A chuck is a mechanical device used to clamp a workpiece on a machine tool. A machine tool attachment that clamps and positions a workpiece by the radial movement of the movable jaws evenly distributed on the chuck body. The chuck is generally composed of a chuck body, a movable jaw and a jaw driving mechanism. The chuck body has a small diameter of 65 mm and a large diameter of 1500 mm, with a through hole passing through the workpiece or rod in the middle; the back is a cylindrical or short conical structure, connected directly to the end of the machine tool spindle or through a flange . Chucks are usually installed on lathes, external and internal grinding machines, and can also be used on milling and drilling machines with various indexing devices.

From the number of chuck jaws, it can be divided into double-jaw chucks, three-jaw chucks, four-jaw chucks, six-jaw chucks and special chucks.

From the use of power, it can be divided into: manual chuck, pneumatic chuck, hydraulic chuck, electric chuck and mechanical chuck.

Structurally, it can also be divided into hollow type and medium solid type.

After long-term use, in order to maintain the good precision of the lathe chuck, lubrication is very important. Improper or inadequate lubrication can cause several problems. Such as abnormal function under low pressure, weakened clamping force, poor clamping accuracy, abnormal wear and blockage, so the chuck should be properly lubricated. Apply grease (black) at least once a day, and inject the grease into the nozzle of the chuck until the grease overflows the surface of the jaws or the inner hole of the chuck (at the inner hole protective sleeve and the connecting nut). However, if the chuck rotates at high speed or a large amount of water-based cutting oil is used for processing, more lubrication is required, which should be determined according to different situations. Always clean the chuck body and sliding surfaces with an air gun or similar tool at the end of the operation. If cutting cast iron, clean it at least once or several times every two months, check whether the parts are damaged or worn, and replace them with new ones immediately if they are serious. After inspection, sufficient oil supply is required before assembly. For different workpieces, use different clamping methods or make special fixtures. The three-jaw chuck is a fixture that can be used to clamp irregular or strange workpieces, which will cause damage to the chuck! If the chuck pressure is abnormal , the chuck will be under high pressure, or the chuck will clamp the workpiece after the machine tool stops, reducing the life of the chuck. Therefore, when you find that the chuck gap is too large, replace the new chuck immediately, and use cutting oil with anti-rust effect to prevent rust inside the chuck, because the rust of the chuck will reduce the clamping force and make the workpiece Unable to clamp.