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Adjusting Bridgeport Y axis Gibs?

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  • Adjusting Bridgeport Y axis Gibs?

    Any suggestion/instructions on adjusting the Y axis gibs would be appreciated. When taking a climb cut yesterday I was surprised at how loose they were.
    Byron Boucher
    Burnet, TX

  • #2
    Gibs or backlash?

    Climb cut problems probably have more to do with clearance between the screw and the nut.

    See the exhaustive recent thread about that.

    Dave

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    • #3
      Byron.

      If you take the cover off the knee that has the y axis wipers on it, (the cover facing the operator) there is a screw on the left hand side and you will see the gib too. Tghten the gib screw a little at a time and run the table in and out to see it it gets too tight at both ends of the travel. Most older machines will have some wear in the center of the travel.

      Brian
      OPEN EYES, OPEN EARS, OPEN MIND

      THINK HARDER

      BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

      MY NAME IS BRIAN AND I AM A TOOLOHOLIC

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      • #4
        If I recall, there is a front and back cover with a screw on each end of the gib. Tightening them against each other keeps the gib from getting looser or tighter as you move the table around.
        Kansas City area

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        • #5
          Originally posted by Toolguy View Post
          If I recall, there is a front and back cover with a screw on each end of the gib. Tightening them against each other keeps the gib from getting looser or tighter as you move the table around.
          Toolguy,
          At least on my B'port, there was only one adjusting screw in both axis and the head goes into a groove in the gib to keep it from moving.
          Brian
          OPEN EYES, OPEN EARS, OPEN MIND

          THINK HARDER

          BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

          MY NAME IS BRIAN AND I AM A TOOLOHOLIC

          Comment


          • #6
            A loose X axis gib causes play in the Y direction.

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            • #7
              Here's a few figures. Gibs most always have 1/4 inch per foot taper; that is, 1:48. 0.001" change in dovetail total clearance requires 0.048" moveement of the gib. If the machine is in good shape and the ways and gib space are clean and dry, run in the gib without the adjuster to seat solidly and measure the protrusion carefully with a scale or better a depth reading with a dial or digital caliper.

              Extact the gib (you may have to give it a bump on the small end to get it started.) Reinstall and run the gib assembled with the adjuster to your scale reading but leaving it 1/16" in the loose direction. That will give you a good place to start. Exercise the slide over its range loosening the gib if the motion becomes stiff. Do not crowd it. A little increasing resistance and you tweak the gib 1/32" in the loose direction.

              0.001" x 0.048" / 0.062" = 0.0013" thereabouts. Four oil films whose algebraic thickness results in 0.0013" dry clearance is pretty stiff given the area of the dovetail slide bearings - WAG: a hundred pounds to squeeze 0.0005" movement over a minute. If the slide is well fitted and lubricated it will be a little stiff to move by hand effort alone but easy to move via the leadscrew.

              Most axis way bearings wear hour glass - that is loose in the middle and tight on the less worn ends. If you have a machining operation that requires close axis control, constant gib adjustment may be necessary. Older machie tools can be a nighmare of constant gib adjustment if spot-on positioning accuracy is required.

              OK that's gibs.

              If the table lunges from climb cuts then the problem is lead screw backlash not gib adjustment. Most better quality machine tools have some means of backlash adjustment. If the leadsccrew has 0.003" backlash with its nut you should be able to climb cut with no fear of the table lunging. 0.010" abacklash and the table can become "lungey" when climb cutting and "anti-lunge" measures will have to be taken. But lead screws wear unequally too; IOW small in the middle, that is wear where there is the most use . If you adjust the lbacklash with the slide in the middle of its travel it may get tight towards the ends.

              There is no cure for slide way bearing wear but there are work-arounds: riding the clamp to provide lunge resistance, a weight and pulley arrangement to load the table against basklash- hell, consider a 2x4 fulcrumed against the column and levered against some part of the set-up. A little muscle against the 2x4 not only inhibits the table from lunging but gives the operator a seat of the pants education of cutting forces in real time.
              Last edited by Forrest Addy; 02-03-2013, 05:09 AM.

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