TABLE OF CONTENTS A dial indicator is a precision mechanism for displaying the small movement of a contact point. It is composed of a case for mounting the parts, a spindle with a contact point and amplifying mechanism, a pointer, and a graduated dial, Fig.3.13. They also have an outer bezel that rotates the graduated scale, allowing zero to be lined up anywhere. The amplifying mechanism is a precision rack-and-pinion gear set.
The dial indicator is a spring-operated relative displacement gage. The case is fixtured and assumed to be stationary. The movement of the contact point in the direction of the spindle relative to the case is the displacement of interest.
Dial indicators come in three basic styles, Fig. 3.14. The AGD and backplunger types are the two styles most commonly used for shaft alignment work. They have sufficient range to accommodate gross initial misalignments without hitting the physical stops. The universal test indicator has a limited range of typically .015 to .030 inch. It is useful for measuring other conditions where space is cramped. It has small contact points and a geometry that allows measurements in tiny places.
Dial indicators, even of one style such as the AGD type, can have different ranges and number graduations. The most useful indicators for shaft alignment work have a range of .250 inch...
