Deep Hole Drilling of High-Performance Polymers (PEEK, PEKK, PTFE)

High-performance engineering polymers — PEEK (polyetheretherketone), PEKK (polyetherketoneketone), PTFE (polytetrafluoroethylene), and their reinforced variants — are increasingly specified in medical implants, aerospace components, and semiconductor equipment for their chemical resistance, high-temperature stability, and radiolucency.

Deep hole drilling of these materials presents challenges that are opposite to those of metals: low thermal conductivity traps heat in the polymer, elastic recovery can reduce hole diameter, and chip evacuation requires different tool geometry.

This guide covers material-specific drilling parameters, tooling requirements, and quality considerations for high-performance polymer deep hole drilling.

Material Characteristics

Polymer Types

Polymer	Max Service Temp	Tensile Strength	Modulus of Elasticity	Key Application	Drilling Difficulty
PEEK (unfilled)	250°C	90–100 MPa	3.6 GPa	Medical implants, aerospace	Moderate
PEEK (30% CF)	250°C	200–250 MPa	15–20 GPa	Aerospace structural	Moderate-difficult
PEKK	260°C	90–110 MPa	4.0 GPa	Aerospace, 3D printing	Moderate
PTFE	260°C	20–35 MPa	0.5 GPa	Seals, chemical equipment	Difficult (soft, deforms)
PPSU (polyphenylsulfone)	180°C	70–80 MPa	2.4 GPa	Medical, food processing	Moderate
POM (acetal)	100°C	60–70 MPa	2.8 GPa	General engineering	Easy

Key Properties Affecting Drilling

Property	PEEK	PTFE	Typical Metal (for comparison)	Impact on Drilling
Thermal conductivity	0.25 W/m·K	0.25 W/m·K	50 W/m·K	Heat stays at cutting zone — melts polymer
Coefficient of thermal expansion	47 × 10⁻⁶/K	120 × 10⁻⁶/K	11 × 10⁻⁶/K	Hole shrinks on cooling — oversize risk
Elastic recovery	5–10%	20–40%	< 0.1%	Hole diameter can be smaller than drill
Melting point	343°C	327°C	1,400°C	Thermal damage is melt/degrade, not burn
Glass transition (Tg)	143°C	130°C	N/A	Mechanical properties degrade above Tg
Abrasive fillers (CF/GF)	Yes (30% CF)	None	N/A	Rapid tool wear with reinforced grades

The Challenge of Drilling Polymers

Thermal Management

The most critical challenge — polymers conduct heat 200× less effectively than steel:

Problem	Cause	Consequence
Heat accumulation at cutting tip	Low thermal conductivity	Polymer melts or softens locally
Chip adhesion	Softened polymer sticks to tool	Chip packing, flute blockage
Re-solidified material on bore	Melted polymer re-solidifies on hole wall	Rough surface, dimensional inaccuracy
Dimensional change on cooling	High CTE + poor heat dissipation	Hole shrinks below target diameter

Chip Control

Polymer chips behave differently from metallic chips:

Material	Chip Type	Chip Control Strategy
Unfilled PEEK	Continuous, stringy ribbon	Sharp tool for chip breakage; peck cycles
CF-reinforced PEEK	Abrasive dust + short chips	Vacuum extraction; coolant flushing
PTFE	Gummy, continuous ribbon	Very sharp tool; high coolant flow
POM	Powdery, short chips	Easy — self-clearing

Tooling Selection

Cutting Tool Material

Tool Material	PEEK (unfilled)	PEEK (CF-reinforced)	PTFE	Best For
Uncoated carbide	✅ Excellent	✅ Good (fine grain)	✅ Excellent	General use
PCD	✅ Excellent	✅ Excellent	Not needed	High-volume CF-reinforced
Diamond-coated	✅ Excellent	✅ Excellent	Not needed	CF-reinforced, long runs
HSS	⚠️ Acceptable	❌ Not suitable	⚠️ Acceptable	Low-volume only

Recommendation: Uncoated fine-grain carbide for unfilled polymers. PCD or diamond-coated for carbon fiber-reinforced grades.

Tool Geometry

Geometry Feature	Metal Drilling	Polymer Drilling	Rationale
Point angle	118–140°	60–90°	Lower point angle reduces thrust — prevents part deflection
Rake angle	0–6°	10–20° positive	Positive rake shears polymer cleanly
Clearance angle	8–12°	12–20°	Higher clearance prevents rubbing and heat buildup
Edge preparation	0.02–0.05 mm hone	Sharp — no hone	Any edge radius increases cutting forces and heat
Coolant hole	Standard	Standard	Coolant is still needed for chip evacuation
Flute polish	Standard	High polish required	Reduces chip adhesion in flute

Tool Coatings

Coating	Purpose	Recommendation
Uncoated	—	✅ Best for unfilled polymers — sharpest edge
DLC (diamond-like carbon)	Reduces chip adhesion	✅ Recommended — prevents polymer sticktion
CrN	Moderate release	⚠️ Acceptable
TiAlN	Thermal barrier	❌ Not needed — polymers don’t generate metal-level heat

Parameter Guidelines

Speed and Feed

Material	Cutting Speed (m/min)	Feed Rate (mm/rev)	Coolant Pressure
PEEK (unfilled)	80–200	0.02–0.10	30–60 bar
PEEK (30% CF)	60–150	0.02–0.08	40–80 bar
PEKK	80–180	0.02–0.08	30–60 bar
PTFE	50–150	0.02–0.15	20–40 bar
PPSU	80–180	0.02–0.10	30–60 bar
POM (acetal)	100–250	0.03–0.15	20–50 bar

Starting parameters (PEEK, Ø6 mm gun drill):

Speed: 120 m/min (6,400 RPM)
Feed: 0.05 mm/rev
Coolant: Water-based emulsion at 40 bar

Peck Cycle Recommendations

L/D Ratio	Peck Depth	Retract	Purpose
< 20:1	Full depth	—	—
20:1–50:1	10–15× diameter	10–20 mm	Chip clearance + heat dissipation
50:1–100:1	5–10× diameter	20–30 mm	Prevent melting at depth
> 100:1	3–5× diameter	30–50 mm	Extended cooling time needed

Coolant Strategy

Coolant Selection

Coolant Type	PEEK (unfilled)	PEEK (CF)	PTFE	Recommendation
Water-based emulsion	✅ Good	✅ Good	✅ Good	Best for most polymer drilling
Compressed air only	⚠️ Short holes only	⚠️ Short holes only	⚠️ Short holes only	Risk of melting at depth
Neat oil	❌ Avoid	❌ Avoid	❌ Avoid	Can attack some polymers
No coolant	❌ Not recommended	❌ Not recommended	❌ Not recommended	Heat accumulation melts polymer

Note: Verify coolant compatibility with the specific polymer grade — some polymers absorb water (hygroscopic) or react with coolant additives.

Coolant Parameter Guidelines

Parameter	Unfilled PEEK	CF-Reinforced PEEK
Pressure	30–60 bar	40–80 bar
Flow rate (Ø6 mm)	10–20 L/min	12–25 L/min
Temperature	20–35°C (no chiller needed)	20–35°C
Filtration	50–100 micron	50–100 micron

Hole Quality

Expected Quality

Quality Metric	PEEK (unfilled)	PEEK (CF-reinforced)	PTFE
Diameter tolerance	IT8–IT10 (H8–H10)	IT9–IT11	IT10–IT12
Surface finish (Ra)	0.8–1.6 µm	1.6–3.2 µm	1.6–4.0 µm
Bore appearance	Smooth, glossy	Slightly rough (fiber ends visible)	Soft, matte finish
Straightness	0.05–0.15 mm per 100 mm	0.08–0.20 mm per 100 mm	0.10–0.30 mm per 100 mm

Common Defects and Solutions

Defect	Cause	Solution
Hole undersize	Elastic recovery after drilling	Use 0.02–0.05 mm oversize drill; reduce feed rate
Bore melting / smearing	Heat accumulation	Increase coolant pressure; peck cycle; reduce speed
Fibers protruding (CF-PEEK)	Cutting edge dull	Replace tool; use PCD tooling
Chip packing	Insufficient chip clearance	Increase peck frequency; polish flutes
Exit burr	Polymer deformation at exit	Reduce feed at exit; backup support
White haze on bore	Coolant incompatibility	Check coolant-polymer compatibility

Material-Specific Guidance

PTFE Drilling

PTFE presents unique challenges due to its extreme softness and high elasticity:

Parameter	PTFE Recommendation	Why
Drill oversize	+0.05 to +0.15 mm	Elastic recovery: PTFE can recover 20–40%
Feed rate	0.05–0.15 mm/rev	High feed reduces time for elastic deformation
Speed	50–150 m/min	Moderate to prevent frictional heat
Tool sharpness	Extremely sharp	Dull tool deforms PTFE rather than cutting
Coolant	Water-based or air blast	Flood is ideal; air acceptable for shallow holes

CF-Reinforced PEEK Drilling

Carbon fiber reinforcement introduces abrasive wear and fiber protrusion issues:

Parameter	CF-PEEK Recommendation	Why
Tool material	PCD or diamond-coated carbide	CF is highly abrasive
Tool life factor	1/3 to 1/2 of unfilled PEEK	Abrasive wear shortens tool life
Speed reduction	20–30% below unfilled PEEK	Reduces heat and fiber damage
Feed adjustment	Similar to unfilled PEEK	Feed has less effect on fiber damage than speed

Applications Requiring Deep Hole Drilling

Component	Material	Typical Hole Spec	Industry
Interference screw (ACL reconstruction)	PEEK	Ø2.0–4.5 mm × 20–40 mm	Medical
Spinal cage	PEEK	Ø3–6 mm × 15–30 mm	Medical
Aerospace bracket	PEEK (30% CF)	Ø4–12 mm × 30–100 mm	Aerospace
Chemical pump housing	PTFE	Ø6–20 mm × 50–150 mm	Chemical processing
Semiconductor wafer handling	PEEK	Ø3–10 mm × 50–200 mm	Semiconductor
Seal/gasket assembly	PTFE	Ø2–15 mm × 20–80 mm	General industrial

Summary

Deep hole drilling of high-performance polymers requires a fundamentally different approach than metal drilling: sharper tools with positive rake, lower point angles, and aggressive coolant to manage heat accumulation. Unfilled PEEK and PEKK drill well with sharp uncoated carbide tools at speeds of 80–200 m/min. Carbon fiber-reinforced grades require PCD or diamond-coated tooling due to abrasive wear. PTFE demands careful oversize compensation for elastic recovery. Liberal coolant use is essential — not primarily for lubrication, but to remove the heat that would otherwise melt the polymer and ruin the bore surface.

For a comparison with other lightweight materials, see the exotic materials drilling guide. For medical implant drilling using PEEK, refer to the medical implant guide.