What is the difference between three-jaw and four-jaw chucks?

Today I will tell you about the difference between installing a three-claw and a four-claw chuck? What are the advantages

　　First of all, when turning, the workpiece must be clamped in the machine tool fixture, aligned and clamped, so that it always maintains the correct position during the entire cutting process.

　　The quality and speed of workpiece installation directly affect the processing quality and production efficiency of the workpiece and should be taken seriously. When turning the outer circle, according to the shape, size, quantity and machining accuracy of the workpiece, it can generally be divided into the following four clamping methods, namely, three-jaw self-centering chuck, four-jaw single-action chuck, one-clamp-one-top clamping and two-pin clamping.

　　The structure of the three-jaw self-centering disc

　　The structural shape of the three-jaw self-centering chuck is shown in the figure. It is a universal fixture widely used on lathes. It mainly consists of an outer shell, three claws, three small bevel gears, a large bevel gear and other parts.

　　When the square row of the chuck wrench is inserted into the square hole 1 of the small bevel gear 2 and rotates, the small bevel gear drives the large bevel gear 3 to rotate. The back of the large bevel gear is flat and threaded 4. The thread on the back of the claw 5 meshes with the flat thread, thereby driving the three claws to move in the radial direction at the same time to clamp or loosen the workpiece.

　　Features of three-jaw self-centering chuck

　　The three-claw self-centering chuck can automatically center and does not need to spend too much time to find the alignment: However, when clamping a long workpiece, the rotation axis of the workpiece far away from the chuck may not necessarily coincide with the rotation axis of the lathe spindle. At this time, alignment must be performed. When the three-claw self-centering chuck is used for a long time and the accuracy decreases, and the processing accuracy of the T workpiece is high, the workpiece also needs to be aligned.

　　The three-jaw self-centering chuck is convenient and fast for clamping workpieces, but the clamping force is small. It is only suitable for clamping large quantities of small and medium-sized regular workpieces, such as cylindrical, regular triangle, regular hexagonal workpieces, etc.:

　　Precautions when using three-jaw self-centering chuck

　　The three-jaw self-centering chuck has different thread numbers on the back of the three jaws. When installing, you must match the numbers 1, 2, and 3 on the jaws with the numbers 1, 2, and 3 on the chuck, and install them in order. If there is no number on the claws, you can line up the three claws side by side and compare the number of threads on the back. The most is 1, the least is 2, and the least is 3. Install them in order.

　　The three-jaw self-centering chuck can also be equipped with front jaws and reverse jaws (the three-jaw self-centering chuck has two pairs of front and reverse jaws, and some only have one pair, which can be assembled into front jaws or reverse jaws).

　　Must note:

　　When clamping workpieces with positive jaws, the diameter of the workpiece should not be too large. Generally, the claws extend out of the chuck circumference by no more than one part of the claw length. Otherwise, due to the small number of meshing teeth between the claws and the plane thread, the threads on the claws will easily break when stressed. When clamping workpieces with larger diameters, reverse claw clamping is generally used. When the outer circle of a larger workpiece with holes needs to be turned, the three claws can be moved centrifugally to support the inner hole of the workpiece for turning.

　　Four-jaw single-action chuck clamping

　　The backs of the four claws have semi-circular arc-shaped threads that mesh with the screw. There is a square hole at the top of each screw for inserting the square tip of the wrench. By turning the chuck wrench, the jaws can be driven to move individually through the screw to adapt to the size of the workpiece being clamped. Through the corresponding cooperation of the four claws, the workpiece can be clamped in the chuck. Similar to the three-jaw self-centering chuck, there is a positioning step (stop) on the back and is integrated with the connecting plate on the lathe spindle.

　　Characteristics of four-jaw single-action chuck

　　Since the four claws of the four-jaw single-action chuck move independently, they cannot automatically center when clamping the workpiece. Therefore, after the workpiece is clamped, it must be aligned so that the rotation axis of the processed part of the workpiece coincides with the rotation axis of the lathe spindle before turning. Although clamping is more troublesome, the clamping force is greater than that of the three-jaw self-centering chuck, and it is suitable for clamping large or irregularly shaped workpieces. The four-jaw single-action chuck can be installed in two forms: forward jaws and reverse jaws, of which the reverse jaws are used to clamp workpieces with larger diameters.