What is roundness?

1. Roundness

Roundness is the actual shape of the element representing the circle on the part, and its equidistant from  center. This is the so-called roundness.

Roundness is an index that limits the amount of variation of the actual circle to the ideal circle.

Line profile is an index that limits the amount of variation of the actual curve to the ideal curve. The tolerance band is the area between the two envelopes enclosing a series of circles of diameter t, and the center of the circle should be on the ideal contour. . You can seen from the line profile tolerance band, the line profile not only requires its contour shape to be correct, but also require a certain dimensional, Its ideal shape is related to the size, similar to the dimensional deviation. The roundness is not the same, it only limits the difference between the radii of the two concentric circles. As for the diameter of the two concentric circles, there is no requirement, and the position of the two concentric circles is uncertain. Therefore, marking the line profile can be similar to the effect of using the inclusion principle.