PEEK CNC Machining: Unfilled, GF30 and CF30 Parts
CHX Metal machines PEEK in unfilled, 30 percent glass-filled and 30 percent carbon-filled grades, holding plus or minus 0.005 mm on critical features after stress-relief annealing. Prototypes run in 3 to 7 days and production in 7 to 15 days, from a minimum of 1 piece, with material certificates supplied per batch.
PEEK is the engineering polymer that replaced metal in a long list of parts: semiconductor wafer handlers, medical instrument components, pump seals, aircraft interior fittings and electrical insulators. It machines well, but only if the process accounts for the two things that ruin PEEK parts — heat and internal stress.
PEEK Grades and What Each One Does
| Grade | Character | Typical part |
|---|---|---|
| Unfilled (natural / black) | Highest elongation and chemical resistance, lowest stiffness | Seals, insulator bodies, fluid handling components |
| PEEK GF30 | 30 percent glass fibre: stiffer, better creep resistance, more abrasive to tooling | Structural brackets, pump housings, valve bodies |
| PEEK CF30 | 30 percent carbon fibre: highest stiffness and lowest thermal expansion, electrically conductive | Wafer handling end effectors, precision fixtures |
| Bearing grade | Graphite and PTFE additions for low friction and wear | Bushings, thrust washers, sliding pads |
Unfilled PEEK has a continuous service temperature around 250 °C, a density near 1.30 g/cm³ and tensile strength around 100 MPa, which is why it holds dimensions in hot fluid service where cheaper polymers creep. Filled grades trade elongation for stiffness and dimensional stability.
Why Machine PEEK Instead of Moulding It
Injection moulding needs a tool that costs more than a small production run of PEEK parts, and PEEK's melt temperature makes that tool expensive to build and to run. Machining wins in three situations: prototypes and design iterations, quantities from one to a few thousand, and parts where the tolerance or the feature geometry cannot be moulded without a secondary operation. Machining also avoids the weld lines and shrinkage that show up in moulded parts at rib intersections.
Machining Rules That Decide Quality
- Sharp, high-rake tooling with polished flutes; a dull cutter rubs, and rubbing melts the surface into a white, stressed layer.
- High speed, moderate feed, low radial engagement so chips clear and heat leaves with them instead of soaking into the part.
- Air blast or flood coolant chosen by feature; compressed air is often better than liquid because PEEK does not need cooling as much as it needs chip evacuation.
- Light clamping with soft jaws and support under thin sections; PEEK deflects far more than aluminium under the same vise pressure.
- Stress relief annealing between roughing and finishing on parts with tight tolerance or large sections, so the material relaxes before the final pass rather than after shipment.
Glass-filled and carbon-filled grades are abrasive: they wear carbide quickly, so inserts are changed on a count rather than on failure, and diamond-coated tooling is used where the finish matters.
Tolerance and Surface Finish
Critical features are machined to ±0.005 mm on annealed, properly supported parts, and verified after the part has cooled and stabilised rather than at the machine with the part still warm. Where a PEEK part is a cover or a guard with no critical fit, we work to ISO 2768-m and say so at drawing review, because applying the tight band there adds cost without function.
Typical finish is Ra 1.6 µm, with Ra 0.8 µm achievable on sealing faces using sharp tooling and a finishing pass. Cosmetic criteria are agreed in writing, since "no machining marks" means different things to different inspectors.
Typical PEEK Parts
- Semiconductor wafer handling end effectors, nest plates and lift pins.
- Medical instrument components and trial parts (the device manufacturer holds the regulatory submission).
- Pump wear rings, seal seats and valve components for chemical service.
- Electrical insulators, standoffs and high-voltage brackets.
- Food and beverage filling machine guides, where PEEK's temperature and chemical resistance matter.
DFM Rules for PEEK
- Keep wall sections uniform; a thick-to-thin transition is where a sink mark or a crack appears after annealing.
- Design corner radii of at least 0.5 mm; sharp internal corners concentrate stress in a notch-sensitive material.
- Avoid threads below M3 in unfilled PEEK; specify a metal insert where the joint will be opened more than a few times.
- State the annealing requirement on the drawing if the part has a tight flatness or bore tolerance.
- Allow for the material's thermal expansion when the part will run hot: PEEK expands roughly four times as much as steel over the same temperature rise.
Send a STEP file and drawing for a feasibility check. Prototypes run in 3 to 7 days and production in 7 to 15 days, from a minimum order of 1 piece, and material certificates are supplied with the parts.
Related Capability Pages
Frequently Asked Questions
Can PEEK be CNC machined? Yes. PEEK machines cleanly with sharp, high-rake tooling and good chip evacuation. The difficulty is not the cut but the heat and the internal stress, so parts with tight tolerance are rough machined, stress-relief annealed, then finished.
What is the difference between unfilled, GF30 and CF30 PEEK? Unfilled PEEK has the highest elongation and chemical resistance but the lowest stiffness. GF30 adds 30 percent glass fibre for stiffness and creep resistance at the cost of tool wear. CF30 adds carbon fibre for maximum stiffness and low thermal expansion, and it conducts electricity.
What tolerance can you hold on PEEK parts? ±0.005 mm on critical features of annealed, well-supported parts; general dimensions follow ISO 2768-m. Unfilled PEEK moves after machining unless it is stress relieved, so the sequence matters as much as the machine.
Why do machined PEEK parts turn white at the edges? That is stress whitening from rubbing rather than cutting: a dull tool, too low a feed or too much heat. It is a process symptom, and it is also a crack initiation site, so we change the tool and the parameters rather than polish it away.
Is PEEK suitable for food and medical contact? PEEK is available in grades intended for those applications and the material certificate states the grade supplied. The compliance decision for a finished device or a food contact surface stays with the customer; we supply parts, certificates and inspection records.
What lead time applies to PEEK parts? Prototypes in 3 to 7 days and production in 7 to 15 days, with annealing adding time on tight-tolerance parts. Orders start at 1 piece.
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