Okamoto ACC 820 ST Spindle Repair

The Okamoto ACC 820 ST is a CNC surface grinder with auto downfeed capability.  It can come fitted with this grease lubricated and coupling driven spindle capable of running up to 3,600 rpm.

CHALLENGE

This Okamoto ACC 820 ST spindle had bearings that were very noisy incoming.  During disassembly we noted that the interior of the front cover was packed with RTV silicone.  After completing the breakdown and evaluation, we found that the grease in all the bearings was washed out by coolant oil.  The #2 front bearing had heat damage as well.  We then measured the critical dimensions and found a few deviations.  First, the wheel hub taper OD had excessive runout >52µ and the taper threads were bent.  Second, the 80mm front bearing journal had scoring and low spots from a previous repair, but was not a cause of failure and we will use as is.  Thrid, the rear bearing shoulder had high runout >5µ.  Our customer also indicated that he would like to have an air dam installed on this spindle to prevent contamination.

SOLUTION

The following actions were performed on this Okamoto ACC 820 ST spindle:

• Clean, inspect overall dimensions.
• This spindle housing style cannot support a fitting for an external air purge system.  We will rework the front labyrinth to accept an internal V-ring seal for mitigation of contamination.
• Grind, chrome plate, and finish grind the wheel hub taper OD
• Rework the taper threads
• Kiss grind the rear bearing shoulder to reduce the runout
• Replace bearings, o-ring, and assembly screws

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.