Drilling vs EDM, Laser & Waterjet

The Four Method Families

Every non-mechanical alternative trades away something mechanical drilling gives for free — speed, straightness, or cost — in exchange for access to holes a drill physically cannot cut.

Mechanical Deep Hole Drilling (Gundrill / BTA / Ejector)

Mechanical drilling is the benchmark the other methods are measured against. It removes material by shear cutting with a single-lip (gundrill) or multi-edge (BTA) tool and evacuates chips with high-pressure coolant. Because it is a cutting process there is no thermal damage — no recast layer, no heat-affected zone — only mechanical residual stress, entry/exit burrs, and work-hardening on difficult alloys.

Gundrilling

Single-lip tools from Ø0.5–50 mm with external chip evacuation along a V-groove. Delivers the best straightness and hole quality of any method at L/D up to 300:1, at IT5–IT11 tolerance and Ra 0.4–6.3 μm. Requires 50–150 bar through-tool coolant and a bushing-guided setup. Typical feed for 1045 steel is ~0.02 mm/rev at 80 m/min cutting speed (15–60 mm/min penetration).

BTA / STS (Single Tube System)

The same diameter range scales to Ø6–2000 mm. Chips are evacuated through the tube center, so BTA needs no peck cycles and feeds 5–7× faster than gundrilling — typically 100–300 mm/min in steel. Carbide guide pads self-pilot the head and burnish the bore wall, giving IT7–IT9, roundness <0.01 mm, axis alignment <0.4 mm/1000 mm, and Ra 0.2–1.6 μm with braced tools. For high-volume, high-L/D production BTA is described as the most economical method available.

Ejector (DTS)

Double-tube system for Ø18–250 mm at up to 100:1 L/D. Needs no face seal on the workpiece, runs at only 10–50 bar, and retrofits onto standard lathes and machining centers — the lowest-entry-cost way into deep hole drilling.

EDM Drilling

Electrical discharge machining erodes material through controlled sparks between a rotating tubular electrode and a conductive workpiece submerged in dielectric fluid. There are no mechanical cutting forces, no drill deflection, and no drill breakage — the electrode simply erodes a micron at a time. That makes EDM the only practical way to drill deep micro-holes in hardened steel, carbide, titanium and nickel superalloys.

Diameter tolerance can hold ±0.002 mm with positional accuracy ±0.005 mm. The main quality trade-off is thermal: EDM always leaves a thin recast (white) layer — 1–2 μm for micro-EDM, 10–15 μm for conventional EDM drilling of aerospace alloys — over a heat-affected zone of 0.01–0.10 mm. For fatigue-critical parts this layer must be removed by polishing or a follow-up electrochemical pass. EDM taper control is good and generally better than laser on thick workpieces.

Laser Drilling

Laser drilling removes material with focused pulses of light, by melt/vaporization (long pulses) or near-pure ablation (femtosecond pulses). It is the fastest hole-making process on the market — a GE patent notes laser drilling is over an order of magnitude faster than rotating EDM in superalloys. Galvo-scanned systems reach 2,000 holes/min for Ø0.2 mm holes and 200 holes/min for Ø0.05 mm micro-hole arrays.

Typical industrial percussion drilling uses Nd:YAG pulses of 600 μs–1 ms at ~10 pulses/sec, with 5–7 pulses per combustor hole and ~10–200 μm removed per pulse. A Ø0.05 mm hole through 2 mm steel can be drilled in under 15 seconds with advanced helical optics. Percussion drilling alone is limited to about 10:1 L/D because slag plugs the hole and taper grows; combined percussion + trepanning reaches 20–30:1, and femtosecond drilling has demonstrated 20:1 with near-zero taper (<0.05°).

Waterjet & Other Methods

Abrasive waterjet (AWJ) drills by eroding material with high-pressure water (typically 275 MPa+) carrying abrasive garnet. It has no tool wear and no thermal effect — no HAZ, no recast — and can drill stacks of different materials in one pass. But it is a piercing/trepanning process, not a true deep-hole method: the jet loses energy with depth, so taper and rounded entry edges are unavoidable.

• Taper is geometric: taper angle = tan⁻¹[(D_entry − D_exit) / (2 × thickness)]. Stand-off distance, pressure, abrasive flow rate and piercing angle all move it; minimum taper (~1.46° value) came from 275 MPa, 15° piercing angle, 2 mm stand-off.
• Surface quality: rougher than drilling — in open-hole titanium fatigue tests AWJ holes cracked earlier at the same stress because roughness and streak orientation act as crack initiators. In bolted/assembled joints the difference disappeared.
• Speed/economics: slow and comparatively expensive for small holes in thick metal; abrasive consumables add up. The niche is heat-sensitive materials, composites, and multi-material stacks.
• ECM (electrochemical): no tool wear, no recast, Ra 0.1–0.8 μm, moderate speed — a finishing partner for EDM rather than a standalone deep-hole method.
• Trepanning: mechanical annular cut that preserves a center core slug, reducing chip volume ~60% — best for large bores (90–600 mm) in expensive alloys.

Side-by-Side Comparison

Material Suitability

Hole Quality & Surface Integrity

Cost & Cycle Time

Which Method for Which Hole

Work through the steps, then read the grid.

Hybrid Approaches

The most useful trend is combining methods so each does what it is best at.

Limitations of Each Method

Key Safety Points

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