External-Coolant

External coolant delivery directs coolant at the drill entry point from outside the bore. It cannot replace through-tool coolant for deep holes, but it plays an important supporting role. I use external coolant on every deep hole drilling job to complement the through-tool system. The Supporting Role of External Coolant External coolant serves three specific functions in deep hole drilling: Lubricates the guide bushing. The bushing rubs against the rotating drill shank and needs constant lubrication to prevent galling. Flushes chips away from the entry area. Chips exiting the flute can accumulate around the bushing and scratch the finished bore surface. Provides initial cooling at drill entry. The first few millimeters of drilling generate heat that external coolant can manage before the through-tool coolant takes over. I use external coolant in combination with through-tool coolant on every gun drilling job. The external coolant stream is aimed at the guide bushing and the drill entry point. The through-tool coolant travels down the drill to the cutting edge. ...