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How Do I find the center of a disk on a mill?

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  • How Do I find the center of a disk on a mill?

    I have some aluminum disks that I need to find the center of .

    I have a mill, but I don't know of a good way locate the center of the disk.

    Same problem with my rotart table. How do I exactly locate the center?

    Marv

  • #2
    A centering head on a combination sqaure works well.

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    • #3
      Find edge with edge-finder on "x" axis and move over exact rad. plus edge-finder offset. Do it again on "y" axis. Repeat foregoing at least once. You should be over center.
      Jim

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      • #4
        marv

        You can use a center in the rotary tabe to quickly locate the approximate center (you need a pointy thing in the mill chuck as well).

        Then use your dial indicator to sweep the outside edge of the table until it is dead nuts. Same for the disks. Or you can use the other two methods mentioned.

        At this point you should be asking yourself why you have not keyed the bottom of your rotary table and vise(s) so they are always at a known distance (normally the middle of the milling table) and you do not have to repeat this procedure every time you use them. But, it is your machine and a good excuse to use the fancy new DRO...

        Peace

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        • #5
          The technique Jim Hubbell describes is what Guy Lautard calls "Osborne's Maneuver" in one of his Machinist Bedside Reader books. It works pretty well. Guy goes into great theoretical detail of how/why it works.

          In case Jim's description isn't sufficient to get the idea, I'll expand a bit.

          Measure diameter of disk carefully before starting. Put edge finder in mill.
          With disk mounted on mill, line up approximately at center of disk.
          Move off the left-hand edge, then move back and find the left edge of the disk with the edge finder.
          From that point, move to right a distance equal to disk radius plus edge finder radius.
          Move off top of disk.
          Move back and pick up top edge of disk with edge finder.
          Move down distance of disk radius plus edge finder radius.
          Repeat above sequence for X-Y again, and you'll be very close to the center, especially if your starting point was reasonably close to the center to begin with.
          You can repeat again to improve even more, but after that you probably won't gain anything. It converges pretty fast.

          ----------
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          • #6
            If you dont have an edge finder, Use a shaft or rod of known diameter. If you have a bunch/lot of them to do build a set of stops on your table. The accuracy required will help choose the method.

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            • #7
              deb,
              set it up in the lathe, center drill and drill and bore it.
              Then, Set it on the mill and tram the hole in.
              Or just tram the od rising above the clamps.
              Or use an edgefinder as listed above.
              mite

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