Offset and runout are similar quantities and measured in similar manners. However, there are subtle differences between them that are very significant for alignment. Offset is what we really want to measure and correct between shafts. Runout is a confounding effect. The definition of each is:

• Offset: The distance that one feature is displaced from a similar feature.

• Runout: The composite deviation of a circular part during one full rotation of 360 .

Offset and runout are both measured with a dial indicator during a 360 rotation. Offset is a subset of runout, which includes other features of out-of-roundness and eccentricity. A runout measurement includes all of these effects, Fig. 3.56.

Figure 3.56: A runout measurement is a composite of these features.

Offset is a vector quantity of one component in relation to another. Offset has an amount and a direction. The direction can be just a positive or negative value when projecting the offset onto two orthogonal planes. The real offset in three-dimensional space has some direction related to its maximum value in polar coordinates.

The offset between two shaft centerlines is the quantity of interest in shaft-to-shaft alignment. It is one-half of the total indicator reading, Fig. 3.57.

Figure 3.57: Offset defines the spatial orientation of one part to another. Eccentricity and out-of-roundness refer to features of one component to itself.

Eccentricity is the distance of the axis from the geometric center. The axis could be the center of a bored hole, the shaft...