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Tapered Oval Measurement Difficulties

I am attempting to measure an internal surface on an old injection mold cavity. The shape of the internal surface is oval at the z zero surface of the part, it is centered on the x y zero of the part and is tapered at +3.5 degrees per side as you descend in the z negative direction down through the part. My measurement strategy so far has been to rotate the CMM wrist to A15B0, take two hits at x zero, B zero z-10 and z-25, create a line through those two points and then create a point by projecting the line to the z zero surface. This method gives me a point that is not compromised by the damage that exists around the edge of the tapered cone and the z zero surface. I would then like to pattern this procedure around the oval at 15 degree intervals as measured normal to the drive curve to generate more points. This is where my lack of knowledge kicks in. If I define the pattern using "Alignment" I can define the angular range, as well as the step but the angle is measured from the x y zero of the part and the distance from x y zero does not change with the angular progression around the oval so that does not work. If I define the pattern using "Curve" I can define the step but it is a distance increment, not an angular increment and the problem I run into is it designates B angles that are not available in my probe definition and makes the data more cumbersome for us to use when we update our CAD file. Is there a way to make the pattern follow the curve at specific angles normal to the surface? Any suggestions from those more knowledgeable than I are very welcome.

Thanks in advance, Glenn

  • If I'm following you correctly, you can't copy/paste with pattern, or loop the first segment of code because of the fact that the oval shape of the part will make the theoretical points depart from the CAD model, when copied, correct?

    You can approach this a couple ways.

    1: Copy/paste with pattern (using alignment changes or paste with pattern increments, it's up to you), then you'd have to click each feature and state find nearest CAD, hoping it stays aligned with your vector.
    --You can also do this and instead of "find nearest cad" button, manually override (via simply typing in coordinate value changes) the z height or radial distance to get it to match your intentions.

    2: (What I would do) Navigate to Insert-> Scan -> Section Cut.  Within this window, you can construct a series of scan lines or vector points based off the cad. Figure out your vector increments for 15° spacing which is -0.03407, you can construct section line scans or vector points for each cut.


    3: Do the same thing as #2 but do it with oval-shaped cuts instead of radial cuts. Then you can cut/paste & group the vector hits into groups based on each probe angle you desire.

  • If you have CAD for the part then I second option #2 from  section cut is a really awesome tool!

    It can be a bit finicky to get exactly what you want but its well worth it in the end. If you want to get really close to your 15deg rotations you could draw it up in your CAD software and use that XY info to adjust the placement of your section lines to correlate with what your looking for.

  • Thanks for your suggestions. This sounds like a great Saturday morning project when nobody is around to disturb me. I'll try method #2 first since I have the CAD file loaded.

    Much appreciated as always.