Nylon (polyamide, PA) is a workhorse engineering plastic for CNC‑machined wear parts such as gears, bushings, bearing liners, wear pads and sliding guides. Its appeal is the combination of 70–100 MPa tensile strength, low friction against steel, and naturally lubricious running in unfilled grades. Two choices determine whether a machined nylon part performs correctly in service: selecting the right grade (PA6, PA6/6 or PA6‑GF30) and designing explicitly for nylon’s moisture‑driven dimensional change.
At a Glance
- Available grades: PA6, PA6/6, PA6-GF30
- Standard tolerance: ±0.10 mm
- Precision tolerance: ±0.05 mm (grade-dependent)
- Min wall thickness: 0.75 mm
- Lead time: 1-5 Days
- Certifications(vetted network): ISO 9001:2015 · AS9100D · ISO 13485:2016
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When nylon is the right choice
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Gears, bushings and wear pads running in oils, greases or dry with moderate load
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Structural plastic components where tensile strength and fatigue resistance matter more than cosmetics
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Applications where some moisture‑driven growth is acceptable and can be designed into the clearance
Choosing the Right Nylon Grade for CNC Machining
PA6, PA6/6, and PA6-GF30 each have distinct mechanical profiles — the differences are consequential to part performance, not incidental. Grade selection is the most common source of dimensional or functional failure in machined nylon components.
Nylon 6 (PA6) - General Purpose and Impact Toughness
For large cross‑section bushings, wear pads, guides, spacers and structural inserts, PA6 is the most cost‑effective grade and machines with very predictable results.
PA6's primary limitation is moisture uptake — a factor covered in full in the Moisture Absorption section below.
Specify PA6 when: cost efficiency, impact toughness, and ease of machining are the priorities, and tolerances are ±0.10 mm or wider, or parts will be used in dry or low-humidity environments.
Nylon 6/6 (PA6/6) - Precision, Strength and Heat Resistance
PA6/6’s more regular crystalline structure produces four real performance advantages over PA6: higher tensile strength, a higher melting point, lower moisture absorption and better dimensional stability under sustained load. For precision mechanical components - gear teeth, close-fitting bearing liners, sliders with tight tolerances, and shaft assemblies - PA6/6 is the more reliable grade.
Specify PA6/6 when: higher tensile strength, better thermal resistance, lower moisture uptake, or tighter dimensional stability over time is required. It is the preferred grade for most precision mechanical components.
Nylon 6 - 30% Glass-Filled (PA6-GF30) - Structural Stiffness and High Temperature
Adding 30% short glass fibre by weight transforms nylon’s behaviour. Flexural modulus jumps to roughly three times that of unfilled PA6, heat deflection temperature reaches 200–215 °C at 1.82 MPa, and thermal expansion drops by more than half. PA6‑GF30 is the grade for genuinely structural nylon parts in high‑temperature assemblies where thermal drift would cause functional failure.
The trade‑offs are important: elongation at break falls to 3–5%, so the material behaves in a brittle manner under impact, particularly in thin sections or at sharp internal corners. The glass fibres also abrade tools quickly; carbide or PCD tooling and reduced cutting speeds are required to maintain surface finish and dimensional accuracy.
Specify PA6-GF30 when: stiffness above 5,000 MPa, heat deflection above 150 °C, or low thermal dimensional drift is required. Not suitable for applications requiring impact toughness or where thin-walled features may see dynamic loading.
Grade Comparison at a Glance
| Property | PA6 | PA6/6 | PA6-GF30 |
|---|---|---|---|
| Tensile Strength (MPa) | 70 – 85 | 80 – 100 | 120 – 175 |
| Melting Point (°C) | 215 – 225 | 255 – 265 | 215 – 225 |
| Heat Deflection Temp @ 1.82 MPa (°C) | 65 – 75 | 75 – 90 | 200 – 215 |
| Moisture Absorption - Equilibrium (%) | 2.5 – 3.5 | 2.0 – 2.5 | 1.0 – 1.5 |
| Elongation at Break (%) | 40 – 80 | 100 – 300 | 3 – 5 |
| Flexural Modulus (MPa) | 2,500 – 3,000 | 2,800 – 3,200 | 7,000 – 9,000 |
| Machinability | Excellent | Good | Moderate (carbide required) |
| Relative Cost | Low | Low–Medium | Medium |
| Best For | Bushings, pads, guides, general components | Precision gears, bearings, structural parts | High-temp structural parts, stiff assemblies |
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Moisture Absorption and Dimensional Stability
Moisture is the single most important material-level characteristic when designing CNC-machined nylon parts. Unlike metals and most other engineering plastics, nylon is hygroscopic — it absorbs water from the atmosphere continuously after machining, producing real, measurable dimensional changes that must be designed for, particularly when specifying tight tolerances or close-clearance fits.
How Moisture Affects Nylon Dimensions
The dimensional change is proportional to moisture content and cross-section — larger sections absorb more and change more. The effect is reversible: dried nylon contracts back toward its as-machined dimensions. Equilibrium is reached over hours for thin sections and several days for thick sections, depending on cross‑section and ambient humidity.
The table below shows equilibrium moisture content and the resulting linear dimensional change for each grade at standard ambient conditions (23 °C / 50% RH) and at full water saturation.
| Grade | Equilibrium Moisture Content (23 °C / 50% RH) | Saturation Moisture Content | Linear Dimensional Change at Equilibrium | Linear Dimensional Change at Saturation |
|---|---|---|---|---|
| PA6 | 2.5 – 3.5% | 7.0 – 9.0% | ~0.6 – 0.9% | ~1.5 – 2.0% |
| PA6/6 | 2.0 – 2.5% | 5.0 – 7.0% | ~0.5 – 0.7% | ~1.2 – 1.5% |
| PA6-GF30 | 1.0 – 1.5% | 3.0 – 4.5% | ~0.2 – 0.3% | ~0.5 – 0.8% |
For a 50 mm shaft bore machined in PA6 at equilibrium moisture: linear dimensional change of ~0.6% equals ~0.30 mm of bore growth. For a part machined dry and measured immediately, then installed in a humid environment, this growth occurs after installation - and a shaft that fit correctly at time of measurement may no longer fit in service.
Designing for Moisture: Tolerance and Fit Considerations
Moisture state at measurement must match the intended service environment. If it doesn't, the tolerance specification must account for the difference explicitly.
Three approaches to managing moisture in nylon tolerance design:
1. Specify measurement conditions on the drawing
State whether dimensions are to be held dry-as-machined (immediately off the machine, sealed in bag) or at a stated equilibrium humidity representing the service environment. For parts that will operate in standard indoor conditions (23 °C / 50% RH), specify measurement after conditioning at those conditions rather than immediately off the machine.
2. Add moisture allowance to tolerance stack
For PA6 parts with features in the ±0.05–0.10 mm range, add the expected dimensional growth to the tolerance budget. A 20 mm bore in PA6 exposed to 50% RH will grow approximately 0.12–0.18 mm from dry state - this growth should be accounted for explicitly in the nominal dimension or tolerance band.
3. Specify PA6/6 or PA6-GF30 where moisture stability is critical
PA6/6 absorbs 20–30% less moisture than PA6 at equivalent humidity. PA6-GF30 absorbs 60–70% less. For assemblies where bore-shaft clearance must remain within ±0.05 mm across a range of humidity conditions, PA6-GF30 is the most reliable choice - its dimensional response to moisture is small enough to be treated as a secondary effect rather than a design variable.
Rule of thumb: For tolerances of ±0.10 mm or wider, moisture can be managed through measurement conditioning. For tolerances of ±0.05 mm or tighter, specify PA6/6 minimum, PA6-GF30 preferred, and call out measurement conditions explicitly on the drawing.
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Nylon Material Properties — PA6, PA6/6 and PA6-GF30 Data
The data tables below represent reference ranges for engineering-grade nylon stock used in CNC machining. Values are representative ranges from engineering‑grade polyamide datasheets and typical CNC‑machined stock; always confirm against the specific supplier datasheet for final structural calculations.
| Material | Density (g/cm³) | Yield Strength (MPa) | Tensile Strength (MPa) | Elongation at Break (%) | Hardness (Shore D) | Melting Point (°C) | CTE (×10⁻⁶/°C) |
|---|---|---|---|---|---|---|---|
| Nylon 6 | 1.13 - 1.15 | 70 - 85 | 70 - 85 | 40 - 80 | ~74-78 | 215 - 225 | 80-90 |
| Nylon 6/6 | 1.14 - 1.15 | 75-90 | 80 - 100 | 100 - 300 | ~76-80 | 255 - 265 | 70-80 |
| Nylon6 (30% Glass Filled) | 1.35 - 1.37 | 100 - 120 | 120 - 175 | 3 - 5 | ~82-86 | 215 - 225 | 25-35 |
Tolerances and Design Limits for CNC-Machined Nylon
Nylon machines to tight tolerances when stock condition, clamping, and process parameters are controlled. The achievable tolerance depends on three variables that do not apply to metals: moisture state at measurement, grade selection, and section size. All three must be addressed at the design stage.
Achievable Tolerances by Grade
The table below reflects what is consistently achievable on CNC milling and turning operations with engineering-grade nylon stock, measured dry-as-machined unless otherwise stated.
| Tolerance Class | Value | PA6 | PA6/6 | PA6-GF30 | Typical Application |
|---|---|---|---|---|---|
| Standard | ±0.10 mm | ✓ | ✓ | ✓ | General geometry, clearance fits, non-critical structural features |
| Precision | ±0.05 mm | ✓ with conditioning | ✓ | ✓ | Sliding fits, shaft and bore assemblies, guide components |
| Fine | ±0.025 mm | Not recommended | ✓ with conditioning | ✓ preferred | Close-clearance bearings, sealing faces, precision assemblies |
| Critical | < ±0.025 mm | Not recommended | Consult at enquiry | ✓ preferred | Requires conditioned stock and post-conditioning dimensional inspection |
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Wall Thickness, Holes and Thread Design
| Feature | PA6 / PA6/6 (Unfilled) | PA6-GF30 | Notes |
|---|---|---|---|
| Minimum wall thickness | 0.75 mm | 1.0 mm | GF30 is more brittle - thinner walls risk chipping and fracture |
| Minimum end mill diameter | 0.8 mm | 1.0 mm | Below minimum, deflection and breakage risk increases |
| Minimum drill diameter | 0.5 mm | 0.8 mm | Standard drill geometry; peck drill above 5:1 depth-to-diameter |
| Max hole depth-to-diameter ratio | 10:1 (peck above 5:1) | 8:1 | Chip evacuation becomes critical at high L/D ratios |
| Tapped holes (direct) | M3 minimum | M3 minimum | Coarse thread; minimum 2× diameter engagement; low-cycle use only |
| Threaded inserts (heat-set / press) | M2 minimum | M2 minimum | Preferred for any repeat-assembly feature |
| Undercut profiles | Square, full-radius, dovetail | Square, full-radius | Dovetail not recommended on GF30 - fracture risk on thin undercut walls |
Internal corner radii: Set internal radii to at least 1/3 of pocket depth, and specify a radius slightly larger than the nearest standard tool size. Sharp internal corners are machinable constraints rather than design options, and in GF30 they also act as stress concentrators under load.
Boss walls for inserts: Minimum boss outer diameter of 2× insert OD. Undersized bosses crack under insert installation load in all nylon grades - particularly GF30. For repeated thermal cycling, prefer heat-set inserts over press-fit.
Rack and slot geometry: For linear guide slots and mating surfaces, design nominal clearance of 0.10–0.15 mm per side for PA6 to accommodate moisture-induced growth in service. For PA6/6, 0.05–0.10 mm per side is sufficient. For PA6-GF30, standard metal-equivalent clearances apply.
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Surface Finish Options for Machined Nylon
As-machined nylon is adequate for most structural and mechanical applications. Where appearance, friction, or bonding requirements demand more, nylon accepts several secondary finishing operations — though the options are narrower than for polycarbonate or ABS due to its surface chemistry and moisture sensitivity.
As-Machined
The default condition after CNC milling or turning. Surfaces show subtle tool paths with a matte, slightly waxy appearance. Ra 1.6–3.2 µm is typical for standard operations; a dedicated finishing pass reduces this to Ra 0.8–1.6 µm. Suitable for structural parts, enclosures, jigs, fixtures, and mechanical components where surface appearance is not a requirement.
Sanding and Polishing
Progressive wet-sanding (400 to 1200 grit, followed by polishing compound) reduces surface roughness to Ra 0.4–0.8 µm on flat or convex surfaces. Produces a smooth, low-friction surface suitable for sliding contact faces, cosmetic external surfaces, and seal-contact areas. Time-intensive and limited to geometrically accessible surfaces. Not suitable for internal bores or complex pocket geometries.
Bead Blasting
Fine glass or ceramic beads produce a uniform matte texture across all exposed faces, eliminating directional tool marks. Ra values typically fall between 1.6 and 3.2 µm depending on bead size and dwell time. Suitable for external cosmetic surfaces on enclosures, housings, and covers where a consistent, non-directional appearance is required.
Painting
Nylon can be painted, but requires careful surface preparation due to its low surface energy. Degreasing followed by light mechanical abrasion and a compatible adhesion primer are the standard preparation steps. Water-based primers are preferred - solvent-based primers should be verified for compatibility to avoid surface damage. Painting is used for colour matching, branding, and UV protection on parts with outdoor or cosmetic requirements. Note that paint adhesion on nylon is less reliable than on ABS or PC - test bond strength before committing to production volumes.
Teflon (PTFE) Coating
A thin PTFE coating further reduces the surface friction coefficient — useful on sliding guides, wear pads, and contact surfaces where nylon's native friction coefficient (0.20–0.30 against steel) is insufficient. Confirm coating thickness and dimensional impact (+5–25 µm per side) with the surface treatment supplier before specifying on a drawing.
Dyeing
Nylon can be dyed using standard polyamide dyes — the colour penetrates the surface layer, producing no dimensional impact and good abrasion resistance. Commonly used for identification coding (grade, batch, orientation) on complex assemblies. Not UV-stable on standard grades.
| Finish | Ra (µm) | Dimensional Impact | Best Used For |
|---|---|---|---|
| As-machined (standard) | 1.6 – 3.2 | None | Structural parts, fixtures, general mechanical components |
| As-machined (precision pass) | 0.8 – 1.6 | None | Bearing bores, sliding contact surfaces |
| Sanded / polished | 0.4 – 0.8 | Negligible | Cosmetic surfaces, low-friction contact faces |
| Bead blasted | 1.6 – 3.2 (uniform) | None | Cosmetic external surfaces, enclosures |
| Painted | Variable (primer‑dependent) | Negligible | UV protection, colour matching, branding |
| PTFE coated | < 0.5 (applied layer) | +5–25 µm per side | Ultra-low friction sliding applications |
| Dyed | No change | None | Colour identification, cosmetic differentiation |
Chemical Resistance of Nylon
Nylon's chemical resistance profile is directly relevant wherever machined parts are exposed to process fluids, lubricants, cleaning agents, or atmospheric conditions. Its polyamide backbone provides good resistance to non-polar media - oils, greases, fuels, and aliphatic hydrocarbons - making it well-suited to lubricated mechanical assemblies, automotive under-hood environments, and food-processing equipment where contact with light oils and brine is routine. It is, however, attacked by strong acids and strong alkalis, and standard unfilled grades degrade under prolonged UV exposure.
Values below are for unfilled PA6 and PA6/6 at 20–23 °C; resistance decreases with elevated temperature and concentration. PA6-GF30 shows similar or marginally better resistance in non-polar media — validate independently for aggressive environments.
| Chemical / Media | Resistance | Notes |
|---|---|---|
| Engine oils, gear oils, greases | Excellent | Suitable for oil-immersed or splash-lubricated environments; primary use case for machined nylon bearings and bushings |
| Aliphatic hydrocarbons (fuels, mineral spirits) | Excellent | Common use case in automotive fuel system components |
| Alcohols - dilute (methanol, ethanol) | Good | Minor swelling possible at high concentration or elevated temperature |
| Weak organic acids | Fair | Resistance decreases with concentration and temperature |
| Strong acids (H₂SO₄, HCl, HNO₃) | Poor | Nylon is attacked by most strong acids - avoid in acid process environments |
| Dilute alkalis | Fair | Acceptable for short-term incidental contact only |
| Strong alkalis | Poor | Attacked - not recommended for alkaline process environments |
| Ketones (acetone, MEK) | Poor | Avoid prolonged contact |
| Aromatic / halogenated solvents | Poor | Avoid |
| Water / humidity | Good | Dimensional change occurs - design accordingly; does not degrade the polymer chain |
| Salt water / brine | Good | Suitable for marine and food-handling environments |
| UV radiation (outdoor / direct sun) | Poor | Standard grades degrade with sustained UV exposure; specify UV-stabilised grades for outdoor use |
Practical selection guidance:
- Food processing— confirm FDA compliance of the specific nylon grade and supplier before specifying for direct food contact; salt water and mild cleaning agents are generally acceptable.
- Chemical process environments— if media involve strong acids, strong alkalis or halogenated solvents, POM (Delrin), HDPE, PTFE or PEEK are usually preferred over nylon.
Nylon Compared with Other Engineering Plastics
When nylon is under consideration, it is usually alongside POM (Delrin/Acetal), ABS, HDPE, PTFE, or polycarbonate - each of which overlaps with nylon in certain applications but diverges in others. Nylon's position is specific: highest tensile and fatigue strength among the common unfilled engineering plastics, genuine self-lubricating behaviour, and the widest chemical resistance against non-polar media. Where it loses ground is dimensional stability in humid environments and resistance to strong acids and alkalis.
| Property | Nylon PA6/6 | POM (Acetal) | ABS | Polycarbonate (PC) | HDPE | PTFE |
|---|---|---|---|---|---|---|
| Tensile Strength (MPa) | 75 – 90 | 60 – 75 | 40 – 55 | 60 – 70 | 20 – 38 | 20 – 35 |
| Wear Resistance | High | High | Low | Low–Medium | Medium | Low–Medium |
| Friction Coeff. (dry, vs. steel) | 0.20 – 0.30 | 0.10 – 0.25 | 0.40 – 0.50 | 0.35 – 0.45 | 0.20 – 0.30 | 0.04 – 0.10 |
| Heat Deflection Temp @ 1.82 MPa (°C) | 75 – 90 | 100 – 110 | 75 – 105 | 125 – 140 | 60 – 85 | 120 |
| Moisture Absorption | Medium–High | Very Low | Low | Low | Very Low | None |
| Dimensional Stability (humid) | Medium | Very High | High | High | High | Medium |
| Impact Strength (Izod, kJ/m²) | 5 – 10 | 5 – 10 | 15 – 35 | 50 – 90 | 10 – 20 | - |
| Machinability | Good | Excellent | Good | Moderate | Good | Good |
| Acid Resistance | Poor | Fair | Poor | Moderate | Good | Excellent |
| Chemical Resistance (non-polar) | Excellent | Good | Moderate | Moderate | Excellent | Excellent |
| Relative Material Cost | Low–Medium | Medium | Low | Medium | Low | High |
| Typical CNC Applications | Gears, bushings, wear pads, bearings | Precision gears, bushings, sliding parts | Housings, enclosures, fixtures | Guards, windows, structural enclosures | Chemical tanks, guides, food contact | Seals, insulators, low-friction liners |
When to choose nylon over the alternatives:
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Over POM (Delrin)- when higher tensile strength, better fatigue resistance, or impact toughness is required. POM wins when dimensional precision in humid environments is the priority, or when the lowest dry friction coefficient is needed without PA6/6-GF30.
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Over ABS- nylon is the clear choice for any wear, friction, or load-bearing application. ABS is more appropriate for housings, enclosures, and non-structural components where ease of finishing and appearance matter more than mechanical performance.
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Over Polycarbonate- when wear resistance, self-lubrication, or chemical resistance against oils and fuels is required. PC is the correct choice when impact resistance at elevated temperature or optical transparency is the priority.
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Over HDPE- nylon is stiffer, stronger, and rated for higher operating temperatures. HDPE is the better choice in aggressive chemical environments - particularly strong acid exposure - and for food-contact applications where dimensional stability under moisture is critical.
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Over PTFE- use nylon when structural load capacity is required. PTFE's extraordinary low friction and chemical inertness come at the cost of near-zero structural capability. PTFE is a specialist sealing and insulating material, not a structural one.
Frequently Asked Questions
What is the difference between Nylon 6 and Nylon 6/6 for CNC machining?
Nylon 6 (PA6) has better impact toughness, easier machinability, and is more cost-effective for general-purpose parts. Nylon 6/6 (PA6/6) offers higher tensile strength, a higher melting point (255–265 °C vs 215–225 °C), lower moisture absorption, and better dimensional stability under load - making it the preferred grade for precision mechanical components.
Does nylon change dimensions after machining?
Yes. Nylon is hygroscopic and absorbs moisture from the atmosphere after machining. A PA6 part will gain approximately 2.5–3.5% moisture by weight at equilibrium in standard ambient conditions, causing measurable dimensional growth. For tolerances tighter than ±0.05 mm, parts should be measured after conditioning to the target service humidity, not immediately off the machine.
Can glass-filled nylon be CNC machined to tight tolerances?
Yes, but carbide or PCD tooling is required. Glass fibres are abrasive and will rapidly degrade HSS tooling, degrading both surface finish and dimensional accuracy. With appropriate tooling and reduced cutting speeds, PA6-GF30 can be machined to tolerances of ±0.05 mm or tighter.
Nylon or POM (Delrin) — which should I specify for CNC machined parts?
The right choice depends on what the part must do in service.
Choose nylon PA6/6 when - tensile strength, fatigue resistance, or impact toughness is the primary requirement — PA6/6 outperforms POM on all three. For high-load, high-wear components such as gears, bearing liners, and structural bushings operating under sustained load, nylon is the stronger and more fatigue-resistant material.
Choose POM (Delrin) when - dimensional precision in humid environments is critical. POM absorbs less than 0.2% moisture versus 2.5–3.5% for PA6, making it far more dimensionally stable across ambient humidity changes — a material-level advantage that cannot be designed around with conditioning alone. POM also has a lower dry friction coefficient (0.10–0.25 vs 0.20–0.30 for nylon), making it the better choice for precision sliding components and low-load dry-running bushings where minimum friction is the priority.
What tolerances can be held when CNC machining nylon?
Standard tolerances of ±0.10 mm are achievable on all grades. Precision tolerances of ±0.05 mm are achievable on PA6/6 and PA6-GF30, and on PA6 with moisture conditioning. Fine tolerances of ±0.025 mm require PA6/6 minimum with drawing-specified measurement conditions, and are best achieved in PA6-GF30. Sub-±0.025 mm requires conditioned stock and controlled-environment measurement - discuss at enquiry stage.
Where Nylon Is Used — Industries and Applications
Nylon is widely used for CNC-machined parts that need low friction, wear resistance and better fatigue strength than commodity plastics.
Industrial & mechanical equipment
Nylon is a strong choice for gears, bushings, bearing liners, wear pads, guide rails and sliding components used in conveyors, automation equipment and general machinery. PA6 suits general wear parts, while PA6/6 and PA6-GF30 are better for tighter tolerances, higher loads and hotter operating conditions.
Automotive, aerospace & electrical assemblies
PA6/6 and glass-filled nylon are used for under-hood spacers, cable guides, insulating standoffs, brackets, connector housings and other non-metal parts where weight reduction, oil resistance, stiffness or electrical insulation matter. For ESD-sensitive, flame-rated or fully traceable applications, the exact grade and QA requirements should be confirmed at enquiry stage.
Food equipment, prototypes & bridge production
Nylon is also used for guides, bushings and wear parts in food and consumer equipment, as well as for functional prototypes and low-volume production parts that need to reflect real in-service mechanical performance. For direct food contact, only supplier-certified compliant grades should be specified.