Machining PEEK: The 5 Hard Problems and How to Hold Tight Tolerances
ProtoTech provides precision CNC machining of PEEK across unfilled, CF30, GF30 and HPV grades. Unfilled PEEK is held to a stable ±0.02 mm tolerance, on workpieces up to 1000 × 600 mm, with critical features verified on a temperature-controlled Zeiss CMM after full stress relaxation. We cover the full chain — from Grade selection to deburring — so your PEEK part leaves the cell dimensionally stable, not just cut.
By Emma Huang, Engineering Team · Published · Reviewed by Ellie Huang, International Manager
The material that fights back
PEEK (polyetheretherketone) is a high-performance semi-crystalline thermoplastic. It survives 260 °C continuous service, resists nearly every chemical, and is radiolucent and biocompatible — which is exactly why semiconductor, medical and aerospace engineers specify it. But those same properties make it awkward on a CNC mill. In short: PEEK is soft, springy, heat-sensitive, and abrasive once filled. Get any one of those wrong and you get burrs, dimensional drift, melted surfaces, or a tool that dies in minutes. The rest of this guide walks through the five failure modes we see most often and the process controls that beat them.
The 5 hard problems
And how we beat them
1 — Dimensional Drift From Elastic Recovery
PEEK's low modulus (≈3.6 GPa unfilled) lets it deflect under clamping and cutting loads, then spring back after the tool passes. Features measure undersize or out of position right off the machine. We counter this with staged annealing and low-force fixturing to minimize residual stress and post-machining dimensional drift, plus sharp polished tooling and light finishing passes.
2 — Heat Buildup and Surface Melting
PEEK's low thermal conductivity (≈0.25 W/m·K) traps heat at the cutting zone. Push too hard and the surface smears, melts and re-welds. For medical-grade PEEK we machine dry with compressed-air cooling — eliminating cutting-fluid contamination risk entirely — while keeping shear-dominant cutting parameters that avoid rubbing and built-up edge.
3 — Burrs and Fuzzing on Edges
PEEK tears and fringes at edges far more than metal, especially on thin walls and small holes. Our deburring strategy combines in-process edge control with cryogenic (dry-ice) deburring to preserve thin-wall geometry — abrasive tumbling would round or distort the very features you specified.
4 — Abrasive Wear From Fillers
Most functional PEEK is filled: CF30 (30% carbon fiber), GF30 (30% glass fiber) or HPV bearing grades. Fillers turn a soft plastic into an abrasive that eats uncoated carbide fast. For carbon- and glass-filled PEEK we standardize on PCD (polycrystalline diamond) tooling for long tool life and consistent surface finish, with tool-life limits that protect your tolerances.
5 — Holding Tight Tolerance Without Crushing
Customers want metal-class tolerances on a material that deflects and creeps. We hold unfilled PEEK to a stable ±0.02 mm, verify all critical dimensions on a temperature-controlled Zeiss CMM after full stress relaxation, and reserve aggressive clamping for nowhere — soft jaws and locating pins, not brute vice pressure.
PEEK vs metal
Quick decision guide
Factor
PEEK
Aluminum
Stainless
Density
~1.3 g/cm³ (light)
2.7
8.0
Service temp
260 °C
~150 °C (softens)
600+ °C
Chemical resist
Excellent
Fair
Good
Machinability
Tricky (burrs/heat)
Easy
Moderate
Stiffness
Low
High
High
Use PEEK when weight, chemical attack or dielectric properties dominate. Use metal when stiffness and tight-tolerance-per-dollar dominate. We machine all three — tell us the dominant requirement and we will steer the material.
FAQ
Frequently asked questions
We machine unfilled PEEK, CF30 (30% carbon-fiber filled), GF30 (30% glass-fiber filled) and HPV bearing-grade PEEK — the grades most often specified for semiconductor, medical and precision-equipment components.
Unfilled PEEK is held to a stable ±0.02 mm. Filled grades and larger envelopes are quoted per drawing after a DFM review; we confirm the achievable window before any cutting begins.
Medical-grade PEEK is machined dry with compressed-air cooling to eliminate any cutting-fluid contamination risk. Other grades may use coolant where heat control benefits; we decide per part and per grade.
We combine in-process edge control with cryogenic dry-ice deburring. Unlike abrasive tumbling, the cryogenic step preserves thin-wall geometry and leaves clean, defined edges.
Up to a 1000 × 600 mm workpiece envelope. Every critical dimension is measured on a temperature-controlled Zeiss CMM after full stress relaxation — not at the machine, where residual heat and stress would lie to you.
Built for qualified programs.
Our form captures production type, annual quantity and project status up front — so we can focus engineering resources on long-term supply relationships, not one-off inquiries.
Need engineering input first?
Talk to our team about special materials, tolerances or a failed-supplier recovery before you send drawings.