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  • centered

    Hey Gang,

    Well i have given the turning between centres thing a try. What i want to know is do i have to take off my 3-jaw chuck for the center to be acurate? What i did do was just put my MT4 in the center of the chuck and use a dog hooked on one of the jaws. Is this an acurate way to turn or should i take the jaw off?

    Spkrman15

  • #2
    By the textbook, you have to remove the chuck so that the center can sit properly in the spindle (tape to taper). Having said that, someon on this board recommend before of putting a rod in the 3 jaw chuck and whipping up a center by setting the compound at 60*. It works well, but if you need to do very accurate turning I would recommend using tapered center in the spindle with a face plate where you can hang the lathe dog.

    Albert

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    • #3
      I'm inclined to believe that a freshly turned center cut on the end of a short piece of scrap rod held in the 3 jaw chuck would offer the greatest accuracy.

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      • #4
        Lynnl,

        I agree that freshly turned center is very accurate provided it's been turned to exactly 60*. However, if you're off by even half a degree, then the work will not sit flush against the center and fail to provide sufficient radial support. I've had instances where the work eventually started to wobble at the end after making series of heavy cuts. Using a center which has been hardened and ground will guarantee that the work will be held both in center and with sufficient support.

        Albert

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        • #5
          When turning between centers, one must keep a check on the tailstock tightness. If part heats up and expands, it can get tight. If it cools, it will loosen. Centers may not be fully seated. Heavy cut can cause center hole to enlarge. etc. etc.
          I use a spud in the three jaw chuck that has a flange to seat against the jaws to keep it from moving back, mark it for jaw #1 for most things. If it is fussy, I recut 60* point.
          Jim H.

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          • #6
            Spkrman15:

            I would not do that because you do not want the lathe dog slapping your lathe jaw. Best to use either a driving head or a faceplate. The lathe dog should be lashed to the driving head or faceplate to minimize movement.

            I use carbide center in the headstock and carbide dead center or a precision long nose CNC type live center at the tailstock.

            I have also made ball centers for taper turning.

            [This message has been edited by Thrud (edited 06-26-2002).]

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            • #7
              Thrud,

              What is a ball center and do you know where
              I can look at one? I've never seen a ball
              center but, you guys have talked about ball
              centers before.

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              • #8
                Ball center is like you're regular center but instead of having a cone shaped end, it has a ball at the end. It's used when turning taper by offseting the tailstock. This shape ensures that the work is constantly supported during the turn.

                Thrud,

                When you use the ball center, do you drill the end will a ball endmill or just go with a regular center drill?

                Albert

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                • #9
                  msrm
                  Here's a link to a picture that John Stevenson posted a while back. http://homepage.ntlworld.com/machines/tapersetup.jpg
                  Shows the ball centers in use.

                  ps..don't tell John what Thrud said about lathe dogs slapping on chuck jaws!

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                  • #10
                    msrm

                    I made mine by cutting the tip of of a hardened & ground center. I used a negative rake HD carbide tool to cut the tip off and machined a small cup for the bearing. Either a chrome or carbide ball ( www.smallparts.com ) is then brazed in after clamping together.

                    Albert

                    I just use Bell type center drills, but I will try the endmill trick when I make new ones - I used odd sized balls! When I wear or break the bell ones I will get the radius type instead.

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