In mounting work between centers for machining, be sure there is no end play between the work and the dead center. However, do not have the work held too tightly by the tailstock center. If you do, as the work revolves, it will heat the center s point, destroying both itself and the center. To help prevent overheating, lubricate the tailstock center with grease or oil. Holding Work on a Mandrel Many parts, such as bushings, gears, collars, and pulleys, require all the finished external surfaces to run true with their center hole, or bore.
General practice is to finish the bore to a standard size within the limit of the accuracy desired.
Then press the piece on a mandrel tightly enough so the work will not slip while being machined Clamp a dog on the mandrel, which is mounted between centers. Since the mandrel surface runs true with respect to the lathe axis, the turned surfaces of the work on the mandrel will be true with respect to the bore of the piece. A mandrel is simply a round piece of steel of convenient length which has been center drilled and ground true with the center holes. This taper allows the standard hole in the work to vary according to the usual shop practice and still provides a drive to the work when the mandrel is pressed into the hole. The center-drilled centers of the mandrel are lapped for accuracy.