Lead Screw Critical Speed Calculator

Calculate the critical rotational speed and recommended operating limit for your lead screw.
Select the screw diameter, lead, unsupported length, and end fixity to view RPM and linear speed.

Configure your screw

Bearing-to-bearing span, or unsupported overhang for fixed–free. Not travel length.
Compare an intended operating speed.

“Fixed” restrains bending and tilt; it still permits shaft rotation. Actual bearing construction determines fixity.

Calculated results

These are screw resonance estimates. The operating limit shown accounts only for critical speed.

How critical speed is calculated

nc = (120,904,000 × C × dr) / L2
nc — Critical speed (RPM)
The estimated rotational speed at which the screw reaches its first bending resonance and can whip excessively.
C — End fixity factor
A dimensionless coefficient determined by the bearing support arrangement at the screw ends.
dr — Root diameter (mm)
The diameter measured at the bottom of the screw threads. Retrieved automatically for your selected diameter and lead.
L — Unsupported length (mm)
The span between bearing supports, or the unsupported overhang for fixed–free mounting. This is not the travel length.

End fixity factors used in this calculator

  • Fixed–free: 0.36
  • Supported–supported: 1.00
  • Fixed–supported: 1.47
  • Fixed–fixed: 2.23

Recommended RPM limit: 0.80 × nc. Linear speed (mm/s): RPM × lead (mm/rev) / 60. The equation estimates critical speed for a rotating steel screw; other component limits may be lower.