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Lesson 9: Narration Script | ||||||||
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The dial on most test indicators is called a “balanced” dial. A balanced dial is most appropriate for measuring relatively small variations in dimensions. |
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Balanced dials measure on either side of the zero. | ||||||||
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Test indicators are best suited for "comparative" measurements. In other words, rather than measuring absolute dimensions, they measure the amount of variation from a set standard or a known zero point. |
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A test indicator would be used for such procedures as measuring the difference between the diameters at several points along a workpiece. This might be done to determine the straightness of the feature. |
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Test indicators are also used to measure flat workpiece surfaces. Here, for example, is a measurement of a parallelism tolerance. |
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Another common use of test indicators is to measure a round, rotating workpiece. This would be done when measuring circularity, runout, or a position tolerance applied to two concentric diameters. |
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In addition to measuring workpieces, test indicators are commonly used in machine setup. | ||||||||
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For example, here you see a test indicator being used to "dial in", or locate the center of, the set point on a workpiece fixture. | ||||||||
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This is an example of a Dial indicator. Rather than having a hinged lever, a dial indicator has a spindle which moves in and out. |
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On the end of the spindle is the Contact Point, which contacts the surface being measured. | ||||||||
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Dial indicators are typically used to perform absolute measurements. An example would be measuring the height of a workpiece. |
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On many dial indicators, the contact point can be replaced with an appropriate size and shape for a particular measurement. Changing the contact point is as simple as unthreading the existing contact point and threading in the replacement. |
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Page 5
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