Ball screw thrust bearings .Wabeco Cnc milling machine

Hi, I was removing the ball screws from my Wabeco CNC mill and noticed that the pairs of thrust bearings were ordinary ball bearings. Surely these should be angular contact bearings which are designed to take end load. Do other bench CNC mills have these fitted. I thought that to remove all ball screw end play, the bearings have to be preloaded. One also has the weight of the spindle assembly and motor pushing down on it. I thought that ball race bearings are not ment to have an end load applyed

I would appreciete any comments on this matter.

John.

Hi John

Conventional ball bearings sometimes called Conrad or deep grove ball bearings can take an axial load, however not as large as the angular contact type. If you measure your existing bearings which hopefully have a manufacturers name on them you should be able to look up the allowable load on the manufacturers web site. If the manufacturers name and number is not on them you will have to make do looking up other manufacturers web sites for a similar size bearing, at least you will get a rough idea of the allowable axial load.

It is surprising that pre loaded bearings have not been fitted, surely defeating the purpose of the ball screws. If provision has not been made maybe you can make up some shim washers and by careful fitting achieve a preload. You may be able to source angular contact bearings that fit the same space. or even conventional thrust bearings, in addition to the ball bearings if there is room to fit them. If not shimming the conventional bearings will help.

Angular contact bearings are not available in the range of sizes available for standard deep groove ball bearings, hopefully they are available for your application. When preloading them it is important not to overload them, consult the manufactures data sheet.

There is also a relationship between the applied load in any direction, and the speed of rotation, in this case negligible, and the life of the bearing, if you accept a certain life the loads can be increased. This information can be obtained from the bigger bearing manufacturers websites.  

Cheers
John

Edited By John McNamara on 13/05/2013 00:59:43

Hi John,

Thanks for your detailed reply. I will try and replace the standard ball bearings with angular contact bearings. There is a thread on the ball screw and preload as adjusted by screwing belt pulley against bearing. It is cross drilled and tapped to lock in position with grub screw.

Not sure shealded angular contact bearings are available. I will have to ask tomorrow.

Regards John.

Hi John,

Shielded angular contact ball bearings are available in some sizes, what are the dimensions?

Regards

James