Angle of a taper

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  • Angle of a taper

    Checking a female taper angle with a tolerance of +/- 01'15" (about .02 degree). Company doesn't want to spend the $ on an airgage. Does the CMM really have the accuracy to check this?

  • #2
    I suggest you try it with one part over and over to see how well it repeats first

    sigpicHave a homebrew


    • #3
      Problem is the difference between repeatability and accuracy. I could repeatedly report an angle of 5 degrees +/- .02 as in spec, but its actually 5.03 degrees.

      I know most CMMs are accurate to .0002" or .0003", but I don't know how that translates into angularity.


      • #4
        Then check its repeatability on the CMM and measure it with a manual method : mold and comparator. Compare results.


        • #5
          sine plate the part with tenth blocks to be sure you are RIGHT on the actual angle.

          Measure the part manually and align.

          Measure the part DCC and align.

          Measure the part DCC and align. Look at the amount of error between the actual and theoreticals.

          Measure the part DCC and align. Look at the amount of error between actual and theoreticals. Still seeing improvement?

          Measure the part DCC. Look at the amount of error. Close to no delta? Is it the same as the sine plate? Yes to both, report it. Still have delta, align and do it again. No delta but doesn't match, don't use the CMM.


          • #6
            I'm going to call this one as not possible on the CMM.

            The gage length of the taper is .200", which (if I remember my SOHCAHTOA correctly) means a deviation of .0002" from one end to the other would be a change of .057 degrees which is outside the tolerance of +/- .02 degrees.

            There's no way to check that on a comparator either, at least not with a x20 lens.


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