Levers and Gears: Anatomy of a Dial Indicator

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Levers and Gears:
Anatomy of a Dial Indicator
 http://www.mahrfederal.com/

Most engineers are afflicted with insatiable curiosity and can't help but take things apart. However, as dial indicators are highly sensitive instruments, we'd like to help them resist this urge with the following anatomical description. Mechanical dial indicators (comparators) are characterized by a sensitive contact, a measuring system that transfers and magnifies the mechanical motion, and a means of indicating the measurement.

The American Society of Mechanical Engineers has the responsibility of preparing standards which encompass the inspection and the means of measuring various dimensional characteristics, as well as the instruments used to make those measurements. Since most dial indicators used in the United States are built to and used to measure inch specification, they generally do not fall under ISO specifications. Rather, ASME has updated old commercial and AGD standards into the most recent ASME B89.1.10-2000. This spec defines many aspects of dial indicators, including the various sizes, resolutions, and suggestions for construction, and of course, statements about performance.

Getting down to the nuts and bolts, a dial indicator is enclosed by a metal case that protects the instrument's mechanism. The case also serves as the rigid framework to support the means of amplifying the motion from the contact point to a hand moving against a graduated dial.

Why metal? With all the composites and plastics available one would think it would be easy to reduce costs by using a composite case. But we have to remember that we are in the measurement world here, and we can't go against certain basic measuring rules. In this case (no pun intended), the case is part of the measuring loop, and we know that temperature is one of the biggest contributors to measurement errors. If the case or any part of the indicator is not affected by temperature the same way as the part or the stand, then small errors will creep into the results.

They Point you in the Right Direction

Our mechanical indicators have precision gears and pinions for maximum accuracy. They are available in a wide variety of ranges, resolutions and sizes along with waterproof and perpendicular versions. Since most of the indicators are built at our factory in Providence RI, we can configure and customize to virtually any special requirement. We have hundreds of indicators stocked in our depot for immediate delivery - when you need it!