The dial gauge or dial indicator consists of a small clock and a stylus probe as shown in Figure 18.18. Very small pressure on the stylus probe in upward direction results in rotation of pointer, i.e., the linear movement of stylus is converted into angular movement of pointer. Thus, this device is used to measure the linear vertical movement and to determine the errors in geometrical form such as ovality, out of roundness, lobed form, taper, etc. and the surface errors such as parallelism, squareness, alignment, etc. The dial is divided into 100 divisions. One complete revolution of the indicator corresponds to 1 mm linear movement of the stylus. Thus, each division on the dial indicates a movement of 0.01 mm. The indicator is set to zero, initially, at a certain reference surface, and the instrument or the surface to be measured is brought into contact with stylus. The movement of the indicator can be directly read from the dial.
Figure 18.18 (a) Mechanism of Working of Dial Gauge and (b) Dial Gauge
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