POM vs Nylon: Which Is Better for CNC Machined Parts?

CNC-machined POM acetal gear beside a nylon wear pad for material comparison

Quick answer

Choose POM (acetal) when dimensional stability, low moisture swell, and clean CNC tolerances matter most. Choose nylon when impact toughness, abrasion resistance, or higher continuous temperature outweigh size control. If the part must hold fit in humidity, start with POM.

POM and nylon are two of the most requested engineering plastics on CNC RFQs. Both machine well compared with metals, both can run dry against steel, and both show up in gears, bushings, and wear components—yet they fail for very different reasons. This guide is written from a machining and application perspective so you can specify the polymer that survives the real environment, not only the datasheet.

POM and Nylon at a Glance

POM (acetal / Delrin-type stock)

POM is a semi-crystalline acetal available as homopolymer and copolymer bar and plate. Homopolymer grades are typically stiffer; copolymer grades tolerate hot water and alkalis better. Moisture uptake stays very low (often under ~0.25% at equilibrium in many grades), which is why POM is the default for precision sliding parts.

Strengths: stiffness, fatigue resistance, low friction, excellent chip control on CNC
Limits: continuous service roughly around 100°C for many unfilled grades; poor UV without additives
Shop reality: holds ±0.025–0.05 mm routinely; ±0.025 mm achievable with stable fixturing and light finish passes

Nylon (PA6 / PA66 and filled grades)

Nylon is tougher and often stronger dry than POM, especially PA66. Glass-filled grades raise stiffness and HDT; oil- or MoS₂-filled grades improve sliding life. The trade-off is hygroscopic swell—parts can grow enough in humid air or washdown to kill fits that looked perfect at the mill.

Strengths: impact, abrasion, higher temperature capability than unfilled POM in many cases
Limits: moisture swell, pre-dry discipline before machining, looser “as-machined” size stability
Shop reality: dry stock first; expect more process control than POM for the same tolerance band

For melting behavior and heat at the cutter, see our plastic melting point chart for CNC materials. If weight and stock selection matter, cross-check the plastic density chart.

Head-to-Head Comparison for CNC Parts

Property	POM (typical unfilled)	Nylon PA66 (dry, typical)
Tensile strength	~60–70 MPa	~80–90 MPa
Impact toughness	Moderate	Higher
Moisture absorption	Very low	High (can exceed several % by weight)
Dimensional stability	Excellent	Environment-dependent
Continuous use temp	~90–100°C class	~120–150°C class (grade-dependent)
CNC machinability	Excellent, clean chips	Good with drying & sharp tools
Typical tolerance ease	Easier for tight fits	Harder without moisture control

Moisture and tolerance—the deciding factor

A nylon part that measures perfect in a dry shop can grow enough after humid storage or steam cleaning to seize on shafts or change gear mesh. POM rarely surprises you that way. If print notes say “must maintain fit after shipping / washdown,” POM (often copolymer) is usually the safer call.

Friction, wear, and load

Unfilled POM is outstanding for light-to-moderate duty dry bearings and precision gears. For heavy abrasive wear or shock, filled nylon or UHMW-PE wear grades may outperform both—material choice should follow duty cycle, not brand familiarity.

Machining differences that show up on the invoice

POM: sharp carbide, high RPM, steady chip evacuation; avoid rubbing that melts the kerf
Nylon: dry stock (commonly ~80°C for a few hours—follow supplier guidance), moderate feeds, sharp tools to limit tearing
Both: separate rough and finish when heat would steal tolerance

Shop tip: If a nylon RFQ demands ±0.05 mm on a long span in an uncontrolled climate, ask whether the drawing assumes dry or conditioned state. Clarify that before you quote—or recommend POM.

When to Choose POM vs Nylon

Choose POM when…	Choose nylon when…
Fits and backlash must stay stable	Impact or abrasion dominates
Humidity, washdown, or outdoor storage is likely	Continuous temperature exceeds POM comfort zone
You need fast, tight-tolerance CNC with clean chips	Glass-filled stiffness or structural toughness is required
Food-contact / FDA-capable acetal grades are specified	Cost of swell is acceptable and drying is controlled

Related acetal deep-dives: POM melting point notes for machinists and POM vs PET for precision parts.

Decision Checklist

List environment: humidity, chemicals, temperature, UV.
List mechanical duty: static fit, sliding, impact, abrasion.
List tolerance and whether size must hold after weeks of storage.
If size stability wins → POM. If toughness/heat wins and moisture is managed → nylon.
Confirm grade (homo/copolymer, PA6/PA66, filled) before locking the CAM plan.

Frequently Asked Questions

Is POM stronger than nylon?

Dry nylon usually shows higher tensile and impact strength. POM often wins in service because moisture does not pull its properties around as aggressively.

Is Delrin tougher than nylon?

Generally no—nylon is tougher. Delrin-type POM is more rigid and dimensionally stable.

Does nylon need drying before CNC?

Yes for most precision work. Skip drying and you risk warp, poor finish, and moving dimensions after the job leaves the shop.

Which is better for gears in humidity?

POM in most cases. Nylon tooth profiles can change as moisture content rises.

Conclusion

For CNC machined parts, POM is the practical default whenever tolerance and moisture stability drive success. Nylon earns the job when toughness, abrasion, or temperature demand it—and when your process can manage drying and conditioned size. Share the duty cycle with your machinist; the right polymer choice prevents the expensive “it fit in the shop” failure mode.

PlasticCNCPro machines both families daily. Send drawings with environment notes and target tolerances—we will recommend grade and a machining plan that matches how the part actually lives.