Guides / Process

Drilling Titanium: Speeds, Heat and Why Holes Fail First

Of every operation a titanium part goes through, drilling is the one that punishes a wrong assumption fastest. A milling cutter that runs a little hot wears a little faster. A drill that runs hot in a titanium hole can seize, break, or leave a hole that is out of round and work hardened on the way out.

Why drilling concentrates the problem

Milling and turning both expose fresh material to the cutting edge continuously, with a chip that carries some heat away as it curls off. Drilling is different. The tool is buried in the material on all sides, the chip has to travel back up the flutes to escape, and there is far less surface area for heat to leave through.

The number that explains the rest of this article: roughly 60 percent or more of the heat generated drilling titanium ends up in the drill itself, against around 15 percent in steel. The drill is doing the job the material’s thermal conductivity should be doing and is not.

Speed down, feed up

The instinct when something is running hot is to slow everything down. In titanium drilling, the correct move is more specific: reduce surface speed, but increase the chip load rather than reducing it too.

A chip load that is too light means the cutting edge rubs across the material instead of shearing it cleanly, which generates friction heat on top of the cutting heat and work hardens the surface the next flute has to cut through. A heavier, deliberate chip load gets the edge into the material and out again with less total time in contact.

This is the opposite of what feels intuitive, and it is one of the more common mistakes on a shop’s first titanium job.

Coolant has to reach the tip, not just the hole

Flood coolant poured over the top of a drilling operation cools the surface of the part. It does very little for the cutting edge buried at the bottom of the hole.

Through spindle coolant, delivered down the centre of the drill and out at the cutting edge, is what actually manages heat where it is generated. At high pressure, typically 70 bar and above, it also helps push chips back up and out of the flutes, which matters more in titanium than in most materials because titanium chips are tougher and more prone to jamming.

A shop without through spindle coolant can still drill titanium. It has to run slower, peck more often, and accept a longer cycle. That is a legitimate way to do it, and a shop that is honest about needing to run that way is more trustworthy than one that claims the same cycle time without the coolant to support it.

Hole depth and when to change strategy

Depth to diameter	Approach
Up to 3 times	Routine, standard drill, flood or through spindle coolant
3 to 5 times	Peck cycles usually needed to clear chips
5 to 8 times	Through spindle coolant strongly preferred, dedicated peck strategy
Above 8 times	Gun drilling or a specialist deep hole process, different machine setup entirely

A hole at 10 times diameter is not the same job as a hole at 3 times diameter, even though both are “a hole.” If your part has a deep drilled feature, say the depth to diameter ratio on the RFQ rather than leaving a shop to discover it in the model.

Tapping is drilling’s harder sibling

Everything above gets worse when the next operation is tapping the same hole. A tap has more contact area between the tool and the hole wall than a drill does, which means more heat with even less room for coolant to reach the cutting action. Titanium’s tendency to gall against a similar metal adds a second failure mode on top of the heat problem: a chased or seized tap in a near finished part is an expensive mistake.

The commonly cited fix, a reduced thread depth around 65 percent rather than a full 75 percent engagement, gives up a small amount of thread strength in exchange for meaningfully lower tapping torque and heat. For most fastener applications the strength loss does not matter, and asking for it on the drawing when it does not is a legitimate way to make the feature cheaper and more reliable.

Work hardening compounds through a hole pattern

A drill that rubs instead of cuts work hardens the hole wall. If the next hole in a pattern is close to the first, the work hardened zone can extend into it, meaning each subsequent hole in a tightly spaced pattern can be marginally harder to cut than the last. Shops that run titanium regularly plan tool changes around this rather than running one drill until it fails partway through a pattern.

What to put on the RFQ

• Hole depth to diameter ratio for anything past 3 times, so the shop can plan the right strategy rather than discover it.
• Whether a thread needs full depth or whether 65 percent engagement is acceptable.
• Whether through holes can be drilled from both sides to halve the effective depth, if the geometry allows it.

None of this requires you to know titanium machining. It requires telling the shop what the hole actually needs to do, and letting them decide how to get there.

If you have holes to quote

We introduce titanium RFQs to shops that run this material in production, including the deep and tapped hole work that separates a real titanium shop from one that has only cut it occasionally. Send your RFQ, or read the design rules that cover hole depth alongside the other drawing decisions that move a titanium price.

Frequently asked questions

Keep reading

• Welded Titanium Assemblies and the Alpha Case Problem
• What Buyers Should Know Before Requesting a Titanium Quote