Ejector Drilling Tools
Ejector drilling (DTS) uses a specialized tool system built around the double-tube boring bar and Venturi-effect drill head. While the cutting action is similar to BTA drilling, the tooling is more complex due to the dual-tube design and Venturi nozzle geometry.
This guide covers DTS drill heads, boring bars, Venturi nozzles, guide pads, and the manufacturers producing compatible tooling.
The DTS Drill Head
The drill head is the most complex component of the ejector drilling system. It combines cutting edges, guide pads, and Venturi passages in a single assembly.
Head Design
| Feature | Description |
|---|---|
| Body material | Alloy steel, heat-treated |
| Cutting inserts | 2–4 indexable carbide inserts |
| Guide pads | 2 replaceable carbide pads |
| Venturi section | Internal slots that create suction |
| Connection | Threaded to inner tube |
| Diameter range | 18–200 mm |
Insert Types
Ejector drill heads use the same insert geometries as BTA heads:
| Insert Type | Shape | Typical Application |
|---|---|---|
| S-type (square) | 80° or 90° corner | General steel, cast iron |
| TPMX (triangular) | 3 cutting edges | Alloy steel, stainless |
| TXN | Special geometry | Titanium, superalloys |
For detailed coating and grade selection, see our BTA drilling tools guide — the same insert specifications apply to DTS heads.
Venturi Nozzles
The Venturi slots in the drill head are the most critical feature. They must be precisely machined to create the correct pressure drop and suction:
- Slot width: Typically 1–3 mm depending on diameter
- Number of slots: 2–4 around the inner tube circumference
- Angle: 15–30° relative to the tube axis
- Flow area: Calculated to split approximately 60–70% of total flow through the slots
If the Venturi slots become worn or blocked by debris, the suction effect is lost and chip evacuation stops immediately.
The Boring Bar
The boring bar is the longest and most expensive component of the ejector drilling system. It consists of two concentric tubes and the coolant swivel connection.
Construction
| Component | Material | Function |
|---|---|---|
| Outer tube | Alloy steel (4140/4340) | Torque transmission, coolant supply path |
| Inner tube | Alloy steel or seamless tube | Chip evacuation path |
| Swivel connection | Hardened steel with seals | Rotating coolant transfer |
| Connection threads | Precision-ground | Drill head attachment |
Boring Bar Specifications
| Parameter | Standard | Precision |
|---|---|---|
| Outer tube straightness | 0.1 mm per meter | 0.05 mm per meter |
| Tube concentricity | 0.05 mm TIR | 0.02 mm TIR |
| Maximum length | 5 m (16 ft) standard | 8 m (26 ft) special |
| Swivel seals | Mechanical or lip seals | Cartridge seals for high-pressure |
Boring Bar Sizing
The boring bar outer diameter is smaller than the hole diameter by a specific clearance:
| Hole Diameter | Boring Bar OD | Annular Clearance |
|---|---|---|
| 20 mm | 16 mm | 2 mm per side |
| 40 mm | 32 mm | 4 mm per side |
| 60 mm | 48 mm | 6 mm per side |
| 80 mm | 64 mm | 8 mm per side |
| 100 mm | 80 mm | 10 mm per side |
The annular clearance must be large enough for coolant flow but small enough to maintain chip transport velocity.
Guide Pads
DTS drill heads use the same type of carbide guide pads as BTA heads. Two pads are positioned behind the cutting inserts to provide self-piloting and bore burnishing.
| Pad Parameter | Typical Range |
|---|---|
| Material | Tungsten carbide (6–12% Co) |
| Number | 2 (standard on DTS heads) |
| Width | 4–12 mm (diameter-dependent) |
| Length | 10–30 mm |
| Interference | 0.01–0.03 mm oversized |
For pad maintenance and wear patterns, see our gun drill guide pads guide.
Coolant Swivel
The coolant swivel transfers high-pressure coolant from the stationary machine supply to the rotating boring bar. It is a critical component for CNC lathe retrofits.
| Specification | Typical Range |
|---|---|
| Pressure rating | Up to 60 bar |
| Flow rating | Up to 400 L/min |
| Speed rating | Up to 3,000 RPM |
| Mounting | Turret or tailstock |
| Seal type | Mechanical carbon face or lip seal |
Manufacturers
Sunnen (USA) — DirectDex Line
Sunnen’s DirectDex product line is a direct replacement for the discontinued Sandvik CoroDrill 800 series. It is the most readily available DTS tooling on the market today.
| Product | Details |
|---|---|
| DTS drill heads | Direct replacement for Sandvik 800-series heads |
| Boring bars | Compatible with existing Sandvik adapters |
| Inserts and pads | CVD and PVD coated grades for all material groups |
| Diameter range | 18–200 mm |
Best for: North American buyers needing Sandvik-compatible tooling.
BTA BORE UK
UK-based manufacturer producing replacement DTS heads compatible with Sandvik and Botek boring bars.
| Product | Details |
|---|---|
| Solid drill heads (STS & DTS) | Push and pull boring configurations |
| Trepanning heads | Custom designs available |
| Custom boring bars | Made-to-order |
| Diameter range | 25–300 mm |
Best for: European buyers, custom tooling needs.
Botek (Germany)
Botek is primarily known for BTA tooling but also produces ejector/DTS tooling for compatible systems.
| Product | Details |
|---|---|
| DTS drilling tools | Range from 18 mm diameter |
| Brazed and indexable heads | Standard geometries |
| Premium carbide grades | Long tool life |
Best for: High-precision applications, European market.
Sandvik Coromant (Legacy)
Sandvik developed the original CoroDrill 800 DTS system. While Sandvik has phased out the product line, many shops still have Sandvik boring bars and use replacement heads from Sunnen or BTA BORE.
Tool Selection Guide
| Your Requirements | Recommended DTS Tooling |
|---|---|
| Diameter 18–40 mm | Standard Sunnen DirectDex or Botek DTS head |
| Diameter 40–100 mm | Same, with indexable insert heads |
| Diameter 100–200 mm | Sunnen or BTA BORE, typically custom |
| Retrofitting a CNC lathe | Complete system: boring bar + swivel + drill head package |
| High-volume production | Indexable insert heads for quick edge changes |
| Difficult material (titanium, Inconel) | AlTiN-coated inserts, premium carbide grade |
| Budget-sensitive | Compatible replacement heads from Sunnen or BTA BORE |
Tooling Cost Comparison
| Component | Cost Range | Expected Life |
|---|---|---|
| DTS drill head (Ø40 mm) | $300–$600 | 5,000–20,000 holes (indexable) |
| Boring bar (2 m) | $800–$2,000 | 50,000+ holes |
| Coolant swivel | $1,000–$3,000 | 10,000–20,000 hours |
| Indexable inserts (per edge) | $3–$8 | 100–500 holes per edge |
| Guide pads (set) | $60–$120 | 1,000–3,000 holes |
Summary
Ejector drilling tools are built around the double-tube boring bar and Venturi-effect drill head. The drill head combines cutting inserts, guide pads, and Venturi nozzles in one assembly. With Sandvik’s phase-out of the CoroDrill 800 line, replacement tooling is now available from Sunnen (DirectDex) and BTA BORE UK. For shops adding deep hole drilling to a CNC lathe, a complete DTS tooling package — boring bar, drill head, and coolant swivel — is the most cost-effective path to deep hole capability.
For DTS process details, see how ejector drilling works. For parameter selection with DTS tooling, see ejector drilling parameters. For a complete overview, visit the ejector drilling guide.