# Ball Screw Load and Life Ratings

Seems there is still a lot of confusion on load and life ratings when it comes to ball screws.  Many people are familiar with the classic L10 life equation L10 = (Ca/P)^3 x 10^6 revolutions where Ca is the dynamic capacity in N and P is the mean applied axial load in N.  Recently we fielded several inquiries on applications where an engineer wanted to know whether s/he can apply a force equal to Ca and achieve 1 million revolutions of life.  Or even higher than Ca and achieve less than 1 million revolutions.  The basic answer is NO!  Here is why:

# Dynamic capacity and ball screw life

Life of a ball screw is determined by material fatigue and wear from surface erosion of balls and races. While surface erosion is hard to predict, fatigue can be calculated. The equations that I will use here are the ones from the ISO 3408 standard, which is widely used. Continue reading

# How much load can a ball screw carry?

There is enormous confusion about this subject. And granted, it is not easy. There are generally two figures given for a particular ball screw, the dynamic load capacity, and the static load capacity. Do they mean that you can put a load up to to the dynamic capacity on the ball screw wile it’s running, or a load up to the static capcity wile it’s not? No to both! Continue reading