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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. #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  

  2. #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

  3. #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).

  4. #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

  5. #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

  6. #30
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    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

  7. #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

  8. #32
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    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.

  9. #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

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