The error of roundness in precision parts machining can be checked by the roundness meter method and the two-point three-point method. The roundness meter method involves placing the workpiece to be measured on the roundness meter table, aligning the axis of rotation, and making contact between the roundness meter probe and the outer circle of the workpiece and rotating it. Through the sensor, amplifier, filter, calculation circuit, and finally display the measurement results.
If the output is the actual contour of the graphics, available concentric circle template set, the difference between the radius of the two inclusive concentric circles as the roundness error of a cross-section. Roundness meter is suitable for measuring parts with high accuracy requirements.
Two-point method and three-point method When the shape of the measured contour is an even number of prismatic circles, available two-point method to measure roundness error. Using calipers, micrometers, micrometers and other measuring instruments, along the entire circumference of the diameter of the cut-off circle to measure the maximum difference, half of its roundness error as the cut-off circle, the calculation formula is:
As the largest and smallest diameter of the circle is not necessarily concentric, so this method is only an approximate measurement.
When the measured contour for the odd prismatic circle, with two-point method can not measure the roundness error, then available three-point method of measurement. V-frame to support the measured workpiece, with the indicator to measure the maximum difference between the workpiece rotary week, take its general as the circularity error of the section. Commonly used V-frame clamp angle α have 60 °, 72 °, 90 °, 108 ° and 120 °, etc.. The three-point method in precision parts machining can also be used for high-precision measurement.
