#### How Runout is Measured

The typical, non-CMM way to measure runout is to put a small dial indicator on the surface of the cylinder, zero-out the indicator, and then spin the cylinder. This indicator measures any difference along that circle as the cylinder rotates.

Runout with a Dial Indicator

A CMM essentially does the same thing. Instead of spinning the cylinder, however, the CMM's probe rotates around the cylinder and takes a finite number of hits.

The tolerance band for runout would look something like this:

Sample Runout Tolerance Band (Dotted Lines)

The tolerance band has these properties:

- It has a width the size of the plus tolerance.

- It is parallel to the datum vector (the axis of some other line or cylinder).

- It is fixed at a certain radius from the cylinder’s axis.