Still have backlash after service... How much should I expect?


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Thread: Still have backlash after service... How much should I expect?

  1. #1
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    Default Still have backlash after service... How much should I expect?

    Hi guys I just did some maintenance on my Y axis. Coupler was loose on my ballscrew giving me alot of backlash. While I had it apart i tightened up everything related to backlash. I shimmed thrust bearings nice and tight, reballed the ballscrew to restore preload, shimmed the coupler to preload the rubber more, and added another set screw to the coupler and loctited it on.

    Put it all back together and i still have about 0.0005 backlash. This is huge improvement over what i had, but still a significant amount. How much would you expect in a box way 4020 with brand new everything? I guess every box way machine would have some backlash to overcome the friction of the box ways. I am checking with MPG which they say not to do, but I really dont understand this. Every machine ive used before moves 0.001 when you move one notch, and when you reverse it moves 0.001 the other way. I dont see why a fadal should be any different.

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    Member handlewanker's Avatar
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    Default Re: Still have backlash after service... How much should I expect?

    Hi....this is like sewing a new patch on an old coat......the ballscrew itself wears unevenly and if you only get .001" somewhere along the way after a refit that is phenomenal......you'll have to replace the actual screw too if you want perfection.

    BTW.....reballing the nut will only make it tight in one spot and looser in others while the worn parts on the screw will still give you backlash

    A double ball nut will not help with this problem as it's preload setting is designed to resist loading in both directions from the cutting force on a new ballscrew not as a wear compensator.

    In cases where a well used ball screw is going to be put back in service you would need two separate ball nuts working back to back and a resilient spacer between them to prevent an over tight fit on the unworn sections and a slack fit on the worn areas etc.

    Depending on the loading from the cutting forces the resilient spacer can be made from the hard rubber material used in tool and die work......the resilient material must be firm enough to resist compression from the ballscrew reversal.
    Ian..



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    Default Re: Still have backlash after service... How much should I expect?

    Reballing is a great option for slightly worn screw. The balls and nut tend to wear first anyway. I agree with what your saying, the center of my screw is looser then the ends, but only by maybe a tenth or two at the most. I can certainly live with that. And the balls only cost me $20 vs over $1000 for a new screw. Im super happy with how it turned out. I also did my Z axis and that one was even better, no looser spot in the middle at all.

    So anybody have an answer to original question? What should i expect? Would a brand new box way fadal have close to zero backlash or will you always see a few tenths or more due to friction?



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    Default Re: Still have backlash after service... How much should I expect?

    You really can't measure the backlash the way you are doing it.

    Try this using an indicator
    move Y to +1.1000 on the DRO
    move Y to +1.0000 on the DRO
    Set 0 on the indicator
    Move to 0 on the DRO
    Move to +1.0000 on the DRO
    The backlash is the delta between the indicator readings.

    Next check by measuring in the negative direction.

    If it's possible to move the table using the keypad in one movement rather the the MPG it would work better.

    Do it a few times to see if it's consistent.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Still have backlash after service... How much should I expect?

    http://www.fadalcnc.com/media/pdf/Ba..._Procedure.pdf

    You may have done it this way but i figured I'd throw it out there.



  6. #6

    Default Re: Still have backlash after service... How much should I expect?

    .0005 is normal and using your MPG is how they set the backlash at the factory. If its .0005 backlash across the screw enter it into the control BL,2,5,5,5 for Y axis you have 3 spots for backlash for XYZ Just enter BL and it will give you your backlash compensation for each axis and position for backlash.



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    Default Re: Still have backlash after service... How much should I expect?

    Just a follow up, I did try running a program similar to whats in the manual and surprisingly it did seem to read a couple tenths less backlash. Its cutting good now in any case. thanks for the help.



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Still have backlash after service... How much should I expect?

Still have backlash after service... How much should I expect?