Coolant-Delivery

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. ...

The rotating union transfers coolant from the stationary supply line to the rotating spindle. It is one of the most common failure points on a deep hole drilling machine. A failed union causes pressure loss and coolant spray, and it can also cause mist to flood the work zone. In my experience, roughly 30% of unscheduled downtime on deep hole machines traces directly back to this component. Anatomy of a Rotating Union The union sits between the machine coolant manifold and the spindle shaft. Inside, a stationary housing holds the inlet port while a rotating shaft connects to the spindle bore. The two halves meet at a mechanical seal face. Standard designs use silicon carbide seal faces running against a carbon ring. In larger machines rated above 80 bar, I have seen tungsten carbide faces used instead. The shaft rotates with the spindle, so the seal must maintain contact pressure while the spindle runs at several thousand RPM. ...

Through-tool coolant delivers coolant through the center of the drill directly to the cutting edge. Flood coolant sprays coolant over the outside of the drill and relies on flow to reach the cutting zone. In deep hole drilling, the choice between these two methods determines whether the process succeeds or fails. How Through-Tool Coolant Works For gun drilling, through-tool coolant is essential. Coolant enters through a rotating union at the spindle, travels down the center of the gun drill tube, and exits at the cutting edge. The coolant cools the cutting edge and then flushes chips back along the external flute of the drill. ...