a revolving center, also known as a live center in some countries, is constructed so that the 60° center runs in its own bearings and is used at the non-driven or tailstock end of a machine. it allows higher turning speeds without the need for separate lubrication, and also greater clamping pressures. cnc lathes use this type of center almost exclusively and they may be used for general machining operations as well. spring-loaded centers are designed to compensate for center variations, without damage to the work piece or center tip. this assures the operator of uniform constant tension while machining. some live centers also have interchangeable shafts. this is valuable when situations require a design other than a 60° male tip. a live center, which may be hard or soft, is a plain center placed in the revolving mandrel; it moves and is therefore live.