How to measure the error of roundness in precision parts machining?

The roundness error in precision parts machining can be checked using roundness meter method, two-point method, and three-point method. The roundness meter rule is to place the measured workpiece on the roundness meter workbench, align the rotation axis, and make the roundness meter probe contact and rotate with the outer circle of the workpiece. By using sensors, amplifiers, filters, and computational circuits, the final measurement results are displayed. ​ If the output is the actual contour shape, a concentric circle template set can be used, and the difference in radii between two concentric circles can be used as the roundness error of a certain section. The roundness meter is suitable for measuring parts with high precision requirements. When the shape of the measured contour is an even edged circle, the two-point method and three-point method can be used to measure the roundness error. Using measuring instruments such as calipers, micrometers, and micrometers, measure the maximum difference in diameter along the entire circumference of a regular circle, and take half of it as the roundness error of the circle. The calculation formula is: Due to the fact that the circles with the largest and smallest diameters may not be concentric, this method is only an approximate measurement. When the measured contour is an odd edged circle, the roundness error cannot be measured using the two-point method. In this case, the three-point method can be used for measurement. Support the tested workpiece with a V-shaped frame, measure the maximum difference in rotation of the workpiece with an indicator, and take it as the roundness error of the section. The commonly used V-frame angles α include 60 °, 72 °, 90 °, 108 °, 和 120 °. The three-point method can also be used for high-precision measurement in precision parts machining.