Nylon CNC Machining — Properties and Grades
Nylon (polyamide, PA) is one of the most versatile engineering thermoplastics. It is tougher than Delrin at impact, bonds well to adhesives and coatings, and PA66 glass-filled grades offer useful stiffness at elevated temperatures. The tradeoff is higher moisture absorption than acetal — nylon absorbs 2–8% moisture depending on grade, which causes dimensional swelling and slight reduction in stiffness. For most mechanical applications at room temperature, nylon and Delrin perform similarly; the right choice depends on the specific load, environment and temperature.
Nylon Grades We Machine
| Grade | Key property | Best for |
|---|---|---|
| PA6 (Nylon 6) | Cast, large blocks available; good toughness | Large bushings, wear pads, structural blocks |
| PA66 (Nylon 6/6) | Higher melting point, stiffer than PA6 | Gears, wear parts at elevated temperature |
| PA12 (Nylon 12) | Lowest moisture absorption in the nylon family | Precision parts, fuel system components, low-moisture environments |
| MDS-filled Nylon | Molybdenum disulfide filled — reduced friction | Bearings, bushings, gears (self-lubricating) |
| Glass-Filled Nylon (PA66-GF30) | 30% glass fibre — high stiffness, heat resistance | Structural load-bearing parts, elevated temperature |
Mechanical Properties (PA66 — dry as-machined)
| Property | PA66 (dry) | PA66-GF30 (dry) |
|---|---|---|
| Tensile strength | ~83 MPa | ~185 MPa |
| Flexural modulus | ~2.9 GPa | ~9.0 GPa |
| Max continuous service temp | ~105–120 °C | ~130–150 °C |
| Water absorption (equilibrium) | ~2.5–3% | ~1.5% |
| Density | 1.14 g/cm³ | 1.37 g/cm³ |
Note: nylon properties change significantly with moisture content — parts stabilise at ~2–3% moisture in normal ambient conditions, which reduces stiffness and strength from the "dry" values above. Design critical nylon parts for conditioned (ambient-exposed) properties.
How We Machine Nylon
- Tolerances: ±0.05 mm for moisture-critical features; ±0.025 mm achievable on features not subject to significant moisture variation.
- Tooling: Sharp uncoated carbide at high speeds; nylon has a tendency to melt and smear at the tool tip if feed is too light — keep positive cutting action at all times.
- Moisture conditioning: Parts destined for wet or outdoor service should be conditioned before final machining to avoid dimensional change in service.
- Glass-filled grades: PA66-GF30 is significantly more abrasive — carbide tooling required, tool life reduced versus unfilled nylon.
Typical Nylon CNC Parts
- Bearings and bushings — MDS-filled nylon for self-lubricating applications
- Gears for light loads — quieter than metal, self-lubricating; suitable for light-to-medium duty
- Cable guides and pulleys — smooth, durable surface for rope and cable
- Pipe fittings and flanges — PA12 for fuel/chemical compatibility
- Structural support blocks — cast PA6 blocks for machinery mounting
- Rollers and wear pads — conveyor, packaging machinery
- Replacement plastic parts — nylon components in legacy machinery reproduced from worn parts; see our replacement parts service
Nylon vs Delrin for CNC Machined Parts
| Nylon (PA66) | Delrin (POM-H) | |
|---|---|---|
| Tensile strength (dry) | ~83 MPa | ~68 MPa |
| Moisture absorption | ~2.5–3% (dimensional change) | ~0.25% (minimal) |
| Impact toughness | Higher | Good |
| Friction / wear | Good (MDS grade: excellent) | Very good |
| Dimensional stability | Lower in humid environments | Better |
| Best for | Gears, structural parts, high-impact | Precision bushings, valve parts, guides |
Default to Delrin/acetal for precision parts requiring dimensional stability in varying humidity. Use nylon when higher impact resistance, elevated temperature performance (GF30) or specific chemical compatibility (PA12) is needed.
Frequently Asked Questions
Does nylon absorb water and does this affect machined parts?
Yes. PA6 and PA66 absorb 2.5–3% moisture at equilibrium in ambient conditions, which causes ~0.5–1% linear dimensional change and reduces stiffness. For precision gears and tight-tolerance bearing bores, we machine to dimension after conditioning the stock at the expected ambient humidity. PA12 has the lowest moisture absorption of the nylon family (~0.7%) if dimensional stability is critical. Delrin (POM) is the first choice when moisture-driven dimensional change is unacceptable.
Which nylon grade is best for gears?
PA66 or MDS-filled PA66 for light-to-medium duty gears at up to ~120 °C. MDS (molybdenum disulfide) fills reduce the friction coefficient and improve wear life significantly. For higher loads or elevated temperatures, consider PA66-GF30 (glass-filled) for stiffness, or PEEK for extreme conditions. Nylon gears run quieter than metal and do not require lubrication in most applications.
Can you machine glass-filled nylon (PA66-GF30)?
Yes. Glass-filled nylon is significantly more abrasive than unfilled grades — we use carbide tooling and accept shorter tool life. The result is a stiffer, stronger part with better elevated-temperature performance. Specify the glass content and grade when enquiring.
What is the maximum temperature for nylon parts in continuous service?
Unfilled PA66: ~105–120 °C continuous. PA66-GF30: ~130–150 °C. PA12: ~100 °C. Above these ranges, nylon softens progressively. For higher temperatures (150–250 °C) consider PEEK, PEI, or PTFE. We advise on material selection when the service temperature is a critical parameter.
Can you reproduce legacy plastic machine parts in nylon from a worn sample?
Yes. Nylon parts in old machinery — gears, bushings, guide rails, cam followers — are routinely reproduced from worn or broken samples. We measure the worn geometry, reconstruct dimensions, and machine new parts in the appropriate grade. If the original material grade is unknown, we recommend PA66 or MDS-nylon based on the application — both are likely to match or exceed the original performance.
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