Deep Hole Drilling Coolant System Components
The coolant system for deep hole drilling is not off-the-shelf — it must be engineered for the specific method, diameter range, and production volume. Each component must be selected to work together as a system.
This guide covers the key components of deep hole drilling coolant systems, their specifications, and how to select them.
High-Pressure Coolant Pumps
Pump Types
| Pump Type | Max Pressure | Max Flow | Efficiency | Best For |
|---|---|---|---|---|
| Centrifugal | 10–20 bar | High | Moderate | Low-pressure, high-volume (BTA) |
| Gear pump | 50–100 bar | Moderate | Good | General gun drilling |
| Piston pump | 100–200+ bar | Low-moderate | High | High-pressure gun drilling |
| Screw pump | 40–80 bar | Moderate | Good | BTA and ejector systems |
Pump Selection by Method
| Method | Recommended Pump Type | Typical Spec |
|---|---|---|
| Gun drilling (small dia, < 6 mm) | Piston pump | 70–140 bar, 20–60 L/min |
| Gun drilling (standard) | Gear or piston | 35–100 bar, 30–120 L/min |
| BTA drilling | Screw or centrifugal | 20–60 bar, 100–500 L/min |
| Ejector drilling | Screw or gear | 20–40 bar, 80–350 L/min |
| Trepanning | Screw or centrifugal | 20–40 bar, 150–600 L/min |
Key Pump Parameters
| Parameter | What It Means | How to Select |
|---|---|---|
| Pressure rating | Maximum pressure the pump can deliver | Must exceed system requirements by 20% |
| Flow curve | Flow rate versus system pressure | Must maintain adequate flow at operating pressure |
| Viscosity range | Coolant viscosity the pump can handle | Must match coolant type (neat oil vs. emulsion) |
| Seal material | Material compatibility with coolant | Viton for oil; Buna-N for emulsion |
Filtration Systems
Filter Types
| Filter Type | Micron Rating | Flow Capacity | Cost | Best For |
|---|---|---|---|---|
| Paper / roll filter | 10–50 µm | High | Moderate | Primary filtration, high volume |
| Bag filter | 5–100 µm | Moderate | Low | Simple systems, moderate flow |
| Cartridge filter | 1–50 µm | Moderate | Moderate | Point-of-use, high pressure |
| Magnetic separator | Ferrous only | Very high | Low | Primary chip removal (steel) |
| Hydrocyclone | 5–20 µm | High | Moderate | Central systems, no consumables |
Recommended Configuration
For gun drilling (single machine):
- Primary: magnetic separator or paper filter (50–100 µm)
- Secondary: 10–20 µm cartridge filter (point-of-use)
For BTA/ejector drilling (single machine):
- Primary: drag conveyor or paper filter
- Secondary: 10–20 µm paper or bag filter
- Chip separator: required (BTA and DTS generate high chip volume)
For central systems (multiple machines):
- Primary: drag conveyor + magnetic separator
- Secondary: 10–20 µm paper filter
- Polishing loop: 3–5 µm bypass filter
Chip Separators
BTA and ejector drilling require chip separation because chips are evacuated through the tool and returned with the coolant.
| Separator Type | Chip Size | Capacity | Best For |
|---|---|---|---|
| Drag conveyor | Bulk chips | Very high | BTA, high-volume |
| Drum screen | 0.5–5 mm | High | DTS, medium chips |
| Hydrocyclone | Fine particles | Moderate | Fines removal |
| Settling tank | All sizes | Depends on residence time | Simple systems, low volume |
Rule of thumb: The chip separator must handle 100% of the maximum chip volume generated at peak production.
Coolant Chillers
Chiller Types
| Chiller Type | Cooling Capacity | Temperature Control | Cost |
|---|---|---|---|
| Refrigeration chiller | 5–50 kW | ±1°C | High |
| Heat exchanger (plate-and-frame) | Dependent on plant water | ±3°C | Moderate |
| Dry cooler / radiator | Moderate | ±5°C | Low |
| Large sump (natural) | Limited | ±5–10°C | Very low |
Chiller Sizing
| Production Volume | Recommended Cooling |
|---|---|
| < 100 holes/week | Natural cooling (large sump) |
| 100–500 holes/week | Heat exchanger or small chiller |
| > 500 holes/week | Refrigeration chiller |
| Precision work (IT7+) | Refrigeration chiller (temperature stability) |
Chiller sizing formula:
Required cooling capacity (kW) = Flow rate (L/min) × ΔT (°C) × 0.0698
Where ΔT = desired temperature drop (typically 5–10°C).
Coolant Swivels
The coolant swivel transfers coolant from the stationary supply to the rotating tool. It is essential for gun drilling and ejector drilling on CNC machines.
| Parameter | Typical Range | Gun Drilling | Ejector Drilling |
|---|---|---|---|
| Pressure rating | Up to 140 bar | 140 bar | 60 bar |
| Speed rating | Up to 10,000 RPM | 3,000–10,000 RPM | 1,000–3,000 RPM |
| Flow rating | Up to 400 L/min | 15–120 L/min | 80–350 L/min |
| Seal material | Viton, Buna-N, PTFE | Viton (oil) | Viton |
Swivel Maintenance
| Interval | Action |
|---|---|
| Daily | Check for leaks |
| Weekly | Verify pressure at swivel output |
| Monthly | Inspect shaft for scoring |
| Every 2,000–5,000 hours | Replace seals |
Hoses and Fittings
| Component | Rating | Material | Notes |
|---|---|---|---|
| High-pressure hose | 2× system pressure | Wire-reinforced rubber | Minimum bend radius |
| Fittings | Same as hose | Steel or stainless | JIC or SAE standard |
| Manifold blocks | System pressure | Steel or aluminum | Custom drillings for coolant distribution |
| Rotary unions | Pressure + RPM | Steel with seals | For rotating coolant delivery |
System Design Checklist
- Pump pressure rating exceeds system requirements by 20%
- Pump flow curve provides adequate flow at operating pressure
- Primary filtration: 50–100 µm (chip removal)
- Secondary filtration: 10–20 µm (fine filtration)
- Point-of-use filter at the tool (for gun drilling)
- Chip separator capacity matches chip volume (BTA/DTS only)
- Chiller or sump maintains 30–40°C
- Coolant swivel pressure-rated for system max
- All hoses and fittings rated to 2× system pressure
- Pressure gauge at tool-side (not just at pump)
- Flow meter for BTA and ejector systems
Summary
Coolant system components must be selected as an integrated system, not purchased individually. The pump must match the method’s pressure and flow requirements. Filtration must be multi-stage: primary chip removal followed by fine filtration. Chillers maintain temperature stability for consistent tool life and hole quality. Coolant swivels transfer coolant to rotating tools, requiring regular seal maintenance. Properly sized and maintained coolant systems are the foundation of reliable deep hole drilling operations.
For coolant system fundamentals, see deep hole drilling coolant systems. For troubleshooting, see coolant system troubleshooting. For a complete overview, visit the tools and equipment guide. To choose the right filter for your machine, see the coolant filter selection guide.