Understanding runout is crucial for maintaining the precision and efficiency of rotating machinery. Runout refers to the deviation from true circularity or concentricity in a rotating object, such as a shaft or a cylindrical part. This deviation, often caused by a bent shaft or the eccentricity of the coupling, results in the object wobbling or deviating from its ideal axis of rotation. Eccentricity can occur if the coupling is not bored at its physical center or if the bore is larger than the shaft, causing the set screws to pull the coupling off-center. Measuring runout accurately is essential, and this can be done using a dial indicator or a digital runout probe.

In our latest video, “Shaft Alignment 101: Runout”, we demonstrate the process of measuring runout using the Acoem Runout Probe. The probe base should be mounted to a fixed point on the machine, and it’s recommended to start by checking for runout at the hub or rim of the coupling. This allows for the detection of both eccentricity and a bent shaft. Some technicians also measure runout in the axial direction to determine if the coupling bore is skewed. Ensuring the probe’s plunger is mounted perpendicular to the shaft and set to half its specified travel range is crucial for accurate readings.

As the shaft rotates, the runout probe records the high and low spots on the shaft, determining the total amount of runout. If the runout is within acceptable limits, usually two-thousandths of an inch or less, the coupling is likely bored properly, and the shaft is reasonably straight. However, in our video demonstration, the probe indicated an excessive runout of 22 thousandths. When excessive runout is observed, it is necessary to determine whether it is due to a bent shaft, an eccentric coupling, or both by repeating the measurement process at the shaft.

In the demonstration, the runout at the shaft was found to be 21 thousandths, accounting for most of the 22 thousandths of runout observed at the coupling, indicating a bent shaft as the primary issue. Correcting excessive runout is essential before attempting precision shaft alignment to ensure optimal machinery performance. 

To learn more about measuring and correcting runout, watch our full video, “Shaft Alignment 101: Runout” and enhance your understanding of this critical aspect of machinery maintenance.