Deep hole drilling is generally performed on dedicated deep hole drilling machines which are manufactured and assembled to optimize the processes for straightness and efficiency. Advances in technology allow CNC machining centers, equipped with high pressure, through-spindle coolant, to be capable of gundrilling up to a limited depth-to-diameter ratio. UNISIG produces highly capable BTA and gundrilling machines, with applications exceeding 400:1 D:d ratios.

A deep hole is defined by its depth-to-diameter ratio (D:d), and typically holes greater than 10:1 are considered deep holes. Deep hole drilling into metal has a range of applications across several industries, with its origins tracing back to the need for straighter, more accurate gun barrels, and expanding as other industries integrated deep hole drilling processes to improve their own applications.

Deep hole drilling processes work by using special tools and setups to deliver high pressure coolant, evacuate chips cleanly, and achieve depth-to-diameter holes into metal beyond what a common CNC machine can reach. This allows manufacturers to achieve their manufacturing tolerances and production requirements reliably, accurately, and efficiently.

Deep hole drilling consists of BTA drilling and gun drilling, with additional processes designed for specific tolerance objectives and generally performed on BTA-style deep hole drilling machines. Deep hole drilling is used in a variety of materials from aluminum to super-alloys, and is capable of achieving tight diameter control, straightness, and superior surface finish into workpieces.