Guide

An uneven distribution of the mass of a body with regard to its axis of rotation is termed unbalance.   During rotation, unbalances lead to centrifugal forces, vibrations and noise, which can be more noticeable at higher speeds.   [AUSWUCHTEN] A dynamic unbalance is when the axis of rotation does not match with one of the principal axes of inertia.  A static unbalance is a special case of dynamic unbalance.   In this case, the axis of rotation lies parallel to the corresponding principal axis of inertia. Another special case is a couple unbalance. In this case the axis of rotation intersects the corresponding principal axis of inertia at the centre of gravity.If a rotational movement of a body with an unbalance sets it in resonance vibration, the body rotates with critical rotational speed because the system is developing resonant vibrations.Undesired unbalances on rotating machine parts impair the service life and safety of the machine, and the quality of the machining process.In order to compensate for unbalances on bodies, these must be balanced. …

Alongside the required dynamics of a machine that are necessary for its functioning, undesired dynamics also exist.  If forces that change with time or forced movements are applied to a system in a machine made of elastic parts and parts having mass, this sets up vibrations in this system. With spindles, this can be an inadequately balanced tool. Although these movements are relatively small compared to the required movements, in certain circumstances they can be hazardous for the machine because they can stimulate the entire machine such that it vibrates.   Resonance effects, where the excitation frequency matches the natural frequency of the machine therefore leading to an increase in the amplitude of the vibrations, are an extremely heavy dynamic load for a machine. …