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Tool is Rising (Backing Out) - Why?

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  • #16

    Paul, did the top and bottom surfaces of the cross slide mic parallel before you started? They should have been (from the factory) unless the casting warped during/after machining. If they were, then the problem is in the saddle. John


    • #17
      Wouldn't a few light passes on a surface grinder have been easier? Trueing up both surfaces.

      Something jerked the compound/cross slide enough to cause that warpage.

      Is that broken compound off of this lathe?

      The area at the shoe holes is raised. Something pulled the compound up or maybe the shoes were upside down and then overtightened. Whatever, the damage was done.
      Last edited by topct; 01-09-2007, 06:33 PM.


      • #18
        The cutting tool isn't rising, except for the initial deflection at the start of the cut. The problem is in the wear of the crossslide's slides, crosslide's ways, carriage slides and the bed's ways. If you don't already have Connelly's book "Machine Tool Reconditioning", it would be money well spent.
        You are attempting to shape/plane the top of the cross slide by traversing the carriage and moving the cross slide. All movements are on worn surfaces.
        This really seems better solved by scraping.


        • #19
          I would proceed as follows and leave the thing a few thou proud of the finished hieght.Then with a homemade clamp to mount a router motor between centers finish grind to the final height moving the carrage in both axis.That should yield dead flat to the centeline of the spindle which is the best you can hope for.
          I just need one more tool,just one!


          • #20
            Wow. Much more response than I expected. Thanks to all. I have a lot to think about and check.

            Some additional facts that I have without additional checking:

            Yes, the ways are worn. The worn area is about 10" long and my scraping effort is in the center of this area so I am hoping that the wear is fairly uniform and it's not a factor. This seems to be the case since I can not detect any differences from left to right and that is where it would appear if the ways were the primary cause.

            If you look closely at my second picture you can see where the first passes took material off. It is primarly near the hole at the rear for the Acme nut mount and above the two clamp holes by the central hole. There is also a line on the left side of that big hole and no corresponding one on the right side. That's mysterious in my mind.

            I know that the tool is moving up because I had the DI on it (on the tool post anyway) for the entire time for the last two passes. These two passes were only about 20 minutes apart (I had to give my arms a rest and have a bathroom break). And I sharpened the tool between them.

            Yes, the compound is very tightly chucked. But there are some aluminum shims to prevent damage to it and that may be the problem. Perhaps some cold flow there. Or slipage. I may try putting a DI on the top (right side in the photos) of the compound slide to see if it is moving to the right.

            I haven't tried checking the spindle bearings lately, but the last time I checked there was only a few tenths of movement there. I haven't used the lathe that much to bring that up to over a thousanth. But I will check.

            I have thought of hand scraping, but it would be my first effort there. Boy would I need a lot of advise. Or Forrest's up and coming CD. Is that a reality yet. I do intend to get one as I don't think I would be able to attend any classes. I had hoped to get if roughed in somewhat close first.

            I like the suggestion that the chips may be doing it. The clearance angle on the tool would make a perfect wedge shaped opening for them to get wedged in. I now see the real reason for clappers. I wonder if I regrind the tool with no clearance if that would keep the chips out. But then, it rises a bit on the forward cutting stroke and I would have thought it would tend to dig in and cut deeper, not move up. Perhaps a larger rake angle also.

            Another thought I have had is to try to grind it flat. Mount my Unimat on the vertical column and square it to the surface and take off a half thousanth or so at a time. But I hate to make all that abrasive dust. Then there's the suggestions for sandpaper backed up with plywood or glass. I actually like that as I have some telescope mirror grinding experience and I think I could make it work. When it gets close, check it on the surface plate and do local touchups.

            In any case, it is presently a lot flatter than it was before I started so the effort is not wasted.

            Anyway, thanks to all and if I didn't mention your idea, I will be looking at all of them before my next session. I knew I would get a lot of ideas that I had not considered. Thanks to all.
            Paul A.
            SE Texas

            Make it fit.
            You can't win and there IS a penalty for trying!