The rotational speed describes the number of revolutions a shaft or spindle makes per unit of time and is usually expressed in revolutions per minute (rpm). It is a fundamental kinematic parameter from which many other parameters, such as circumferential speed, feed rate or power consumption, can be derived.
In a ball screw drive, the rotational speed of the spindle, in combination with the lead of the threaded spindle, directly determines the linear movement of the nut. The feed rate v is calculated as the product of the rotational speed n and the pitch P, i.e. v=n×P. An increase in rotational speed therefore results in a higher feed rate, provided that the mechanical and dynamic limits – such as the critical rotational speed of the spindle or the permissible rotational speed of the nut – are not exceeded.
In practice, factors such as stiffness, vibration behaviour and lubrication limit the usable speed range. For this reason, ball screws are always designed with the maximum permissible speed in mind, in order to ensure smooth running, accuracy and service life.