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IndustryArena Forum > Mechanical Engineering > Linear and Rotary Motion > Terrible backlash on my BF20L machine
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  1. #1
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    Terrible backlash on my BF20L machine

    Hi,

    A year ago I installed Chinese single ball nuts on X and Y. I know, they are Chinese after all but outside the machine they felt not tight but not loose either. So I installed them. Now I have 0.0875mm backlash on the X and 0.1375mm on the Y which I believe is far from acceptable.

    Is there anything I can do to tune up and decrease the backlash to an acceptable range (what range is acceptable anyway?) or is double ball nut the only way to go?

    Best,
    Suat

  2. #2
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    Re: Terrible backlash on my BF20L machine

    I use double nutted ball screws . Get the nut preloaded and be sure to run an oil line to the nut. Be sure the end bearings are in good shape and preloaded.

  3. #3
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    Quote Originally Posted by Azalin View Post
    Hi,

    A year ago I installed Chinese single ball nuts on X and Y. I know, they are Chinese after all but outside the machine they felt not tight but not loose either. So I installed them. Now I have 0.0875mm backlash on the X and 0.1375mm on the Y which I believe is far from acceptable.

    Is there anything I can do to tune up and decrease the backlash to an acceptable range (what range is acceptable anyway?) or is double ball nut the only way to go?

    Best,
    Suat
    Sounds about right. You should fit double (DFU) nuts and AC bearings/carriers. The problem is that those single nuts generally have a slight wobble. Feel OK when they're off but once on the machine the wobble creates a delay in carriage movement. You could find some oversized balls to re-ball the nuts, but DFU is the way to go. You can also pack a DFU's spacer with thin tin-foil/aluminium-foil to make it tighter. Not much you can do with a single.

    I had single on the minimill and had exactly the same results. So,I fitted DFU and AC bearings (in custom bearing blocks) onto a new 25LV mill. Tightened the DFU using the foil method. I'm down to 0.025mm on both axis.

  4. #4
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    Re: Terrible backlash on my BF20L machine

    Actually I already have DFU's but problem is that I don't have a second mill to remove the material to make them fit. My best option is tu use a die grinder for it.

  5. #5
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    Quote Originally Posted by Azalin View Post
    Actually I already have DFU's but problem is that I don't have a second mill to remove the material to make them fit. My best option is tu use a die grinder for it.
    If talking about the X axis fitting I used an angle grinder with 1mm thick cutting disc. I covered the oil hole, and went in tiny cuts at a time being careful not to heat the nut.

  6. #6
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    Re: Terrible backlash on my BF20L machine

    OK I'll give it a try. Thanks @dazp1976 and @gabedrummin

  7. #7
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    Re: Terrible backlash on my BF20L machine

    Hello again,

    I cut the X axis DFU flange. Now I'll make a locking mount for it.

    PS: I did cut ball nuts in the past but this one was unbelievably hard. I broke 4 cutting inserts to get it done.


  8. #8
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    Re: Terrible backlash on my BF20L machine

    Here's the X axis ball nut housing (or mount) I just made. It takes the first part and one third of the second part DFU 1605. The only thing I'm concern is that I made it off aluminum. Should I make a new one using steel?

    Sent from my MI 5s Plus using Tapatalk

  9. #9
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    Re: Terrible backlash on my BF20L machine

    I'm surprised how this jigsaw cut cast iron like butter.

    Sent from my MI 5s Plus using Tapatalk

  10. #10
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    Quote Originally Posted by Azalin View Post
    I'm surprised how this jigsaw cut cast iron like butter.

    Sent from my MI 5s Plus using Tapatalk

    Yep.
    I didn't go as far as that on the front of the Y axis. I did just enough to get 203mm. I tidied up the rear as well and changed how the carriage bolted onto the Y nut. This made my carriage move back a bit further because front overhang was a bit much I thought.

  11. #11
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    Re: Terrible backlash on my BF20L machine

    I also changed the oil lines for m 6mm to 4mm. I'd like to use copper tubes instead but I never had luck with them.

    Sent from my MI 5s Plus using Tapatalk

  12. #12
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    Re: Terrible backlash on my BF20L machine

    I put the machine all together. Now I measure 0.0213mm on both axes. However I noticed the long 2 segment arm of the magnetic base for the dial indicator is moving a little when the dial pin touches the gantry. So the backlash could be even smaller.

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