Doosan Mynx 7500 Spindle Repair

The Doosan Mynx 7500 is a CNC vertical machining center.  It can come fitted with this grease lubricated and belt driven spindle that is capable of running up to 12,000RPM.

CHALLENGE

Our customer sent in this Doosan Mynx 7500 spindle stating that the spindle started to be hard to spin by hand and was making humming noises.  Once the spindle arrived at Northland Tool we completed a full disassembly and evaluation.

This is what we found:

• The ID taper had 14µ of runout assembled and was worn.
• All of the bearings were washed out from coolant, most likely from the rotary union. (Pic 1)
• The drawbar had damage from the bellevilles, the tail had significant damage and was bent 40µ. (Pic 2)
• There was a broken bolt in the drawbar retainer that will have to be machined out.
• The ID taper failed our air gauging and had 10µ of runout bare shaft.
• The drive dogs were loose and sustained damage from tooling. (Pic 3)

SOLUTION

The following actions were performed on this Doosan Mynx 7500 spindle:

• Clean and inspect overall dimensions
• Replace bolts, o-rings, bearings, and quad-rings
• Grind-Plate-Grind (GPG) ID 40 taper
• Straighten tail of DB where rotary union seats, GPG rod and tail damage
• Replace bellevilles and gripper fingers
• Machine out bolt in drawbar retainer
• Machine new drive dogs

RESULT

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