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A 3-jaw chuck is a type chuck with 3 jaws on it. The 3-jaw chuck is a subtype of the scroll chucks. There are other types of chucks such as the 4-jaw chucks, vacuum chucks or the collect chucks. The chucks are one of the work holding systems that are widely applied in lathe machining. The other major work holding system is the vise. The work holding systems are also known as the clamping systems when it comes to general chucks or vices. Among all the options of clamping systems, the 3-jaw chucks and 4-jaw chucks are the most common choices in the modern lathe tooling. 4-jaw chucks are the subtypes of the scroll chucks as well.
The universal chuck refers to the work holding system that secures a work piece with jaws on it. The jaws on a chuck are movable. It works like a claw to clamp the work piece. How great a chuck’s clamping force can be is mainly depended on the power system that it uses. A chuck is mounted to the spindle on a lathe for turning works. Conventionally, the open and close of the jaws on the universal chucks are controlled manually by a screw; nowadays, there are chucks powered with electricity or with fluid power system in order to give a better output of the clamping force.
Though the vices and chucks both utilize the jaws as the main major for work holding, they are still different. The first difference to notice between them is the look, or what people say the configuration of the devices. The base of a chuck is in a round shape with a hollow center, which makes it look like a ring while that of a vice is more of a geometry design, which makes it look like a box. This feature can be told from their names: the base of a chuck is called a faceplate, but the base of a vice can be called a tombstone.
The second difference is the motions of the jaws. There are only 2 jaws on a vice while there can be 3 or 4 jaws on a chuck. On a vice, a movable jaw moves toward the fixed one on a groove, but the jaws on a chuck move inward and outward to or from the center. This feature allows the chucks to secure a work piece by not only closing the jaws to clamp one but also pushing the jaws outward against the recess, or the mortise, on the bottom of a work piece to secure it.
As the name suggested, a 3-jaw chuck has 3 jaws on it. A 3-jaw chuck contains 3 metal jaws on top of it. The jaws can be called dogs. There are actually two pieces of each jaw: the top jaw and the bottom jaw. The top jaws are arranged in a radially symmetrical pattern on the faceplate. They are connected to the faceplate with a rack. The rack controls the motion of the jaws. Under the faceplate, the bottom jaws are interlocked to each other to make sure the movement of the 3 jaws is in unison. This mechanism is called self-centering. It allows the jaws to work and respond to the control a lot faster.
A 4-jaw chuck looks much alike to a 3-jaw chuck. From how they look, the configuration seems to be the same and it is only the matter of one additional jaw to most people. However, the truth of matter is, they are significantly different from each other in clamping mechanisms and purposes.
The self-centering clamping allows the jaws of 3-jaw chucks to move in unison, but the jaws of 4-jaw chucks are actually independent to each other. This design allows different levels of opening and closing to better secure a work piece and it offers more flexibility to the turning work as well. Moreover, a 3-jaw chuck is better at holding circular or hexagonal cross-sections while a 4-jaw chuck clamps square or octagon shape blocks better. Given the features that make the 3-jaw chucks and 4-jaw chucks different from each, they both play an irreplaceable role in modern lathe machining for specific working or processing operations.
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