Measuring ball screw bearing balls

Bearing ball manufactures have specialized equipment to measure the size and spherical deviation of bearing balls. Hear in the field, we have micrometers and the skill of the operator. The most common size ball in CNC machines is 1/8” and very difficult to measure. When a load is applied to the ball with the micrometer, it causes a flat spot. This is known as “plastic deformation”. As I open factory sealed balls with the lot size marked on the box I have consistently over the years measured at least .0001” under the lot size. Skill of the operator comes into play when measuring a sphere of any size but the smaller the ball the more critical the feel on the micrometer becomes. It is not recommended to use a caliper, no matter how accurate, because the “feel” is less. You will always measure a smaller size with the caliper. The size of the balls you remove from the screw is the starting point for choosing an oversize ball to reload with, so take care with this first step.