Half sphere diameter measurement

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  • Half sphere diameter measurement

    My part is half of a sphere that is not split exactly on center, when I do an auto circle the measured value dosent seem to be correct. I have checked the diameter a few other ways and have gotten the right result using the other methods, dont understand why I cant get it on the cmm. Is it the sharp edge on the radius that is throwing it off? When I check using my other methods I'm getting a .0003 dev but on the cmm I'm getting a .001 dev. Any ideas?

    Thanks

  • #2
    You must be measuring the Sphere as a sphere at multiple levels. You can adjust the hits to cover the full surface. Also calibrate the probe at 4 or 5 levels on the calibration sphere. This will give you better accuracy.

    Is it a titleist or a nike?
    sigpicThanks a Millionth

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    • #3
      I dont need to measure the sphere, I just need to find out the diameter around where it is split in half. We do all brands.

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      • #4
        hmm, I think that you still need to measure a sphere then measure a plane that is cut then construct intersection points of the plane and the sphere and use those points to get the radius, although I havn't tried that but it should work

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        • #5
          Not being split on center, off course, will be a diameter less than the diameter of the sphere. Lay the flat side down parrallel to the machine table allowing the leading edge to be free to probe. Use a shank probe and take multiple hits as an OD around the leading edge. Align the machine table as plane. Whats your handicap??
          Last edited by Gary Fitzgerald; 03-13-2009, 01:17 PM.
          sigpicThanks a Millionth

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          • #6
            Originally posted by Gary Fitzgerald View Post
            Not being split on center off course will be a diameter less than the diameter of the sphere. Lay the flat side down parralel to the machine table allowing the leading edge to be free to probe. Use a shank probe and take multiple hits as an OD around the leading edge.
            that should do it too.

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            • #7
              Unless he's checking the bigger half. then he'll just get the sphere dia
              Kami

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              • #8
                Are you trying to measure inside or outside diameter?
                Is the part larger or smaller than 1/2 of the sphere?

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                • #9
                  I'm measuring outside, the split is level to the table and it is smaller than the true diam of the sphere, meaning that the split is offset towards the pole.

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                  • #10
                    Set hemisphere on plate.
                    Plane on plate.
                    Measure sphere.
                    Construct circle (intersect sphere into plane).
                    Lately, it occurs to me
                    What a long, strange trip it's been.

                    2017 R1 (Offline programming)

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                    • #11
                      Originally posted by John Riggins View Post
                      Set hemisphere on plate.
                      Plane on plate.
                      Measure sphere.
                      Construct circle (intersect sphere into plane).
                      That is one way to do it.

                      Another way assuming the face is quite flat:
                      Split face up
                      measure plane on split face
                      level z and origin z on the plane
                      measure a circle at z=-.001

                      That -.001 will have some effect. The larger the sphere diameter, the less effect it will have.

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                      • #12
                        +1 for John Riggins method. That's the most sensible method. It works no matter where a sphere is sliced (above or below c/line).
                        Kami

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                        • #13
                          Originally posted by cmmgolf View Post
                          I'm measuring outside, the split is level to the table and it is smaller than the true diam of the sphere, meaning that the split is offset towards the pole.
                          Being the master of the obvious that I am, I feel compelled to point out the fact that a split in a sphere other than one exactly at the equator will always be smaller than the true diam of the sphere.

                          Ya' all lernt something today.
                          sigpic What's our Vector, Victor?

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                          • #14
                            Originally posted by Otto Square View Post
                            Being the master of the obvious that I am, I feel compelled to point out the fact that a split in a sphere other than one exactly at the equator will always be smaller than the true diam of the sphere.

                            Ya' all lernt something today.
                            No way!!!!
                            Really?

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                            • #15
                              Originally posted by lambo View Post
                              No way!!!!
                              Really?
                              Think about it........ It'll blow your mind.
                              sigpic What's our Vector, Victor?

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