Maintenance technicians may not always find it practical or possible to accurately calculate the total misalignment in a system while determining if it is in acceptable alignment. It is also difficult to visualize small fractions of an angle such as 1/2 and 1/4 degrees.
These can be more clearly illustrated with the following rules of thumb:
For v-belt drives, 1/2-degree angle = approximately 1/10-inch per foot between the drive shafts.
For synchronous, 60-degree angle, and V-ribbed drives: 1/4-degree angle=approximately 1/16-inch per foot between the drive shafts.
These rules can be used to estimate the amount of angular and parallel misalignment visually rather than having to calculate actual numerical values.