BTA is the single-tube system for deep hole drilling — named after the Boring and Trepanning Association that standardized it in mid-20th-century Germany. It feeds coolant between the tube and the hole wall and pulls chips back through the tube center, which lets it drill big bores 5–10× faster than a gundrill.
BTA comes from the Boring and Trepanning Association, the industry body that standardized the single-tube deep hole drilling system in Germany in the 1930s–1940s. The name stuck as the generic term for the process, which is also called the Single Tube System (STS). It is one of the three core deep hole methods, alongside gundrilling and ejector (double-tube) drilling.
A pressure head (BOZA) clamps against a flat, square workpiece face and carries the starting bushing.
High-pressure oil (about 225–250 psi minimum, rising past 1,400 psi with depth) flows down the annular gap between the tube outer wall and the bore.
The multi-edge head cuts; coolant carries chips through the open spaces in the head and back through the tube center to the machine spindle.
| Element | What it does |
|---|---|
| Pressure head (BOZA) | Seals the workpiece, feeds coolant, holds the starting bushing |
| Round drill tube | Chip conduit + coolant boundary; fully round for maximum torsional rigidity |
| Multi-edge head | Carbide inserts + guide pads; burns the bore as it cuts |
| Characteristic | BTA (STS) | Gundrilling |
|---|---|---|
| Diameter | Ø20–500+ mm | Ø0.5–50 mm |
| Chip removal | Internal (tube center), >60% area | External V-flute, 22–26% area |
| Feed rate | 5–10× faster | Baseline |
| Straightness | Good (≈0.05–0.1 mm/m) | Best (≤0.03 mm/m with counter-rotation) |
| Surface finish | Ra 0.8–3.2 μm | Ra 0.4–1.6 μm |
| Machine | Dedicated BTA machine | Gundrill machine or CNC |