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  • Workholding in Lathe

    As quick attempt to hold something that is center-drilled, I pop a dead center into the spindle, through my three-jaw. While holding the piece between centers, I tighten the three-jaw and cut away.

    I haven't seen you more experienced guys do this, so is there something I am missing?

    Ed
    Ed Bryant

  • #2
    For best accuracy, chuck up a short piece in the 3jaw and cut a fresh 60deg point on the end to engage the center of your workpiece.
    That will insure it's turning true to the lathe centerline.

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    • #3
      ED,
      I presume you had a driving dog on this or was it just pressure that was driving the shaft ?
      .

      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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      • #4
        If I understand, the dead center is installed in the lathe spindle, the work is held between centers, the three jaw chuck is tightened on the workpiece and the piece is machined.

        This being the case, little is gained by use of the dead center in the spindle.

        If the piece is supported by the live and dead centers, and a dog is used, using the three jaw chuck to drive the dog as John has described, that will work. The only shortcoming with that method is there will be more of the piece left unturned as it is obstructed by the chuck.
        Jim H.

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        • #5
          aahh, missed that bit about gripping with he chuck.
          As you say not a lot of gain.
          If the chuck was a lot of run out it will move it off the centre anyway.
          .

          Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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          • #6
            I too misunderstood. I thought the dead center was being gripped in the chuck.

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            • #7
              Nope - the chuck will put the stock where it wants. The only way to hold stock acurately in a worn 3 jaw is either to regrind the jaws and that is not as easy as it sounds or (quick and dirty) turn a few thou off the backplate spigot then the stock can be centred accurately by loosening the backplate screws, gentle use of a soft hammer and clocking with a DTI.
              Works for me but I only do small stuff !!
              http://myweb.tiscali.co.uk/remark/pa.../workshop.html
              Mark
              What you say & what people hear is not always the same thing.
              www.remark.me.uk

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              • #8
                Makes sense to me to hold a center in the chuck, but I always use my 4 jaw.
                This allows you to adjust the center to be truly centered.

                It's fine to take off the chuck and put the center into the spindle taper, but on my lathe it's a PITA to dismount and remount the chuck. No BIG deal, but it gets old after a while. I've even gone so far as to make up a collet chuck to hold in the 4 jaw; this lets me use ER-20 collets without having to dismount the chuck, and lets you turn eccentrics using a collet if you want. Pretty much the best of both worlds for me.

                Regards,

                Jeff E.

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                • #9
                  I keep a center button handy, it is just a stub with a 60* point turned on it. I marked #1 jaw so it will go back on center. If I am concerned about it being dead accurate, I will take a skim cut on it after chucking. Make it big enough, and it will last many dressings.
                  Jim H.

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                  • #10
                    Or use one of these in the spindle.



                    It's called a Giromat and it's a centre and face driver all in one.
                    You put your work between centres and tighten up, the teeth dig in the spindle end face and drive the work.
                    The more pressure you apply the more it climbs up the ramps and bites in.

                    Very handy for doing the whole length of a bar without having to turn round.
                    .

                    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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                    • #11
                      I know what he means. When I am going to bore a small cylinder, I put a dead center in the headsock and tailstock. With the jaws on my four jaw open, I place the cylinder between centers then close the jaws. I remove the chuck, remove the center and put the old chuck back on. Of course I indicate it before boring, but for me it is a fast way to set a odd shape steam cylinder in the lathe for centering. Maybe I'm just lazy?

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                      • #12
                        As usual, when I have a "great idea" that the old-timers already had, it is a great one. When I have a "great idea" that I don't hear about, it isn't so great. Thanks for the feedback guys - helpful as always.

                        Ed
                        Ed Bryant

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