Cutting data and tooling notes for machining plastics — acrylic, POM (Delrin), PTFE, PE and nylon. Speeds, feeds, cutter geometry, and how clamping and coolant differ from metal.
Complete reference tables and engineering data for plastic machining. All values verified against ISO, ANSI, and manufacturer standards.
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.
Plastics have low thermal conductivity and low melting points. Heat generated at the cutting edge cannot escape through the chip fast enough, so the plastic melts. Solutions: use razor-sharp tools (positive rake, polished flutes), increase feed rate (thicker chip carries away more heat), use compressed air or mist coolant for cooling, and reduce spindle speed.
Plastics have 5-10x higher thermal expansion than metals -- a temperature change of 5 deg C can shift a dimension by 0.02 mm on a 100 mm part. Measure at 20 deg C. Account for stress relaxation: machined plastics may change dimension over hours to days after machining. Rough, then let the part rest, then finish. Use rigid workholding but avoid crushing the part.
Sharp, high-positive rake angles (10-20 deg ), polished flutes, large clearance angles (10-15 deg ), and large chip gullets. Special "O-flute" or single-flute end mills for plastics prevent chip re-welding. Standard metal-cutting end mills with 2-3 flutes work if sharp. Avoid dull or coated tools -- the coating's rounded edge smears rather than cuts plastic.
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.
Continue with closely related resources from the machining reference library.
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MACHINING PLASTICS? Plastics are unforgiving of the wrong rake and of any heat in the cut. See how we check that geometry matches the material.
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Cutting formulas with the units worked through · Speed and feed starting points for all six ISO material groups · How to read a carbide grade past its ISO code. 12 pages.
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