PEEK CNC Machining: Complete Guide to Grades, Properties and Applications                                                                                                                                                                                                                                                                                              

PEEK (Polyether Ether Ketone) is one of the top-performing thermoplastic engineering polymers available. With a continuous service temperature of 250°C, great chemical resistance, and mechanical strength that matches many metals, PEEK has become the go-to material for tough applications in aerospace, medical devices, oil and gas, semiconductor, and automotive industries.

However, PEEK cannot be injection molded by common injection machines — its extremely high melt temperature (around 370°C) and melt viscosity make regular injection molding impractical. The main way to shape PEEK into precision parts is CNC machining. This makes PEEK CNC machining a specialized skill that only experienced manufacturers can deliver consistently.

At Eastmaster Manufacturing in Shenzhen, we have over 25 years of experience in precision CNC machining of high-performance engineering plastics, including PEEK, PTFE, POM, and other advanced polymers. This complete guide covers everything you need to know about PEEK CNC machining — from material grades and properties to machining settings, design tips, and quality control.

What Is PEEK and Why CNC Machine It?

PEEK is a semi-crystalline thermoplastic polymer in the PAEK (Polyaryletherketone) family. Its molecular structure — alternating ether and ketone links with aromatic rings — gives it amazing thermal stability, chemical resistance, and mechanical strength.

Key properties of PEEK:

    Continuous service temperature: 250°C (482°F)

    Short-term peak temperature: 300°C (572°F)

    Tensile strength: 90-100 MPa

    Flexural modulus: 3.5-4.0 GPa

    Density: 1.30-1.32 g/cm³

    Water absorption: <0.5% at 24 hours immersion

    Flame rating: UL 94 V-0 (without additives)

    Biocompatibility: ISO 10993 and USP Class VI compliant (medical grades)

Unlike metals, PEEK can be machined to tight tolerances without the risk of galvanic corrosion, and it weighs around 70% less than stainless steel. These properties make PEEK CNC machining a great alternative to metal parts in weight-sensitive and corrosion-prone applications.

Because PEEK cannot be injection molded due to its extremely high melt viscosity and processing temperature needs, CNC machining is the most practical and widely used method for making PEEK parts — from rapid prototypes to full production runs.

PEEK Grades for CNC Machining

Not all PEEK is the same. Different grades are made for different uses, and the choice of grade greatly affects how easy it is to machine, the cost, and how well the final part performs.

Unfilled (Virgin) PEEK

Unfilled PEEK — also called virgin or natural PEEK — is the base polymer without reinforcing fillers. It gives the best mix of toughness, chemical resistance, and machinability. Unfilled PEEK produces the smoothest surface finishes during CNC machining and is the top choice for applications that need high purity or biocompatibility.

    Best for: Medical implants, semiconductor parts, food-contact parts, chemical processing equipment

    Machinability: Excellent — produces clean, burr-free cuts with proper tooling

    Surface finish: Can reach Ra 0.4-0.8 μm with sharp carbide tools

Glass-Filled PEEK (30% GF)

Adding 30% glass fiber greatly increases stiffness, strength, and dimensional stability. Glass-filled PEEK has higher rigidity and lower thermal expansion, making it good for structural parts that must stay precise at high temperatures.

    Best for: Aerospace brackets, automotive engine parts, industrial pump parts

    Machinability: Good — glass fibers cause moderate tool wear; carbide tools recommended

    Surface finish: Ra 0.8-1.6 μm (slightly rougher due to fiber exposure)

Carbon-Filled PEEK (30% CF)

Carbon fiber reinforcement gives the highest stiffness-to-weight ratio and adds electrical conductivity — a unique feature among engineering plastics. Carbon-filled PEEK is used where ESD (electrostatic dissipation) or electromagnetic shielding is needed.

    Best for: Semiconductor wafer handling, ESD-sensitive areas, aerospace structural parts

    Machinability: Moderate — carbon fibers are abrasive; diamond-coated or CVD tools extend tool life

    Surface finish: Ra 1.2-2.0 μm (fibers can cause micro-chipping on edges)

PEEK Grade Comparison for CNC Machining:

Property	Unfilled PEEK	30% GF PEEK	30% CF PEEK
Tensile Strength	90-100 MPa	140-150 MPa	130-145 MPa
Flexural Modulus	3.5 GPa	9.0-10.0 GPa	12.0-15.0 GPa
Density	1.30 g/cm³	1.51 g/cm³	1.42 g/cm³
Thermal Expansion	47 × 10⁻⁶ /°C	22 × 10⁻⁶ /°C	16 × 10⁻⁶ /°C
Electrical Conductivity	Insulator	Insulator	Conductive (10³-10⁵ Ω)
Tool Wear	Low	Moderate	High
Relative Cost	1.0×	1.2-1.4×	1.5-2.0×

CNC Machining Settings for PEEK

PEEK behaves differently from metals and standard engineering plastics during CNC machining. Its semi-crystalline structure means it softens slowly rather than melting sharply, and it is sensitive to heat buildup from cutting forces. Picking the right settings is key to getting good surface quality, tight tolerances, and long tool life.

Milling Settings（H3）

Parameter	Unfilled PEEK	GF/CF Filled PEEK
Cutting Speed (Vc)	200-500 m/min	100-300 m/min (reduce 30-50% for filled grades)
Feed Rate (fz)	0.05-0.15 mm/tooth	0.03-0.10 mm/tooth
Depth of Cut (ap)	1-3 mm (roughing), 0.2-0.5 mm (finishing)	0.5-2 mm (roughing), 0.1-0.3 mm (finishing)
Coolant	Compressed air or mist preferred; flood OK	Flood coolant recommended to manage fiber dust
Tool Material	Solid carbide, polished flutes	Solid carbide or diamond-coated (CVD/PVD)

Turning Settings

    Cutting speed: 150-400 m/min for unfilled PEEK; 80-200 m/min for filled grades

    Feed rate: 0.05-0.20 mm/rev (finishing); 0.15-0.40 mm/rev (roughing)

    Depth of cut: 0.5-2.0 mm (roughing); 0.1-0.5 mm (finishing)

    Tool geometry: Sharp cutting edge with positive rake angle (10-15°) to reduce cutting forces and heat

Key Machining Tips for PEEK

    Keep heat down: PEEK softens at high temperatures. Use sharp tools, good feed rates, and enough cooling to stop thermal deformation.

    Avoid pausing: Stopping or pausing during cutting can cause local melting and poor surface quality. Keep the tool moving consistently.

    Manage workholding: PEEK has a lower elastic modulus than metals. Too much clamping force can bend the part. Use soft jaws or gentle fixtures.

    Control chip removal: PEEK chips can be stringy (especially unfilled grades). Make sure chips are cleared well to stop re-cutting and surface damage.

    Post-machining annealing: For tight tolerance parts, heat PEEK parts at 200°C for 2-4 hours after machining to remove internal stresses and keep dimensions stable.

What Tolerances and Surface Finish Can PEEK Hold?

PEEK can hold tighter tolerances than most other engineering plastics, getting close to the precision you can get with metals. This is one of the main reasons engineers pick PEEK for high-precision work.

Tolerance Capabilities

    Standard machining tolerances: ±0.05 mm (±0.002") for general features

    Precision machining: ±0.02 mm (±0.0008") for key dimensions

    Tightest possible: ±0.01 mm (±0.0004") with temperature-controlled room and post-machining annealing

    Hole tolerances: H7 doable with reaming; H8 standard with drilling

    Surface finish: Ra 0.4-0.8 μm for unfilled PEEK; Ra 0.8-1.6 μm for filled grades

For comparison, these tolerances are close to what you can get with aluminum CNC machining, making PEEK a good replacement for metal parts in many precision uses.

Things That Affect Tolerance

    Thermal expansion: PEEK grows about 47 μm/m/°C (unfilled). Temperature changes during machining and measuring can affect results.

    Moisture absorption: Although low (<0.5%), moisture can cause small size changes in wet areas.

    Internal stress: Machining creates internal stresses that can cause slow size changes over time. Annealing removes this effect.

    Filler content: Glass or carbon fiber reduces thermal expansion but adds direction-dependent behavior — sizes along the flow direction differ from across it.

Common Uses of PEEK CNC Machined Parts

Medical and Surgical Devices

PEEK's biocompatibility (ISO 10993, USP Class VI), X-ray transparency, and ability to withstand sterilization make it great for surgical tools, spinal implants, dental devices, and drug delivery parts. CNC machining allows fast iteration of custom implant designs and patient-specific instruments.

Aerospace and Defense

PEEK replaces aluminum and titanium in brackets, connectors, ducting, and interior parts where saving weight and resisting flame are critical. Its UL 94 V-0 rating and low smoke/toxicity make it fit for cabin interior uses.

Oil and Gas / Downhole

PEEK withstands H₂S, NaCl, hydrocarbons, and temperatures up to 250°C continuously — conditions that destroy most polymers and corrode metals. CNC machined PEEK seals, gaskets, insulators, and wear pads are used in downhole tools and subsea equipment.

Semiconductor and Electronics

In semiconductor manufacturing, PEEK's low particle generation, chemical purity, and great electrical properties make it ideal for wafer carriers, CMP retention rings, test sockets, and ion implant parts. Carbon-filled PEEK gives ESD-safe handling for sensitive devices.

Automotive

PEEK is used in transmission parts, turbocharger compressor wheels, fuel system parts, and EV battery connectors. CNC machining allows low-volume production and rapid prototyping for automotive development programs.

Design Tips for PEEK CNC Machined Parts

Designing parts for PEEK CNC machining needs an understanding of the material's special characteristics. Following these tips helps make sure parts can be made well, cost less, and perform reliably.

    Keep wall thickness even: Avoid sudden changes. Use gradual 3:1 slope ratios to lower internal stress and distortion.

    Set realistic tolerances: Don't over-specify. ±0.05 mm is doable for most features; save ±0.02 mm only for key mating surfaces.

    Think about chip removal: Deep pockets and narrow slots need enough room for tool clearance and chip clearing. Design with tool access in mind.

    Plan for annealing: For tight tolerance parts, plan to anneal after rough machining, then finish machine to final sizes.

    Avoid sharp inside corners: Use generous corner radii (at least 0.5 mm) to reduce stress buildup and help tools last longer.

    Plan for holding the part: Include holding features (tabs, flats, or datum surfaces) that let you hold the part securely without too much clamping force.

    State surface finish needs: Ra 0.8 μm is standard for PEEK. Finer finishes (Ra 0.4 μm) are doable but cost more.

PEEK vs. Other High-Performance Plastics for CNC Machining

PEEK is not the only high-performance engineering plastic, but it is often the best choice for the toughest applications. Here is how it compares to other options commonly used in CNC machining of engineering plastics:

Property	PEEK	PTFE	POM (Delrin)	PEI (Ultem)
Max Temp (continuous)	250°C	260°C	90°C	170°C
Tensile Strength	100 MPa	20-30 MPa	60 MPa	110 MPa
Chemical Resistance	Excellent	Superior	Poor (acids)	Good
Machinability	Good	Poor (gummy)	Excellent	Good
Biocompatibility	Yes (implant grade)	Yes	No	Yes (select grades)
Relative Cost	High	Medium	Low	Medium-High

PEEK is the top choice when thermal performance, chemical resistance, and mechanical strength all need to be excellent at the same time. For less demanding temperature needs, POM or PEI may give better value for the cost.

Why Choose Eastmaster for PEEK CNC Machining

Eastmaster Manufacturing has specialized in CNC precision machining of high-performance engineering plastics for over 25 years. Our capabilities include:

    Full range of PEEK grades: Unfilled, 30% GF, 30% CF, and medical-grade implantable PEEK

    3, 4, and 5-axis CNC machining centers with high-speed spindles (up to 24,000 RPM)

    Temperature-controlled machining room for tight tolerance work

    Post-machining annealing capability for stress relief and dimensional stability

    Full dimensional inspection with CMM, optical comparator, and surface roughness testers

    ISO 9001 and ISO 13485 certified quality management

    D-U-N-S verified: 66-849-8033

Whether you need a single prototype part or a production batch of thousands, our engineering team can help you pick the right PEEK grade, improve your design for CNC machining, and deliver parts that meet your exact specs.

Contact Eastmaster today to discuss your PEEK CNC machining project.

• Email: info@eastmaster.com 
• Phone: +86 755 22676100
• WhatsApp / WeChat available on the right side.