[chmedly]

I have a pair of used BK mounts. One of them fits tightly on a screw but the other one has a "wobble" when mounted on the same screw. I am assuming that the angular contact bearings in the wobbly one are either worn or the tension needs to be adjusted. The screws have been marked with paint marker. Is the tension entirely adjusted with these external screws or are there internal adjustments? I'm very tempted to take it apart. Any suggestions about how to fix this?

Attachment 428710

[joeavaerage]

Hi,
my understanding is that angular contact bearings for such purposes are sold as a matched pair. They are ground
in such a manner that when the outer annular rings are clamped the inners are under the right preload.

A regular angular contact bearing say a 7204 (20mm ID) might be $20, a matched pair of P4 grade 7204's for CNC
machines could be $200 or more.

That your bearing pair has a 'wobble' suggests to me that the ball separator has failed in one or both bearings. You will
have to disassemble them to find out. Should you ever wish to reassemble them you MUST mark every pieces orientation
as you disassemble otherwise all semblance of matched precision is lost.

Depending on your budget and how hard and fast you want to operate these bearings you could try a couple of angular contact
bearings and rely on 'random matching'. If you assemble them 'with a fitters magic feel' you'll probably get away with it, at least
for non-demanding applications. Other than that you are up for a matched pair......and if you think $200 a set sounds bad spare
a thought for specialist machine makers who use high angle of contact bearings especially for axial thrust capability and all
ceramic at over $1000 a pair!!!

Craig

[ihavenofish]

Nah. the bearings they put in these smaller blocks are $50-$100 per matched pair at misumi. P5 grade is all you need general (radial runout is not very important, nor is high speed). The expensive stuff its spindle bearings, which are not even vaguely similar to ball screw support bearings in geometry or spec.

If thats a higher end block from thk or nsk, the bearing pair will likely be pinned together and not seperable or adjustable in any way. Cheaper blocks may have 2 separate bearings.

Note that the bearings are meant to "wobble" to a degree. They are oriented face to face so they can tolerate shaft misalignment. So wobble alone does not indicate anything. You need to measure axial movement.