Engineering Plastics for CNC Machining

Last updated September 27, 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. They also machine faster than metals, so they are often the cheapest route to a rigid, functional part. OpusFab lists two CNC plastics, ABS and POM (Delrin). The current list, with live pricing for your part, is in the quote editor.

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 stabilised.

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.

Choosing between ABS and POM

  • Pick ABS for appearance prototypes, enclosures, and parts that will be glued, painted, or bonded into an assembly.
  • Pick POM when the part moves or carries load: anything that slides, rotates, or needs to hold a dimension over time.

Plastics not currently listed

A few common engineering plastics are not in the editor at the moment:

  • Polycarbonate (PC): extreme impact strength and transparency, for guards and lenses.
  • Nylon (PA6/PA66): tough and self-lubricating, for wear pads and rollers. For complex nylon parts, SLS printing is often the better route anyway.
  • PEEK: the high-performance option, holding strength to about 250°C and resisting almost all chemicals.

If your part needs one of these, request a custom quote and the team will confirm availability.

Practical notes

  • Plastics are softer than metals, so machined surfaces can look slightly different from metal parts. Raw (As-Machined) is the standard finish.
  • Both plastics machine to the same CNC tolerance tiers as metals: Standard (±0.05mm) and Precision (±0.01mm).
  • 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 aluminium fits your part? Choosing a Process walks through the decision.