Copper and its alloys — brass and bronze — behave entirely differently from steel in deep hole drilling. Where steel produces predictable chips and responds primarily to cutting speed, copper alloys vary from one of the most machinable materials in existence (free-cutting brass, C360) to one of the most difficult for chip control (pure copper, C110). A parameter set that works perfectly for brass will produce built-up edge and chip packing in pure copper within the first few millimeters of drilling.
This guide covers deep hole drilling of the full range of copper alloys — pure copper, free-cutting brass, cartridge brass, and the major bronze families — with material-specific cutting data, tool selection guidance, and solutions for the chip control problems that distinguish copper alloy drilling from steel drilling.
Material Overview
Copper alloys are classified into three families based on their primary alloying element. Each family has distinctly different machining behavior.
Pure Copper — C11000 (ETP), C10100 (OFHC), C10200 (OF)
| Property | Value |
|---|---|
| Composition | 99.9% Cu minimum |
| Tensile strength (annealed) | 200–250 MPa |
| Tensile strength (cold worked) | Up to 450 MPa |
| Hardness | 35–80 HB (softest of the copper family) |
| Elongation | 35–55% |
| Thermal conductivity | ~401 W/m·K (highest of any common engineering metal) |
| Electrical conductivity | 100% IACS |
| Machinability rating | 20% (relative to C360 brass = 100%) |
Deep hole drilling characteristics: Pure copper is the most challenging copper alloy to deep hole drill. Its high ductility produces long, stringy chips that do not break naturally. It has a strong tendency to form built-up edge (BUE) on the cutting tool. Its high thermal conductivity removes heat rapidly from the cutting zone, which sounds beneficial but actually prevents the localized heating that helps chip breaking in steel. Copper’s softness also allows it to smear rather than shear cleanly.
Free-Cutting Brass — C36000
| Property | Value |
|---|---|
| Composition | Cu 61–63%, Zn 35–37%, Pb 2.5–3.7% |
| Tensile strength | 300–450 MPa |
| Hardness | 55–100 HB |
| Machinability rating | 100% (the industry benchmark) |
Deep hole drilling characteristics: C360 is the easiest copper alloy to drill. The lead content acts as a chip breaker and internal lubricant, producing short, well-broken chips. High cutting speeds and feed rates are possible. Tool life is excellent. This is the default choice for deep hole drilling when the application permits leaded brass.
Cartridge Brass — C26000
| Property | Value |
|---|---|
| Composition | Cu 70%, Zn 30% |
| Tensile strength (hard) | Up to 525 MPa |
| Hardness (hard) | ~82 HRB |
| Hardness (soft) | ~64 HRF |
| Machinability rating | 30% |
Deep hole drilling characteristics: C260 is more ductile than C360 and contains no lead. Chips are stringier and require higher feed rates to break. Cutting speeds must be reduced by 15–25% compared to C360.
Aluminum Bronze — C95400, C95500
| Property | Value |
|---|---|
| Composition | Cu 83–88%, Al 10–11.5%, Fe 3–5% |
| Tensile strength | 550–700 MPa |
| Hardness | 160–210 HB |
| Machinability rating | 60% |
Deep hole drilling characteristics: Aluminum bronze machines like a tough steel, not a soft copper alloy. Its strength and work-hardening tendency require reduced cutting speeds and rigid setups. Uncoated carbide tools wear more rapidly than with steel. This is the most demanding bronze for deep hole drilling.
Bearing Bronze — C93200 (SAE 660)
| Property | Value |
|---|---|
| Composition | Cu 81–85%, Sn 6–8%, Pb 5–8%, Zn 2–4% |
| Tensile strength | 240–310 MPa |
| Hardness | 60–80 HB |
| Machinability rating | 70% |
Deep hole drilling characteristics: Bearing bronze machines readily. The lead and tin content help chip breaking. Moderate cutting speeds with carbide tooling produce good surface finish. This is the most commonly bronze used for deep hole drilling applications.
Phosphor Bronze — C51000, C52100, C54400
| Property | Value |
|---|---|
| Hardness (soft) | 149–163 HB |
| Hardness (1/2 hard) | 187–202 HB |
| Machinability rating | 20–40% |
Deep hole drilling characteristics: Phosphor bronze work-hardens readily and requires sharp cutting tools. In the soft condition it can produce stringy chips. The half-hard condition breaks chips better but increases tool wear. This bronze family is frequently specified for deep hole drilled components in marine and electrical applications due to its corrosion resistance and spring properties.
Machinability Comparison
| Material | Machinability Rating | Chip Type | Relative Tool Wear |
|---|---|---|---|
| C360 Free-cutting brass | 100% (benchmark) | Short, broken | Very low |
| C932 Bearing bronze | 70% | Short to moderate | Low |
| C954 Aluminum bronze | 60% | Moderate to stringy | Moderate |
| C260 Cartridge brass | 30% | Stringy | Low to moderate |
| C510 Phosphor bronze | 20–40% | Stringy (soft); moderate (hard) | Moderate |
| C110 Pure copper | 20% | Long, stringy, gummy | Moderate to high |
Cutting Parameters for Gun Drilling
The following values are compiled from manufacturer data for carbide-tipped gun drills on copper alloys. Starting values are at the conservative end of each range.
Free-Cutting Brass C360
C360 allows the highest cutting speeds of any copper alloy. The lead content provides excellent chip breaking and lubricity.
| Diameter (mm) | Speed (SFM) | Speed (m/min) | Feed (IPR) | Feed (mm/rev) |
|---|---|---|---|---|
| 3–5 | 400–600 | 120–180 | 0.001–0.004 | 0.03–0.10 |
| 5–10 | 350–550 | 105–165 | 0.003–0.008 | 0.08–0.20 |
| 10–15 | 300–500 | 90–150 | 0.006–0.012 | 0.15–0.30 |
| 15–20 | 280–450 | 85–135 | 0.008–0.016 | 0.20–0.40 |
| 20–30 | 250–400 | 75–120 | 0.010–0.020 | 0.25–0.50 |
| 30–50 | 220–350 | 65–105 | 0.012–0.024 | 0.30–0.60 |
C360 can tolerate higher feeds than steel at equivalent diameters because the cutting forces are lower and chip evacuation is easier.
Cartridge Brass C260
C260 requires approximately 20% lower speeds than C360 due to its higher ductility and lack of lead.
| Diameter (mm) | Speed (SFM) | Speed (m/min) | Feed (IPR) | Feed (mm/rev) |
|---|---|---|---|---|
| 3–5 | 320–480 | 95–145 | 0.001–0.003 | 0.03–0.08 |
| 5–10 | 280–440 | 85–135 | 0.003–0.006 | 0.08–0.15 |
| 10–15 | 240–400 | 75–120 | 0.005–0.010 | 0.13–0.25 |
| 15–20 | 225–360 | 70–110 | 0.007–0.013 | 0.18–0.33 |
| 20–30 | 200–320 | 60–95 | 0.008–0.016 | 0.20–0.40 |
For C260, ensure feed rate is high enough to produce broken chips. If chips are stringy, increase feed incrementally until they break.
Pure Copper C110
Pure copper is the most challenging copper alloy for deep hole drilling. The following values are conservative starting points. Success depends more on chip control than cutting speed.
| Diameter (mm) | Speed (SFM) | Speed (m/min) | Feed (IPR) | Feed (mm/rev) |
|---|---|---|---|---|
| 3–5 | 200–350 | 60–105 | 0.001–0.003 | 0.03–0.08 |
| 5–10 | 180–300 | 55–90 | 0.003–0.006 | 0.08–0.15 |
| 10–15 | 160–280 | 50–85 | 0.005–0.010 | 0.13–0.25 |
| 15–20 | 140–250 | 45–75 | 0.006–0.012 | 0.15–0.30 |
Reduce speed if BUE is observed. Copper conducts heat away from the cutting edge so rapidly that the localized heating needed for ductile chip formation does not occur. A sharp, polished cutting edge is essential. Uncoated fine-grain carbide performs better than coated grades for pure copper.
Bearing Bronze C932
| Diameter (mm) | Speed (SFM) | Speed (m/min) | Feed (IPR) | Feed (mm/rev) |
|---|---|---|---|---|
| 3–5 | 300–500 | 90–150 | 0.001–0.004 | 0.03–0.10 |
| 5–10 | 280–450 | 85–135 | 0.003–0.008 | 0.08–0.20 |
| 10–15 | 250–400 | 75–120 | 0.006–0.012 | 0.15–0.30 |
| 15–20 | 225–350 | 70–105 | 0.008–0.015 | 0.20–0.38 |
| 20–30 | 200–300 | 60–90 | 0.010–0.018 | 0.25–0.45 |
Aluminum Bronze C954
Aluminum bronze requires the most conservative parameters of the copper alloy family — comparable to alloy steel at equivalent hardness.
| Diameter (mm) | Speed (SFM) | Speed (m/min) | Feed (IPR) | Feed (mm/rev) |
|---|---|---|---|---|
| 5–10 | 100–180 | 30–55 | 0.003–0.005 | 0.08–0.13 |
| 10–15 | 90–160 | 27–50 | 0.005–0.008 | 0.13–0.20 |
| 15–20 | 80–140 | 24–43 | 0.006–0.010 | 0.15–0.25 |
| 20–30 | 70–120 | 21–37 | 0.008–0.012 | 0.20–0.30 |
Use TiAlN-coated carbide for aluminum bronze. Treat this material like 4140 steel at 200–250 HB. Expect tool life to be approximately 60–70% of what you would achieve in alloy steel at equivalent speeds.
Phosphor Bronze C510/C544
| Diameter (mm) | Speed (SFM) | Speed (m/min) | Feed (IPR) | Feed (mm/rev) |
|---|---|---|---|---|
| 5–10 | 175–250 | 53–76 | 0.003–0.006 | 0.08–0.15 |
| 10–15 | 150–225 | 46–68 | 0.005–0.009 | 0.13–0.23 |
| 15–20 | 130–200 | 40–60 | 0.006–0.011 | 0.15–0.28 |
Use sharp cutting edges. Phosphor bronze work-hardens — a dull tool accelerates wear rapidly.
Cutting Parameters for BTA Drilling
For BTA drilling of copper alloys at diameters above approximately 20 mm, the following ranges apply based on tool manufacturer data.
Brass/Bronze (General) — BTA with Carbide Inserts
| Diameter (mm) | Speed (SFM) | Feed (mm/rev) |
|---|---|---|
| 12.7–17.5 | 295–722 | 0.20 |
| 17.5–24.4 | 295–722 | 0.33 |
| 24.4–35.1 | 295–722 | 0.41 |
| 35.1–47.8 | 295–722 | 0.51 |
Brass and bronze allow the highest BTA speeds of any material group. The limiting factor is typically machine spindle speed, not tool cutting speed. Feed rates can be aggressive. Upper feed range values should be verified for machine power.
Copper (Pure) — BTA with Carbide Inserts
| Diameter (mm) | Speed (SFM) | Feed (mm/rev) |
|---|---|---|
| 12.7–17.5 | 100–250 | 0.10–0.15 |
| 17.5–24.4 | 100–250 | 0.20–0.25 |
| 24.4–35.1 | 100–250 | 0.25–0.30 |
| 35.1–47.8 | 100–250 | 0.30–0.36 |
Copper requires lower speeds and feeds than brass in BTA drilling due to the same chip control challenges faced in gun drilling. BTA’s internal chip evacuation helps with the stringy chip problem, but the cutting edge still requires adequate feed to shear rather than burnish the copper.
Coolant Requirements
Brass and Bronze
Brass and most bronzes have good natural lubricity and do not require high coolant pressure for lubrication. The primary function of coolant in brass deep hole drilling is chip evacuation.
| Material | Recommended Coolant | Pressure Range |
|---|---|---|
| C360 Brass | Oil or emulsion (5–8%) | 300–600 PSI (21–41 bar) |
| C932 Bearing bronze | Oil or emulsion (5–8%) | 400–700 PSI (28–48 bar) |
| C954 Aluminum bronze | Oil recommended; emulsion acceptable | 500–900 PSI (35–62 bar) |
| C510 Phosphor bronze | Oil recommended | 400–700 PSI (28–48 bar) |
Pure Copper
Copper requires more careful coolant management than brass because of its chip control difficulties. The coolant must provide both chip evacuation and lubrication to reduce BUE formation.
| Parameter | Recommendation |
|---|---|
| Coolant type | Low-viscosity oil preferred (provides better lubricity than emulsion) |
| Pressure | 500–1,000 PSI (35–70 bar) |
| Filtration | 10 µm minimum — copper chips are ductile and can clog filters |
| Temperature | Maintain below 100°F (38°C) — copper’s high thermal conductivity transfers heat to the coolant rapidly |
Coolant tip for copper: If BUE is observed despite adequate pressure, consider increasing coolant concentration (for emulsion) or switching to oil. The lubricity of the coolant is more important than its cooling capacity for copper.
Tool Selection
Carbide Grade
| Material | ISO Grade | Coating | Edge Preparation |
|---|---|---|---|
| C360 Brass | K10–K20 | Uncoated or TiAlN | Sharp edge |
| C260 Brass | K15–K25 | TiAlN | Light hone, 0.01–0.03 mm |
| C110 Copper | K10–K15 | Uncoated (polished) | Sharp, polished edge |
| C932 Bearing bronze | K15–K25 | TiAlN | Light hone |
| C954 Aluminum bronze | K20–K30 | TiAlN or AlTiN | Honed edge, 0.03–0.05 mm |
| C510 Phosphor bronze | K15–K25 | TiAlN | Sharp edge |
Key recommendation for copper: An uncoated, polished fine-grain carbide grade outperforms coated grades for pure copper. Copper does not generate enough heat at the cutting interface to activate the thermal barrier properties of TiAlN coatings. The polished surface resists material adhesion better than a coated surface.
Gun Drill Head Profile
- Profile H — Recommended for all nonferrous materials up to 5 mm diameter. Larger back taper than standard profiles.
- Profile I — Specifically designed for aluminum and brass. Provides best hole finish for copper alloys in diameters above 5 mm. Suitable for intersecting holes and interrupted cuts.
- Profile A — Suitable for brass and aluminum in larger diameters. Features large coolant gaps between pads.
For bronze (particularly aluminum bronze), use Profile G (universal) or Profile E, which provide better chip control for the tougher chip formations typical of these materials.
BTA Drill Head
- Brazed carbide heads for diameters under 20 mm
- Indexable heads for diameters 20 mm and above
- Use C2 grade (ISO K20) for general brass/bronze, K10 for pure copper
- Diamond-ground chip formers may be needed for copper — consult the tool manufacturer
Surface Finish and Dimensional Accuracy
| Material | Gun Drilling (Ra) | BTA Drilling (Ra) |
|---|---|---|
| C360 Brass | 0.2–1.0 µm | 0.8–2.0 µm |
| C260 Brass | 0.4–1.6 µm | 1.0–2.5 µm |
| C110 Copper | 0.4–1.6 µm (with sharp tool) | 1.0–3.0 µm |
| C932 Bearing bronze | 0.4–1.6 µm | 0.8–2.5 µm |
| C954 Aluminum bronze | 0.8–2.0 µm | 1.0–3.0 µm |
| C510 Phosphor bronze | 0.4–1.6 µm | 1.0–2.5 µm |
Diameter tolerance: IT7–IT9 achievable for brass and bronze gun drilling; IT8–IT10 for pure copper and BTA drilling.
Brass and bearing bronze can achieve surface finishes comparable to or better than steel because of their natural lubricity. Pure copper is more variable — the same material properties that make chip control difficult also make consistent surface finish harder to achieve.
Common Problems
Built-Up Edge (BUE) — Pure Copper and Cartridge Brass
Symptom: Rough bore surface, fluctuating torque, visible copper material adhered to the cutting edge after tool retraction.
Cause: Copper’s high ductility and thermal conductivity prevent the localized heating that normally causes the chip to shear cleanly. Instead, the chip material welds to the carbide edge.
Solution:
- Use an uncoated, polished carbide grade with a sharp cutting edge
- Increase cutting speed if possible (above 250 SFM for copper) to generate more heat at the cutting interface
- Verify that feed rate is adequate — very low feeds (below 0.02 mm/rev) increase BUE tendency
- Use oil-based coolant for better lubricity
- For cartridge brass (C260), increasing feed is the most effective single adjustment
Stringy Chips — Copper and Soft Bronze
Symptom: Long, continuous chips that wrap around the tool, chip packing in the flute or evacuation tube, torque fluctuations.
Cause: Feed rate too low for the material’s ductility. Soft copper alloys do not break chips naturally.
Solution:
- Increase feed rate until chips break into 6–12 mm segments. For copper, this typically requires 0.08–0.15 mm/rev minimum at diameters above 5 mm.
- Use a gun drill with a chip breaker geometry appropriate for nonferrous materials (Profile I or A).
- If feed rate is already at the upper end of the recommended range, consult the tool manufacturer for a chip breaker modification.
- For BTA drilling, verify that the chip former geometry is designed for ductile materials — standard chip formers designed for steel may not break copper chips effectively.
Copper Packing on Guide Pads
Symptom: Oversized holes, poor surface finish, visible copper transfer to guide pads.
Cause: Copper adheres to the carbide guide pads during the burnishing process. This is unique to pure copper and high-copper alloys.
Solution:
- Verify that guide pad material grade is appropriate for nonferrous applications (some manufacturers offer specialized grades)
- Use sharp cutting edges to minimize the volume of material that reaches the guide pads as burnishing stock
- Consider reducing feed rate slightly to decrease the burnishing load on the guide pads
Work Hardening — Aluminum Bronze and Phosphor Bronze
Symptom: Cutting forces increase progressively through the hole, tool squeal, rapid flank wear.
Cause: These bronzes work-harden when the cutting edge rubs rather than shears — typically from a dull tool or inadequate feed rate.
Solution:
- Maintain minimum feed rate of 0.05 mm/rev for aluminum bronze, 0.03 mm/rev for phosphor bronze
- Use TiAlN-coated carbide with adequate edge hone
- Regrind tools before significant wear develops — aluminum bronze is particularly aggressive on uncoated carbide
- Never dwell while the tool is cutting
Depth Adjustment Factors
When drilling copper alloys at depths exceeding 7× diameter, apply the following adjustments:
| Drilling Depth | Speed Factor | Feed Factor |
|---|---|---|
| < 7×D | 1.0 | 1.0 |
| 7×D to 12×D | 0.9 | 1.0 |
| 12×D to 20×D | 0.8 | 0.9 |
| > 20×D | 0.7 | 0.8 |
For copper (C110), add an additional 5% reduction at each depth level beyond 7×D due to the increased chip evacuation difficulty.
Application Examples
Heat Exchanger Tube Sheet — Naval Brass
Heat exchanger tube sheets are often made from naval brass (C464) or aluminum bronze. Deep holes are gun drilled for tube insertion:
- Typical diameter: 12–30 mm
- Depth: 50–500 mm
- Method: Gun drilling with carbide-tipped tool
- Coolant: Oil at 400–700 PSI
- Note: Tube sheets often have hundreds of closely spaced holes. Tool wander between holes must be controlled — use pilot holes and verify entry position accuracy.
Bearing Cage — Phosphor Bronze
Phosphor bronze bearing cages may require deep holes for lubrication passages:
- Typical diameter: 3–10 mm
- Depth: 50–150 mm
- Method: Gun drilling
- Coolant: Oil preferred; cutting oil flood minimum
- Note: Work hardening is the primary risk. Use sharp tools and replace at the first sign of increased cutting pressure.
Electrical Contact — Pure Copper
High-power electrical contacts and switchgear components may require deep, precise holes for cooling or mounting:
- Typical diameter: 5–15 mm
- Depth: 50–200 mm
- Method: Gun drilling with uncoated polished carbide
- Coolant: Oil at minimum 500 PSI
- Note: Expect shorter tool life than brass. Plan tool changes based on hole count, not cutting time. Chip control is the critical issue.
Summary
Copper alloy deep hole drilling covers an exceptionally wide range of behavior — from the easiest-to-drill material in existence (C360 brass) to one of the most challenging for chip control (pure copper).
- Free-cutting brass (C360) — Maximum speeds, aggressive feeds, excellent surface finish, long tool life. The easiest deep hole drilling material in common use.
- Cartridge brass (C260) — Reduce speeds 20% from C360. Monitor chip breaking. Increase feed if chips are stringy.
- Bearing bronze (C932) — Good machinability. Use carbide tooling with TiAlN coating at moderate speeds.
- Phosphor bronze (C510) — Work-hardens readily. Use sharp tools and maintain minimum feed rates.
- Aluminum bronze (C954) — Treat like steel. Use reduced speeds, TiAlN-coated carbide, and rigid setups.
- Pure copper (C110) — The most difficult copper alloy for deep hole drilling. Use uncoated polished carbide, sharp edges, adequate feed for chip breaking, and higher coolant pressure. Expect shorter tool life than brass.
For related reading, see the Material Machinability Ratings for Deep Hole Drilling, the Speeds and Feeds Reference for Deep Hole Drilling, and the Deep Hole Drilling Troubleshooting Guide.