Titanium is one of those materials that makes engineers nervous. They know it's strong, light, and corrosion-resistant. They also know it's expensive and "hard to machine." So they either avoid it entirely or spec it without understanding what drives the cost.

After machining titanium parts for aerospace, medical, and industrial customers over the years, I've learned that titanium isn't hard to machine — it's different to machine. The shops that struggle with it are usually shops that treat it like stainless steel. It's not stainless. It's a different animal.

This guide covers what I've learned machining Grade 2 and Grade 5 (Ti-6Al-4V) — when each grade makes sense, what tolerances are realistic, how surface finish works differently on titanium, and what you should know before you send a drawing.

Grade 2 vs Grade 5: the only two grades most people need

There are dozens of titanium alloys. For 90% of CNC machined parts, you're choosing between two:

Grade 2 (commercially pure). Unalloyed titanium. Lower strength (minimum 345 MPa yield) but excellent corrosion resistance and good formability. Easier to machine than Grade 5 because it's softer and doesn't have the abrasive alloying elements. Used for chemical processing equipment, heat exchangers, marine hardware, and medical implants where high strength isn't required but corrosion resistance is critical.

Grade 5 (Ti-6Al-4V). The workhorse. 6% aluminum, 4% vanadium, balance titanium. Minimum 880 MPa yield strength — that's in the range of some heat-treated steels, at roughly 40% less weight. This is the aerospace grade. Used for structural components, fasteners, surgical implants, bicycle frames, and anything where you need maximum strength-to-weight.

Here's how they compare on paper:

Property Grade 2 Grade 5 (Ti-6Al-4V)
Yield Strength 275-450 MPa 880-920 MPa
Tensile Strength 345-550 MPa 900-950 MPa
Density 4.51 g/cm³ 4.43 g/cm³
Hardness 80-100 HRB 30-36 HRC
Maximum Service Temp ~350°C ~400°C
Machinability Rating ~40% (relative to steel) ~25% (relative to steel)
Relative Material Cost 1x (baseline) 1.3-1.5x

The machinability numbers tell the story. If 1018 carbon steel is 100% machinability, Grade 2 titanium is around 40% and Grade 5 is around 25%. That means slower feeds, lighter depths of cut, and more tool changes. All of which add machine time and cost.

Why titanium costs more to machine

It comes down to four properties that make titanium difficult compared to aluminum or steel:

Low thermal conductivity. This is the big one. Titanium conducts heat about 15% as well as carbon steel and about 5% as well as aluminum. When the cutting tool engages the material, the heat doesn't leave with the chip — it stays at the cutting edge. Tool tip temperatures in titanium can reach 900°C. Compare that to aluminum where the chip carries most of the heat away.

What this means in practice: you run lower speeds (30-60 surface meters per minute vs 150-300 for stainless, vs 300+ for aluminum), you keep coolant flowing, and you change tools more often. A carbide end mill that lasts 200 parts in aluminum might last 50 parts in titanium.

High strength at elevated temperature. Most metals soften when they get hot during cutting. Titanium holds its strength. At 500°C, Grade 5 still has about half its room-temperature strength. This means the cutting force doesn't drop as the tool heats up — you're effectively cutting a material that refuses to get easier to cut.

Work hardening. Titanium doesn't work-harden the way stainless steel does, but a dull tool rubbing instead of cutting will harden the surface and make subsequent passes more difficult. This is why you never let a tool dwell on a titanium surface — keep the feed rate up, keep the tool moving through the material.

Chemical reactivity at high temperature. At cutting temperatures, titanium reacts with the tool material. Titanium atoms diffuse into the carbide tool, weakening the cutting edge. This is called galling or built-up edge — bits of titanium weld themselves to the tool, the cutting edge fails, and the surface finish goes bad. High-performance coated carbide tools (AlTiN or TiAlN coating) are mandatory. Uncoated tools in titanium will fail within minutes.

Realistic tolerances for titanium

The standard "±0.01mm" tolerance claim you see on every machining website needs context when the material is titanium.

For aluminum or brass, ±0.01mm (0.0004") on a turned diameter is routine. For titanium, it's achievable — but it costs more to hold. Here's what I tell customers:

Tolerance Aluminum Stainless Titanium Grade 5
±0.05mm Standard, no premium Standard Standard
±0.02mm Standard Slight premium Moderate premium
±0.01mm Achievable Premium Significant premium
±0.005mm Needs discussion Difficult Needs discussion, may not guarantee

The issue with tight tolerances on titanium is thermal expansion during machining. Even with flood coolant, a titanium part will warm up during cutting and then contract when it cools. A bore that measures dead-on at the machine might be undersize by 0.005mm when it reaches room temperature. Good shops compensate for this — they measure at controlled temperature, they know the coefficient of thermal expansion, and they adjust. But it's another variable that adds time and inspection effort.

Surface finish on titanium

Titanium can produce excellent surface finishes — Ra 0.4 μm is achievable with the right tooling and parameters. But you can't get there the same way you would with aluminum.

In aluminum, you can slow down the feed rate on the finish pass and get a mirror surface. In titanium, slowing down too much causes rubbing, which generates heat, which causes galling, which ruins the finish. The approach is: sharp tool, correct speed, correct feed, flood coolant, one clean pass.

Common surface finishes for titanium parts:

Process Typical Ra Notes
As-machined (turned) 0.8-1.6 μm Standard for non-critical surfaces
As-machined (milled) 0.8-3.2 μm Depends on cutter, stepover
Bead blasted 1.0-2.5 μm Uniform matte appearance
Brushed 0.5-1.0 μm Linear grain, decorative
Polished 0.1-0.4 μm Mirror finish, labor-intensive
Anodized (Type II) Same as substrate Color options: blue, gold, purple, green, black
Passivated Same as substrate Nitric or citric acid — removes free iron, enhances natural oxide layer

Titanium anodizing is different from aluminum anodizing. On aluminum, anodizing grows an aluminum oxide layer that adds thickness and changes dimensions slightly. On titanium, anodizing creates a thin, transparent titanium dioxide layer. The color comes from light interference — different voltages produce different oxide thicknesses and therefore different colors. The part doesn't change dimension measurably. Titanium anodize is more decorative than protective because titanium is already naturally corrosion-resistant. It won't chip or peel like paint.

Design considerations for titanium parts

Thin walls are the enemy. A 16mm thick aluminum wall behaves predictably under cutting forces. A 1mm wall in titanium is spring — it deflects, vibrates, and generates chatter. If you need thin walls in titanium, plan for slower machining, more frequent tool changes, and possibly wire EDM as an alternative for the thin features.

Deep holes are also a problem. The low thermal conductivity means the drill tip gets hot fast. Deep-hole drilling in titanium (depth > 5x diameter) usually needs peck drilling cycles or specialized carbide drills with through-coolant. If your part has a 2mm hole that's 40mm deep in titanium, expect to pay for it.

Sharp internal corners should be avoided. Titanium's combination of high strength and low ductility makes it notch-sensitive. Sharp internal corners concentrate stress. Where aluminum might deform slightly at a sharp corner, titanium can crack. Standard DFM practice — specify the largest internal radius the design allows, minimum 0.5mm, preferably more.

Threaded holes in titanium benefit from roll-form taps rather than cut taps. Roll forming doesn't remove material — it displaces it, creating a stronger thread with better fatigue resistance. But roll tapping requires more torque, and in small diameters (M2 and below), the risk of tap breakage is real. If your design has small threaded holes in titanium, talk to the shop before finalizing the thread spec.

When titanium is worth the cost

For most applications, aluminum or stainless steel does the job for less money. Titanium earns its premium in specific situations:

If your part doesn't hit at least one of those, you're probably better off in 7075 aluminum or 17-4 PH stainless.

One thing I've noticed: customers who come to us for titanium parts usually come back. Not because titanium is pleasant to machine (it isn't) but because once you've designed around titanium's properties and experienced the performance, aluminum feels like a compromise. Titanium parts have a quality feel — dense, strong, permanent. That matters for some products and not at all for others.

Bottom line

Titanium isn't magic. It's a material with specific advantages (strength-to-weight, corrosion resistance, biocompatibility) and specific costs (material price, slower machining, shorter tool life). The key is matching the material to what the part actually needs.

If you're considering titanium for a part, send the drawing and tell the shop what the part does — the loads, the environment, the temperature range. A shop that knows titanium will tell you honestly whether it's the right call or whether you'd be better off in 7075 aluminum or 17-4. If the shop says "sure, no problem" without asking any questions about your application, find a different shop.