Ejector Drilling Parameters
Ejector drilling parameters fall between BTA and gun drilling — higher feed rates than gun drilling but slightly lower than BTA, with lower coolant pressure than either. The Venturi effect assists chip evacuation, reducing the need for extreme coolant pressure but requiring adequate flow volume to maintain the suction effect.
This guide provides practical parameter tables for ejector drilling common engineering materials, with special attention to the differences when running on a retrofitted CNC lathe versus a dedicated deep hole drilling machine.
Key Differences from BTA Parameters
| Parameter | Ejector Drilling (DTS) | BTA Drilling (STS) | Why the Difference |
|---|---|---|---|
| Coolant pressure | 20–40 bar | 30–60 bar | Venturi effect assists chip evacuation |
| Coolant volume | Similar to BTA | High | Venturi requires minimum flow to maintain suction |
| Feed rate | 90% of BTA | Baseline | Venturi creates slight back-pressure on chip evacuation |
| Cutting speed | Same as BTA | Same as BTA | Same insert grades and materials |
Cutting Speed by Material
Cutting speed for ejector drilling is the same as for BTA drilling, since the same carbide insert grades and geometries are used.
| Material Group | Cutting Speed (m/min) | Cutting Speed (SFM) |
|---|---|---|
| Low-carbon steel (< 0.25% C) | 70–130 | 230–430 |
| Medium-carbon steel (0.25–0.55% C) | 60–110 | 200–360 |
| Alloy steel (low alloy, annealed) | 50–100 | 160–330 |
| Tool steel / high alloy | 40–80 | 130–260 |
| Stainless steel (austenitic 304/316) | 40–70 | 130–230 |
| Stainless steel (martensitic/ferritic) | 50–80 | 160–260 |
| Gray cast iron | 50–80 | 160–260 |
| Ductile iron | 40–70 | 130–230 |
| Aluminum (wrought, 6061) | 80–200 | 260–660 |
| Aluminum (cast) | 60–150 | 200–490 |
| Brass (free machining) | 60–150 | 200–490 |
| Titanium (Ti-6Al-4V) | 15–30 | 50–100 |
| Nickel alloys (Inconel 718) | 10–20 | 33–65 |
| Hardened steel (HRC 40+) | 15–25 | 50–80 |
Feed Rate by Drill Diameter
Feed rates for ejector drilling are approximately 90% of BTA rates due to the slightly less efficient chip evacuation.
| Drill Diameter (mm) | Feed Rate: Steel (mm/rev) | Feed Rate: Cast Iron (mm/rev) | Feed Rate: Aluminum (mm/rev) |
|---|---|---|---|
| 18–25 | 0.08–0.20 | 0.12–0.30 | 0.12–0.40 |
| 25–40 | 0.10–0.25 | 0.15–0.35 | 0.15–0.50 |
| 40–65 | 0.12–0.30 | 0.20–0.40 | 0.20–0.60 |
| 65–100 | 0.15–0.35 | 0.25–0.45 | 0.25–0.65 |
| 100–150 | 0.20–0.40 | 0.30–0.50 | 0.30–0.70 |
| 150–200 | 0.25–0.45 | 0.35–0.55 | 0.35–0.75 |
Note: On a retrofitted CNC lathe with less rigid setup, use the lower end of the feed range.
Coolant Pressure by Drill Diameter
Ejector drilling requires lower coolant pressure than BTA because the Venturi effect assists chip evacuation.
| Drill Diameter (mm) | Coolant Pressure (bar) | Coolant Pressure (PSI) |
|---|---|---|
| 18–25 | 30–40 | 435–580 |
| 25–40 | 25–35 | 360–510 |
| 40–65 | 20–30 | 290–435 |
| 65–100 | 20–25 | 290–360 |
| 100–150 | 15–25 | 220–360 |
| 150–200 | 15–20 | 220–290 |
Critical note: The Venturi effect requires a minimum coolant flow rate to generate suction. If the flow drops below this threshold, the Venturi effect collapses and chip evacuation stops immediately. Always verify flow rate, not just pressure.
Minimum Flow Rate Requirements
| Drill Diameter (mm) | Minimum Flow (L/min) | Recommended Flow (L/min) |
|---|---|---|
| 20 | 60 | 80–120 |
| 40 | 100 | 120–180 |
| 60 | 130 | 150–250 |
| 80 | 160 | 200–300 |
| 100 | 200 | 250–350 |
Depth Ratio Adjustments
As the hole gets deeper, the Venturi effect becomes slightly less efficient due to the increasing length of the chip return path.
| Depth Ratio | Speed Adjustment | Feed Adjustment | Coolant Pressure |
|---|---|---|---|
| Up to 30:1 | 100% | 100% | Standard |
| 30:1 to 60:1 | 90% | 85% | Increase 10% |
| 60:1 to 100:1 | 80% | 75% | Increase 15% |
CNC Lathe Parameter Adjustments
When running ejector drilling on a retrofitted CNC lathe (versus a dedicated machine), reduce parameters to compensate for lower rigidity:
| Factor | Adjustment vs Dedicated BTA Machine |
|---|---|
| Cutting speed | Reduce 10–15% |
| Feed rate | Reduce 15–20% |
| Coolant pressure | Same (but verify pump capacity) |
| Max depth ratio | Reduce to 50:1 (limited by boring bar support) |
Practical Examples
Example 1: Ejector drilling 4140 steel, Ø40 mm × 1,200 mm deep on CNC lathe
- Material: 4140 alloy steel (annealed)
- Cutting speed: 80 m/min → spindle speed = 80 ÷ (0.040 × π) = 637 RPM
- Feed rate: 0.18 mm/rev → 115 mm/min
- Coolant pressure: 30 bar (435 PSI)
- Coolant volume: ~150 L/min
- Depth ratio: 30:1 → no reduction needed
- Setup: CNC lathe with coolant swivel and single steady rest
Example 2: Ejector drilling 304 stainless steel, Ø25 mm × 1,000 mm deep
- Material: 304 stainless steel (austenitic)
- Cutting speed: 55 m/min → spindle speed = 55 ÷ (0.025 × π) = 700 RPM
- Feed rate: 0.12 mm/rev → 84 mm/min
- Coolant pressure: 35 bar (510 PSI)
- Coolant volume: ~100 L/min
- Depth ratio: 40:1 → reduce speed 10% to 50 m/min, feed 15% to 0.10 mm/rev
- Adjusted: 637 RPM × 0.10 mm/rev = 64 mm/min
Example 3: Ejector drilling gray cast iron, Ø80 mm × 2,400 mm deep
- Material: Gray cast iron (GG25)
- Cutting speed: 70 m/min → spindle speed = 70 ÷ (0.080 × π) = 279 RPM
- Feed rate: 0.30 mm/rev → 84 mm/min
- Coolant pressure: 25 bar (360 PSI)
- Coolant volume: ~250 L/min
- Depth ratio: 30:1 → no reduction needed
Chip Monitoring
| Chip Appearance | Indication | Action |
|---|---|---|
| Short C-shaped chips — silver or light straw | Good parameters | Maintain |
| Long, stringy chips | Feed too low | Increase feed 10–15% |
| Powdered or dusty chips | Feed too high; tool dull | Reduce feed; check tool |
| Blue or burned chips | Excessive heat | Reduce speed; increase coolant |
| Irregular chip flow | Venturi effect disrupted | Check coolant flow volume |
CNC Machine Considerations
When setting up ejector drilling on a standard CNC machine:
Coolant system:
- Verify pump capacity meets minimum flow rate for the drill diameter
- Install a pressure gauge at the coolant swivel (not just the pump)
- Ensure filtration to 10–20 micron — Venturi slots are narrow and can be blocked by debris
Spindle:
- Verify through-tool coolant capability (for machining center setups)
- For lathe setups, use a coolant swivel mounted on the turret
Workholding:
- Standard chuck or collet is sufficient (no pressure head needed)
- For through-holes, ensure clearance behind the workpiece for tool exit
Summary
Ejector drilling parameters are similar to BTA drilling with two key differences: coolant pressure can be 10–20% lower (20–40 bar), and feed rates should be approximately 90% of BTA rates. The Venturi effect requires maintaining a minimum coolant flow rate — pressure alone is not sufficient. On retrofitted CNC machines, reduce cutting speed by 10–15% and feed by 15–20% to compensate for lower rigidity.
For process step-by-step guidance, see how ejector drilling works. For troubleshooting parameter-related problems, see common ejector drilling problems. For CNC setup details, see ejector drilling CNC setup. For a complete overview, visit the ejector drilling guide.