Equivalent Load: Considering the preload with double nuts

The preload graph demonstrates, how external loads cause a load increase in one nut, and a load decrease in the other one. At an external load of 2.83 times the preload, the tensioning nut is released completely. Even though this may happen without damaging the ballscrew, in most applications the preload should be set in order to keep all external loads within the preload range. To evaluate the resulting axial forces a computer program is needed. However, approximate values can be calculated by means of the following rule of thumb:

The resulting axial loads F_i^* now can be used for calculating the dynamic equivalent axial load F_m^* by means of the formula for calculation of the equivalent Load.