Guides / Process

Drilling Pure Tungsten Without Cracks: Tools, Exit Chipping and Hole Limits

October 9, 2026 · Reviewed October 4, 2026

Drilling is where pure tungsten shows its worst side. A hole looks like a simple feature, but it concentrates stress at the drill tip, traps heat at the bottom and leaves a thin brittle skin at the exit. A drill that works well in steel can chip, crack or break in tungsten within seconds.

This guide explains why pure tungsten behaves this way, how experienced shops drill it, what limits to expect for depth and diameter, and when to specify EDM instead. It applies to pure tungsten and to the sintered grades of tungsten. Heavy alloy drills much more like cast iron and is covered elsewhere.

Why pure tungsten cracks when drilled

Pure tungsten has the highest melting point of any metal and a very high hardness for a metal. It also has a ductile-to-brittle transition above room temperature, so at shop temperature it fractures rather than flows. A cutting edge in steel shears a continuous chip. In tungsten the same edge starts a crack ahead of the cut, and the chip breaks away in small fragments.

Three features of a drilled hole make this worse.

• The chisel edge at the centre of the drill does not cut, it pushes. That thrust loads the brittle material in tension.
• The bottom of the hole is a confined space. Heat and fines build up there.
• The exit leaves a thin web. As the drill breaks through, the remaining layer is too thin to resist the thrust and it breaks outward.

Material condition matters as well. Stress-relieved, worked tungsten (rolled, swaged or forged) cuts more cleanly than a coarse as-sintered blank, which can hide porosity and grain boundary weakness. If a hole will sit close to an edge, tell the shop how the blank was made. The sintered versus wrought blanks guide explains the difference.

Tools and settings shops use

The approach is the same across most shops that drill tungsten regularly, though details vary.

Parameter	Typical practice	Reason
Drill material	Solid micro-grain carbide	Holds an edge against tungsten hardness
Point geometry	Split point or thinned web, 118 to 140 degrees	Cuts a smaller chisel edge, lowers thrust
Coolant	Flood or through-tool, filtered	Removes heat and fines from the hole bottom
Feed	Low and constant, reduced at breakthrough	Prevents exit chipping
Cycle	Peck, with full retract on deeper holes	Clears fines, limits heat build-up
Machine	Rigid, low runout, no spindle wobble	Runout snaps small carbide drills

Spindle speed is kept moderate. High speed raises heat at the tip and tungsten does not tolerate thermal shock well. Exact figures depend on the drill diameter, the machine and the grade, and a shop will often run a test hole on scrap before committing to the real part.

A pilot drill helps on larger diameters. A small pilot hole removes the chisel edge loading, and the larger drill then cuts mostly with its lips. Some shops also pre-spot the position with a short, stiff centre drill so the main drill does not walk.

Controlling exit chipping

The cheapest improvement is to back up the exit. Clamping a sacrificial plate of steel, graphite or ceramic-filled material behind the part gives the drill something to break into. Another approach is to drill from one side to about two thirds of the thickness and then drill from the other side to meet it. This leaves a small step in the middle but avoids a ragged exit on a visible face.

Reducing the feed in the last 0.5 mm before breakthrough also helps. On a CNC machine this is a simple program change. A sharp drill matters here because a worn edge pushes harder than it cuts.

Allow for a small chamfer on the exit when the design permits. A 0.2 to 0.5 mm chamfer removes the most fragile edge and gives a clean finish to what remains. If the drawing shows a sharp edge and the shop sees chipping risk, expect a question about it.

How deep and how small

Practical limits for drilled holes in pure tungsten are different from steel.

Hole feature	Typical limit	Alternative if beyond
Depth to diameter, peck drilling	Up to about 3 to 5 times diameter	EDM hole drilling
Smallest drilled diameter	Around 0.5 to 1 mm, and risky	EDM or laser drilling
Position tolerance	±0.05 mm typical	Jig grinding or EDM for tighter
Diameter tolerance as drilled	About ±0.05 mm	Reaming or EDM
Surface of drilled hole	Rough, with some micro-chipping	Honing, lapping or EDM

These are typical figures, and they depend on the grade, the machine and the drill. For deeper or finer holes the shop will usually suggest EDM drilling. EDM removes material with spark erosion, so it applies no cutting force and does not care about brittleness. It is slower and leaves a thin recast layer, and a shop may remove that layer if the hole is functional. For the wire version of the process, see wire EDM for tungsten parts.

When EDM is the better first choice

Choose EDM drilling when any of these apply.

1. The hole is smaller than about 1 mm in diameter.
2. The depth exceeds five times the diameter.
3. The hole sits near an edge or between thin walls.
4. The hole must be burr-free and exit-chip-free on a visible face.
5. The part is expensive and a drill break would scrap it.

For through holes in thin tungsten plate the choice often comes down to risk. One broken drill in a finished blank costs more than the extra time for EDM. If a hole is not critical, a shop may still drill it conventionally and accept some risk. State on the RFQ which holes are critical so the shop can plan around them.

A typical process route for a drilled hole

A well-run job follows a repeatable sequence, and knowing it helps you read a quote. The shop first confirms the blank: its density, its surface and whether it shows cracks or porosity under a dye penetrant or a visual check. It then sets up the part with soft, even clamping so the clamp itself does not load the brittle material. Next comes the spot or pilot operation, then the main drill with peck cycles, and finally any chamfer, ream or deburr. Between these steps a careful shop inspects the hole under magnification for hairline cracks radiating from the wall. A crack found at this stage costs the price of one part. A crack found after the part is installed in a furnace or vacuum chamber costs far more.

If the quote shows an unusually low price for a hole-heavy tungsten part, ask how many drills the shop expects to use. Carbide drills in this material are consumables, and a shop that plans for two or three per part will price accordingly. A shop that plans for none is probably either very experienced or not thinking about the risk.

Heat, fines and safety

Drilling tungsten produces hard, abrasive fines that wear the drill flutes, the chuck and the machine ways. Flood coolant with good filtration protects both the drill and the machine. Dry drilling is a poor idea, partly for heat and partly because fine tungsten dust is a respiratory hazard that shops manage with wet processing and extraction. Used coolant and swarf from tungsten are usually collected and sold or recycled because the material has real scrap value, and a good shop keeps swarf separate from other metals for that reason.

Doped and alloyed tungsten

Not all pure tungsten drills the same. Doped grades used for lamp and furnace parts have a different grain structure, and tungsten-rhenium alloy is notably more ductile and drills with less chipping, though it costs far more. Tungsten copper and tungsten heavy alloy drill far more like hard brass and cast iron, so the cautions in this guide apply less. If your design has a choice of grade and the hole is the hard part, a short conversation with the shop about an alternative grade can save money. The guide to what each grade allows compares the options.

Threads in tungsten

Tapping pure tungsten is rarely a good idea. A tap cuts with many edges at once and the thread root is a stress concentrator in a brittle material. Thread milling with a carbide cutter gives better results, and many designers avoid threads in pure tungsten entirely and use a threaded heavy alloy or steel insert, or a clamp, in their place. If the application needs a thread, discuss the grade. Tungsten heavy alloy takes threads far more easily. The threading and tapping guide covers the options.

What to put on the drawing

• Mark which holes are critical and give the tolerance on each.
• State the exit condition: chamfer size or “sharp edge acceptable with minor chipping”.
• Give the depth and diameter so the shop can see the ratio.
• Specify the surface finish inside the hole only if it matters.
• Name the process if you have a preference, for example “EDM drilled”.
• State the blank type, sintered or wrought, if you know it.

Leaving a hole feature on a pure tungsten drawing without any of this information invites a quote that assumes the cheapest process and a later argument about quality. The shop would rather ask than guess. The drawing mistakes guide lists other common omissions.

Checklist before you request a quote

1. List every hole with diameter, depth and tolerance.
2. Mark the critical holes and say what failure looks like.
3. Say whether the grade is pure tungsten, doped tungsten or another material.
4. Give the quantity, since EDM setup cost spreads better over a batch.
5. Send a STEP file along with the dimensioned drawing.

Holes sit inside the wider decision path in our guide on how to machine tungsten.

When the drawing is ready, send your RFQ. We match it with up to three shops that machine pure tungsten and reply within 24 business hours.

Frequently asked questions

Sources

• Tungsten (Wikipedia)

Keep reading

• Thin Tungsten Plate and Foil: How Shops Machine It Without Cracks or Warp
• Grinding Tungsten Heavy Alloy: Which Wheel, What Finish, How Tight