[keebler303]

I finally got to tear down my mill to find the source of 0.01-0.015" play I have in my Z axis. When I use a bigger drill or plunge an endmill I can see a good bit of play in the Z axis movement. On smaller tools, the weight of the spindle is sufficient to keep this from affecting my work.

I tore down the head and found that the two bearings holding the ballnut have a significant amount of play between the inner races and outer races. The bearings is in now are Fafnir 9114PP. These appear to be deep groove ball bearings, I would have expected AC bearings in this application.

Are these the bearings used from the factory?
Is it standard to shim the bearings to remove backlash and carry on?
If I replaced the bearings with the same would that remove the backlash or will I still need to shim them?

Thanks in advance
Matt

[gus]

I replaced these a long time ago in a boss7, and I think I recall them being direction specific. I also replaced the y ballscrew bearings and I remember those had the paint dots on them, and it would make sense the z would be the same

[keebler303]

Thanks gus

I pulled the seals off of one of them and they do appear to be plain old deep groove ball bearings. I'd think that the Z axis sees less force than the Y so bridgeport may have cheaped out on those bearings but I think its also quite possible that someone replaced them with the wrong bearing. This Fafnir part is a deep groove bearing but Timken has several angular contact bearings with 9114 designation as well.

I'm thinking about just shimming the play out and putting it back together. The bearings look to be in good shape and new AC bearings would cost more than I paid for the whole dang mill.

Thanks
Matt