Centre displacement device for eccentric turning of large workpieces

Large cylindrical inhomogeneous workpieces are commonly mounted on lathes using four-jaw independent chuck. Adjusting the rotation centre of the workpiece is done manually and is thus prone to human error. Flexible workpiece rotation centre adjusting is especially prone to errors because contact with the workpiece is changed every time the rotation centre is adjusted. A device for centre displacement adjusting was developed. The main principle is that with the new device, the rotation centre of the workpiece can be adjusted without changing the contact with the workpiece. The device is mounted on the lathe spindle by replacing the chuck. The working principle of the device is that the rotating centre of the workpiece is adjusted by changing the angular displacement between two eccentric members in the device. Rotation of the eccentric members is locked with a spring force produced by a steel membrane. The membrane is operated with hydraulic pressure so that pressurization unlocks the rotation of the eccentric members and vice versa. The test device is equipped with a 315 mm standard three-jaw chuck and is designed to withstand 2500 Nm of maximum throughput torque. The device was validated using a static torque load measurement. According to the conducted tests, the device is capable of operating with at least 2800 Nm of throughput torque. The maximum eccentricity is 20 mm and the hydraulic pressure needed to operate the membrane is 250 bar. The device increases the accuracy of the machining process and moreover reduces the risk of accidents.