Avoid interrupted cuts. Because the tungsten carbide head is fairly brittle, a gun drill should always cut into solid material to avoid breaking of the cutting edge. This is not always possible because the channels used in molds do frequently intersect. However, the designer and the machine operator can take certain measure to minimize the risk of damage to the drill. The larger the drill, the easier it is to drill, within reason. Particularly for air lines, if the final hole is small, e.g. , 4mm diameter, the approach holes should be 8mm or 10mm if possible, rather than drilling a very long hole with a 4mm drill. Avoid offsetting of centerlines of channels. Where the holes meet, there is an interrupted cut, also the cutting edge finds more resistance away from the centerline of the already existent hole and makes the drill wander off in the direction of least resistance. In a way, this is similar to the drill finding a “ soft spot” in the material. For intersecting channels having a large difference in diameter, the small hole must always be drilled first, before drilling the large hole. Otherwise, the small drill would lose its guidance as it passes through the large hole, finally, always locate the entrance of a deep hole so that it can be drilled with standard bushings.