Gun drills were originally used to process gun barrels, hence the name. The drilling accuracy is generally IT7-IT11, and the surface roughness Ra of the drilled hole is generally 

3.2-0.4μm.

Gun drills have the characteristics of obtaining good accuracy and surface roughness in one drilling, and have been used for processing small deep holes and special holes. 

With the increasing application in recent years, the scope of application of gun drills has been continuously expanding. It is not only used to process through holes, but also 

blind holes, stepped holes, inclined holes, etc.

Gun drills are composed of three parts: drill blade, drill tube, and drill shank. The drill blade material is high-speed steel and cemented carbide and is welded to the drill tube. 

At present, cemented carbide is commonly used as the drill blade material.

Gun drilling processing belongs to the external chip removal processing method. The working principle is: the cutting fluid enters the small hole on the gun drill shank, enters

the inside of the drill tube, reaches the drill blade for cooling and lubrication, and discharges the removed chips from the V-groove of the tool.

Advantages of gun drills:

(1) High hole processing accuracy and good economy (2) High cutting performance stability (3) Good hole coaxiality (4) Excellent drilling quality and chip removal 

performance (5) High reliability of the processing process.

Gun drills do not have a self-centering function, so a drill sleeve (i.e., guide sleeve) or guide hole must be used to position the tool during processing.

Precautions for using gun drills

Improper use of deep hole drilling tools may cause serious personal injury, such as cuts.

Deep hole drilling tools do not have a self-centering function and are also unbalanced. Therefore, at the beginning of processing, the tool must pass through a sufficiently 

long guide sleeve or guide hole for guidance.

The gun drill should not rotate when entering the guide sleeve or guide hole. Turn on the coolant first, then start the spindle.

After the processing hole depth is reached, turn off the coolant and start to retract the tool. The spindle should stop rotating when retracting the tool.

The guide sleeve is a consumable part. When the inner diameter of the guide sleeve is worn out by more than 0.2mm, it needs to be replaced.

Tool support: When the hole depth of the gun drill exceeds 30-40 times the drill bit diameter, graded drilling or additional auxiliary support should be performed, with one 

support added for every 30-40 times the diameter.