A gas gauge can be used.
    Because of its accurate reading and low cost compared with the plug gauge, it can also detect the roundness, taper, center distance between two holes, coaxiality, perpendicularity, etc., and it is more and more widely used in small dimensional tolerance detection. When measuring the workpiece, the workpiece is placed horizontally and smoothly on the work table, and the probe is inserted into the hole after calibration. The value indicated by the measuring instrument is the inner diameter; The difference of the value of the rotating probe is roundness. Whether the hole has taper can be measured by moving the probe up and down a certain distance in the hole, and the taper value can be obtained by converting the trigonometric function. Because the measurement requires the workpiece to be smoothly placed on the workbench, and some parts of the shell, especially large shell products, are large and heavy, which requires the workbench to be large enough and mobile equipment at the same time. It is obvious that this type of detector is not suitable for the detection of large shells.

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