Engineering Calculators

Engineering Calculators


Critical Speed


Critical speed is the first resonant frequency (speed) of the rotating shaft. Resonance in a rotating shaft can be catastrophic and even break the shaft. However, not all ball screws will necessarily exhibit such behaviour since the nut represents another support of the shaft, permanently changing the unsupported length of the shaft and its resonant frequency.

It is necessary to confirm if the ballscrew rotational speed is within 80% of the critical speed of the ballscrew.

Figure 3.17 shows a diagram which summarizes the allowable rotational speed of the ballscrew shaft.

The allowable rotational speed is regulated also by dm - n value (dm: Diameter of the central circle of steel ball, n: Revolution speed-RPM) Which expresses the peripheral speed.


For precision (Accuracy grade C7-C0) dm - n is lower that and equal to 70,000.


To make this calculation we have provided a handy calculator to measure the critical speed of a ballscrew.

The output from this calculator will show the approximate point at which the ballscrew will start to resonate (Whip) and you should consider to set the maximum RPM to 80% of this speed.

A is simple - simple (eg. BF at one end and BF at the other.)

B is Fixed - Simple (eg. BK at one end and BF at the other end)

C is Fixed - Fixed (eg. BK at both ends)

D is Rotating nut and fixed screw.

Critical Speed Calculator

Column Strength Calculator