 is general-purpose and affordable; 7075 offers higher strength for aerospace-grade parts.

🟥 Stainless Steel (304, 316, 17-4 PH)

• Advantages: Corrosion-resistant, strong, and sterilizable

• Best for: Medical devices, food-grade parts, marine equipment

• Machinability: Moderate; tougher to cut than aluminum but manageable with sharp tooling

• Post-Processing: Passivation or electropolishing improves corrosion resistance

304 is common for general use; 316 is ideal for chemical resistance; 17-4 PH offers high strength and good machinability.

🟩 Brass (C360)

• Advantages: Easy to machine, excellent surface finish, corrosion-resistant

• Best for: Gears, valves, connectors, decorative parts

• Machinability: One of the best metals to machine

• Finish Options: Polishes well, often left uncoated

Great for parts that require conductivity and aesthetics.

🟨 Copper

• Advantages: Highest electrical and thermal conductivity

• Best for: Electrical contacts, heat exchangers, RF components

• Machinability: Poorer than brass; needs sharp tools and slow feeds

• Surface Finish: Oxidizes quickly unless coated

Ideal for thermal management but expensive and tough to cut cleanly.

🟫 Bronze (e.g., C932)

• Advantages: Durable, wear-resistant, corrosion-resistant

• Best for: Bearings, bushings, thrust washers

• Machinability: Moderate; softer than steel but gums up tools if feeds aren’t optimized

• Finish: Naturally smooth with good load-carrying properties

Explore CNC machining for bronze parts where friction, lubrication, and durability are essential:
👉 CNC machining bronze

⬛ Steel (1018, 1045, A36)

• Advantages: Strong, affordable, and available in many grades

• Best for: Structural components, shafts, tools

• Machinability: Better with free-machining grades

• Finish Options: Can be heat-treated or coated for wear resistance

Steel is suitable for rugged mechanical applications but often requires rust protection.

Common Plastics for CNC Machining

Plastics are lightweight, corrosion-resistant, and often easier to machine than metals.

⚪ ABS (Acrylonitrile Butadiene Styrene)

• Advantages: Inexpensive, lightweight, impact-resistant

• Best for: Prototypes, enclosures, brackets

• Machinability: Easy to cut and shape; can warp if overheated

Good for short-run testing or low-stress applications.

🟣 PEEK (Polyether Ether Ketone)

• Advantages: High-performance, biocompatible, and thermally stable

• Best for: Medical implants, aerospace, electrical insulators

• Machinability: Requires special tooling and lower speeds

• Finish: Smooth and non-reactive

Used when strength and chemical resistance matter.

🟠 Delrin (Acetal)

• Advantages: Rigid, low-friction, high dimensional stability

• Best for: Gears, bushings, wear components

• Machinability: Excellent; low chip adhesion

• Finish: Naturally smooth and consistent

Ideal for tight-tolerance parts needing smooth operation.

🔵 Polycarbonate

• Advantages: Strong, transparent, and impact-resistant

• Best for: Optical parts, housings, safety shields

• Machinability: Cuts cleanly; can crack if overfed

• Finish: Polishes well; can be flame-treated

Comparing Key Material Attributes

Final Tips on CNC Material Selection

1. Don’t over-engineer. Avoid using high-cost materials when a general-purpose one will perform adequately.

2. Prototype in plastic or aluminum before committing to harder or expensive alloys.

3. Match finish requirements with the material’s ability to accept coatings or polishing.

4. Ask your machinist. CNC shops can offer guidance on what material suits your budget and tolerances.

5. Consider application life. Is the part for temporary use or long-term performance?

Final Thoughts

Choosing the right material for CNC machined parts isn’t just about mechanical strength—it’s about balancing performance, cost, and manufacturability.
With a solid understanding of material behavior and project needs, you can avoid costly mistakes, reduce lead times, and ensure your parts perform exactly as required.

If you’re considering bronze for bearings, bushings, or wear-resistant parts, explore high-precision CNC machining bronze services that deliver both durability and tight tolerances.