Kuraki KMV-130 Spindle Repair

The Kuraki KMV-130 is a double-column CNC vertical machining center equipped with a grease-lubricated, 25 HP spindle with a 2-speed gearbox that runs at up to 4,500 RPM with a CAT-50 tooling taper.

 



CHALLENGE

Upon initial inspection, the bearings on this Kuraki spindle were extremely noisy when the shaft was rotated by hand. The interior of the spindle was found to be heavily contaminated with brown sludge. While disassembling the unit, our technician discovered that the front shaft nut was loose and the pair of front angular contact bearings had lost preload, which caused there to be an unacceptable amount of end-play on the shaft. Measurement of critical dimensions revealed that the 100 mm front bearing journal was out-of-round, -15/-24µm (ISO = ±5µm) and showed fretting wear due to loss of preload. The front bearing journal shoulder measured with 6µm runout and the tooling taper ID had visible pitting and damage. The rear roller spacer spun on the shaft as a result of a loose rear shaft nut, which damaged the spacer and nut. Gripper fingers (collet) had significant wear on critical tool retention surfaces which could cause tooling to fit loosely and create a potential safety hazard.  

SOLUTION

The following actions were performed for this Kuraki KMV-130 spindle repair:
  • Rework the rear roller spacer and nut
  • Kiss grind the front bearing journal shoulder
  • Grind, chrome-plate & finish grind the tooling taper ID and 100 mm front bearing journal
  • Replace all bearings, Belleville washers, o-rings and assembly screws

RESULT

After adjusting bearing preload, reassembly of all components, 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.

DETAILED CAUSE OF FAILURE

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