With Steve Rose Deep thoughts on gundrilling I magine drilling a hole the length of a rifle or shotgun barrel. Gundrilling is ideal for these applications. Gundrilling relies on high-pressure coolant to lubricate the cutting action and to flush chips. The drill design is like a creased tube, with an inner diameter hole that allows a large volume of coolant to flow through the drill. The external crease in the tube allows the returning coolant and chips to be removed.
Coolant flows out of the drill through one or two holes in the drill tip.
The drill tip is available in various grades of carbide, depending on the material being drilled. The tip is not perfectly round. It is designed with two skid pads, which support the cutting action and burnish the resultant hole. Machines are available specifically for gundrilling. These machines have high-pressure coolant and are designed to provide superior concentricity.