FANUC 6MB axis rumble

[moldmker]

1981 Kitamura Mycenter 2
Fanuc 6mb
Fanuc DC Servo Mod. 5
3 phase rotary converter

Above machine has been installed in my shop for several months.
There is a rumble in the X-axis that sounds like bearing noise.
Listening with stethoscope, rumble comes from the servo.
Interpolated cuts seem less than smooth. Table travel does feel smooth.

I have never disassembled a large servo but am pretty meticulous with complicated assemblies, so I'm sure I can handle the mechanical aspect of it.

Should servo disassembly be my first step? Is there any part of the servo I should not take apart?

Could the noise be a drive issue?

I don't recall the noise when it was at the previous owner's shop. For some reason they had the backlash parameter at .006" and I reduced it to .0004" for better results.

Thanks,
Bob

[Al_The_Man]

What you should do is disconnect the motor from the ballscrew and see if you still get the noise, it could be a chipped ball or similar in the Ballscrew.
This should eliminate the motor itself.
They are most likely DC servo's, the brushes should be checked as a matter of course, the min. brush length is dependent on model, but is around 10mm.
Al.

[moldmker]

Al,

Thanks...pulled the servo and it ran quiet.
Pulled the thrust bearings and they were beat to heck.
Ballscrew/nut feels smooth.
Will replace bearings and make sure oilers are working.

Thanks again,
Bob