Fall, 2009 | Front Page | | < Previous | | Next > | Volume 3, No. 4

Indicators in their various forms are used for a wide variety of tasks such as layout, inspection and quality control. The major indicator classes are (1) Mechanical Dial indicators, (2) Electronic Indicators, (3) Lever Style Test Indicators, and (4) Back Plunger Dial Indicators. This Tools & Rules Online article is a brief overview of dial and electronic indicators. Lever Style and Back Plunger Dial Indicators will be covered in a future article. Starrett dial indicators are manufactured to fine watch making standards with jeweled bearings, precisely finished gears and pinions, and a shockless hardened stainless steel gear train. The result is a gage that can measure to 50 millionths of an inch, as necessary. The contact point is attached to a spindle or rack. Movement is transmitted to a pinion and then through a train of gears to a hand that sweeps the dial of the indicator. As a result, a small movement of the contact is transformed into a larger, observable and measurable movement of the hand on the dial. Dial or Electronic? Dial and electronic indicators each have their unique advantages. The hands of an analog dial indicator show clockwise or counter-clockwise distance from zero that is more easily readable than a digital electronic display when being visually monitored by an operator. Basic electronic indicators show a numeric value that works well for inexperienced operators and simple applications. Electronic indicators with output provide the important ability to collect and record data in one step. The DataSure Wireless Data Collection System has an End Node available for all Starrett and most competitor electronic indicators (Left: indicator with End Node). The output also works with cable-based hardware. Selecting a Dial Indicator The complete Starrett line of analog mechanical dial indicators includes over 180 models that meet or exceed all known performance specifications.  Below are some facts and factors to help you make your selection. 1) Select the dial size that gives you the readability you need. We offer five regular dial sizes that cover most applications’ space limitations and readability requirements. These five sizes conform to the industry standard American Gage Design Specifications (AGD). The size ranges relate to bezel diameters. Size 0 is a smallest, followed increasingly larger sizes, AGD 1 through AGD 4.The most widely used size is AGD 2, but all five sizes are relatively common. 2) Choose the accuracy, readout and range that you actually need – don’t select a .00010" or 0.001mm readout if .0010" or 0.01mm is right for your job. We offer a wide variety count hands styles, as well as revolution counters for long range indicators.  Graduations are available for reading in .001", .0005", .00025", .0001" and .00005" – with ranges from 12" down to .006". For metric indicators we offer .01mm, .002mm, and .001mm with ranges up to 125mm. Dials may have balanced or continuous graduations. 3) Consider any special features you may need:   a) Inch millimeter reading,   b) special shockless movement,   c) antimagnetic,   d) long range,   e) long stem,   f) special backs,   g) special contacts,   h) special holders, and other options.

While our indicator line covers most applications, our Special Gage Division will be happy to work with you to create a custom indicator, as required.

Indicator Loading & Accuracy • Indicators should be “loaded” 1/8-1/4 of a turn before testing or measuring. Most accuracies are specified plus or minus one graduation over the full range -- usually 2-1/2 turns. Longer ranges have slightly wider tolerances. • For the best results, adjust the setup so that the final critical measuring zone is between “10 o’clock and 2 o’clock” from zero. • For accurate measurement of larger ranges, AGD specifies 2-1/3 turn indicators to cover the appropriate range. They recommend loading the indicator to about 1-1/3 turns, then setting zero on the master. This should ensure that the indicator will show the accurate deviation for a full revolution, both plus and minus.

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