Appearance
The DF System (Double Feeder) eliminates the single most restrictive requirement of standard BTA drilling: the need for a coolant sealing head at the workpiece face. By delivering coolant through the annular space between two concentric tubes and evacuating chips through the inner tube, the DF System creates a self-contained coolant circuit within the tool assembly. This design allows deep hole drilling on machines that cannot accommodate external coolant sealing — standard CNC lathes, horizontal machining centers, and multi-tasking machines — dramatically expanding the range of equipment that can perform BTA-quality deep hole drilling.
DF System Design Principles
DF vs. BTA vs. Ejector Comparison
| Feature | Standard BTA (Single Tube) | Ejector (Jet-Suction) | DF System (Double Feeder) |
|---|---|---|---|
| Tube configuration | Single tube — coolant in annulus — chips through tube | Dual concentric tubes — ejector venturi at drill head | Dual concentric tubes — coolant through outer annulus |
| Coolant sealing | Requires sealing head at workpiece face | No external seal — venturi creates suction | No external seal — self-contained circuit |
| Coolant pressure | 10–100 bar | 5–40 bar | 15–80 bar |
| Coolant flow direction | Forward through annulus — returns through tube | Forward through inner tube — ejector section reverses flow | Forward through outer annulus — returns through inner tube |
| Chip evacuation | Through inner tube — pushed by coolant | Through inner tube — pulled by venturi suction | Through inner tube — pushed by positive pressure |
| Hole diameter range | 15–300 mm | 18–120 mm | 15–80 mm |
| Machine compatibility | Dedicated BTA machines with coolant sealing | Standard lathes — no sealing head needed | Standard CNC lathes — machining centers |
| Depth-to-diameter ratio | Up to 200:1 | Up to 100:1 | Up to 100:1 |
DF System Coolant Flow Path
| Component | Flow Path | Pressure Range | Purpose |
|---|---|---|---|
| Coolant supply inlet | To outer tube annulus | 15–80 bar | Entry point from machine coolant system |
| Outer tube annulus | Between outer and inner tube | 15–80 bar (declining) | Coolant delivery to drill head |
| Drill head coolant holes | Through drill head body to cutting edges | 10–60 bar | Cutting edge cooling and chip breaking |
| Chip return path | Through inner tube bore | Near atmospheric with back pressure | Chip and coolant return to collection tank |
| Coolant outlet | From inner tube to chip tank | 0–2 bar | Gravity discharge into chip separation system |
DF System Setup and Applications
Machine Requirements for DF Drilling
| Machine Parameter | Requirement | Notes |
|---|---|---|
| Spindle through-bore | ≥ drill tube OD + 5 mm | Tube passes through spindle for deep hole drilling |
| Coolant pressure | 20–80 bar (recommended 40 bar minimum) | Lower than BTA but sufficient for chip transport |
| Coolant flow rate | 50–300 L/min depending on diameter | Sized for drill head coolant hole area |
| Coolant filtration | ≤50 micron recommended | Protects drill head coolant holes from blockage |
| Spindle power | 5–30 kW depending on diameter | Lower than BTA — DF system has lower hydraulic losses |
| Feed axis thrust | 20–100 kN depending on diameter | Comparable to BTA requirements |
| Coolant tank capacity | ≥5× pump flow per minute | Adequate settling time for chip separation |
FAQ
What is the main advantage of the DF System over standard BTA?
The main advantage of the DF System over standard BTA is the elimination of the external coolant sealing head. Standard BTA requires a pressure-tight seal between the drill tube and the workpiece entry face, which means the workpiece must have a prepared entry surface and the machine must include a sealing head assembly — typically a dedicated component on BTA-specific machines. The DF System's self-contained coolant circuit means it can be used on standard CNC lathes, horizontal machining centers, and multi-tasking machines without modification to the workpiece or the machine for coolant sealing. This makes the DF System particularly valuable for job shops and facilities that need deep hole drilling capability without investing in dedicated BTA machine tools.
How does the DF System compare to the ejector drilling system?
The DF System and the ejector (jet-suction) system are similar in that both use dual concentric tubes and eliminate the need for external coolant sealing. The key difference is the chip evacuation mechanism. The ejector system uses a venturi section at the drill head to create a partial vacuum that pulls chips through the inner tube — requiring lower coolant pressure but generating less chip transport force. The DF System uses positive coolant pressure to push chips through the inner tube — providing more reliable chip transport at higher pressures but requiring more robust tube sealing. The DF System generally offers better chip evacuation in materials that produce heavy or stringy chips, while the ejector system offers lower coolant pressure requirements and is gentler on the machine coolant system.
What coolant pressure is needed for DF drilling?
DF drilling typically requires 40–80 bar coolant pressure at the tool inlet for effective chip evacuation, depending on the hole diameter and depth. This is lower than standard BTA (which can require 80–150 bar) because the dual-tube design has a larger chip evacuation cross-section and lower hydraulic resistance. The minimum recommended pressure is 20 bar for small diameters under 20 mm, stepping up to 60–80 bar for larger diameters above 50 mm or for deep holes exceeding 50:1 depth ratio. Coolant flow rate is the more critical parameter — the system must deliver sufficient volume to maintain chip transport velocity in the inner tube (typically 4–8 m/s return velocity). The required flow rate is calculated from the inner tube cross-sectional area and the target return velocity.
What types of machines can be retrofitted for DF drilling?
The DF System can be retrofitted to a wide range of standard machine tools. CNC lathes with a spindle through-bore large enough to pass the DF drill tube are the most common retrofit candidates — the DF tube assembly mounts through the spindle and the drill head extends from the spindle nose. Horizontal machining centers with sufficient Z-axis travel and a through-spindle coolant system rated for the required pressure can also be adapted for DF drilling with the addition of a guide bushing support at the spindle face. Multi-tasking mill-turn machines with Y-axis capability offer particularly good DF drilling potential because they can combine deep hole drilling with other operations. The retrofit typically requires a coolant system upgrade (higher pressure pump, additional filtration), a DF tube support system, and a guide bushing arrangement at the workpiece.
What are the limitations of the DF System?
The DF System has several limitations compared to standard BTA. The maximum hole diameter is typically limited to 80 mm because the dual-tube construction becomes impractically heavy and rigid at larger diameters. Maximum depth-to-diameter ratio is approximately 100:1 — less than the 200:1+ achievable with standard BTA — because the longer dual-tube assembly has lower torsional rigidity and the chip evacuation path through the inner tube creates back pressure at extreme depths. Coolant flow is restricted by the annular area between the two tubes, limiting the maximum flow rate compared to single-tube BTA. The dual-tube design also requires more complex tube connections and sealing at each joint, increasing the maintenance requirement. The DF System is best suited for medium-diameter, moderate-depth applications where machine flexibility is the primary requirement.
Disclaimer: The DF System specifications and setup parameters provided in this article are general guidelines based on industry-standard practices. Actual DF System designs vary by manufacturer and specific application requirements. System selection should consider workpiece material, hole geometry, machine capabilities, and production volume. The authors and publisher assume no liability for any damages or losses arising from the use of this information — always follow original equipment manufacturer guidelines for your specific equipment. Content is for informational purposes only and does not constitute professional engineering advice. Verify all parameters with qualified personnel before implementation as of 2026.