Did you know that over 30% of prototype failures stem from poor material selection? When it comes to CNC milled prototypes, choosing the right plastic material is crucial for success. From medical devices to aerospace components, each plastic brings unique properties that can make or break your project’s performance.
The 8 best plastic materials for CNC-milled prototypes are:
- Acetal (Delrin) – Best for precision components requiring high stability
- PEEK – Ideal for high-performance aerospace and medical applications
- Nylon (PA) – Perfect for durable industrial components
- Polycarbonate (PC) – Excellent for impact-resistant transparent parts
- Acrylic (PMMA) – Optimal for visual displays and optical clarity
- ABS – Great for cost-effective functional prototypes
- Polypropylene (PP) – Suitable for chemical-resistant applications
- PTFE (Teflon) – Best for low-friction requirements
While this list gives you a quick overview, each material has specific machining requirements, cost implications, and performance characteristics that could significantly impact your project. Let’s dive deeper into why these materials stand out and how to choose the perfect one for your specific application.
Table of Contents
#1 Acetal (Delrin): The Precision Champion
When precision meets performance, Acetal (commonly known as Delrin) takes center stage in the CNC machining world. This engineering thermoplastic has earned its reputation as the go-to material for high-precision components, and here’s why engineers consistently choose it for their critical applications.
Key Properties:
- Tensile Strength: 11,000 psi
- Heat Deflection Temperature: 180°F (82°C)
- Coefficient of Friction: 0.20
- Water Absorption (24hrs): 0.25%
Perfect Applications:
- Precision Gears: Thanks to its exceptional dimensional stability
- Bearings and Bushings: Due to inherent low friction properties
- Mechanical Components: Ideal for parts requiring tight tolerances
- Food Processing Equipment: FDA compliant grades available
The material’s combination of high strength, excellent dimensional stability, and low friction makes it a reliable choice for demanding applications. When machined, Acetal maintains its integrity under repeated stress cycles, making it particularly valuable for parts that require consistent performance over time.
Machining Considerations:
- Optimal Cutting Speed: 500-1000 sfm
- Feed Rate: 0.005-0.015 ipr
- Tool Recommendation: Carbide-tipped tools for best results
- Cooling: Light coolant recommended during machining
- Watch for melting at high speeds
- Maintain proper cooling throughout the process
- Consider stress relief before final machining
Cost-Benefit Analysis:
With a price range of $1.47-$4.90 per kg, Acetal offers excellent value for precision components. Its exceptional machinability and reduced wear on cutting tools result in lower overall production costs, making it an economical choice for high-precision applications.
Pro Tip: For optimal results, always specify POM-C (homopolymer) grade when ordering Acetal for CNC machining. This variant offers better dimensional stability and machinability compared to copolymer alternatives.
#2 PEEK: The High-Performance Specialist
When extreme conditions demand exceptional performance, PEEK (Polyether Ether Ketone) stands as the premium choice in the plastics world. This high-performance thermoplastic has revolutionized industries from aerospace to medical, offering a unique combination of mechanical strength and chemical resistance that few materials can match.
Key Properties:
- Tensile Strength: 16,000 psi
- Heat Deflection Temperature: 600°F (315°C)
- Chemical Resistance: Excellent against most solvents
- Continuous Service Temperature: Up to 480°F (250°C)
Perfect Applications:
- Aerospace Components: For high-temperature environments
- Medical Implants: Due to biocompatibility and sterilization resistance
- Industrial Bearings: For extreme operating conditions
- Chemical Processing Equipment: Thanks to superior chemical resistance
Despite its premium price point, PEEK’s exceptional performance in extreme conditions makes it invaluable for critical applications. Its ability to maintain mechanical properties at high temperatures, combined with excellent chemical resistance and dimensional stability, makes it irreplaceable in demanding environments.
Machining Considerations:
- Optimal Cutting Speed: 300-800 sfm
- Feed Rate: 0.003-0.012 ipr
- Tool Recommendation: Sharp carbide tools required
- Cooling: Flood coolant recommended
- Avoid excessive heat buildup during machining
- Use conservative cutting parameters initially
- Allow for proper chip evacuation
Cost-Benefit Analysis:
PEEK commands a premium price of $30-90 per kg, with specialized grades reaching $100 per kg. While this makes it one of the most expensive engineering plastics, its unmatched performance in extreme conditions and long service life justify the investment for critical applications where failure isn’t an option.
Pro Tip: When machining PEEK, starting with conservative cutting parameters and gradually optimizing based on results yields the best surface finish and dimensional accuracy. Consider using 30% glass-filled PEEK for enhanced dimensional stability in precision applications.
#3 Nylon (PA): The Versatile Performer
Meet the chameleon of engineering plastics – Nylon (Polyamide). This versatile material combines flexibility with durability, making it a popular choice across diverse industries. Its balanced property profile and excellent wear resistance have made it a staple in both prototype development and production parts.
Key Properties:
- Tensile Strength: 12,400 psi
- Heat Deflection Temperature: 167°F (75°C)
- Impact Resistance: Excellent
- Moisture Absorption: 1.5% (24hrs)
Perfect Applications:
- Automotive Parts: For its vibration-dampening properties
- Medical Devices: Due to good biocompatibility
- Industrial Rollers: Thanks to excellent wear resistance
- Moving Parts: Ideal for components requiring flexibility
Nylon’s unique combination of toughness, flexibility, and wear resistance makes it perfect for parts that need to bend without breaking. Its self-lubricating properties and excellent fatigue resistance make it particularly valuable for moving components and parts subject to repeated stress.
Machining Considerations:
- Optimal Cutting Speed: 400-1000 sfm
- Feed Rate: 0.004-0.012 ipr
- Tool Recommendation: Sharp HSS or carbide tools
- Cooling: Compressed air cooling preferred
- Monitor moisture content before machining
- Allow for dimensional changes due to moisture absorption
- Use sharp tools to prevent material pulling
Cost-Benefit Analysis:
Priced between $5-15 per kg, Nylon offers a balanced cost-to-performance ratio. Its excellent machinability and long wear life, combined with its versatile properties, make it a cost-effective choice for many industrial applications.
Pro Tip: For critical dimensions, consider using moisture-stabilized grades of Nylon, or condition the material in a controlled environment before machining to account for moisture-related dimensional changes.
#4 Polycarbonate (PC): The Impact Resistance Expert
When transparency meets toughness, Polycarbonate emerges as the clear winner. This engineering plastic has earned its reputation as the go-to material for applications requiring both optical clarity and exceptional impact resistance, making it invaluable for prototypes that need to combine visibility with durability.
Key Properties:
- Tensile Strength: 9,500 psi
- Heat Deflection Temperature: 270°F (132°C)
- Light Transmission: 88%
- Impact Strength: 12-16 ft-lb/in (Izod)
Perfect Applications:
- Protective Covers: For its outstanding impact resistance
- Vision Systems: Due to optical clarity
- Safety Equipment: Thanks to its combination of strength and transparency
- Electronic Housings: Ideal for visible internal components
Polycarbonate offers an unmatched combination of optical clarity and impact resistance. Its ability to withstand heavy impacts while maintaining transparency makes it irreplaceable in applications where visibility and durability are equally important.
Machining Considerations:
- Optimal Cutting Speed: 500-1000 sfm
- Feed Rate: 0.004-0.012 ipr
- Tool Recommendation: Carbide tools with positive rake angles
- Cooling: Light mist coolant or compressed air
- Avoid excessive heat generation
- Maintain sharp cutting edges to prevent chipping
- Use appropriate speeds to prevent melting
Cost-Benefit Analysis:
At $4-8 per kg, Polycarbonate provides excellent value when both optical clarity and impact resistance are required. This moderate price point, combined with its easy machinability and minimal need for surface finishing, makes it a cost-effective choice for transparent prototypes.
Pro Tip: When machining transparent parts, use high cutting speeds with light feeds to achieve the best optical clarity. Consider annealing the material after machining to relieve internal stresses and prevent crazing.
#5 Acrylic (PMMA): The Clarity Master
In the world of transparent plastics, Acrylic (Polymethyl Methacrylate) reigns supreme for optical clarity. This material offers the perfect balance of visual excellence and machinability, making it the preferred choice for prototypes where aesthetics and clarity are paramount.
Key Properties:
- Tensile Strength: 8,000 psi
- Heat Deflection Temperature: 190°F (88°C)
- Light Transmission: 92%
- UV Resistance: Excellent
Perfect Applications:
- Display Cases: For superior optical clarity
- Lighting Fixtures: Due to excellent light transmission
- Point of Sale Displays: Thanks to aesthetic appeal
- Architectural Models: Ideal for transparent design elements
Acrylic combines exceptional optical properties with good machinability. Its superior light transmission and UV resistance make it perfect for long-term outdoor applications, while its surface quality after machining reduces the need for post-processing.
Machining Considerations:
- Optimal Cutting Speed: 600-1000 sfm
- Feed Rate: 0.003-0.010 ipr
- Tool Recommendation: Single-flute cutters for best finish
- Cooling: Compressed air or mist cooling
- Keep tools sharp to prevent chipping
- Use higher speeds for polished edges
- Avoid overheating to prevent crazing
Cost-Benefit Analysis:
With a market price of approximately $3.35 per kg, Acrylic represents an excellent value for optical applications. Its competitive pricing, combined with superior machining characteristics and minimal need for post-processing, makes it highly cost-effective for prototype development.
Pro Tip: To achieve crystal-clear edges, progress through increasingly finer cuts, finishing with a very light pass. Flame polishing can provide an optically clear edge finish when needed.
#6 ABS: The Cost-Effective Solution
When balancing performance with budget becomes crucial, ABS (Acrylonitrile Butadiene Styrene) steps into the spotlight. This versatile thermoplastic has become a favorite among prototype developers for its excellent price-to-performance ratio and forgiving machining characteristics.
Key Properties:
- Tensile Strength: 6,500 psi
- Heat Deflection Temperature: 190°F (88°C)
- Impact Resistance: Good
- Surface Finish: Excellent
Perfect Applications:
- Consumer Electronics: For cost-effective housings
- Automotive Prototypes: Due to good impact resistance
- Functional Testing Models: Thanks to balanced properties
- Rapid Prototyping Parts: Ideal for iterative design phases
ABS offers a sweet spot between cost and performance. Its good dimensional stability and excellent surface finish capabilities make it perfect for prototype development where multiple iterations might be needed, without breaking the budget.
Machining Considerations:
- Optimal Cutting Speed: 300-800 sfm
- Feed Rate: 0.004-0.012 ipr
- Tool Recommendation: Standard HSS tools work well
- Cooling: Compressed air cooling recommended
- Monitor heat buildup carefully
- Use moderate speeds to prevent melting
- Keep tools sharp for best surface finish
Cost-Benefit Analysis:
Priced at $1.50-3.00 per kg, ABS is one of the most economical choices for CNC machined prototypes. This low price point, coupled with its good machinability and surface finish, makes it particularly attractive for iterative prototyping where multiple versions may be needed.
Pro Tip: When machining ABS, maintain moderate speeds and feeds to prevent heat buildup. This material responds well to conventional machining parameters, making it an excellent choice for shops new to plastic machining.
#7 Polypropylene (PP): The Chemical Resistant Option
When chemical resistance meets flexibility requirements, Polypropylene emerges as the practical solution. This versatile thermoplastic delivers exceptional chemical resistance and fatigue properties, making it particularly valuable for prototypes that need to withstand aggressive environments.
Key Properties:
- Tensile Strength: 4,800 psi
- Heat Deflection Temperature: 200°F (93°C)
- Chemical Resistance: Excellent
- Fatigue Resistance: Outstanding
Perfect Applications:
- Chemical Storage Components: For superior chemical resistance
- Laboratory Equipment: Due to inertness to most chemicals
- Packaging Prototypes: Thanks to excellent fatigue resistance
- Living Hinge Designs: Ideal for flexible applications
Polypropylene’s combination of chemical resistance and flexibility makes it unique among machining plastics. Its ability to withstand repeated flexing without failure, coupled with excellent chemical resistance, makes it invaluable for specific applications where these properties are crucial.
Machining Considerations:
- Optimal Cutting Speed: 300-800 sfm
- Feed Rate: 0.005-0.015 ipr
- Tool Recommendation: Sharp HSS tools
- Cooling: Compressed air preferred
- Use sharp tools to prevent pulling
- Control heat generation carefully
- Support thin sections during machining
Cost-Benefit Analysis:
At $1.10-1.50 per kg, Polypropylene is among the most affordable options for CNC machining. This low price point, combined with its chemical resistance and durability, makes it an extremely cost-effective choice for chemical-resistant applications.
Pro Tip: When machining thin sections, use adequate support and cooling to prevent distortion. Consider using higher molecular weight grades for better machinability and mechanical properties.
#8 PTFE (Teflon): The Low-Friction Pioneer
When it comes to minimizing friction and maximizing non-stick properties, PTFE (Polytetrafluoroethylene) stands alone. This unique material, widely known as Teflon, offers unmatched low friction characteristics and chemical inertness, making it essential for specialized prototype applications.
Key Properties:
- Tensile Strength: 3,900 psi
- Heat Deflection Temperature: 250°F (121°C)
- Coefficient of Friction: 0.05-0.10
- Chemical Resistance: Nearly Universal
Perfect Applications:
- Bearing Surfaces: For lowest friction requirements
- Seal Components: Due to chemical inertness
- Food Processing Parts: Thanks to FDA compliance
- Chemical Handling Equipment: Ideal for aggressive environments
PTFE’s incredibly low coefficient of friction and universal chemical resistance make it irreplaceable in certain applications. Its ability to perform in extreme chemical environments while maintaining its non-stick properties makes it a crucial material for specialized prototypes.
Machining Considerations:
- Optimal Cutting Speed: 300-750 sfm
- Feed Rate: 0.004-0.010 ipr
- Tool Recommendation: Sharp HSS or carbide tools
- Cooling: Usually not required
- Use sharp tools to prevent material deformation
- Maintain positive rake angles
- Allow for material recovery after machining
Cost-Benefit Analysis:
With a price range of $20-40 per kg, PTFE sits in the higher tier of engineering plastics. However, its unique low-friction properties and universal chemical resistance make it cost-effective in specialized applications where other materials would rapidly degrade or fail.
Pro Tip: When machining PTFE, plan for material recovery time as it tends to “cold flow.” Design parts with slightly undersized dimensions to account for this characteristic expansion.
Conclusion
Selecting the right plastic material for your CNC milled prototype requires careful consideration of multiple factors – from mechanical properties and machinability to cost-effectiveness. Whether you need the precision of Delrin, the high-performance capabilities of PEEK, or the cost-effectiveness of ABS, each material offers unique advantages for specific applications.
Need help choosing the perfect material for your next project? Our manufacturing experts at okdor.com are ready to guide you through the selection process, ensuring your prototype meets all performance requirements while optimizing costs.
Frequently Asked Qestions
PEEK is the best choice for high-temperature applications, with a heat deflection temperature of 600°F (315°C) and continuous service temperature up to 480°F (250°C). It maintains its mechanical properties even under extreme heat conditions.
Polypropylene ($1.10-1.50/kg) and ABS ($1.50-3.00/kg) are the most cost-effective materials for CNC milled prototypes. ABS offers better surface finish and dimensional stability, while Polypropylene provides superior chemical resistance.
Acrylic (PMMA) is the best choice for transparent prototypes, offering 92% light transmission – the highest among machinable plastics. It provides superior optical clarity and excellent UV resistance at a reasonable price of $3.35/kg.
PTFE (Teflon) offers the best chemical resistance, being inert to virtually all chemicals. For a more economical option, Polypropylene also provides excellent chemical resistance at a fraction of the cost.
Acetal (Delrin) is the optimal choice for precision gears and bearings due to its excellent dimensional stability, low friction coefficient (0.20), and good wear resistance. Its high strength and machinability make it perfect for tight-tolerance components.
Polycarbonate (PC) provides the highest impact resistance among commonly machined plastics, with an Izod impact strength of 12-16 ft-lb/in. It’s ideal for protective covers and safety equipment where impact resistance is crucial.
