Gundrilling vs BTA drilling: which deep-hole method fits your job?

Deep-hole drilling covers a wide range of holes, and the right method depends mainly on three things: diameter, depth, and how many parts you’re making. Here’s how to think about the choice.

Gundrilling: precision at smaller diameters

Gundrilling uses a single-flute tool and high-pressure through-coolant to produce deep holes with excellent straightness and surface finish. It shines at smaller-to-medium diameters and where precision matters most — often eliminating a secondary reaming or honing operation.

BTA / STS: productivity at larger diameters

BTA drilling uses a different coolant and chip-evacuation principle, enabling larger diameters and much higher material-removal rates. When a hole is big and you’re making many of them, BTA usually wins on cycle time.

A simple rule of thumb

• Small diameter, highest precision, lower volume -> gundrilling
• Larger diameter, high productivity -> BTA / STS

In practice the boundary depends on your material, machine and tolerances — which is where a quick conversation with an application engineer saves a lot of trial and error. If you’re weighing a deep-hole job, tell us about the part and we’ll recommend the method and tooling.