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  • Crossslide binding

    I have 12x36 lathe. The cross slide binds at a certain position.
    I took the crossslide apart.
    The tapered gib was roughly machined and not flat. I have lapped it and it is perfectly flat now.
    Dovetail recess where taper gib goes is not flat ether. You can feel gib rocking. The height point seems to be in the middle.

    How do you fix such a problem? Scraping?
    How do check if I have matched gib and dovetail taper?

    Thanks,
    Alex

  • #2
    Repost this with a "Pinging Forest Addy" in the heading

    Forrest - more then anyone else I know will answer this question correctly.

    My guess (and I am the trully uninformed) would be did the cross slide warp with age? or was it originally milled that way?

    additionally - since your local - you might want to check this out - http://bbs.homeshopmachinist.net/showthread.php?t=41122
    JoeFin
    Senior Member
    Last edited by JoeFin; 04-29-2010, 10:57 AM.

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    • #3
      There's no quick or easy solution, you have to start at the beginning and work your way to the end. And yes, it involves scraping.

      The process is to verify that the bottom of the cross slide is flat, this is done by transfering marking compound from a surface plate. This is done by spreading a thin layer of marking compound on the surface plate and placing the cross slide flats on the marked plate. The high points on the cross slide ways will pick up indicating compound, the low points will not. Flat is when you can see ~20 marked points per square inch on the flats. If it's not flat you have to scrape it flat. This involves scraping off the high points, resetting the surface plate and remarking the ways. It will take several cycles to get things flat. (You might also want to be watching the compound mount at this time, make sure that this stays flat in relation to the ways).

      When the cross slide is flat you can use it to scrape in the flats of the saddle. You mark the now flat ways of the cross slide and use them to transfer marking compound to the saddle. Make sure that you don't change the relationship of the saddle ways to the bed - level the bed and match the saddle ways and top of the cross slide as you scrape them in.

      When the flats of the saddle are flat you can scrape in the verticals of the dovetails. This is a bit harder as you have to make sure that you don't introduce cross slide error. You'll also need a 'fitters rule' or flat that is angled and can be used to indicate the vertical dovetail ways. Do the inside one, making sure that it remains perpendicular to the spindle axis, then do the outside one keeping the distance across the dovetail consistent.

      When the saddle is done you can use the dovetail verticals to indicate the cross slide and gib. I do the inside dovetail first, when that's matching I scrape the moving side of the gib flat then make a decision which of the static sides will be done first - the gib or matching cross slide dovetail. I usually do the gib, scraping it flat then using it to mark the cross slide vertical.

      If you haven't done it before it's quite the job. If there's a lot of wear on the lathe the work can be doubled as you're having to correct for wear at the same time as you're creating new surfaces. If you mark badly once (easy to do with the verticals, even easier with the gib and cross slide) you can introduce an error that will take 2-3 cycles to remove.

      Really, what you need to do is to get a copy of Connely's "Machine Tool Reconditioning". If you read that 3-4 times before and during the process above you'll have a pretty good idea what to do when you're done.

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      • #4
        I had a similar problem with a HF lathe.

        I ended up disassembling the whole thing, cleaning everything, and scraping all of the dovetails and gibs. After a lot of lapping and fitting, I have a lathe that performs quite reasonably, now.

        When I started, you could actually lift the carriage up, off of the ways 1/8", by hand.

        Knowing how to adjust the gibs is also a big help.
        saltmine
        Senior Member
        Last edited by saltmine; 04-29-2010, 03:02 PM.
        No good deed goes unpunished.

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        • #5
          Russ(rkepler) hit it on the head. I differ in Russ's approach to the gib, I do it last.
          Here's what's involved.
          http://www.practicalmachinist.com/vb...update-146913/
          Harry

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          • #6
            I had the same problem with the gibb on my compound cross slide. It had a high spot in it. I don't have a clue as to how it ended up like that other than internal stresses are at work. I indicated the high spot and ground it out. The results were satisfactory. I think I posted some pictures of the setup in my listing. Go back and look up my past post.

            JL...................

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            • #7
              Sometimes all it takes is some cleaning. The good thing about walking through the scraping is that you will find the problem, and the only cost if there isn't an alignment problem is some marking compound and some time. If everything is good as you go through the process you don't *have* to scrape anything. But the original post mentioned "lapping the gib" and in my opinion if you change the gib you really need to check everything from the start then refit the gib.

              If you get to the end of the process and everything looked OK then they's always the possibility of a problem in the cross slide screw & nut assembly.

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