Plastic CNC Machining Guide: POM, PEEK, PTFE, Nylon

Why Machine Plastic at All?

For functional parts, machining beats printing on three things that matter: you get the real certified grade (PEEK 450G, POM-C, virgin PTFE), the part is isotropic, and you hold tight tolerance with a clean, sealed edge. Printed plastic approximates the material, is layered, and rarely seals. For a gear, a bushing, an insulator or a food-contact component, machined plastic is the standard route. See how it stacks up against printing in our machining vs 3D printing guide.

The general rules below apply across the family; the materials overview covers metals too if your assembly mixes both. For parts bound for medical devices or aerospace programs, the certified grade and traceability matter most.

Plastic	Common name	Key property	Machining quirk	Typical use
POM	Acetal / Delrin	Low friction, stable	Springy — sharp tools, avoid burrs	Gears, bushings, fixtures
PEEK	—	High temp, chemical resistant	Work-hardens, holds heat	Aerospace, medical, semiconductor
PTFE	Teflon	Non-stick, inert	Deforms under clamp & tool	Seals, insulators, gaskets
PA	Nylon	Tough, wear resistant	Hygroscopic — moves with moisture	Wear parts, rollers
UHMW	—	Abrasion resistant	Very soft, chatters easily	Wear strips, chutes
PC	Polycarbonate	Clear, impact tough	Prone to stress cracking	Covers, guards
ABS	—	Easy, cheap	Soft, melts at edge if dull	Housings, jigs

The Five Tricks That Keep Plastic in Tolerance

1. Sharp tools, always

Plastic springs back from a dull edge and smears instead of shearing. A fresh carbide cutter with high rake and a polished flute gives a clean cut and no burr. The moment a tool goes dull you get heat, melt and a ragged edge — so tool changes are scheduled, not waited for.

2. Back the whole face (fixturing)

This is where PTFE and UHMW fail if you're careless. They have low rigidity and will deflect or creep under a vice jaw. A support fixture that backs the entire machined face, plus light clamp pressure, keeps the part from moving during the cut and from growing when you let go. Over-tightening is as bad as under-tightening.

3. Light passes, no dwelling

PEEK work-hardens under a dwelling tool; a hesitant cut leaves a hardened skin that destroys the next tool. Keep the tool moving, take moderate depths, and use coolant to pull heat out. For most plastics, high surface speed with a light feed beats a heavy single pass.

4. Respect thermal and moisture movement

Plastics expand more than metal and some absorb water. Nylon can take on moisture and grow over a day. For a tight fit, hold the part at a stable room temperature and, for hygroscopic grades, machine and measure close together in time. If the part will see a warm environment, tolerance it for the warm size, not the cold one off the machine.

5. Don't forget the edge finish

A sealed, burr-free edge matters on plastics more than on metal — burrs catch, and a melted edge wrecks a seal. Our surface finish chart shows what each finish adds; for most plastic functional parts the as-machined edge is fine, but a sealing face may want a light pass to a defined Ra.

Grade-by-Grade Notes

POM (Acetal / Delrin)

The friendly one. Stable, low friction, holds dimension well, machines like a dream if the tool is sharp. The only trap is the springy burr at the exit — deburr as you go. First choice for gears, bushings and fixtures.

PEEK

The premium one — high temperature, chemical and radiation resistance, and it holds tolerance beautifully once you respect its two quirks (work-hardening, heat). Sharp carbide, coolant, rigid setup, keep moving. Used in aerospace, medical and semiconductor where the certified grade is non-negotiable.

PTFE (Teflon)

The tricky one. Almost no rigidity, creeps under clamp load, springs from the tool. Fixture the whole face, light passes, sharp tools, gentle clamping. The reward is a genuine non-stick, chemical-inert seal or insulator that printing simply can't match. Virgin vs filled (glass, bronze) changes the cutting entirely — filled grades wear tools fast.

Nylon (PA)

Tough and wear-resistant, but hygroscopic. Great for wear parts and rollers; plan around moisture movement if the fit is tight. Cast nylon (PA6-G) is more dimensionally stable than extruded for larger sections.

UHMW

Extreme abrasion resistance but very soft and chattery. Back it fully, take gentle passes, expect to fight vibration. Perfect for wear strips and chute liners where nothing else survives.

For context on how plastic compares to the metals people usually weigh it against, our aluminium vs stainless vs titanium comparison covers the metal side; titanium is the one to avoid unless you truly need it.

POM (Delrin / Acetal) CNC machined flange hub — low-friction plastic turned component — **POM flange hub**
Acetal turned to a clean, sealed edge — ideal for low-friction parts.

POM and PEEK CNC machined plastic parts — engineering plastics for medical and semiconductor use — **POM & PEEK parts**
PEEK for high-temp/medical; POM for stable, low-friction use.

Nylon (PA) CNC machined plastic parts — tough, wear-resistant turned and milled components — **Nylon (PA) parts**
Tough, wear-resistant parts — plan around moisture movement.

Selection Table

Which Plastic for Your Part?

Pick by what the part has to survive.

If the part must…	Start with	Watch out for
Slide, gear, low friction	POM	Springy burr at exit
Take heat + chemicals (certified)	PEEK	Work-hardening, tool heat
Seal, insulate, stay inert	PTFE (virgin)	Deflects under clamp & tool
Absorb wear, take impact	Nylon PA	Moisture movement
Survive abrasion (liners)	UHMW	Chatter, softness
Be clear and impact-tough	Polycarbonate	Stress cracking at edges

FAQ

Plastic Machining Questions

Can you CNC machine plastic instead of 3D printing it?

Yes, and for many engineering plastics it is the better route. Machining gives you the real certified grade (PEEK 450G, POM-C, etc.), isotropic properties, tight tolerances and a clean sealed edge — none of which printed plastic reliably delivers. It is the standard choice for functional, load-bearing or food/medical-contact parts.

Why does PTFE (Teflon) deform while machining?

PTFE has almost no rigidity and a very low modulus, so it springs away from the tool and then springs back — and it creeps under clamping pressure. The fixes are a proper support fixture that backs the whole face, very sharp tools, light passes, and avoiding over-tightening the vice. Cut it too aggressively and the part grows out of tolerance the moment you release it.

Is PEEK hard to machine?

It machines cleanly if you respect two things: it work-hardens and it holds heat. Use sharp carbide at moderate speed with plenty of coolant, take a rigid setup, and don't let the tool dwell — a dwelling tool work-hardens the surface under it. With that, PEEK turns and mills like a well-behaved engineering plastic and holds excellent tolerance.

What tolerance can I hold on machined plastic?

Routinely ±0.05 mm on a stable plastic like POM or nylon, and ±0.02–0.03 mm is achievable on a well-fixtured, temperature-stable part. The catch is thermal and moisture movement: plastics expand and absorb moisture more than metal, so for a tight fit you should hold the part at room temperature and, for hygroscopic grades like nylon, machine and measure close together in time.

Got a plastic part that printing keeps getting wrong?

Send the drawing and the grade you need. We'll machine it from certified stock and hold the tolerance — including the sealed edge printing can't give you.

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Plastic CNC Machining Guide: POM, PEEK, PTFE, Nylon & How to Cut Them