Almost every micro hole quote starts with the wrong number. Diameter alone decides very little — the process, the price, and the list of shops that can actually do the work are set by depth-to-diameter ratio, how much taper you can live with, and what the exit side has to look like.
This guide covers what micro-EDM, ultrashort-pulse laser, nanosecond laser, and mechanical drilling really deliver in tungsten-family materials; why cycle times differ by three orders of magnitude between them; how a 50 µm hole gets measured at all; and what to put in the RFQ so quotes are comparable.
- Specify diameter, depth, taper allowance, and exit condition together. A supplier's "smallest hole" figure describes a favorable case, not your part.
- Taper is normal, not a defect. A published study measured a laser through-hole at 50 µm entry and 25 µm exit across 300 µm of material; perpendicular laser drilling typically leaves 5–10° of positive taper.
- Tungsten resists thermal processes for the same reason it is useful: a 3,422 °C melting point and roughly 170 W/m·K of thermal conductivity carry heat away from the cut.
- Cycle time drives cost, and the spread is enormous — a laser hole can take about 200 ms, a comparable micro-EDM hole two to five minutes. Volume decides which is cheaper.
- Below about 0.1 mm, air gauging runs out. Agree the inspection method — optical, µCT, or sectioning — before production, not at receiving.
Diameter Is the Least Useful Number in Your RFQ
Shops advertise their smallest hole because it is the easiest thing to publish. It is also the least transferable. A 30 µm capability demonstrated in 0.2 mm of stock says almost nothing about a 30 µm hole through 2 mm of tungsten, because the constraint changes from spot size to debris evacuation, electrode wear, and beam delivery down a deepening channel.
- Aspect ratio
- Depth divided by diameter. This is the number that decides feasibility. Fine-hole EDM is commonly quoted as stable at 15:1, workable to 20:1, and controllable to about 25:1; laser trepanning heads are typically cited around 10:1.
- Taper allowance
- How much the hole is permitted to narrow from entry to exit. This single line changes the process and often the supplier, because zero taper requires specific beam delivery or a second operation.
- Exit condition
- Whether the exit diameter, burr, and edge quality are controlled or merely incidental. On a flow orifice the exit is the functional feature; on a vent it may not matter at all.
- Which tungsten
- Unalloyed tungsten, tungsten heavy alloy, and cemented carbide behave differently. All three are electrically conductive, so EDM is available for each — but only tungsten heavy alloy is a realistic candidate for a mechanical drill.
Two quotes that differ by 5× usually differ by assumption, not by margin. One supplier priced a hole with free taper and an uncontrolled exit; the other priced a straight hole with a specified exit diameter. Both read the same drawing.
What Each Process Actually Does in Tungsten
Four processes compete for this work, and they are not interchangeable. The table gives realistic published envelopes rather than best-case records.
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| Process | Practical diameter | Aspect ratio | Fits which tungsten |
|---|---|---|---|
| Fine-hole / micro-EDM | 30–40 µm at the low end; 0.3–1.0 mm for stable production | 15:1 stable, to about 25:1 under control | All three; the material only has to conduct |
| Ultrashort-pulse laser (ps / fs) | 2–100 µm typical; single-digit microns demonstrated | About 10:1 with a trepanning head | All three; the usual answer for the smallest holes |
| Nanosecond UV laser | 30–500 µm | Approx. 1:6 demonstrated in 300 µm carbide | Carbide and ceramics; more recast than USP |
| Mechanical micro drilling | 0.1 mm and up | 20×d to 50×d with purpose-built drills | Tungsten heavy alloy only |
Fine-hole EDM: the default for conductive hard materials
Because material is removed by spark erosion rather than force, hardness is irrelevant and cemented carbide is no harder to drill than tool steel. Service providers publish minimum holes around 30–40 µm using micro-pipe electrodes down to about 35 µm, positional work in the 1 µm range, and surface finishes to 4 µin Ra, on workpieces up to about 2″ thick. Published research on micro-EDM in cemented carbide reports 40–70 µm holes with roundness near 1 µm and aspect ratios approaching 15. The trade is time and electrode wear, both of which get worse as the hole gets smaller and deeper.
Ultrashort-pulse laser: the answer below about 30 microns
Picosecond and femtosecond pulses remove material faster than heat can conduct into the surrounding metal, which is exactly the property tungsten's high thermal conductivity otherwise defeats. Micro hole service providers publish a 2–100 µm production range with capability below that in favorable geometry, and taper-free drilling around 18 µm has been demonstrated in tungsten. Where the hole is smaller than an EDM electrode can practically be made, this is the route.
Nanosecond laser: faster and hotter
Nanosecond UV sources handle carbide and ceramics at 30–500 µm, with a demonstrated 50 µm hole through 300 µm of tungsten carbide. Removal is by melt ejection rather than cold ablation, so expect more recast, more spatter, and a larger heat-affected zone than an ultrashort-pulse process. On a vent or a wire pass-through that may be irrelevant; on a metering orifice it is not.
Mechanical micro drilling: only one of the three materials
Purpose-built micro drills reach 0.1 mm and up, in versions rated to 20×, 30×, and 50× diameter, with through-tool coolant on the deepest variants. Note what those drills are made of: solid carbide. Cemented carbide is the tool here, not the workpiece. Unalloyed tungsten's room-temperature brittleness and carbide's hardness both rule out conventional drilling; tungsten heavy alloy, with a ductile nickel-iron matrix, is the one that genuinely drills. Even then, micro drills break from re-cutting chips, so full-retract peck cycles and reliable evacuation matter more than speeds and feeds.
Taper Is a Specification, Not a Defect
Every one of these processes produces a hole that is wider at the entry than at the exit, because energy and debris both have to travel through the hole being made. The magnitude surprises people who have not measured it.
In a published µCT study of ultrashort-pulse laser drilling, a through-hole measured roughly 50 µm at entry and 25 µm at exit across 300 µm of material — the exit was half the entry. Blind holes in the same work converged toward about 5° of taper as drilling time increased. For perpendicular laser incidence generally, positive taper in the 5–10° range is the expected result rather than an error. EDM produces its own taper as the electrode wears and the gap widens near the entry, which is why deep-hole EDM tolerance loosens from roughly ±0.02–0.05 mm on shallow holes toward ±0.1 mm as depth increases.
If you need straight walls, say so and pay for it
- Trepanning head: orbits the beam to cut the hole's perimeter; 30–500 µm at aspect ratios to about 10:1
- Tilted-beam or helical drilling: deliberately compensates the natural cone to reach zero or negative taper
- Multi-axis scan head: 100–500 µm holes but at low aspect ratios, around 1:5 or less
- EDM with electrode compensation: reduces but does not eliminate taper; a second finishing pass costs cycle time
The decision belongs to the designer, not the shop. If the hole is a metering orifice, the exit diameter is the functional dimension and taper has to be controlled. If it is a vent, a coolant passage, or a wire feedthrough, accepting 5–10° of taper may cut the price substantially. A drawing that dimensions only the entry diameter has left the most expensive question unanswered.
Why Tungsten Specifically Resists Micro Drilling
The properties that make tungsten worth specifying are the same ones that make a small hole in it expensive.
- Melting point
- At 3,422 °C, tungsten has the highest melting point of any metal. Every thermal process — laser, EDM, plasma — has to deliver more energy per unit of removed material than it would in steel.
- Thermal conductivity
- Around 170–175 W/m·K, roughly three times that of steel. Heat leaves the interaction zone before it can do useful work, which is why long-pulse lasers struggle and ultrashort pulses succeed.
- Brittleness
- Unalloyed tungsten is brittle at room temperature and cemented carbide has almost no plastic reserve. Mechanical drilling risks chipping at entry and exit rather than clean cutting.
- Electrical conductivity
- The one property working in your favor. All three tungsten materials conduct, so EDM is available for every one of them — which is not true of the technical ceramics they often compete with.
There is a useful consequence buried in the thermal numbers. Because heat is conducted away so efficiently, a nanosecond pulse spends much of its energy heating material that will not be removed, producing recast and a wider heat-affected zone for the same hole. Shortening the pulse into the picosecond and femtosecond range removes material before conduction has time to act. In tungsten, pulse duration is not a refinement — it is often what determines whether the hole is clean or merely present.
Cycle Time Decides the Economics
Micro hole pricing confuses buyers because per-hole cost varies by orders of magnitude between processes that produce visually similar results.
Published figures make the spread concrete. An ultrashort-pulse laser through-hole in the study cited above took about 200 ms and roughly 80,000 pulses. Micro-EDM research on cemented carbide reports under two minutes for a 150 µm hole and about five minutes for a 40 µm hole. That is a difference of several hundred times per hole. For a part with one hole, it barely matters; for a part with four hundred, it is the entire quote.
What actually sits in the price
- Process development and first-article proving, which is often the largest single item on a low-volume job
- Fixturing and part-to-part registration at micron scale
- Electrode consumption and dressing, or optics setup and beam characterization
- Cycle time per hole multiplied by hole count
- Post-processing if recast, spatter, or burrs must be removed
- Inspection, which on micro holes can exceed the drilling cost
This is why a single prototype hole can cost more than a hundred production holes, and why "can you just put a 0.1 mm hole in this piece of tungsten" is a hard question to answer cheaply. If you are prototyping, ask about existing setups — a supplier already running a comparable electrode or optics recipe can absorb your part far more cheaply than one starting from scratch.
How a 50-Micron Hole Gets Measured
Specifying a tolerance you cannot verify is how micro hole programs stall at receiving inspection. Below roughly 0.1 mm the familiar tools stop applying, and the method has to be agreed in advance.
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| Method | Practical floor | What it tells you | Limitation |
|---|---|---|---|
| Pin or plug gauge | Around 0.5 mm | Go / no-go on the narrowest section | Fragile and impractical at micro scale; tells you nothing about taper |
| Air gauging | About 0.1 mm | Diameter with almost no contact force | Runs out below roughly 0.1 mm; needs a matched master |
| Optical measurement | Single-digit microns | Entry and exit diameter, roundness, edge condition | Sees the two ends only; the channel between them is invisible |
| Micro X-ray CT (µCT) | Voxel sizes near 1 µm | Full internal geometry, taper profile, constrictions | Slow and costly; a sampling tool, not a 100% inspection |
| Destructive sectioning | Any size | Recast layer, wall condition, true profile | Consumes the part and can introduce preparation artifacts |
Two practical implications. First, if taper matters, the drawing has to dimension both entry and exit, because no single-ended method reports both. Second, decide what is a 100% check and what is a sampled check, and put it in the RFQ — µCT on every hole is rarely affordable, but µCT on first article plus optical entry and exit in production is a defensible plan that a capable supplier will recognize.
How to Qualify a Supplier
Micro hole suppliers cluster into laser job shops, EDM specialists, and refractory-metal machining houses. Each will steer you toward the process they own, which is reasonable but worth accounting for.
Questions that separate suppliers
- Which processes do you own in-house — micro-EDM, ultrashort-pulse laser, nanosecond laser, or mechanical?
- Have you drilled this diameter at this aspect ratio in this specific tungsten material?
- What entry-to-exit ratio should we expect, and can you show measured data?
- What pulse duration is your laser, and what recast or HAZ does it leave here?
- What is the cycle time per hole, and how does it scale with our hole count?
- How do you compensate electrode wear on deep EDM holes?
- How will you inspect the hole, and what is sampled versus 100%?
- Do you remove recast and burrs, and is that included in the quote?
- What is the process development charge, and is it separate from piece price?
- What yield should we assume, and who pays for scrapped blanks?
Treat a published minimum hole size as a demonstration, not an offer. Figures such as 2 µm, 30 µm, or 40 µm were achieved in a particular material at a particular thickness. Ask for a feasibility review against your material, thickness, aspect ratio, taper allowance, hole count, and inspection plan — and expect a serious supplier to ask for a sample blank before committing.
What to Send With the RFQ
Micro hole RFQs fail on missing context more than on missing dimensions. These ten items make quotes comparable.
- Material by name and standard — unalloyed tungsten, a specified ASTM B777 tungsten heavy alloy class, or a named WC-Co grade — never just "tungsten."
- Material thickness at the hole, which with the diameter defines the aspect ratio.
- Entry diameter with tolerance, and exit diameter with tolerance if the exit is functional.
- Permitted taper, stated as an angle or as an entry-to-exit ratio.
- Hole count per part, pattern, and positional tolerance between holes.
- Whether the hole is through or blind, and the depth tolerance if blind.
- Acceptable recast layer, heat-affected zone, burr, and spatter on both faces.
- Required internal surface condition if the hole meters flow or carries a fiber, wire, or fluid.
- Inspection method and acceptance criteria, including what is sampled and what is 100%.
- Quantity, prototype versus production intent, and any program requirements such as defense end use or material origin documentation.
Fix the process before you compare prices. Once the aspect ratio, taper allowance, and hole count point to EDM, ultrashort-pulse laser, or mechanical drilling, the list of suppliers that can produce and verify the hole becomes short and specific.
FAQ About Tungsten Micro Hole Drilling
- What is the smallest hole that can be drilled in tungsten?
- Laser micro hole services publish a production range of 2–100 µm with capability below that in favorable geometry, and taper-free drilling near 18 µm has been demonstrated in tungsten. Fine-hole EDM providers publish minimums around 30–40 µm. Every one of those figures assumes a specific thickness and aspect ratio, so treat them as evidence the capability exists rather than as a specification for your part.
- EDM or laser for a micro hole in tungsten?
- Roughly: EDM below about 1 mm down to 30–40 µm when aspect ratio matters more than speed, since it holds 15:1 comfortably and about 25:1 under control. Ultrashort-pulse laser when the hole is smaller than a practical electrode, when hole counts are high, or when cycle time dominates. Nanosecond laser when the material is carbide or ceramic and a larger heat-affected zone is acceptable.
- Can a micro hole in tungsten be drilled mechanically?
- In tungsten heavy alloy, yes — its ductile nickel-iron matrix machines with carbide tooling, and purpose-built micro drills go down to 0.1 mm with depth ratings to 20×, 30×, and 50× diameter. In unalloyed tungsten and cemented carbide, no. Note that those micro drills are themselves made of cemented carbide, which is a common source of confusion in this search.
- How much taper should I expect?
- More than most people assume. A µCT study of ultrashort-pulse laser through-holes measured about 50 µm entry against 25 µm exit through 300 µm of material, and perpendicular laser drilling generally leaves 5–10° of positive taper. Trepanning, helical, or tilted-beam drilling reduces or eliminates it at additional cost. State the permitted taper on the drawing.
- Why is one hole so expensive?
- Because the cost is mostly setup. Process development, fixturing, electrode or optics preparation, and first-article inspection are largely independent of hole count, so a single prototype hole absorbs all of it. Ask whether the supplier has an existing recipe close to your requirement — that is usually the difference between an affordable prototype and an unaffordable one.
- Does the hole need post-processing?
- It depends on the process and the function. EDM leaves a recast layer, and nanosecond laser drilling leaves recast and spatter; ultrashort-pulse drilling leaves substantially less. If the hole meters flow, carries a fiber or wire, or sees cyclic loading, specify whether recast is acceptable and who removes it. Leaving this unstated is a common reason two quotes are not comparable.
- How do I inspect holes this small?
- Air gauging works down to roughly 0.1 mm and stops there. Optical measurement gives entry and exit diameters and edge condition but cannot see the channel between them. Micro X-ray CT resolves the full internal geometry at voxel sizes near 1 µm but is slow enough to be a sampling tool. Destructive sectioning shows recast and wall condition at the cost of the part. Most workable plans combine µCT or sectioning at first article with optical checks in production.
- Why did two suppliers quote so differently for the same drawing?
- Usually different assumptions about taper, exit condition, and recast. One may have priced a hole with free taper and an uncontrolled exit while the other priced a straight-walled hole with a specified exit diameter and recast removal. Ask each to state the process, the expected entry-to-exit ratio, and what post-processing is included.
