Drilling is a process that creates a hole in a given material. In order to remove parts from the material and create the hole, a drill bit or cutting tool is needed. The cutting tools can be a high-strength metal shaft with a sharp tip and cutting edges on the sides; they can also be accelerated jets of high temperature energy that removes electrically conductive materials such as the plasma cutter. The drilling processes as well as the cutting tools may come in various forms with a number of methods and gun drilling is one of them. To perform a drilling process as such, gun drills are required.
Gun drilling is a type of deep hole drilling process in which a specially designed drill bit is involved: the gun drills. A deep hole drilling refers to the process in which a hole is created in a metal material at high depth-to-diameter ratios. That is, the given object usually has a rather small diameter and a long depth. The gun drilling, as the name suggests, was originally applied to make gun barrels. Accordingly, the gun drills that are used in this process have the configuration of a long thin shaft so that it can reach to the deepest end of the material.
Specifically speaking, gun drilling is effective in diameters from 1 to 50 mm, which is about 0.04 to 2 inches. In a deep hole drilling process as such, the primary concern of the entire operation is the evacuation of the chips. Since the gun drill has to advance deeply into the workpiece to create the hole, the evacuation of the chips can be very difficult. If the chips are not removed from the hole promptly, the accumulation of debris will jeopardize the operation. To this end, the gun drills have a particular design that helps remove the chips from the hole.
Gun drills are a type of cutting tool that has a long narrow shaft. A gun drill bit can be almost as thin as a needle or a wire. The length and the diameter of the gun drills determine how deep and how narrow the holes are. They are usually the single flute drills which allow efficient chip evacuation and while performing the operation. The flute refers to the number of cutting edges on the side of a drill bit. Usually, the fewer the flutes are, the more space for chip evacuation.
In addition to the single flute design, there is another trick that the gun drills have to boost the evacuation of debris. The structure of a piece of gun drill bit is very much similar to a needle. Inside the shaft of a gun drill, there is often a channel along the shaft where liquid lubricants, or say coolant, can pass. Through the tiny channel, the high pressure coolant can be exhausted from the cutting end of the drill to remove the chips, even at extreme depths. With the one flute design and coolant exhaustion feature, the gun drills are able to make holes that are deeper than the ones that other types of drilling process create.
The key difference between a regular drilling process and a deep hole drilling process is that the latter involves a series of steps to create a hole. In most cases, a regular drilling process involves only one step essentially and there is not much preparation required. However, in order to create a deep hole with precision and accuracy, certain steps are taken before the deep hole drilling takes place.
The pilot hole is required before creating the end result. It is a shallow hole which serves as the guiding hole, or the reference hole, for the following drilling process. At this stage, a conventional short-shaft drill bit is used. Drilling a pilot hole actually contains two steps: first using a short drill bit to create a shallow pit on the surface of the work piece and then use a regular drill bit to drill a deeper pilot hole as a startup.
After the reference pilot hole is drilled, the gun drilling, or deep hole drilling can be performed. The actual deep hole drilling process involves three steps. The first round of drilling is conducted with a shorter gun drill which makes a hole about 40 times deeper than the hole diameter. In the second drilling, a thinner yet longer gun drill bit is used to create a hole about 80 times deeper than the hole diameter. Lastly, a hole with the depth that is about 120 times the hole diameter is created. A typical gun drilling process involves these steps so that an end result can be achieved.
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