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  • turning problem

    ok, so I am turning a shaft, 9 inches long on my old logan. between centers, the end closest to the head stock measures .515. the far end measures .505.
    I think the bed is worn near the head, and the apron is moving away from the work, does that sound right? and is there anything I can do about it?
    san jose, ca. usa

  • #2
    Is your tail-stock perfectly in alignment? What do you measure if you take a light cut from a stiff piece of stock without tail-stock support?

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    • #3
      Originally posted by lakeside53 View Post
      Is your tail-stock perfectly in alignment? What do you measure if you take a light cut from a stiff piece of stock without tail-stock support?
      I have checked the tailstock and adjusted it recently, it was off. It is as close as I can get it now.
      san jose, ca. usa

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      • #4
        Originally posted by gambler View Post
        ok, so I am turning a shaft, 9 inches long on my old logan. between centers, the end closest to the head stock measures .515. the far end measures .505.

        and is there anything I can do about it?
        Easy: re-adjust tailstock so that both ends come out same diameter. (You still might get slight barrel/ huor-glass shape but it will be a lot smaller error)

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        • #5
          How did you adjust your TS ??? There are a few different methods.

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

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          • #6
            Originally posted by MattiJ View Post
            Easy: re-adjust tailstock so that both ends come out same diameter. (You still might get slight barrel/ huor-glass shape but it will be a lot smaller error)
            If he has substantial wear in the bed he'll have to adjust his TS where ever he puts it. No real easy fix.

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

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            • #7
              I bought a test bar on ebay, made in India which has a MT2 at one end, centres both ends and is 11" long overall. It runs better than 0.0001" tir and has been very useful in getting the alignment and height of the tailstock corrected. Don't make the same mistake as me in expecting live centres to be spot on, but use dead centres for testing. I put a piece of 3/8" diameter bar in a collet and turned a 60 degree tip (using a chuck would be ok too), which must be true to the axis of the spindle as long as it is undisturbed. Try the alignment test with the tailstock quill retracted and also with it fully extended to see if there is a difference.

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              • #8
                Originally posted by gambler View Post
                ok, so I am turning a shaft, 9 inches long on my old logan. between centers, the end closest to the head stock measures .515. the far end measures .505.
                I think the bed is worn near the head, and the apron is moving away from the work, does that sound right? and is there anything I can do about it?
                Even if lathe was new this happens on long bars
                This why the make follower rest so bar does not flex

                Dave

                Sent from my SAMSUNG-SM-J320A using Tapatalk
                Last edited by smithdoor; 07-10-2018, 11:02 AM.

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                • #9
                  Originally posted by smithdoor View Post
                  Even if lathe was new this happens on long bars
                  This why the make Fowler rest so bar does not flex

                  Dave

                  Sent from my SAMSUNG-SM-J320A using Tapatalk
                  I didn't know that Fowler made them. I always thought they were called follower rests or traveling steadies.
                  Location: Long Island, N.Y.

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                  • #10
                    Originally posted by RichR View Post
                    I didn't know that Fowler made them. I always thought they were called follower rests or traveling steadies.
                    Phone struck again need to prof read before sending

                    Dave

                    Sent from my SAMSUNG-SM-J320A using Tapatalk

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                    • #11
                      If it's tapering without the tailstock, then it's probably bed wear.
                      My old 1980's Jet lathe has significant bed wear, and it turns a .001" to .002" taper over 10".
                      I have to "Bump" my cross feed as I'm turning, to get shafts perfectly straight.
                      Just like the old timers did.

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                      • #12
                        I'm surprised no one has asked the main question yet. Has the lathe bed ever been tested to ensure it is straight and parallel? A key part of any bench lathe setup is that it be trued up (often called "leveled") before you can trust it to do long parallel cuts.

                        Now some Logan lathes have a motor and primary drive cabinet. But that does not mean you can just plunk it onto a floor and KNOW that the bed is in flat from end to end. It still needs to be checked.

                        A good and surprisingly easy way to do this is chuck up a long and stout bar in the lathe that sticks out about 4 to 5 inches. Relieve the middle of the exposed bar by about .04" leaving two full diameter "collars" at the end and in close to the chuck jaws. Now skim cut the two collars and mic them. Using shims under the bed mounting bolts or the adjustable feet on the cabinet twist the bed until you measure the same size on both collars. Note that this does NOT involve using the tail stock. You don't want the TS in the equation at this point.

                        Once you remove any twist in the bed you can now use the identical size collars to check for any bowing by running a DTI over the tops of the collars. Any difference there is an indication of the bed sagging down or bowing upwards and that too can and should be corrected. Confirm you don't affect the zeroing of the twist by taking another skim cut and adjust as needed until you get same size test collars and a DTI reading the top of the collars shows no difference between them.

                        NOW bring the TS up to the end collar. If you chose your bar stock well it is roughly the same size as the TS ram. So with the mic'ed size of the collar and the TS ram you can use a dial gauge between them to set the ram to center side to side using just a little math so you know the step it should be. And while you are at it run the dial gauge over the tops and see if your TS ram is also centered for height. If needed put shims between the base and upper piece. And again while you are there extend the TS ram a few inches and check that it's both at the correct height and not angled up or down.

                        After all that the bed should be as true as it can be. If it still cuts a taper or a barrel or wasp waist long shaft then it truly is bed wear.

                        But unless you can see the wear quite easily I'm guessing it's just the bed has a bit of twist to it and you need to run this "collar skimming" test and true up the bed.
                        Chilliwack BC, Canada

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                        • #13
                          While serving my apprenticeship, we had an old Sheldon lathe that was significantly worn at the headstock end. I got to use that machine, the real machinists got to use the real lathes.
                          More than once I had to gradually move the cross-feed in a few thousandths while turning to compensate for the wear. Not precise or desirable, but you work with what you have. Learning to make good parts on a bad machine is what makes a machinist.
                          It's all mind over matter.
                          If you don't mind, it don't matter.

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                          • #14
                            I like MattiJ and BCRiders post best so far. If you're turning taper only then you need to adjust your TS again for the length of the project at hand. The reason as to why your previous adjustment of the TS doesn't work is likely wear or bed twist or both. A simple readjust at your current length should get you much closer at both ends. You may then get some barrel shape due to deflection without a follow rest, but it should be minor and easy to remedy with a file depending on the ratio of dia:length.

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                            • #15
                              On my lathe the follower can be mounted on either side of the saddle. If it's mounted between the tool post and the chuck and your moving towards the tail stock it's called a follower rest. If it mounted between the too post and the tail stock and you feeding towards the tail stock it's called a leader rest. Are you following me???

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

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