Acetal and nylon are two of the most commonly machined engineering plastics, and for good reason. Both materials machine well, offer excellent mechanical properties, and serve in demanding applications. When customers ask which material to choose, the answer depends on the specific application requirements, operating environment, and performance priorities.
This comparison focuses on practical machining considerations and application characteristics to help guide material selection for CNC machined plastic parts.
Machining Characteristics
Acetal (Delrin, POM)
Acetal is one of the easiest engineering plastics to machine. It cuts cleanly with sharp, well-defined edges and produces minimal burring. The material holds tight tolerances consistently and exhibits low tool wear compared to many other plastics.
Key machining characteristics include:
- Excellent dimensional stability during and after machining
- Minimal moisture absorption, which helps maintain tolerances over time
- Low friction coefficient makes chip evacuation straightforward
- Machines well at higher speeds with sharp tooling
- Produces short, easily managed chips
- Minimal internal stress, reducing warping risk
Acetal's low moisture absorption is particularly valuable for precision parts. The material won't swell significantly when exposed to humidity, which means parts maintain their machined dimensions in varying environmental conditions.
Nylon (Polyamide, PA)
Nylon machines well but requires more attention to certain factors. The material is tougher and more abrasion-resistant than acetal, which can increase tool wear slightly. Nylon's tendency to absorb moisture is the primary consideration when machining to tight tolerances.
Key machining characteristics include:
- Machines cleanly with appropriate tooling and speeds
- Higher moisture absorption than acetal
- Can produce stringy chips that require management
- Benefits from sharp tooling to prevent heat buildup
- May require dimensional compensation for post-machining moisture absorption
- Tougher material can dull tools faster than acetal
The moisture absorption characteristic of nylon means that parts may change dimensions slightly after machining as they equilibrate with ambient humidity. For applications with tight tolerances, this factor needs consideration during the quoting and manufacturing process.
Material Properties and Application Considerations
Mechanical Strength and Toughness
Nylon generally offers higher tensile strength and better impact resistance than acetal. This makes nylon the preferred choice for parts subjected to shock loads, repeated impacts, or high-stress applications. Gears, bushings, and wear components in demanding environments often specify nylon for this reason.
Acetal provides excellent stiffness and maintains its mechanical properties across a wide temperature range. While not quite as tough as nylon under impact, acetal offers superior dimensional stability and creep resistance under sustained loads.
Wear and Friction
Both materials exhibit low friction and good wear resistance, making them suitable for bearing surfaces, slides, and wear components. Acetal typically has a slightly lower coefficient of friction and performs well in dry-running applications. Nylon excels in applications with some lubrication or where abrasion resistance is critical.
Chemical Resistance
Acetal resists most organic solvents, fuels, and weak acids but is attacked by strong acids and oxidizing agents. Nylon offers good resistance to oils, greases, and many solvents but is affected by strong acids and bases. Neither material is suitable for all chemical environments, so specific chemical exposure should be evaluated against material compatibility data.
Temperature Range
Acetal maintains its properties well from approximately -40°F to 180°F, with some grades rated higher. Nylon's temperature range varies by grade but generally performs well from -40°F to 200°F or higher. Both materials lose strength and stiffness at elevated temperatures, so continuous operating temperature matters for design.
Moisture Sensitivity
This is often the deciding factor between acetal and nylon. Acetal absorbs very little moisture (typically less than 0.25%), while nylon can absorb 2% to 9% depending on grade and environmental conditions. For precision parts where dimensional stability is critical, acetal's low moisture absorption provides a significant advantage.
Nylon parts in high-humidity environments will absorb moisture and swell slightly. This isn't necessarily a problem if accounted for in design and machining, but it does require consideration for tight-tolerance applications.
Common Applications
When Acetal Is Typically Specified
- Precision gears and gear components
- Tight-tolerance bushings and bearings
- Valve components and flow control parts
- Conveyor components and wear strips
- Electrical insulators requiring dimensional stability
- Food processing equipment (FDA-compliant grades available)
When Nylon Is Typically Specified
- High-strength structural components
- Impact-resistant parts and housings
- Wear pads and abrasion-resistant components
- Rollers and wheels under heavy loads
- Cable management and electrical components
- Applications where toughness outweighs dimensional precision
Material Selection Guidance
The choice between acetal and nylon for CNC machined parts should be driven by application requirements rather than machining convenience alone. Consider these questions:
- What are the critical tolerances, and how will moisture affect them?
- What loads, impacts, or stresses will the part experience?
- What is the operating temperature range?
- Will the part be exposed to chemicals, and which ones?
- Is wear resistance or low friction the priority?
- Are there regulatory requirements such as FDA compliance?
In many cases, either material will perform adequately, and the decision comes down to specific performance priorities or cost considerations. When in doubt, providing application details to your machine shop allows for informed material recommendations based on similar past projects.
What to Include in Your RFQ
When requesting a quote for CNC machined plastic parts, clear and complete information helps ensure accurate pricing and appropriate material selection. The engineering drawing typically serves as the controlling specification, but additional context improves the quoting process.
Essential RFQ Information
Engineering Drawings or CAD Files: Provide a dimensioned drawing in PDF format or a STEP file when available. The drawing should include all critical dimensions, tolerances, and geometric controls. CAD files allow for programming efficiency but should be accompanied by a drawing that defines requirements.
Material Specification: Specify acetal, nylon, or indicate that you're open to recommendations. If a specific grade is required (such as acetal copolymer or nylon 6/6), include that information. If you're uncertain about material selection, describe the application environment and performance requirements.
Quantity: State the number of parts needed. Prototype quantities and production runs may use different manufacturing approaches, affecting both pricing and lead time. If you anticipate repeat orders, mention that as well.
Tolerances: If the drawing doesn't specify tolerances, provide general tolerance expectations or identify which dimensions are critical. Standard machining tolerances differ from precision tolerances, and this affects both cost and manufacturing approach.
Surface Finish Requirements: Specify if a particular surface finish is required, whether as-machined, specific Ra values, or cosmetic appearance. Most machined plastic parts are quoted with a standard machined finish unless otherwise specified.
Required Completion Date: Provide a realistic target date or indicate if the project is time-sensitive. Lead times vary based on shop workload, material availability, and part complexity.
Inspection Requirements: Note if dimensional inspection reports, material certifications, or other documentation will be required. Some customers need first article inspection reports or ongoing inspection documentation, which should be identified during quoting.
Special Notes: Include any application-specific information, secondary operations, special packaging, or other requirements that affect manufacturing or delivery.
Practical RFQ Checklist
Use this checklist when preparing your request for quote:
- Engineering drawing (PDF) or STEP file attached
- Material specified or application details provided
- Quantity clearly stated
- Critical tolerances identified
- Surface finish requirements noted if applicable
- Target delivery date provided
- Inspection or certification needs specified
- Any secondary operations or special requirements listed
- Contact information for questions
Prototype vs Production Considerations
The quantity and intended use of machined parts influence both the manufacturing approach and cost structure. Prototype parts may prioritize speed and design verification, while production runs emphasize repeatability and cost efficiency.
For smaller quantities, the focus is often on quick turnaround and flexibility for potential design changes. Larger production runs benefit from optimized programming, tooling selection, and process refinement that reduces per-piece cost.
When requesting a quote, indicate whether the parts are for prototyping, initial production, or ongoing manufacturing. If you expect the design to evolve, mention that as well. This context helps the machine shop provide appropriate recommendations for tooling and setup.
Request a Quote for Your CNC Machined Plastic Parts
Whether you're comparing acetal vs nylon for a specific application or need CNC machined plastic parts in other materials, Anco Precision can help. We machine both acetal and nylon regularly for customers across various industries, from prototype quantities through production runs.
If you have an active project, send us your drawing or STEP file along with material preference, quantity, critical tolerances or requirements, and your required delivery date. We'll review your project and provide a quote based on your specifications.
For material selection questions or application-specific guidance, include details about the operating environment and performance requirements. We're happy to discuss options and provide recommendations based on similar parts we've machined.
Contact Anco Precision to request a quote for your CNC machined plastic parts project.