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Lathe Turning unwanted taper

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  • Lathe Turning unwanted taper

    Hey All,

    I got a lathe from a friend who used it and since the move it is turning an quite unwanted taper. It is a 14x40 lathe. I moved into my shop and since then without using the tailstock - just the chuck to hold a piece of work it is turning about a .020 taper in 2". Any suggestions on what to try to fix this - or what could be causing it.

    Edward

  • #2
    So it was turning true before you moved it???

    .020" in two inches is pretty far out. How much lathe experience do you have?
    It's only ink and paper

    Comment


    • #3
      Sounds very much like it is taking up the lost motion, or "backlash".

      The 0.020 is really too much to explain by most any other means, unless the lathe now obviously looks like a pretzel.

      To cure the backlash problem, be sure you always move the tool to cutting position by a motion which takes at least one turn of the positioning screw (crosslide or compound) in the direction that moves the point of the tool towards the work.

      Another possible is if the machine has a taper attachment, and it is not secured right for non-taper turning. it could be set for a taper, or it could be loose and allowing the crosslide to move.
      1601

      Keep eye on ball.
      Hashim Khan

      Comment


      • #4
        Push off from slop in the crossfeed would not produce a taper. It would produce a slight taper or rounded starting cut and then start cutting a straight cut.

        He needs to tell more about the lathe and his experience as a machinist.

        This is another thread with little info expecting a good answer. Any answer given is all assumption and guess work. Don't get sucked into it. Require more information.
        It's only ink and paper

        Comment


        • #5
          If it is a run of the mill Chinese lathe there is the possibility that the headstock has been knocked out of alignment in the move. Try running an indicator across the face of the head stock spindle and see what the result is.

          Comment


          • #6
            Running the indicator across the face of the chuck using the crossfeed would be a better way.
            It's only ink and paper

            Comment


            • #7
              The DRO on the machine doesn't move one bit when feeding toward the chuck - which is the bigger end. I've done plenty of machining before - have an A.S. in machining from the local JC and am an ME. It does have a taper turning attachment and I've unlocked it so it just rides along. I've thought of temporarily combating the problem by setting the turning taper. I never thought of everything getting knocked out of alignment. It was moved very carefully and rolled to the current position. I'm not sure if it was producing a taper before, but knowing my friend - it wasn't. He's very meticulous. I think I'm giong to take a dial indicator across the face and then re-level the machine.

              Edward

              Comment


              • #8
                He might be turning 1/2" hanging out 2"+ with no center taking .050" a pass.

                He just dont know what he is doing at all.

                Dont blame the tool, the problem is in the mirror 99% of the time. Iv run junk and made working parts.

                I am from the school that never uses a taper attachment, its a way to screw thing up by a mile, fake all tapers and use a file. Iv run lathes where some idiot used the taper attachment and left the lathe all messed up with .200" backlash.

                Im sure once you get a 14X40 lathe figured out you might see <.001" per inch or less taper.(on a good size part)

                Almost all lathes cut some taper. I used to run a german Mouser lathe that would do less then .002" in 6 feet in a 6" diameter, I had to dial it in on roughting passes. you just need to learn how metal bends away from the tool and make up for it.

                Just slow down and learn to use the machine and you will do fine.
                Last edited by tattoomike68; 09-21-2007, 02:38 AM.

                Comment


                • #9
                  Ok Ed, run an indicator mounted on the cross slide across the face of the chuck and see if it stays on "0" or runs out and report back.
                  It's only ink and paper

                  Comment


                  • #10
                    Make sure you arent' trying to turn a coat hanger wire. Turning thick stock like maybe 1" thick and only 2 or 3" inches long can be done without a tailstock. Suggest lighter cuts, shorter stock sticking out of chuck or use of a tailstock. Good luck, have fun!
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                    It is true, there is nothing free about freedom, don't be so quick to give it away.

                    Comment


                    • #11
                      If the workpiece is long enough, try using a slip bushing on the outboard side of the headstock. it's possible that the workpiece is simply being pushed over due to tool pressure. Without the tailstock there to hold the piece on the correct axis, the piece will move, resulting in a taper. Simply relying upon the chuck to hold the piece true is a recipe for failure. With the workpiece securely held in place, and running true, .020 would certainly be excessive in a two inch turning. Something else is happening.
                      There is no shortage of experts, the trick is knowing which one to listen to!

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                      • #12
                        I'm turning graphite - 3" diameter and 3" long. It is pretty soft stuff so I'm not thinking it deflects. I'm turning them in .010 passes until I get to my final cut, which is .005".

                        Edward

                        Comment


                        • #13
                          Originally posted by Carld
                          Push off from slop in the crossfeed would not produce a taper. It would produce a slight taper or rounded starting cut and then start cutting a straight cut.
                          Not an EVEN taper, but it WOULD be different at start and end....... taper shape depends on how stiff the crossfeed is....and the DOC.

                          Bigger at chuck end disposes of that anyhow, and also knocks out the idea of workpiece flex.

                          If DRO is not showing any issues then the cutter is moving straight. It appears that the OP knows something, and won't be in trouble from a real basic lack of understanding.

                          IIRC, a number of chinese lathes are not scraped-in and instead have screw adjustments for the headstock alinement. Some just have a bunch of beer can shims here and there.

                          Either way, the headstock alinement sounds like it has been disturbed, and may need to be re-adjusted.
                          1601

                          Keep eye on ball.
                          Hashim Khan

                          Comment


                          • #14
                            How about a gap bed lathe with the gap shifted out of alignment? When the carrige hits the gap and moves in or out? I have to align my gap with a dial indicator after removing the gap. JIM
                            jim

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                            • #15
                              How was the lathe set up after it was moved? Was any attention paid to being sure it was aligned? The usual (but not the only) way to check a lathe is to put a sensitive level across the ways at the headstock end and the tailstock end and be sure the lathe bed isn't twisted.

                              If the lathe is one of those on which the headstock alignment can be adjusted relative to the lathe bed...that's another possible source of error.
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