How to Drill, Ream, and Tap Titanium Alloys Effectively

Titanium’s low thermal conductivity, elastic recovery, chemical affinity, and concentrated cutting heat make holemaking difficult. Successful drilling, reaming, and tapping require rigid tools, positive but strong cutting edges, reliable chip evacuation, and abundant cutting fluid.

Drill Structure and Geometry

Twist Drills

Conventional twist drills need a strengthened web, accurately ground lips, polished flutes, and geometry that limits rubbing and promotes chip removal. Short, rigid drills reduce deflection. Cobalt-bearing high-speed steel and suitable tungsten-cobalt carbide are preferred; avoid allowing a dull edge to work-harden the hole surface.

Four-Land Twist Drills

A four-land construction improves guidance and hole straightness while distributing contact. Clearance and coolant delivery remain critical because extra margins can raise friction if the tool is not sharp.

Deep-Hole Drills

Deep-hole drilling demands internal coolant, controlled chip breaking, and uninterrupted evacuation. Pecking or staged withdrawal may be required when the tool cannot remove chips continuously.

Drilling Data and Process Control

Reduce cutting speed as hole depth, alloy strength, or diameter increases. Maintain a positive feed so the lips cut rather than rub. Flood the cutting zone with a compatible coolant and check chips for discoloration or adhesion. For Ti-6.5Al-3.5Mo-1.5Zr-0.3Si deep holes, the source process uses a dedicated drill and emphasizes cooling, chip evacuation, and surface-finish control.

Reaming Titanium

Reamer Geometry

Reamers require high rigidity, accurate margins, generous clearance, and smooth chip spaces. A small margin guides the tool, but an excessive land increases rubbing and heat. Straight-flute HSS, straight-flute carbide, and stepped carbide reamers use different cutting-section geometry.

Reaming Practice

Use a low, stable speed and sufficient feed to cut beneath the work-hardened layer. Keep stock allowance uniform, avoid stopping in the hole, and supply cutting fluid continuously. Tool runout, predrilled-hole accuracy, and thermal growth directly affect final size and roundness.

Tapping Titanium

Tap Materials

High-performance cobalt- or aluminum-bearing HSS is commonly used. The tap must resist edge chipping while maintaining a sharp profile. Thread form, hole depth, and coolant access determine whether a standard, corrected-tooth, or skip-tooth design is preferable.

Tap Structure and Geometry

Corrected-tooth taps reduce cutting load by modifying the engagement pattern. Adequate rake and clearance reduce adhesion, while polished flutes and relieved teeth provide space for chips.

Tap-Drill Diameter

Titanium springs back after cutting, so the tap-drill diameter is often selected toward the larger permissible end to reduce torque without violating thread requirements. Verify the actual thread percentage, material response, and gauging result. For blind holes, provide enough chip space below the full thread and avoid bottoming the tap.

Practical Checklist

• Use a rigid, low-runout setup and a sharp tool.
• Prevent dwelling and rubbing, which create heat and work hardening.
• Deliver coolant directly to the edge and evacuate chips before recutting.
• Reduce speed for deeper holes and stronger alloys.
• Monitor torque, chip form, surface finish, and size; replace tools before chipping begins.
• Validate every starting value on the actual machine, tool, coolant, hole depth, and alloy condition.