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"Squaring" up a Logan Lathe Carriage

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  • "Squaring" up a Logan Lathe Carriage

    I've had this Logan a few years and after a cleaning I decided to check the level. I squared up the bed and thought I would check the level of the carriage.
    It's easier to see in the photo, what I am talking about but the level is off by 20 thousandths. (That's a feeler gauge under the level). It's level across the bed itself.
    Is this something that's adjustable? I have a parts manual but it doesn't look like something I can "adjust". Is it a major undertaking given that I am pretty handy, but entirely self taught?

  • #2
    It's level across the bed itself. Is this something that's adjustable?
    This might trigger another endless discussion ...

    You either level the lathe directly on the bed, or on the carriage. There is absolutely no relation between the both. There even doesn't have to be one.
    So no, you can't adjust that and no, you don't have to fix that. And if you fix it, it will be an absolute waste of time.

    Edit:
    This lathe will make you scratch your head how to level it.


    Nick
    Last edited by MuellerNick; 09-24-2010, 08:00 AM.

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    • #3
      Originally posted by MuellerNick
      This lathe will make you scratch your head how to level it.
      Although Nick's comment is tongue in cheek, it is worth giving serious consideration as it will assist you in clarifying what you are trying to achieve.

      There is no fundamental reason why a lathe should be level; we merely adopt the convention of setting it level as it is easy to measure this property. What you are trying to achieve is the same measurement (whatever it might be) at each end of the bed, thus ensuring there is no twist in the bed.

      From your picture, the level seems to be on top of the front of the saddle. There is no reason why the manufacturer would pay special attention to getting this part parallel to the ways. Were you to remove the cross-slide and place the level on the dovetails on which the cross-slide runs, you would hope that these are parallel to the ways.

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      • #4
        Originally posted by djc
        Were you to remove the cross-slide and place the level on the dovetails on which the cross-slide runs, you would hope that these are parallel to the ways.
        I thought that too, at first but now I am not sure that the lathe wouldn't work perfectly well if the crosslide moved straight up and down. I think the only requirement here is that the point of the tool intersect the spindle center line and it can do that from any angle if you set the tool properly. Of course the movement does need to be at an accurate right angle to the spindle axis, although some lathes apparently are made a little off so facing cuts are slightly concave.

        These topics probably prompt a lot of discussion considered repetitive and unnecessary by many but it seems to help me better get my head around some of the issues.
        Don Young

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        • #5
          at each end of the bed, thus ensuring there is no twist in the bed.
          This is one part. The other one is to get it straight (no bow, no sag).
          As djc said, the level is just a very convenient way to measure that.


          Nick

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          • #6
            SkyMoCo --

            It looks like your level instrument is well supported by your lathe carriage, with the bubble fairly well centered in the vial. That's good.

            Now you need to do a few more things:

            1. Carefully note the position of the bubble in the vial; you should be able to judge the position of the bubble to the nearest half-millimeter or 0.020 inch. (That's one-quarter of the 2 millimeter vial graduation commonly found on Asian and European vials, or one-fifth of the 1/10 inch division more common on American and older-British vials.)

            2. Without disturbing the level on the carriage, run the carriage down to the other end of the lathe bed. Allow the bubble to settle within the vial, and again determine the bubble position within the vial.

            3. If the bubble settles in the same position within the vial at both ends of the lathe bed, the bed is as "level" (code word meaning "not twisted") as can be achieved with the level instrument being used. If the bubble settles in different positions within the vial at the ends of the lathe bed, the bed is "not level" (code words meaning "twisted").

            4. If, after finding the lathe bed is not level, you want to make it level, you should expect that the adjustment process will be one of successive approximations until its close enough to being level that further adjustment is unnecessary. Expect the first adjustment to correct most of the error, a second adjustment to correct most of the remaining error, and a third adjustment to correct most of the still-remaining error.

            John

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            • #7
              I guess I wasn't being that clear. The bed is nice and level when I check across and up and down the ways. I just kinda assumed that it would be just as level on the carriage and worried me when it wasn't.

              While I was at it, I checked my tail stock alignment and it's off for sure. On a logan, there are two setscrews on the tailstock base. Are these what I use for setting the alignment. I've read lots of what I need to do, but nothing specific to a 12" Logan.

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              • #8
                Testing the level of the saddle using the saddle wings as the reference is only valid if you know that the tops of the wings are parallel to the cross slide ways. Run the level test using the cross slide ways, and not the wings, the reading should be the same as the transverse reading for the bed.
                If your results are the same as you found when testing the wings, then I think you have a problem.
                This issue is well covered in these 2 topics;
                http://www.practicalmachinist.com/vb...ew-toy-163406/
                http://www.practicalmachinist.com/vb...update-146913/
                Tailstock is also covered. There is no difference in test and alignment procedures between manufacturers.
                You may want to read this;
                http://bbs.homeshopmachinist.net/showthread.php?t=43414
                Harry
                Last edited by beckley23; 09-26-2010, 04:40 PM.

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                • #9
                  I understand the procedure to follow in squaring up the tailstock, but what I wasn't sure of of is where are the adjusting screws. Are they under the slotted bolts or some other place on the tailstock.

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                  • #10
                    but what I wasn't sure of of is where are the adjusting screws.
                    I really don't know your lathe. But the adjustment screws should be near the separating plane of the base and top part. There exist different constructions, but basically one screw moves the top to the back and the opposing one to the front.
                    So relive the back screw a bit and push the TS-top to the back with the front screw.

                    Nick

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                    • #11
                      This has been said already in different ways, but what you are measuring by placing your level where you have placed it is something that does not matter.

                      If you are confident that the ways themselves are level from front to rear, lay a parallel across them, mount an indicator on your cross slide, and run the tip of the indicator across the top of the parallel by running the cross slide through its full length of travel.

                      I believe this will tell you what you really care about, which is, "no matter what the position of the cross slide, will the tool be the same height above the ways?".
                      "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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