But a limit is put to th~ diminution of the radii of journals and pivots by the conditions 01 durability and of proper lubrication, and also by conditions 01 strength and stiffness.
Friction of Pivots and Collars.When a shaft is acted upon b a force tending toshift it lengthways, that force must be balanced by the reaction of a bearing against a pivot at the end of the shaft; or, if that be impossible, against one or more collars, or rings projecting from the body of the shaft.
Hence the pivots already mentioned wear unequally at different points, and tend to alter their figures.
In mechanism it is usually the central line either of a rotating shaft or axle having journals, gudgeons, or pivots turning in fixed bearings, or of a fixed spindle or dead centre round which a rotating bush turns; but it may sometimes be entirely beyond the limits of the turning body.
(A) The pivots or bearings of the polar axis are placed at its extremities.