A split nut is a device commonly found on a metal lathe […]
A split nut is a device commonly found on a metal lathe and automatic feed-milling machines. It consists of two halves of a threaded fixture that can be closed around a threaded shaft or opened to slide freely along the shaft when the halves are separated. Commonly linked together with adjusting bolts, the split nut can be tightened to allow the threads to engage a rotating threaded rod, thereby driving the tool holder along the lathe bed by riding on the threaded rod. This enables the split nut to be loosened to disengage the threaded drive rod, which allows the tool holder to be manually slid back and forth along the lathe bed by hand.
A lead screw, or power screw as it is also known, is a threaded bar or rod that converts radial or rotational motion into linear or straight line motion. This is achieved by passing the threaded rodthrough a corresponding opposite thread cut into a movable work piece as is seen in bench vices and car jacks. When the lead screw is turned, the work piece will move up or down the threads depending on the direction of the screw. The main difference between a lead screw and a regular fastener such as a nut and bolt is that a lead screw’s thread is far coarser and typically square in profile to reduce friction.
Although a power screw works on the same principle as a simple nut and bolt, the threads used in both applications differ considerably. The screw thread on a bolt, for instance, is of a V profile and is cut with a fairly fine or dense thread pitch, i.e., number of threads per inch of bolt length. This arrangement increases the friction caused when the nut is turned along the bolt and aids in creating a very secure locking effect when the nut is fully tightened. The thread pitch on a lead screw is far coarser, i.e., less threads per inch of screw length, which creates less friction and allows for easier and quicker turning of the screw while still producing a secure grip when tightened. The thread profile of a power screw is also typically square which, although more expensive to machine, produces the highest efficiency level.
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