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PC (Polycarbonate) CNC Machining Material Manual

Cnc plastic materials
Last updated: May 23, 2026

PC (Polycarbonate / Lexan / Makrolon) — 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: Polycarbonate (PC)             │
│  (Lexan / Makrolon / transparent PC)           │
│  Category: Amorphous engineering plastic       │
│            (transparent impact-resistant resin)│
│  Density: 1.20~1.22 g/cm³                      │
│  Tensile Strength: 60~70 MPa                   │
│  Flexural Strength: 90~100 MPa                 │
│  Hardness: Rockwell M70~M75 / R118             │
│  Heat Deflection Temp.: 130~140 ℃              │
│  Machinability: ★★★★☆ (good, heat-sensitive)   │
│  Impact Resistance: ★★★★★ (virtually unbreak.) │
│  Chemical Resistance: ★★☆☆☆                    │
│  Cost: ★★★★☆ (higher than PMMA/ABS)            │
│  Keywords: transparent, tough, impact-resistant│
│            safety shield, electrical insulation│
└──────────────────────────────────────────────┘

1. Material Overview

1.1 Introduction

PC (Polycarbonate) is a transparent, tough, high-impact engineering plastic widely used when a part must combine optical visibility with mechanical safety. It is much tougher than PMMA (acrylic) and is often described as virtually unbreakable in guard, shield, and protective-window applications.

  • English Name: Polycarbonate / PC
  • Common Nicknames: Transparent PC, engineering PC, bullet-resistant plastic (application-dependent)
  • Famous Brand Names: Lexan (SABIC), Makrolon (Covestro), Panlite

1.2 Two Main Types ⭐ Important

Type Full Name Characteristics
Clear / Optical PC Transparent polycarbonate sheet/rod High impact strength with approx. 88~90% light transmission; used for covers, windows, guards
Flame-Retardant PC FR PC, UL94 V-0 / V-2 grades Improved flame performance and electrical safety; common for electrical housings and insulators ⭐ Common for CNC
Glass-Filled PC GF-PC, usually 10~30% glass fiber Higher stiffness, lower creep, better dimensional stability; less transparent and more abrasive to tools

💡 Clear PC is selected when visibility + safety are required. FR PC is selected for electrical and equipment parts where flame rating matters. Glass-filled PC is selected when stiffness is more important than transparency.

1.3 Raw Material Forms

Common forms for CNC machining:

  • PC Rod (round bar): turned transparent parts, spacers, insulators
  • PC Sheet/Plate: milled windows, covers, guards, enclosures
  • Common colors: clear, smoke/tinted, black, natural translucent, custom colors

2. Composition & Physical Properties

2.1 Material Composition

PC is an amorphous thermoplastic polymer containing carbonate groups in its molecular chain. Its amorphous structure gives it transparency, good dimensional stability, and no true crystalline melting point. Commercial PC is commonly produced from bisphenol-A polycarbonate resin, with additives used for UV resistance, flame retardancy, color, or glass-fiber reinforcement.

Type Molecular Structure
Standard PC Amorphous polycarbonate resin with carbonate linkages, transparent and tough
FR PC PC resin with flame-retardant additive package for UL94 V-0 / V-2 grades
Glass-Filled PC PC resin reinforced with glass fiber for stiffness and creep resistance

2.2 Physical Properties

Property Value
Density 1.20~1.22 g/cm³
Melting Point No true melting point (amorphous); softening range approx. 145~155 ℃
Heat Deflection Temp. 130~140 ℃
Long-term Service Temp. -40115130 ℃
Thermal Conductivity 0.19~0.22 W/(m·K)
Water Absorption 0.15~0.35% (moderate-low)
Coefficient of Thermal Expansion 65~70×10⁻⁶ /℃
Light Transmission Approx. 88~90% (clear grades)

💡 PC offers good dimensional stability and low shrinkage for an amorphous plastic, but it absorbs some moisture. For precision machining or optical work, dry stock and avoid sudden temperature changes.

3. Mechanical & Chemical Properties

3.1 Mechanical Properties

Property Value
Tensile Strength 60~70 MPa
Flexural Strength 90~100 MPa
Elastic Modulus 2200~2400 MPa
Elongation 80~120% (grade-dependent)
Hardness Rockwell M70~M75 / R118
Impact Strength Extremely high; virtually unbreakable in many practical uses
Coefficient of Friction 0.35~0.45 (not self-lubricating)

⚠️ PC has far higher impact resistance than PMMA, ABS, and many other transparent plastics. However, it scratches more easily than PMMA and often needs hard coating for optical covers.

3.2 Chemical Resistance

Medium Resistance
Water, neutral salts ✅ Good
Dilute acids ✅ Fair to good
Oils, greases ⚠️ Generally fair, verify grade compatibility
Alcohols ⚠️ Limited; stress cracking possible
Alkalis ❌ Poor, especially strong alkalis
Ketones, aromatic solvents, chlorinated solvents ❌ Poor; swelling, crazing, stress cracking
UV light (long-term outdoor) ⚠️ Fair, requires UV-stabilized or coated grades

3.3 Notable Characteristics

  • Extreme impact strength: the first choice for transparent safety shields and protective windows
  • Transparent + tough: approx. 88~90% light transmission with much higher toughness than PMMA
  • Good heat resistance: continuous service commonly around 115~130 ℃ depending on grade/load
  • Good electrical insulation: widely used for electrical covers, insulators, and housings
  • Naturally flame-retardant tendency: many grades burn less readily than common plastics; FR grades can meet UL94 V-0 / V-2

4. CNC Machining Process ⭐⭐ Core

4.1 Machinability Rating

★★★★☆ Good machinability, but heat-sensitive and stress-sensitive — PC can be CNC machined accurately, but it requires more process control than POM or PMMA:

  • Sharp polished tools are essential; dull tools cause heat, melting, and cloudy edges
  • Chips can become gummy if heat is not removed quickly
  • Transparent parts show scratches, tool marks, and stress whitening easily
  • Drilled and tapped holes are prone to cracking or crazing if internal stress is not relieved
Item Recommendation
Tool Material Sharp carbide preferred; polished HSS acceptable for some drilling/turning
Cutting Edge Very sharp, polished edge to reduce friction and gumming
Rake Angle Positive rake angle (10°~20°)
Helix Angle High helix for chip evacuation and low cutting pressure
Flutes 12 flutes for small tools; 23 flutes for rigid setups with good chip clearance
Operation Spindle Speed (RPM) Feed Rate (mm/min) Depth of Cut (mm)
Rough Milling 8000~16000 800~2500 0.5~3
Finish Milling 10000~20000 300~1200 0.1~0.5
Turning 1000~3000 0.05~0.25/rev 0.2~1.5
Drilling 1000~4000 30~150 —

📌 Parameters are for reference only; adjust based on machine rigidity, tool diameter, grade, wall thickness, and whether the part is optical/transparent.

4.4 Machining Challenges & Solutions

Challenge Cause Solution
Melting / gumming Cutting heat, dull tools, poor chip evacuation Use sharp polished tools, high RPM with moderate feed, air blast, peck cycles
Stress cracking / crazing Residual stress in stock; aggressive coolant/solvents; tight drilled/tapped holes Anneal before machining and before/after drilling/threading; avoid solvent coolants; use proper hole clearance
Cloudy or scratched surface Tool rubbing, chips recutting, poor handling Use climb finishing passes, air evacuation, protective film, clean soft fixtures
Drill grabbing or exit cracking High thrust and heat at hole exit Use plastic drill geometry, backing support, peck drilling, reduced feed near breakthrough
Dimensional drift after machining Internal stress release and moisture/temperature change Rough machine → anneal → finish machine; store dry; stabilize temperature before inspection

4.5 Annealing Recommendation ⭐

To reduce cracking, crazing, and dimensional movement, annealing is strongly recommended for precision PC parts and especially for drilled/tapped transparent parts:

Reference Annealing Process:
• Temperature: 120~125 ℃
• Time: approx. 30~60 min per 25mm of wall thickness
• Cooling: slow furnace cooling to below 60 ℃ before removal

💡 For PC, the safest workflow is dry stock if needed → rough machining → annealing → finish machining → optional final annealing. This is especially important around holes, threads, sharp inside corners, and solvent-exposed parts.

4.6 Cooling Methods

  • Air blast: preferred for most PC machining; removes chips without introducing chemical stress cracking
  • Dry cutting: acceptable when tools are sharp and chip evacuation is excellent
  • Water-soluble coolant: use only PC-compatible fluids; test before production
  • ❌ Avoid aggressive cutting fluids, alcohols, ketones, chlorinated solvents, and alkaline cleaners

5. Surface Treatment

PC supports more finishing options than POM, but transparent parts require careful handling because scratches and stress marks are visible:

Process Feasibility Notes
Polishing ✅ Good Mechanical polishing can improve clarity; avoid overheating and stress whitening
Vapor polishing ✅ Feasible Can improve transparent edges; requires controlled process and ventilation
Hard coating ✅ Common Improves scratch and chemical resistance for windows, guards, and covers
Painting ✅ Feasible Better paintability than POM/PTFE; surface cleaning and primer improve adhesion
Bonding / adhesives ✅ Good Bonds with compatible solvent cements, epoxies, acrylic adhesives; avoid stress cracking
Laser marking ✅ Feasible Works well on filled/colored grades; clear grades may need additives or coating
Dyeing / tinting ⚠️ Limited Usually supplied as tinted sheet/rod; post-dyeing is less common

💡 If a transparent part needs scratch resistance, specify hard-coated PC. If the top priority is optical clarity and scratch resistance with low impact load, choose PMMA instead.

6. Applications & Material Selection

6.1 Typical Application Industries

Industry Application Parts
Machine safety Machine guards, safety shields, impact-resistant viewing windows
Industrial equipment Transparent covers, protective enclosures, inspection windows
Lighting Light covers, lenses, LED diffusers, protective lamp housings
Electrical / electronics Insulators, terminal covers, FR housings, equipment panels
Medical and lab equipment Transparent covers, fixtures, trays, protective lab parts
Automotive / transport Interior covers, protective lenses, impact-resistant trim parts
Precision components Impact-resistant machined parts, spacers, structural transparent parts

6.2 Pros & Cons Summary

✅ Advantages ❌ Disadvantages
Extremely high impact strength; much tougher than PMMA Lower scratch resistance than PMMA; often needs hard coating
Transparent with approx. 88~90% light transmission Lower optical clarity than PMMA
Good heat resistance for a transparent plastic Poor resistance to many solvents and alkalis
Good dimensional stability and electrical insulation Prone to stress cracking around holes/threads if not annealed
Paintable, bondable, hard-coatable, vapor-polishable More expensive than PMMA and ABS
FR grades available; naturally flame-retardant tendency Gummy and heat-sensitive during machining

6.3 Material Selection Guide

✔ Recommended for PC:

  • Transparent guards, covers, and windows requiring high impact resistance
  • Parts where PMMA is too brittle or unsafe under impact
  • Electrical insulators and FR-grade housings requiring good dielectric performance
  • Medical, lab, and machine components needing toughness + visibility
  • Impact-resistant precision machined parts with moderate heat exposure

✘ Not recommended for:

  • Best optical clarity and scratch resistance → choose PMMA
  • Strong solvent, alkali, or chemical exposure → choose PTFE, PVDF, or suitable chemical-resistant plastic
  • Low-cost non-transparent housings → choose ABS
  • High-wear sliding parts → choose POM or nylon
  • High temperature (>130℃ continuous) → choose PEEK, PPS, or PI

⚠️ Safety & Handling Notes

Hazard Detail Precaution
Combustible dust Fine PC chips/dust can be combustible and may irritate airways Use dust extraction; avoid dust accumulation and ignition sources
Fume generation Overheating from dull tools can produce irritating fumes Keep tools sharp, control heat, ensure ventilation/extraction
Solvent stress cracking Many solvents, cutting fluids, alcohols, and alkaline cleaners can cause crazing/cracks Avoid aggressive fluids; test coolant/cleaner compatibility before use
Surface scratching Clear PC scratches easily during clamping, deburring, and cleaning Keep protective film on as long as possible; use soft jaws and clean gloves
Storage PC absorbs some moisture and can mark or warp if stored poorly Store dry, flat, indoors, away from UV and heat sources

⚠️ Never assume a coolant or cleaner is safe for PC. Even if the part looks fine after machining, residual stress plus incompatible chemicals can cause delayed crazing or cracking around holes, threads, and sharp corners.

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