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

  1. #13
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    Default Re: Ball screw support bearing questions. Are $420 bearings necessary on this machine

    If you want better accuracy out of the machine, install scales on the table and Z axis. Then close the loop at the controller level. I use 1 micron magnetic scales on my machines, a bit more bullet proof than glass scales. This automatically compensates for some backlash and any ball screw lead error, doesn't solve all of the world's problems, but we aren't working for NASA here. This is not a substitute for a mechanically tight machine, but it helps a bunch. My machines typically hold +/- 0.0002 as close as I can measure in my non-climate controlled shop.

    I don't think the lack of room behind the coupler is significant, once properly adjusted you should not have to touch the nut for the next 10 or more years. You could move the coupler a bit closer to the motor to get more room. Maybe replace the socket head cap screw with a grade 8 hex bolt, then you could get an end wrench in there.

    I am not a fan of Oldham couplers, I prefer a servo-beam style, these are what I use https://www.automationdirect.com/adc...ervo_couplings

    Jim Dawson
    Sandy, Oregon, USA


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

    I will likely just live with what I get after the ball screw service and new bearings....quit trying to provoke higher OCD LOL

    I had thought about changing that hex screw to a cap and maybe just make a better wrench or put some flats on the nut. I still need to think about this. Kinda need the mill working to mod them though! Catch 22.

    I also thought about these couplers and changing them a few times. I had to bore, ream, and broach one side of them for the new motors. The original motors had tapered shafts. I ended up just machining them out back then and reusing them. There are no issues with them now, but the style does not allow misalignment in certain ways like others could.

    I will check that link. Thanks. I was actually looking around a little a couple days ago thinking about changing them again. The way the oldham clamps to the ball screw with the tapered washer compression thing kinda mars them up.

    *edit* for those couplers you link, would you machine a flat on the ball screw or do something else for set screws? Just took a quick glance, but I am going to look at them more now to see how they mount up...This is something I am interested in doing. I like that these can allow more error in misalignment and won't wear over time where the "flex" is in a way that could allow backlash (even though the current ones seem to be well aligned and tight).



  3. #15
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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
    I will likely just live with what I get after the ball screw service and new bearings....quit trying to provoke higher OCD LOL
    Sorry

    Jim Dawson
    Sandy, Oregon, USA


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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
    Yeah, I do wonder if some of that accuracy is fudged in with no backlash compensation, encoder characteristics, original DC servos capability etc. as well though. Dunno.

    I sent the ball screws to Thread-Craft, Inc. based on a few peoples comments on the forums and talking to them. I also called a couple other places. One place I called pretty much let me know I didn't want to send them there.

    I am just hoping their price comes in line with what the other place that had a couple good references quoted me.

    The ball screws are NSK, they have a good reputation. However, I have no idea the original specs.

    Oh, about the nut, when I was talking about the nut, I meant the bearing backlash adjusting nut. I marred the OD of it trying to get it off (which has no affect on anything other than aesthetics). The function portion of it is still perfect (the parts that go against the bearings and it's threads etc). I will clean it up the OD surface. I would like to figure out a better way to get a wrench on it than the 3 holes for a spanner though. I could not get it off using the spanner I have, even once the coupler was out of the way. There is not enough room to even get the spanner I have in there with the coupler on. You also cannot loosen the thread locking bolt without taking the coupler off (and removing the motor most likely). Maybe if I made a custom hex wrench I could. The coupler has to be removed with a puller. This is not convenient for future checking/adjusting and is not going to work well for any kind of a real torque reading. The best I could do with it as it is would be to go by feel for tightening it.

    Couple simple parts I made with it before this last round of upgrades attached. I only made a few parts in all these years I had it.
    NSK make great ballscrews but if it has the spec's of .002/12" it is there lowest grade C5 grade has .0005 /12" which is what most milling machines use the high end machines use C3 grade
    this will be in the number of the Ballscrew

    One of the best Ballscrew rebuilders is Ballscrew International, Thread-Craft, Inc. look to be very good as well I have not used them but would use them if I had no others to use

    That wimpy pin wrench was not going to work for something like this, I usually make a wrench to suit for a job like this, if I don't have anything, here is one type I made for a job like this

    This Nut could easily be from 60 Ft lbs to 200 Ft Lbs depending on the thread diameter

    Attached Thumbnails Attached Thumbnails Ball screw support bearing questions. Are 0 bearings necessary on this machine?-hpim2751-jpg   Ball screw support bearing questions. Are 0 bearings necessary on this machine?-hpim2747-jpg  
    Mactec54


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

    That is a nice tool. Is there anywhere I can buy something suitable? Finding time to make something is a challenge....and no mill at the moment, but I have a lathe, welders, and drill press.

    I could probably cobble something together that will do the job, but it wouldn't look as nice.



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

    By the way, was looking around for couplers. Hard to find anything with a 6mm key way and/or 22mm shaft. The motor shafts are 22m, with a 6mm wide key. I am not sure on the ball screw diameter, it is smaller, but I have to measure it.



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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
    That is a nice tool. Is there anywhere I can buy something suitable? Finding time to make something is a challenge....and no mill at the moment, but I have a lathe, welders, and drill press.

    I could probably cobble something together that will do the job, but it wouldn't look as nice.
    It does not have to look nice as long as it can do the job that's all that matters, I doubt that you will find anything like what it needs to do the job

    Mactec54


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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
    By the way, was looking around for couplers. Hard to find anything with a 6mm key way and/or 22mm shaft. The motor shafts are 22m, with a 6mm wide key. I am not sure on the ball screw diameter, it is smaller, but I have to measure it.
    Most couplers are modified to fit the shaft and a Key way you have to cut to match what every your fitting too

    Mactec54


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    Default 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.



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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?