Home Forums Quality Inspection How accurate are CMM machines

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    How accurate is CMM? Can you calculate CMM accuracy?

    rach black

    According to Mitutoyo, the most recent CMM achieves a measuring accuracy of 0.28 micrometers, which is the best in the world.

    Thomes JJ

    The accuracy of coordinate measurement devices is often expressed in terms of an uncertainty factor that decreases linearly with increasing distance. This pertains to the repeatability of the touch probe used by a CMM as well as the accuracy of the linear scales used by the CMM. The typical repeatability of a probe can produce measurements that are accurate to within.001 millimeters or.00005 inches (half of one ten-thousandth) across the entirety of the measuring volume. For machines with three, three plus two, or five axes, the probes are regularly calibrated utilizing standards that can be traced, and the machine movement is validated utilizing gauges to verify accuracy.

    In accordance with ISO 10360, the length measurement variation remains below E=(0.8+L/600) m throughout the whole measuring volume. The high measuring point density enables the measurement of the smallest component tolerances and the precise calculation of the relative position of these individual measurements, even at greater distances. Consequently, optical measurement of the entire component is no longer required. Measuring the pertinent surface parameters is all that is required. This minimizes total measuring times.

    The ambient thermal environment in which a coordinate measuring machine operates is one of the primary factors that determine the level of accuracy that may be achieved by the device. Temperature changes cause the scales, the structure of the machine, and the artifacts that are being measured to expand, compress, and in some cases deform in a manner that is not linear. This is because the temperature is a nonlinear variable.

    How to verify the accuracy of CMM?
    Two calibration standards certify the accuracy of the CMM coordinate measuring system. The CMM CalibrationTool is designed for long-distance measurements and verification and is made of Invar steel and calibrated by DAkkS. It shows calibrated sphere distances of 10, 50, 100, 200, 300, and 400 millimeters (mm). The Advanced CMM Calibration Tool calibrated by METAS is used to verify smaller distances and form deviations.

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