The working of the dial meter depends on the shape of the dial and the working principle used in the dial micrometer. It has basically two dial shapes. One is a sector-based and the second is a circular dial micrometer. The first mechanism (sector-based) is based on the lever while the second (circular dial) is based on the gear and pinion.
The main parts of the dial micrometer are dial indicator, dial gauge, locking screw, plunger, mini dial (this dial is used to represent the revolutions of the indicator) and the magnification mechanism.
Gear and Pinion Type
The working principle of the gear and pinion type dial micrometer is based on the movement of the plunger through the gears and pinion. As the plunger moves, its movement is multiplied several times through the series of multiple gears and pinions. This multiplied movement moves the needle in the micrometer’s dial and shows the measurement.
The plunger inside the assembly moves linearly with respect to any change produced in the specimen while recording measurements. The plunger has a rack at its end which is meshed with the pinion in the gear system. The first gear through which the rack meshes, is further meshed with the series of gears that multiplies the movement of the plunger with the increased accuracy of the measurement. This gear and pinion system is connected to another pinion at the other end that is further connected to the dial indicator. The multiplied linear motion is then converted to the rotational motion and is shown on the main scale.
The backlash in the gear system is the main concern. To avoid the backlash produced, a hairspring is provided in the gear system. One more hairspring is also provided at the plunger to retract its movement to the original position once the measurements are taken.
The working principle of the lever type dial micrometer is based on the connection of the dial indicator with the lever pivoted near to the plunger. Once the plunger moves relative to the change in the specimen while taking measurements it rotates around its pivot causing motion to the dial indicator showing the measurement of the specimen. The relative motion of the plunger with respect to the specimen is basically magnified by the pivot that is placed far from the dial indicator. Hence a small change in the plunger causes magnified movement in the dial indicator. The compound lever mechanism contains multiple levers connected to the dial indicator by the help of the fork joints to get more accurate and precise measurements.