A machinist once described titanium to us like this: “Stainless gives you a warning. It gets rough, it gets loud, it tells you it’s unhappy. Titanium doesn’t warn you. It just breaks — or burns — or makes a part that’s scrap before you even know it’s wrong.”
That is not an exaggeration. It is the reason titanium projects so often end in frustration, and it is the reason the ones that work are engineered deliberately rather than “figured out on the machine.”
The Part: A Bone Screw With a Hole Through Its Middle
The project that frames this article is a familiar one to us: a medical device manufacturer machining titanium bone screws. The job is a cannulated screw — a screw with a Ø1.5mm hole drilled through its entire length, so it can be threaded over a guide wire during surgery.
- Hole diameter: Ø1.5mm
- Hole depth: 80–120mm through the screw
- That is a depth-to-diameter ratio approaching 80:1 — a micro hole, eighty times deeper than it is wide, drilled through one of the most difficult materials in machining.
At that ratio, the tool is a needle. The cutting edge is deep in the part, invisible and unreachable. And the material is titanium alloy (Ti-6Al-4V) — which behaves the way it does for four specific reasons.
Why Titanium Fights You, Specifically
Four properties of titanium combine to make deep hole drilling brutally hard:
- It holds heat. Titanium conducts heat roughly one-sixth as well as steel. The heat that should flow away through the workpiece stays in the cutting edge, which softens the edge, which makes it cut less efficiently, which makes more heat. In a Ø1.5mm hole there is almost no volume of material to absorb that heat — it all concentrates at the cutting zone.
- It work-hardens. Like stainless, the surface of titanium hardens the instant the edge passes. Every subsequent cut has to chew through a harder layer.
- It springs back. Titanium is elastic. Under cutting pressure the workpiece surface gives way, and the cutting edge — especially a micro drill, which flexes easily — can lose contact, then snap back into it. That bouncing is what causes vibration, wandering, and size errors in small holes.
- Its chips burn. At the temperatures reached in a deep cut, titanium chips can ignite — the “white chips” that glow in the dark of a chip tray are real, and inside a 100mm-deep hole, a burning chip is a disaster for both the tool and the part.
Any one of these would be manageable. All four together, in an 80:1 micro hole, is a different world.
The Approach That Works
The fixes for titanium are not exotic, but every one of them is mandatory. Miss any of them and the process fails; get them all right and it becomes repeatable.
1. Oil-based coolant, not water-based. Water-based coolant is a poor choice for titanium. Titanium needs the lubricity of oil at the cutting edge to prevent welding and built-up edge, and the oil film also helps keep titanium chips from igniting in the cut. High-pressure through-tool delivery is non-negotiable — at 80:1, chips have to be forced out of the hole, not coaxed.
2. Cool the edge, don’t speed it up. Titanium’s cutting-speed ceiling is low. Cranking the spindle up to make the job “go faster” does the opposite — it multiplies the heat at the edge and kills the tool in seconds. The right answer is a controlled, moderate speed with enough feed for the edge to bite beneath the work-hardened layer.
3. A drill geometry made for titanium. The gun drill for this job is not an off-the-shelf tool. It is ground with a geometry that suits the material — a positive rake to shear rather than push, a polished flute so chips don’t weld to it, and an edge treatment that resists micro-chipping. On a Ø1.5mm tool, these details are the difference between 50 holes and 5.
4. Rigid guidance and a clean start. At 80:1, the hole direction is decided in the first few millimeters. A guide bushing and a precise pilot start keep the micro drill on line; without them, the hole wanders and the tolerance is gone before the drill is a quarter of the way in.
5. Let the machine hold the process. This is where a machine purpose-built for micro deep hole drilling earns its place — the rigid spindle, the high-pressure coolant system, the automated part handling that takes the human variability out of loading a 1.5mm drill. We run this exact class of job on our medical gun drilling machines, which pair high-speed spindles with the chip evacuation and guidance that micro holes demand. The bone screw project is documented end to end in our medical gun drilling case study.
The Result
With the process engineered rather than improvised, the numbers stopped being a gamble:
- The 80:1 through-hole drilled clean and straight, hole after hole — the straightness and surface finish held across the full screw length.
- Tool life became predictable — measured in a consistent number of holes per drill, not “until it breaks.”
- Scrap fell to a single-digit percentage — from a starting point where a meaningful share of parts were being lost.
- The process transferred to new screw geometries — once the parameters were locked, a new part was a parameter change, not a crisis.
The Takeaway: Titanium Isn’t Machined by Confidence
There is a saying in shops that work with titanium: don’t trust the material, and don’t trust luck. Titanium will not show you a worn edge and let you plan around it. It will simply fail.
So the way to win with titanium is not to try harder on the machine — it is to engineer the process first: the right coolant, the right tool geometry, the right parameters, the right machine. For the medical industry this matters more than anywhere, because a scrap titanium part is not just money lost — it is a supply chain that someone’s surgery is waiting on. The same process-first discipline applies across materials — here is the stainless steel version of the same rescue.
If you are fighting a titanium part, don’t start with the feed override. Start with the process — send us the material, the hole spec, and your current pain, and we will tell you what the first correct setup looks like.