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

  1. #41
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    Default Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    Quote Originally Posted by the_gentlegiant View Post
    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.
    That would be a no if the Bearing where taped together as a set they are not factory packaged that way, there is nothing wrong with universal Ground they just cost more to make as you have 2 extra face's that have to be match Ground

    Sales people will sell you what ever they can get there hands on, you can always buy any of the configurations if you have a need DB / DF / DT if you know where to look, if you can't get what you want then any Bearing with the right spec's can be Ground to give any preload you want, I have done hundreds of regular AC bearing this way by Grinding them to any of the required spec's I mostly only do Back to Back and matched sets of 3 and 4 Bearings it's a simple process, you measure the Bearing OffSet take them apart and Grind where needed, demag and clean then reassemble no more to it


    Universal ground is by no means the name of the game as you put it, it is just a convenience for the Bearing seller ( less stock to carry ) so those statements are not correct or true in any way

    Triple and Quad sets can be a better buy as Universal, the reason the installer have a better chance of installing them correctly and for those that don't know what they are doing when installing Bearings sets like this

    Mactec54


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

    Quote Originally Posted by mactec54 View Post
    That would be a no if the Bearing where taped together as a set they are not factory packaged that way, there is nothing wrong with universal Ground they just cost more to make as you have 2 extra face's that have to be match Ground

    Sales people will sell you what ever they can get there hands on, you can always buy any of the configurations if you have a need DB / DF / DT if you know where to look, if you can't get what you want then any Bearing with the right spec's can be Ground to give any preload you want, I have done hundreds of regular AC bearing this way by Grinding them to any of the required spec's I mostly only do Back to Back and matched sets of 3 and 4 Bearings it's a simple process, you measure the Bearing OffSet take them apart and Grind where needed, demag and clean then reassemble no more to it


    Universal ground is by no means the name of the game as you put it, it is just a convenience for the Bearing seller ( less stock to carry ) so those statements are not correct or true in any way

    Triple and Quad sets can be a better buy as Universal, the reason the installer have a better chance of installing them correctly and for those that don't know what they are doing when installing Bearings sets like this
    Hello Mactec,

    That's what I was pretty much suspecting. That it was a distributor thing limiting the stock needed on hand then it was anything else. You still see all the "set" information in the books including the part numbers, but over the last two decades the ability of me to call for and find matched sets of DB/DF or whatever, has grown more and more difficult. If my memory serves me and sometimes it doesn't, I don't think I've had any luck in the last decade. I'm not doing hundreds either, nor am I interested in grinding super precision bearings in house. I pretty much hold my breath from the minute they're out of the package until they're installed and covered again. Also I never dreamed of cracking one apart. Must be a trick that only you insiders know. :-)

    I've used the same guy all these years. He's still in business, and doesn't even have or need a website to stay that way. I think a lot of people and re-builders in this area have also gone to him for as long or longer. I may have to try and call around. Although I swear I have at some point or another and always seem to get the same "we can get you universal ground" spiel out of all of them. Ha... maybe it's a Midwest thing. Or maybe they say they'd have to order in and I say I don't have the time to wait. They are so few and far between it's hard to keep track of this stuff.

    Honestly I'm hoping my rebuilding days are over. After the last monster machine I did I believe I've about had it. I didn't think of it at the time of purchase, but a pallet system adds a mountain of parts, systems and complexity to a machine tool. This machine has a Fanuc built-in 10k spindle that if anything around here is going to need work it will be that. It's already making noises I'm not particularly fond of. (The spindle is the one and only thing I didn't touch in the rebuild.) I thought for once in my life I might send something out to the real pros and let them have at it. Although I can't believe how simple the design is. Just a broadly set (8"?) angular contact pair at the bottom and another loner at the top. No triples or quads or rollers or nothing. This is a thru the flange coolant 25/30 hp 40 taper on about a 16,000lb machine. The bearings are also air/oil supplied which is something I've never dealt with. So I don't know... best to let the pros do it?

    I'm feeling bad here for Jevs and his dilemma. All that work and not happy with it. Not sure it was the right machine and ball screw setup to go after, but I bet there's been some learning getting done. Sadly it's the painful hard way. Seems none of us get to escape that completely.

    Dave



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

    Unfortunately there is no way to get shims for these bearings other than to try and make them yourself or pay a fortune for something custom made. Not sure why no one makes an adequate size, but they don't in the thickness I would need for a reasonable price.

    Rather than waste more time and money fighting what I suspect are just too light of a bearing, I decided to do what I should have done to start with....spec my own bearings and make them work.

    I studied all the spec sheets forever and those bearings are just too light and never going to last if I set them with even more preload with a shim. At least I don't think they would.
    They are also way under spec compared to what is being sold as actual ball screw support bearings these days. The axial ratings are crap comparatively.

    So, I ordered two much cheaper sets of Nachi 20TAB04DB/GMP4. Found them for $220 shipped total (for both sets). The only issue with fitting them is that they are 2mm wider for the pair. I compensated by taking 2mm off the lip of my retaining plate. Also, since the bearings are about flush now with no recess to catch the retaining plate lip, I 3D printed some sleeves for the mounting bolts to help center the retaining plate up as good as possible before it starts compressing against the outer race. I just wanted to make sure it didn't shift a little and have the retainer plate lip catch the edge of the bearing bore and not the outer race.

    I also used shorter head bolts for the retaining plate so I can get my wrench in there easier to tighten the nut to spec. I have to have the motor coupler and motor on there to hold the screw because the cheap skates did not put any flats on the ball screw or a hex hole in the end. The coupler has flats for a big wrench. There is no way to grab the ball screw itself to tighten the nut. If I ever get new ones I will have them made with flats for a wrench or something.

    With all that said, I got it all back together finally.

    It is now much better, but it still takes a lot of force to move this metal on metal ways bed! I did go through and adjust all the gibbs. Replace one bad wiper and I also checked all the oilers etc. I am changing the oiler programming to turn it on whenever the machine is enabled. I also added an orange flash to the ways oiler button in case I manually shut it off and forget to turn it back on (Mach 4). That won't likely happen since every enable turns it back on.

    I think it is now about as good as it is going to get with these bearings and screws.

    I now have:
    .0005" backlash in X
    .0014" backlash in Y

    This really seems like more of a pressure build to make things move type of backlash. Nothing really moves freely.

    It takes a lot of pressure to get things moving on this machine. I can still measure a little in out of the nut, but it is way less than before (like couple ten thou). I am sure there is a little wind up and maybe takes a bit of pressure on the ball screw nuts.

    Even with the gibbs loose it takes both hands and feet to move the X (ball screw out).
    I cannot budge Y even with two hands and two feet (ball screw out and gibbs loose). It takes a big breaker bar
    It seems to move easy with the screw, but you can tell it still has to build some decent pressure up before it breaks stiction and the whole newtons law...objects at rest...saying. I can see why they went to that Turquite stuff or whatever it is.

    This seems to be as good as I am going to get with what parts it is made with.

    Without going to double ball nuts or something and maybe more substantial bearings I don't see any way I can get better. So, I set the backlash comp for these numbers and I am moving on.

    One thing is for sure, these bearings work much better.

    After going back and forth with NSK for months and doing everything they wanted, I am asking for an RMA. No one should have told me 25 degree bearings were okay to put in there. I think the bearings and ball screws are under spec'd even from design at 30 degree with heavy preload, but who knows what they had available in 1978 or so and what their budget was...

    Attached Thumbnails Attached Thumbnails Ball screw support bearing questions. Are 0 bearings necessary on this machine?-20200204_181017-jpg   Ball screw support bearing questions. Are 0 bearings necessary on this machine?-20200203_161753-jpg   Ball screw support bearing questions. Are 0 bearings necessary on this machine?-20200204_185736-jpg   Ball screw support bearing questions. Are 0 bearings necessary on this machine?-20200208_195157-jpg  

    Ball screw support bearing questions. Are 0 bearings necessary on this machine?-20200204_203449-jpg   Ball screw support bearing questions. Are 0 bearings necessary on this machine?-20200204_211647-jpg  


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

    Quote Originally Posted by jevs View Post
    Unfortunately there is no way to get shims for these bearings other than to try and make them yourself or pay a fortune for something custom made. Not sure why no one makes an adequate size, but they don't in the thickness I would need for a reasonable price.

    Rather than waste more time and money fighting what I suspect are just too light of a bearing, I decided to do what I should have done to start with....spec my own bearings and make them work.

    I studied all the spec sheets forever and those bearings are just too light and never going to last if I set them with even more preload with a shim. At least I don't think they would.
    They are also way under spec compared to what is being sold as actual ball screw support bearings these days. The axial ratings are crap comparatively.

    So, I ordered two much cheaper sets of Nachi 20TAB04DB/GMP4. Found them for $220 shipped total (for both sets). The only issue with fitting them is that they are 2mm wider for the pair. I compensated by taking 2mm off the lip of my retaining plate. Also, since the bearings are about flush now with no recess to catch the retaining plate lip, I 3D printed some sleeves for the mounting bolts to help center the retaining plate up as good as possible before it starts compressing against the outer race. I just wanted to make sure it didn't shift a little and have the retainer plate lip catch the edge of the bearing bore and not the outer race.

    I also used shorter head bolts for the retaining plate so I can get my wrench in there easier to tighten the nut to spec. I have to have the motor coupler and motor on there to hold the screw because the cheap skates did not put any flats on the ball screw or a hex hole in the end. The coupler has flats for a big wrench. There is no way to grab the ball screw itself to tighten the nut. If I ever get new ones I will have them made with flats for a wrench or something.

    With all that said, I got it all back together finally.

    It is now much better, but it still takes a lot of force to move this metal on metal ways bed! I did go through and adjust all the gibbs. Replace one bad wiper and I also checked all the oilers etc. I am changing the oiler programming to turn it on whenever the machine is enabled. I also added an orange flash to the ways oiler button in case I manually shut it off and forget to turn it back on (Mach 4). That won't likely happen since every enable turns it back on.

    I think it is now about as good as it is going to get with these bearings and screws.

    I now have:
    .0005" backlash in X
    .0014" backlash in Y

    This really seems like more of a pressure build to make things move type of backlash. Nothing really moves freely.

    It takes a lot of pressure to get things moving on this machine. I can still measure a little in out of the nut, but it is way less than before (like couple ten thou). I am sure there is a little wind up and maybe takes a bit of pressure on the ball screw nuts.

    Even with the gibbs loose it takes both hands and feet to move the X (ball screw out).
    I cannot budge Y even with two hands and two feet (ball screw out and gibbs loose). It takes a big breaker bar
    It seems to move easy with the screw, but you can tell it still has to build some decent pressure up before it breaks stiction and the whole newtons law...objects at rest...saying. I can see why they went to that Turquite stuff or whatever it is.

    This seems to be as good as I am going to get with what parts it is made with.

    Without going to double ball nuts or something and maybe more substantial bearings I don't see any way I can get better. So, I set the backlash comp for these numbers and I am moving on.

    One thing is for sure, these bearings work much better.

    After going back and forth with NSK for months and doing everything they wanted, I am asking for an RMA. No one should have told me 25 degree bearings were okay to put in there. I think the bearings and ball screws are under spec'd even from design at 30 degree with heavy preload, but who knows what they had available in 1978 or so and what their budget was...
    That might be a bad move using shorter retaining screws you need them well threaded into the Housing or they will flex under load

    Mactec54


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    Quote Originally Posted by mactec54 View Post
    That might be a bad move using shorter retaining screws you need them well threaded into the Housing or they will flex under load
    Shorter heads. Not threads. Low profile socket head cap screws. Thread length and engagement is the same. The plate would flex before the bolt head, so all good there.



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Ball screw support bearing questions. Are 0 bearings necessary on this machine?

Ball screw support bearing questions. Are 0 bearings necessary on this machine?

Ball screw support bearing questions. Are 0 bearings necessary on this machine?