While Wire Cut EDM uses the side of molybdenum wire drawn through a block of metal, Small Hole Drilling EDM plunges the end of a narrow wire into the workpiece. Since EDM does not use mechanical force, a thin, fragile electrode can be moved into a hard alloy without concern for it bending or breaking.
Traditional drilling operations struggle to pierce a hole through hard surfaces at an angle. Drill bits work well when they are perpendicular to the surface and the sharp point at the tip can bore into the material. The contact surfaces and forces at the tip are irregular when the angle is reduced though. Drill bits bow to one side and tend to walk down the surface, so the positioning is not reliable. This also causes a high amount of fatigue stress and usually breaks small drill bits. But Small Hole Drilling EDM has none of these issues.
Small Hole Drilling EDM can be used to put a deep hole at a very shallow angle through a hardened ball bearing with the ball simply sitting on a stand to prevent it from rolling away. It almost doesn`t need to be clamped in place.
The electrode isn`t exactly a simple wire – the point at the end of a two dimensional line. It`s more like an injection needle; a small hollow tube through which dielectric fluid is pumped. The fluid helps to cool and irrigate the hole and carry away any particles. The tube is also continually and slowly rotated to further aid in passing debris away from the tip.
As you might imagine, Small Hole Drilling EDM is usually the best way to pierce through the middle of a block of hard metal before Wire Cut EDM can take over and work sideways.