A deep hole is defined by its depth to diameter ratio (D:d), typically greater than 10:1.

Gundrilling is a precision process to drill deep holes in a variety of materials, from aluminum to superalloys. Good finish, tight diameter control and straightness are part of the finished process.

Advances in technology allow common CNC machining centers, equipped with high pressure through-spindle coolant, to be capable of gundrilling.

Holes deeper than 20:1 generally require a dedicated gundrilling machine to achieve highest productivity and process reliability.

UNISIG produces the most capable deep hole drilling machines on the market, with applications exceeding 400:1 depth to diameter ratio.

1. Rotating Tool

Typically used for non-symmetrical components or round parts requiring holes off-center

Cutting speed is determined by tool spindle speed

Drill drift can be significant compared to rotating workpiece or counter-rotating process

2. Rotating Workpiece

Used for round parts with a deep hole on-center

Cutting speed is determined by part, balanced to allow high rotating speeds

Drill drift is reduced compared to rotating tool only

3. Counter-rotating Tool and Workpiece

Used for round parts with a deep hole on-center

Cutting speed determined by combination of tool and workpiece rotation

Provides best hole straightness and concentricity compared to rotating workpiece or rotating tool

Gundrill Tooling

Small diameter drilling, typically 1 - 50mm [0.04 -2.00in] diameter holes

High-pressure coolant is introduced through the spindle and gundrill center

Chips are discharged on the outside of the tool

Special forms can be ground in tool tip

BTA/STS tooling

Larger diameter drilling, typically 20 - 200mm [0.79 - 8 inch]

Counter-boring and trepanning tools cover larger range, up to 500mm [20 inch] diameter

High-pressure coolant is introduced around the outside of the tool

Chips are discharged through the tool center and machine spindle

High penetration rates and power requirements compared to gundrill tooling

Process monitoring and control integration for automatic recovery

Gundrilling Machines

High-pressure cutting fluid, typically 1,500 - 3,000psi

High spindle speeds and running accuracy

BTA/STS machines

High horsepower and torque