PA (Nylon / Polyamide) — CNC Machining Material Manual

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Rating legend — ★★★★★ best · ★☆☆☆☆ worst. For machinability/wear/heat resistance more stars = better; for cost, fewer stars = cheaper.

📋 Material Quick-Reference Card

┌──────────────────────────────────────────┐
│  Material Name: Polyamide (PA / Nylon)    │
│  (PA6 / PA66 / Cast Nylon / MC Nylon)     │
│  Category: Semi-crystalline engineering   │
│            plastic                        │
│  Density: 1.13~1.15 g/cm³                 │
│  Tensile Strength: 70~90 MPa (dry)        │
│  Flexural Strength: 90~110 MPa            │
│  Hardness: M80~M90 / R110~R120 Rockwell   │
│  Melting Point: PA6 ~215 ℃ / PA66 ~255 ℃ │
│  Machinability: ★★★★☆ (good, slightly     │
│                 gummy/stringy)            │
│  Wear Resistance: ★★★★★ (excellent)       │
│  Chemical Resistance: ★★★★☆               │
│  Cost: ★★★☆☆ (moderate, grade-dependent) │
│  Keywords: tough, wear-resistant, self-   │
│            lubricating, moisture-sensitive│
└──────────────────────────────────────────┘

1. Material Overview

1.1 Introduction

PA (Polyamide), commonly known as nylon, is a tough, wear-resistant, self-lubricating engineering plastic widely used for CNC-machined transmission and bearing parts. Compared with POM, nylon generally offers better impact toughness and abrasion resistance, but its dimensional stability is worse because it absorbs much more moisture.

• English Name: Polyamide / Nylon / PA
• Common Nicknames: Nylon, PA6, PA66, Cast Nylon, MC Nylon
• Common Filled Grades: Glass-filled nylon, MoS₂-filled nylon, oil-filled nylon

1.2 Main Types ⭐ Important

💡 Cast nylon (MC nylon / PA6-cast) is especially common for large CNC-machined wear parts because it is available in thick plates, large rods, and tubes that are difficult to obtain in extruded nylon.

1.3 Raw Material Forms

Common forms for CNC machining:

• PA Rod (round bar): bushings, rollers, pulleys, turned sleeves
• PA Sheet/Plate: wear pads, guide blocks, cams, fixture parts
• PA Tube: large bushings, bearing sleeves, spacer rings
• Common colors: natural white/cream, black, blue, green; filled grades vary by supplier

2. Composition & Physical Properties

2.1 Material Composition

PA is a family of polyamide polymers containing amide groups in the molecular chain. It is a semi-crystalline engineering plastic: the crystalline phase provides wear resistance, fatigue resistance, and strength, while the polymer structure gives nylon its toughness.

2.2 Physical Properties

⚠️ Nylon’s most important design issue is moisture absorption. PA absorbs water from air and coolant, causing swelling, dimensional change, and property change. It becomes tougher but softer when wet. For precision parts, nylon is less dimensionally stable than POM.

3. Mechanical & Chemical Properties

3.1 Mechanical Properties

💡 PA is often selected when a part must survive shock load, abrasion, and repeated movement. It is tougher than POM, but less stable for tight-tolerance parts exposed to humidity.

3.2 Chemical Resistance

3.3 Notable Characteristics

• Excellent wear and abrasion resistance: suitable for sliding, rolling, and impact-wear components
• High toughness: better impact toughness than POM, especially after moisture conditioning
• Self-lubricating behavior: usable for bushings, bearings, rollers, and guide parts
• Fatigue resistant: good for repeated load and cyclic mechanical movement
• Good chemical resistance: especially to fuels, oils, greases, and many solvents
• Moisture-sensitive dimensions: absorbs water, swells, and changes mechanical properties over time

4. CNC Machining Process ⭐⭐ Core

4.1 Machinability Rating

★★★★☆ Good machinability — PA machines well, but is not as dimensionally stable or as crisp-cutting as POM:

• Cuts easily with sharp tools, but can feel slightly gummy or stringy
• Excellent for wear parts, rollers, bushings, pulleys, and large cast nylon components
• Burrs and stringy chips are more common than with POM
• Tight tolerances require moisture control, stress relief, and a staged machining process

4.2 Recommended Tooling

4.3 Recommended Cutting Parameters

📌 Parameters are for reference only; adjust based on machine rigidity, tool diameter, stock grade, moisture condition, and part geometry.

4.4 Machining Challenges & Solutions

4.5 Annealing Recommendation ⭐

To reduce machining distortion and relieve internal stress, stress relief is critical for tight-tolerance nylon parts. Use a staged process whenever precision matters:

Reference Stress-Relief / Conditioning Process:
• Rough machine leaving allowance: 0.3~1.0mm per side where possible
• Heat treatment: follow supplier recommendation for PA grade
• Typical range: ~80~120 ℃, held according to wall thickness
• Cooling: slow, uniform cooling to room temperature
• Final step: finish machine after the part reaches a stable condition

💡 For high-precision PA parts, use dry/conditioned stock → rough machining → stress relief/conditioning → finish machining → controlled inspection. Always consider later humidity exposure; a dry nylon part may grow after delivery.

4.6 Cooling Methods

• Air blast: preferred for many PA parts; removes stringy chips without adding moisture
• Water-soluble coolant: acceptable when heat control is needed, but may be absorbed by nylon and change dimensions
• Mist cooling: useful for drilling or deep pockets; dry/condition parts before final measurement
• ❌ Avoid overheating, melting, or rubbing cuts caused by dull tools and poor chip evacuation

5. Surface Treatment

PA has better surface treatment potential than POM, but it still requires correct pretreatment because nylon absorbs moisture and has a relatively low-energy surface:

💡 For appearance-critical PA parts, specify the exact grade, color, moisture condition, and post-treatment process in advance. Filled nylon, oil-filled nylon, and cast nylon may behave differently during dyeing or painting.

6. Applications & Material Selection

6.1 Typical Application Industries

6.2 Pros & Cons Summary

6.3 Material Selection Guide

✔ Recommended for PA:

• Impact-bearing wear parts requiring toughness plus abrasion resistance
• Bearings, bushings, rollers, pulleys, sprockets, sheaves, cams, and wear pads
• Large machined parts where cast nylon stock is more practical than molded or extruded plastics
• Sliding parts where oil-filled or MoS₂-filled nylon can reduce friction
• Applications where PA’s toughness is more important than POM’s dimensional stability

✘ Not recommended for:

• Tight-tolerance precision parts exposed to changing humidity → choose POM or moisture-stable engineering plastics
• Parts requiring minimal water absorption → choose POM, PE, PTFE, or PEEK depending on load/temperature
• High temperature continuous service beyond nylon grade limits → choose PEEK, PTFE, or PI
• Strong acid / strong oxidizer exposure → choose PTFE or PVDF
• Thin precision walls where swelling, warping, or stress release cannot be tolerated

⚠️ Safety & Handling Notes

⚠️ Never ignore moisture condition when machining nylon. A PA part can be accurate immediately after machining and then grow after absorbing water in storage or service. For precision work, specify moisture condition, inspection timing, and final operating environment.

🔗 Related Pages

• Plastic Materials Handbook (overview)
• POM (Acetal) — key competitor/complement with better dimensional stability
• PE (Polyethylene) — lightweight, chemical-resistant plastic with lower stiffness