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10:1 Rule - What spec do you use?

There's been some debate here about what the CMM is capable of measuring to when it comes to the 10:1 rule. Obviously we can change the resolution on the dimensions we want reported way out. What number do you guys reference for this?
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  • Josh, so just to review and give others a look at the math, if I take a look at my cert for the Global with SP25 we have it showing Uncertainty of 0.462 (microns) to a ball bar length of 754.4.

    So dividing the ball bar 754.4 / 1000mm =.7544 unit of measurement

    Multiplying the unit of measurement times my uncertainty (.7544 * 0.462) = 0.3485328 microns

    So if my smallest tolerance on that machine is 15 microns (times 10% or 0.10) = 0.0015mm =1.5 microns

    Since the uncertainty (0.3485328 microns) is less than the 10 times less than my smallest tolerance (1.5 microns) I am good to go. Slight smile


    Am I looking at this correctly per your post or am I missing something here?? Confused

    TIA, 4/1/96


    April,
    We (and by "we" I myself and my friend the Hexagon Regional Service Manager who's been certifying CMMs for 20-plus years) have never seen a cert reference a "ball-bar length". Ball bars are of variable length, so that makes no sense.
    The uncertainty is almost always microns per meter.
    Take another look at the cert, shoot scan it and post it if you can.
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  • Josh, so just to review and give others a look at the math, if I take a look at my cert for the Global with SP25 we have it showing Uncertainty of 0.462 (microns) to a ball bar length of 754.4.

    So dividing the ball bar 754.4 / 1000mm =.7544 unit of measurement

    Multiplying the unit of measurement times my uncertainty (.7544 * 0.462) = 0.3485328 microns

    So if my smallest tolerance on that machine is 15 microns (times 10% or 0.10) = 0.0015mm =1.5 microns

    Since the uncertainty (0.3485328 microns) is less than the 10 times less than my smallest tolerance (1.5 microns) I am good to go. Slight smile


    Am I looking at this correctly per your post or am I missing something here?? Confused

    TIA, 4/1/96


    April,
    We (and by "we" I myself and my friend the Hexagon Regional Service Manager who's been certifying CMMs for 20-plus years) have never seen a cert reference a "ball-bar length". Ball bars are of variable length, so that makes no sense.
    The uncertainty is almost always microns per meter.
    Take another look at the cert, shoot scan it and post it if you can.
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