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The three different types of tool systems commonly used for drilling deep holes are the Single Tube System (STS), Double Tube System (DTS), and conventional gundrills. All of the systems are designed to cut holes without chip congestion, but differ in the way chips are removed. See our Product Index for available sizes, and to request a catalog please complete our Catalog Request Form.

STS- Single Tube System

In the STS, coolant is pumped under high pressure around the OD of the drill. Chips are forced through an opening near the cutting edge of the tool and then exhausted out through the hollow drill tube at the back.
Why does the STS offer greater overall reliability? Rigidity is a limiting factor in gun drilling. Gun drills have a V-shaped flute from which chips are removed externally. This design makes gun drills less resistant to torque or thrust than the STS tools. Not only can torque cause high deflection or twisting, but axial forces can cause either deflection or buckling. The gun drill feed rate is therefore usually kept to between one-tenth and one-half the common feed rate for STS holes.
The DTS also has its limitations - especially in drilling very deep holes. The boring bars used have a double-walled shank in which coolant is fed between the inner and outer walls, and chips exit through the inner wall. As the hole depth increases, more coolant and pressure are required to move the coolant to the cutting edge, but the double-wall design causes the volume of coolant to diminish as the hole lengthens. As a result, the coolant flow may not be sufficient to protect the cutting edge and remove the chips. This problem may occur even in relatively short holes, especially those of small diameter.
STS drilling does not have these problems. STS tools are rigid enough to drill deep holes while holding exact tolerances in ID dimensions and straitness. Moreover, the pressurized coolant system provides enough cooling and chip removal to prevent chip congestion. The volume of coolant used helps to support the cylindrical drill tube and the drilling head, while a double-feeder attachment provides vacuum-assisted chip removal.

STS Product Index

DTS- Double Tube System

In the DTS, pressurized coolant is fed between inner and outer tubes in the drill shank up to the drill head or cutting edge. Chips are driven back through the inner tube in the shank and forced out the back.
Unlike alternative gun drilling and the STS, the DTS has unit construction which can be easily adapted to normal metal cutting machines, such as lathes or milling machines. It can be used on either a vertical or horizontal machine with only minor modifications for coolant induction.
The coolant is fed through the connector. Approximately two-thirds of the coolant flows between the inner diameter of the outer tube and the outer diameter of the inner tube. The remaining coolant is drawn off through the nozzle, creating a vacuum which causes a backward ejection of chips through the ID of the inner tube.

DTS Product Index