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PEEK CNC Machining: Best Practices, Tolerances & Surface Finish

PEEK Machining Characteristics

Why PEEK Machines Well

· Low cutting forces — reduces tool wear and machine deflection

· Clean chip formation — no stringy chips or built-up edge

· No abrasive fillers (unfilled grades) — extends tool life

· Good thermal conductivity — dissipates cutting heat

· Dimensional stability — maintains tolerances after machining

Challenges

· Low thermal conductivity (compared to metal) — heat builds up at cutting zone

· Softening temperature (143°C Tg, 343°C melt) — can smear if overheated

· Internal stress — from manufacturing process, can cause warpage

· Filled grades (GF30, CF30) — abrasive, require special tooling

Tool Selection

Unfilled PEEK

Tool Type	Recommendation	Notes
End mills	Carbide, 2-flute, sharp	Positive rake, polished flutes
Drills	Carbide, 118° point	Peck drilling recommended
Turning inserts	Carbide, sharp, positive	C-grade or uncoated
Taps	Spiral flute	For blind holes

Filled PEEK (GF30/CF30)

Tool Type	Recommendation	Notes
End mills	PCD or CVD diamond coated	Glass/carbon fibre is abrasive
Drills	Carbide, diamond coated	Extended tool life
Turning inserts	CBN or PCD	Premium tooling required

Machining Parameters

Spindle Speed & Feed

Operation	Unfilled PEEK	Filled PEEK (GF30/CF30)
Face milling	200–400 m/min, 0.1mm/tooth	100–200 m/min, 0.08mm/tooth
End milling	150–300 m/min, 0.05–0.1mm/tooth	80–150 m/min, 0.03–0.08mm/tooth
Drilling (Ø10mm)	3000–6000 RPM, 0.1mm/rev	1500–3000 RPM, 0.08mm/rev
Turning	200–400 m/min, 0.05–0.15mm/rev	100–200 m/min, 0.05–0.1mm/rev
Tapping	500–1000 RPM	300–500 RPM

Coolant Recommendations

· Air blast: Preferred for unfilled PEEK — prevents chip melting, no contamination

· Flood coolant: Use for deep holes and aggressive cuts

· MQL (Minimum Quantity Lubrication): Good compromise

· No coolant: Possible for light finishing cuts

Achievable Tolerances

Dimension Type	Standard Tolerance	Precision Tolerance
Linear (≤25mm)	±0.10mm	±0.025mm
Linear (>25mm)	±0.15mm	±0.05mm
Hole diameter	H8	H7
Bore diameter	H8	H7
Flatness (per 100mm)	0.05mm	0.02mm
Surface finish (Ra)	1.6µm	0.4µm
Thread class	6H/6g	4H/4g

Surface Finish Options

Method	Ra Achievable	Application
Standard milling	1.6–3.2µm	General purpose
Finish pass	0.8–1.6µm	Visible surfaces
Diamond turning	0.1–0.4µm	Optical/sealing
Polishing	0.05–0.1µm	Medical implants
Bead blasting	1.0–2.0µm	Matte finish
Anodising	N/A	Not applicable to PEEK

Stress Relief Procedure

PEEK stock contains internal stresses from the manufacturing process. For precision parts:

1. Rough machine to within 0.5mm of final dimensions

2. Stress relieve at 150°C for 2 hours (air or nitrogen atmosphere)

3. Cool slowly to room temperature (≤ 30°C/hour)

4. Finish machine to final dimensions

This procedure reduces warpage in thin-wall and asymmetrical parts by 70–90%.

Best Practices Summary

1. Use sharp, polished carbide tools with positive geometry

2. Keep cutting temperature below 140°C (PEEK softening point)

3. Use air blast for chip removal and cooling

4. Apply stress relief between rough and finish operations

5. Take light finish passes (0.1–0.25mm) for best surface finish

6. Use soft jaws or vacuum fixtures to prevent clamping distortion

7. Allow 24-hour acclimatisation before final inspection

8. Dry PEEK before machining (if moisture-sensitive operation)

For PEEK product information, see our PEEK Plastic Sheet Guide. For machining services, contact NAGOMER.

FAQ

Q1: Can PEEK be CNC machined with standard equipment?

Yes, PEEK can be machined with standard CNC mills, lathes, and drills using carbide tooling. No specialized equipment is needed. However, parameters (speed, feed, depth of cut) must be optimized for PEEK’s thermal properties to prevent melting or smearing.

Q2: What tolerance can be achieved when machining PEEK?

Standard machining achieves ±0.10mm for dimensions up to 25mm. With proper stress relief and finish passes, precision tolerances of ±0.025mm are achievable. Surface finishes of Ra 0.4µm are possible with diamond turning.

Q3: Should PEEK be stress-relieved before or after machining?

Stress relief should be performed between rough and finish machining. Rough machine to within 0.5mm, stress relieve at 150°C for 2 hours, cool slowly, then finish machine. This reduces warpage by 70–90% in precision parts.

Q4: What tools are needed for glass-filled PEEK (GF30)?

Glass-filled PEEK requires PCD (polycrystalline diamond) or CVD diamond-coated tools due to the abrasive nature of glass fibres. Standard carbide tools wear rapidly and may need replacement after every 1–2 parts.

Need precision-machined PEEK components? Contact NAGOMER for CNC machining services, or explore our PEEK stock shapes.

NAGOMER — Professional Engineering Plastics Solutions

www.nagomer.com | info@nagomer.com