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  • Radius

    I currently have (for a lack of better term) bowl shaped cavity that we will be injection molding into. There are no tooling prints for it. The engineering dept wants to know what the radius is. I told them I could scan it and export the data but they didn't want that. Do you know of an way that I could accurately calculate the radius for this part. I thought about just measuring a line across the part at different intervals and dimensioning the radius out. Is this accurate enough or is there another way to accomplish this? Any help would be appreciated. Thanks.

  • #2
    How accuarte is accurate. I would think if you have at least 33% of the radius to measure then you could take a boat load of points inside and calclate the radius and be fairly close. My .02
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    • #3
      I may be way off here, never tried it myself, but
      can't you take lots of points, construct a best fit sphere from them
      and check the radius of the sphere.
      Then to check deviation, dimension each point to surface of sphere.


      • #4
        I would try measuring what is there as a sphere and also in straight lines thru (or near) the center. Based on those results I would try to guess at the radius/diameter & center. From there I would calculate and take vector points to construct into a sphere and/or dimension the individual points for radius. You do not say how large the cavity is, but if it is small a casting checked on a comparator, maybe with a transparent template, might be the best way to go. HTH
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        • #5
          Personally I would measure the sphere manually, set XYZ to zero, then re-measure with auto sphere using as many points as necessary to get good repeatability.
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          • #6

            The cavity is approx. 6 in in diameter and 1" deep at the center. I am using version 3.7 if it matters.


            • #7
              Another way you many want to go about it is to try to measure the cavity as a sphere to get a good idea where the center is. Then you can more accurately measure it in DCC mode as another sphere. Then take those results to mesure it even more accurately. Repeat as necessary until you are very certain that you have purged most of the cosine error out. Then either go by the radius of the last spher you measured, or measure a circle or scan line down the center and use that data.

              I would also want to make sure that what you are measuring is truely round. You might want to do a circularity analysis on a circle measured thru the center.


              • #8
                I work for and injection house myself. Is the cavity Spherical or is it a changing contour. Obviously the two are quite different animals. If it is spherical in nature and the open end of the cavity is Planar, Just use the drop method with a height gage or depth gage and calculate the radius using the Chord Length and Height to the deepest point.
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