BTA stands for Boring and Trepanning Association which developed this deep hole drilling system. It involves a single drill tube in which high pressure coolant is supplied to the drill through the annular area between the drilled hole and the tube outer diameter. The chips are evacuated through the I.D. of the tube. The drill head is screwed to this drill tube which is much stronger compared to the kidney shaped shank of a gun drill, hence much higher metal removal rates are possible. This involves the use of a Pressure head which is basically a high pressure seal between the workpiece and the drill bush. BTA/STS drilling is generally used for ф19 and above.
Since the chip removal is internal, no v shaped groove is required in the shank, so its cross-section is completely round and this provides more rigidity to the entire system. BTA drilling finds its application in Industries like Oil & Gas, Defence, Steel, Aircraft, Aerospace, Hydraulic Cylinders, and Power etc. For larger diameter deep hole drilling, BTA drilling is the only available option which provides high productivity and precision.
Another system which evolved from BTA single tube system is the Ejector drilling system. It is a system with twin tubes where the coolant is pumped through the space between the inner and outer tube. This eliminates the use of Pressure head and simplifies the system. This was introduced mainly to tool up conventional machines to do Deep hole Drilling.