Introduction to Drilling

• Drilling 

Drilling is a cutting process that uses a drilling rig machine to cut a hole of circular cross-section in solid materials like land or mud. This rig includes the drill bit which is usually a rotary cutting tool, often multi-pointed. This drilling bit is pressed against the land of mud and it is rotated at rates from hundreds to thousands of revolutions per minute. This forces the cutting edge against the land or mud, cutting off the apparatus from the hole as it is drilled. 

In rock drilling, the hole is usually not made through a circular cutting motion. Instead, the hole is usually made by hammering a drill bit into the hole with quickly repeated short movements coming from the Drilling rig machine. The hammering action can be performed from outside the hole (top-hammer drill) or within the hole (down-the-hole drill, DTH). Drilling may affect the mechanical properties of the land by creating low residual stresses around the hole opening and a very thin layer of highly stressed and disturbed material on the newly formed surface hole. 

This causes the land to become more capable of corrosion and crack propagation at the stressed surface. A finish operation may be done to avoid these detrimental conditions. Drilled holes are characterized by their sharp edge on the entrance side and the presence of burns on the exit side (unless they have been removed).

• The deep hole drilling

The deep hole drilling is defined as drilling a hole of depth greater than ten times the diameter of the hole. These types of holes require special equipment like Hydraulic drilling rig to maintain the straightness and tolerances from deep down the hole. Other considerations are roundness and surface finish which also can be tackled with high-end devices. 

This type of deep hole drilling is generally achievable with a few tooling methods, usually mud drilling or earth drilling. These are differentiated due to the internal or external chip removal method. Using methods such as a DTH cum rotary drilling rig machine and counter-rotating the land are common techniques to achieve the required straightness and smoothness of the deep holes. Secondary tooling methods include powerful drilling, deep water well drilling, skiving, and burnishing, pull boring, or bottle boring. 

Finally, a new kind of drilling technology is available to face this drilling - vibration drilling, this type of drilling is achieved through portable drilling rigs such as DTH drilling rig and rotary drilling rig. Further, this technology breaks up the chips of the hard land by a small controlled axial vibration of the drill. The small chips are easily removed by the flutes of the drill. A high tech monitoring system is used to control force, torque, vibrations, and acoustic emission from the earth's core. Here, Vibration is considered a major defect in deep hole drilling which can often cause the drill to break. A special coolant is usually used to aid in this type of drilling.

Furthermore, this is usually the most economical method of testing and it provides the physical sample for the soil classification.

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