Dewey Wu General Manager & senior mechanical engineer at EPOC CRAFTER, 15 years in design engineering, quality, and metallurgy. Hands-on across CNC machining, metalwork, sheet metal, and prototyping (subtractive + 3D printing).
Nylon (polyamide) is a semi-crystalline thermoplastic with tensile strength from 70 MPa (PA6, dry) to 190 MPa (PA66 GF30, dry) measured per ISO 527, a melting point of 218°C (PA6) to 265°C (PA66), and water absorption that causes 0.2-0.3% linear dimensional change per 1% of moisture content absorbed, figures that apply directly to CNC machined parts in service.
Dry-as-molded (DAM) data on a supplier TDS shows PA66 tensile strength at 83 MPa. At 50% RH equilibrium, that same grade drops to 53 MPa, a 36% reduction. Tensile modulus falls from 3,100 MPa to 1,200 MPa under the same condition (ISO 527, Zytel 101L). For a machined bore held to ±0.05 mm, the moisture-driven dimensional shift alone can consume the entire tolerance band before the part reaches the customer. This guide covers six property layers (mechanical strength, thermal resistance, moisture sensitivity, tribology, chemical resistance, and CNC machinability), across PA6, PA66, PA12, and GF30 variants, with data referenced to ASTM D638-22, ASTM D570-98, ASTM D648-01, ISO 527, and ISO 75. For detailed CNC cutting parameters, see Nylon Mechanical Properties & Machinability.
1.What Nylon Is, Chemically, and Why It Behaves the Way It Does
Nylon is a polyamide built from repeating amide linkages (-CO-NH-) that hydrogen-bond between adjacent chains, producing toughness, a defined melting point, and moisture sensitivity, all from the same bond.
The amide linkage is polar. In the solid state, adjacent chains lock together through hydrogen bonds between the carbonyl oxygen and the amine hydrogen, producing a tightly packed semi-crystalline structure that gives nylon its stiffness and strength at room temperature.
Water molecules attack the same bond sites. When nylon absorbs moisture, water inserts between chains at the amide groups, disrupting the hydrogen bond network. The result is measurable: PA66 tensile modulus drops from 3,100 MPa dry to 1,200 MPa at 50% RH equilibrium (ISO 527, Zytel 101L). Strength follows the same direction. The part does not fail, it becomes more ductile, more compliant, and dimensionally larger.
The higher the density of amide groups along the chain, the more water absorption sites exist. This is the structural mechanism behind one of the most useful grade-selection rules in nylon: longer carbon chains between amide groups mean lower moisture uptake.
1.1PA6, PA66, PA12. Different Monomer Structures, Different Property Fingerprints
PA6 is produced from caprolactam, a single six-carbon monomer. PA66 is produced from hexamethylene diamine and adipic acid, two six-carbon monomers joined alternately, giving it a more symmetric chain structure and denser hydrogen bonding per unit length. PA12 uses a twelve-carbon monomer, so amide groups are spaced further apart, with a -CH2/-CONH- ratio of approximately 11:1 versus 5:1 in PA6. That structural difference produces three distinct property fingerprints:
| Tensile strength, dry (MPa) | ISO 527 | 70-85 | 80-90 | 50-60 |
| Melting point (°C) | ISO 11357 | 218-222 | 258-265 | 178-180 |
| Water absorption, 24h (%) | ISO 62 | 1.0-1.5 | 0.7-1.3 | 0.2-0.3 |
| Equilibrium moisture, 50% RH (%) | ISO 62 | ~3.5 | ~2.5 | ~0.9 |
| Density (g/cm³) | ISO 1183 | 1.12-1.15 | 1.13-1.15 | 1.01-1.02 |
PA66’s melting point is approximately 40°C higher than PA6 because the symmetric chain structure allows tighter molecular packing and stronger crystalline order. PA12’s equilibrium moisture content at 50% RH is roughly one-quarter that of PA6, directly because of the lower amide group density per unit chain length.
PA6 and PA66 are not interchangeable in precision CNC applications even when their room-temperature dry tensile strength looks similar. For a full grade-versus-grade breakdown including glass-filled and modified variants, see PA6 vs PA66 vs PA12: Nylon Grades Compared.
Engineering Note: PA6 and PA66 are not interchangeable in precision CNC applications even when their room-temperature dry tensile strength looks similar. The moisture-driven dimensional change between the two grades, compounded over weeks in the field, can shift a bearing fit from H7/p6 interference to clearance.
2.The Six-Property Stack. A Selection Framework for CNC Nylon Parts
The Six-Property Stack is a six-layer elimination method: work through mechanical strength, thermal resistance, moisture sensitivity, tribology, chemical resistance, and CNC machinability in sequence. The first layer that fails ends the evaluation for that grade.
The sequence is deliberate. Layers 1 and 2 are hard physical limits. No design change fixes a grade that melts or yields under load. Layer 3 is the most commonly underestimated because it does not appear during initial qualification; dimensional drift from moisture absorption shows up weeks or months after delivery. Layers 4 and 5 are application-specific filters. Layer 6 is the procurement and process layer, it does not override material suitability but it does affect cost and lead time.
| 1 | Mechanical strength | Required stress exceeds grade capability at operating moisture and temperature |
| 2 | Thermal resistance | Operating temperature approaches or exceeds HDT at applied load |
| 3 | Moisture sensitivity | Dimensional shift at equilibrium moisture exceeds tolerance band |
| 4 | Tribology | PV value or friction coefficient incompatible with wear life requirement |
| 5 | Chemical resistance | Exposure medium degrades amide bonds or causes stress cracking |
| 6 | CNC machinability | Filler content or geometry drives tool cost or tolerance risk beyond budget |
Most nylon selection errors happen at Layer 3, not Layer 1. An engineer selects PA6 based on dry tensile strength, the part passes initial inspection, and then tolerance drift appears in the field as the part equilibrates to ambient humidity. Running Layer 3 before locking the grade, not after, is what separates a stable production part from a field return.
According to Dewey Wu, General Manager and Senior Mechanical Engineer at EPOC CRAFTER: “We see Layer 3 failures regularly on parts that passed every incoming inspection check. The customer machined to drawing at DAM conditions, shipped the part, and six weeks later the bore was 0.08 mm oversize. PA66 at 50% RH equilibrium absorbs roughly 2.5% moisture by weight, which translates to approximately 0.6% linear dimensional growth. On a 50 mm bore that is 0.30 mm, six times a typical H7 tolerance band.”
2.1 How to Apply the Stack to a Real Selection Decision
Start with your operating load and calculate the required stress. Check that value against the grade’s tensile strength at the expected moisture condition and temperature, not the DAM value from the TDS front page. If the grade clears Layer 1, move to Layer 2.
For Layer 2, read HDT at 1.82 MPa (ISO 75 Method A), not at 0.455 MPa. The 0.455 MPa value runs higher and is not conservative for loaded structural parts. If your operating temperature stays at least 20°C below the HDT at 1.82 MPa, the grade passes Layer 2 with margin.
For Layer 3, calculate the linear dimensional shift at equilibrium moisture for your service environment. PA66 in a 50% RH indoor environment will reach approximately 2.5% moisture content and 0.6% linear growth. If that shift consumes more than 30% of your tightest tolerance, the grade needs either a moisture-stable alternative (PA12, GF reinforcement) or a post-machining stabilization step. For tolerance specifications on machined nylon parts, see Tolerances & Standards.
For industry-specific use cases, achievable CNC tolerances by feature type, and a pre-order checklist, see the nylon parts engineering applications and procurement guide
Engineering Note: Layers 4, 5, and 6 are covered in detail in 6 and 7. The full grade comparison table appears in 8.
3.Mechanical Properties. What the Numbers Actually Mean
Every number on a TDS is a snapshot at one moisture condition, one temperature, and one test speed. PA66 dry tensile strength is 83 MPa; at 50% RH it is 53 MPa; at 121°C dry it is 43 MPa. Three conditions, three numbers, all from the same grade.
3.1 Tensile Strength and Modulus. DAM vs 50% RH
The table below uses Zytel 101L (PA66, unreinforced) as the reference grade because it carries the most complete published dataset across conditions. Values per ISO 527 (modulus at 1 mm/min, strength at 50 mm/min, 23°C).
| Yield stress (MPa) | 83 | 53 | -36% |
| Tensile modulus (MPa) | 3,100 | 1,200 | -61% |
| Yield strain (%) | 4.5 | 25 | +456% |
| Strain at break (%) | 40 | >50 | |
| Charpy impact, notched, ISO 179/1eA (kJ/m²) | 5 | 15 | +200% |
The modulus drop from 3,100 MPa to 1,200 MPa is the number that matters most for deflection-critical parts. A bracket or gear tooth designed to DAM stiffness will deflect 2.6 times further at equilibrium humidity. That is not a safety factor issue, it is a geometry issue that shows up as interference, misalignment, or noise in service.
The impact strength increase at 50% RH is real and useful. Moisture acts as a plasticizer, shifting the failure mode from brittle fracture to ductile deformation. For parts that see shock loading in humid environments, conveyor components, outdoor brackets, automotive underhood clips, the conditioned value is the relevant design input, not the DAM value.
Engineering Note: For any structural or tolerance-critical application, request the 50% RH conditioned values before finalizing a design, the DAM value alone understates dimensional risk by a factor of two or more on stiffness and by 36% on yield strength.
3.2 Temperature Effect on Tensile Strength. Four Key Nodes
PA66 (Zytel 101L, unreinforced) tensile strength at four temperatures, per ASTM D638-22, DAM and 50% RH conditions:
| -40°C | 114 | 110 |
| +23°C | 83 | 77 |
| +77°C | 62 | 41 |
| +121°C | 43 | 38 |
At -40°C, strength is highest but ductility collapses. Zytel 101L brittle temperature is -80°C (DAM, ASTM D746), so the material does not fracture at -40°C, but elongation at break drops to 15% from 60% at room temperature. Parts that see impact loading at low temperature need toughened grades (ST801 or equivalent), not standard PA66.
At 121°C, DAM strength is 43 MPa, still structurally useful for light loads, but flexural modulus at this temperature drops to approximately 538 MPa (ASTM D790, Zytel 101L DAM). A part designed for 2,827 MPa room-temperature stiffness is operating at roughly one-fifth of that stiffness at 121°C.
Engineering Note: The 77°C row is the most practically relevant for automotive underhood and industrial motor-adjacent applications. At 50% RH and 77°C simultaneously, effective tensile strength is 41 MPa, roughly half the room-temperature DAM value. Size the section for this combined condition, not for the room-temperature datasheet figure.
3.3 Glass Fiber Reinforcement. The 2x Strength and 3x Stiffness Gain
Adding 30% glass fiber (GF30) to PA66 changes the property profile substantially. The comparison below uses PA66 unfilled vs PA66 GF30, dry, 23°C:
| Tensile strength, ISO 527 (MPa) | 80-90 | 170-190 | ~2.1x |
| Flexural modulus, ISO 178 (MPa) | 2,800-3,500 | 9,000-11,000 | ~3.2x |
| HDT @1.82 MPa, ISO 75 (°C) | 75-90 | 210-230 | ~2.6x |
| Elongation at break (%) | 40-60 | 2.5-3.5 | -94% |
| Water absorption, 24h, ISO 62 (%) | 0.7-1.3 | 0.4-0.8 | ~-40% |
| Notched Charpy, ISO 179/1eA (kJ/m²) | 4-8 | 9-13 | ~1.6x |
The stiffness gain is the primary reason to specify GF30. For a given cross-section, the part deflects three times less under the same load. The HDT jump from 75-90°C to 210-230°C makes GF30 the only grade that clears the 150°C threshold without switching to a specialty polymer.
The trade-off is elongation. PA66 GF30 at 2.5-3.5% elongation at break behaves more like a ceramic than an unreinforced thermoplastic under sudden impact. Stress concentrations at sharp corners, thin walls, or abrupt section changes become fracture initiation sites. In CNC machined GF30 parts, internal corner radii below 0.5 mm are a structural risk, not just a machining preference.
Engineering Note: GF reinforcement reduces moisture absorption and dimensional shift, but does not eliminate it. PA66 GF30 equilibrium moisture at 50% RH is approximately 1.8-2.0%, producing linear dimensional growth of roughly 0.35%. For bore tolerances tighter than ±0.03 mm, post-machining stabilization at target humidity is still required even with GF30.
4.Moisture Absorption. The Property That Changes After Delivery
PA66 tensile modulus at 50% RH is 1,200 MPa vs 3,100 MPa dry. The part that left the supplier’s floor passed every inspection check. The part that arrived three weeks later has different dimensions and different stiffness, nothing failed, the material absorbed moisture from the air.
4.1 What ASTM D570 Actually Measures
ASTM D570-98 defines water absorption as mass increase after immersion in distilled water at 23°C for 24 hours. That number, the “24h water absorption” on every TDS, is a time-point measurement, not a saturation value.
For a PA6 specimen at 3.2 mm thickness, reaching 95% of saturation takes approximately 1,000 hours at 23°C (ASTM D570-98, Table 1). A 10 mm thick part takes approximately 10,000 hours. The 24h immersion value captures early-stage absorption kinetics, not the equilibrium state your machined part will reach in service.
Machined surfaces absorb moisture faster than molded surfaces. Cut edges expose the interior polymer structure directly to the environment. A machined PA6 rod does not behave identically to a molded PA6 disc of the same nominal composition, the cut surface accelerates the absorption front inward (ASTM D570-98, Section 3.4).
Engineering Note: When comparing water absorption values across suppliers, verify that both figures use the same test condition. ASTM D570 defines six distinct procedures: 24h immersion, 2h immersion, long-term saturation, 2h boiling water, 30 min boiling water, and 50°C/48h immersion. A “water absorption 1.2%” at 24h and another at 50°C/48h are not the same measurement and cannot be directly compared.
4.2 Dimensional Change, The Number You Need for Tolerance Calculations
DuPont Module II Nylon data gives the most actionable dimensional change figures for PA66 in engineering conditions:
| Moisture Condition | Moisture Content (by weight) | Linear Dimensional Change |
| Dry as molded (DAM) | 0% | 0% (reference) |
| 50% RH equilibrium | ~2.5% | ~0.6% |
| 100% RH / water saturated | ~8.5% | ~2.6% |
The average linear dimensional change rate for PA66 is approximately 0.24% per 1% moisture content absorbed (0 to 50% RH range). The practical working figure for indoor environments is 0.2-0.3% linear change per 1% moisture.
PA6 reaches approximately 3.5% moisture at 50% RH, producing proportionally higher dimensional change than PA66. PA12 at 50% RH reaches approximately 0.9% moisture content, producing linear change well under 0.3%, which is why PA12 is specified for precision components in variable humidity environments despite its lower tensile strength.
For a concrete tolerance calculation: a PA66 part machined at DAM conditions with a 50 mm bore diameter will grow approximately 0.30 mm (0.6% of 50 mm) after reaching 50% RH equilibrium. A typical H7 tolerance on a 50 mm bore is ±0.025 mm. The moisture-driven growth is twelve times the tolerance band. For dimensional tolerance reference data on CNC machined plastics, see Tolerances & Standards.
Engineering Note: There are two ways to manage this. Machine the part after pre-conditioning to the target service humidity, so the part is dimensionally stable at delivery. Or machine to an adjusted target dimension that accounts for calculated moisture growth, this works only when the service humidity is known and stable. EPOC CRAFTER uses the first approach for precision nylon components with bore tolerances tighter than ±0.05 mm.
4.3 Comparing ASTM D570 and ISO 62
ASTM D570 uses a 50.8 mm diameter, 3.2 mm thick disc as the standard molded specimen. ISO 62 uses a 60 mm x 60 mm x 1 mm flat specimen. The thinner ISO 62 specimen reaches a higher absorption value in the same immersion time because the absorption front penetrates a larger proportion of the cross-section within 24 hours.
When you see “water absorption per ISO 62” and “water absorption per ASTM D570” side by side for the same material, the ISO 62 value will typically be higher for the 24h measurement. For cross-supplier comparison, verify the specimen geometry and test duration, not just the standard number.
5.Heat Resistance. Reading HDT Values Without Getting Burned
PA66 HDT at 0.455 MPa is approximately 130°C. At 1.82 MPa, the same grade measures 75-90°C. Same material, same standard (ASTM D648 / ISO 75), 40-55°C difference, because the two load conditions are not variants of the same measurement. They produce different numbers, and using the wrong one in a design calculation is a fast path to a field failure.
5.1 What HDT Measures and What It Does Not
ASTM D648-01 defines heat deflection temperature as the temperature at which a specimen deflects 0.25 mm at its midpoint under a specified bending stress, with the bath temperature rising at 2.0 ± 0.2°C per minute. The specimen is a rectangular bar loaded as a simply supported beam, immersed in a liquid heat transfer medium.
HDT is not the melting point. PA66 melts at 258-265°C (ISO 11357). HDT at 1.82 MPa is 75-90°C for unfilled PA66. The gap reflects that the material softens progressively under load well below the crystalline melting transition.
HDT is not the continuous use temperature. ASTM D648-01 Section 5.1 states explicitly that HDT data cannot be used to predict material behavior at elevated temperature in service unless the time, temperature, loading mode, and surface fiber stress match the test conditions. A part operating continuously at its HDT will deform.
HDT is not load-independent. The 0.455 MPa and 1.82 MPa results are not interchangeable and there is no fixed conversion between them (ASTM D648-01, Sections 4.1 and 7.1.4). When comparing HDT values across suppliers, verify which load condition was used.
Engineering Note: For structural parts under any meaningful load, use the 1.82 MPa HDT as your reference and apply a minimum 20°C margin below it as the practical operating limit. The 0.455 MPa value is useful for quality control comparison between production lots, not for design calculations.
5.2 Grade-by-Grade HDT Comparison
HDT values below at 1.82 MPa (ISO 75-2 Method A / ASTM D648-01), dry condition. Moisture reduces HDT for unfilled grades, at 50% RH equilibrium, unfilled PA66 HDT drops approximately 10-15°C from the dry value
| PA6, unfilled | 65-80 | 145-180 | ~50-60°C |
| PA66, unfilled | 75-90 | 180-220 | ~55-70°C |
| PA12, unfilled | 50-55 | 140-160 | ~35-40°C |
| PA6 GF30 | 200-215 | 210-220 | ~180°C |
| PA66 GF30 | 210-230 | 220-235 | ~190°C |
PA12’s low HDT at 1.82 MPa (50-55°C) limits its use despite excellent moisture stability. PA12 is the right choice for precision dimensional stability in humid environments, not for thermally demanding applications. At operating temperatures above 40°C under load, PA12 will creep.
5.3 Glass Fiber Reinforcement and Thermal Capability
GF30 reinforcement transforms nylon’s thermal behavior. PA66 GF30 HDT at 1.82 MPa is 210-230°C. That represents a 135-155°C increase over unfilled PA66. For parts operating near hot surfaces, motors, or exhaust systems where ambient temperature exceeds 100°C, unfilled PA66 is not suitable; PA66 GF30 clears 180°C with margin. For automotive nylon component specifications, see Automotive.
A test method detail worth tracking: ASTM D648-01 notes that specimens approximately 13 mm wide may produce HDT values 2-4°C higher than specimens 4 mm wide, because wider specimens conduct heat less efficiently to the core (ASTM D648-01, Section 9.1, Note 8). When two suppliers report HDT values 3°C apart for nominally identical grades, specimen width difference is a plausible explanation.
Engineering Note: In 5-axis CNC machined GF30 parts, GF reinforcement reduces moisture absorption but does not eliminate dimensional drift. PA66 GF30 equilibrium moisture at 50% RH is approximately 1.8-2.0%, producing linear growth of roughly 0.35%. Bore tolerances tighter than ±0.03 mm still require post-machining stabilization.
6.Friction, Wear, and Chemical Resistance
Nylon’s dynamic coefficient of friction against steel ranges from 0.17 to 0.43 without lubrication. That range reflects genuinely different tribological behavior across operating conditions, specifying “nylon” for a bearing application without defining PV value, lubrication regime, and mating surface is an incomplete specification.
6.1 Coefficient of Friction and PV Limits
DuPont General Design Principles data for Zytel 101L (PA66, unreinforced) against steel, no lubricant, 23°C, 2.1 MPa contact pressure, 3 m/min sliding speed:
| Zytel 101L / Steel | 0.31-0.74 | 0.17-0.43 |
| Zytel 101L / Zytel 101L | 0.36-0.46 | 0.11-0.19 |
| Delrin 500 / Zytel 101L | 0.10 | 0.20 |
The wide range in the nylon-on-steel pair reflects surface condition sensitivity. Clean, smooth steel produces the lower end. Rough or oxidized steel surfaces drive friction toward the upper bound. Surface finish of the mating metal part is as important a design variable as the nylon grade itself.
Maximum PV value for Zytel 101L without lubrication is 6 MPa·m/min (DuPont General Design Principles). Exceed this and frictional heat generation outpaces dissipation, leading to localized softening and accelerated wear. For intermittent contact applications the effective PV limit is higher because the contact surfaces have time to cool between cycles.
Engineering Note: For gear and bushing applications, nylon-on-steel wear rate under equivalent PV conditions runs lower than nylon-on-nylon contact. The harder steel counterface provides a more stable wear surface. Nylon-on-nylon contact generates more frictional heat per unit area because both surfaces deform, concentrating stress at asperity contacts.
6.2 Modified Grades for Tribological Applications
MoS2-filled nylon (typically 0.3-0.5% molybdenum disulfide by weight) reduces dynamic friction coefficient against steel by approximately 20-30% compared to unfilled grades. The MoS2 particles act as a solid lubricant at the contact interface, reducing adhesive wear without requiring external lubrication.
PTFE-filled nylon reduces friction further. Dynamic CoF against steel can drop below 0.10, but PTFE content above approximately 15% by weight begins to reduce tensile strength measurably. For CNC machined bushings where dimensional precision matters, PTFE-filled grades require tighter process control because the PTFE phase can produce inconsistent surface finish.
6Both MoS2-filled and PTFE-filled grades are available in PA6 and PA66 base resins. GF reinforcement can be combined with either modifier for applications requiring both high stiffness and low friction. The combination raises tooling cost due to abrasive fiber content plus modified surface chemistry.
6.3 Chemical Resistance. A Decision Table
Nylon’s chemical resistance derives from its semi-crystalline structure and the relative stability of the amide bond under neutral and alkaline conditions. The amide bond is vulnerable to hydrolysis under acidic conditions, strong acids cleave the backbone, reducing molecular weight and causing strength loss that does not recover when the acid is removed
| Dilute inorganic acids | Dilute HCl, H2SO4 | Poor to moderate | Chain hydrolysis at amide bond; strength loss accelerates with temperature |
| Concentrated inorganic acids | Concentrated H2SO4, HNO3 | Not recommended | Rapid degradation; avoid all contact |
| Dilute alkalis | Dilute NaOH, KOH | Good to moderate | Stable at low concentration; degrades at high concentration or temperature |
| Aliphatic hydrocarbons | Gasoline, diesel, mineral oil | Good | Excellent resistance; primary reason for automotive fuel system use |
| Aromatic hydrocarbons | Toluene, xylene | Good | Generally compatible; monitor for stress cracking under sustained load |
| Alcohols | Ethanol, isopropanol | Good | Compatible with short-chain alcohols at room temperature |
| Esters / ketones | Acetone, MEK, ethyl acetate | Moderate to poor | Swelling and potential stress cracking; test before specifying |
| Oils and lubricants | Mineral oil, hydraulic fluid | Good to excellent | Suitable for oil-immersed applications |
| Oxidizing agents | Strong oxidizers, peroxides | Poor | Rapid oxidative attack on polymer backbone |
| Zinc chloride solutions | ZnCl2 | Poor | Stress cracking at moderate concentration; brittle fracture under load at neutral pH |
Zinc chloride deserves specific attention. ZnCl2 solutions cause stress cracking in nylon at concentrations that do not visibly attack the surface, the failure mode is sudden brittle fracture under load rather than progressive softening. Parts exposed to metalworking fluids containing zinc compounds are at risk. This failure mode is distinct from acid hydrolysis and occurs at neutral or mildly acidic pH.
Engineering Note: Chemical resistance data is reported at room temperature with no applied stress. Both temperature and stress accelerate attack. A part that passes a 23°C immersion test for 24 hours in a given chemical may fail within hours when that same chemical is applied at 60°C with a sustained tensile stress of 20 MPa. Test the part at operating temperature under representative load before approving the grade.
6.4 PA6 vs PA66 Chemical Resistance, and Where PA12 Fits
PA6 and PA66 have similar chemical resistance profiles because both are aliphatic polyamides with the same functional group (amide bond) as the primary site of chemical attack. PA66’s higher crystallinity provides marginally better hydrolysis resistance in dilute acid conditions at elevated temperature, but the difference is not large enough to make PA66 a reliable substitute for PA6 in genuinely aggressive acid environments.
PA12’s longer carbon chain between amide groups provides measurably better hydrolysis resistance than PA6 or PA66 in dilute acid and steam environments. For hot water, steam cleaning, or weak acid exposure applications where dimensional stability is also required, PA12 is the correct grade rather than an improved PA66. For a full material properties database including chemical resistance ratings, see Materials & Properties.
7.CNC Machinability of Nylon
Nylon cuts without work-hardening and generates continuous chips that evacuate predictably from the cut zone on standard CNC equipment. The critical variables are tool material (HSS vs carbide, determined by GF content), coolant selection (pure water or air only, metalworking fluids attack polyamide), and moisture state of the stock at machining.
7.1 Tool Selection. The GF Content Dividing Line
The tool selection rule for nylon is straightforward: unfilled grades accept HSS, GF-reinforced grades require carbide. Glass fibers are abrasive at the microscopic level, each fiber contact event removes tool material. HSS tools on GF30 nylon lose edge geometry within minutes, producing burrs, dimensional drift, and surface finish degradation that compounds across a batch. For EPOC CRAFTER’s CNC machining capabilities on engineering plastics, see CNC Machining at epocrafter.com/cnc-machining/.
Per Ensinger Engineering Plastics Machining Guide: “Non-reinforced thermoplastics can be machined with cutting tools of high-speed steel. For reinforced materials, hard metal tools are required.”
For unfilled PA6 and PA66, sharp HSS tools with positive rake angles (10-15°) and polished flute geometry produce the best results. Positive rake reduces cutting forces, which matters because nylon’s low stiffness means high cutting forces deflect the part rather than cutting it, introducing dimensional error as taper or out-of-round on bored features.
For PA6-GF30 and PA66-GF30, uncoated carbide (K-grade, fine grain) is the baseline. PCD tooling extends tool life on high-volume GF30 work but is only justified at production quantities above approximately 200-300 parts per setup. TiAlN-coated carbide is not recommended for GF30 nylon, the coating reduces thermal conductivity at the cutting edge, concentrating heat that accelerates fiber-matrix debonding at the machined surface.
Engineering Note: Tool sharpness is more critical for nylon than for aluminum or steel. A dull tool on nylon generates heat through friction rather than through shear, and nylon’s low thermal conductivity means that heat concentrates at the cutting zone. Localized temperatures above approximately 180°C cause surface melting and smearing on unfilled grades, producing a glazed layer with degraded dimensional accuracy and poor adhesion for subsequent bonding or coating.
7.2 Cutting Parameters. Unfilled and GF30 Grades
Published cutting parameter data for nylon from tooling manufacturers is sparse compared to metals. The ranges below combine Ensinger guidance with engineering practice for CNC turning and milling of PA6, PA66, and GF30 variants.
Turning. Unfilled PA6/PA66 (HSS tooling):
| Cutting speed (Vc) | 200-400 m/min |
| Feed rate (f) | 0.1-0.3 mm/rev |
| Depth of cut (ap) | 0.5-3.0 mm |
| Tool geometry | Positive rake 10-15°, sharp edge, polished flute |
Turning. PA6-GF30 / PA66-GF30 (carbide tooling):
| Cutting speed (Vc) | 150-300 m/min |
| Feed rate (f) | 0.05-0.2 mm/rev |
| Depth of cut (ap) | 0.3-2.0 mm |
| Tool geometry | Positive rake 5-10°, uncoated K-grade carbide |
GF30 grades run at lower cutting speed than unfilled nylon because higher speed increases frictional heat at the fiber-matrix interface, accelerating surface degradation. Feed rate on GF30 is also reduced to maintain surface finish, higher feeds on reinforced grades produce a rougher surface with exposed fiber ends that affect dimensional measurement and sealing surface function.
7.3 Coolant and Chip Control
Standard metalworking cutting fluids attack nylon. Most water-soluble coolants and oil-based cutting fluids contain additives, emulsifiers, corrosion inhibitors, biocides, that cause swelling, stress cracking, or surface degradation on polyamide parts.
Per Ensinger Machining Guide: liquid cooling for nylon should use pure water only, and cutting fluid compatibility with the plastic must be confirmed before use.
Three coolant approaches work for CNC nylon. Dry cutting is suitable for light finishing passes and short cycle times on unfilled grades, with chip evacuation by compressed air; dry cutting is not appropriate for deep bore operations on unfilled nylon, chip accumulation in the bore raises local temperature above 150°C and causes surface glazing that compromises dimensional accuracy. Compressed air cooling handles most turning and milling on unfilled PA6 and PA66. Pure water mist or flood cooling with deionized or distilled water is appropriate for GF30 grades and high-speed operations where heat generation is higher.
Chip form for unfilled nylon is continuous ribbon on turning operations. Long chips wrap around tooling if not managed. A chip breaker geometry or periodic tool retraction breaks chips into manageable segments. GF30 chips are shorter and more brittle, chip wrapping is less of an issue, but abrasive chip fragments must be cleared from the work zone to prevent re-cutting damage to the machined surface.
7.4 Pre-Machining Moisture Management
Nylon stock absorbs moisture from the moment it leaves the supplier’s packaging. For precision work, bore tolerances tighter than ±0.05 mm, or shaft fits requiring interference or transition fit classifications, the stock moisture condition at machining must be controlled and documented.
Machine at DAM conditions by drying stock at 80°C for 8-12 hours before machining, sealing immediately after, and machining within a short time window. The finished part will grow dimensionally as it absorbs moisture in service, calculate the expected growth and machine to the adjusted target dimension.
Machine at target service humidity by conditioning stock at the expected service relative humidity until equilibrium, then machine to the drawing dimension directly. For PA66 rod stock at 25 mm diameter, equilibration at 50% RH takes several weeks. Ensinger Machining Guide recommends preheating nylon to approximately 115°C (240°F) before drilling or sawing operations, at approximately one hour per 10 mm of cross-section, to reduce internal stress and prevent cracking during machining.
Engineering Note: Post-machining dimensional stabilization is a separate step from pre-machining moisture management. A part machined at DAM conditions and then exposed to 50% RH for 72 hours before inspection will measure larger than the machined dimension. Specify the inspection humidity condition on the drawing, not just the dimensional tolerance.
7.5 Achievable Tolerances on CNC Machined Nylon
| External diameter | ±0.05-0.10 mm | ±0.02-0.05 mm |
| Bored hole | ±0.05-0.10 mm | ±0.02-0.05 mm |
| Linear dimension | ±0.10-0.20 mm | ±0.05-0.10 mm |
| Thread (tapped) | ISO tolerance class 6H | ISO tolerance class 6H |
| Flatness | 0.05-0.15 mm/100 mm | 0.02-0.05 mm/100 mm |
For GF30 grades, achievable tolerances are tighter than unfilled grades at equivalent conditions because lower moisture absorption reduces dimensional drift. PA66-GF30 bore tolerances of ±0.03 mm are achievable under controlled conditions. For DFM guidelines on designing nylon parts for tight-tolerance CNC machining, see DFM Design Guidelines at epocrafter.com/dfm-design-guidelines/.
8.Grade Selection Summary. PA6, PA66, PA12, and GF Variants
The Six-Property Stack gives you the elimination logic. This section gives you the data to run it. Read across a row to see the full property profile of one grade. Read down a column to compare grades on a single property.
8.1 Master Properties Table
All values at 23°C unless noted. Dry (DAM) condition except where 50% RH is specified. ISO test methods used throughout; ASTM equivalents noted where the data source requires.
| Tensile strength, DAM (MPa) | ISO 527 | 70-85 | 80-90 | 50-60 | 150-180 | 170-190 |
| Tensile strength, 50% RH (MPa) | ISO 527 | 45-55 | 53-60 | 45-55 | 120-140 | 140-160 |
| Tensile modulus, DAM (MPa) | ISO 527 | 2,000-3,000 | 3,000-3,500 | 1,200-1,600 | 8,000-10,000 | 9,000-11,000 |
| Tensile modulus, 50% RH (MPa) | ISO 527 | 700-1,200 | 1,200-1,500 | 1,000-1,400 | 5,000-7,000 | 6,000-8,000 |
| Elongation at break, DAM (%) | ISO 527 | 40-70 | 40-60 | 200-300 | 3-4 | 2.5-3.5 |
| Flexural modulus, DAM (MPa) | ISO 178 | 2,000-3,000 | 2,800-3,500 | 1,100-1,500 | 8,000-10,000 | 9,000-11,000 |
| Charpy impact, notched, DAM (kJ/m²) | ISO 179/1eA | 4-8 | 4-8 | 8-15 | 8-12 | 9-13 |
| Charpy impact, notched, 50% RH (kJ/m²) | ISO 179/1eA | 10-18 | 13-18 | 15-25 | 10-14 | 11-15 |
| HDT @1.82 MPa, DAM (°C) | ISO 75-2A | 65-80 | 75-90 | 50-55 | 200-215 | 210-230 |
| HDT @0.455 MPa, DAM (°C) | ISO 75-2A | 145-180 | 180-220 | 140-160 | 210-220 | 220-235 |
| Melting point (°C) | ISO 11357 | 218-222 | 258-265 | 178-180 | 218-222 | 258-265 |
| Water absorption, 24h (%) | ISO 62 | 1.0-1.5 | 0.7-1.3 | 0.2-0.3 | 0.5-1.0 | 0.4-0.8 |
| Equilibrium moisture, 50% RH (%) | ISO 62 | ~3.5 | ~2.5 | ~0.9 | ~2.0 | ~1.8 |
| Linear dimensional change, 50% RH (%) | ~0.8 | ~0.6 | ~0.2 | ~0.4 | ~0.35 | |
| Density (g/cm³) | ISO 1183 | 1.12-1.15 | 1.13-1.15 | 1.01-1.02 | 1.34-1.38 | 1.36-1.40 |
| CoF vs steel, dynamic, dry | 0.17-0.43 | 0.17-0.43 | 0.20-0.35 | 0.30-0.40 | 0.30-0.40 | |
| CNC tooling requirement | HSS acceptable | HSS acceptable | HSS acceptable | Carbide required | Carbide required |
8.2 Grade Decision Logic. When to Use Each
PA6, unfilled. PA6 is the cost baseline for general-purpose nylon machining. Specify PA6 when operating temperature stays below 70°C under load, humidity is controlled or the application tolerates dimensional variation, and budget is the primary constraint. Do not specify PA6 when bore or shaft tolerances are tighter than ±0.05 mm in variable humidity environments. Do not specify PA6 for operating temperatures above 80°C under any meaningful structural load. Do not specify PA6 in contact with dilute acids or zinc chloride solutions. For applications where PA6 and POM (acetal) are both candidates, PA6 offers higher impact toughness (4-8 kJ/m² notched Charpy DAM vs POM’s typical 5-7 kJ/m²) but higher moisture sensitivity; POM is the better choice when dimensional stability in humidity is more important than impact resistance.
PA66, unfilled. PA66 is the preferred general-purpose grade when PA6 does not clear Layer 1 or Layer 2 of the Six-Property Stack. The 10°C HDT advantage over PA6, higher dry tensile modulus (3,000-3,500 MPa vs 2,000-3,000 MPa), and slightly lower equilibrium moisture make it the default upgrade from PA6 for structural applications. Cost premium over PA6 is typically 15-25% depending on form and quantity. Do not specify PA66 for operating temperatures above 100°C under structural load, at that point unfilled PA66 is above its practical HDT margin and GF reinforcement is required.
PA12, unfilled. PA12 is the precision dimensional stability grade. Equilibrium moisture content at 50% RH is approximately 0.9%, roughly one-quarter of PA6, producing linear dimensional change under 0.2% in typical indoor environments. For components where dimensional stability across a range of humidity conditions is the primary requirement, PA12 outperforms PA6 and PA66 regardless of their higher strength. Do not specify PA12 for structural applications above 40°C under load, its HDT at 1.82 MPa is 50-55°C, making it unsuitable for any thermally demanding application.
PA6 GF30. PA6 GF30 is the entry point for reinforced nylon when PA6 strength and HDT are insufficient but PA66 GF30 cost is a constraint. Tensile strength of 150-180 MPa DAM and HDT of 200-215°C at 1.82 MPa clear most elevated-temperature structural requirements. The melting point remains 218-222°C, so processing temperatures are lower than PA66 GF30, which can reduce tooling and cycle cost in production. Do not specify PA6 GF30 where elongation at break above 5% is required, the 3-4% value means the part will fracture rather than deform under overload. Carbide tooling is mandatory and must be costed into the machining quote.
PA66 GF30. PA66 GF30 is the highest-performance standard nylon grade for CNC machined parts: tensile strength 170-190 MPa, flexural modulus 9,000-11,000 MPa, HDT 210-230°C at 1.82 MPa, and lower moisture absorption than unfilled grades. This is the grade most commonly specified in automotive underhood components, industrial gearing, and structural brackets in variable-temperature environments. Do not specify PA66 GF30 where impact resistance under shock loading is the primary requirement, at 2.5-3.5% elongation at break, the material fractures rather than absorbs energy at stress concentrations.
8.3 Quick-Reference Selection Table
| Lowest cost, general purpose | PA6 unfilled | |
| Higher strength than PA6, same processability | PA66 unfilled | PA12 (too low strength) |
| Maximum dimensional stability in humidity | PA12 unfilled | PA6, PA66 (too high moisture) |
| Operating temperature 100-200°C under load | PA6 GF30 or PA66 GF30 | All unfilled grades |
| Highest strength and stiffness | PA66 GF30 | All unfilled, PA6 GF30 |
| Precision bore, variable humidity, no GF | PA12 or pre-conditioned PA66 | PA6 (higher moisture) |
| Low friction, dry running bearing | PA66 + MoS2 or PTFE filled | GF30 grades (higher CoF) |
| Impact resistance priority | PA66 toughened or PA6 unfilled | GF30 grades (brittle) |
| Food contact or FDA compliance | PA6 or PA66 food-grade certified | Standard industrial grades |
| Humidity stability preferred over strength | PA12 or PA66 GF30 | PA6 (highest moisture uptake) |
8.4 What GF Reinforcement Does Not Fix
GF reinforcement improves tensile strength by 2.1x, flexural modulus by 3.2x, and HDT at 1.82 MPa by 2.6x. Three limitations remain unchanged.
Chemical resistance is unchanged. PA66 GF30 in contact with dilute HCl degrades at the same rate as unfilled PA66 because the amide bond, not the glass fiber, is the attack site. The fiber-matrix interface may accelerate degradation in aggressive chemical environments by providing additional surface area for chemical ingress.
Creep resistance improves but does not disappear. PA66 GF30 under sustained load at elevated temperature still creeps, though more slowly than unfilled PA66. For bolted joints and press fits that must maintain clamping force over years, calculate creep relaxation at operating temperature and load.
Anisotropy is introduced. CNC machined parts from GF30 rod or plate stock inherit fiber orientation from the extrusion process. Bore dimensions machined perpendicular to fiber orientation may behave differently from bores machined parallel to fiber orientation. For critical tolerance features, verify stock orientation relative to the machined feature before finalizing the process plan.
9.Frequently Asked Questions
Q1: What are the mechanical properties of nylon?
Nylon mechanical properties vary by grade and moisture condition. PA66 unfilled dry tensile strength is 80-90 MPa (ISO 527); at 50% RH equilibrium that drops to 53-60 MPa. Tensile modulus dry is 3,000-3,500 MPa; at 50% RH it falls to 1,200-1,500 MPa. PA6 GF30 dry tensile strength reaches 150-180 MPa with flexural modulus of 8,000-10,000 MPa. PA66 GF30 reaches 170-190 MPa tensile strength and 9,000-11,000 MPa flexural modulus. Charpy notched impact strength for unfilled grades is 4-8 kJ/m² dry, rising to 13-18 kJ/m² at 50% RH, moisture plasticizes the matrix and improves impact resistance while reducing stiffness. No single number describes nylon’s mechanical properties; the moisture condition and temperature must always accompany the value.
Q2: What is the tensile strength of nylon 6 vs nylon 66?
PA6 dry tensile strength is 70-85 MPa; PA66 dry tensile strength is 80-90 MPa, both per ISO 527 at 23°C. The gap narrows at 50% RH equilibrium: PA6 drops to 45-55 MPa, PA66 to 53-60 MPa. The more significant difference is in tensile modulus (PA6: 2,000-3,000 MPa vs PA66: 3,000-3,500 MPa dry) and melting point (PA6: 218-222°C vs PA66: 258-265°C per ISO 11357). Specify PA66 over PA6 when operating temperature exceeds 80°C under load or when dry stiffness is a design constraint. For non-critical structural applications at room temperature and controlled humidity, PA6 is the cost-optimized choice.
Q3: Does nylon absorb water and how does it affect dimensions?
PA66 reaches approximately 2.5% moisture content by weight at 50% RH equilibrium, producing approximately 0.6% linear dimensional growth. PA6 reaches approximately 3.5% moisture at 50% RH with proportionally higher dimensional change. For a 50 mm diameter PA66 bore machined dry, equilibrium at 50% RH produces approximately 0.30 mm of diametral growth, twelve times a typical H7 tolerance band. The 24-hour water absorption value on a supplier TDS (per ASTM D570-98 or ISO 62) is a time-point measurement at 23°C immersion, not the equilibrium value the part reaches in service. For precision CNC parts, machine at the target service humidity or calculate the moisture growth and adjust the machined dimension accordingly.
Q4: What temperature can nylon withstand?
The answer depends on the grade and the load condition. Unfilled PA66 HDT at 1.82 MPa is 75-90°C per ISO 75-2 Method A, the practical upper limit for loaded structural parts. At 0.455 MPa the HDT reads 180-220°C, but that value is not appropriate for loaded design calculations. PA66 GF30 HDT at 1.82 MPa is 210-230°C, suitable for continuous structural use up to approximately 190°C. HDT is not the melting point and not the continuous use temperature, ASTM D648-01 Section 5.1 explicitly states that HDT data cannot be used to predict behavior at elevated temperature in service unless loading conditions match the test. PA12 HDT at 1.82 MPa is only 50-55°C, limiting its use to near-ambient applications despite excellent moisture stability.
Q5: Is nylon machinable on a CNC?
Nylon machines on standard CNC turning and milling equipment without work-hardening. Unfilled PA6 and PA66 accept HSS tooling with cutting speeds of 200-400 m/min and feed rates of 0.1-0.3 mm/rev, with positive rake angles of 10-15°. GF30 grades require carbide tooling, glass fiber destroys HSS cutting edges within a single setup. Coolant must be pure water or compressed air; standard metalworking cutting fluids attack polyamide and cause swelling or stress cracking. Achievable bore tolerances under controlled conditions are ±0.02-0.05 mm for PA66 GF30 and ±0.05-0.10 mm for unfilled grades without moisture management.
Q6: What is the difference between PA6 and PA66?
PA6 is produced from caprolactam, a single six-carbon monomer. PA66 is produced from hexamethylene diamine and adipic acid, two six-carbon monomers, giving it a more symmetric chain and denser hydrogen bonding. PA66 melting point is 258-265°C vs PA6’s 218-222°C (ISO 11357); PA66 dry tensile modulus is 3,000-3,500 MPa vs PA6’s 2,000-3,000 MPa (ISO 527); and PA66 equilibrium moisture at 50% RH is approximately 2.5% vs PA6’s 3.5%, giving PA66 better dimensional stability in humid environments. PA6 is less expensive and machines at equivalent conditions. For CNC machined parts, PA6 suits non-critical structural applications; PA66 is specified when stiffness, temperature resistance, or dimensional stability in humidity is a design requirement.
Q7: Can nylon replace metal in structural applications?
Nylon replaces metal in structural applications where the load, temperature, and environment fall within the material’s capability. PA66 GF30 tensile strength of 170-190 MPa at roughly one-third the density of aluminum (1.36-1.40 g/cm³ vs 2.70 g/cm³) enables 40-50% weight reduction on equivalent structural sections. Replacement is not appropriate when operating temperature exceeds 200°C, when sustained tensile stress drives creep over years, when chemical exposure includes strong acids or zinc chloride, or when tolerances tighter than ±0.02 mm are required without moisture control. Nylon thermal conductivity is 0.25 W/m·K vs 160 W/m·K for aluminum 6061, heat dissipation applications are not candidates for nylon substitution.
Q8: What chemicals attack nylon?
Strong inorganic acids, concentrated HCl, H2SO4, HNO3, attack nylon by hydrolyzing the amide bond, cleaving the polymer backbone and causing irreversible strength loss. Dilute acids cause slower degradation that accelerates with temperature and applied stress. Zinc chloride solutions cause stress cracking at moderate concentration even at neutral pH, brittle fracture under load with no visible surface attack. Oxidizing agents and peroxides attack the backbone through oxidative degradation. Nylon resists aliphatic hydrocarbons, oils, lubricants, hydraulic fluids, and most alcohols well. Esters and ketones (acetone, MEK, ethyl acetate) cause swelling and potential stress cracking and should be tested before use in chemical contact applications.
Q9: How does glass fiber reinforcement change nylon properties?
Adding 30% glass fiber by weight to PA66 increases tensile strength approximately 2.1x (from 80-90 MPa to 170-190 MPa), flexural modulus approximately 3.2x (from 2,800-3,500 MPa to 9,000-11,000 MPa), and HDT at 1.82 MPa approximately 2.6x (from 75-90°C to 210-230°C). Water absorption drops approximately 40%. Trade-offs: elongation at break drops from 40-60% to 2.5-3.5%, making GF30 brittle at stress concentrations; HSS tooling is no longer viable and carbide is required; and anisotropy is introduced in molded stock. GF30 is not an upgrade to unfilled nylon, it is a different material with different failure modes and machining requirements.
Q10: What is the coefficient of friction of nylon?
PA66 (Zytel 101L) dynamic coefficient of friction against steel without lubrication ranges from 0.17 to 0.43 depending on contact pressure, sliding speed, and surface condition of the mating steel (DuPont General Design Principles, 23°C, 2.1 MPa, 3 m/min). Maximum PV value without lubrication is 6 MPa·m/min, exceed this and frictional heat accumulation causes surface softening and accelerated wear. Moisture improves tribological performance by plasticizing the surface layer, reducing stick-slip tendency and lowering effective dynamic friction. For applications requiring friction below 0.10, MoS2-filled or PTFE-filled nylon grades reduce dynamic CoF against steel to 0.08-0.15 at some cost to tensile strength.
Related Resources
Related Capability: CNC Machining, covers EPOC CRAFTER’s turning, milling, and boring capabilities for engineering plastics including nylon, with achievable tolerances and lead time data.
Related Material Guide: Materials & Properties, full material selection database covering metals, plastics, and composites with downloadable property tables for engineering comparison.
Related Article: Nylon Mechanical Properties & Machinability: Tensile Strength, HDT, Moisture Effects, and CNC Parameters, detailed mechanical data tables and CNC cutting parameters for PA6, PA66, and GF30 variants across the full temperature and humidity range.
Related Article: PA6 vs PA66 vs PA12: Nylon Grades Compared. Properties, Modifications, and When to Switch Materials, grade-by-grade comparison including glass-filled, MoS2-filled, and PTFE-filled variants with switching decision logic.
Related Article: Nylon Parts for Engineering Applications, industry use cases with grade and compliance callouts, achievable CNC tolerances by feature type, and the 3T Procurement Checklist for specifying nylon parts to a machine shop
Related Standards Reference: Tolerances & Standards, covers ISO 2768, GD&T application to plastic parts, and inspection requirements for CNC machined polymer components.
If your application sits at the edge of what unfilled nylon handles: operating temperature above 80°C, bore tolerance tighter than ±0.05 mm, or chemical exposure that includes anything acidic, the grade decision needs to be made before the drawing is finalized, not after the first article fails inspection. Send your part drawing and operating conditions to EPOC CRAFTER’s engineering team and we will run the Six-Property Stack against your specific requirements and recommend the correct grade and machining approach.
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