# Critical speed for a leadscrew

## Description

The critical speed is the speed that excites the natural frequency of the screw. For a steel leadscrew or steel ballscrew, the critical speed is approximately

Furthermore the **running speed** for a leadscrew (or ball screw) is typically limited to, at most, 80% of the calculated critical speed.

Constant **C** values for steel leadscrew or steel ballscrew, depending on the ends:

C = 0.36 for one end fixed, one end free

C = 1.00 for both ends simple

C = 1.47 for one end fixed, one end simple

C = 2.23 for both ends fixed

## Variables

N | Critical speed (rpm) |

d_{r} | Smallest (root) diameter of the leadscrew (in) |

C | Constant for steel leadscrew or steel ballscrew depending on the end of the leadscrew (rpm*in) |

L | Length between bearing supports (in) |