Engineering Plastics for CNC Machining
Last updated September 26, 2026
CNC machining is not just for metals. Engineering plastics are cut from solid stock on the same machines, and they solve problems metals cannot: electrical insulation, low friction, chemical resistance, and low weight. The current list of plastics, with live pricing for your part, is in the quote editor. This article covers the five you will meet most often.
POM (acetal, brand name Delrin)
POM is stiff, dimensionally stable, and has very low friction with low moisture absorption. It machines cleanly and holds tolerances well for a plastic.
Typical uses: gears, bushings, bearings, sliding parts, jigs, and fixtures. Weaknesses: it is hard to glue, and it is not ideal for prolonged outdoor UV exposure.
ABS
ABS is tough, impact resistant, inexpensive, and easy to machine, glue, and paint. It is the default choice for prototype enclosures, housings, and structural mockups.
Weaknesses: limited heat resistance (it softens around 100°C) and poor UV resistance unless stabilized.
Polycarbonate (PC)
PC is the impact champion: it is the material behind safety glasses and machine guards. It is transparent, stiff, and heat resistant to about 120-130°C.
Weaknesses: it scratches more easily than acrylic, can stress-crack on contact with some chemicals, and needs sharp tooling to machine cleanly. Typical uses: guards, lenses, covers, and light pipes.
Nylon (PA6/PA66)
Nylon is tough, wear resistant, and self-lubricating, which makes it a classic material for gears, wear pads, rollers, and low-speed bearings.
Its big weakness is moisture absorption: nylon parts swell and change properties with humidity, so tight tolerances are hard to hold. If dimensional stability matters more than toughness, POM is usually the better pick.
PEEK
PEEK is the high-performance option. It keeps its strength up to about 250°C continuous use, resists almost all chemicals, wears well, and is available in medical implant grades.
It machines well, but the raw material is very expensive, often ten times the cost of common plastics. Use PEEK when nothing else survives the environment: aerospace, oil and gas, medical, and semiconductor tooling.
Quick comparison
| Material | Strengths | Weaknesses | Typical uses |
|---|---|---|---|
| POM (Delrin) | Low friction, stable, machines well | Hard to bond | Gears, bushings, fixtures |
| ABS | Tough, cheap, easy to finish | Low heat and UV resistance | Enclosures, prototypes |
| PC | Extreme impact strength, clear | Scratches, chemical sensitivity | Guards, lenses |
| Nylon | Wear resistant, self-lubricating | Absorbs moisture | Wear pads, rollers |
| PEEK | Heat and chemical resistance | Very expensive | Demanding environments |
Practical notes
- Plastics are softer than metals, so machined surfaces can look slightly different from metal parts. Raw (As-Machined) is the standard finish.
- Plastics expand and contract more with temperature than metals. Leave room in designs that span wide temperature swings.
- If you need a plastic part with complex internal geometry, SLS nylon printing may be a better route than machining. See 3D Printing Resins and Nylons.
- Not sure whether a plastic or aluminum fits your part? Choosing a Process walks through the decision.