VN 12 table backlash adjustment questions.
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  1. #1
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    Default VN 12 table backlash adjustment questions.

    I ran into a puzzle- my VN 12 x-axis has some unexplained backlash.

    The leadscrew nut has about .005" backlash, necessary because the screw is worn some. (It get tight at the ends of the travel on the unworn threads if no backlash. I can easily feel the free play in the handle, and when it comes up against the nut threads.

    But- AFTER the freeplay is taken up, I still get no table movement for another .005".

    Almost like the leadscrew nut is loose, or maybe the angular thrust bearings on the leadscrew to table connection are moving a little.

    IIRC, this machine has a housing on the table that accepts two angular thrust bearings, that trap a shoulder on the leadscrew, and the bearing are pushed together by a threaded collar. I tried tightening the collar, but it is pretty snug. I was wondering if perhaps the collar is not putting pressure on the bearing outer race, maybe bottoming in the threads?
    Any ideas?

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    maybe bottoming in the threads
    Be a fairly simple thing to do - put a washer where it does some good and see if snugging it up the nut eliminates the .005"

    You could also see if the last time it was apart if they actually reinstalled the bearings back to back - that is why they are angular contact - so you can get them to do some work

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    Quote Originally Posted by johnoder View Post
    Be a fairly simple thing to do - put a washer where it does some good and see if snugging it up the nut eliminates the .005"

    You could also see if the last time it was apart if they actually reinstalled the bearings back to back - that is why they are angular contact - so you can get them to do some work
    Took it apart, tried a washer- no joy. Then pulled the bearing caps and re-tightened them- no joy. I did not check the bearing for face to face, but think they are OK- I did replace them when the machine was rebuilt and am "pretty sure" I would have put them in correctly, as the reason for them was known-to take thrust loads.

    I will keep looking, maybe just have to figure on more backlash than apparent.

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    Have you tried using a dial indicator to locate the point of "looseness"? I was thinking of anchoring the indicator to the table and reading the end of the screw. If no movement there, move to screw to nut, etc.

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    Quote Originally Posted by Rick Hand View Post
    Have you tried using a dial indicator to locate the point of "looseness"? I was thinking of anchoring the indicator to the table and reading the end of the screw. If no movement there, move to screw to nut, etc.
    Good idea- I have been wondering if the leadscrew nut has some float- not the leadscrew in the nut, but the nut to table connection.

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    Quote Originally Posted by stoneaxe View Post
    Good idea- I have been wondering if the leadscrew nut has some float- not the leadscrew in the nut, but the nut to table connection.
    I tried the dial indicator on my VN12 and have no play in the bearing but plenty in the nut.


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