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  1. #1
    Join Date
    Sep 2006
    Location
    Collie,WA
    Age
    52
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    758

    Default Now ball Screw Re-fit

    Gents,
    I have decided to try and see if I can fit the new ball screw as 'correctly' as possible and was wondering if anyone had any tips. ( I have electrical background.)
    I also found a paper shim under one side the the ball nut mounting block, which made me uneasy.....
    I have goggled until my eyes bled but did not see a simple and definitive method.

    What I WAS going to do was remount the ball screw on the bearings , refit the motor and leave the cap screws attaching the carriage to the ball nut mount OFF.
    Drive the carriage back and forth electrically, with a dial indicator on it and try to see if there's any run out. I assume I'll be able to fit shims between ball nut mount and carriage to eliminate any run out......?

    Maybe I can just use feeler gauges to measure any 'gap' at either end of the ball nut travel?

    Am I on the right track?....lol

    Steve

  2. #2
    Join Date
    Sep 2006
    Location
    Collie,WA
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    758

    Default

    I have made a discovery....something that annoys me, but I should not surprise me.....oh well...ya gets what ya pay for......
    It appears that the 'carriage' needs to packed about 1.5 mm away from the linear rail blocks, in order to bring the ball screw inline with the bearing locations.
    I didn't expect it to be THAT far out. I seems that the bearing mounts for the ball screw have been machined in the wrong place. ( to me )
    Base is upside down in the pics.

    Stepper end:
    20160625_170242_001 (Small).jpg

    Non drive end:
    20160625_170507 (Small).jpg

    Where I need to pack to fix problem:
    20160625_170253 (Small).jpg

    I'll make 4 packers with holes drilled, fit them and see how it goes.
    Amazing.....

    Steve

  3. #3
    Join Date
    Jun 2008
    Location
    Victoria, Australia
    Age
    68
    Posts
    5,079

    Default

    Hi Steve,

    Not as unusual as you might think, when you get the mounting right, you should check the travel at the limits, if it's going to bind or tighten up, that's where you will see it.

    Ray

  4. #4
    Join Date
    Sep 2006
    Location
    Collie,WA
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    Default

    Thanks Ray,
    yes...will do. i may even re-visit the other two axis's and see if they are the same, although they did feel quite free. ( I went through them first )

  5. #5
    Join Date
    Sep 2006
    Location
    Collie,WA
    Age
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    Default

    Some more developments....
    I made some shims today and after re-fitting the Gantry base, I felt some significant resistance to movement along the rails.
    I completely removed the base and checked each linear Bearing block and found TWO that were lumpy!( both on same side. )

    Stop work and order 4 news ones......sigh. It least they are cheap....

    This is getting beyond a joke....lol

    The machine is more apart than complete now!!!!
    Its going to be a corker when its done..

    Steve

  6. #6
    Join Date
    Sep 2012
    Location
    North Yorkshire UK
    Posts
    1,631

    Default

    Hi Steve,

    Based on the earlier pictures of the old bearings, it wouldn't surprise me if they were not sat quite square in the first place. Even a slight twist in the bed could throw them out enough to cause some damage.
    Best Regards:
    BaronJ.

  7. #7
    Join Date
    Sep 2006
    Location
    Collie,WA
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    Default

    Yes, I think you're right. When I re-fit the Gantry base and if I find things binding, I don't know how I'll fix it. I found a couple of bits of cardboard shimming in a couple of places, when I took the Gantry Base off the first time, but how did they determine where to put these shims? How do you measure that? A mystery to me....lol
    Maybe they used trial and error... I will just work through it and see how I go.
    Steve

  8. #8
    Join Date
    Jun 2008
    Location
    Victoria, Australia
    Age
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    Default

    Quote Originally Posted by Sterob View Post
    Yes, I think you're right. When I re-fit the Gantry base and if I find things binding, I don't know how I'll fix it. I found a couple of bits of cardboard shimming in a couple of places, when I took the Gantry Base off the first time, but how did they determine where to put these shims? How do you measure that? A mystery to me....lol
    Maybe they used trial and error... I will just work through it and see how I go.
    Steve
    Trial and error probably, you can buy brass shim packs from bearing suppliers, that would be more robust than cardboard.

    If you have a big enough surface plate, you can do a bit more precise survey, set up the gantry and check for flatness and square, use a dial indicator or a height gauge to clock the motor shaft positions and ball screw mounting blocks, and thrust bearing centers, then you can determine the amount to shim and where.

    Shim Brass Assortment 6 Sheets X 150mm X 150mm 05mm 25mm Thick Champion CA32 | eBay

    Ray

  9. #9
    Join Date
    Sep 2006
    Location
    Collie,WA
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    Default

    Thanks Ray,
    I have some of those shim packs.I even managed to find them.....
    I don't have a surface plate. ( I might be able to borrow one)
    I guess I could take measurements referenced to the surface plate?
    Will have to think about it.

    Steve

  10. #10
    Join Date
    Sep 2006
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    Collie,WA
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    Default

    I had a chance to spend some time on this today.
    I was trying to work out how I was going to measure shim sizes and had a brain wave.....( Obvious when you think about it...lol)

    Pack the Gantry away from the ball screw, so it clears the Gantry plate and then measure the clearance with feeler gauges and shim to suit.....It worked a treat. any error will be to sag in the ball screw but I figure it will STILL be alot closer than it was.
    In the end, I had to shim the gantry by 2.1 mm so the ball screw mount had clearance. That gave me a way to measure it.....That 2.1 mm interference must have put a fair bit of load on the ball screw ( especially at the ends of travel!)and Stepper.
    My new ball screw should have a lot easier time of it from now on.....
    Steve

  11. #11
    Join Date
    Sep 2012
    Location
    North Yorkshire UK
    Posts
    1,631

    Default

    Hi Steve,

    2.1 mm is an awfully large amount, no wonder the original nuts were knackered. Did you use the brass shim material ? A quick swipe around the edges with clear nail varnish will stop any moisture from causing corrosion between the brass and alloy.
    Best Regards:
    BaronJ.

  12. #12
    Join Date
    Sep 2006
    Location
    Collie,WA
    Age
    52
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    758

    Default

    Hi Baron,
    Yes, I used brass shim. i cleaned it much as I could before fitting so it should be ok.
    I can now see that the nut mounts is not parallel with the gantry base,( Can see it in the pic ) but I can fix that easily once the new linear bearings arrive and are fitted. ( I guess that why that put the cardboard shims in there in the first place...lol. )
    Have been conflicted on to how to lubricate the ball screws. Have had Dry Lube recommended to me, but others have said use a light oil.
    Light oil will be messier but it just seems 'right'. Will have to keep the screw clean and give them quick squirt each session.
    20160703_180408 (Small).jpg

  13. #13
    Join Date
    Sep 2012
    Location
    North Yorkshire UK
    Posts
    1,631

    Default

    Hi Steve,

    I would go with a light oil. Something like sewing machine oil. I've also seen on some ball screw mechanisms oiled felt washers for supplying lubrication and I suspect also for cleaning the track. Once you have whetted the felt you would only have to check them occasionally.
    Best Regards:
    BaronJ.

  14. #14
    Join Date
    Sep 2006
    Location
    Collie,WA
    Age
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    758

    Default

    Thanks Baron....I'll give light machine oil a go.

  15. #15
    Join Date
    Sep 2006
    Location
    Collie,WA
    Age
    52
    Posts
    758

    Default

    Gents,
    I finally had some time to continue with this problem.
    My new linear bearings arrived and I fitted them to the machine. I saw a You Tube video where a guy noticed that the hole locations on some linear bearings were different on each side. It made it very difficult for him to obtain very smooth gantry movement.
    I checked mine and found the same anomaly. I noted the differences and set the blocks up and refitted the gantry bottom. Checked the movement and all was fine.
    The gantry appears to run very smoothly.
    I ran the Y axis back and forth a few times at max speed and did not encounter any problems. I think I am good to go.

    Still waiting for the new flexible couplings to arrive, but I can fit them quite easily later.

    I tried oil on the rails and it seemed to be too thick in the cool weather we're having, so I tried Inox. That seems much better.

    Here's a (boring ) video I took...lol

    https://www.dropbox.com/s/kbo7f4ad53...20run.mp4?dl=0


    Steve

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