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Turning: Chucks
The chuck is integral to a lathe's functioning because it fixtures the part to the spindle axis of the machine. Below is shown a three-jaw chuck with jaws that are all driven by the same chuck key. This arrangement provides convenience in that parts can be mounted and dismounted quickly.

Three-Jaw Chuck
The inner construction of the three-jaw chuck is shown below. A spiral gear meshes with cog teeth on the jaws to move all three jaws in or out simultaneously. Parts can be fixtured on outer or inner surfaces since there are gripping surfaces on the inner and outer surfaces of the chuck jaws.


Four-Jaw Chuck
If the part needs to be off center or is not a solid of revolution (axially symmetric), a four-jaw chuck with independently-actuated jaws needs to be used. Such a chuck is depicted below.


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