Why is there a separate warranty for the V2-50 spindle?
The warranty for the spindle only on the V2-50 is 3-months from time of delivery. The warranty for the rest of the machine is 1-year from time of delivery to you. The warranty policy can be found here.
It is common for machine tool manufacturers to warranty the spindle for less time than the rest of the machine as they are the most prone part to improper use. If you use your machine during the first three months and there is a factory defect then it should become apparent during that time. If you use the spindle properly then it should last without issue. With proper use the NSK spindle is rated up to 3,000 hours at 50,000 RPM.