Appearance
A hydraulic component manufacturer needs to deep-drill 3,000 manifolds per year from C11000 electrolytic copper, with 10 mm diameter × 400 mm deep coolant passages. Standard steel-optimised gun drilling parameters produce severe built-up edge, stringy chip clogging, and rapid tool failure within eight holes. Copper's high ductility and thermal conductivity demand fundamentally different parameters: for gummy electrolytic copper, carbide gun drills at 30–60 m/min with 70–140 bar coolant pressure and aggressive chipbreaker geometry; for free-machining tellurium copper C14500, speeds up to 250 m/min with standard chipbreaker geometry; for leaded brass, the most easily deep-drilled copper alloy with excellent chip breakage and tool life exceeding 500 holes per regrind.
Copper Alloy Properties for Deep Hole Drilling
| Property | C11000 ETP Copper | C14500 Tellurium Copper | Leaded Brass (C36000) | Phosphor Bronze (C51000) |
|---|---|---|---|---|
| Hardness (HB) | 80–110 | 90–120 | 80–110 | 150–200 |
| Tensile strength (MPa) | 220–280 | 250–320 | 340–470 | 310–550 |
| Elongation (%) | 40–55 | 15–25 | 15–25 | 20–40 |
| Thermal conductivity (W/m·K) | 390 | 345 | 120 | 70–90 |
| Machinability rating | 20% | 85% | 100% | 40% |
| Chip formation tendency | Stringy, continuous | Short, brittle | Broken, fine | Segmented to stringy |
| BUE tendency | High | Low | Very low | Moderate |
Cutting Parameter Recommendations
| Parameter | C11000 ETP Copper | C14500 Tellurium Copper | Leaded Brass | Bronze (Phosphor / Aluminium) |
|---|---|---|---|---|
| Cutting speed — carbide gun drill (m/min) | 30–60 | 100–250 | 80–160 | 40–80 |
| Cutting speed — HSS gun drill (m/min) | 15–30 | 40–80 | 40–60 | 15–30 |
| Feed rate — 6 mm dia (mm/rev) | 0.015–0.030 | 0.040–0.080 | 0.050–0.100 | 0.020–0.040 |
| Feed rate — 10 mm dia (mm/rev) | 0.020–0.040 | 0.060–0.120 | 0.080–0.150 | 0.030–0.060 |
| Feed rate — 20 mm dia (mm/rev) | 0.030–0.060 | 0.100–0.200 | 0.120–0.250 | 0.040–0.080 |
| Coolant pressure (bar) | 70–140 | 35–70 | 20–50 | 50–100 |
| Recommended coating | AlCrN / uncoated polished | Uncoated polished | Uncoated | AlTiN |
| Expected surface finish Ra (µm) | 0.8–1.6 | 0.4–0.8 | 0.4–0.8 | 0.8–1.6 |
WARNING
C11000 electrolytic copper is one of the most challenging non-ferrous materials for deep hole drilling despite its low hardness. The material's extreme ductility (45–55% elongation) produces long, stringy, snarled chips that clog evacuation passages and wrap around the drill. Its high thermal conductivity (390 W/m·K — ten times that of steel) pulls heat away from the cutting edge, paradoxically making chip formation more difficult by keeping the chip too cool to fracture. Successful deep hole drilling of electrolytic copper requires: (1) aggressive chipbreaker geometry with reduced land width and increased chipbreaker depth; (2) coolant pressure at the high end of the range (100–140 bar) for hydraulic chip transport; (3) polished carbide tools to reduce the adhesive tendency of copper; and (4) reduced cutting speeds (30–50 m/min) to manage cutting forces. Even with optimised parameters, tool life in C11000 is typically 40–80 holes per regrind — significantly less than in free-machining copper alloys.
Feed Rate by Drill Diameter
| Drill Diameter (mm) | C11000 ETP Feed (mm/rev) | C14500 Feed (mm/rev) | Brass Feed (mm/rev) | Bronze Feed (mm/rev) |
|---|---|---|---|---|
| 3 | 0.008–0.020 | 0.025–0.050 | 0.030–0.060 | 0.012–0.025 |
| 6 | 0.015–0.030 | 0.040–0.080 | 0.050–0.100 | 0.020–0.040 |
| 8 | 0.018–0.035 | 0.050–0.100 | 0.060–0.120 | 0.025–0.050 |
| 10 | 0.020–0.040 | 0.060–0.120 | 0.080–0.150 | 0.030–0.060 |
| 12 | 0.025–0.050 | 0.070–0.140 | 0.100–0.180 | 0.035–0.065 |
| 16 | 0.030–0.055 | 0.080–0.160 | 0.110–0.200 | 0.040–0.070 |
| 20 | 0.030–0.060 | 0.100–0.200 | 0.120–0.250 | 0.040–0.080 |
| 25 | 0.035–0.070 | 0.120–0.240 | 0.150–0.300 | 0.045–0.090 |
Tool Geometry for Copper Alloys
| Geometry Parameter | C11000 ETP Copper | C14500 / Brass | Bronze |
|---|---|---|---|
| Point angle | 110–120° | 118–130° | 118–130° |
| Rake angle | 12–18° positive | 8–14° positive | 6–10° positive |
| Relief / clearance angle | 10–14° | 8–12° | 8–12° |
| Chipbreaker | Aggressive — deep, wide | Standard or none | Standard |
| Edge preparation | Sharp with polished rake | Sharp | Sharp with light hone |
| Coating | Uncoated polished / AlCrN | Uncoated polished | AlTiN / TiAlN |
| Carbide grade | Micrograin (0.5–1.0 µm) | Micrograin | Micrograin |
| Tip displacement | 0.25–0.28 × D | 0.25 × D | 0.23–0.25 × D |
| Guide bushing tolerance | G6 | G6 | G6 |
TIP
For copper alloys, tool surface finish matters as much as geometry. A polished rake face — whether achieved with uncoated carbide or a smooth PVD coating — reduces the tendency of copper to cold-weld to the tool surface. Built-up edge forms rapidly on rough tool surfaces in C11000 electrolytic copper. For tellurium copper C14500 and leaded brass, the built-up edge tendency is much lower and standard uncoated carbide gun drills perform well. The tellurium content in C14500 creates copper telluride particles that act as chip breakers — this is why machinability jumps from 20% (pure copper) to 85% with only 0.4–0.7% tellurium addition.
Coolant Selection and Parameters
| Coolant Type | Suitability | Pressure Required | Key Requirements |
|---|---|---|---|
| Neat oil (mineral) | Excellent | As specified per alloy | Good filterability, 10–15 cSt viscosity |
| Semi-synthetic (emulsion) | Good | As specified per alloy | 8–12% concentration, anti-corrosion additives |
| Neat oil with EP additives | Recommended for bronze | Per alloy spec | Sulphurised EP for bronze reduces tool wear |
| Water-based | Poor — avoid | — | Causes staining, inadequate lubricity |
| MQL (oil mist) | Fair (shallow holes only) | 5–10 bar air | Not suitable for deep holes > 15× diameter |
Chip Control in Copper Alloy Deep Hole Drilling
| Chip Type | Appearance | Material | Risk Level | Corrective Action |
|---|---|---|---|---|
| Segmental / short (ideal) | Small disconnected segments | C14500, brass (natural) | Low | Maintain parameters |
| Stringy continuous ribbon | Long snarled chip > 100 mm | C11000, some bronze | Critical | Increase feed 20–30%, check chipbreaker, increase coolant pressure |
| Needle / splinter | Sharp fine fragments | Brass (excessively brittle) | Medium | Reduce feed, check material lead content |
| Powder / dust | Fine particles | Any copper alloy | High | Speed too high, tool worn — reduce speed, inspect tool |
| BUE chips | Irregular, smeared appearance | C11000 (common) | Critical | Replace tool, increase speed, use polished coating |
| Burned / discoloured | Brown/blue tint | Any | Critical | Speed too high, coolant insufficient — stop immediately |
Surface Finish Expectations
| Condition | Ra (µm) | Rz (µm) | Application Suitability |
|---|---|---|---|
| Optimised carbide gun drill, new | 0.4–0.8 | 3–8 | Hydraulic components, valve spools |
| Production drilling, mid-life | 0.8–1.6 | 8–15 | General engineering |
| Worn tool or poor parameters | 1.6–3.2 | 12–25 | Unacceptable — requires tool change |
| BTA drilling, new head | 1.6–3.2 | 12–25 | Acceptable with secondary finishing |
| With BUE present (C11000) | > 3.2 | > 25 | Reject — stop and replace tool |
Troubleshooting
| Symptom | Likely Cause | Solution |
|---|---|---|
| Built-up edge in C11000 | High ductility, insufficient speed, rough tool surface | Increase speed to 40–60 m/min, use polished uncoated carbide, verify coolant |
| Stringy chip clogging | Feed too low, chipbreaker ineffective | Increase feed 20–30%, modify chipbreaker geometry, increase coolant pressure |
| Rapid tool wear in bronze | Abrasive phosphor or aluminium content | Reduce speed, switch to AlTiN coating, increase coolant pressure |
| Poor surface finish (Ra > 1.6) | BUE, worn tool, inadequate coolant | Replace tool, verify coolant pressure and filtration |
| Hole oversize (> +0.05 mm) | Tool wear, guide pad wear, misalignment | Replace tool, inspect guide pads, check alignment |
| Chip packing at entry | Insufficient pilot hole, coolant pressure too low | Verify pilot hole depth and concentricity, increase coolant pressure |
| Tool breakage | Chip packing, coolant interruption | Implement peck cycle, verify coolant flow continuity |
| Coolant pressure drop | Filter clogging, pump cavitation | Change filter, check coolant level and pump |
| Exit burr excessive | Dull tool, ductile material | Replace tool, reduce feed for last 3 mm |
| Chatter / vibration | Excessive overhang, feed too low | Reduce overhang, increase feed 15%, check bushing fit |
FAQ
What cutting speed is recommended for gun drilling C11000 electrolytic copper?
For C11000 electrolytic tough pitch copper, recommended cutting speed is 30–60 m/min (100–200 SFM) with carbide gun drills. The low end of the range (30–40 m/min) is preferred for deep holes exceeding 30× diameter to manage chip formation. Running above 70 m/min increases cutting temperature and exacerbates built-up edge formation. For HSS gun drills, reduce speed to 15–30 m/min. C11000's machinability rating of 20% (versus free-cutting brass at 100%) means it requires significantly slower speeds than other copper alloys.
What feed rate should be used for deep hole drilling tellurium copper C14500?
For C14500 tellurium copper, recommended feed rate depends on hole diameter: 0.040–0.080 mm/rev for 6 mm, 0.060–0.120 mm/rev for 10 mm, and 0.100–0.200 mm/rev for 20 mm diameter. C14500 can tolerate significantly higher feed rates than pure copper due to its free-machining tellurium content. The general guideline is feed per revolution ≈ D/100 to D/200 where D is drill diameter in mm. The tellurium addition produces short, brittle chips that evacuate easily — C14500 is the most productive copper alloy for deep hole drilling.
What coolant pressure is needed for copper alloy deep hole drilling?
Coolant pressure requirements vary significantly by alloy: C11000 electrolytic copper requires 70–140 bar (1,000–2,000 PSI) — the high end is needed to evacuate stringy chips; C14500 tellurium copper requires 35–70 bar (500–1,000 PSI); leaded brass requires 20–50 bar (300–700 PSI); and bronze requires 50–100 bar (700–1,400 PSI). Oil-based coolant is recommended for all copper alloys. Coolant filtration to 15–20 µm is essential — unfiltered coolant recirculates chips that damage guide pads and the cutting edge.
How do you prevent built-up edge when drilling electrolytic copper?
Built-up edge in C11000 electrolytic copper is prevented by: (1) using polished uncoated carbide gun drills — a smooth rake face reduces copper adhesion more effectively than most coatings; (2) maintaining cutting speed at 40–60 m/min — too slow encourages BUE, too fast causes thermal issues; (3) using coolant pressure above 100 bar to flush chips and cool the cutting zone; (4) employing a positive rake angle of 12–18° to reduce cutting forces; (5) maintaining a sharp edge — replace tools at first sign of surface finish degradation. If AlCrN coating is used, it must be polished (smooth surface finish) — standard AlCrN can be too textured for copper.
What is the best copper alloy for deep hole drilling?
Leaded brass (C36000) is the easiest copper alloy to deep hole drill with a machinability rating of 100%. It produces short, broken chips naturally, requires low coolant pressure (20–50 bar), achieves excellent surface finish (Ra 0.4–0.8 µm), and delivers tool life exceeding 500 holes per regrind. Tellurium copper C14500 (85% machinability) is the second-best option with similar characteristics. The most difficult is pure electrolytic copper C11000 (20% machinability) which requires aggressive chipbreaker geometry, high coolant pressure, and produces unavoidable stringy chips. For production deep hole drilling in copper, specify C14500 or leaded brass whenever possible.
Can BTA drilling be used for copper alloys?
Yes, BTA drilling works well for copper alloys at diameters above 12 mm. Recommended parameters: cutting speed 40–120 m/min (depending on alloy), feed rate 0.05–0.25 mm/rev, coolant pressure 20–80 bar. BTA offers advantages in chip evacuation for copper alloys — the internal chip tube provides a direct path for chip removal, which is particularly beneficial for the stringy chips produced by pure copper. However, BTA surface finish (Ra 1.6–3.2 µm) is typically poorer than gun drilling. For copper alloys prone to built-up edge, BTA indexable inserts with polished rake faces and positive geometry are recommended.
What tool geometry works for electrolytic copper deep hole drilling?
For C11000 electrolytic copper, use a gun drill with: point angle 110–120° (shallower than standard), positive rake angle 12–18°, relief angle 10–14°, and aggressive chipbreaker geometry with deeper and wider chipbreaker slots than standard. The tip displacement should be increased to 0.25–0.28 × D to improve chip flow. The carbide grade should be micrograin (0.5–1.0 µm) for toughness, and the tool should be polished — either uncoated carbide or with smooth AlCrN coating. The shallower point angle reduces thrust forces in the ductile material, while the aggressive chipbreaker is essential for breaking the tenacious copper chips.
What surface finish can be expected when gun drilling brass?
With an optimised carbide gun drill in good condition, surface finish of Ra 0.4–0.8 µm is achievable in leaded brass — among the best of any deep hole drilled material. The fine, broken chip formation and low cutting forces produce a smooth hole wall. Production runs typically achieve Ra 0.8–1.6 µm through the tool life. C14500 tellurium copper achieves similar results. C11000 electrolytic copper achieves Ra 0.8–1.6 µm with a new tool, degrading more rapidly as the tool wears due to BUE formation. Bronze produces Ra 0.8–1.6 µm with optimised parameters.
How does tellurium improve copper machinability for deep hole drilling?
Tellurium (added at 0.4–0.7% in C14500) forms fine, hard copper telluride (Cu₂Te) particles throughout the copper matrix. These particles act as stress raisers that cause the chip to fracture into short, brittle segments rather than forming the long, continuous ribbons characteristic of pure copper. The machinability rating jumps from 20% to 85%. For deep hole drilling specifically, the short chip formation eliminates the primary challenge — chip evacuation — enabling higher feed rates, lower coolant pressure requirements, and significantly longer tool life. Unlike lead in brass, tellurium does not significantly reduce the electrical conductivity of copper, making C14500 suitable for electrical and thermal applications that require both machinability and conductivity.
What is the most common mistake in deep hole drilling copper alloys?
The most common mistake is treating all copper alloys the same. Parameters that work well for C14500 tellurium copper or leaded brass will cause immediate tool failure in C11000 electrolytic copper. Each copper alloy class requires fundamentally different cutting speeds, feed rates, coolant pressures, and tool geometries. The second most common mistake is underestimating chip control requirements — copper alloys produce some of the most challenging chip forms in deep hole drilling, from the stringy snarled ribbons of pure copper to the fine needle-like chips of leaded brass. Always verify chip form during process setup and adjust parameters accordingly. A third frequent error is using coolant pressure that is too low — many operators transfer steel-oriented coolant pressures (30–60 bar) that are insufficient for copper, especially for C11000 which needs 100+ bar.
Summary
Deep hole drilling of copper alloys requires material-specific strategies that vary dramatically by alloy composition. The machinability range spans from leaded brass at 100% (excellent, short chips, 500+ holes per regrind) to C11000 electrolytic copper at 20% (stringy chips, BUE-prone, 40–80 holes per regrind). C14500 tellurium copper offers the best balance of machinability and conductivity at 85% rating with naturally short chips. Cutting speeds range from 30–60 m/min for C11000 up to 250 m/min for C14500. Coolant pressure varies from 20–50 bar for brass to 70–140 bar for pure copper. Chip control is the dominant challenge across all copper alloys — chipbreaker geometry must be tailored to the specific alloy's ductility, and coolant pressure must be sufficient for hydraulic chip evacuation. Tool geometry adjustments include shallower point angles (110–120°) and more aggressive chipbreakers for ductile copper, and standard geometry for free-machining brass and tellurium copper. Surface finish of Ra 0.4–0.8 µm is achievable in brass and C14500, and Ra 0.8–1.6 µm in C11000 and bronze. For production applications, specifying a free-machining copper alloy (C14500 or leaded brass) is the most effective strategy for reliable, economical deep hole drilling.