#### Critical Speed Ball Screw and Lead Screws Formulas and Calculator

WEBCritical Speed Ball Screw and Lead Screws Formulas and Calculator: The critical speed is the lowest rational speed that a shaft is in resonance. n c = f c ( d r / L c2) 10 7. Where: n c = critical speed (rpm) d r = root diameter of screw (mm) f c = factor based on end speed support bearings. L c = unsupported length of screw (mm)