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Machining characteristics of common engineering plastics

Engineering plastics machine very differently from metals. They are softer, melt at lower temperatures, and are far more flexible. The primary challenge is controlling heat -- plastic melts rather than chips when overheated. This guide covers the key parameters for common plastics.

• Delrin / Acetal (POM): The most machinable plastic. Excellent dimensional stability. Chips well with sharp tools. Speeds 200-500 m/min. Dry or light air blast.
• Nylon (PA6, PA66): Absorbs moisture (dimensional change). Flexible; requires sharp tools and rigid workholding. Speeds 150-400 m/min. Coolant can cause swelling -- use dry or air.
• PTFE (Teflon): Very soft. Creeps under clamping. Hard to hold tight tolerances. Speeds 100-300 m/min. Sharp tools essential; dull tools smear the surface.
• Acrylic (PMMA): Brittle. Chips and cracks at edges. Use sharp tools, light cuts, and slow feeds. Speeds 100-300 m/min. Coolant recommended to prevent melting and stress cracking.
• PEEK: High-performance thermoplastic (250 deg C continuous use). Machines like a soft metal. Speeds 150-400 m/min. Excellent dimensional stability. More expensive than most metals per kg.

How to use this Plastic Machining Reference Guide

Identify your plastic type. Delrin and PEEK machine best; PTFE and soft nylons are challenging. Use sharp, uncoated carbide tools with high-positive rake angles. Control heat with air blast or light mist coolant. Account for thermal expansion in your measurements. For tight tolerances, rough, rest, then finish.