Mazak VTC-20 Spindle Repair

Mazak VTC-20 Spindle Repair

The Mazak VTC-20 is a CNC vertical machining center.  It comes equipped with a grease lubricated and coupling driven spindle capable of running up to 8,000 rpm.


Our customer indicated that this spindle would occasionally make a banging noise while in operation. When we broke the spindle down for evaluation, we observed that the grease in the spindle bearings was partially washed out by coolant contamination. But the root cause of failure was loss of preload of the bearings, which occurred when the hydraulic nut loosened up on the rear of the shaft. The spindle-side half of the direct-drive coupling actually bolts to the hydraulic nut, so any motor misalignment or other disturbance of that connection will cause this type of failure. In this case, one of the mounting bolts had been broken off, and the coupling pilot OD and shaft mounting ID were both egged and tapered. The loss of preload also allowed the inner bearing spacer to spin on the shaft, damaging the spacer ID. We observed significant damage in the front of the spindle, including severe egging of the front bearing housing ID, severe wear, runout in the tooling taper, and a cracked gripper sleeve.



Our overhaul of this vertical machining center spindle included a grind, chrome plate, and finish grind of the front bearing housing ID, the shaft CT40 tooling taper, and the inner bearing spacer ID. These grinding operations were accomplished in-house on one of our Kellenberger grinders. We also repaired the hydraulic nut and trued up the inner and outer bearing spacers in our machine shop. We replaced the bearings, belleville washers, gripper sleeve, spindle-side drive coupling, o-rings, and assembly screws.



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.


  • Bell mouthed taper from years of heavy use and decreased drawbar force.

  • A look into the taper showing the poor contact surface.

  • This is the wear on the spindle shaft from the inner bearing spacer. The nut holding the bearing preload had loosened allowing the inner spacer to move and over time damage the shaft.

  • View of the fretting done to the interior of the front bearing spacer

  • Pointed out here are the cracks in the tool retention sleeve. These cracks allowed the sleeve to expand causing a decrease in drawbar force. This let the tooling move in the taper causing the damage.

  • This is the inner and outer front bearing spacer together. Notice the contaminated grease left after the bearings were removed.

  • The contaminated grease in the front bearing.

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More Case Studies

Repair History - Here are examples of similar spindle repairs that may contain additional information that will help you. If you have additional questions, please contact us.

I really didn’t expect this; You guys really pulled it off! My many thanks to your outstanding crew for helping us get back into production.

Dan Eaton, Taylor Metalworks

Its great not to be sending spindles out on a regular basis since you addressed my problems, but I know they will still be coming sooner or later. Never a problem when we get them back , run better than new. Hope everything is ok there. Please tell everyone there that we here appreciate everything that you do to keep us up and running and the quick turnarounds. Have delt with the rest now deal with the best. Have a great week end and up and coming holiday.

Northland Customer

Thank you NTE just received spindle today and WOW ! what a nice job. Can’t wait to use it. Thank the Northland team for us for a job well done 

Northland Customer

Both of the spindles that you repaired are on the machines and running great. We don’t have any spares for those grinders. We probably will not be purchasing a spare, as you have been able to turn around the repairs quickly and the price of a spare is cost prohibitive.

Northland Customer

I am writing to thank Northland Tool for going the extra mile and saving my company from expensive machine downtime and expensive repairs. We have always sent our Chiron spindles for repair as a shaft with bearings. None of our previous rebuilders pointed out the bearing fretting or the fact that the housing in the machine was out of tolerance and causing premature failure to the spindles. After Northland fixed the housings the spindles have never sounded as good or run as well! Great job guys!

Northland Customer

The detailed cause of failure reports and the expert technical advice that Northland Tool provides is bar none the best I have ever seen. We struggled to keep two of our large our milling spindles running for longer than 6 to 12 months. Northland Tools evaluation showed that the hydraulic nuts were not holding the assembly together causing premature spindle failure. We discussed this in detail and mutually decided to modify the spindle shaft to prevent this from occurring again. The first spindle we performed this on is still in the machine running like new after 3 years. That’s over three times the life of previous repairs and it’s still going strong. Easily over $40,000.00 of savings so far on that one machine and counting.

Northland Customer

Your people go above and beyond the call of duty when it comes to spindle repair. When we had difficulty with the spindle installation and we were able to talk directly to a spindle technician that helped us troubleshoot the issue it helped us out of a bind. We have sent several spindles to you and have nothing but great things to say.

Northland Customer

Thank you for your attention with my quick turn spindle repair. Your status updates allowed me to plan around machine downtime and I now know that you deliver on your promises. In the past other spindle repair vendors talked a big game and consistently failed to deliver. You not only delivered my spindle before the due date but you kept me informed throughout the entire repair process.

Northland Customer

You performed a miracle with my BIG PLUS spindle. After crashing the spindle severely damaging the taper we found that a replacement spindle was not only cost prohibitive but had a long delivery. Your repair was a fraction of the cost of new and you never would know that the spindle was damaged to the extent it was.

Northland Customer