PEEK CNC Machining
PEEK is the material you specify when the part has to survive something the cheaper plastics cannot: 250 °C continuous, steam and solvents, repeated sterilisation, or a load at temperature. It is also the most expensive plastic we machine, and the gap to PTFE or POM is large enough that the choice should be justified by a property the part actually needs.
Specification at a glance
- Generic name
- PEEK (polyetheretherketone)
- Family
- Semi-crystalline engineering thermoplastic
- Tensile strength
- ≈ 100 MPa (unfilled)
- Density
- 1.30 g/cm³
- Continuous service temperature
- ≈ 250 °C
- Glass transition (Tg)
- ≈ 143 °C
- Water absorption (24 h)
- ≈ 0.1–0.5%
- Common grades
- Unfilled, 30% glass-filled, 30% carbon-filled, bearing grade
- Typical finish
- As machined · annealed after machining for tolerance-critical parts
- MOQ
- From 50 pieces (samples from 1)
PEEK is not a general-purpose plastic with a better datasheet. It is a specialist material that earns its price in four specific conditions, and loses to cheaper plastics in every other case.
Where PEEK is the right answer
Temperature plus load. Continuous service around 250 °C, with a tensile strength near 100 MPa at room temperature that it largely retains at 150 °C. Nylon and POM soften well before that; PTFE creeps under load at any temperature.
Chemical exposure. PEEK resists most organic solvents, acids, bases and hydrocarbons. It is attacked by concentrated sulphuric acid and some halogenated compounds, but for the solvents, fuels and cleaning agents that appear in pumps and process equipment, it is effectively inert.
Steam and sterilisation. Repeated autoclave cycles do not hydrolyse PEEK the way they attack nylon. That is why it appears in medical instruments, dental handpieces and food-processing hardware.
Low water absorption. Around 0.1–0.5% in 24 hours, against nylon’s several percent. A PEEK part holds its dimension in a wet environment, which matters for anything with a close fit.
Where it is the wrong answer
Cost. PEEK stock can cost ten times POM and twenty times PTFE by weight, and it machines slower with faster tool wear. On a part that only needs moderate strength and no heat resistance, specifying PEEK multiplies the price for a property nobody uses.
Impact. Unfilled PEEK is strong but not tough the way polycarbonate is. For a housing or a cover that gets dropped, PC or ABS-polycarbonate is the better material.
UV. PEEK is not a UV-stable material for long outdoor exposure. If the part lives in sunlight, that is a separate specification.
Very tight tolerance in thin sections. Like any semi-crystalline plastic, PEEK moves after machining if the section is thin. Stress-relief annealing helps; a design that removes the thin section helps more.
How it machines
PEEK cuts cleanly with sharp, positive-rake tooling and generous coolant or air blast. Two practical rules:
Keep the heat in the chip, not in the part. PEEK conducts heat poorly, so a dull tool pushes heat into the workpiece and the surface can smear or discolour. Sharp tools and a feed that takes a real chip keep the cut cool.
Anneal after machining for tolerance-critical parts. Cutting releases internal stress; a stress-relief anneal brings the part back to a stable state before final inspection.
Filled grades behave differently: 30% glass or carbon fill raises stiffness and lowers the thermal expansion, but both are abrasive and shorten tool life. A bearing grade (PEEK with PTFE and graphite) is used where the part itself is the wear surface.
What to send with a PEEK inquiry
Grade (unfilled, glass-filled, carbon-filled, bearing), the temperature the part actually sees, the chemical it contacts, whether it carries load, the tolerance on the critical fit, and the quantity. Those six items decide both the price and whether PEEK is necessary — and if it is not, we will say so at quotation rather than after the parts are made.
Frequently asked
- What is PEEK used for in machined parts?
- Seals, bearings, valve seats, pump components, electrical insulators and semiconductor parts — anything that needs temperature resistance plus chemical resistance plus a load-bearing surface.
- PEEK vs PTFE — which should I choose?
- PTFE has the lower friction and the better chemical resistance, but it creeps under load and has a much lower stiffness. PEEK holds a load at temperature and keeps its dimensions. If the part carries load, PEEK; if it is a sliding seal at low load, PTFE is usually cheaper.
- Why is PEEK so expensive?
- The polymer itself is expensive to synthesise, the stock costs many times a commodity plastic by weight, and it machines slower with faster tool wear. The price reflects material and cycle time together.
- Does PEEK need annealing?
- For tolerance-critical parts, yes — machining releases internal stress in a semi-crystalline plastic, so a stress-relief anneal after cutting keeps the part stable. For non-critical parts it can be skipped.
- Can PEEK be sterilised?
- Yes. It withstands steam autoclave cycles and repeated disinfection without the dimensional change that nylon shows — which is why it appears in medical instruments and dental components.
Related pages
Other Engineering Plastics materials
Have a part in PEEK?
Send the drawing, the grade and the quantity. You get DFM feedback and a price within 24 hours, and orders start at 50 pieces per style and material.