How to use the chuck properly when encountering rectangular or special-shaped workpieces?

In machining, rectangular workpieces or special-shaped workpieces are often encountered. For the processing of rectangular workpieces, if a four-jaw chuck is used for clamping, the adjustment is time-consuming, the positioning accuracy is low, and a high level of lathe technology is required. If a V-shaped vise is used to position the clamping mechanism, the attachments are complicated and manufacturing is difficult. For special-shaped workpieces, such as designing special fixtures, there are many processes, long time, low efficiency, high cost, manufacturing and assembly accuracy are limited by certain conditions, and special fixtures lack versatility.

As one of the most basic and common fixture types in machining, the three-claw chuck moves equally radially when clamping the workpiece. Therefore, the three-claw chuck is used to clamp the workpiece. The clamping part is generally a cylindrical surface or a flat surface. But if the workpiece does not have a surface suitable for clamping by the claw, how to clamp it? From a simple attachment when clamping square materials with a rectangular cross-section, to a special fixture design when clamping irregular-section blanks, to the implementation process of modifying a three-jaw chuck (soft jaw) to process special-shaped surfaces, the application scenarios range from small to wide, and the processing technology of the corresponding workpieces ranges from easy to difficult. There are corresponding solutions below for reference by designers with different needs.

Case: Three-jaw chuck clamping quadrilateral workpiece

To process steel plates into round bars for tensile testing, thermal simulation, etc., it is necessary to use a lathe to process the sawn quadrilateral blanks into circular specimens. At this time, there will be a problem of clamping the quadrilateral blanks on the lathe's three-claw or four-claw chuck.

1. Three-jaw chuck clamps quadrilateral blanks with a rectangular cross-section

(1) Place three U-shaped chucks on the jaws of the three-jaw chuck to clamp the square workpiece.

For the clamping method, first install the clamp onto the jaws, and then place the workpiece. The clamp is suitable for a specific cross-sectional size. It can also be adjusted by adding a gasket, which can expand its range of use and make the tooling clamp suitable for rectangular workpieces within a certain size range.

(2) Working principle of the fixture

Before processing the square workpiece, install the clamp s on the jaws of the three-jaw chuck, install the 90° V-shaped clamp on the lower jaw, and install the upper left and right jaws on the clamps that are inclined at 15° to the flat head (i.e. ∠FOE=15° in the picture). Tighten and fix with screws. Due to the wide variety of sizes of square workpieces processed, the workpiece will be eccentric, and the eccentricity can be corrected with spacers. In order to ensure that the center O of the square workpiece is coaxial with the tip of the tailstock, it is necessary to ensure that the distance from the center O of the workpiece to the three jaws of the three-jaw chuck is the same.

(3) Advantages of using jackets

When the cross-section of the blank is rectangular, gaskets of corresponding sizes can be added between the three jaws and the chuck according to the specific size of the square material. This method is convenient and concise for clamping the square material with a rectangular cross-section, and the clamping is reliable, and can be adapted to the clamping of square materials on the three-jaw chuck.

2. Three-jaw chuck clamps quadrilateral blanks with irregular cross-sections

For the turning processing of experimental specimen blanks with non-uniform sizes and irregular cross-sections, in order to ensure that the quadrilateral blank is processed into a round experimental specimen within the specified size range, it can be considered to design the tooling fixture by first centering both ends of the blank and then clamping it with the two-point method. The clamp mainly consists of 5 parts, positioning component and positioning device, clamping device, clamp body, etc.

(1) Design principle of fixture

One end of the quadrilateral workpiece is fixed to the clamping area of ​​the fixture through bolts. The size of the clamping area can be controlled by adjusting the bolts according to the size of the blank. One end of the workpiece is placed on the dead center of one end of the three-jaw chuck through the positioning center hole before clamping, and the workpiece is driven to rotate through the connection between the lever and the jaws. In order to ensure that the clamp and the workpiece do not swing during rotation, the lever of the clamp can be fixed on the claw through the bolt on the lever.

(2) Advantages of this set of fixtures

The two-center method is used to clamp workpieces with an irregular quadrilateral cross-section on a three-jaw chuck using a special fixture. When the size of the blank is limited, the quadrilateral workpiece needs to be turned into a round bar. In order to ensure that the clamping center of the quadrilateral workpiece is concentric with the active tip of the tailstock and ensure that the clamping is firm, reliable and convenient, before clamping, first mark the two end faces of the workpiece, find the center of the end face and drill the center hole. Then, use a special fixture and two apex points to use the method of one clamp and two tops to position the workpiece with the straight line determined by the two center holes. This clamping method is quick, simple, safe and reliable.