Hurco VM2 Spindle Repair

Our customer sent in this Hurco VM2 spindle because it started leaving chatter on the parts they produce. If you look at the picture below it appears the taper had been ground in the machine with a portable taper grinder. Grinding the taper in the machine can give you poor results as you are depending on worn spindle bearings and a non rigid assembly (taper grinder) to hold micron tolerances. As you can see in the picture below, it caused chatter marks in the taper which causes poor tooling contact, premature tooling wear, and tooling run out.

CHALLENGE

Our customer indicated that the spindle would heat up after a period of operation, affecting the part finish.
During incoming testing, the front bearing vibration (measured in acceleration) steadily increased as the run continued.  Upon disassembly, we found that the front bearings exhibited some light contamination and the grease was beginning to wash out.  Shaft tooling taper shows a spiral wear pattern from an in machine grinding attempt.

SOLUTION

The following actions were performed on this Hurco VM2 spindle:

• Clean, inspect overall dimensions
• Replace sealed bearing quad set, Bellevilles & o-rings
• Kiss grind taper

RESULT

After reassembly of all components, adjusting bearing preload, and undergoing break-in and testing procedures, this spindle passed our final quality inspection before being returned to our customer with a 1-year warranty.