1. Three-jaw chuck
The three jaws of the three-jaw chuck move synchronously and can automatically center. Generally, no correction is required after the workpiece is installed. However, if the workpiece is long, the rotation center of the part far away from the chuck may not necessarily coincide with the rotation center of the lathe spindle, and the workpiece needs to be corrected. If the three-jaw chuck has been used for a long time and the accuracy decreases, and the processing part of the workpiece requires higher accuracy, it also needs to be corrected.
The three-jaw chuck is convenient for clamping workpieces and saves time, but the clamping force is small, so it is suitable for clamping small and medium-sized parts with regular shapes, such as cylindrical, regular triangle, and regular hexagon. Artifacts etc.
Three-jaw automatic centering chuck specifications are: 150mm, 200mm, 250mm.
2. Four-jaw chuck
The four jaws of the four-jaw chuck move independently. Therefore, after the workpiece is installed, the rotation center of the workpiece must be corrected to the rotation of the lathe spindle. Only when the centers coincide can be turned.
It is more troublesome to correct the workpiece with the four-jaw chuck, but the clamping force is large, so it is suitable for installing large or irregularly shaped workpieces.
The four-jaw chuck can be clamped in two forms: forward jaw and reverse jaw. The reverse claw can clamp workpieces with larger diameters.
3. Back center
There are two types of back center: fixed center and live center.
(1) Fixed center
The fixed center has good rigidity and accurate centering, but it generates too much heat due to sliding friction with the center hole of the workpiece, and it is easy to remove the center hole or center. Burned out. Therefore, the dead center is only suitable for low-speed machining of workpieces with high precision requirements.
(2). Live center
The live center changes the sliding friction between the workpiece and the center hole into the rolling friction of the bearing inside the center. It can work normally at very high speeds and overcome the problem of It eliminates the shortcomings of the dead top, so it is increasingly used. However, there is a certain accumulation of assembly errors in the live center, and when the rolling bearing is worn, the center will swing radially, thus reducing the machining accuracy.