Plastic Materials for CNC Machining: POM, PEEK, ABS, PC and Nylon Compared

Choosing the right plastic for CNC machining matters more than most buyers expect. Two parts with identical geometry can differ four-fold in price and ten-fold in wear life depending on whether they are cut from cheap POM or aerospace-grade PEEK. This guide covers the plastics we machine every week, what each is actually good at, and how to pick without over-specifying.

The Shortlist

Material	Best for	Machinability	Relative cost
POM (Delrin / acetal)	Bushings, gears, sliding parts, jigs	Excellent	Low
Nylon (PA6 / PA66, cast & extruded)	Wear pads, rollers, tough structural parts	Good — watch moisture	Low–mid
ABS	Housings, enclosures, prototypes	Very good	Low
PC (polycarbonate)	Impact-resistant covers, guards, lens frames	Good	Mid
PTFE	Chemical seals, low-friction liners	Soft, gummy — needs care	Mid–high
PEEK	High temperature, medical, aerospace, chemical	Good but slow	Very high

POM: The Default Engineering Plastic

Acetal (POM-C) is the workhorse. It machines like brass — clean chips, crisp edges, often no coolant needed — and it holds tolerance well because it is dimensionally stable and absorbs almost no moisture. Stiffness, low friction and good fatigue resistance make it the first choice for bushings, gears, cams, conveyor components and inspection fixtures. Its limits: it does not like strong acids, UV exposure, or continuous service above about 90 °C.

Nylon: Tough but Moisture-Sensitive

Nylon is the tough one — high impact strength, excellent abrasion resistance, tolerant of shock loads. It is the right answer for wear pads and rollers. The trap is moisture: nylon absorbs water from the air and grows, roughly 0.2–0.5% dimensionally between dry and conditioned states, and it keeps moving after machining. For tight-tolerance parts, machine from moisture-conditioned stock, or design with clearance and accept the movement. Cast (MC) nylon machines better and is more stable than extruded.

ABS and PC: Prototypes and Enclosures

ABS machines beautifully and takes paint, which makes it the default for prototype housings that must look like the production part. PC is the impact option: roughly 200 times more impact-resistant than glass, stable to about 120 °C, and optically clear in its natural state. Both are low-cost and easy to machine, so they are rarely the reason a quote comes back high.

PTFE and PEEK: Buy Them for a Reason

PTFE (Teflon) has the lowest friction of any solid and near-universal chemical resistance, but it is soft and cold-flows under load — it will creep out of a press fit. Machine it for seals, chemical-handling parts and low-friction liners, and design mechanical support rather than relying on the material's compressive strength.

PEEK is the premium choice, and the premium is real: stock costs many times more than POM, and it machines slowly because it is abrasive and cuts hot. You buy it for continuous service near 250 °C, for steam and chemical sterilisation, for implant-grade biocompatibility, and for aerospace parts where weight and fire performance are specified. If none of those apply, PEEK is usually money wasted. Compare this with the metal options in our guide to plastic machining materials.

Machining Plastics: What Changes

Plastics cut roughly 5–10 times faster than steel, but they follow their own rules:

• Heat is the enemy. Plastics conduct heat poorly, so chips must carry it away. If chips smear instead of breaking, change the feed decisively — never let the tool rub.
• Clamp lightly. Plastics deform under vise pressure. Soft jaws and light clamping prevent the classic "machined round, springs back oval" failure.
• Sharp tools, high rake. Purpose-ground geometry for plastics beats general-purpose tooling.
• Watch thermal growth. A part that measures perfectly hot will shrink; let it stabilise before final inspection.
• Stress relief matters. Extruded stock carries internal stress; rough out, let it relax, then finish.

These are the same physical rules we apply on every machined part, adjusted per material family.

How to Specify Without Over-Spending

1. Start with POM or ABS unless you have a stated reason not to.
2. Add nylon only for wear or impact duty, and plan for moisture movement.
3. Add PC when impact resistance or clarity is specified.
4. Move to PTFE for chemical or extreme low-friction duty, with support for creep.
5. Move to PEEK only when temperature, sterilisation, biocompatibility or fire performance demand it.
6. Always put the service condition on the drawing — temperature, chemicals, load and cycle rate — not just the material name.

How Renjiu Handles Plastic Parts

We machine POM, nylon, ABS, PC, PTFE, PEEK, HDPE, PVC and acrylic daily, holding tolerances down to ±0.02 mm on stable grades. Because we also machine the matching metal components, plastic-and-metal assemblies stay within one tolerance stack. Send your model and service conditions through our RFQ form and we will recommend the lowest-cost plastic that actually meets the duty — including where a metal part would be cheaper and better. For the metal side, see our materials overview.