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A lathe dog, also known as a lathe carrier, is a device that clamps around the workpiece and allows the rotary motion of the machine's spindle to be transmitted to the workpiece.
A carrier is most often used when turning between centers on a lathe, but it may be used on dividing heads or any similar situation. It is used in conjunction with a drive plate and drive pins: the plate is mounted directly on the machine spindle (as with a chuck) and the drive pin is attached to the plate. In use the carrier and workpiece are inserted between centers and the leg of the carrier rests against the drive pin.
Carriers may be of the straight leg or bent leg type. The straight leg requires the drive pin, the bent leg fits into a slot machined into the drive plate. The bent leg type is considered safer as there are (slightly) fewer protruding parts to cause accidents.
Spindle speeds are reduced when working with carriers, due to the unbalanced nature of the setup. Care must also be taken by the operator when using carriers, as it is easy to get snagged on one.