Checking Spindle Runout
Spindles are designed and assembled with extremely high tolerances. Since they spin at very high speeds, balance is crucial. During machine operation, crashes or incidents can occur that damage the spindle.
Checking runout is a way to verify if your spindle is holding a tool in perfect axis alignment. If you were to observe a tool from directly underneath while it is spinning, runout would appear as a wobble. However, because spindles spin very quickly, runout greater than .001" is unacceptable. Even if you don't have a bearing problem yet, one is likely to develop over time.
Knowing the runout on your spindle provides the information needed to either start the process of replacing the spindle or send it out for repair in a way that best accommodates your production schedule. Alternatively, it may give you peace of mind that your spindle is still in good condition.