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IndustryArena Forum > Mechanical Engineering > Linear and Rotary Motion > Ball screw support bearing questions. Are $420 bearings necessary on this machine?
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  1. #21
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    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    You have any recommendations for a specific coupler to go from 22mm keyed shaft (motor) to 13mm Ball screw (smooth shaft)? They are so far apart.

  2. #22
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    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Okay, so I have been doing a ton of research on these bearings the last week. I think the first number I was quoted is completely wrong. I sent pictures off and asked for second and 3rd opinions and got something else.
    Being unsure and wanting to know exactly what I need, I decided to research and try to decode them myself.
    It appears that last digit on my bearings is really a 5.
    I happen to work with a Japanese lady, so I asked her why this last number would look weird since it is like this on both bearing sets. She says the person that was making these just happens to make their 5's that way.
    She said when they (Japanese) make a 5. They make it by starting at the top, making the line down, then the curve, then add the top line (across). This explains why the line across the top is offset down the vertical line (just sloppy writing of the person).

    Based on this and asking her, she thinks it is definitely a 5.

    Based on that and finding an NSK Conversion Data PDF that explains it all I came up with this:
    7204 = 47mmOD, 27mm ID, 14mm Wide
    A = Contact angle of 30 Degrees
    DB = Back to Back arrangement
    C9 = Heavy Preload
    P5 = ISO 5, ABEC 5

    This converts to
    7204ATYNDBHP5
    or
    7204ATRDBHP5

    Depending on the cage. I believe no designation (like my part is TR), But TYN seems more common and is better.

    So, I am settling on 7204ATYNDBHP5

    Before doing all of this, I got another place telling me that NSK came back with this part number
    7204ATYNDBHP4

    Now, I am not sure if they thought the P5 might be a P4 because of the way it looks in the picture, or if they are recommending a P4 (ISO 4, ABEC 7) because it is better and possibly what they recommend in this application. I have asked, but I have not got the response yet.

    I am pretty sure the P4 is a lot more expensive though (double the cost).

    Do you guys think I should stick with what my bearing seems to say at P5, or go with what NSK says and a P4???

    The P4 part numbers are in the $300's range, but I think the P4, can be had for the $100's range.
    Attached Thumbnails Attached Thumbnails 20191102_190745.jpg   20191105_183717.jpg   20191105_183727.jpg   20191105_183638.jpg  


  3. #23

    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    This is where you look into your wallet and decide what something is worth to you. But first I would suggest getting out the bearing tolerance tables that are readily available and look at the differences between P4 and P5 or ABEC 5 and ABEC 7 as I think the cross is. Those extra 100's of green ones will likely add up to a couple tenths here, a couple tenths there. Maybe a thou here or there. Decide after you understand what you're getting and if it's going to make a difference.

    That C9 Heavy preload is something I've never come across. I've seen only light preload if I remember right. Maybe I'm thinking spindle bearings. You sure that C9 isn't an internal clearance call out? Not even sure you're going to find a heavy preload on the shelf somewhere.

    I do think all your digging has you on the right track. 30 degree contact angle and a DB arrangement are totally typical in this application.

    Anyway... check out those tolerance tables and see what you get for your hard earned dollars.

    Dave

  4. #24
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    344

    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Yeah, C9 = Heavy Preload is correct. It took me awhile to figure that one out. I actually found another series bearing and manufacturer where C9 means Light Preload, but that does not apply here.

    I finally found a PDF from NSK called "NSK Conversion Data". This included the cross over from the Old-NSK to current NSK numbers.

    NSK said it was a Heavy Preload bearing and gave me a part number before I decoded it myself (second vendor I tried contacted them). I eventually also found it in the documentation.

    The only thing in question now really is the P4 or P5 thing.

    I will have to research the P4 vs P5 tomorrow to see if there is any real benefit. I cannot imagine it is going to cause much difference in error of the ball screw movement between the two, but I will see if I can figure it out a real number.

    I am still waiting for some pricing responses and other questions to be answered. The pricing may make some difference in the decision. I think P5 would at least equal what the OEM put in there, so either way it should be as good as or better than new.

  5. #25
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    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    I made a summary chart on ISO 4 (P4) vs ISO 5 (P5) for this size bearing (from charts on a website I found).

    The real possible difference seems to be as follows:

    -.00005" possible extra Bore tolerance
    -.00005" possible extra ID tolerance**
    .00005" possible extra Radial Runout in the inner ring
    .0001" possible extra Radial Runout in the outer ring

    This seems pretty insignificant based on the specs of this machine, so it really is going to come down to weather or not this tiny possible difference is worth the price difference. Without knowing prices, I cannot answer this question really.

    I have asked for quotes for both scenarios so I can figure out which way to go. Pricing these bearings sucks because you cannot just find them online. I have to bug people for quotes and they are all over the place.
    Attached Thumbnails Attached Thumbnails ISO 4 vs ISO 5.jpg  

  6. #26

    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Quote Originally Posted by jevs View Post
    Pricing these bearings sucks because you cannot just find them online. I have to bug people for quotes and they are all over the place.
    Did you ever call Tull Bearing like I suggested in my very first response a week or two ago?. You're not bugging people. Quoting prices is what they do all day as part of their job. Just know what you want. Give them the numbers and leave it at that.

    BTW - I thought the differences would be minimal. Still think you're going to have trouble finding that heavy pre-load. I wouldn't worry about it if you can't.

    Dave

  7. #27
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    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Quote Originally Posted by the_gentlegiant View Post
    Did you ever call Tull Bearing like I suggested in my very first response a week or two ago?. You're not bugging people. Quoting prices is what they do all day as part of their job. Just know what you want. Give them the numbers and leave it at that.

    BTW - I thought the differences would be minimal. Still think you're going to have trouble finding that heavy pre-load. I wouldn't worry about it if you can't.

    Dave
    I sure did. Honestly, up until yesterday, it was not so clear what bearings I even needed though. So, I got a price from them, but it was for the first bearing that I think is no longer even a viable option. The heavy preload does not seem to be a problem getting. I think you can get anything, but it may be a couple week special order.

    At this point, these are the viable options (for NSK brand):

    7204ATYNDBHP5
    7204ATRDBHP5
    7204ATYNDBHP4
    7204ATRDBHP4
    7204ATRDUHP4Y
    7204ATYNDUHP4Y

    Some people have been trying to quote me the Universal version (DU), but I am not so sure that is a good idea. It seems like it would be better to just get the matched set (DB) for the configuration I need. If you get the DU option then you also need the Y which adds extra precision on the inner and out bores to ensure the universals will mate up good. This only comes with a P4 grade (ISO 4, ABEC 7).

  8. #28

    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Quote Originally Posted by jevs View Post
    At this point, these are the viable options (for NSK brand):

    7204ATYNDBHP5
    7204ATRDBHP5
    7204ATYNDBHP4
    7204ATRDBHP4
    7204ATRDUHP4Y
    7204ATYNDUHP4Y

    Some people have been trying to quote me the Universal version (DU), but I am not so sure that is a good idea. It seems like it would be better to just get the matched set (DB) for the configuration I need. If you get the DU option then you also need the Y which adds extra precision on the inner and out bores to ensure the universals will mate up good. This only comes with a P4 grade (ISO 4, ABEC 7).
    Jevs-Jevs-Jevs... you're heading down the rabbit hole again. I know because years ago I would go down there myself. If you rattle off that whole list to a person on the phone they WILL hate you! : - )

    Seriously, forget the Y, forget the DB. Honestly nobody sells the matched sets anymore. Haven't for years. The only place you find them is in dusty old boxes found on eBay. You can take the universals and set them up in any configuration no problem. Use those DUHP4 and P5 numbers and call Tull again. Remember you're still working on a forty plus year old machine. The bearing manufacturing capabilities today are also over 40 years matured from when your machine was made. I believe that's much of the reason why they can offer universal in the first place and know the needs of their customers will still be satisfied.

    Understand the rabbit hole always looks interesting, but it is always dark down there too.

    Dave

  9. #29

    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Hi Jevs,

    Just a quick aside about your bearing quest. Remember that in any bearing arrangement or setup, the accuracy of the mating components are as important as those you're looking for in the bearings. Ask yourself how do your mating components measure up in out of roundness, squareness, nicks, bumps, burrs, dirt, because all transfer their maladies to the bearing in some way or another. And don't forget that a lot of bearings are ruined as they're being installed.

    Do you have the proper tools at hand for the assembly? Are they clean as can be? Work area spotless? Mating parts clean as you can get them? No smoking? Ha... no heavy handed hammers! Do you have a syringe for adding the grease if they come ungreased?

    Okay... aside over.
    Dave

  10. #30
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    Feb 2005
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    344

    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Good info. All the docs I read still make it seem like the matched sets are the preferred way, so I would have never guess they are opting for the universal more. No one has mentioned that before now.

    The couple that did quote the universals all put the Y on the end though, but if getting rid of the Y helps the price with no negative, then I am for it.
    Here is a link that explains what Y does for you with the universal bearings (DU).
    http://nsk.com.br/upload/file/NSK_CA...4f_148-151.pdf

    Do you have any good info on the cage style? TYN vs TR.
    From what I am reading the TYN cage (lower friction, lower noise) is better than the Phenolic Resin (TR) (more stable in high speed). This is a low speed movement application. The max RPM of this application is limited to 1250 RPM. Max speed the ball screw nut can move is 250 in/min (.200" pitch screw, 5 rotations per inch).
    I can go with either on the cage I guess, but I do wonder if the TYN would be a better choice? I am not sure what the original is. I suspect the original is TR, because TYN may have not even been invented yet?

    I am trying to post as much info as I can in this thread, because it is a learning experience and might save someone else in the future on the same path as me (down the rabbit hole).

    I have everything needed for assembly, cleaning, etc except I do not have a proper tool to torque the nut. I don't know what the nut torque should be and I guess I am going to have to make a custom socket (without a mill). I am also not sure how you hold the ball screw when your tightening the nut since these do not have a hex hole in the end of the shaft like newer ones might.

    As for the condition of the mating parts, they are what they are. As far as I know this is the first time they have been apart and should be as good as new. I can say the bore for the bearings to go into and the plate that secures to the outer race do not seem to be anything super high precision. As far as I can tell the outer plate that holds the outer races is just cut on a lathe. The ball screws and the face of the retaining nut should be as good as new, but I would be pretty sure these were not made to ABEC 7 standards....which makes me question paying extra for the bearings (but again I do not know cost difference yet).

    I had thought about getting new bearing securing nuts for the ball screws, but it seems all the new ones use a brass tipped set screw to secure them rather than the method of pinching the threads like these do. Do you think there is any benefit to pursuing this?

    Thanks

  11. #31

    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Hi Jevs,

    A lot of times those special cage designs are in the books but not on the shelves. I spent many hours with my head in the bearing books and ran into the same kind of things you're running into. Also that Y designation again is talking millionths or one tenth at best. If you can get that for free then why not, but I wouldn't hold off for it. They mentioned advantages in very high speed applications. Not what you've got.

    Either type of locknut will likely work. What you will get with a new one is a perfectly square mating surface. You can look to SKF for the pinch type. The nut literature might have a torque setting.

    "I can say the bore for the bearings to go into and the plate that secures to the outer race do not seem to be anything super high precision. As far as I can tell the outer plate that holds the outer races is just cut on a lathe. The ball screws and the face of the retaining nut should be as good as new, but I would be pretty sure these were not made to ABEC 7 standards....which makes me question paying extra for the bearings (but again I do not know cost difference yet)."

    Ha-ha... look in the mirror and repeat these sentences over and over to yourself. Then go and buy your bearings (Using the basic letters and numbers) and move on to other things.
    Good luck. You'll do fine. Especially if you get that thing back together and start making stuff. You'll forget soon enough about all this bearing stuff in your forum thread once you're up and running. Belieeeeve me... you won't look back.

    My last 2 cents. Got to get back to work.

    Dave

  12. #32
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    Feb 2005
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    344

    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    I finally got a good phone number for NSK and talked to NSK directly which clarifies a lot of things. Now I am full circle back to the original part number I was quoted.

    First of all I confirmed all this DB DF stuff is nonsense and obsolete. They are all pretty much DU(Universal) and they just put DU's together to make a set with the "old" DB, DF, etc. part numbers.

    No one is using the 30 degree stuff anymore really, and moving on with 25 degree (A5).

    TR vs TYN does not really matter in this case. Buy whatever is available, but the person I talked to would prefer the TR anyway due to better support. Again, either will work in my application fine.

    Get the P4Y is pretty much the consensus for them and what they use in their current ball screw support bearing stuff.

    Basically, it sounds like they are making a lot of higher quality bearings and then just marking them what they need to be, to be sold LOL.

    With all of the information gained in that short phone call, it explained a lot. However, now I am back to the 7204A5TRDUHP4Y and the price tag that comes with them. However they are in stock and are the up to date current part number of things.

    The good thing about all of this, is that now I feel comfortable with knowing I am buying the correct thing.

    I also talked to an Engineer there and he said the nut should be tightened to 150 in/lb.

  13. #33

    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Cool Jevs, Sounds like you finally got there. That's great! I'm suppose to be getting back to programming, but I thought of one last thing to try to ease the worries a little.

    The main and practically only function of the ball screw support bearing angular contact set is to handle thrust loads transmitted to it through the screw shaft, and allowing the forces associated with moving X amount of weight at speed to be minimized to such an extent that the drive system can manage those forces easily and accurately. All the minutia of the tolerances and fits and runouts and all that which have been fussed about, don't play into the system nearly as much as they might in say a spindle setup.

    Try to imagine how a few tens of millionths of error in size or runout of a bearing set is going to affect a ball nut, or better yet, a machine table when sitting what, anywhere from 10 - 40 inches away. Why wouldn't those errors in form and size simply vanish into the looseness of the rest of the many systems linked to them? I'm guessing the errors would have to be greater by at least a factor of ten or a hundred or more before they would appear at the table and into the workpiece. I think surface finish would be the first to go and size or location a distant second. Just some conjecture, but really when you think about it. Still don't get me wrong. I'm glad great stuff is available, albeit at a price, but to or at what extent do these amazing tolerances matter? Especially in this application. Just sayin...

    Now really, back to work.

    Dave

  14. #34
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    So I paid about $700 for these bearings. Installed them with the rebuilt ball screws.
    I have worse backlash than before on X and just a little better on Y

    X .0021 Backlash
    Y .0019 Backlash

    The bearing retaining nut moves in and out and you can feel the slop by hand. I think everyone spec'd me the wrong bearings. They suck!

    And yes I tried everything to look for an issue. I filled them properly to spec with grease and kept everything perfectly clean.

    The rebuilt ball screws feel way better and much tighter than when I sent them in. They also run way quieter now. I do not suspect any issue with the screws since the support bearing retaining nut moves in and out near the amount of backlash. Also the fact that both axis have near the same backlash now. The heavier one actually has .0002 less than the lighter load. However, you can feel this backlash before much pressure at all even gets applied to the ball screw nut.

    Nothing I try takes the slop out. I just think they are not the right spec and won't hold the tolerance in this application. The only thing that might fix it is a spacer between the outer races which totally defeats what precision I thought I was buying. They may not last long doing that either.

    25 degree contact angle for support bearings seems super suspect to me now. The originals were 30, but I see most modern stuff is 60!

    NSK engineer hasn't returned my calls so far. Spent over 2k on this and now have worse backlash on X than the 40 plus year old stuff.

    The advertised "ball screw support bearings" I find are 1mm wider each than mine. I can probably accommodate these with a new retainer plate or cutting the lip down on the original.

    Not sure what to do now that I wasted all this time and money.

    I can accommodate it with backlash compensation, but that does not sound like a good substitute considering I actually have worse backlash on X now even thought the screw nut is much tighter.

  15. #35

    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Hi Jevs, I was wondering how your werre doing with your project. Sorry it doessn't sound good.

    Confused about the "slop" in the bearing retaining (lock?) nut. You mean to say that the lock nut wasn't able to be screwed in far enough to fully clamp the bearings on to the shaft?

    You know in a DB arrangement which you probably have, the clamping of the inner ring to the shaft is what sets up the preload in the bearing pair. With you having heavy preload that becomes even more important that you have the nut run fully home and with sufficient torque. That outer ring clamp is only for holding that bearing/shaft stationary against the floor of the housing bore. What is normally done is you measure the bore depth, the bearing width (usually on the package with amount of deviation from nominal listed) and the depth of the clamp ring on the back side of the fixing plate. What you want is the the plate outer surface (not clamping ring) to be just barely clear of touching the face of the housing. 0.0004 - 0.0015" or so is plenty. Then evenly tighten the screws that hold all in. You don't want to distort the outer ring by over tightening or unequal tightening.

    I can't recall what the typical contact angle is on the support bearings I've installed. I'm not at the shop with all my bearing books and records. 25 does seem a little low and more towards spindle bearing contact angles, but the 60 thing mentioned could be something very new and not applicable to your older machine.

    The great thing is you can likely rework the bearing install without completely taking everything apart again.

    Yes using backlash comp is done by every machine. Problem is modern controls usually have two settings. One for backlash at rapid speed and one for slow or feed. Not sure how much n practice does that makes a difference.

    Wish I could be more help. Very sorry you're not happy after all that work.

    Maybe if you had more or better pictures of the old setup. Bearings, housing, bores, plates.

  16. #36
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    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Quote Originally Posted by the_gentlegiant View Post
    Jevs-Jevs-Jevs... you're heading down the rabbit hole again.

    Seriously, forget the Y, forget the DB. Honestly nobody sells the matched sets anymore. Haven't for years.

    Dave
    That's totally Bs what some people will post is amazing
    Mactec54

  17. #37
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    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Quote Originally Posted by jevs View Post
    So I paid about $700 for these bearings. Installed them with the rebuilt ball screws.
    I have worse backlash than before on X and just a little better on Y

    X .0021 Backlash
    Y .0019 Backlash

    The bearing retaining nut moves in and out and you can feel the slop by hand. I think everyone spec'd me the wrong bearings. They suck!

    And yes I tried everything to look for an issue. I filled them properly to spec with grease and kept everything perfectly clean.

    The rebuilt ball screws feel way better and much tighter than when I sent them in. They also run way quieter now. I do not suspect any issue with the screws since the support bearing retaining nut moves in and out near the amount of backlash. Also the fact that both axis have near the same backlash now. The heavier one actually has .0002 less than the lighter load. However, you can feel this backlash before much pressure at all even gets applied to the ball screw nut.

    Nothing I try takes the slop out. I just think they are not the right spec and won't hold the tolerance in this application. The only thing that might fix it is a spacer between the outer races which totally defeats what precision I thought I was buying. They may not last long doing that either.

    25 degree contact angle for support bearings seems super suspect to me now. The originals were 30, but I see most modern stuff is 60!

    NSK engineer hasn't returned my calls so far. Spent over 2k on this and now have worse backlash on X than the 40 plus year old stuff.

    The advertised "ball screw support bearings" I find are 1mm wider each than mine. I can probably accommodate these with a new retainer plate or cutting the lip down on the original.

    Not sure what to do now that I wasted all this time and money.

    I can accommodate it with backlash compensation, but that does not sound like a good substitute considering I actually have worse backlash on X now even thought the screw nut is much tighter.
    Yes 25 degree is to light for a machine like yours
    Mactec54

  18. #38

    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Quote Originally Posted by mactec54 View Post
    That's totally Bs what some people will post is amazing
    About the only miss placed or potentially BS word in what was said is "nobody." Should have used "few." The manufacturing process has gotten so refined that "Universal ground" is the name of the game these days. At least that's what I have always run into in the many times I've sought them out in what would be the rebuild/replacement market. Who knows what OEMs see. Believe me, I've sought matched pair and triple sets, you name it, including matching bore and ring diameters to my needs. All with little to no luck. The last time my bearing supplier ever let me go in the back room and pick the bearings I wanted was let me see... never. You find old shelf stock of matched pairs on ebay sometimes. Even Mori Seiki sent me universal ground the one time I went to them for what I think was a triple set. They were all taped together as a group, so that was close. :-) They even had a different ball compliment count. Go figure.

  19. #39
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    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Why not just add shims where needed and be done with the problem? That's what I did on my X axis, no new bearings. Got it to about 0.0002 as near as I can measure and pretty sure that's in the ball nut. Still need to do the Y axis, have about 0.002.... Some day, maybe this spring.
    Jim Dawson
    Sandy, Oregon, USA

  20. #40
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    Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Why not just add shims where needed and be done with the problem?
    My thoughts too.

    Cheers
    Roger

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