Increasing Accuracy of Radii

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  • Increasing Accuracy of Radii

    Hey y'all, I'm an untrained inexperienced PC-DMIS user. I started learning on my own a week and a half ago at the request of my boss at my internship for GE. I am working on a OPTIV optical CMM. We are measuring several radii on notches on the part as well as angles and distances for chamfers.

    I am having a tough time with repeatability for some of these radii. There are two in particular that have a 30 degree arc to measure from and a 40 degree arc to measure from. This is too small to be reliable with my current method. Originally it just took the measurements and printed the report. Now, I inserted IF statements if OUTTOL <> 0 etc. in order to rerun that peice of the program. Even still I am hoping there is a better way to assure accuracy in this case. Maybe a combination of runs and then create a radius of best fit? Any ideas are welcome!

    I hope I provided enough information. Also thanks to everyone who has posted so much useful information on other posts that have helped advance my learning curve. Also I have to use my office computer as the shop computer(with PC-DMIS) is not connected to the internet. So it is not convenient for me to copy and paste my own code.

  • #2
    Tech Sheet
    Measuring a Small Arc


    Steps to measure a circle with less than 90 degree’s of arc:

    1. Measure the small arc as a Measured Circle (a measured circle is used in this example although Auto Circle will also work).

    • Measure the circle on-line or
    • Pick it from the Model or
    • Key in the values

    2. In this example, the back arc on the Hexagon Demo Block will be used.







    3. Edit ( F9 ) the circle.
    • Add additional hits.
    • Change the "Best Fit Math Type" to "FIXED RAD".
    • Key in the Nominal Diameter.

    • Check Regenerate Hit Targets

    • Press OK.

    • When prompted "Ok to equally space hits?" answer YES.


    4. Execute the feature Ctrl E to update the measured data.

    5. Dimension the location of the Fixed Radius circle. This will verify the location of the radius.
    6. Enter the location Nominals and Tolerances.







    7. Create an Alignment and set origin on Fixed Radius circle.








    8. Open the Parameter Settings Dialog F10 . Select the Probing Tab and enable polar compensation for the active workplane.

    Note: Skip this step when using CAD and use Vector points rather than Measured points.















    9. With the joystick, measure 3 or more individual Measured Points on the Radius. Note: If you are using CAD, use Vector Points and pick from model.




    10. Dimension the individual points using Location dimension and select the " Prad" check box (Polar Radius). This will verify the size of the radius.



    11. Enter Nominals and Tolerances for the Polar Radius’.






    12. Open the Parameter Settings Dialog F10 and turn off polar compensation.

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