Three-jaw chuck structure and working principle

The Three-Jaw Chuck is a machine tool accessory used for clamping and positioning workpieces. It consists of a chuck body, movable jaws, and a jaw driving mechanism. It clamps workpieces by utilizing the radial movement of three movable jaws uniformly distributed on the chuck body. The working principle of the Three-Jaw Chuck is based on turning any one of the three radial teeth on the chuck handle, which drives the plane thread to rotate and moves the three jaws simultaneously, achieving the function of self-centering workpiece clamping. From a mechanical structure perspective, the three radial teeth of the chuck have the same function; however, after careful inspection, the precision of clamping workpieces is not the same among the three, with significant differences. The self-alignment precision of the Three-Jaw Chuck can reach 0.05 to 0.15 millimeters. 12

The structural features of the three-jaw chuck include:

When rolling one small crown gear, it drives the large crown gear to rotate, and the flat thread on it moves three clamps towards or away from the center, thereby achieving automatic centering.

Three clamps come in positive and negative varieties. Some chuck models allow the clamps to be reversed, turning them into negative clamps. By switching to negative clamps, larger diameter workpieces can be installed.

For smaller workpiece diameters, the workpiece is clamped between three long jaws. For larger diameters or when using forward jaws is not convenient for clamping, the three forward jaws can be replaced with reverse jaws for clamping.

The working principle of the three-jaw chuck extends beyond manual operation. With the increasing demand for efficiency, many chucks have been upgraded to pneumatic or hydraulic chucks. These chucks offer excellent centering performance, reliable operation, rapid action, and ease of use, making them widely applied in CNC lathes.