There are three main types of lathe spindle indexing methods: mechanical indexing, CNC indexing, and optical indexing.
1. Mechanical indexing method
Mechanical indexing is a traditional and fundamental method, mainly achieved through mechanical devices.
(1) Index Plate indexing
This is the most classic method. There are multiple equally spaced positioning holes on the indexing plate, and the spindle angle is fixed by inserting positioning pins. The accuracy of indexing directly depends on the accuracy of the number of holes on the indexing disc and the skills of the operator. The accuracy is usually within ± 1 '(1 arcminute), which is suitable for indexing head operations on general milling and drilling machines.
(2) Worm gear indexing
Rotate the worm gear through the handle to drive the worm wheel connected to the spindle for indexing. The number of turns the handle rotates is controlled through a dial. Its transmission ratio is large (commonly such as 40:1 or 90:1), which can achieve precise indexing at small angles and is the core structure of the universal indexing head.
2. Numerical control indexing method
This is the mainstream method of modern high-precision and high-efficiency machining, which drives the spindle through a servo motor controlled by a CNC system.
(1) Direct division of servo motor
The high torque servo motor is controlled by a high-precision reducer (such as planetary reducer, worm gear reducer) or directly connected to the spindle, and its rotation angle is controlled by a pulse command issued by the numerical control system. The positioning accuracy can reach within ± 5 arc seconds, and the repeated positioning accuracy is ± 1 arc second. It is widely used in turning and milling composite centers, vertical lathes, etc.
(2) Hydraulic or pneumatic locking indexing
After the indexing is in place, the spindle is rigidly locked by a hydraulic or pneumatic driven clamping mechanism (such as a face gear) to withstand cutting forces and improve system rigidity and stability.
3. Optical indexing method
Used in metrology and ultra precision machining applications as a positioning reference and detection method.
(1) Rotary Encoder
The grating encoder is installed coaxially with the spindle and forms a closed-loop control by reading the Moir é fringe signal and providing real-time angular position feedback. This is the core feedback component for achieving high-precision CNC indexing, with a resolution of up to one millionth of a degree.
(2) Multi tooth indexing table
Utilize the meshing and disengagement of a pair of high-precision end face gear discs for indexing. Each division involves all teeth meshing simultaneously, and the error averaging effect enables it to achieve extremely high accuracy of ± 0.1 arcseconds, but it is usually used as a testing instrument rather than a standard configuration for machine tools.
When operating high-precision indexing equipment, it is necessary to strictly follow the regulations, as incorrect operation may result in equipment collision or loss of accuracy.
