There are a number of different types of dial indicators including mechanical, lever and electronic; but the most commonly used is the mechanical dial indicator. They are found on concentricity gauges, case neck sorting tools and neck turning tool adjustment fixtures to name a few.
Dial indicators measure movement that is transmitted by the contact point (probe) which is attached to the spindle. This “up and down” movement is transmitted to a pinion and then through a train of gears to the sweep hand (needle). This allows the user to see the movement transformed to a larger, observable and measurable movement of the sweep hand (needle) on the dial face.
Electronic indicators function in the same way except they have an electronic display instead of a dial face so the operator can more easily monitor the movement by showing the actual numeric value of the measurement/movement on an LED display. These work well for the inexperienced operator.
The lever style dial indicator resembles the standard dial indicator and functions the same way. The exception is that it has a “lever” on top of the dial body that allows the operator to raise and lower the contact point (probe) from the work piece instead of having to grab the spindle with your fingers.
To get accurate measurements, your dial/digital indicator should be “pre-loaded”. By this we mean that the pressure of the contact point (probe) on the work piece being checked should move the sweep hand (needle) 1/8 to 1/4 of a turn on the dial face or approximately .008 to .025 on the Digital indicator display. To “re-zero” the dial indicator, you unlock the dial lock so you can rotate the face of the dial indicator to move the “0” on the dials face into line with the sweep hand (needle). With the digital display indicator just hit the “zero” button.
(TIP) For best results and ease of reading, adjust your set-up so that the measuring zone falls between 10 o’clock and 2 o’clock on the dial face if you are using a dial indicator.
To read your dial indicator properly after preloading and re-zeroing, you must use both the main dial and the small “decades counter” dial. You must add the two dials to get your measurement. For example: If the small “decades counter” dial is showing 3, that equals 0.3. If the sweep hand (needle) is 5 lines (.005) past the 70 (.070) on the large dial face, then you add 0.3 + .070 + .005 for .375 in. For the most part we are just dealing with the large dial face .001 graduation when checking case runout or neck wall thickness variance, etc.
To care for your dial or digital indicator, make sure you keep greases and oils off the dial face or display and use a soft clean cloth to clean them. Wipe down the stem and contact (probe) with a small amount of instrument oil to prevent rust and lightly lube the stem. Be sure to store your dial or digital indicator so it is protected from dust and moisture.
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