Deep Hole Drilling Copper Alloys: Beryllium Copper, Brass, and Bronze

Deep Hole Drilling Copper Alloys

Copper alloys are challenging for deep hole drilling because their high ductility, tendency to form built-up edge, and high thermal conductivity differ significantly from steel. However, they are essential materials in electrical, marine, mold-making, and heat exchanger applications.

This guide covers parameters, tool geometry, and practical tips for deep hole drilling common copper alloys.

Copper Alloy Types

Alloy	Composition	Hardness (BHN)	Machinability Rating	Deep Hole Drilling Difficulty
Free-machining brass (C360)	Cu-35Zn-3Pb	80–110	100 (excellent)	Easy
Cartridge brass (C260)	Cu-30Zn	80–120	30	Moderate
Naval brass (C464)	Cu-39Zn-1Sn	100–150	30	Moderate
Phosphor bronze (C510)	Cu-5Sn-0.2P	150–200	20	Moderate-Difficult
Aluminum bronze (C954)	Cu-11Al-4Fe	180–240	20	Moderate-Difficult
Beryllium copper (C172)	Cu-2Be-0.2Co	250–400 (aged)	15	Difficult
Pure copper (C110)	99.9% Cu	70–90	20	Difficult
Tellurium copper (C145)	Cu-0.5Te	80–100	85	Easy

Cutting Speed

Copper Alloy	Gun Drilling (m/min)	BTA (m/min)	Notes
Free-machining brass	80–200	80–180	High speeds possible
Cartridge brass	40–80	40–70	Lower speed for ductility
Phosphor bronze	30–60	30–50	Abrasive — lower speeds reduce wear
Aluminum bronze	25–50	25–45	Tough, abrasive
Beryllium copper (annealed)	30–60	30–50	Moderate
Beryllium copper (aged, HRC 40+)	10–25	10–20	Hard, abrasive
Pure copper	20–40	20–35	Very difficult — maximum heat control needed
Tellurium copper	60–120	60–100	Free-machining

Feed Rate

Copper Alloy	Gun Drilling (mm/rev)	BTA/Ejector (mm/rev)
Free-machining brass	0.025–0.050	0.15–0.35
Cartridge brass	0.015–0.030	0.10–0.25
Phosphor bronze	0.015–0.025	0.08–0.20
Aluminum bronze	0.012–0.025	0.08–0.20
Beryllium copper (annealed)	0.015–0.025	0.10–0.20
Beryllium copper (aged)	0.010–0.020	0.06–0.15
Pure copper	0.010–0.020	0.08–0.18
Tellurium copper	0.020–0.045	0.12–0.30

Tool Geometry Requirements

Key Differences from Steel Tooling

Feature	For Steel	For Copper Alloys
Rake angle	0–6°	8–15° (positive) — reduces cutting forces in ductile materials
Flute surface	As-ground	Polished — prevents chip adhesion, BUE
Edge preparation	0.02–0.05 mm hone	Sharp (< 0.02 mm hone) — sharp edges cut, not burnish
Clearance / relief	6–10°	8–12° — prevents rubbing on gummy surface
Chip breaker	Recommended	Required — ductile copper needs forced chip breaking

Tool Material

Copper Alloy	Carbide Grade	Coating
Brass, free-machining	K10, K20	Uncoated or TiN
Bronze, phosphor bronze	K10, K20	TiAlN
Beryllium copper	Micrograin carbide	AlTiN or DLC
Pure copper	K10, fine-grain	DLC (best BUE resistance) or uncoated

Coolant Requirements

Copper Alloy	Coolant Type	Pressure (bar)	Key Consideration
Brass	Emulsion or oil	30–80	Moderate — brass is easy
Phosphor bronze	Oil	40–100	EP additives help
Beryllium copper	Oil with EP additives	60–120	Heat control is critical
Pure copper	Oil	80–150	Maximum cooling needed

Coolant Temperature

Copper’s high thermal conductivity (385 W/m·K — 10× steel) means heat generated at the cutting edge is rapidly conducted away. This is beneficial for the tool but means the coolant must remove heat from the workpiece — target coolant temperature at 25–35°C.

Chip Control

Chip Type	Indication	Cause	Fix
Long, continuous ribbon	Poor chip breaking	Feed too low	Increase feed 20%
Built-up edge (BUE)	Rough surface finish	Speed too low or tool not polished	Increase speed 15%; check flute polish
Dust-like chips	Overheating	Speed too high	Reduce speed 20%
Galling on guide pads	Material transfer	Wrong coating or clearance	Switch to DLC coating; increase clearance

Application Examples

Example 1: Electrical Connector (Tellurium Copper)

Parameter	Value
Material	C145 tellurium copper
Hole	4 mm × 60 mm deep
Method	Gun drilling
Cutting speed	80 m/min → 6,366 RPM
Feed	0.030 mm/rev
Coolant	Oil, 50 bar
Tool	K10 carbide, uncoated, polished flute

Example 2: Mold Coolant Channel (Beryllium Copper)

Parameter	Value
Material	C172 beryllium copper (aged, HRC 40)
Hole	6 mm × 300 mm deep
Method	Gun drilling
Cutting speed	20 m/min → 1,061 RPM
Feed	0.015 mm/rev
Coolant	Oil with EP, 100 bar
Tool	Micrograin carbide, AlTiN coating

Summary

Copper alloy deep hole drilling requires specific tool geometry adjustments — higher rake angles (8–15°), polished flutes, and sharp edge preparation — to prevent built-up edge and chip adhesion. Free-machining brass and tellurium copper are the easiest copper alloys to drill, approaching steel in machinability. Pure copper and aged beryllium copper are the most difficult — beryllium copper for its high hardness in the aged condition, and pure copper for its extreme ductility. DLC-coated tools significantly reduce built-up edge in gummy copper alloys. For material-specific parameters, see deep hole drilling parameters quick reference. For exotic materials, see deep hole drilling exotic materials.