Deep Hole Drilling Parameters
Cutting parameters in deep hole drilling are more constrained than in conventional machining. The tool operates at the bottom of a narrow hole where coolant access and chip evacuation are the limiting factors, not the machine’s power or speed capability.
This guide provides an overview of parameter selection across all deep hole drilling methods, with reference to method-specific parameter guides for detailed tables.
Parameter Differences by Method
| Parameter | Gun Drilling | BTA Drilling | Ejector Drilling |
|---|---|---|---|
| Cutting speed | 15–200 m/min | 15–200 m/min | 15–200 m/min |
| Feed rate | 0.007–0.085 mm/rev | 0.10–0.70 mm/rev | 0.08–0.45 mm/rev |
| Coolant pressure | 35–140 bar | 20–60 bar | 20–40 bar |
| Coolant volume | 15–120 L/min | 100–500+ L/min | 80–350 L/min |
| Depth ratio limit | Up to 300:1 | Up to 100:1 | Up to 100:1 |
| Tolerance | ±0.025 mm | ±0.05 mm | ±0.04 mm |
| Surface finish Ra | 0.4–0.8 µm | 0.8–3.2 µm | 0.8–3.2 µm |
Speed-Feed-Coolant Relationship
The three primary parameters interact in a way that differs from conventional machining:
In conventional drilling: Speed and feed can be optimized independently. Coolant is secondary.
In deep hole drilling: All three are tightly coupled. A change in any one parameter affects the others.
| Change | Effect on Chip Evacuation | Effect on Tool Life | Effect on Surface Finish |
|---|---|---|---|
| Increase speed | Minimal | Reduces significantly | Degrades slightly |
| Increase feed | Improves (thicker chips) | Reduces moderately | Degrades (thicker feed marks) |
| Increase coolant pressure | Improves (better chip flushing) | Extends (better cooling) | Improves (cleaner cut) |
| Increase coolant flow | Improves (better transport) | Extends | Improves |
Parameter Selection Priority
When selecting parameters for a deep hole drilling operation, follow this priority:
- Set coolant first — Meet minimum pressure and flow for the method and diameter
- Select cutting speed — Based on material and desired tool life
- Select feed rate — Based on chip evacuation requirements and surface finish target
- Fine-tune — Adjust coolant, speed, and feed together for the specific operation
This sequence differs from conventional machining, where speed and feed are selected first and coolant is an afterthought.
Starting Parameters by Method
Gun Drilling Starting Points
| Material | Speed (m/min) | Feed (mm/rev, Ø12 mm) | Coolant Pressure (bar) |
|---|---|---|---|
| Low-carbon steel | 120–180 | 0.025–0.050 | 35–70 |
| Alloy steel | 100–140 | 0.025–0.045 | 35–70 |
| Stainless steel | 50–80 | 0.020–0.040 | 50–100 |
| Aluminum | 80–160 | 0.025–0.175 | 20–35 |
For complete tables, see gun drilling speeds and feeds guide.
BTA Drilling Starting Points
| Material | Speed (m/min) | Feed (mm/rev, Ø40 mm) | Coolant Pressure (bar) |
|---|---|---|---|
| Low-carbon steel | 70–130 | 0.15–0.35 | 30–50 |
| Alloy steel | 50–100 | 0.15–0.30 | 35–55 |
| Stainless steel | 40–70 | 0.12–0.25 | 40–60 |
| Aluminum | 80–200 | 0.25–0.60 | 15–30 |
For complete tables, see BTA drilling parameters guide.
Ejector Drilling Starting Points
| Material | Speed (m/min) | Feed (mm/rev, Ø40 mm) | Coolant Pressure (bar) |
|---|---|---|---|
| Low-carbon steel | 70–130 | 0.12–0.30 | 25–40 |
| Alloy steel | 50–100 | 0.12–0.25 | 25–35 |
| Stainless steel | 40–70 | 0.10–0.20 | 30–40 |
| Aluminum | 80–200 | 0.20–0.50 | 15–25 |
For complete tables, see ejector drilling parameters guide.
Depth Ratio Adjustments
As depth-to-diameter ratio increases, parameters must be reduced:
| Depth Ratio | Speed Adjustment | Feed Adjustment | Coolant Increase |
|---|---|---|---|
| < 20:1 | 100% | 100% | None |
| 20:1–40:1 | 90% | 90% | None |
| 40:1–60:1 | 85% | 80% | 10% |
| 60:1–100:1 | 80% | 75% | 20% |
| > 100:1 | Gun drilling only | 65% | 30% |
For detailed adjustments, see depth ratio parameter adjustments guide.
Chip Shape as a Parameter Indicator
Monitor chip shape as a real-time indicator of parameter correctness:
| Chip Shape | What It Means | Action |
|---|---|---|
| Short C-shaped, silver/straw | Parameters correct | Maintain |
| Long, stringy | Feed too low | Increase feed 10–15% |
| Powdered / dusty | Feed too high or tool dull | Reduce feed; check tool |
| Blue / burned | Speed too high or coolant insufficient | Reduce speed; increase coolant |
| Variable shape | Inconsistent material or coolant fluctuation | Check material; verify coolant |
Summary
Parameter selection in deep hole drilling follows a different logic than conventional machining: coolant is the primary parameter, followed by speed for tool life, then feed for chip evacuation. All three are tightly coupled — a change in one affects the others. Start with the method-specific parameter tables, then fine-tune based on chip shape, tool wear, and surface finish. Reduce parameters systematically as depth ratio increases.
For method-specific parameter tables, see the individual guides linked above. For parameter optimization methodology, see process optimization guide. For a complete overview, visit the process parameters guide.