Deep hole drilling is the mechanism by which engineers create holes ten times deeper than the actual hole diameter. It's a common practice in some fields, for instance, aerospace, borehole drilling, and oil and gas extraction. When performing deep hole drilling, a gun-drill tool with a kidney-like shaft utilizes a range of super metal alloys to create a hole with a high depth to diameter ratio. 

Deep hole drilling machines are superior, thanks to their multitasking machine techniques. The multitasking trend was introduced into the aerospace industry because essential components like the landing gear require deep hole machining. Traditionally, engineers used different machines to achieve a particular goal. However, deep hole drilling consolidates operations because a single device performs several tasks.

Explained below are the essentials of aerospace deep hole drilling:

Machinery and Drilling Tools

Countless investigations have been conducted on the mechanical and thermal load of the drilling tool. The drilling tool's design, character, and asymmetry determine its acting forces and torques during the drilling process.

There are several forces to be put into consideration when using deep hole drilling tools. The forces include:

Acting process forces
Acting feed forces
Inertia forces
Feed force (Ff)
Passive force (Fp)
Cutting forces (Fc)

The acting process and inertia forces applied on the head of the drilling tool impact the cooling lubricant flow and forces. In addition, the area of the tool handle or holder applies the acting feed force, drilling torque, and clamping force.

Apart from the mechanical load, the thermal load plays a significant role in deep hole drilling. Keep in mind there is friction between the guiding pad and the walls of the borehole. The heat produced at the cutting tip is not directly transferred to the cooling lubricant but is instead directed to the chips, workpiece, and the tool, then released for intensive cooling.

Cooling Lubricant

The cooling lubricant plays three major roles, which are:

Cooling- By getting rid of the heat generated from the tool and workpiece.
Lubrication- By reducing friction and the wear and tear from the cutting edges and guide pads.
Flushing- By continuously removing the chips.

Additional uses of the cooling lubricant include:

Protecting the metal alloys against corrosion and oxidation.
Reducing the deep hole drilling tool wear and tear, hence increasing durability.
Reduce instances of foaming tendencies and low oil mist formation.
It creates a damping effect on the boring bar by playing a part in sound absorption.

When drilling, adjustment of the viscosity rate and pressure of the cooling lubricant depends on the diameter of the drilled borehole. The commonly used cooling lubricants are water-immiscible minerals with ester oils mixed with