Ejector drilling is the BTA-family process that drops the face seal: two concentric tubes carry coolant down between them, and a Venturi arrangement sucks chips back up the inner tube. Developed by Sandvik, it turns an ordinary lathe or machining center into a deep hole drilling machine.
Ejector drilling — the Double Tube System (DTS) — is a deep hole drilling method invented by Sandvik around 1970 as a variation of BTA, so that internal-chip drilling could run on machine tools that were never built for it. Instead of sealing the workpiece face with a pressure head, it contains the coolant inside its own pair of concentric tubes and uses a Venturi (ejector) effect to draw chips back up the inner tube. It works from an L/D of about 3:1 and up.
Coolant enters through a rotary connector at the spindle and flows down the annulus between the inner and outer tubes.
At the head, coolant sweeps past the cutting edges and guide pads, picking up chips.
About two-thirds of the coolant flows to the cutting zone to cool and push chips toward the inner tube; the rest is sprayed at high speed through crescent nozzles, creating the low-pressure (Venturi) zone that sucks chips back up the inner tube.
| Element | What it does |
|---|---|
| Inner + outer tubes | Concentric pair; annulus delivers coolant, inner tube returns chips |
| Venturi nozzle | Creates the ejector suction that pulls chips out |
| Guide bush only | Replaces the BTA pressure head — no workpiece face seal |