When you move from aluminum to high-performance thermoplastics, everything changes. The speeds. The tooling. The coolant strategy. Even the way you hold the part.
PEEK and PEKK are two of the most sought-after engineering plastics for aerospace, medical, and semiconductor applications. Both offer exceptional chemical resistance, high-temperature stability, and mechanical strength. But from a machinist’s perspective, they behave very differently under the spindle.
PEEK is softer and gummier—prone to burrs that ruin surface finishes. PEKK is stiffer and machines more cleanly—but requires tighter process control to avoid micro-cracking from thermal stress.
If you’re an engineer trying to decide between the two materials—or a machinist troubleshooting a difficult PEEK job—this guide is for you. We’re sharing actual shop-floor parameters we use at Baosheng Industry, not textbook theory.
Explore our CNC machining services for high-performance plastics →
PEEK vs. PEKK: A Quick Materials Snapshot for Engineers
Before we dive into machining parameters, let’s clarify the fundamental differences between these two high-performance thermoplastics.
| Property | PEEK (Unfilled) | PEKK (Unfilled) |
|---|---|---|
| Glass Transition (Tg) | ~143°C (289°F) | ~162°C (324°F) |
| Melting Point | ~343°C (649°F) | ~338°C (640°F) |
| Crystallinity | 30–35% | 25–30% |
| Tensile Strength | 90–100 MPa | 100–110 MPa |
| Flexural Modulus | 3.7–4.0 GPa | 4.0–4.5 GPa |
| Continuous Service Temp | Up to 260°C (500°F) | Up to 260°C (500°F) |
| Typical Applications | Medical implants, fluid handling, electrical insulators, semiconductor wafer guides | Aerospace brackets, oil & gas seals, high-temp connectors, defense components |
| Approx. Material Cost | $$$ (High) | $$$$ (Higher—typically 20–30% more than PEEK) |
| Machinability | Softer, gummier—prone to burrs and “angel hair” | Slightly harder, stiffer—better chip break, cleaner edges |
The Key Takeaway for Engineers:
- Choose PEEK when you need FDA-compliant implantable material, maximum chemical resistance, or a proven medical track record—and you’re willing to manage burr control carefully.
- Choose PEKK when your part operates above 150°C continuously, requires maximum compressive strength, or is exposed to aggressive chemicals—and you need cleaner machined edges.
See our full CNC machining materials guide →
1. PEEK vs. PEKK Tolerances: What’s Actually Achievable
The biggest mistake we see in incoming drawings? Applying metal tolerances to high-performance plastics.
Both PEEK and PEKK are hygroscopic (absorb moisture from the air) and have relatively high coefficients of thermal expansion (CTE). A part machined to ±0.001″ in the morning might shift by a tenth or more by evening if the shop temperature fluctuates.
Here are the realistic tolerance ranges we work with daily at Baosheng:
| Tolerance Feature | PEEK (Unfilled) | PEKK (Unfilled) | Notes |
|---|---|---|---|
| Linear dimensions < 50mm | ±0.05mm (±0.002″) | ±0.038mm (±0.0015″) | PEKK’s stiffer backbone provides better stability |
| Linear dimensions 50–150mm | ±0.10mm (±0.004″) | ±0.075mm (±0.003″) | Thermal expansion becomes significant |
| Hole diameters (standard) | ±0.025mm (±0.001″) | ±0.020mm (±0.0008″) | Reaming recommended for tight holes in both materials |
| Flatness (over 100mm) | 0.10mm (0.004″) | 0.075mm (0.003″) | Stress relief between roughing and finishing is critical |
| Thin walls (min. recommended) | 0.75mm (0.030″) | 0.60mm (0.024″) | PEKK can hold thinner walls with less warping |
| Surface finish (Ra) | 0.8 μm (32 Ra) achievable | 0.4 μm (16 Ra) achievable | PEKK responds better to fine finishing |
Critical DFM Tip: If your design requires a press-fit for a metal dowel pin, specify the hole size after we rough-machine, normalize (let the part stabilize), and then finish. We do this standard on all PEEK and PEKK jobs to eliminate tolerance drift.
Learn why manual DFM catches what automated software misses on plastic parts →
2. PEEK CNC Speeds and Feeds: Our Shop-Floor Parameter Table
This is where textbook values often fail. Running PEEK too slow creates gummy burrs. Running it too fast risks melting the material at the cutting edge.
Here are the actual parameters we use on our shop floor for unfilled PEEK:
| Operation | Tool Type | Surface Speed (SFM) | Feed per Tooth (IPT) | DOC (Roughing) | DOC (Finishing) |
|---|---|---|---|---|---|
| Facing / Peripheral Milling | Uncoated carbide, 2–3 flute, high helix | 400–800 | 0.004–0.012″ | 0.060–0.120″ | 0.005–0.015″ |
| Slot Milling | Uncoated carbide, 2 flute, high helix | 350–650 | 0.003–0.008″ | 0.040–0.080″ | 0.005–0.010″ |
| Drilling | Uncoated carbide, 118°–130° point | 200–350 | 0.004–0.010″ per rev | N/A | Peck every 1×D |
| Reaming | Carbide, straight flute | 80–150 | 0.002–0.004″ per rev | 0.005–0.010″ stock | N/A |
| Tapping | Spiral point or form tap | 30–50 | Per tap spec | 60–65% thread | N/A |
PEEK Tooling Rules (Non-Negotiable):
- Tool material: Sharp, uncoated carbide only. Do not use tools previously used on metals.
- Coating: Avoid TiN, AlTiN, or any coating that generates friction heat. Use polished, uncoated flutes.
- Geometry: High positive rake angle (15°–20°). High helix angle (40°–45°) for chip evacuation.
- Edge prep: Sharp edge. No honing. No chamfer. Any edge rounding will smear the plastic.
PEEK Coolant Strategy:
- Use compressed air or cold air gun for chip evacuation and to keep the cutting edge cool.
- Never use flood coolant unless absolutely necessary. Thermal shock leads to micro-cracks.
- Mist coolant is acceptable for light finishing passes.
Why This Matters: Automated platforms often apply generic plastic parameters that don’t distinguish between PEEK and acrylic. The result? Burrs, melting, and scrapped parts. Our parameters are material-specific and shop-tested.
See how our factory-direct machining avoids platform pricing for exotic materials →
3. PEKK CNC Speeds and Feeds: Tighter Process Window, Better Results
PEKK machines more cleanly than PEEK—if you stay within its narrower process window. Stray outside it, and you’ll get micro-cracks instead of burrs.
| Operation | Tool Type | Surface Speed (SFM) | Feed per Tooth (IPT) | DOC (Roughing) | DOC (Finishing) |
|---|---|---|---|---|---|
| Facing / Peripheral Milling | Uncoated carbide, 2–3 flute, high helix | 300–600 | 0.005–0.010″ | 0.050–0.100″ | 0.005–0.012″ |
| Slot Milling | Uncoated carbide, 2 flute, high helix | 250–500 | 0.004–0.008″ | 0.030–0.060″ | 0.005–0.010″ |
| Drilling | Uncoated carbide, 118°–130° point | 180–300 | 0.003–0.008″ per rev | N/A | Peck every 0.75×D |
| Reaming | Carbide, straight flute | 60–120 | 0.002–0.003″ per rev | 0.005–0.008″ stock | N/A |
PEKK-Specific Process Notes:
- Reduce speeds by 20–25% vs. PEEK. PEKK is stiffer and generates more cutting heat.
- More frequent pecking during drilling (every 0.75×D vs. 1×D for PEEK). Chip packing is a higher risk.
- Cooling is critical. Use cold air gun continuously. Any heat buildup above Tg (~162°C) will cause localized annealing and dimensional instability.
PEKK Tooling: Same rules as PEEK—uncoated carbide, sharp edges, high positive rake. No exceptions.
4. The Burr Problem: How We Achieve Medical-Grade Edges on PEEK
PEEK is notorious for leaving a fine, hair-like burr—machinists call it “angel hair” or “fuzz.” It’s difficult to remove without damaging the surface.
PEKK, due to its stiffer molecular structure, fractures more cleanly at the cutting edge. Burrs are smaller and easier to manage.
Our 4-Step Approach to Burr-Free PEEK Edges:
- Climb Milling Always. Conventional milling pushes the material ahead of the cutter and raises a burr. Climb milling shears cleanly.
- Sharp Tools Only. Tools used for more than 50% of their metal-cutting life should not be used on PEEK. Dedicated tooling for plastics.
- Skip the Deburring Wheel. Mechanical deburring smears PEEK. We rely on cryogenic deflashing or manual removal under magnification with a fresh scalpel.
- Annealing Between Ops. For parts requiring tight flatness, we perform an intermediate annealing step between roughing and finishing.
The result? Edges clean enough for medical implant applications without secondary hand-finishing—which adds cost and variability.
5. PEEK vs. PEKK Machining: Head-to-Head Comparison Table
| Machining Factor | PEEK (Unfilled) | PEKK (Unfilled) | Winner |
|---|---|---|---|
| Ease of Machining | Moderate (burr management required) | Good (cleaner cutting, better chip break) | PEKK |
| Achievable Tolerance | ±0.002″ (< 2″) | ±0.0015″ (< 2″) | PEKK (slightly) |
| Surface Finish Quality | Good (32 Ra typical) | Excellent (16 Ra achievable) | PEKK |
| Burr Formation | High—requires extra process steps | Low to moderate | PEKK |
| Risk of Thermal Damage | Moderate | Higher—requires tight thermal control | PEEK (more forgiving) |
| Cost per Part (Material + Labor) | Lower material cost, but more finishing labor | Higher material cost, but less finishing labor | Application-dependent |
| Dimensional Stability | Good | Better—less post-machining movement | PEKK |
When to Choose PEEK:
- FDA implant-grade material required.
- Cost-sensitive medical or semiconductor project.
- Part geometry is straightforward, burr-prone features are minimal.
When to Choose PEKK:
- Maximum dimensional stability required (tight GD&T).
- Part operates above 150°C in aggressive chemical environment.
- Clean edges are critical and secondary finishing isn’t practical.
- Aerospace or defense application where PEKK’s higher compressive strength is needed.
6. Real Case Study: PEKK Aerospace Connector Housing
Last year, an aerospace client approached us with a challenging PEKK connector housing:
- Material: PEKK (unfilled)
- Critical features: 32 closely spaced pin holes, each requiring ±0.0008″ true position
- Wall thickness: 0.035″ between adjacent holes
- Surface finish: 16 Ra on sealing face
Automated quoting platforms either rejected the part outright (material not available) or quoted with massive surcharges and a “no guarantee on tolerance” disclaimer.
Our approach:
- Rough machined all features, leaving 0.020″ stock.
- Annealed the part to relieve internal stresses.
- Finish machined using cold air gun cooling, uncoated carbide tooling, and optimized peck drilling cycles.
- Verified all 32 hole positions on our CMM.
Result: All holes within ±0.0006″ true position. Sealing face at 14 Ra. Delivered in 14 business days. Cost was 23% below the client’s budgeted amount based on platform quotes.
This is the difference a factory with real plastic machining expertise makes.
Explore our aerospace CNC machining capabilities →
7. Printable Quick-Reference Parameter Card
We’ve compiled the key parameters from this article into a printable quick-reference card that our machinists use on the shop floor.
To get the PDF version delivered to your inbox:
Upload your CAD file for a free DFM analysis and mention “PEEK/PEKK Reference Card” in the notes. We’ll include it with your quote.
Need Help with Your PEEK or PEKK Project?
At Baosheng Industry, we machine hundreds of PEEK and PEKK parts every month for medical device, aerospace, and semiconductor customers. We know these materials intimately—their quirks, their limits, and how to get the best out of them.
Unlike automated platforms with limited material catalogs and generic parameters, we approach every plastic part with material-specific tooling, fixturing, and process strategies.
Upload your CAD file and receive a free DFM analysis within 24 hours—including specific recommendations for your PEEK or PEKK part.
Free DFM Analysis • 24-Hour Engineer Response • AS9100D / ISO 13485 / IATF Certified • ITAR Registered • Open to Factory Visits
Frequently Asked Questions (FAQ)
Q1: What speeds and feeds should I use for machining PEEK?
Answer: For unfilled PEEK, use 400–800 SFM surface speed with uncoated carbide tools at 0.004–0.012 IPT feed. Always use compressed air or cold air gun for cooling. Avoid flood coolant. Reduce speeds if the material shows signs of melting.
Q2: What are the achievable tolerances when CNC machining PEKK?
Answer: PEKK can reliably hold ±0.0015″ (±0.038mm) for features under 2 inches, and ±0.003″ for features up to 6 inches. Its stiffer structure provides better dimensional stability than PEEK, which typically holds ±0.002″ over similar dimensions.
Q3: Why does PEEK burr so much during machining?
Answer: PEEK is relatively soft and ductile, which causes it to deform rather than shear cleanly at the cutting edge. Using sharp, uncoated carbide tools with high positive rake angles and climb milling significantly reduces burr formation.
Q4: Is PEKK easier to machine than PEEK?
Answer: In most respects, yes. PEKK is stiffer and more brittle, which leads to cleaner chip breakage and less burr formation. However, PEKK has a narrower thermal process window—exceeding its glass transition temperature (162°C) can cause micro-cracks.
Q5: Can PEEK and PEKK be machined on standard CNC mills?
Answer: Yes. Both materials can be machined on standard 3-axis and 5-axis CNC mills with the right tooling and parameters. No specialized equipment is required—just material-specific knowledge and process control.
Q6: Do you recommend coolant or dry machining for PEEK and PEKK?
Answer: We recommend compressed air or cold air gun cooling for both materials. Flood coolant can cause thermal shock and micro-cracks, especially in PEKK. Mist coolant is acceptable for light finishing passes on PEEK.
Q7: What’s the cost difference between PEEK and PEKK machining?
Answer: PEKK material costs 20–30% more than PEEK. However, PEKK’s cleaner machining often means less finishing labor, which can partially offset the material premium. The total cost difference depends on part complexity and burr-prone features.
Q8: Does Baosheng offer a printable parameter reference for PEEK/PEKK machining?
Answer: Yes. Request our PEEK/PEKK quick-reference parameter card with your next quote submission. It includes all the speeds, feeds, and tooling recommendations from this guide in a shop-friendly format.
