Nylon CNC Machining: PA6 vs PA66, Tolerances, Moisture and Cost

Nylon CNC machining is widely used for gears, bushings, rollers, wear pads, guides, electrical insulators and functional prototypes. The material is light, tough and naturally resistant to wear, which makes it a practical replacement for metal when a component needs low noise, low friction or reduced weight.

The main challenge is not simply cutting nylon. It is controlling the part after cutting. Nylon absorbs moisture, expands more with temperature than metal and can move when internal stress is released. A dimension that passes inspection in a dry machine shop may change after the part reaches a humid factory, contacts water or operates near a heat source.

This engineering and purchasing guide explains nylon grades, PA6 versus PA66, milling and turning methods, moisture conditioning, realistic tolerances, design rules, inspection requirements and the factors that determine machining cost.

What Is Nylon?

Nylon is the common name for a family of polyamide engineering thermoplastics. It is not one universal material. PA6, PA66, cast nylon, extruded nylon, PA12 and filled or lubricated grades can behave differently during machining and in service.

Compared with aluminum or steel, nylon has lower density, lower stiffness and a much higher rate of thermal expansion. Compared with many general-purpose plastics, it provides a useful combination of toughness, fatigue resistance, abrasion resistance and sliding performance. Those properties explain why machined nylon is common in moving equipment.

CNC machining is suitable for nylon prototypes and low-volume production because it creates accurate holes, pockets, bearing seats, keyways and complex profiles directly from plate, rod or tube without an injection mold.

Why Choose CNC-Machined Nylon?

• Wear resistance: nylon performs well in many sliding, rolling and rubbing applications.

• Low weight: a nylon component can reduce moving mass compared with a metal equivalent.

• Impact and fatigue performance: the material tolerates repeated motion and shock better than many rigid plastics.

• Low noise: nylon gears, guides and rollers can operate more quietly than metal components.

• Electrical insulation: unfilled grades are useful for electrical barriers, fixtures and equipment components.

• Corrosion resistance: nylon does not rust and can eliminate painting or plating in suitable environments.

• Design flexibility: CNC milling and turning support prototypes, replacement parts and small batches with no mold cost.

Nylon should still be selected by service conditions rather than by price alone. Humidity, immersion, temperature, chemicals, load duration, frictional heat and required dimensional stability can change the correct material choice.

Nylon Grades for CNC Machining

PA6 nylon

PA6 offers a useful balance of toughness, impact resistance, wear performance and cost. It is widely available as extruded rod and plate, while cast PA6 is common in large-diameter rod, thick plate and oversized stock. Typical applications include rollers, pulleys, guides, wear strips and large mechanical parts.

PA66 nylon

PA66, also written nylon 66 or nylon 6/6, generally provides higher stiffness and better short-term heat resistance than comparable PA6 grades. It is often chosen for smaller precision mechanical parts, fasteners, electrical components and loaded wear parts. Stock size and local availability should be checked early because they may differ from PA6.

Cast nylon

Cast nylon is produced in large stock shapes and can be economical for thick components that would waste substantial material if machined from a smaller extruded form. Cast grades are popular for large gears, sheaves, bearing blocks and wear pads. Stock variation, casting quality and internal stress must be considered when the part has thin sections or close tolerances.

Oil-filled and internally lubricated nylon

Lubricated grades reduce friction and can improve wear life in bearings, slides and guide components. The lubricant is distributed through the material rather than applied only to the surface. The exact grade should be specified because color, strength, temperature capability and food-contact status vary by product.

MoS2-filled nylon

Molybdenum-disulfide-filled nylon is commonly used where improved stiffness, wear behavior and dimensional control are needed. It is normally dark gray or black. The filler changes mechanical properties and appearance, so it should not be substituted for unfilled nylon without approval.

Glass-filled nylon

Glass fiber increases stiffness and can reduce dimensional movement, but it also makes the material more abrasive. Cutting tools wear faster, machined edges may reveal fibers and surface finish requirements need careful review. Filled stock may also behave differently depending on fiber orientation.

PA12 and specialty polyamides

PA12 absorbs less moisture than PA6 or PA66 and can offer better dimensional stability in humid service. Specialty nylons are available for high temperature, flame resistance, food contact, medical use and other regulated applications. These benefits are grade-specific and must be supported by the required certificate.

PA6 vs PA66: Which Nylon Should You Machine?

The grade name alone does not complete the specification. Two suppliers may offer materials with different additives, stock processes, moisture conditions and certifications. Put the full commercial grade, color, filler, stock form and certificate requirement on the drawing and purchase order.

How Nylon Is CNC Machined

CNC milling

Milling produces pockets, slots, profiles, mounting patterns and three-dimensional surfaces. Sharp tools and adequate chip space are important because a rubbing cutter generates heat and can leave a fuzzy or smeared edge. Low-flute-count tools are often useful for chip evacuation, but the final choice depends on geometry and machine capability.

Roughing and finishing are commonly separated. Roughing removes most of the stock while leaving a controlled allowance. The part can then relax before a finishing pass establishes critical datums and dimensions.

CNC turning

Turning is efficient for bushings, rollers, sleeves, spacers and bearing components. The stock needs broad, even support because excessive chuck pressure can deform the part. Sharp positive-rake tools help cut cleanly with lower force, while stable support reduces chatter on long or thin sections.

Drilling and boring

Drilling nylon can create long chips and concentrated heat. Peck cycles, chip clearance and a sharp drill reduce rubbing. Large or accurate bores may be rough-drilled and then bored or reamed. Thin material around a hole needs support to prevent breakout deformation and an oversized entry burr.

Threading and inserts

Internal and external threads can be machined directly in nylon, especially when the thread is large and the assembly load is moderate. Repeated assembly, high torque or sustained load may cause wear or creep. Metal inserts, through-bolts or compression limiters are safer when the joint will be serviced frequently.

Sawing and routing

Sawing prepares blanks, while CNC routing is useful for large plates, profiles and wear strips. Coarse chip space and clean, sharp edges help prevent heat buildup. Thin plates may require a vacuum fixture, support plate or sacrificial tabs so the part remains flat during the final contour cut.

The Most Important Issue: Moisture Absorption

PA6 and PA66 are hygroscopic. They absorb moisture from humid air or direct water contact and release it in dry conditions. Moisture changes both dimensions and mechanical behavior. A conditioned part is generally more flexible than a dry one, and a close-fitting bore or gear may grow enough to affect assembly.

This does not mean nylon is unsuitable for precision parts. It means the drawing must define the material condition and inspection condition. Without that information, the supplier may inspect a dry machined part while the buyer measures it after conditioning, and both results can be correct for the time and environment of measurement.

Define the service environment

State whether the component will operate indoors, outdoors, in water, near steam, in a climate-controlled enclosure or through seasonal humidity changes. Include the operating temperature and the mating material. A nylon bore around a steel shaft needs enough clearance for moisture and thermal expansion.

Choose a conditioning strategy

Depending on the application, a supplier may machine dry stock and allow for later growth, condition the stock before final machining, or stabilize the part before final inspection. There is no universal conditioning cycle for every grade and thickness. The material supplier's data and a representative production trial should guide the method.

Control packaging and storage

A precision nylon part can continue exchanging moisture after it leaves the machine shop. Packaging, storage duration and climate during shipping may therefore matter. If the part must arrive in a defined state, put the packaging method and allowable time before assembly in the quality plan.

Nylon CNC Machining Tolerances

Achievable tolerance depends on grade, stock condition, part size, wall thickness, moisture state, temperature, workholding, setup count and inspection method. A compact PA66 bushing is easier to control than a large, thin cast-nylon plate with material removed from only one side.

For many machined nylon parts, a general tolerance around ±0.1 mm is a useful starting point for supplier discussion. Tighter limits may be possible on selected features with stable material, controlled conditioning and a defined inspection procedure. Applying a close metal-style tolerance to every dimension normally increases cost without protecting function.

Separate critical and noncritical dimensions

Identify the dimensions that control fit, motion, sealing, alignment or safety. Give wider general tolerances to clearance surfaces and cosmetic geometry. A datum system tied to the assembly is more useful than many unrelated bilateral dimensions.

State the inspection temperature and humidity

Temperature and humidity can change the measured size of nylon. Define the environment and stabilization time when the tolerance is close to expected material movement. For repeat orders, use the same conditioning and inspection method.

Define free-state or restrained measurement

A thin ring, plate or cover may distort under its own weight or under probe pressure. State whether the feature is measured free, supported on specified datums, clamped in a fixture or installed in the mating assembly.

Design Guidelines for Machined Nylon Parts

Keep walls reasonably thick and uniform

Thin walls flex under cutting pressure and can move after unclamping. Use consistent sections, reinforce long spans and avoid removing nearly all material from one side of a thick blank. If a thin feature is essential, provide room for a support fixture.

Add generous internal radii

Internal radii reduce stress concentration and allow a larger, more rigid cutter. Sharp internal corners require a small tool, more machine time and often a poorer surface finish. A relief or dog-bone feature can solve a square assembly corner when necessary.

Allow for expansion around metal hardware

Nylon and metal do not expand at the same rate. Use clearance holes, washers, shoulder bolts or slotted mounts where movement is expected. A fully constrained nylon panel can bow or crack when temperature or moisture changes.

Avoid aggressive press fits

A press fit designed for metal can overstress nylon, and the interference may change with humidity and temperature. Define the full service range and consider a retaining feature, adhesive validated for the grade, split clamp or mechanical fastener.

Design threads for the real load

Use coarse threads, adequate engagement and controlled tightening torque. Add an insert when the joint is repeatedly assembled or carries sustained load. Avoid placing a highly loaded thread close to a thin edge.

Provide tool access

Deep narrow pockets, tiny internal corners and long-reach holes increase heat, vibration and cost. Open the geometry where possible and use standard drill sizes and accessible fastener counterbores.

Workholding, Heat and Burr Control

Support without crushing

Hard jaws concentrated on a small area can dent or distort nylon. Soft jaws, split sleeves, broad pads and shaped nests distribute force. The clamp should resist cutting loads without forcing the part into a shape that disappears after release.

Remove heat with the chip

Nylon is a poor heat conductor compared with metal. Sharp tooling, adequate feed, chip evacuation and an appropriate coolant or air strategy help carry heat away. A dull tool rubs, melts the edge and can change dimensions before inspection.

Plan for burrs

Nylon can form flexible burrs, especially at drilled exits, thread crests and milled edges. Toolpath direction, sharp edges and supported breakthrough reduce the problem. Manual deburring may still be required, but it must not round a sealing land or change a measured edge.

Surface Finish and Secondary Operations

A sharp finishing tool can create a smooth functional surface, although a machined face will still show tool marks under suitable lighting. Specify roughness only where it affects friction, sealing or fatigue. A blanket cosmetic requirement can add inspection and hand-finishing cost.

Bead blasting may create a uniform matte appearance but can alter edges and embed contamination. Tumbling is generally unsuitable for parts with precise edges or threads unless the process is tightly controlled. Painting, printing and bonding require a grade-compatible surface preparation and an adhesion trial.

Review any required treatment with the supplier and compare the available surface finishing services before freezing the drawing.

Stress Relief and Staged Machining

Extrusion, casting and uneven stock removal can leave or release internal stress. A part may bow after the first operation or after material is removed from a thick section. Large, thin or tightly toleranced components can benefit from balanced roughing, a stabilization period and final machining in a separate setup.

Heat treatment is sometimes used to stabilize nylon stock or machined parts, but the cycle must match the exact grade and geometry. Unsupported parts can sag, and an incorrect cycle can alter moisture condition or dimensions. Follow the stock supplier's recommendations and validate the complete process on a representative part.

Nylon vs Delrin for CNC Machining

Nylon and acetal are often compared for gears, bushings and sliding components. Nylon is usually chosen for toughness, impact, wear performance and larger cast stock. Acetal is usually easier to hold dimensionally because it absorbs much less moisture and machines to a crisp finish.

Choose nylon when the design benefits from toughness, fatigue resistance, damping or wear performance and can accommodate environmental movement. Choose acetal when tight dimensional stability, low moisture sensitivity and a clean machined edge are more important. The detailed Delrin CNC machining guide explains the alternative.

If temperature or chemical resistance exceeds the practical range of both materials, compare a high-performance polymer using the PEEK CNC machining guide.

Typical Applications

• Gears, sprockets, pulleys and sheaves.

• Bushings, bearing liners, thrust washers and wear rings.

• Rollers, guide rails, slide blocks and conveyor components.

• Wear pads, scraper blades and impact blocks.

• Electrical insulators, spacers and assembly fixtures.

• Food-processing and packaging equipment parts made from an approved grade.

• Automotive, robotics and automation prototypes.

• Large replacement parts for maintenance and repair.

For a new mechanism, rapid prototyping services can be used to verify fit, noise, friction and assembly clearance before ordering a production batch.

What Drives Nylon Machining Cost?

• Grade and certification: PA6, PA66, PA12, lubricated, glass-filled, food-contact and specialty grades have different prices and lead times.

• Stock size: large cast shapes, thick plate and oversized round stock increase material and freight cost.

• Material removal: a small finished part cut from a large blank creates waste and longer cycle time.

• Geometry: deep pockets, thin walls, long bores and multiple setups require more machining and support.

• Tolerance: close limits may require staged machining, conditioning and controlled inspection.

• Fixtures: soft jaws, mandrels, nests and vacuum fixtures add setup work.

• Deburring: complex intersections and many threaded holes increase manual finishing.

• Quantity: programming and fixture cost are divided across the batch.

• Inspection: first-article reports, material traceability and conditioning records add quality cost.

• Packaging: moisture-control or individually protected parts may require special packaging.

Quality Inspection for Machined Nylon

Inspection should start with material identity and condition. Confirm the grade, filler, color, stock batch and required certificate. Allow the part to stabilize in the specified environment before recording close dimensions.

Use a measurement method that does not distort the component. Light contact force, appropriate supports, vision measurement or a dedicated checking fixture may be needed for thin rings and flexible walls. Record whether the part was measured free, restrained or assembled.

Functional checks can be more reliable than isolated dimensions for gears, bushings and sliding systems. A mating-gauge test, shaft fit, runout check or controlled assembly trial can verify performance while still retaining dimensional data for process control.

RFQ Checklist for Custom Nylon Parts

1. Send a STEP model and a revision-controlled 2D drawing.

2. Specify PA6, PA66, PA12 or the exact commercial grade.

3. State cast or extruded stock, color, filler and lubricant requirements.

4. Identify food-contact, flame, electrical or other certification needs.

5. List service temperature, humidity, water exposure and chemicals.

6. Define the material conditioning and final inspection condition.

7. Mark critical dimensions, fits, datums and surface requirements.

8. State whether flexible features are measured free or restrained.

9. Provide mating shaft, bearing, fastener and assembly information.

10. Define thread inserts, tightening torque and sustained loads.

11. List first-article, inspection-report, traceability and packaging needs.

12. Provide prototype, production and expected repeat-order quantities.

Request a Nylon CNC Machining Quote

Reliable nylon machining begins with the correct polyamide grade and a drawing that accounts for moisture, heat, flexibility and creep. Sharp tools, balanced stock removal, broad support and a defined conditioning method help keep dimensions stable from machining through final assembly.

Send your CAD files, drawing, grade, quantity and service conditions through the Aluprototype request-a-quote page. The engineering team can review manufacturability and prepare a quotation for CNC-milled or CNC-turned nylon components.