Chuck

A chuck is a clamp-like attachment that holds the drill bit or other tools used in drilling equipment. The end of the drill bit called the shank fits into the drill and is secured by the chuck. It is an important part of the downhole drilling assembly and also helps in centralizing the drill bit. Drill chucks can be keyed, keyless or hybrid types. Keyed chucks are engineered to loosen or tighten their hold on a tool by using a key. Keyless chucks can quickly loosen and tighten a tool on the chuck manually or by application of torque. Hybrid chucks can operate as keyed or keyless systems.
Boreholes are drilled using drilling equipment that consists of a drill gripped by a chuck. For keyed chucks, a chuck key is used in order to open and close the jaws of the chuck. The chuck is mounted on a spindle that rotates and this speed is imparted to the drill bit. The chuck should always be well greased and in good condition, because a worn chuck can wear out the bit. Replacing chucks is more economical than replacing cylinders, so a new chuck is fitted every time a cylinder is replaced as it is larger in diameter.
Chuck wear is concentrated in areas that coincide with the exhaust grooves of the drill bit, especially in abrasive drilling conditions. Chuck life can be prolonged by indexing the drill bit such that the exhaust grooves are adjacent to those areas that are less worn out in the chuck.