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Accuracy

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Accuracy
Does the 4 to 1 rule apply to Portable CMM measuring accuracy, how do I best explain this to my superiors? The arm we use states a length accuracy of .016microns or .00062 inches so do I multiply this x 4 = .0025 and tell them that the expected accuracy of the arm would be this? Hence trying to verify position tolerances of .05 micron might be a stretch of the arms capability, even though I can repeat good measurements on a 20,’’ Weber gage within .0005 Every time no matter where I place it in the reach of the arm, this would include the Z axis.

I said that I could say with out a doubt we could verify position tolerances within .2 microns or .008’’, and I would not want them to lose work over my statement if I am not correct
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  • The calibration sticker states that it's repeatable to .016. I had been using it in an environment that is rough "shop floor". It's on the rolling base, with lock down feet, measuring weldments in a weld fixture/jig. This is the condition and environment that the salesman sold it for. Granted this is a rough environment but it does NOT measure to the spec that it was sold to. Yeah I know, I know better, I've been around a long time, but the fact is that I wouldn't trust a Romer to hold anything tighter than +/- .25 mill. Your environment and your parts may allow you to measure a lot closer and more repeatable than this and if it does good for you. The one I finally put in its case and hid in the storage room about a week ago doesn't.

    Bill

    SO Bill just to be sure about your numbers... you trust a Romer to +/- .00025"??
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  • The calibration sticker states that it's repeatable to .016. I had been using it in an environment that is rough "shop floor". It's on the rolling base, with lock down feet, measuring weldments in a weld fixture/jig. This is the condition and environment that the salesman sold it for. Granted this is a rough environment but it does NOT measure to the spec that it was sold to. Yeah I know, I know better, I've been around a long time, but the fact is that I wouldn't trust a Romer to hold anything tighter than +/- .25 mill. Your environment and your parts may allow you to measure a lot closer and more repeatable than this and if it does good for you. The one I finally put in its case and hid in the storage room about a week ago doesn't.

    Bill

    SO Bill just to be sure about your numbers... you trust a Romer to +/- .00025"??
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