Machinable Nylon: Grades, Properties & CNC Design Rules
Machinable nylon is a family of polyamide stock shapes that CNC well when the design needs toughness, wear resistance, and low mass. The catch is moisture: nylon parts get larger and softer after conditioning, so fit-critical features must be designed and machined around the part's real service state.
Use nylon when your part benefits from impact toughness, sliding wear behavior, and lighter weight than acetal.
Do not choose nylon just because it is inexpensive stock plastic. If the part has a precision bore, a close-running fit, or a humidity-sensitive assembly, moisture movement can dominate the design.
In practice, nylon is often the right choice for wear parts and the wrong choice for “quiet” geometry.
What makes nylon machinable
Nylon is a semi-crystalline engineering plastic, also called polyamide, that offers a useful mix of toughness, wear resistance, and low density in stock shapes that can be milled or turned. If you are already weighing it against the acetal (POM/Delrin) guide or a broader material selection guide, the deciding question is simple: does the part need toughness and wear behavior more than it needs dimensional quietness?
That is why nylon shows up in bushings, pads, guides, and lightly loaded structural parts. It cuts cleanly enough for CNC machining services, and it is cheaper than high-end plastics such as PEEK. The engineering tradeoff is moisture absorption: nylon changes size and stiffness after machining, so a dimension that passed inspection dry may behave differently a day later in ambient humidity.
1. Dry stock
Smallest and stiffest condition. This is the state that often looks best on the machine and worst in service if humidity changes later.
2. Moisture uptake
The part becomes tougher and a little less stiff as it absorbs moisture. Size changes are usually more important than the change in strength.
3. Design response
Finish-machine bores, fits, and alignment features after the moisture state is understood, or choose acetal if the assembly cannot tolerate movement.
Nylon grades for CNC: 6 vs 6/6 vs wear-grade filled nylon
The best machinable nylon is not “the strongest nylon.” It is the grade whose property set matches the job. For most CNC programs, the short list is unfilled PA6, unfilled PA6/6, and a wear-oriented MoS2-filled nylon when the part is really a bearing surface.
| Grade | Common form | Tensile strength | Tensile modulus | Service temperature | Water absorption | Best use | Primary caution |
|---|---|---|---|---|---|---|---|
| PA 6 natural | Extruded stock shape | 11,500 psi (79 MPa) | 479,000 psi (3.3 GPa) | 212 °F (100 °C) continuous | 0.3% / 0.6% (24 / 96 hr) | Tough bushings, guides, low-cost wear parts | Takes up more moisture than PA66 and moves more after machining. |
| PA 6/6 natural | Extruded stock shape | 12,300 psi (85 MPa) | 508,000 psi (3.5 GPa) | 212 °F (100 °C) continuous | 0.2–0.4% (24 / 96 hr) | Stiffer structural nylon parts and brackets | Still moisture-sensitive; better than PA6 on stiffness, not on dimensional immunity. |
| MoS2-filled PA 6 | Wear-grade cast stock | 10,000 psi (69 MPa) | 500,000 psi (3.45 GPa) | 200 °F (93 °C) continuous | 0.30% / 6% (24 hr / saturation) | Slide pads, thrust washers, slow-speed bearings | Choose it for friction and PV performance, not because it holds tighter tolerances than unfilled nylon. |
Supplier data above is representative of stock-shape datasheets for Ensinger TECAMID 6 natural, Ensinger TECAMID 66 natural, and Mitsubishi Chemical Advanced Materials Nylatron GSM Blue. Use the exact supplier grade on the print if the application depends on a specific property set.
PA6 natural
The forgiving general-purpose choice. PA6 is tough, easy to source, and works well for guides, wear pads, and non-tight structural geometry.
PA6/6 natural
Slightly stiffer and stronger than PA6. Use it when you need a little more rigidity in the same general temperature band, not because you expect moisture to stop mattering.
MoS2-filled nylon
A wear grade, not a universal upgrade. Pick it for sliding contact and bearing PV, then compare it against the PEEK vs Delrin vs nylon comparison if friction and long-term stability are both important.
Mechanical properties and achievable tolerances
Tolerance planning for nylon is not just a machine-capability problem. It is a material-state problem. The same machine that can hold a metal bore at ±0.001 in. can still deliver a nylon bore that drifts after machining if the stock conditions change.
| Feature type | Typical design target | Stretch target | Why it moves |
|---|---|---|---|
| Profiles, pockets, and non-fit-critical geometry | ±0.005 in. (±0.13 mm) | ±0.003 in. (±0.08 mm) on conditioned stock | Good default band for general machined nylon parts. |
| Precision bores, slots, and bearing seats | ±0.003 in. (±0.08 mm) | ±0.002 in. (±0.05 mm) only with moisture control | Finish-machine after the part reaches its intended moisture state. |
| Press-fit or close-running mating features | Validate by assembly, not by nominal size alone | Consider acetal if the fit cannot move in service | Humidity can erase a metal-style interference assumption. |
Worked sizing example
If a nylon feature grows by only 0.25% after conditioning, a 2.000 in. (50.8 mm) bore becomes 2.005 in. (50.93 mm). That is the full width of a standard ±0.005 in. CNC tolerance band. This is why nylon fits must be designed around service moisture, not just the inspection report from the day the part leaves the machine.
Moisture absorption and dimensional stability
Moisture does two things to nylon at the same time: it changes size and it changes mechanical feel. Dry nylon is smaller, stiffer, and more brittle. Conditioned nylon is larger, tougher, and more forgiving in impact. Neither state is universally “better.” The mistake is pretending the two states are interchangeable.
This is the core reason many teams end up in the acetal vs nylon comparison: acetal gives away some toughness, but it makes precision sizing easier because ambient humidity moves it far less.
Practical shop rules for moisture-sensitive nylon parts
- Rough-machine thick stock before final sizing if the part has critical bores, dowel features, or bearing fits.
- Inspect precision features after the part has reached the moisture state it will actually see in service or assembly.
- Avoid specifying metal-style press fits unless the interference is validated on conditioned parts.
- Call out the exact nylon grade on the drawing. “Nylon” alone is too vague when moisture behavior matters.
What to put on the print
Specify the resin family and stock grade:PA6 natural,PA6/6 natural, orMoS2-filled PA6.
If fit matters, note whether the dimension applies to dry, conditioned, or assembly-state parts. That single line can eliminate a lot of inspection confusion.
If you need help deciding between nylon and a more stable plastic, upload the part for a machined-plastics quote with DFM feedback.
Design rules for CNC nylon parts
Good nylon parts are designed around what nylon does after the cutter leaves the surface. The rules below are not abstract “best practices.” They are the operating habits that keep nylon from surprising you in assembly.
Condition stock before final sizing
Nylon does not leave the machine in its final service state. If the part has bores, bearing seats, dowel locations, or snap details, rough-machine first, let the stock stabilize, then finish-machine the critical features.
Keep fit-critical tolerances realistic
Standard CNC tolerance is still ±0.005 in. (±0.13 mm), but machined nylon should only be pushed tighter when moisture state, section thickness, and inspection timing are controlled. If the assembly must stay dimensionally quiet in humidity, acetal is usually the safer call.
Design threads for plastic behavior
Direct-tapped nylon works for light clamp loads and limited assembly cycles. For repeated service, higher torque, or smaller safety margin, specify metal inserts instead of assuming a plastic thread will behave like aluminum or steel.
Manage heat and chip wrapping
Nylon cuts cleanly with sharp tools, but it also makes long, stringy chips and softens if heat builds. Use sharp positive-rake tooling, give chips somewhere to go, and avoid rubbing passes that smear the surface instead of cutting it.
Use wear grades intentionally
MoS2-filled or oil-filled nylon is for sliding and bearing duty. It is not a universal “premium nylon.” If the part needs stiffness or a paintable cosmetic surface, an unfilled engineering grade is usually the better baseline.
Need help deciding whether nylon is actually the right plastic?
MakerStage quotes machined nylon, acetal, PEEK, and other engineering plastics for prototypes and production parts. If you send the drawing, we can route it through CNC machining services and flag where humidity, fits, or wear behavior should influence the material choice.
Nylon vs acetal: when to choose each
The short answer is simple. Choose nylon when toughness and sliding behavior matter most. Choose acetal when geometry must stay predictable with the least conditioning drama. For a deeper side-by-side breakdown, use the related comparison guide in the section below.
| If your part needs... | Choose nylon when... | Choose acetal when... |
|---|---|---|
| Impact resistance and low weight | Choose nylon when the part sees shock, sliding wear, or repeated contact. | Choose acetal only if humidity-driven movement is still acceptable. |
| Precision fits and stable bores | Use nylon only if you can condition and finish-machine to the service state. | Choose acetal when the assembly needs predictable size right after machining and in ambient humidity. |
| Bushings, wear strips, and sliding surfaces | Choose nylon or a wear grade when toughness and bearing PV matter more than exact geometry. | Choose acetal when dry-running friction and dimensional repeatability are the priority. |
| Humid or wet service environment | Use nylon only if swelling, softer conditioned properties, and clearance growth are built into the design. | Choose acetal when the part must stay dimensionally consistent with less conditioning overhead. |
Common questions about machinable nylon
Is nylon a good plastic for CNC machining?
Yes, when the design benefits from toughness, wear resistance, and low weight. Nylon machines well with sharp tools, but it is not as dimensionally stable as acetal because moisture uptake changes part size and stiffness after machining. Use nylon for wear parts and impact-prone components, not as the default for precision fits.
What nylon grade machines best for CNC parts?
For most machined parts, start with unfilled PA6 or PA6/6 and choose based on stiffness versus toughness. PA6 is tougher and common in stock shapes; PA6/6 is a little stiffer and stronger. Use MoS2-filled nylon only when the part is really a bearing or wear surface, not just because it sounds more specialized.
Can machined nylon hold tight tolerances?
It can, but only if you control moisture state and feature geometry. General nylon features are usually designed around ±0.005 in. (±0.13 mm), while conditioned fit-critical features can be pushed toward ±0.002–0.003 in. (±0.05–0.08 mm). If the fit cannot drift in humidity, use acetal instead.
Should I choose nylon 6 or nylon 6/6 for a machined part?
Choose PA6 when you want a tougher, forgiving general-purpose nylon and PA6/6 when you need a bit more stiffness and strength. The difference is real, but neither grade becomes moisture-proof. The final choice still depends more on fit sensitivity and environment than on a single strength number.
When should I use MoS2-filled nylon?
Use MoS2-filled nylon for slow-speed sliding contact, bearings, thrust washers, and wear pads where lower friction and better PV performance matter. It is not a universal upgrade for every nylon part. For brackets, covers, and general housings, unfilled nylon is usually simpler and easier to source.
Is nylon or acetal better for bushings and gears?
It depends on what is failing first. Nylon is attractive when you need impact toughness and forgiving wear behavior, especially in lubricated contact. Acetal is usually better when gear mesh accuracy, bore stability, and dry-running dimensional repeatability matter more than raw toughness.
Ready to quote a nylon part?
Send the model or drawing and call out the exact nylon grade, fit-critical features, and expected environment. If the part would be safer in acetal or another engineering plastic, we can flag that before you buy the wrong stock.
Related engineering-plastics resources
Acetal (POM/Delrin) guide
Engineering-plastics hub for dimensional stability, grades, and low-friction behavior.
Acetal vs nylon comparison
Direct material-selection comparison when both plastics are on the table.
PEEK vs Delrin vs nylon comparison
Broader CNC-plastics decision guide when nylon is competing with higher-end options.
Material selection guide
Top-level framework for choosing metals and plastics by load, environment, and cost.