What is the difference between roundness and circular runout, and how to measure it?

Can radial circular runout measurement replace coaxiality error measurement? Can it replace roundness error measurement?

This question depends on the specific situation:

1: When the shape error of the measured surface is small, if the axis of the measured cylindrical surface is coaxial with the axis of the reference cylinder, the coaxiality error of the measured surface is zero, and the radial runout error is equal to the roundness error;

2. When the shape error of the measured surface is small (negligible), if the axis of the measured cylindrical surface is different from the axis of the reference cylindrical surface, there will be coaxiality error and radial runout error on the measured surface, and the two values are equal.

3. When the shape error of the measured surface is small, if the axis of the measured cylindrical surface is different from that of the reference cylinder, the radial runout error is approximately equal to roundness error+coaxiality error;

Strictly speaking, for the same measured component, it is not necessary to mark the coaxiality or roundness after marking the radial circular runout, otherwise the coaxiality tolerance value must be less than the runout tolerance value.

Radial circular runout is a comprehensive tolerance, which not only controls coaxiality error, but also contains roundness error.

When the axis of the measured cylindrical surface is coaxial with the reference line, the radial circular runout error will occur because of the roundness error of the measured element;

When the measured element is an ideal circle, but there is coaxiality error, radial circle runout error will also occur.

It can be seen that as long as there is coaxiality or roundness error, there must be radial circular runout error, and vice versa.