Deep Hole Drilling Exotic Materials: Ceramics, Composites, and Plastics

Deep Hole Drilling Exotic Materials

Some materials cannot be deep hole drilled with conventional carbide tooling, or require specialized approaches that differ significantly from metal drilling. Ceramics, fiber-reinforced composites, engineering plastics, and glass each demand unique tooling and methods.

This guide covers deep hole drilling strategies for non-metallic and exotic materials.

Composite Materials (CFRP, GFRP)

Carbon fiber and glass fiber reinforced polymers are increasingly common in aerospace, automotive, and sporting goods.

Challenges

Challenge	Why	Consequence
Abrasive fibers	Carbon and glass fibers are extremely hard	Rapid tool wear — only diamond tooling works
Delamination	Fibers can separate at entry and exit	Scrapped parts
Heat sensitivity	Epoxy resin matrix softens above its Tg (~150°C)	Resin melting, fiber pullout
Dust	Drilling produces fine, conductive dust (CFRP)	Health hazard; machine contamination

Recommended Method

Method	Suitability	Tooling
Gun drilling	Fair — only with diamond tooling	PCD or CVD diamond-tipped
Conventional drilling	Poor — delamination at entry/exit	Diamond-coated step drills
EDM	Not applicable	CFRP not conductive
Laser	Good for thin composites	No tool wear

Tooling

Tool Type	Material	Life Expectancy
Gun drill tip	CVD diamond or PCD	10–50× carbide life
Guide bushing	Cemented carbide	Standard
Backup (exit support)	Hard plastic or wood	Prevents exit delamination

Parameters (Gun Drilling, CVD Diamond Tooling)

Material	Speed (m/min)	Feed (mm/rev)	Notes
CFRP (woven fabric)	50–100	0.010–0.025	Use backup plate at exit
CFRP (unidirectional)	40–80	0.008–0.020	Avoid fiber fraying
GFRP	40–80	0.010–0.030	Glass fibers more abrasive than carbon
Kevlar	30–60	0.010–0.020	Very tough; use sharpest tool possible

Coolant

Parameter	Recommendation
Coolant type	Compressed air or mist (most common)
Coolant pressure	Low — just enough for dust control
Liquid coolant	Not recommended (resin absorbs fluid)

Engineering Plastics

Plastics like PEEK, PTFE, nylon, acetal (Delrin), and polycarbonate can be deep hole drilled but require modified parameters.

Challenges

Challenge	Why	Consequence
Low melting point	Plastics soften at low temperatures	Melted plastic on tool; poor finish
Springback	Elastic recovery reduces drilled diameter	Undersize holes
Chip control	Plastic can produce stringy, sticky chips	Chip packing; built-up edge
Thermal expansion	Plastic expands more than steel	Oversize holes at temperature

Parameters (Gun Drilling)

Material	Speed (m/min)	Feed (mm/rev, Ø12 mm)	Coolant
PEEK	30–60	0.015–0.040	Air mist or light coolant
PTFE / Teflon	20–50	0.010–0.030	Air mist
Nylon (PA66)	40–80	0.010–0.040	Coolant recommended
Acetal / Delrin	50–100	0.015–0.050	Coolant recommended
Polycarbonate	30–60	0.010–0.030	Coolant required

Tooling for Plastics

Feature	Recommendation
Tool material	Carbide (K10–K15), polished
Coating	Uncoated or DLC
Edge	Sharp — no edge hone
Nose grind	N-4 (wider relief angle)
Flute	Highly polished — prevents material adhesion

Ceramics

Ceramics present the greatest challenge: they are extremely hard, brittle, and non-conductive (except for some advanced ceramics).

Challenges

Challenge	Why
Extreme hardness	Harder than carbide — cannot be cut mechanically
Brittleness	Cracks and chips under mechanical load
Non-conductive	EDM requires conductive materials

Recommended Methods

Material	Primary Method	Alternative
Alumina (Al₂O₃)	Laser drilling	Diamond grinding
Zirconia (ZrO₂)	Laser drilling	Diamond grinding
Silicon carbide (SiC)	Laser or diamond	—
Macor (glass-ceramic)	Conventional gun drilling (possible)	Diamond tooling
Green ceramics (unfired)	Gun drilling (before firing)	Carbide tooling

Machinable Ceramics

Some ceramics (Macor, Shapal) are machinable with carbide tooling before final firing:

Material	Speed (m/min)	Feed (mm/rev)	Coolant
Macor (machinable glass-ceramic)	20–50	0.008–0.020	Air or mist
Green ceramics (unfired)	30–80	0.010–0.030	Air (must keep dry)

Pre-Firing Drilling

For most ceramics, the practical approach is to drill the hole before firing (green state). The material is much softer and can be machined with standard carbide tooling. After firing (sintering), the hole diameter will shrink by approximately 15–20% — account for this when selecting the pre-fire drill diameter.

Glass

Method	Diameter	Depth	Feasibility
Laser drilling	0.01–2 mm	Up to 20:1	Good — fastest method
Diamond core drilling	2–50 mm	Up to 10:1	Good — common for larger holes
Ultrasonic drilling	1–20 mm	Up to 5:1	Good for hard/brittle glass
Conventional gun drilling	Not possible	—	Glass shatters under mechanical load

Method Selection Matrix

Material	Method 1	Method 2	Tool Material	Coolant
CFRP/GFRP	Gun drilling (diamond)	Laser (thin)	CVD diamond/PCD	Air
Kevlar	Gun drilling (diamond)	Laser	PCD	Air
PEEK	Gun drilling	Conventional drilling	Carbide, polished	Coolant or mist
PTFE	Gun drilling	—	Carbide, polished	Air mist
Alumina ceramic	Laser	Diamond grinding	Diamond	Water
Zirconia	Laser	—	Diamond	Water
Green ceramic	Gun drilling	Conventional	Carbide	Air
Glass	Laser	Diamond drill	Diamond	Water
Graphite	Gun drilling (diamond)	—	CVD diamond	Air

Summary

Exotic materials require method-specific approaches. Composites (CFRP/GFRP) can be deep hole drilled with diamond-tipped gun drills and air cooling, but require backup plates to prevent exit delamination. Plastics (PEEK, PTFE, nylon) use standard carbide tooling with reduced speeds (30–80 m/min), polished flutes, and sharp edges. Ceramics are best drilled before firing (green state) or with laser/EDM methods after firing. Glass requires diamond tooling or laser drilling — conventional mechanical drilling will shatter it.

For non-conventional methods, see EDM and laser drilling guide. For tool materials, see cutting tool materials guide. For a complete overview, visit the materials-specific drilling guide.