Shizuoka X axis thrust bearing pics (and part# help)

Here is a pic with the X axis motor removed and the locknut removed, showing the
outer bearing:
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This *normal* outer bearing has the words NSK JAPAN 6205Z on it. There is a
handwritten P6 on it as well.
In order to read the part numbers of the thrust bearings, I had to take them
out. Here is a pic of the outer set (there is a duplicate set on the inside,
though I didn't take those out I assume they are the same part#).
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The order in the pic from left to right is outer to inner. On the second set of
bearings it is inner to outer.
The part # for the thrust bearing is NACHI JAPAN 205. One of the pieces also
has handwritten "205ps" and "SSB973"
The thrust bearing raceways measure 25mm ID by 47mm OD by 4.18mm thick. The
center bearing retainer piece measures 26.26mm ID by 45.42mm OD with a ball
bearing diameter of 7.93mm.
I liberally greased everything and reassembled. I tried tightning the locknut
thinking I could take out some of the play in the thrust bearing but no matter
how tight I got the nut, it didn't seem to affect the play. This makes me think
the play is in the *normal* NSK bearings and not the actual thrust bearings?
The balls in the thrust bearing I removed looked good, and the 4 that I measured
were within 0.0001" of each other. Upon reassembly, I still get the same
0.0015" backlash in the x axis, but perhaps the once per rev thud sound and
vibration is a bit reduced.
Opinions on what to do next?
Thanks for all the help so far!
Rick
Reply to
rick
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Theyre not terribly expensive..........
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You may be able to put a .0015 shim in there someplace, depending on how its all setup--without my being there and seeing exactly how its laid out its kinda hard to visualize, and though one of our machines has that same type setup, its been a while since I've had that one apart.
Dont tighten the crap out of the nut if thats how the thrust preload is adjusted--doing so will quickly ruin the bearings.
Reply to
PrecisionMachinisT
Well, is the .0015" backlash actually in the leadscrew, or in the leadscrew nut? You should be able to put a dial indicator on the end of the leadscrew and measure the axial free play of the leadscrew itself. Once you remove the free play there, then you can look for other sources. Don't assume all the backlash is in one place.
What is this once/rev thud? Do you mean as you are moving consistantly in one direction it goes thud-thud-thud? That sounds like something seriously wrong. Does it have ballscrews? If so, some investigation with the entire ballscrew/nut assembly out of the machine sounds in order.
Jon
Reply to
Jon Elson
Wow, thanks for the links! They were cheap enough that I decided to just order a complete set to replace all the bearings on the X axis. Hopefully this will fix some or all of the backlash problem, if not it was still pretty cheap.
The more I think about it, it seems like tightening the nut should have adjusted all of the play out of the bearings no matter how worn they were...maybe I am just not understanding the bearing stackup. The 6205Z bearings are radial, for side loads, so they should have no axial play, and the thrust bearings are in three piece sets, so when compressed hard enough together they should not have play either.
Anyway, I will let you know how things work after I install these new bearings.
Thanks,
Rick
Reply to
rick
I did this already (dial indicator on the end of the ballscrew) and measured the entire x axis backlash as ballscrew freeplay (thus pointing to bad/loose thrust bearings). Perhaps I was fooled in my measurement by a non-flat end on the ballscrew...I will try it again on the other end with the motor removed and rotating the ballscrew shaft back and forth by hand.
It is not so much a loud thud as more of a slight bump in the volume of the turning ballscrew, and a slight vibration at low IPM. It is noticably better after I took out the thrust bearings and reinstalled them packed with grease, though I still have the backlash problem.
Taking the ballscrew out...uhg...rather avoid that for now, unless there is a way to get it out without taking the whole milling table (heavy!) off the mill.
Thanks,
Rick
Reply to
rick
You're entirely welcome, but should you ever need $pindle bearings, Gunner is still the king.........
Yes, it wouldnt make sense to use a setup having a mix of angular contact and flat thrust bearings in a ballscrew application, because this only allows higher thrust loads in one direction........
Curious, is the end of the ballscrew opposite the motor mount supported by a radial bearing also ???
Good luck.
Reply to
PrecisionMachinisT
Darn, remeasurement of the end of the ballscrew referenced to the mill table using a dial indicator shows less than 0.00025 play, while the whole x axis still has about 0.0015 backlash. I think my measurement yesterday was flawed by a layer of tarnish or crud on the end of the ballscrew. When I thought I was seeing a 0.00125 play in the thrust bearings, it was just the dial indicator tip riding up on a dried layer of grease that looked like metal.
So...back to the problem actually being in the ballscrew/ballnut. What are regrind/reballs? $800+? Any known good companies to do that?
Rick
Reply to
rick
I'm not sure where you are, but I have a place in Rockford, IL that gives good turn-around time and the prices are good. This is from memory, so don't quote me, but I had a ball screw rebuilt a couple years ago...1 1/2" diameter screw, double row ball screw nut, and 42" total length and, again from memory here, about $300.00us.
If this will help, let me know and I'll track the number and stuff down...which is at work now.
Mike
Reply to
The Davenports
$300 seems awfully cheap. Did they do a good job? (heh, you mentioned fast and cheap...)
It would be great to have the name or number of that company. Even if I didn't go with them, at least it would arm me with a price basis.
Thanks!
Rick
Reply to
rick
Oops, missed answering this question. The opposite end of the ballscrew from the motor mount is indeed supported by the same type (6205Z) of radial bearing.
Rick
Reply to
rick
based on my experience..you may have a servo going out. This sort of sound is typical of a servo with a loose magnet or a bad front bearing.
This would be a totally separate issue from the worn ballscrew/worn thrust bearings
Gunner
Liberals - Cosmopolitan critics, men who are the friends of every country save their own. Benjamin Disraeli
Reply to
Gunner
[ ... ]
Hmm ... just out of curiosity -- can you measure any shift in the ballnut's attachment to the saddle? That is another possible source of the backlash you are experiencing. I would also check that out before spending whatever a rebuild for the ballscrews and nuts would cost you.
Good Luck, DoN.
Reply to
DoN. Nichols
.0015 really aint that all that bad, and its compensable in most cases--perhaps the milling of a protruding boss being the only main exception......otherwise, learn to use a boring head......
Likely the backlash can be adjusted through parameter seting, let us know the controller make/ model and someone might chime in here--Im sure I have data on the Fanuc 6 if that is the case, twist my arm and I can probly find the settings.
Meanwhile, you got yerself a spare set of thrust bearings at a pretty damned good price..............
Reply to
PrecisionMachinisT
I'll find it tomorrow...PLEASE remember that I got that number from memory...and I don't remember for sure what I had for lunch today :).
And yes, they did very good work.
But I'll post the info about the place tomorrow.
Mike
Reply to
The Davenports
yeah, I can live with .0015 for awhile. It really only makes a difference when interpolating circles, and even then is probably OK for most stuff. Should even be ok for thread-milling. Like you said, I can get a boring head if I want super precision holes.
I run EMC. I know how to set the backlash in that, but thanks!
Rick
Reply to
rick
Maybe. I will run the motor by itself and see what it sounds like. It could also be what another poster suggested, and my ballnut is not tight on the saddle. Perhaps every revolution it is riding up on its mounting bolts and also causing the backlash. Not real hopefull the problem is this simple, but when I get the thrust bearings I will take the table off and check. It will be a good time to make sure the autoluber is doing its job too. Perhaps I can just take the table *mostly* off and get access to the ballnut on the Y saddle. Otherwise I have to figure out how to lift 400+ pounds without a hoist or crane. :-(
Rick
Reply to
rick

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