[timber_MG]

I bought a ball screw on ebay along with my water cooled spindle and decided the end supports were really good value. So all goes well (re-assembling a ball-nut not withstanding after a little mishap when unpacking) and something didn't seem right with the fixed end.

On closer inspection the fixed end bearing had a lot of play, even when pre-loaded which took me by surprize given how snugly the bearings fit.

So I took off the spacer and seal to reveal the bearings and could feel the back lash in the bearings moving axially in the block. Taking a vernier caliper to the problem revealed 0.46mm backlash measured off the outer race of one of the bearings by moving the bearings by hand.

Have I missed something in assembling these? Do I need to insert some sort of washer/spacer inside of these bearings? Do I need to open the unit at the bearing plate?

Any help would be gladly appreciated. I will post some pictures when I am back home.

[andyb4]

The beaings are probably angular contact which means that they will only take thrust in one direction. If you look at the sides of the bearings you will see that the opening on one side is larger than the other side. These need to be oppisite each other. By that I mean put the two larger openings together or the two smaller openings together. If you push on the inner race it will seem to come out of the inner in one direction more than the other. When the direction of thrust is correct the bearing will run smooth. The side you are pushing on is the larger opening. Also both the inner and outer race need to be held in place tightly. The inner two on the shaft and the outer two in the housing. Hope this helps.

[timber_MG]

I have not yet opened the bearing block (nor do I really want to), but the play is in the outer races of the bearings leading me to suspect that there is something gravely wrong with the unit or something has gone missing in the assembly. If I put on the nut and move the ball screw axially i can see both bearing's outer races move in unison (I will check that they face one another but I am pretty sure that they do)

Should I open it up and if so is there anything I should be wary of?

[Mike Everman]

yes, be wary of ebay. ha,
don't be afraid to take it apart. as andy said, the large openings should face away from each other.
There is also a step in the end plate usually, that must go toward the bearing set to clamp the outer races axially. that plate may be on inside out. just a guess. a picture would be good.

[timber_MG]

Well, I undid the cap screws on the bearing plate and I cannot get the unit to budge. Is the assembly so tight that one has to apply heat to the bearing block or are these sometimes glued in position?

Thanks for the feedback guys. I will try and get some pictures of the unit and am awaiting feedback from the seller.

The rest of the assembly is in for machining. I should start a thread on another subforum to document the build.

[timber_MG]

I have finally managed to take apart the bearing block revealing two NSK 7001 AC bearings, the bearing housing, plate and 4 screws. I don;t think these bearings can pre-load by themselves (I assume that must have been some kind of precision spacer between the outer races in the block.

I have attached an image of how I measured the backlash.

Thank you for your input. At first I though I had not assembled something correctly, but it is becoming clear that there is something amiss.

[andyb4]

The outside races need to be held between two shoulders, one in the bearing block, and the other on the end cap. From your picture it appears that the end cap does not retain the outer races. Does the cap where you are measuring from have a shoulder to push against the outer race? If it does the is probably a missing spacer. Also by what it looks like your setup has the larger openings facing away from each other. With this setup the shaft needs to be held in place or you may see some play with the inner races, although this doesn't seem to be the case as you discribe.

[timber_MG]

Chai from linearmotionbearings has sent me a replacement....with the same problem.

What I will now do is have a grinding shop make up a ring that I can place between the two outer bearing races and tighten the assembly up against the bearing plate...or can one buy such spacer rings off the shelf perhaps?

[Thazul]

Hi timber_MG,
I believe mcmaster.com has what you are looking for,
Catalog pages 3198 through 3200 have precision bearing shims.

http://www.mcmaster.com/#catalog/115/3198/=28l6ay

Metric ones start on page 3200

hope that helps!

Best regards,

Andy

[timber_MG]

Now only to find a source that will ship to South Africa or a local source.

Thank you so much.