Gun drills (through coolant drill) are straight fluted drills which allow

cutting fluid Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists) ...

(either compressed air or a suitable liquid) to be injected through the drill's hollow body to the cutting face. They are used for deep hole drilling—a depth-to-diameter ratio of 300:1 or more is possible.

Gun barrel A gun barrel is a crucial part of gun-type weapons such as small firearms, artillery pieces, and air guns. It is the straight shooting tube, usually made of rigid high-strength metal, through which a contained rapid expansion of high-pres ...

s are the obvious example; hence the name. Other uses include moldmaking, diemaking, and the manufacture of combustion engine parts such as

crankcase In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, resulting in the fuel ...

cylinder head In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern o ...

, and

woodwind Woodwind instruments are a family of musical instruments within the greater category of wind instruments. Common examples include flute, clarinet, oboe, bassoon, and saxophone. There are two main types of woodwind instruments: flutes and re ...

musical instrument A musical instrument is a device created or adapted to make musical sounds. In principle, any object that produces sound can be considered a musical instrument—it is through purpose that the object becomes a musical instrument. A person who pl ...

s, such as

uilleann pipes The uilleann pipes ( or , ) are the characteristic national bagpipe of Ireland. Earlier known in English as "union pipes", their current name is a partial translation of the Irish language terms (literally, "pipes of the elbow"), from thei ...

, as gun drills can drill long straight holes in metal, wood, and some plastics. The coolant provides lubrication and cooling to the cutting edges and removes the

swarf Swarf, also known as chips or by other process-specific names (such as turnings, filings, or shavings), are pieces of metal, wood, or plastic that are the debris or waste resulting from machining, woodworking, or similar subtractive (material-r ...

or chips from the hole. Modern gun drills use

carbide In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. Interstitial / Metallic carbides The carbides of t ...

tips to prolong life and reduce total cost when compared with steel tips. Speed of drilling depends on the material being drilled, rotational speed, and the drill diameter; a high speed drill can cut a hole in P20 steel at 30 inches per minute. Gun drilling can be done on several kinds of

machine tool A machine tool is a machine for handling or machining metal or other rigid materials, usually by cutting, boring, grinding, shearing, or other forms of deformations. Machine tools employ some sort of tool that does the cutting or shaping. Al ...

s. On

lathes A lathe () is a machine tool that rotates a workpiece about an axis of rotation to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, and turning, with tools that are applied to the workpiece to cr ...

, it is generally practical with hole depths of less than 50 diameters. There are also purpose-built gun drilling machines, where longer aspect ratios can be drilled.

Requirement

With a standard twist drill, it is difficult to drill a straight and accurately sized hole of a depth more than about 5 times the diameter. This is a problem in many manufacturing processes, especially the firearms industry: the barrel of a gun must be very straight and accurately sized. Gun barrels are far longer than their inside diameter; as an example, the caliber barrel of the M16 rifle is long, nearly 90 times the diameter of the bore. The gun drill was developed to drill such long, straight holes. Gun drilling is possible over a range of depths and diameters. For diameters between , gun drilling can be performed successfully with special equipment. It is a common process between in diameter. It is also possible for the range, however less efficient than BTA deep hole drilling.

Types

There are three basic types of deep hole drilling. Processes are categorized by how the cutting coolant flushes heat and chips from the cutting face. The three types of deep drilling are: * Gun drilling - The cutting tool is a fluted solid rod that has a hole bored down the center. Coolant is pumped through a hole in the inside of the drill. It flows back outside the drill, through the flute, bringing the chips with it. * BTA / STS (Boring and Trepanning Association / Single Tube System) - The cutting tool is a tube. Coolant is pumped in around the outside of the cutting tool and carries chips out through the center tube. For the tube to be strong enough and have an inner diameter large enough to carry chips away, the hole must be more than in diameter. * Ejector system - The cutting tool is a tube with another tube nested inside. Coolant flows through the smaller tube to the cutting face and then coolant and chips flow back through the larger tube. This is only an acceptable technology for holes of over in diameter.

References

External links

on rifle barrel drilling
Gun drill article
on definition and applications of gundrilling {{Metalworking navbox, machopen Firearm construction Hole making

Requirement

Types

References

Further reading

External links