ナイロン vs POM（ジュラコン/デルリン）CNC加工：2026年ガイド（吸湿・グレード・公差）
ナイロンとPOM/デルリン加工のエンジニアガイド：すべてを決める吸湿の違い、POM-H vs POM-C、ナイロングレード、調湿、切削のコツ、公差、摩擦、コスト。
ナイロンとPOM（アセタール／デルリン）は、PEEKほどの費用をかけずに、丈夫で自己潤滑性のある部品が必要なときに選ぶ2つのエンジニアリングプラスチックです — 歯車、ブッシュ、摺動部品。データシート上は似ていますが、多くのプロジェクトを左右する違いが一つあります：ナイロンは水を吸って膨張し、POMは吸わない。本ガイドは、現場が実際に行うやり方で選択を扱います — 吸湿、グレード、加工、公差、コスト。
Nylon vs POM head-to-head
Nylon (PA 6, PA 6/6)
- Tougher & more impact-resistant; higher heat tolerance.
- Absorbs moisture — swells up to ~0.6–1.2%, must be conditioned.
- Higher friction against steel (~0.3–0.4).
- Best for: impact parts, wear pads, high-load bushings, cast nylon large parts.
POM / Delrin (acetal)
- Dimensionally stable — absorbs only ~0.2%, barely moves.
- Machines beautifully — the easiest plastic to hold tight tolerances.
- Lower friction against steel (~0.2), naturally self-lubricating.
- Best for: precision gears, bearings, tight-tolerance parts, sliding components.
The short version: choose POM when tolerance, low friction and machinability matter; choose nylon when toughness, impact resistance and heat matter. The rest of this guide is the detail behind that rule. For where these sit among all machinable materials, see our material selection guide.
The moisture difference (the one that decides projects)
This is the single most important fact about these two plastics. Nylon is hygroscopic — it absorbs water from the air and swells measurably. A nylon part machined bone-dry can grow enough over a few humid days to lose a press-fit or bind a gear mesh. POM is nearly immune: it takes on so little moisture that its dimensions stay put.
Nylon grades you can machine
"Nylon" (polyamide, PA) is a family. The grade changes strength, moisture behaviour and machinability.
| Grade | Character | Best for |
|---|---|---|
| PA 6 | Tough, slightly more moisture uptake | General wear parts, good impact |
| PA 6/6 | Stiffer, higher heat, strong | Gears, bearings, structural parts |
| Cast nylon (PA 6 cast) | Large stock sizes, low stress | Big rollers, sheaves, large bushings |
| MoS₂-filled (nylon MDS) | Internally lubricated, darker | Low-friction bearings and wear parts |
| Glass-filled (PA + 30% GF) | Much stiffer, low creep, abrasive | Structural parts; wears tools faster |
POM grades: Delrin (homopolymer) vs acetal copolymer
A frequent confusion: Delrin is a brand name for POM homopolymer (POM-H); "acetal" usually means POM copolymer (POM-C). They machine similarly but differ in a way that matters for some parts.
POM-H (Delrin / homopolymer)
- Higher tensile & flexural strength (~75–80 MPa), better fatigue life.
- Slightly stiffer and harder.
- Watch-out: can have a porous "centreline" in thick rod; can be more prone to outgassing.
- Best for high-load gears, precision mechanical parts.
POM-C (acetal copolymer)
- Slightly lower strength (~65–70 MPa) but better chemical & hot-water resistance.
- No centreline porosity — better for thick or pressure-tight parts.
- Marginally easier on tooling.
- Best for valve/pump parts, food/medical, thick sections.
Machinability & cutting tips
Both machine well — POM is arguably the single easiest plastic to CNC — but plastics fail differently from metals: the enemy is heat and melting, not tool wear. Read the chips to read the cut.
- Sharp tools, positive rake, polished flutes. Plastics want a clean shearing cut; dull tools rub, heat, and melt the surface.
- High speed, moderate feed. Start at the high end of the speed range; POM makes short, clean chips at high rpm.
- Air, not flood. Compressed air clears chips and cools without the thermal shock or moisture pickup that coolant causes — especially important for nylon.
- Read the chips: short clean chips (2–8 mm) = good; long stringy chips = rubbing (increase speed / sharpen); powdery, hot chips = melting (reduce speed/feed).
- Support thin walls and long parts. Both plastics are far less stiff than metal and deflect under clamping and cutting load.
| Operation | Tool | Surface speed | Feed | Cooling |
|---|---|---|---|---|
| Turning | Sharp carbide, positive rake | 200–500 m/min | 0.1–0.3 mm/rev | Air |
| Milling | Polished 2-flute carbide | 200–400 m/min | 0.05–0.2 mm/tooth | Air |
| Drilling | Slow-helix plastic drill | 50–120 m/min | Peck for depth | Air, frequent peck |
Conditioning nylon stock (the step that saves the part)
For a tight-tolerance nylon part, conditioning the stock to its service moisture content before machining is what keeps it in size afterward. POM doesn’t need this; nylon does.
1. Know the service humidity
Decide the moisture content the part will equilibrate to in use — dry indoor, humid, or submerged.
2. Condition the stock
Bring the raw stock to that equilibrium moisture (controlled humidity, or a moisture-soak/anneal per the material supplier). This is where most nylon dimensional problems are prevented.
3. Rough machine
Remove bulk material, leaving finishing stock, so any stress from machining redistributes before finishing.
4. Stress-relieve (tight tolerance)
For precision parts, an intermediate anneal relieves machining stress that would otherwise warp the finish pass.
5. Finish machine
Cut to final size with sharp tools and air cooling.
6. Store & pack conditioned
Keep parts at their service humidity; note the conditioned state on the traveller for repeatability.
Tolerances & finish
| Feature | POM (acetal) | Nylon (conditioned) | Notes |
|---|---|---|---|
| Outer diameter | ±0.025 mm | ±0.05 mm | Nylon looser due to moisture/compliance |
| Bore diameter | ±0.03 mm | ±0.05 mm | Reamed/bored; thin walls compliant |
| Linear dimensions | ±0.05 mm | ±0.1 mm | Both less stiff than metal |
| Flatness / parallelism | 0.025–0.05 mm | 0.05–0.1 mm | Support thin sections |
| Surface finish Ra | 0.4–0.8 µm | 0.8–1.6 µm | POM finishes brighter and cleaner |
For the very tightest polymer tolerances or sub-millimetre features, we route work through our precision manufacturing and micro-machining cells.
Friction, wear & gears
Both are self-lubricating, which is why they dominate gears, bushings and sliding parts — but they’re not equal. POM’s lower friction (~0.2 vs nylon’s 0.3–0.4 against steel) and dimensional stability make it the default for precision gears and bearings. Nylon’s toughness and higher load/temperature capacity win for high-impact or heavily-loaded wear parts, especially in large cast sizes.
- Precision gears / bearings / cams: POM — low friction, dimensionally stable, quiet.
- High-impact or shock-loaded wear parts: nylon — tougher, absorbs impact.
- Large rollers / sheaves / wear pads: cast nylon — available in big low-stress stock.
- Internally-lubricated bearings: MoS₂-filled nylon or filled acetal for extended life.
Chemical resistance & FDA grades
- POM resists fuels, solvents and neutral chemicals well but is attacked by strong acids and oxidisers. Copolymer (POM-C) handles hot water and alkalis better than homopolymer.
- Nylon resists many solvents, oils and alkalis but is attacked by strong acids and degraded by long-term moisture/hot water; UV degrades unstabilised grades.
- Food & medical: both are available in FDA-compliant / food-contact grades — call out the grade explicitly on the drawing if the part contacts food or is used in a device.
- Colour: natural POM is white; Delrin often black. Nylon is natural/off-white or black. Both take limited colour compared with dyed plastics.
Nylon/POM vs PEEK, PTFE, polycarbonate
| Property | POM (acetal) | Nylon (PA) | PEEK | PTFE | PC |
|---|---|---|---|---|---|
| Continuous temp | ~90 °C | ~100–120 °C | ~250 °C | ~260 °C | ~120 °C |
| Strength | High | High | Very high | Low | Medium |
| Moisture stability | Excellent | Poor | Excellent | Excellent | Good |
| Friction / wear | Excellent | Good | Excellent | Lowest | Poor |
| Machinability | Easiest | Good | Difficult | Gummy | Good |
| Relative cost | Low | Low | Very high | High | Medium |
Step up to PEEK only when temperature, chemical or strength demands exceed what nylon/POM deliver — it costs 20–40× more. Below that, POM and nylon cover the vast majority of engineering-plastic parts.
Which one should you choose?
Send the drawing and the service conditions to our engineers through the CNC machining service and we’ll confirm the material, grade and any conditioning before cutting.
Frequently asked questions
The questions engineers ask most about machining nylon and POM.
よくあるご質問
- Moisture. Nylon absorbs water and swells up to ~0.6–1.2%, which can push a machined part out of tolerance; POM absorbs only ~0.2% and stays dimensionally stable. POM also has lower friction and machines more easily; nylon is tougher, more impact-resistant and handles a bit more heat. Choose POM for precision and low friction, nylon for toughness and impact.
- Delrin is a brand name for acetal homopolymer (POM-H). "Acetal" on its own usually means acetal copolymer (POM-C). Homopolymer (Delrin) is stronger and stiffer with better fatigue life; copolymer resists hot water and chemicals better and avoids the centreline porosity that thick homopolymer rod can have. Both machine similarly.
- Nylon is hygroscopic — it absorbs moisture from the air and swells. A part machined from dry stock can grow enough over days to lose a press-fit or bind a gear. Prevent it by conditioning the stock to its service moisture content before machining, designing the tolerance to allow for swelling, or switching to POM if dimensional stability is critical.
- No — compressed air is preferred. Both plastics generate low cutting heat at proper speeds, and flood coolant causes thermal shock and (for nylon) moisture pickup. Air clears chips and keeps the cut cool. Watch the chips: short and clean is good, long and stringy means the tool is rubbing, powdery and hot means it’s melting.
- For precision gears, POM (acetal) is usually better: lower friction against steel (~0.2 vs nylon’s 0.3–0.4), dimensionally stable, quiet running, and it holds tight tolerances. Nylon is the choice when the gear sees heavy impact or shock loading, where its toughness matters more than absolute dimensional stability.
- Only when the application genuinely exceeds what nylon/POM offer — continuous temperatures above ~120 °C, aggressive chemicals, sterilisation, or very high mechanical loads. PEEK costs 20–40× more, so for ordinary gears, bushings and wear parts, POM or nylon is the right, far cheaper choice.
What’s the main difference between nylon and POM (Delrin)?
Is Delrin the same as acetal?
Why does my machined nylon part change size after machining?
Do I need coolant to machine POM or nylon?
Which is better for gears — nylon or POM?
When should I use PEEK instead of nylon or POM?
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著者について
JLYPT Engineering Team
Engineering-Plastics Machining Specialists
We machine acetal (POM/Delrin) and nylon every week — gears, bushings, wear pads, manifolds, insulators. This guide is the practical knowledge our team uses to pick between them, condition nylon stock so parts hold size, and machine both to tight tolerances without melting or moisture surprises.
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