How to Measure Roundness Error in Precision Parts Processing

In the processing of precision parts, the roundness error can be checked using the roundness meter method and the two point and three point method. The principle of a roundness tester is to place the measured workpiece on the roundness tester workbench, align the rotation axis, and make the measuring head of the roundness tester come into contact with the outer circle of the workpiece and rotate. The measurement results are ultimately displayed through sensors, amplifiers, filters, and calculation circuits. If the output is an actual contour shape, a concentric circle template set can be used, with the difference in the radii of two concentric circles as the roundness error of a certain section. The roundness tester is suitable for measuring parts with high precision requirements.

Two point method and three point method can be used to measure roundness error when the shape of the measured contour is an even number of edges and circles. Using measuring instruments such as calipers, micrometers, and micrometers, measure the maximum difference in diameter along the entire circumference of a regular cross-section, and use half of it as the roundness error of that cross-section. The calculation formula is:

Due to the fact that the circles with the largest and smallest diameters are not necessarily concentric, this method is only an approximate measurement.

When the measured contour is an odd number of edges and circles, 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 measured 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 cross-section. Commonly used V-frame angle α There are 60 °, 72 °, 90 °, 108 °, and 120 °. The three-point method can also be used for high-precision measurement in  Precision Parts machining.