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A gun drill is a fluted drill used for boring. The bit has one or two holes in the tip through which fluid or compressed air is pumped in order to provide coolant. This tool is used for jobs that require long straight holes, such as its namesake guns, for which it was originally created. Other items it may drill include musical instruments like the clarinet or certain kinds of pipes. It can be used on metal, plastic, wood, or composite materials.
Though the essential design of the gun drill tends to be the same, it comes in hundreds of different sizes and variations. Cutting tips can be made out of metal or carbide, though the latter has tended to be more popular due to better durability. The speed and power of the equipment running the drill and coolant pressure vary as well, depending on the type of project and the materials to be used.
Coolant is used on a gun drill primarily because of the length of the hole made with a boring tool. It helps to keep the cutting front from overheating during a long stretches of activity. Coolant is also used to pull material that the drill has cut away from the drilling site. It can pull these chips as far as the entrance of the hole, though they can also be deposited through a hole situated in the middle of the drill bit lengthwise.
Gun drills are either external or internal chip removal types. The external removal type removes chips along the outside of the drill shaft along a special groove, while the internal type removes cut material by pushing it up through the hollow middle of the tool. Most gun drills have one hole in the tip, though there can be two holes for larger jobs. The hole shape is usually round, though it can come in a longer, more uneven kidney shape.
Most gun drill attachments are used on equipment known as deep hole drilling machines. These consist of large, long consoles with the drill attachment resting on the top and stretching most of the length of the machine. They can have anywhere from one to several spindles to which the drill attachment or attachments are affixed. A typical deep hole drilling machine is operated via an electronic screen and keyboard similar in appearance to a laptop computer.