Lathe jaws are the components found on a lathe that hold the material to be turned or worked on. Commonly found in metal lathe construction, lathe jaws can be individually tightened or tightened automatically to center the workpiece by turning a single adjustment screw. Most typical in a three- or four-jaw configuration, lathe jaws are made of hardened steel and have a smooth gripping surface which holds the workpiece in place by pressure instead of physically biting into the material, much like the chuck on a power drill motor. Due to the extreme pressure exerted on the workpiece by the lathe jaws, fragile work pieces may not be clamped into the jaws and must use an alternative drive method.
In order for an object to be turned into a perfectly-centered workpiece, it must be properly secured into the lathe jaws. Failure to ensure the item is centered will cause it to wobble when it is spun, preventing it from being accurately turned on its center. An out-of-round object or one that is out of center can, however, be turned round. This will require that more material be taken off of one side of the piece than the other, and will leave an out-of-round piece of stock on the end that was locked into the jaws that must be removed. This is very costly, as the amount of material that is removed is excessive and turned into waste.
Lathes are typically sized according to the diameter of their chuck or by the size material that can be safely turned in their jaws. Most lathes have replaceable chucks that allow for a change in chuck size and style to fit a particular project. Many times, the chucks will require changing to provide either three or four lathe jaws. Some jaws are designed to be used inside of the diameter of an open piece of metal. In this application, the jaws are inserted into the workpiece and opened to tighten against the inner walls of the hollow pipe or workpiece.
The chuck of a lathe is turned by a very powerful motor. It is very critical that no clothing be allowed to come into contact with the lathe jaws while they are moving, as serious injury or death could result. One of the most common injuries to lathe operators comes from failure to remove the adjustment key from the lathe jaws. This tool can fly out of the chuck at a very high rate of speed, causing serious injury.