Pre load issues with BK bearings blocks from LMB

[ghassall]

Hi Guys

I know a few people have purchases ball screw and bearing blocks from LMB on ebay.
I have an issue trying to pre load and remove the end float from my ball screws.
I have a dial indicator mounted to the router base with the point on the end of the ball screw shaft. No matter how tight i do the pre load nut up on the ball screw i can not remove all the end float from the screw. I have around 0.13mm at the moment.
I have pressed the bearings out of the block and have come to the conclusion that the "Made in China" brand of angular contact bearings that are used in these BK mounts are c%$p. They are manufactured with no in-built pre load (clearance between inner races) and no matter how tight you do the pre load nut up you will never remove all the end float of the screw in the bearing standard state as the inner races are touching.
If i bolt the bearings together the other races have a far amount of slop. You can fit about 0.15mm between the two other races with the inner ones bolted together.
Also the bearings are mounted in the blocks in a face-to-face ( \ / ) configuration. After a little investigation and coming across a great page on the net, it seams that a face-to-face configuration is used when the inner races are 'fixed' and the pre load of the bearings is adjusted by pressure on the outer race. This is not how BK blocks are designed.

So i see i have to options (if i don't want to buy new bearings)
1. Leave them in the face-to-face config and shim the inner race. I was think of 0.2mm which should remove the 0.13mm float and add a bit of pre load.
2. Flip the bearings so they are back-to-back, shim the other race and then the nut on the ball screw can be used to adjust the pre load?

Has anyone had experience with these sorts of issues?

Thanks

[derekj308]

Hi ghassall

I don't have experience with these bearings but I can offer a logical POV. I suspect that the bearings were installed incorrectly as face to face configuration. I would expect that the bearings used are meant to be installed back to back. Is this BK assembly one of a few you bought and it is the only troublemaker? Can you compare to your other BK assemblies that have no float?

I think you could press them back in as back to back configuration and then tweak the torque on the preload nut until you get just the preload you desire. Instead of pressing them in you could freeze the bearings and heat the housing for a smooth drop in and no pick up. Before doing that I suggest installing the bearings back to back onto the screw without the housing since they are already out. As you do up the preload nut by hand you should see the axial float disappear and the outer races touching. I would also check the depth of the two outer races when touching and compare it to the depth of the bore in the block and the depth of the retaining plate spigot just to ensure that your 0.13mm float is not partly due to float of the outer races. You should have some clearance between the retaining plate and the housing.

Cheers

[timber_MG]

I too had a problem with their blocks. With mine, the outer races shifted around and I had my machinist shim the block. I will be using normal dual row angular contact bearings for my router and see what performance I get.