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.
Trenchlesspedia Explains Chuck
A drill is a rotary cutting tool used to bore holes through soil or rock. The drill bit is gripped by a chuck at one end and is rotated while it is pressed against the target material. While drilling downhole, drills experience a huge amount of abrasive and erosive conditions as drilled rock bits mixed with fluid are sent back out along its side.
Drill failure along with damage to the drill chuck is a common problem experienced in abrasive drilling conditions. The drill chuck is located close to the transition zone between the drill face where the rock is cut and the walls of the drilled hole where air movement is erratic.
Chuck is usually the first part to wear out and the rate of wear depends on the formation being drilled, drilling speed, and airflow. The chuck should be regularly checked for wear and loss of thickness at the bit shoulder end and replaced when required. A worn-out chuck or an improperly worn chuck can cause heavy spline wear. The splines should also be checked for damage each time the bit is removed. Some important points to remember:
- A chuck with badly worn splines should not be used with a new bit.
- A new chuck can get damaged if the drill bit splines are worn out.
- Monitor regularly to ensure that the chuck outside diameter is greater than or equal to the outside diameter of the cylinder.
- Replace with a new chuck every time a cylinder is replaced with a new one to prevent wear carryover from a used chuck.
- Index the drill bit such that exhaust grooves are adjacent to less worn chuck areas.
- Ensure smooth application of correct thrust to prevent distortion at the chuck reaction seat that can reduce its service life.
- Use correct anti-seize on chuck thread when screwing the drill bit and chuck to prevent difficulty during drill bit stripping.
- Renew chuck, cylinder, or both to prevent them from being lost in the hole.