The Deep Hole Gun Drill and its Function

A typical gun drill consists of three parts: a carbide tip, a heat treated alloy shank, and a steel driver. All are typically silver brazed together, and are designed to allow coolant to pass through its entire length. The shank must be properly formed, heat treated, and aligned to absorb cutting torque, sagging, and the whipping associated with high RPM's. Any size, feature, or length configuration can be optioned from .045" to 1.625" diameter.

The drill is positioned and held in the spindle nose, then guided into the workpiece through a pre-started hole or guide bushing that prevents vibration and ensures accuracy. Gun drill cutting edges form thin, curled chips that are carried away from the bore by high pressure lubricant. The off-center design of the cutting edges creates pressure within the bore that is carried by pads behind the drill tip. The coolant that flushes the chips also lubricates these pads, which burnish the surface and develop the fine finish for which deep hole gun drilling is known.

The Deep Hole Gun Drill and its Function


Drivers are manufactured to industry standards as well as any specified diameter, length, or feature, such as flats, "O" ring groove, and ID or OD threads. Standard drivers have an undercut to .750" diameter and two "whistle notch" flats above.


Sterling Gun Drills shanks are manufactured from aircraft grade alloy steel tubing that is formed, heat treated, and trued to exacting specifications.

Drill Tip

Single flute solid carbide drill tips are supplied in all diameters from .078" to 1.625" in a number of styles. Sterling Gun Drills' standard tip has a round or kidney oil hole. Twin hole tips or other variations are available. Our smallest drills (.045" to .160") can be ordered with a solid carbide shank / tip. Our larger diameter drills are offered with solid carbide tips (to 1.625"). Standard pad form (contour) is the R-1 low-land, non-micable style.

Other styles are available as conditions warrant. Retipping, reconditioning, resharpening, resizing and surface coatings are available.

Standard drills can be ordered by just specifying drill diameter and overall length. All will be supplied with R-1 (low land) contour and N-8 (30x 20) nose grind, either facet or sweep grind.

More information about Gun Drill Styles & their uses?