Producing small-diameter holes in conductive material regardless of hardness, at depths and aspect ratios conventional drilling cannot reach. The three common uses are start holes for wire EDM, functional holes such as cooling and vent holes in tooling and turbine components, and removing broken taps, drills and studs from parts that would otherwise be scrapped.

By eroding rather than cutting. The tubular electrode is centred over the broken tap and discharges erode the tap material away, and because the process applies no mechanical force and follows the electrode rather than the surrounding metal, the thread is left intact. It works equally well on hardened taps, which are exactly the ones that break and which no extractor will grip.

Because any enclosed profile cut by wire EDM needs a hole through which the wire can be threaded, and in hardened material a small-hole EDM machine is the only practical way to produce one. Shops running wire EDM almost always have a hole drilling machine alongside it, and many wire machines can be specified with an integrated drilling head for the same reason.

Far higher than conventional drilling, because the electrode is flushed internally at high pressure and rotated, which clears debris from the bottom of a deep hole and keeps the electrode running true. Depth to diameter ratios that would break a twist drill are routine. The limits come from electrode straightness, guide quality and the ability to keep flushing effective as depth increases.

Yes, and this is one of its distinctive capabilities. A twist drill entering a curved or angled surface deflects and wanders because the cutting edges engage unevenly. An EDM electrode applies no force, so it starts cleanly on a slope or a curve. Cooling holes entering aerofoil and mould surfaces at shallow angles are a standard application.

Thin brass or copper tubes, single or multi-channel, consumed as they work and replaced as they shorten. Consumption is a normal running cost and is proportional to the depth drilled. A ceramic or carbide guide positioned close to the workpiece supports the tube and keeps the hole straight, and guide condition has a direct effect on hole accuracy and electrode life.

The material must conduct electricity, the process leaves a recast layer that matters where holes are fatigue-critical, and it is slower than drilling in materials that can simply be drilled. Hole roundness and straightness depend on guide and electrode condition. For soft material and modest depths, conventional drilling is faster and cheaper and there is no reason to use EDM.