You have a hardened part that needs a small, deep hole, and a drill bit will not do the job. An EDM drilling machine burns that hole with a spinning, energized tube electrode and high-pressure dielectric flow. It works on any conductive metal, whatever its hardness, and leaves no cutting force on thin walls. That makes it the standard way to put wire EDM start holes in hardened tool steel and cooling holes in nickel alloys.

For most shops, a small-hole electrical discharge machining (EDM) driller is the right tool for start holes and small precision holes in hardened or tough conductive alloys. It trades speed for reach, since it is slower than twist drilling in soft steel. In return it will reach depths and hardness levels where carbide drills chip, wander, or snap off inside the part. A broken drill in a finished die is a costly failure, and small-hole EDM avoids that risk.

The harder part is choosing the machine. Hole diameter, depth ratio, entry angle, hole count, and breakthrough risk all change what a machine needs. The sections below help you match those specs to a manual or computer numerical control (CNC) setup, then check a new or used unit before you buy.

How Does an EDM Drilling Machine Produce a Hole?

An EDM drilling machine removes metal with thousands of small sparks between a tube electrode and the part. It never makes physical contact. The servo holds a tiny spark gap while the electrode feeds down, and the hole grows slightly larger than the tube.

How Do the Electrode, Discharge, and Flushing Work Together?

Small hole EDM uses a brass or copper tube, often with one or more internal channels. The power supply sends pulses across the gap. Each pulse melts and vaporizes a small crater in the workpiece and wears a little from the electrode tip.

Three actions keep the burn stable:

• Rotation spreads wear evenly around the tip, which keeps the hole round and stops a core from forming.
• High-pressure flushing pushes dielectric fluid down the tube bore and carries debris up and out of the hole.
• Servo control backs off when the gap fills with debris, then feeds forward once it clears.

Most hole drilling EDM machines run deionized water as the dielectric fluid. Water carries debris out well at high pressure and cools the zone quickly. When flushing fails, debris bridges the gap. The machine then starts arcing, cutting slows, and the hole wall turns rough.

Why Can the Process Drill Hardened Conductive Materials?

EDM drilling ignores hardness because heat does the work. A study published by NIST notes that micro-EDM removes material by melting and vaporization instead of shearing. It also found that the volume removed grows in a straight line with discharge energy. Hardness on its own does not stop the burn the way it stops a drill, although heat treatment can shift the removal rate somewhat.

What changes the burn is the material's thermal and electrical behavior. Melting point, conductivity, and heat transfer all set the removal rate and the electrode wear ratio. Carbide, titanium, and nickel superalloys all drill well, though each needs its own settings. The one firm limit is conductivity: ceramics, glass, and most composites will not burn. The same logic drives sinker EDM for hardened parts and complex geometry.

Where Does Small-Hole EDM Fit in Production?

Small-hole EDM earns its place in two jobs: start holes for wire EDM, and finished holes in parts too hard or too delicate to drill. Outside those jobs, other methods usually win on cost.

Creating Start Holes for Wire EDM

Wire cut EDM needs a hole to thread the wire before it can cut an inside profile. In a hardened die plate, that hole has to go in after heat treat. Machining the plate soft and drilling first is an option, but heat treat distortion can then move the hole out of position.

A small-hole driller puts the start hole right where the program needs it, in the hardened plate. The operator can place it close to the profile, so the wire has less idle travel before it starts cutting. The hole only needs to be large enough for threading, so a mid-size tube burns it fast. For moldmaking and die work, this is often the main reason a shop buys the machine.

Drilling Precision Features in Difficult Materials

Finished small hole drilling is the second major use. Here the hole is part of the product, so its size, position, and wall condition all go through inspection. Common examples include:

• Film cooling holes in turbine blades and vanes for aerospace engine components
• Fluid and flushing passages in hardened forging and extrusion dies
• Small ports in stainless and titanium parts for medical device manufacturing
• Fuel system and injector features in automotive parts

Turbine work shows the stakes. Some hollow airfoil castings have internal cavities only 0.03 inch wide, so the electrode must stop right after it breaks through. At the micromachining end, precision machines hold hole accuracy to about a micron. Industry demands vary a great deal, a theme covered in this look at EDM demands across aerospace, energy, and forging. Hard dies in forging operations raise yet another set of needs.

When Is Conventional Drilling a Better Choice?

A twist drill or gun drill is faster and cheaper when the material is soft or pre-hardened below the carbide limit. It also wins when the hole is large and a normal cutting burr can be removed later. A carbide drill can finish in seconds a hole that takes minutes to burn.

Other processes compete too. Laser drilling is fast for very shallow holes, though depth and wall quality trade off, as covered in this comparison of EDM vs laser cutting for tight tolerance parts. Any EDM leaves a recast layer, so review the process limits and trade-offs of EDM before you commit a new part to it.

What Determines Hole Quality and Cycle Time?

Hole quality and cycle time come mostly from three things: how the electrode wears, how well debris leaves the hole, and how the machine handles breakthrough. The power supply settings sit on top of all three.

Electrode Diameter, Wear, and Hole Geometry

The finished hole is larger than the tube by the spark gap on each side, plus some side clearance. Machines commonly handle tubes from about 0.003 inch up to around 0.156 inch, depending on model and options. Smaller tubes flex more, so long, thin electrodes need guide support near the part surface.

Tip wear is fast in drilling, and in some jobs the tube loses nearly as much length as the hole depth gained. A worn tip can round over and taper the hole or leave the bottom out of round. On blind holes, the depth control has to track wear or the hole comes up short. Better power supply tuning reduces tip wear, which improves roundness and gives more holes per electrode.

Flushing, Depth, and Breakthrough Control

Deep holes get harder to flush as they go. Pressure drops along the tube, and debris has farther to travel up the gap. Burn rate slows with depth, and arcing risk climbs past about 20 to 30 diameters in many setups.

Breakthrough is where a lot of time goes. One industry report found that much of the drilling time falls in the last 2 or 3 percent of hole depth. When the tip exits, flushing pressure escapes and the servo hunts to clear the gap. The same report describes a 10 to 20 percent cycle time drop from better breakout detection alone. It also covered a long electrode as small as 0.0125 inch drilling straighter with less back-strike.

Burr-Free Edges, Recast, and Inspection Requirements

EDM produces burr-free holes because nothing pushes metal ahead of a cutting edge. That helps a lot on cross holes and exit edges that are hard to deburr. Entry edges can still show a slight radius or wash from sparks along the side of the tube.

The wall carries a recast layer and a heat-affected zone. Its thickness follows discharge energy, so aggressive settings cut faster but leave more recast. Rotating parts in aerospace and energy often limit recast depth and check for microcracks through sectioning. Sinker EDM faces the same trade-off, as this guide on stable burns and lower recast explains. Build that inspection step into your cycle time estimate.

How Should You Specify a Machine for the Job?

Start with your hardest hole, not your average one. The part that pushes diameter, depth, angle, or hole count to the limit will decide the machine.

Match Hole Diameter, Depth, Angle, and Workpiece Size

Write down four numbers before you talk to any vendor:

• Diameter range: the smallest and largest tube you will run, plus guide sizes for each
• Depth ratio: the deepest hole divided by its diameter
• Entry angle: steep angles on curved surfaces need a tilting head or rotary axis
• Workpiece envelope: part weight, height under the head, and X/Y travel for the full hole pattern

EDM hole drilling machines vary widely in reach. Some ZNC benchtop models are rated for workpieces up to about 550 pounds. Large CNC units carry 2,000-pound parts on tables near 60 by 50 inches. Check the open height with your tallest fixture in place, not just the table rating.

Choose Manual Positioning or CNC for the Hole Pattern

Manual or ZNC machines suit start holes and low hole counts. The operator jogs to each location, sets depth, and burns. That works well for a few start holes in a die plate, and these machines cost far less.

CNC small hole EDM makes sense when hole count, position tolerance, or angle rises. A CNC unit runs full patterns from a program, holds position to the scale accuracy, and repeats across batches. Machine platform choices also shape reliability over time, so review the full EDM equipment range and how your drilling and sinker work share the floor.

Assess Electrode Handling, Rotary Access, and Automation

Electrode changes limit unattended running. An automatic electrode changer swaps spent tubes and guides on its own. One production drill carries 60 electrodes and 30 guides and loads the next electrode when one wears out.

Rotary tables and tilt axes open access to angled holes on blades, vanes, and rounded parts. Submersible rotary tables let the part burn fully under dielectric, which steadies breakthrough into internal cavities. When no standard machine fits, custom EDM machines and multi-head and multi-lead setups can burn several features at once. The engineering method behind those builds is covered under EDM machine customization.

What Should Buyers Verify Before Purchase?

Proof on your own part is worth more than any spec sheet. Before you sign a purchase order, get evidence in three areas.

Test the Actual Material and Hole Specification

Send a real part or a coupon of the same alloy and heat treat. Ask for your exact diameter, depth, and angle, plus your worst breakthrough condition. Then measure the results yourself:

• Burn time per hole, including electrode changes
• Electrode length used per hole
• Entry and exit diameter, taper, and position
• Recast depth from a sectioned sample, if your spec limits it

A vendor burn in easy material at a shallow depth tells you little about your job. Coatings and internal cavities change the burn, so include them in the test part.

Check Utilities, Consumables, Service Access, and Total Cost

Confirm input power, floor space, and the dielectric system needs. Deionized water systems need resin, filters, and conductivity monitoring. Tubes, guides, and collets are ongoing costs that scale with hole count.

Price the consumables per hole and add them to labor and machine time. Ask who stocks guides and electrodes for your model, and how fast a field technician can reach your plant. Source filtration and tooling from EDM components and accessories suppliers who know the process. Also look at how EDM machine manufacturers approach reliability before you commit to a platform.

Evaluate Used Equipment Through a Demonstration Burn

Used EDM drilling machines can cost very little. Listings include a 1997 hole driller priced at $3,500 in fair condition. The low price only pays off if the machine burns well and parts are still available.

Ask the seller to run a demo burn under power at your target diameter and depth. Watch for servo hunting, arcing, and pump pressure drops. Check the axes for backlash and the spindle for runout, and confirm the control still loads programs. A machine calibration check for EDM accuracy after install will show how far the positioning has drifted. Plan for EDM repair and maintenance on pumps, seals, and power supply boards early on.

Match the Drilling Process to the Hole Specification

Buy for the hole, not the brochure. A manual driller that burns clean start holes in hardened plate beats a large five-axis unit that sits idle. A cheap used unit is no bargain for turbine cooling holes if it cannot sense breakthrough and back-strikes cavity walls.

Your worst hole sets the spec. Its depth ratio sets the flushing and servo needs, and its angle sets the axes. Its recast limit decides how hard you can push the power supply, and your yearly hole count decides whether automation pays back. Test that hole in your material before you spend money.

EDM Zap Parts Inc. has worked on EDM equipment since 1971, and you can read more about our company history. If your holes feed into sinker work, review our EDM power supplies and custom engineering solutions. Call 1-630-852-1699, email info@edmzap.com, or use the EDM Zap contact form to discuss your application. You can also visit EDM Zap Parts Inc. to see our full range of support.

Frequently Asked Questions

What Is EDM Hole Drilling?

EDM hole drilling burns small holes with a rotating tube electrode and high-pressure dielectric flushing through the tube. It works on any conductive metal, whatever its hardness, and it leaves no cutting burr.

How Much Does an EDM Drilling Machine Cost?

Cost ranges from a few thousand dollars for an older used manual unit to far more for a new multi-axis CNC system with automation. Add electrodes, guides, resin, filters, and service to the purchase price to find your real cost per hole.

When Is a CNC Small-Hole EDM Machine Worth Considering?

A CNC machine is worth it when you drill many holes per part, need tight position tolerance, or burn angled holes. For a few start holes in die plates, a manual or ZNC machine usually covers the work at lower cost.

Can a Small-Hole EDM Machine Drill a Start Hole for Wire EDM?

Yes, start holes are one of the most common jobs for these machines. You can burn them after heat treat in hardened plate, so the hole stays in the right spot for wire threading.

What Should I Check Before Buying a Used EDM Drilling Machine?

Watch a demonstration burn at your own hole size and depth, and look for arcing, servo hunting, or pump pressure loss. Then check axis backlash, spindle runout, control function, and whether guides and parts are still available for that model.